* [PATCH v2 01/21] kbuild: do not allocate .modinfo in vmlinux
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 02/21] kallsyms: index symbols by token to speed up table compression Lorenzo Stoakes (ARM)
` (20 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
Commit 3e86e4d74c04 ("kbuild: keep .modinfo section in vmlinux.unstripped")
placed MODULE_INFO() strings in the .modinfo section in vmlinux.unstripped,
however it left the section allocatable, so it gets assigned an address and
on arm64, arm and riscv, the section is tagged as PT_LOAD.
This is useless as the data is ultimately stripped anyway.
Doing this results in a lot of unnecessary work - each pass copies the
whole file, 450 MIB with relocations for an x86 allmodconfig build and 250
MiB for an arm64 allmodconfig build.
This adds ~0.7s on the serial tail of every build for arm64 and ~0.2s for
x86 (the tail is single-threaded work done after parallel work has
finished).
Nothing requires .modinfo to exist at an address, so fix this by using
--dump-section which prevents the allocation.
Image, bzImage, System.map and modules.builtin.modinfo are unchanged and
the stripped vmlinux differs only in its program headers.
The objcopy passes are on the serial tail of every build that links
vmlinux, no-op builds are unchanged.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 11.2s 11.1s -0.15s (-1%)
x86 defconfig, touch mm/vma.c, clang 11.3s 11.1s -0.19s (-2%)
x86 defconfig, clean, gcc 32.5s 32.3s -0.16s (-1%)
x86 defconfig, clean, clang 34.5s 34.2s -0.26s (-1%)
x86 allmodconfig, touch mm/vma.c, gcc 40.1s 39.7s -0.44s (-1%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
include/asm-generic/vmlinux.lds.h | 2 +-
scripts/Makefile.vmlinux | 22 ++++------------------
2 files changed, 5 insertions(+), 19 deletions(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2988aa12f66..7be9e0321867 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -855,7 +855,7 @@
KLP_SYMID
#define MODINFO \
- .modinfo : { *(.modinfo) . = ALIGN(8); }
+ .modinfo (INFO) : { *(.modinfo) . = ALIGN(8); }
#ifdef CONFIG_GENERIC_BUG
#define BUG_TABLE \
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index fcae1e432d9a..88881826335c 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -89,11 +89,8 @@ remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel.*'
remove-symbols := -w --strip-unneeded-symbol='__mod_device_table__*'
-# To avoid warnings: "empty loadable segment detected at ..." from GNU objcopy,
-# it is necessary to remove the PT_LOAD flag from the segment.
quiet_cmd_strip_relocs = OBJCOPY $@
- cmd_strip_relocs = $(OBJCOPY) $(patsubst %,--set-section-flags %=noload,$(remove-section-y)) $< $@; \
- $(OBJCOPY) $(addprefix --remove-section=,$(remove-section-y)) $(remove-symbols) $@
+ cmd_strip_relocs = $(OBJCOPY) $(addprefix --remove-section=,$(remove-section-y)) $(remove-symbols) $< $@
targets += vmlinux
vmlinux: vmlinux.unstripped FORCE
@@ -102,21 +99,10 @@ vmlinux: vmlinux.unstripped FORCE
# modules.builtin.modinfo
# ---------------------------------------------------------------------------
-# .modinfo in vmlinux.unstripped is aligned to 8 bytes for compatibility with
-# tools that expect vmlinux to have sufficiently aligned sections but the
-# additional bytes used for padding .modinfo to satisfy this requirement break
-# certain versions of kmod with
-#
-# depmod: ERROR: kmod_builtin_iter_next: unexpected string without modname prefix
-#
-# Strip the trailing padding bytes after extracting .modinfo to comply with
-# what kmod expects to parse.
quiet_cmd_modules_builtin_modinfo = GEN $@
- cmd_modules_builtin_modinfo = $(cmd_objcopy); \
- sed -i 's/\x00\+$$/\x00/g' $@; \
- chmod -x $@
-
-OBJCOPYFLAGS_modules.builtin.modinfo := -j .modinfo -O binary
+ cmd_modules_builtin_modinfo = $(OBJCOPY) -O binary -j .modinfo --dump-section .modinfo=$@ $< $@.tmp; \
+ rm -f $@.tmp; \
+ sed -i 's/\x00\+$$/\x00/g' $@
targets += modules.builtin.modinfo
modules.builtin.modinfo: vmlinux.unstripped FORCE
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 02/21] kallsyms: index symbols by token to speed up table compression
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 01/21] kbuild: do not allocate .modinfo in vmlinux Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 03/21] kallsyms: output binary data to speed output and kallsyms assembly Lorenzo Stoakes (ARM)
` (19 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
The kallsyms program compresses symbols by figuring out the most commonly
used substrings in all of the input symbols then uses special character
codes to represent them.
For instance, 0xf7 might end up representing "write_", then every single
symbol that contains "write_" can use 0xf7 as a shorthand and save 5 bytes
each time.
'Special' character codes are any byte value that is not used in any
symbol, either due to being an invalid character, or not being present in
any symbol (e.g. if no symbol contains 'z', then 'z' can be used as special
character).
It does this by first figuring out which special characters are available
in insert_real_symbols_in_table(), then iterating through every available
special character, counting how many times each pair of adjacent characters
appear in symbols in build_initial_token_table().
These adjacent pairs are known as 'tokens'.
Token counts are initially obtained by build_initial_token_table(), then
optimize_result() calls find_best_token() to determine the token that
appeared the most number of times and assigns it the next special
character.
Finally, optimize_result() calls compress_symbols() to replace every token
in every symbol with its special character, which updates token_profit[] as
it does so.
This process is repeated for each remaining available special character,
with tokens now perhaps containing previously assigned special
characters (e.g. if 'wr' was assigned 0x80, then the token representing
'wri' would be '\x80i').
This compresses that token by 50% in each symbol it appears in (two bytes
are now represented by one) and thus by repeatedly doing this kallsyms
obtains good symbol compression.
However, compress_symbols() is seriously inefficient - it iterates through
EVERY symbol for EVERY special character assignment, i.e. ~256 *
nr_symbols.
Modern x86-64 kernels, for instance, have ~158,000 symbols, so millions of
iterations are performed, most of which are entirely unnecessary (tokens
don't appear in most symbols).
In practice kallsyms spends half its runtime doing this, two or three times
per vmlinux link step.
Fix this by tracking which symbols each token appears in token_syms[], and
only compress symbols which actually need to be updated.
Each time a token is compressed that token can no longer appear in any
symbol, so that token_syms[] entry can be freed.
However new token_syms[] entries must be created for each new token
containing the assigned special character, but this is bounded by the
number of replacements in the symbol which is very small.
In testing on an x86-64 platform using clang, each kallsyms invocation
dropped from 0.59s to 0.33s with CONFIG_KALLSYMS_ALL set and from 0.38s to
0.22s without it set.
The data was carefully checked and verified to be byte-for-byte identical
for six symbol sets (two vmlinux passes, vmlinux.o, three userspace
binaries) with all option combinations.
As part of this change, additionally refactor the code to be a little
easier to follow.
kallsyms runs two or three times on the serial tail of every build that
links vmlinux, no-op builds do not link and are unchanged.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 11.1s 10.6s -0.53s (-5%)
x86 defconfig, touch mm/vma.c, clang 11.1s 10.5s -0.64s (-6%)
x86 defconfig, clean, gcc 32.3s 31.3s -1.0s (-3%)
x86 defconfig, clean, clang 34.2s 33.3s -0.89s (-3%)
x86 allmodconfig, touch mm/vma.c, gcc 39.7s 38.7s -1.0s (-3%)
x86 allmodconfig, touch mm/vma.c, clang 40.3s 39.1s -1.3s (-3%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
scripts/kallsyms.c | 138 +++++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 124 insertions(+), 14 deletions(-)
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 494852ade6d8..350d118c3b9e 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -58,12 +58,47 @@ static unsigned int table_size, table_cnt;
static int all_symbols;
static int pc_relative;
+/* A dynamic array of symbols, encoded by symbol index. */
+struct sym_arr {
+ unsigned int *sym_indexes;
+ unsigned int cnt, cap;
+};
+
static int token_profit[0x10000];
+static struct sym_arr token_syms[0x10000];
/* the table that holds the result of the compression */
static unsigned char best_table[256][2];
static unsigned char best_table_len[256];
+static unsigned int sym_arr_last(const struct sym_arr *arr)
+{
+ return arr->cnt ? arr->sym_indexes[arr->cnt - 1] : UINT_MAX;
+}
+
+static void sym_arr_maybe_expand(struct sym_arr *arr)
+{
+ if (arr->cap > arr->cnt)
+ return;
+
+ arr->cap = arr->cap ? arr->cap * 2 : 16;
+ arr->sym_indexes = xrealloc(arr->sym_indexes,
+ arr->cap * sizeof(*arr->sym_indexes));
+}
+
+static void sym_arr_add(struct sym_arr *arr, unsigned int sym_idx)
+{
+ sym_arr_maybe_expand(arr);
+ arr->sym_indexes[arr->cnt++] = sym_idx;
+}
+
+static void sym_arr_free(struct sym_arr *arr)
+{
+ free(arr->sym_indexes);
+ arr->sym_indexes = NULL;
+ arr->cnt = 0;
+ arr->cap = 0;
+}
static void usage(void)
{
@@ -458,6 +493,15 @@ static void write_src(void)
printf("\n");
}
+static unsigned int token_index(unsigned char first, unsigned char second)
+{
+ return first + (second << 8);
+}
+
+static unsigned int sym_token_index(const unsigned char *symbol, int first_idx)
+{
+ return token_index(symbol[first_idx], symbol[first_idx + 1]);
+}
/* table lookup compression functions */
@@ -467,7 +511,7 @@ static void learn_symbol(const unsigned char *symbol, int len)
int i;
for (i = 0; i < len - 1; i++)
- token_profit[ symbol[i] + (symbol[i + 1] << 8) ]++;
+ token_profit[sym_token_index(symbol, i)]++;
}
/* decrease the count for all the possible tokens in a symbol */
@@ -476,16 +520,76 @@ static void forget_symbol(const unsigned char *symbol, int len)
int i;
for (i = 0; i < len - 1; i++)
- token_profit[ symbol[i] + (symbol[i + 1] << 8) ]--;
+ token_profit[sym_token_index(symbol, i)]--;
+}
+
+static void token_add_symbol(unsigned int token_idx, unsigned int sym_idx)
+{
+ struct sym_arr *arr = &token_syms[token_idx];
+
+ /* Symbol indexes kept in sorted order, check for duplicate. */
+ if (sym_arr_last(arr) == sym_idx)
+ return;
+
+ sym_arr_add(arr, sym_idx);
+}
+
+static void symbol_index_all_tokens(const unsigned char *symbol, int len,
+ unsigned int sym_idx)
+{
+ int i;
+
+ for (i = 0; i < len - 1; i++) {
+ const unsigned int token_idx = sym_token_index(symbol, i);
+
+ token_add_symbol(token_idx, sym_idx);
+ }
+}
+
+/*
+ * The symbol just got compressed. The only parts of the symbol that changed
+ * meaningfully are those containing the newly assigned compressed char, so
+ * index those.
+ */
+static void symbol_index_new_tokens(const unsigned char *symbol, int len,
+ unsigned int sym_idx, int compressed_chr)
+{
+ int i;
+
+ for (i = 0; i < len - 1; i++) {
+ const unsigned int token_idx = sym_token_index(symbol, i);
+
+ if (symbol[i] == compressed_chr ||
+ symbol[i + 1] == compressed_chr)
+ token_add_symbol(token_idx, sym_idx);
+ }
}
-/* do the initial token count */
static void build_initial_token_table(void)
{
unsigned int i;
for (i = 0; i < table_cnt; i++)
learn_symbol(table[i]->sym, table[i]->len);
+
+ /*
+ * The initial occurrence counts tell us exactly how much memory should
+ * be reserved for each token's symbol array.
+ */
+ for (i = 0; i < ARRAY_SIZE(token_syms); i++) {
+ const int nr_syms = token_profit[i];
+
+ if (!nr_syms)
+ continue;
+
+ token_syms[i].cap = nr_syms;
+ token_syms[i].sym_indexes =
+ xmalloc(nr_syms * sizeof(unsigned int));
+ }
+
+ /* For every symbol, index every token -> symbol it is present in. */
+ for (i = 0; i < table_cnt; i++)
+ symbol_index_all_tokens(table[i]->sym, table[i]->len, i);
}
static unsigned char *find_token(unsigned char *str, int len,
@@ -502,27 +606,30 @@ static unsigned char *find_token(unsigned char *str, int len,
/* replace a given token in all the valid symbols. Use the sampled symbols
* to update the counts */
-static void compress_symbols(const unsigned char *str, int idx)
+static void compress_symbols(const unsigned char *str, int compressed_chr)
{
- unsigned int i, len, size;
+ const unsigned int token_idx = sym_token_index(str, 0);
+ struct sym_arr *arr = &token_syms[token_idx];
+ unsigned int sym_idx, j, len, size;
unsigned char *p1, *p2;
- for (i = 0; i < table_cnt; i++) {
+ /* Iterate through all symbols this token is found in and compress. */
+ for (j = 0; j < arr->cnt; j++) {
+ sym_idx = arr->sym_indexes[j];
- len = table[i]->len;
- p1 = table[i]->sym;
+ len = table[sym_idx]->len;
+ p1 = table[sym_idx]->sym;
- /* find the token on the symbol */
p2 = find_token(p1, len, str);
if (!p2) continue;
/* decrease the counts for this symbol's tokens */
- forget_symbol(table[i]->sym, len);
+ forget_symbol(table[sym_idx]->sym, len);
size = len;
do {
- *p2 = idx;
+ *p2 = compressed_chr;
p2++;
size -= (p2 - p1);
memmove(p2, p2 + 1, size);
@@ -536,11 +643,14 @@ static void compress_symbols(const unsigned char *str, int idx)
} while (p2);
- table[i]->len = len;
+ table[sym_idx]->len = len;
- /* increase the counts for this symbol's new tokens */
- learn_symbol(table[i]->sym, len);
+ learn_symbol(table[sym_idx]->sym, len);
+ symbol_index_new_tokens(table[sym_idx]->sym, len, sym_idx,
+ compressed_chr);
}
+
+ sym_arr_free(arr); /* No symbol contains this token any more. */
}
/* search the token with the maximum profit */
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 03/21] kallsyms: output binary data to speed output and kallsyms assembly
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 01/21] kbuild: do not allocate .modinfo in vmlinux Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 02/21] kallsyms: index symbols by token to speed up table compression Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 20:16 ` Markus Elfring
2026-09-14 9:22 ` [PATCH v2 04/21] kbuild: do not sort nm output where the order is irrelevant Lorenzo Stoakes (ARM)
` (18 subsequent siblings)
21 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
kallsyms generates an assembly file that consists mostly of .byte entries
containing compressed names, token strings and name-sorted sequence
numbers.
For an x86-64 build with 158k symbols that is a 37 MiB .S file which takes
0.57s to assemble each of the two to three times it is built over a kernel
build.
Each time it is generated it also takes kallsyms a similar amount of time
to output it.
Avoid this overhead by instead outputting this data as binary and importing
it into the assembly using the .incbin directive.
Tables that are wider than a byte remain part of the assembly to ensure
endianness and relative relocations are performed correctly.
With this change, the output assembly file shrinks from 37 MiB to 9.8 MiB,
with a 2.6 MiB binary data file alongside it, and the object remains
identical.
The generated binary file is deleted correctly on build clean along with
all other ephemeral data.
On an x86-64 system with CONFIG_KALLSYMS_ALL set:
before after delta
scripts/kallsyms 0.24s 0.18s 0.06s
assemble 0.57s 0.16s 0.41s
Per kallsyms invocation/assembly, for a total of 0.47s time saving upon
invocation.
An incremental build on the same system was reduced from 11.15s to 9.65s,
indicating a total of 1.5 seconds saved over the build.
The kallsyms runs and their assembly are on the serial tail of every build
that links vmlinux, no-op builds are unchanged.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 10.6s 9.7s -0.89s (-8%)
x86 defconfig, touch mm/vma.c, clang 10.5s 9.3s -1.2s (-11%)
x86 defconfig, clean, gcc 31.3s 30.3s -1.0s (-3%)
x86 defconfig, clean, clang 33.3s 31.7s -1.6s (-5%)
x86 allmodconfig, touch mm/vma.c, gcc 38.7s 37.2s -1.4s (-4%)
x86 allmodconfig, touch mm/vma.c, clang 39.1s 36.4s -2.6s (-7%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
scripts/kallsyms.c | 84 ++++++++++++++++++++++++++++++++++++-------------
scripts/link-vmlinux.sh | 2 +-
2 files changed, 64 insertions(+), 22 deletions(-)
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 350d118c3b9e..89f5207f74d2 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -5,7 +5,10 @@
* This software may be used and distributed according to the terms
* of the GNU General Public License, incorporated herein by reference.
*
- * Usage: kallsyms [--all-symbols] in.map > out.S
+ * Usage: kallsyms [--all-symbols] [--pc-relative] in.map out.bin > out.S
+ *
+ * The byte tables go to out.bin and are pulled into out.S with .incbin;
+ * wider tables stay assembler source for endianness and relocations.
*
* Table compression uses all the unused char codes on the symbols and
* maps these to the most used substrings (tokens). For instance, it might
@@ -102,7 +105,7 @@ static void sym_arr_free(struct sym_arr *arr)
static void usage(void)
{
- fprintf(stderr, "Usage: kallsyms [--all-symbols] in.map > out.S\n");
+ fprintf(stderr, "Usage: kallsyms [--all-symbols] [--pc-relative] in.map out.bin > out.S\n");
exit(1);
}
@@ -319,6 +322,26 @@ static void output_label(const char *label)
printf("%s:\n", label);
}
+static long bin_pos(FILE *file)
+{
+ const long pos = ftell(file);
+
+ if (pos < 0) {
+ perror("kallsyms: ftell");
+ exit(EXIT_FAILURE);
+ }
+
+ return pos;
+}
+
+static void write_incbin(const char *filename, long start, long end)
+{
+ if (start >= end)
+ return;
+
+ printf("\t.incbin \"%s\", %ld, %ld\n", filename, start, end - start);
+}
+
/* uncompress a compressed symbol. When this function is called, the best table
* might still be compressed itself, so the function needs to be recursive */
static int expand_symbol(const unsigned char *data, int len, char *result)
@@ -371,11 +394,12 @@ static void sort_symbols_by_name(void)
qsort(table, table_cnt, sizeof(table[0]), compare_names);
}
-static void write_src(void)
+static void write_src(FILE *out_bin_file, const char *out_bin_name)
{
- unsigned int i, k, off;
+ unsigned int i, off;
unsigned int best_idx[256];
unsigned int *markers, markers_cnt;
+ long bin_start;
char buf[KSYM_NAME_LEN];
printf("\t.section .rodata, \"a\"\n");
@@ -390,6 +414,7 @@ static void write_src(void)
markers = xmalloc(sizeof(*markers) * markers_cnt);
output_label("kallsyms_names");
+ bin_start = bin_pos(out_bin_file);
off = 0;
for (i = 0; i < table_cnt; i++) {
if ((i & 0xFF) == 0)
@@ -413,26 +438,24 @@ static void write_src(void)
/* Encode length with ULEB128. */
if (table[i]->len <= 0x7F) {
/* Most symbols use a single byte for the length. */
- printf("\t.byte 0x%02x", table[i]->len);
+ fputc(table[i]->len, out_bin_file);
off += table[i]->len + 1;
} else {
/* "Big" symbols use two bytes. */
- printf("\t.byte 0x%02x, 0x%02x",
- (table[i]->len & 0x7F) | 0x80,
- (table[i]->len >> 7) & 0x7F);
+ fputc((table[i]->len & 0x7F) | 0x80, out_bin_file);
+ fputc((table[i]->len >> 7) & 0x7F, out_bin_file);
off += table[i]->len + 2;
}
- for (k = 0; k < table[i]->len; k++)
- printf(", 0x%02x", table[i]->sym[k]);
+ fwrite(table[i]->sym, 1, table[i]->len, out_bin_file);
/*
* Now that we wrote out the compressed symbol name, restore the
- * original name and print it in the comment.
+ * original name for the comments below.
*/
expand_symbol(table[i]->sym, table[i]->len, buf);
strcpy((char *)table[i]->sym, buf);
- printf("\t/* %s */\n", table[i]->sym);
}
+ write_incbin(out_bin_name, bin_start, bin_pos(out_bin_file));
printf(".size kallsyms_names, . - kallsyms_names\n");
printf("\n");
@@ -445,13 +468,15 @@ static void write_src(void)
free(markers);
output_label("kallsyms_token_table");
+ bin_start = bin_pos(out_bin_file);
off = 0;
for (i = 0; i < 256; i++) {
best_idx[i] = off;
expand_symbol(best_table[i], best_table_len[i], buf);
- printf("\t.asciz\t\"%s\"\n", buf);
+ fwrite(buf, 1, strlen(buf) + 1, out_bin_file);
off += strlen(buf) + 1;
}
+ write_incbin(out_bin_name, bin_start, bin_pos(out_bin_file));
printf(".size kallsyms_token_table, . - kallsyms_token_table\n");
printf("\n");
@@ -484,12 +509,13 @@ static void write_src(void)
sort_symbols_by_name();
output_label("kallsyms_seqs_of_names");
- for (i = 0; i < table_cnt; i++)
- printf("\t.byte 0x%02x, 0x%02x, 0x%02x\t/* %s */\n",
- (unsigned char)(table[i]->seq >> 16),
- (unsigned char)(table[i]->seq >> 8),
- (unsigned char)(table[i]->seq >> 0),
- table[i]->sym);
+ bin_start = bin_pos(out_bin_file);
+ for (i = 0; i < table_cnt; i++) {
+ fputc(table[i]->seq >> 16, out_bin_file);
+ fputc(table[i]->seq >> 8, out_bin_file);
+ fputc(table[i]->seq >> 0, out_bin_file);
+ }
+ write_incbin(out_bin_name, bin_start, bin_pos(out_bin_file));
printf("\n");
}
@@ -798,6 +824,9 @@ static void sort_symbols(void)
int main(int argc, char **argv)
{
+ const char *out_bin_name;
+ FILE *out_bin_file;
+
while (1) {
static const struct option long_options[] = {
{"all-symbols", no_argument, &all_symbols, 1},
@@ -813,14 +842,27 @@ int main(int argc, char **argv)
usage();
}
- if (optind >= argc)
+ if (optind + 2 != argc)
usage();
+ out_bin_name = argv[optind + 1];
+ out_bin_file = fopen(out_bin_name, "w");
+ if (!out_bin_file) {
+ perror(out_bin_name);
+ exit(EXIT_FAILURE);
+ }
+
read_map(argv[optind]);
shrink_table();
sort_symbols();
optimize_token_table();
- write_src();
+ write_src(out_bin_file, out_bin_name);
+
+ /* Write errors are latched in the stream, so one check at the end covers them all. */
+ if (ferror(out_bin_file) || fclose(out_bin_file)) {
+ perror(out_bin_name);
+ exit(EXIT_FAILURE);
+ }
return 0;
}
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index ab0b8125c8cb..e88604150d2c 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -132,7 +132,7 @@ kallsyms()
fi
info KSYMS "${2}.S"
- scripts/kallsyms ${kallsymopt} "${1}" > "${2}.S"
+ scripts/kallsyms ${kallsymopt} "${1}" "${2}.bin" > "${2}.S"
info AS "${2}.o"
${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 03/21] kallsyms: output binary data to speed output and kallsyms assembly
2026-09-14 9:22 ` [PATCH v2 03/21] kallsyms: output binary data to speed output and kallsyms assembly Lorenzo Stoakes (ARM)
@ 2026-09-14 20:16 ` Markus Elfring
2026-09-14 21:44 ` David Laight
0 siblings, 1 reply; 58+ messages in thread
From: Markus Elfring @ 2026-09-14 20:16 UTC (permalink / raw)
To: Lorenzo Stoakes, linux-kbuild, x86, Albert Ou, Alexandre Courbot,
Alexandre Ghiti, Alexey Gladkov, Alice Ryhl, Andreas Hindborg,
Ard Biesheuvel, Arnd Bergmann, Benno Lossin, Bill Wendling,
Björn Roy Baron, Boqun Feng, Borislav Petkov,
Catalin Marinas, Daniel Almeida, Danilo Krummrich, Dave Hansen,
Gary Guo, Gustavo A. R. Silva, H. Peter Anvin, Ilias Apalodimas,
Ingo Molnar, Jonathan Corbet, Josh Poimboeuf, Justin Stitt,
Kees Cook, Linus Torvalds, Mark Rutland, Masahiro Yamada,
Miguel Ojeda, Nathan Chancellor, Nick Desaulniers,
Nicolas Schier, Onur Özkan, Palmer Dabbelt, Paul Walmsley,
Peter Zijlstra, Randy Dunlap, Tamir Duberstein, Thomas Gleixner,
Trevor Gross, Will Deacon
Cc: LKML, kernel-janitors, linux-hardening, linux-doc, linux-efi,
rust-for-linux, linux-arch, llvm, linux-riscv, linux-arm-kernel,
David Laight, Jens Axboe
…
> +++ b/scripts/kallsyms.c
…
> @@ -413,26 +438,24 @@ static void write_src(void)
> /* Encode length with ULEB128. */
> if (table[i]->len <= 0x7F) {
> /* Most symbols use a single byte for the length. */
> - printf("\t.byte 0x%02x", table[i]->len);
> + fputc(table[i]->len, out_bin_file);
> off += table[i]->len + 1;
> } else {
> /* "Big" symbols use two bytes. */
> - printf("\t.byte 0x%02x, 0x%02x",
> - (table[i]->len & 0x7F) | 0x80,
> - (table[i]->len >> 7) & 0x7F);
> + fputc((table[i]->len & 0x7F) | 0x80, out_bin_file);
> + fputc((table[i]->len >> 7) & 0x7F, out_bin_file);
> off += table[i]->len + 2;
> }
> - for (k = 0; k < table[i]->len; k++)
> - printf(", 0x%02x", table[i]->sym[k]);
> + fwrite(table[i]->sym, 1, table[i]->len, out_bin_file);
>
> /*
> * Now that we wrote out the compressed symbol name, restore the
> - * original name and print it in the comment.
> + * original name for the comments below.
> */
> expand_symbol(table[i]->sym, table[i]->len, buf);
> strcpy((char *)table[i]->sym, buf);
> - printf("\t/* %s */\n", table[i]->sym);
> }
> + write_incbin(out_bin_name, bin_start, bin_pos(out_bin_file));
> printf(".size kallsyms_names, . - kallsyms_names\n");
> printf("\n");
>
…
I suggest to avoid return value ignorance a bit more.
https://cmu-sei.github.io/secure-coding-standards/sei-cert-c-coding-standard/rules/error-handling-err/err33-c/
https://cwe.mitre.org/data/definitions/252.html
Regards,
Markus
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 03/21] kallsyms: output binary data to speed output and kallsyms assembly
2026-09-14 20:16 ` Markus Elfring
@ 2026-09-14 21:44 ` David Laight
2026-09-15 7:10 ` [v2 " Markus Elfring
0 siblings, 1 reply; 58+ messages in thread
From: David Laight @ 2026-09-14 21:44 UTC (permalink / raw)
To: Markus Elfring
Cc: Lorenzo Stoakes, linux-kbuild, x86, Albert Ou, Alexandre Courbot,
Alexandre Ghiti, Alexey Gladkov, Alice Ryhl, Andreas Hindborg,
Ard Biesheuvel, Arnd Bergmann, Benno Lossin, Bill Wendling,
Björn Roy Baron, Boqun Feng, Borislav Petkov,
Catalin Marinas, Daniel Almeida, Danilo Krummrich, Dave Hansen,
Gary Guo, Gustavo A. R. Silva, H. Peter Anvin, Ilias Apalodimas,
Ingo Molnar, Jonathan Corbet, Josh Poimboeuf, Justin Stitt,
Kees Cook, Linus Torvalds, Mark Rutland, Masahiro Yamada,
Miguel Ojeda, Nathan Chancellor, Nick Desaulniers,
Nicolas Schier, Onur Özkan, Palmer Dabbelt, Paul Walmsley,
Peter Zijlstra, Randy Dunlap, Tamir Duberstein, Thomas Gleixner,
Trevor Gross, Will Deacon, LKML, kernel-janitors,
linux-hardening, linux-doc, linux-efi, rust-for-linux,
linux-arch, llvm, linux-riscv, linux-arm-kernel, Jens Axboe
On Mon, 14 Sep 2026 22:16:12 +0200
Markus Elfring <Markus.Elfring@web.de> wrote:
> …
> > +++ b/scripts/kallsyms.c
> …
> > @@ -413,26 +438,24 @@ static void write_src(void)
> > /* Encode length with ULEB128. */
> > if (table[i]->len <= 0x7F) {
> > /* Most symbols use a single byte for the length. */
> > - printf("\t.byte 0x%02x", table[i]->len);
> > + fputc(table[i]->len, out_bin_file);
> > off += table[i]->len + 1;
> > } else {
> > /* "Big" symbols use two bytes. */
> > - printf("\t.byte 0x%02x, 0x%02x",
> > - (table[i]->len & 0x7F) | 0x80,
> > - (table[i]->len >> 7) & 0x7F);
> > + fputc((table[i]->len & 0x7F) | 0x80, out_bin_file);
> > + fputc((table[i]->len >> 7) & 0x7F, out_bin_file);
> > off += table[i]->len + 2;
> > }
> > - for (k = 0; k < table[i]->len; k++)
> > - printf(", 0x%02x", table[i]->sym[k]);
> > + fwrite(table[i]->sym, 1, table[i]->len, out_bin_file);
> >
> > /*
> > * Now that we wrote out the compressed symbol name, restore the
> > - * original name and print it in the comment.
> > + * original name for the comments below.
> > */
> > expand_symbol(table[i]->sym, table[i]->len, buf);
> > strcpy((char *)table[i]->sym, buf);
> > - printf("\t/* %s */\n", table[i]->sym);
> > }
> > + write_incbin(out_bin_name, bin_start, bin_pos(out_bin_file));
> > printf(".size kallsyms_names, . - kallsyms_names\n");
> > printf("\n");
> >
> …
>
> I suggest to avoid return value ignorance a bit more.
> https://cmu-sei.github.io/secure-coding-standards/sei-cert-c-coding-standard/rules/error-handling-err/err33-c/
> https://cwe.mitre.org/data/definitions/252.html
And I suggest you do some real coding...
The error is sticky and can be checked using ferror().
Code that looks at the return value from fprintf() fwrite() etc is very
often broken because the only time they can actual fail is when the
buffer is flushed during close.
Adding error checks to every call just make the code unreadable.
David
>
> Regards,
> Markus
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [v2 03/21] kallsyms: output binary data to speed output and kallsyms assembly
2026-09-14 21:44 ` David Laight
@ 2026-09-15 7:10 ` Markus Elfring
0 siblings, 0 replies; 58+ messages in thread
From: Markus Elfring @ 2026-09-15 7:10 UTC (permalink / raw)
To: David Laight, Lorenzo Stoakes, linux-kbuild
Cc: x86, Albert Ou, Alexandre Courbot, Alexandre Ghiti,
Alexey Gladkov, Alice Ryhl, Andreas Hindborg, Ard Biesheuvel,
Arnd Bergmann, Benno Lossin, Bill Wendling, Björn Roy Baron,
Boqun Feng, Borislav Petkov, Catalin Marinas, Daniel Almeida,
Danilo Krummrich, Dave Hansen, Gary Guo, Gustavo A. R. Silva,
H. Peter Anvin, Ilias Apalodimas, Ingo Molnar, Jonathan Corbet,
Josh Poimboeuf, Justin Stitt, Kees Cook, Linus Torvalds,
Mark Rutland, Masahiro Yamada, Miguel Ojeda, Nathan Chancellor,
Nick Desaulniers, Nicolas Schier, Onur Özkan,
Palmer Dabbelt, Paul Walmsley, Peter Zijlstra, Randy Dunlap,
Tamir Duberstein, Thomas Gleixner, Trevor Gross, Will Deacon,
LKML, kernel-janitors, linux-hardening, linux-doc, linux-efi,
rust-for-linux, linux-arch, llvm, linux-riscv, linux-arm-kernel,
Jens Axboe
>> I suggest to avoid return value ignorance a bit more.
>> https://cmu-sei.github.io/secure-coding-standards/sei-cert-c-coding-standard/rules/error-handling-err/err33-c/
>> https://cwe.mitre.org/data/definitions/252.html
>
> And I suggest you do some real coding...
> The error is sticky and can be checked using ferror().
Are there further warnings to reconsider also according to unchecked and unused return values?
> Code that looks at the return value from fprintf() fwrite() etc is very
> often broken because the only time they can actual fail is when the
> buffer is flushed during close.
Is this a special implementation detail?
> Adding error checks to every call just make the code unreadable.
Some developers got used to corresponding programming possibilities.
Interests might grow also for aspect-oriented software development,
doesn't it?
Regards,
Markus
^ permalink raw reply [flat|nested] 58+ messages in thread
* [PATCH v2 04/21] kbuild: do not sort nm output where the order is irrelevant
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (2 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 03/21] kallsyms: output binary data to speed output and kallsyms assembly Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 05/21] kbuild: only emit vmlinux relocations when required Lorenzo Stoakes (ARM)
` (17 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
Unless instructed otherwise, nm sorts by name.
There are places where this is unnecessary - an invocation from
scripts/sorttable every vmlinux link, scripts/check-function-names.sh run
after every vmlinux.o link, and the x86 VOFFSET and ZOFFSET listings
between vmlinux and bzImage.
Both GNU nm and llvm-nm accept the same '-p' parameter to disable sorting
in these instances, so use that to prevent this unnecessary work.
Each nm run on its own, x86-64, median of 5:
GNU nm 2.47 llvm-nm 22
before after delta before after delta
defconfig
sorttable, nm -S vmlinux 0.080s 0.039s -0.041s 0.265s 0.113s -0.152s
check-function-names.sh 0.072s 0.033s -0.039s 0.244s 0.102s -0.142s
VOFFSET 0.077s 0.034s -0.043s 0.261s 0.113s -0.148s
ZOFFSET 0.007s 0.005s -0.002s 0.005s 0.005s 0.000s
TOTAL -0.125s -0.442s
allmodconfig
sorttable, nm -S vmlinux 0.156s 0.063s -0.093s 0.539s 0.223s -0.316s
check-function-names.sh 0.149s 0.054s -0.095s 0.537s 0.217s -0.320s
VOFFSET 0.146s 0.052s -0.094s 0.524s 0.221s -0.303s
ZOFFSET 0.007s 0.005s -0.002s 0.006s 0.004s -0.002s
TOTAL -0.284s -0.941s
llvm-nm appears to be a lot slower than GNU nm, so these builds naturally
improve the most.
The four run one after another in the serial tail of every build that links
vmlinux so impact kernel builds directly.
In an allmodconfig the decompressor is built in parallel while the modules,
so only the two before the vmlinux link contribute to build time.
The build outputs remain unchanged.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
---------------------------------
x86 defconfig, touch mm/vma.c, gcc 9.7s 9.5s -0.18s (-2%)
x86 defconfig, touch mm/vma.c, clang 9.3s 9.0s -0.27s (-3%)
x86 defconfig, clean, gcc 30.3s 30.1s -0.16s (-1%)
x86 defconfig, clean, clang 31.7s 31.2s -0.55s (-2%)
x86 allmodconfig, touch mm/vma.c, clang 36.4s 35.8s -0.67s (-2%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
arch/x86/boot/Makefile | 2 +-
arch/x86/boot/compressed/Makefile | 2 +-
scripts/check-function-names.sh | 3 ++-
scripts/link-vmlinux.sh | 2 +-
4 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index 3f9fb3698d66..4a9bce32586d 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -74,7 +74,7 @@ SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))
sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|efi.._stub_entry\|efi\(32\)\?_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|_e\?data\|_e\?sbat\|z_.*\)$$/\#define ZO_\2 0x\1/p'
quiet_cmd_zoffset = ZOFFSET $@
- cmd_zoffset = $(NM) $< | sed -n $(sed-zoffset) > $@
+ cmd_zoffset = $(NM) -p $< | sed -n $(sed-zoffset) > $@
targets += zoffset.h
$(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 06934f9691d6..6ec5e031db1d 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -76,7 +76,7 @@ HOST_EXTRACFLAGS += -I$(srctree)/tools/include
sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABbCDGRSTtVW] \(_text\|__start_rodata\|_sinittext\|__inittext_end\|__bss_start\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p'
quiet_cmd_voffset = VOFFSET $@
- cmd_voffset = $(NM) $< | sed -n $(sed-voffset) > $@
+ cmd_voffset = $(NM) -p $< | sed -n $(sed-voffset) > $@
targets += ../voffset.h
diff --git a/scripts/check-function-names.sh b/scripts/check-function-names.sh
index 08071133e5a5..94883e690627 100755
--- a/scripts/check-function-names.sh
+++ b/scripts/check-function-names.sh
@@ -13,7 +13,8 @@ if [ ! -f "$objfile" ]; then
exit 1
fi
-bad_symbols=$(${NM:-nm} "$objfile" | awk '$2 ~ /^[TtWw]$/ {print $3}' | grep -E '^(startup|exit|split|unlikely|hot|unknown)(\.|$)')
+bad_symbols=$(${NM:-nm} -p "$objfile" | awk '$2 ~ /^[TtWw]$/ {print $3}' |
+ grep -E '^(startup|exit|split|unlikely|hot|unknown)(\.|$)')
if [ -n "$bad_symbols" ]; then
echo "$bad_symbols" | while read -r sym; do
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index e88604150d2c..970ca10f8fa9 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -161,7 +161,7 @@ mksysmap()
sorttable()
{
- ${NM} -S ${1} > .tmp_vmlinux.nm-sort
+ ${NM} -p -S ${1} > .tmp_vmlinux.nm-sort
${objtree}/scripts/sorttable -s .tmp_vmlinux.nm-sort ${1}
}
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 05/21] kbuild: only emit vmlinux relocations when required
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (3 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 04/21] kbuild: do not sort nm output where the order is irrelevant Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 06/21] elf-parse: add section flags, symbol binding and a read-only mapping Lorenzo Stoakes (ARM)
` (16 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
A kernel build consists of more than one linking pass on vmlinux.o and
vmlinux, at minimum two, and with CONFIG_KALLSYMS and BTF enabled on x86-64
for example there are 5 such stages.
For architectures that build their own relocation tables (x86, riscv, mips,
s390), vmlinux is linked with the --emit-relocs parameter specified.
However, this is only required on the final vmlinux link.
Symbol tables of trial links preceding it don't need it because they
already check that System.map matches kallsyms symbols on each build.
GNU ld is slow at emitting relocation tables, so this results in a
reduction in build time.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 9.5s 9.1s -0.42s (-4%)
x86 defconfig, clean, gcc 30.1s 29.5s -0.59s (-2%)
x86 allmodconfig, touch mm/vma.c, gcc 37.2s 35.8s -1.4s (-4%)
Note that this has little impact on LLVM ld which performs this operation
more efficiently.
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
Makefile | 2 +-
scripts/link-vmlinux.sh | 5 +++++
2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/Makefile b/Makefile
index 0f1b80100b47..dd4c10afbb7f 100644
--- a/Makefile
+++ b/Makefile
@@ -1263,7 +1263,7 @@ LDFLAGS_vmlinux += --orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL)
endif
ifneq ($(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS),)
-LDFLAGS_vmlinux += --emit-relocs --discard-none
+LDFLAGS_vmlinux += --discard-none
endif
# Align the architecture of userspace programs with the kernel
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 970ca10f8fa9..ed5ff97c0667 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -96,6 +96,11 @@ vmlinux_link()
ldflags="${ldflags} ${wl}--strip-debug"
fi
+ # Only the final link actually requires the relocations.
+ if [ "${output}" = "${VMLINUX}" ] && is_enabled CONFIG_ARCH_VMLINUX_NEEDS_RELOCS; then
+ ldflags="${ldflags} ${wl}--emit-relocs"
+ fi
+
if [ -n "${generate_map}" ]; then
ldflags="${ldflags} ${wl}-Map=vmlinux.map"
fi
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 06/21] elf-parse: add section flags, symbol binding and a read-only mapping
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (4 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 05/21] kbuild: only emit vmlinux relocations when required Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 07/21] kallsyms: reimplement mksysmap in C Lorenzo Stoakes (ARM)
` (15 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
Extend elf-parse to be able to read the symbol table of vmlinux in kallyms.
This requires the ability to open ELF files in read-only mode, so provide
elf_map_ro() to do so.
It also requires accessors for section flags and symbol bindings, so
provide these via shdr_flags() and sym_bind().
Also, check for the file being an ELF file first in elf_parse(). This is
the logical thing to check for first, but additionally prevents kallsyms
from having to check this it self.
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
scripts/elf-parse.c | 48 +++++++++++++++++++++++++++++++++++-------------
scripts/elf-parse.h | 19 +++++++++++++++++++
2 files changed, 54 insertions(+), 13 deletions(-)
diff --git a/scripts/elf-parse.c b/scripts/elf-parse.c
index 99869ff91a8c..87aa95b1e5e1 100644
--- a/scripts/elf-parse.c
+++ b/scripts/elf-parse.c
@@ -17,15 +17,21 @@ struct elf_funcs elf_parser;
* Get the whole file as a programming convenience in order to avoid
* malloc+lseek+read+free of many pieces. If successful, then mmap
* avoids copying unused pieces; else just read the whole file.
- * Open for both read and write.
+ * Open for both read and write if writable is true, otherwise open
+ * read-only.
*/
-static void *map_file(char const *fname, size_t *size)
+static void *map_file(char const *fname, size_t *size, bool writable)
{
- int fd;
+ int fd, prot = PROT_READ, flags = MAP_PRIVATE;
struct stat sb;
void *addr = NULL;
- fd = open(fname, O_RDWR);
+ if (writable) {
+ prot |= PROT_WRITE;
+ flags = MAP_SHARED;
+ }
+
+ fd = open(fname, writable ? O_RDWR : O_RDONLY);
if (fd < 0) {
perror(fname);
return NULL;
@@ -39,7 +45,7 @@ static void *map_file(char const *fname, size_t *size)
goto out;
}
- addr = mmap(0, sb.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+ addr = mmap(0, sb.st_size, prot, flags, fd, 0);
if (addr == MAP_FAILED) {
fprintf(stderr, "Could not mmap file: %s\n", fname);
goto out;
@@ -57,6 +63,12 @@ static int elf_parse(const char *fname, void *addr, uint32_t types)
Elf_Ehdr *ehdr = addr;
uint16_t type;
+ if (memcmp(ELFMAG, ehdr->e32.e_ident, SELFMAG) != 0 ||
+ ehdr->e32.e_ident[EI_VERSION] != EV_CURRENT) {
+ fprintf(stderr, "unrecognized ELF file %s\n", fname);
+ return -1;
+ }
+
switch (ehdr->e32.e_ident[EI_DATA]) {
case ELFDATA2LSB:
elf_parser.r = rle;
@@ -78,12 +90,6 @@ static int elf_parse(const char *fname, void *addr, uint32_t types)
return -1;
}
- if (memcmp(ELFMAG, ehdr->e32.e_ident, SELFMAG) != 0 ||
- ehdr->e32.e_ident[EI_VERSION] != EV_CURRENT) {
- fprintf(stderr, "unrecognized ELF file %s\n", fname);
- return -1;
- }
-
type = elf_parser.r2(&ehdr->e32.e_type);
if (!((1 << type) & types)) {
fprintf(stderr, "Invalid ELF type file %s\n", fname);
@@ -103,7 +109,9 @@ static int elf_parse(const char *fname, void *addr, uint32_t types)
elf_parser.shdr_name = shdr32_name;
elf_parser.shdr_type = shdr32_type;
elf_parser.shdr_entsize = shdr32_entsize;
+ elf_parser.shdr_flags = shdr32_flags;
elf_parser.sym_type = sym32_type;
+ elf_parser.sym_bind = sym32_bind;
elf_parser.sym_name = sym32_name;
elf_parser.sym_value = sym32_value;
elf_parser.sym_shndx = sym32_shndx;
@@ -133,7 +141,9 @@ static int elf_parse(const char *fname, void *addr, uint32_t types)
elf_parser.shdr_name = shdr64_name;
elf_parser.shdr_type = shdr64_type;
elf_parser.shdr_entsize = shdr64_entsize;
+ elf_parser.shdr_flags = shdr64_flags;
elf_parser.sym_type = sym64_type;
+ elf_parser.sym_bind = sym64_bind;
elf_parser.sym_name = sym64_name;
elf_parser.sym_value = sym64_value;
elf_parser.sym_shndx = sym64_shndx;
@@ -174,12 +184,13 @@ int elf_map_long_size(void *addr)
return ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32 ? 4 : 8;
}
-void *elf_map(char const *fname, size_t *size, uint32_t types)
+static void *__elf_map(char const *fname, size_t *size, uint32_t types,
+ bool writable)
{
void *addr;
int ret;
- addr = map_file(fname, size);
+ addr = map_file(fname, size, writable);
if (!addr)
return NULL;
@@ -192,6 +203,17 @@ void *elf_map(char const *fname, size_t *size, uint32_t types)
return addr;
}
+void *elf_map(char const *fname, size_t *size, uint32_t types)
+{
+ return __elf_map(fname, size, types, true);
+}
+
+/* For tools that only read the file. */
+void *elf_map_ro(char const *fname, size_t *size, uint32_t types)
+{
+ return __elf_map(fname, size, types, false);
+}
+
void elf_unmap(void *addr, size_t size)
{
munmap(addr, size);
diff --git a/scripts/elf-parse.h b/scripts/elf-parse.h
index f4411e03069d..453286e63032 100644
--- a/scripts/elf-parse.h
+++ b/scripts/elf-parse.h
@@ -37,10 +37,12 @@ struct elf_funcs {
uint64_t (*shdr_offset)(Elf_Shdr *shdr);
uint64_t (*shdr_size)(Elf_Shdr *shdr);
uint64_t (*shdr_entsize)(Elf_Shdr *shdr);
+ uint64_t (*shdr_flags)(Elf_Shdr *shdr);
uint32_t (*shdr_link)(Elf_Shdr *shdr);
uint32_t (*shdr_name)(Elf_Shdr *shdr);
uint32_t (*shdr_type)(Elf_Shdr *shdr);
uint8_t (*sym_type)(Elf_Sym *sym);
+ uint8_t (*sym_bind)(Elf_Sym *sym);
uint32_t (*sym_name)(Elf_Sym *sym);
uint64_t (*sym_value)(Elf_Sym *sym);
uint16_t (*sym_shndx)(Elf_Sym *sym);
@@ -143,6 +145,7 @@ SHDR_ADDR(addr)
SHDR_ADDR(offset)
SHDR_ADDR(size)
SHDR_ADDR(entsize)
+SHDR_ADDR(flags)
SHDR_WORD(link)
SHDR_WORD(name)
@@ -211,6 +214,21 @@ static inline uint8_t sym_type(Elf_Sym *sym)
return elf_parser.sym_type(sym);
}
+static inline uint8_t sym64_bind(Elf_Sym *sym)
+{
+ return ELF64_ST_BIND(sym->e64.st_info);
+}
+
+static inline uint8_t sym32_bind(Elf_Sym *sym)
+{
+ return ELF32_ST_BIND(sym->e32.st_info);
+}
+
+static inline uint8_t sym_bind(Elf_Sym *sym)
+{
+ return elf_parser.sym_bind(sym);
+}
+
SYM_ADDR(value)
SYM_WORD(name)
SYM_HALF(shndx)
@@ -298,6 +316,7 @@ static inline void w8le(uint64_t val, uint64_t *x)
}
void *elf_map(char const *fname, size_t *size, uint32_t types);
+void *elf_map_ro(char const *fname, size_t *size, uint32_t types);
void elf_unmap(void *addr, size_t size);
int elf_map_machine(void *addr);
int elf_map_long_size(void *addr);
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 07/21] kallsyms: reimplement mksysmap in C
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (5 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 06/21] elf-parse: add section flags, symbol binding and a read-only mapping Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 16:33 ` Markus Elfring
` (2 more replies)
2026-09-14 9:22 ` [PATCH v2 08/21] kbuild: cache list, composite object state per object Lorenzo Stoakes (ARM)
` (14 subsequent siblings)
21 siblings, 3 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
mksysmap is a sed script consisting of 30 patterns which link-vmlinux.sh
uses to generate *.syms files, and which kallsyms is then called against to
generate *.kallsyms files, with the final vmlinux build ultimately
generating System.map.
For an x86-64 allmodconfig build, this involves three nm runs over a 250
MiB file and half a million lines written and read each time - 0.5s per
pass for llvm-nm, and 0.2s for GNU nm, with parsing on top of that.
This is unnecessary, instead have kallsyms simply read the ELF file
directly making use of the existing elf-parse library in scripts/.
This changes kallsyms such that its input is no longer the output from nm,
but rather an ELF file.
However, if the input file is empty, it outputs an empty table, which
retains the same behaviour on first pass that the build system expects.
System.map is byte-identical to nm | mksysmap for GNU nm and llvm-nm on
two x86 configurations each, and for llvm-nm on arm64, arm, s390 and
loongarch defconfigs, so are the kallsyms tables of every pass.
Relinking vmlinux, link steps included:
before after
allmodconfig clang 9.1s 7.9s
allmodconfig gcc 7.8s 7.6s
defconfig clang 3.7s 3.0s
defconfig gcc 3.5s 3.4s
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 9.1s 8.6s -0.43s (-5%)
x86 defconfig, touch mm/vma.c, clang 9.0s 8.0s -1.1s (-12%)
x86 defconfig, clean, gcc 29.5s 28.9s -0.64s (-2%)
x86 defconfig, clean, clang 31.2s 29.8s -1.4s (-5%)
x86 allmodconfig, touch mm/vma.c, gcc 35.8s 35.0s -0.77s (-2%)
x86 allmodconfig, touch mm/vma.c, clang 35.8s 33.7s -2.0s (-6%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
scripts/Makefile | 4 +-
scripts/kallsyms-sysmap.c | 269 ++++++++++++++++++++++++++++++++++++++++++++++
scripts/kallsyms.c | 162 ++++++++++++++++------------
scripts/kallsyms.h | 44 ++++++++
scripts/link-vmlinux.sh | 15 +--
scripts/mksysmap | 94 ----------------
6 files changed, 415 insertions(+), 173 deletions(-)
diff --git a/scripts/Makefile b/scripts/Makefile
index 3434a82a119f..d46932113b5f 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -3,7 +3,7 @@
# scripts contains sources for various helper programs used throughout
# the kernel for the build process.
-hostprogs-always-$(CONFIG_KALLSYMS) += kallsyms
+hostprogs-always-y += kallsyms
hostprogs-always-$(BUILD_C_RECORDMCOUNT) += recordmcount
hostprogs-always-$(CONFIG_BUILDTIME_TABLE_SORT) += sorttable
hostprogs-always-$(CONFIG_ASN1) += asn1_compiler
@@ -13,6 +13,7 @@ hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS) += rustdoc_test_builder
hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS) += rustdoc_test_gen
hostprogs-always-$(CONFIG_TRACEPOINTS) += tracepoint-update
+kallsyms-objs := kallsyms.o kallsyms-sysmap.o elf-parse.o
sorttable-objs := sorttable.o elf-parse.o
tracepoint-update-objs := tracepoint-update.o elf-parse.o
@@ -30,6 +31,7 @@ rustdoc_test_builder-rust := y
rustdoc_test_gen-rust := y
HOSTCFLAGS_tracepoint-update.o = -I$(srctree)/tools/include
+HOSTCFLAGS_kallsyms-sysmap.o = -I$(srctree)/tools/include
HOSTCFLAGS_elf-parse.o = -I$(srctree)/tools/include
HOSTCFLAGS_sorttable.o = -I$(srctree)/tools/include
HOSTLDLIBS_sorttable = -lpthread
diff --git a/scripts/kallsyms-sysmap.c b/scripts/kallsyms-sysmap.c
new file mode 100644
index 000000000000..64b2e11d0344
--- /dev/null
+++ b/scripts/kallsyms-sysmap.c
@@ -0,0 +1,269 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Obtain symbols from vmlinux for usage by kallsyms. Replaces mksysmap.
+ *
+ * To retain compatibility, it provides the same output as nm, only faster.
+ */
+
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <xalloc.h>
+
+#include "elf-parse.h"
+#include "kallsyms.h"
+
+/* The mapped file and its symbol table. */
+struct elf_file {
+ void *base;
+ size_t size;
+ const char *shdrs;
+ unsigned int shnum, shentsize;
+ const char *shstrtab;
+ Elf_Shdr *symtab;
+ const char *strtab;
+ size_t nr_syms;
+};
+
+/* What mksysmap dropped from System.map, by name. */
+static const char *const sysmap_omit_prefixes[] = {
+ "$", ".L", "__efistub_", "__pi_$", "__pi_.L", "__kvm_nvhe_$",
+ "__kvm_nvhe_.L", "__kcfi_typeid_", "__kvm_nvhe___kcfi_typeid_",
+ "__pi___kcfi_typeid_", "__crc_", "__kstrtab_", "__kstrtabns_",
+ "__mod_device_table__",
+};
+static const char *const sysmap_omit_suffixes[] = {
+ "_from_arm", "_from_thumb", "_veneer",
+};
+static const char *const sysmap_omit_names[] = {
+ "L0", "_SDA_BASE_", "_SDA2_BASE_",
+};
+
+/* __<alnum>*Thunk_: the linker's range extension thunks on arm. */
+static bool is_range_thunk(const char *name)
+{
+ const char *p;
+
+ if (!string_starts_with(name, "__"))
+ return false;
+ for (p = name + 2; isalnum((unsigned char)*p); p++)
+ ;
+ return p - name >= 7 && *p == '_' && strncmp(p - 5, "Thunk", 5) == 0;
+}
+
+/* __UNIQUE_ID_modinfo_<n>: the MODULE_INFO() strings of built-in code. */
+static bool is_modinfo_id(const char *name)
+{
+ static const char prefix[] = "__UNIQUE_ID_modinfo_";
+ const char *p;
+
+ if (!string_starts_with(name, prefix))
+ return false;
+ for (p = name + strlen(prefix); isdigit((unsigned char)*p); p++)
+ ;
+ return !*p;
+}
+
+static bool sysmap_omits(const char *name, char type)
+{
+ size_t i;
+
+ /* Absolute, undefined and debugging symbols. */
+ if (type == 'a' || type == 'N' || type == 'U' || type == 'w')
+ return true;
+
+ for (i = 0; i < ARRAY_SIZE(sysmap_omit_prefixes); i++)
+ if (string_starts_with(name, sysmap_omit_prefixes[i]))
+ return true;
+ for (i = 0; i < ARRAY_SIZE(sysmap_omit_suffixes); i++)
+ if (string_ends_with(name, sysmap_omit_suffixes[i]))
+ return true;
+ for (i = 0; i < ARRAY_SIZE(sysmap_omit_names); i++)
+ if (strcmp(name, sysmap_omit_names[i]) == 0)
+ return true;
+
+ return is_range_thunk(name) || is_modinfo_id(name) ||
+ strstr(name, ".long_branch.") || strstr(name, ".plt_branch.");
+}
+
+static Elf_Shdr *elf_section(const struct elf_file *elf, unsigned int index)
+{
+ return (Elf_Shdr *)(elf->shdrs + (size_t)index * elf->shentsize);
+}
+
+static const char *elf_section_name(const struct elf_file *elf, Elf_Shdr *shdr)
+{
+ return elf->shstrtab + shdr_name(shdr);
+}
+
+static Elf_Sym *elf_symbol(const struct elf_file *elf, size_t index)
+{
+ const char *base = elf->base;
+
+ return (Elf_Sym *)(base + shdr_offset(elf->symtab) +
+ index * shdr_entsize(elf->symtab));
+}
+
+/* nm's letter for a symbol defined in a section, as BFD classifies it. */
+static char section_symbol_type(Elf_Shdr *shdr, const char *secname)
+{
+ static const char *const debug_prefixes[] = {
+ ".debug", ".zdebug", ".gnu.debuglto_.debug_",
+ ".gnu.linkonce.wi.", ".line", ".stab",
+ };
+ const uint64_t flags = shdr_flags(shdr);
+ size_t i;
+
+ if (flags & SHF_EXECINSTR)
+ return 't';
+ if (flags & SHF_ALLOC) {
+ if (shdr_type(shdr) == SHT_NOBITS)
+ return 'b';
+ return flags & SHF_WRITE ? 'd' : 'r';
+ }
+ for (i = 0; i < ARRAY_SIZE(debug_prefixes); i++)
+ if (string_starts_with(secname, debug_prefixes[i]))
+ return 'N';
+ if (shdr_type(shdr) != SHT_NOBITS && !(flags & SHF_WRITE))
+ return 'n';
+ return '?';
+}
+
+/* The letter nm prints for a symbol, or 0 for one it leaves out. */
+static char elf_symbol_type(const struct elf_file *elf, Elf_Sym *sym)
+{
+ unsigned int bind = sym_bind(sym), type = sym_type(sym);
+ unsigned int shndx = sym_shndx(sym);
+ Elf_Shdr *shdr;
+ char c;
+
+ if (type == STT_SECTION || type == STT_FILE)
+ return 0;
+ if (shndx == SHN_COMMON)
+ return 'C';
+ if (shndx == SHN_UNDEF) {
+ if (bind == STB_WEAK)
+ return type == STT_OBJECT ? 'v' : 'w';
+ return 'U';
+ }
+ if (type == STT_GNU_IFUNC)
+ return 'i';
+ if (bind == STB_WEAK)
+ return type == STT_OBJECT ? 'V' : 'W';
+ if (bind == STB_GNU_UNIQUE)
+ return 'u';
+ if (bind != STB_GLOBAL && bind != STB_LOCAL)
+ return '?';
+
+ if (shndx == SHN_ABS) {
+ c = 'a';
+ } else if (shndx < elf->shnum) {
+ shdr = elf_section(elf, shndx);
+ c = section_symbol_type(shdr, elf_section_name(elf, shdr));
+ } else {
+ return '?';
+ }
+
+ return bind == STB_GLOBAL ? toupper(c) : c;
+}
+
+/* nm -n order: by address, then by name. */
+static int compare_symbols(const void *a, const void *b)
+{
+ const struct sysmap_symbol *sa = a, *sb = b;
+
+ if (sa->addr != sb->addr)
+ return sa->addr < sb->addr ? -1 : 1;
+ return strcmp(sa->name, sb->name);
+}
+
+static void elf_open(struct elf_file *elf, const char *path)
+{
+ Elf_Ehdr *ehdr;
+ unsigned int i;
+
+ elf->base = elf_map_ro(path, &elf->size, (1 << ET_EXEC) | (1 << ET_DYN));
+ if (!elf->base)
+ exit(EXIT_FAILURE);
+
+ ehdr = elf->base;
+ elf->shdrs = (const char *)elf->base + ehdr_shoff(ehdr);
+ elf->shnum = ehdr_shnum(ehdr);
+ elf->shentsize = ehdr_shentsize(ehdr);
+ elf->shstrtab = (const char *)elf->base +
+ shdr_offset(elf_section(elf, ehdr_shstrndx(ehdr)));
+
+ for (i = 0; i < elf->shnum && !elf->symtab; i++)
+ if (shdr_type(elf_section(elf, i)) == SHT_SYMTAB)
+ elf->symtab = elf_section(elf, i);
+
+ if (!elf->symtab) {
+ fprintf(stderr, "%s: no symbol table\n", path);
+ exit(EXIT_FAILURE);
+ }
+
+ elf->strtab = (const char *)elf->base +
+ shdr_offset(elf_section(elf, shdr_link(elf->symtab)));
+ elf->nr_syms = shdr_size(elf->symtab) / shdr_entsize(elf->symtab);
+}
+
+/* The symbols "nm -n | mksysmap" would list, in that order. */
+static struct sysmap_symbol *elf_read_symbols(const struct elf_file *elf,
+ size_t *nr_kept)
+{
+ struct sysmap_symbol *syms = xmalloc(elf->nr_syms * sizeof(*syms));
+ size_t i, n = 0;
+
+ for (i = 1; i < elf->nr_syms; i++) {
+ Elf_Sym *sym = elf_symbol(elf, i);
+ const char *name = elf->strtab + sym_name(sym);
+ char type = elf_symbol_type(elf, sym);
+
+ if (!type || sysmap_omits(name, type))
+ continue;
+
+ syms[n].addr = sym_value(sym);
+ syms[n].name = name;
+ syms[n].type = type;
+ n++;
+ }
+
+ qsort(syms, n, sizeof(*syms), compare_symbols);
+ *nr_kept = n;
+ return syms;
+}
+
+struct sysmap *sysmap_read(const char *path)
+{
+ struct sysmap *map = xcalloc(1, sizeof(*map));
+ struct elf_file elf = {};
+
+ elf_open(&elf, path);
+ map->syms = elf_read_symbols(&elf, &map->nr_syms);
+ map->addr_width = elf_map_long_size(elf.base) * 2;
+ /* The names point into the mapping; keep it until the map is freed. */
+ map->file = elf.base;
+ map->file_size = elf.size;
+
+ return map;
+}
+
+void sysmap_write(const struct sysmap *map, FILE *out)
+{
+ size_t i;
+
+ for (i = 0; i < map->nr_syms; i++) {
+ const struct sysmap_symbol *s = &map->syms[i];
+
+ fprintf(out, "%0*llx %c %s\n", map->addr_width, s->addr, s->type,
+ s->name);
+ }
+}
+
+void sysmap_free(struct sysmap *map)
+{
+ free(map->syms);
+ elf_unmap(map->file, map->file_size);
+ free(map);
+}
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 89f5207f74d2..d996a43c4078 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -5,7 +5,12 @@
* This software may be used and distributed according to the terms
* of the GNU General Public License, incorporated herein by reference.
*
- * Usage: kallsyms [--all-symbols] [--pc-relative] in.map out.bin > out.S
+ * Usage: kallsyms [--all-symbols] [--pc-relative] [--sysmap=out.map] in out.bin > out.S
+ * kallsyms --sysmap=out.map in
+ *
+ * in is vmlinux; an empty file stands for the first link, which has no
+ * symbols yet, and gives an empty table. --sysmap also writes the symbols
+ * in System.map format.
*
* The byte tables go to out.bin and are pulled into out.S with .incbin;
* wider tables stay assembler source for endianness and relocations.
@@ -21,7 +26,6 @@
*
*/
-#include <errno.h>
#include <getopt.h>
#include <stdbool.h>
#include <stdio.h>
@@ -29,10 +33,10 @@
#include <string.h>
#include <ctype.h>
#include <limits.h>
-
+#include <sys/stat.h>
#include <xalloc.h>
-#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
+#include "kallsyms.h"
#define KSYM_NAME_LEN 512
@@ -105,11 +109,13 @@ static void sym_arr_free(struct sym_arr *arr)
static void usage(void)
{
- fprintf(stderr, "Usage: kallsyms [--all-symbols] [--pc-relative] in.map out.bin > out.S\n");
+ fprintf(stderr, "Usage: kallsyms [--all-symbols] [--pc-relative] [--sysmap=out.map]\n"
+ " in out.bin > out.S\n"
+ " kallsyms --sysmap=out.map vmlinux\n");
exit(1);
}
-static char *sym_name(const struct sym_entry *s)
+static char *sym_entry_name(const struct sym_entry *s)
{
return (char *)s->sym + 1;
}
@@ -150,37 +156,12 @@ static void check_symbol_range(const char *sym, unsigned long long addr,
}
}
-static struct sym_entry *read_symbol(FILE *in, char **buf, size_t *buf_len)
+static struct sym_entry *add_symbol(unsigned long long addr, char type,
+ const char *name)
{
- char *name, type, *p;
- unsigned long long addr;
- size_t len;
- ssize_t readlen;
+ size_t len = strlen(name);
struct sym_entry *sym;
- errno = 0;
- readlen = getline(buf, buf_len, in);
- if (readlen < 0) {
- if (errno) {
- perror("read_symbol");
- exit(EXIT_FAILURE);
- }
- return NULL;
- }
-
- if ((*buf)[readlen - 1] == '\n')
- (*buf)[readlen - 1] = 0;
-
- addr = strtoull(*buf, &p, 16);
-
- if (*buf == p || *p++ != ' ' || !isascii((type = *p++)) || *p++ != ' ') {
- fprintf(stderr, "line format error\n");
- exit(EXIT_FAILURE);
- }
-
- name = p;
- len = strlen(name);
-
if (len >= KSYM_NAME_LEN) {
fprintf(stderr, "Symbol %s too long for kallsyms (%zu >= %d).\n"
"Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n",
@@ -205,7 +186,7 @@ static struct sym_entry *read_symbol(FILE *in, char **buf, size_t *buf_len)
sym->addr = addr;
sym->len = len;
sym->sym[0] = type;
- strcpy(sym_name(sym), name);
+ strcpy(sym_entry_name(sym), name);
return sym;
}
@@ -226,14 +207,9 @@ static int symbol_in_range(const struct sym_entry *s,
return 0;
}
-static bool string_starts_with(const char *s, const char *prefix)
-{
- return strncmp(s, prefix, strlen(prefix)) == 0;
-}
-
static int symbol_valid(const struct sym_entry *s)
{
- const char *name = sym_name(s);
+ const char *name = sym_entry_name(s);
/* if --all-symbols is not specified, then symbols outside the text
* and inittext sections are discarded */
@@ -283,36 +259,55 @@ static void shrink_table(void)
table_cnt = pos;
}
-static void read_map(const char *in)
+static void add_table_entry(struct sym_entry *sym)
{
- FILE *fp;
- struct sym_entry *sym;
- char *buf = NULL;
- size_t buflen = 0;
+ sym->seq = table_cnt;
- fp = fopen(in, "r");
- if (!fp) {
- perror(in);
- exit(1);
+ if (table_cnt >= table_size) {
+ table_size += 10000;
+ table = xrealloc(table, sizeof(*table) * table_size);
}
- while (!feof(fp)) {
- sym = read_symbol(fp, &buf, &buflen);
- if (!sym)
- continue;
+ table[table_cnt++] = sym;
+}
- sym->seq = table_cnt;
+static bool file_is_empty(const char *path)
+{
+ struct stat st;
- if (table_cnt >= table_size) {
- table_size += 10000;
- table = xrealloc(table, sizeof(*table) * table_size);
- }
+ if (stat(path, &st)) {
+ perror(path);
+ exit(EXIT_FAILURE);
+ }
+
+ return st.st_size == 0;
+}
+
+/*
+ * Read the symbols from vmlinux, writing System.map if asked to. The first
+ * link has no symbols yet: an empty file gives an empty table.
+ */
+static void read_elf(const char *path, FILE *sysmap_out)
+{
+ struct sysmap *map;
+ size_t i;
+
+ if (file_is_empty(path))
+ return;
+
+ map = sysmap_read(path);
+ if (sysmap_out)
+ sysmap_write(map, sysmap_out);
+
+ for (i = 0; i < map->nr_syms; i++) {
+ const struct sysmap_symbol *s = &map->syms[i];
+ struct sym_entry *sym = add_symbol(s->addr, s->type, s->name);
- table[table_cnt++] = sym;
+ if (sym)
+ add_table_entry(sym);
}
- free(buf);
- fclose(fp);
+ sysmap_free(map);
}
static void output_label(const char *label)
@@ -375,7 +370,7 @@ static int compare_names(const void *a, const void *b)
const struct sym_entry *sa = *(const struct sym_entry **)a;
const struct sym_entry *sb = *(const struct sym_entry **)b;
- ret = strcmp(sym_name(sa), sym_name(sb));
+ ret = strcmp(sym_entry_name(sa), sym_entry_name(sb));
if (!ret) {
if (sa->addr > sb->addr)
return 1;
@@ -751,7 +746,7 @@ static void optimize_token_table(void)
/* guess for "linker script provide" symbol */
static int may_be_linker_script_provide_symbol(const struct sym_entry *se)
{
- const char *symbol = sym_name(se);
+ const char *symbol = sym_entry_name(se);
int len = se->len - 1;
if (len < 8)
@@ -808,8 +803,8 @@ static int compare_symbols(const void *a, const void *b)
return wa - wb;
/* sort by the number of prefix underscores */
- wa = strspn(sym_name(sa), "_");
- wb = strspn(sym_name(sb), "_");
+ wa = strspn(sym_entry_name(sa), "_");
+ wb = strspn(sym_entry_name(sb), "_");
if (wa != wb)
return wa - wb;
@@ -824,13 +819,14 @@ static void sort_symbols(void)
int main(int argc, char **argv)
{
- const char *out_bin_name;
- FILE *out_bin_file;
+ const char *in, *sysmap = NULL, *out_bin_name;
+ FILE *sysmap_out = NULL, *out_bin_file;
while (1) {
static const struct option long_options[] = {
{"all-symbols", no_argument, &all_symbols, 1},
{"pc-relative", no_argument, &pc_relative, 1},
+ {"sysmap", required_argument, NULL, 's'},
{},
};
@@ -838,13 +834,33 @@ int main(int argc, char **argv)
if (c == -1)
break;
- if (c != 0)
+ if (c == 's')
+ sysmap = optarg;
+ else if (c != 0)
usage();
}
- if (optind + 2 != argc)
+ if (optind + 2 != argc && !(sysmap && optind + 1 == argc))
usage();
+ in = argv[optind];
+ if (sysmap) {
+ sysmap_out = fopen(sysmap, "w");
+ if (!sysmap_out) {
+ perror(sysmap);
+ exit(EXIT_FAILURE);
+ }
+ }
+
+ if (optind + 1 == argc) {
+ read_elf(in, sysmap_out);
+ if (fclose(sysmap_out)) {
+ perror(sysmap);
+ exit(EXIT_FAILURE);
+ }
+ return 0;
+ }
+
out_bin_name = argv[optind + 1];
out_bin_file = fopen(out_bin_name, "w");
if (!out_bin_file) {
@@ -852,7 +868,11 @@ int main(int argc, char **argv)
exit(EXIT_FAILURE);
}
- read_map(argv[optind]);
+ read_elf(in, sysmap_out);
+ if (sysmap_out && fclose(sysmap_out)) {
+ perror(sysmap);
+ exit(EXIT_FAILURE);
+ }
shrink_table();
sort_symbols();
optimize_token_table();
diff --git a/scripts/kallsyms.h b/scripts/kallsyms.h
new file mode 100644
index 000000000000..12096978075f
--- /dev/null
+++ b/scripts/kallsyms.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef KALLSYMS_H
+#define KALLSYMS_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <array_size.h>
+
+static inline bool string_starts_with(const char *s, const char *prefix)
+{
+ return strncmp(s, prefix, strlen(prefix)) == 0;
+}
+
+static inline bool string_ends_with(const char *s, const char *suffix)
+{
+ size_t len = strlen(s), suffix_len = strlen(suffix);
+
+ return len >= suffix_len && strcmp(s + len - suffix_len, suffix) == 0;
+}
+
+/* A symbol as nm lists it. */
+struct sysmap_symbol {
+ unsigned long long addr;
+ const char *name;
+ char type;
+};
+
+/* The symbols of an ELF file that System.map lists, in its order. */
+struct sysmap {
+ struct sysmap_symbol *syms;
+ size_t nr_syms;
+ int addr_width; /* hex digits of an address */
+ void *file; /* the mapping the names point into */
+ size_t file_size;
+};
+
+struct sysmap *sysmap_read(const char *path);
+void sysmap_write(const struct sysmap *map, FILE *out);
+void sysmap_free(struct sysmap *map);
+
+#endif /* KALLSYMS_H */
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index ed5ff97c0667..c520741f85c2 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -123,11 +123,15 @@ kallsymso_changed()
! cmp -s "${kallsymso_prev}.sym" "${kallsymso}.sym"
}
-# Create ${2}.o file with all symbols from the ${1} object file
+# Create ${2}.o with the kallsyms tables for ${1} (the vmlinux, or an empty
+# listing for the first pass); list the symbols used in ${3} if given.
kallsyms()
{
local kallsymopt;
+ if [ -n "${3:-}" ]; then
+ kallsymopt="--sysmap=${3}"
+ fi
if is_enabled CONFIG_KALLSYMS_ALL; then
kallsymopt="${kallsymopt} --all-symbols"
fi
@@ -150,18 +154,15 @@ kallsyms()
# Perform kallsyms for the given temporary vmlinux.
sysmap_and_kallsyms()
{
- mksysmap "${1}" "${1}.syms"
- kallsyms "${1}.syms" "${1}.kallsyms"
-
+ kallsyms "${1}" "${1}.kallsyms" "${1}.syms"
kallsyms_sysmap=${1}.syms
}
# Create map file with all symbols from ${1}
-# See mksymap for additional details
mksysmap()
{
- info NM ${2}
- ${NM} -n "${1}" | sed -f "${srctree}/scripts/mksysmap" > "${2}"
+ info SYSMAP ${2}
+ scripts/kallsyms --sysmap="${2}" "${1}"
}
sorttable()
diff --git a/scripts/mksysmap b/scripts/mksysmap
deleted file mode 100755
index 856b26ba2ac0..000000000000
--- a/scripts/mksysmap
+++ /dev/null
@@ -1,94 +0,0 @@
-#!/bin/sed -f
-# SPDX-License-Identifier: GPL-2.0-only
-#
-# sed script to filter out symbols that are not needed for System.map,
-# or not suitable for kallsyms. The input should be 'nm -n <file>'.
-#
-# System.map is used by module-init tools and some debugging
-# tools to retrieve the actual addresses of symbols in the kernel.
-#
-# readprofile starts reading symbols when _stext is found, and
-# continue until it finds a symbol which is not either of 'T', 't',
-# 'W' or 'w'.
-#
-# ---------------------------------------------------------------------------
-# Ignored symbol types
-#
-
-# a: local absolute symbols
-# N: debugging symbols
-# U: undefined global symbols
-# w: local weak symbols
-/ [aNUw] /d
-
-# ---------------------------------------------------------------------------
-# Ignored prefixes
-# (do not forget a space before each pattern)
-
-# local symbols for ARM, MIPS, etc.
-/ \$/d
-
-# local labels, .LBB, .Ltmpxxx, .L__unnamed_xx, .LASANPC, etc.
-/ \.L/d
-
-# arm64 EFI stub namespace
-/ __efistub_/d
-
-# arm64 local symbols in PIE namespace
-/ __pi_\$/d
-/ __pi_\.L/d
-
-# arm64 local symbols in non-VHE KVM namespace
-/ __kvm_nvhe_\$/d
-/ __kvm_nvhe_\.L/d
-
-# lld arm/aarch64/mips thunks
-/ __[[:alnum:]]*Thunk_/d
-
-# CFI type identifiers
-/ __kcfi_typeid_/d
-/ __kvm_nvhe___kcfi_typeid_/d
-/ __pi___kcfi_typeid_/d
-
-# CRC from modversions
-/ __crc_/d
-
-# EXPORT_SYMBOL (symbol name)
-/ __kstrtab_/d
-
-# EXPORT_SYMBOL (namespace)
-/ __kstrtabns_/d
-
-# MODULE_DEVICE_TABLE (symbol name)
-/ __mod_device_table__/d
-
-# ---------------------------------------------------------------------------
-# Ignored suffixes
-# (do not forget '$' after each pattern)
-
-# arm
-/_from_arm$/d
-/_from_thumb$/d
-/_veneer$/d
-
-# ---------------------------------------------------------------------------
-# Ignored symbols (exact match)
-# (do not forget a space before and '$' after each pattern)
-
-# for LoongArch?
-/ L0$/d
-
-# ppc
-/ _SDA_BASE_$/d
-/ _SDA2_BASE_$/d
-
-# MODULE_INFO()
-/ __UNIQUE_ID_modinfo_[0-9]*$/d
-
-# ---------------------------------------------------------------------------
-# Ignored patterns
-# (symbols that contain the pattern are ignored)
-
-# ppc stub
-/\.long_branch\./d
-/\.plt_branch\./d
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 07/21] kallsyms: reimplement mksysmap in C
2026-09-14 9:22 ` [PATCH v2 07/21] kallsyms: reimplement mksysmap in C Lorenzo Stoakes (ARM)
@ 2026-09-14 16:33 ` Markus Elfring
2026-09-14 16:54 ` Markus Elfring
2026-09-14 17:01 ` Markus Elfring
2 siblings, 0 replies; 58+ messages in thread
From: Markus Elfring @ 2026-09-14 16:33 UTC (permalink / raw)
To: Lorenzo Stoakes, linux-kbuild, x86, Albert Ou, Alexandre Courbot,
Alexandre Ghiti, Alexey Gladkov, Alice Ryhl, Andreas Hindborg,
Ard Biesheuvel, Arnd Bergmann, Benno Lossin, Bill Wendling,
Björn Roy Baron, Boqun Feng, Borislav Petkov,
Catalin Marinas, Daniel Almeida, Danilo Krummrich, Dave Hansen,
Gary Guo, Gustavo A. R. Silva, H. Peter Anvin, Ilias Apalodimas,
Ingo Molnar, Jonathan Corbet, Josh Poimboeuf, Justin Stitt,
Kees Cook, Linus Torvalds, Mark Rutland, Masahiro Yamada,
Miguel Ojeda, Nathan Chancellor, Nick Desaulniers,
Nicolas Schier, Onur Özkan, Palmer Dabbelt, Paul Walmsley,
Peter Zijlstra, Randy Dunlap, Tamir Duberstein, Thomas Gleixner,
Trevor Gross, Will Deacon
Cc: LKML, kernel-janitors, linux-hardening, linux-doc, linux-efi,
rust-for-linux, linux-arch, llvm, linux-riscv, linux-arm-kernel,
Jens Axboe
…
> +++ b/scripts/kallsyms-sysmap.c
> @@ -0,0 +1,269 @@
…
> +void sysmap_write(const struct sysmap *map, FILE *out)
> +{
> + size_t i;
> +
> + for (i = 0; i < map->nr_syms; i++) {
> + const struct sysmap_symbol *s = &map->syms[i];
> +
> + fprintf(out, "%0*llx %c %s\n", map->addr_width, s->addr, s->type,
> + s->name);
> + }
> +}
…
How do you think about to achieve more complete error detection?
https://cmu-sei.github.io/secure-coding-standards/sei-cert-c-coding-standard/rules/error-handling-err/err33-c/
https://cwe.mitre.org/data/definitions/252.html
Regards,
Markus
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 07/21] kallsyms: reimplement mksysmap in C
2026-09-14 9:22 ` [PATCH v2 07/21] kallsyms: reimplement mksysmap in C Lorenzo Stoakes (ARM)
2026-09-14 16:33 ` Markus Elfring
@ 2026-09-14 16:54 ` Markus Elfring
2026-09-14 17:01 ` Markus Elfring
2 siblings, 0 replies; 58+ messages in thread
From: Markus Elfring @ 2026-09-14 16:54 UTC (permalink / raw)
To: Lorenzo Stoakes, linux-kbuild, x86, Albert Ou, Alexandre Courbot,
Alexandre Ghiti, Alexey Gladkov, Alice Ryhl, Andreas Hindborg,
Ard Biesheuvel, Arnd Bergmann, Benno Lossin, Bill Wendling,
Björn Roy Baron, Boqun Feng, Borislav Petkov,
Catalin Marinas, Daniel Almeida, Danilo Krummrich, Dave Hansen,
Gary Guo, Gustavo A. R. Silva, H. Peter Anvin, Ilias Apalodimas,
Ingo Molnar, Jonathan Corbet, Josh Poimboeuf, Justin Stitt,
Kees Cook, Linus Torvalds, Mark Rutland, Masahiro Yamada,
Miguel Ojeda, Nathan Chancellor, Nick Desaulniers,
Nicolas Schier, Onur Özkan, Palmer Dabbelt, Paul Walmsley,
Peter Zijlstra, Randy Dunlap, Tamir Duberstein, Thomas Gleixner,
Trevor Gross, Will Deacon
Cc: LKML, kernel-janitors, linux-hardening, linux-doc, linux-efi,
rust-for-linux, linux-arch, llvm, linux-riscv, linux-arm-kernel,
Jens Axboe
…
> +++ b/scripts/kallsyms.c
…
> @@ -838,13 +834,33 @@ int main(int argc, char **argv)
…
> + in = argv[optind];
> + if (sysmap) {
> + sysmap_out = fopen(sysmap, "w");
> + if (!sysmap_out) {
> + perror(sysmap);
> + exit(EXIT_FAILURE);
> + }
> + }
> +
> + if (optind + 1 == argc) {
> + read_elf(in, sysmap_out);
> + if (fclose(sysmap_out)) {
> + perror(sysmap);
> + exit(EXIT_FAILURE);
> + }
> + return 0;
> + }
> +
> out_bin_name = argv[optind + 1];
> out_bin_file = fopen(out_bin_name, "w");
> if (!out_bin_file) {
…
How do you think about to avoid a bit duplicate source code
by using a goto chain?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst?h=v7.3-rc3#n572
Regards,
Markus
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 07/21] kallsyms: reimplement mksysmap in C
2026-09-14 9:22 ` [PATCH v2 07/21] kallsyms: reimplement mksysmap in C Lorenzo Stoakes (ARM)
2026-09-14 16:33 ` Markus Elfring
2026-09-14 16:54 ` Markus Elfring
@ 2026-09-14 17:01 ` Markus Elfring
2 siblings, 0 replies; 58+ messages in thread
From: Markus Elfring @ 2026-09-14 17:01 UTC (permalink / raw)
To: Lorenzo Stoakes, linux-kbuild, x86, Albert Ou, Alexandre Courbot,
Alexandre Ghiti, Alexey Gladkov, Alice Ryhl, Andreas Hindborg,
Ard Biesheuvel, Arnd Bergmann, Benno Lossin, Bill Wendling,
Björn Roy Baron, Boqun Feng, Borislav Petkov,
Catalin Marinas, Daniel Almeida, Danilo Krummrich, Dave Hansen,
Gary Guo, Gustavo A. R. Silva, H. Peter Anvin, Ilias Apalodimas,
Ingo Molnar, Jonathan Corbet, Josh Poimboeuf, Justin Stitt,
Kees Cook, Linus Torvalds, Mark Rutland, Masahiro Yamada,
Miguel Ojeda, Nathan Chancellor, Nick Desaulniers,
Nicolas Schier, Onur Özkan, Palmer Dabbelt, Paul Walmsley,
Peter Zijlstra, Randy Dunlap, Tamir Duberstein, Thomas Gleixner,
Trevor Gross, Will Deacon
Cc: LKML, kernel-janitors, linux-hardening, linux-doc, linux-efi,
rust-for-linux, linux-arch, llvm, linux-riscv, linux-arm-kernel,
Jens Axboe
> mksysmap is a sed script consisting of 30 patterns which link-vmlinux.sh
> uses to generate *.syms files, and which kallsyms is then called against to
> generate *.kallsyms files, with the final vmlinux build ultimately
> generating System.map.
…
> This is unnecessary, instead have kallsyms simply read the ELF file
> directly making use of the existing elf-parse library in scripts/.
…
Are there further opportunities for parallel data processing for an improved
processing pipeline in this software area?
Regards,
Markus
^ permalink raw reply [flat|nested] 58+ messages in thread
* [PATCH v2 08/21] kbuild: cache list, composite object state per object
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (6 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 07/21] kallsyms: reimplement mksysmap in C Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 09/21] kbuild: implement and use depcheck to check dependency timestamps Lorenzo Stoakes (ARM)
` (13 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
When each object's command line is expanded, kbuild has to figure out on
multiple occasions whether it's built-in or part of a module and which
composite object it belongs to.
This causes the time spent on each directory in the kernel tree to grow
O(n^2) with its object count, which is especially problematic for instance
in drivers/gpu/drm/amd/amdgpu with 310 objects.
No-op builds (i.e. make -j $(nproc) when nothing has changed) are
particularly impacted by this.
Fix the issue by caching this data and looking it up instead of getting it
over and over again.
This has a particularly large impact on allmodconfig builds.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, no-op make, gcc 1.1s 1.1s -0.02s (-2%)
x86 defconfig, no-op make, clang 1.3s 1.3s -0.01s (-1%)
x86 allmodconfig, no-op make, gcc 15.3s 14.5s -0.83s (-5%)
x86 allmodconfig, no-op make, clang 16.2s 15.5s -0.65s (-4%)
x86 allmodconfig, touch mm/vma.c, gcc 35.0s 34.3s -0.77s (-2%)
x86 allmodconfig, touch mm/vma.c, clang 33.7s 33.2s -0.51s (-2%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
scripts/Makefile.build | 8 ++++++++
scripts/Makefile.lib | 7 +++----
2 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 4349108e75e1..2cabfe85b798 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -122,6 +122,14 @@ multi-obj-m := $(addprefix $(obj)/, $(multi-obj-m))
subdir-ym := $(addprefix $(obj)/, $(subdir-ym))
endif
+# Cache which list each object is in and which composite objects it belongs to,
+# once per object for $(part-of-builtin), $(part-of-module) and $(modname-multi).
+$(foreach o, $(real-obj-y) $(lib-y), $(eval part-of-builtin_$o := y))
+$(foreach o, $(real-obj-m), $(eval part-of-module_$o := y))
+$(foreach m, $(multi-obj-ym), \
+ $(foreach o, $(call suffix-search, $m, .o, -objs -y -m), \
+ $(eval modname-multi_$o += $(m:.o=))))
+
ifndef obj
$(warning kbuild: Makefile.build is included improperly)
endif
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0a4fdd8bd975..2f447bc25e7b 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -2,8 +2,7 @@
# Finds the multi-part object the current object will be linked into.
# If the object belongs to two or more multi-part objects, list them all.
-modname-multi = $(sort $(foreach m,$(multi-obj-ym),\
- $(if $(filter $*.o, $(call suffix-search, $m, .o, -objs -y -m)),$(m:.o=))))
+modname-multi = $(sort $(modname-multi_$*.o))
__modname = $(or $(modname-multi),$(basetarget))
@@ -149,8 +148,8 @@ endif
# If $(is-kernel-object) is 'y', this object will be linked to vmlinux or modules
is-kernel-object = $(or $(part-of-builtin),$(part-of-module))
-part-of-builtin = $(if $(filter $(basename $@).o, $(real-obj-y) $(lib-y)),y)
-part-of-module = $(if $(filter $(basename $@).o, $(real-obj-m)),y)
+part-of-builtin = $(part-of-builtin_$(basename $@).o)
+part-of-module = $(part-of-module_$(basename $@).o)
quiet_modtag = $(if $(part-of-module),[M], )
modkern_cflags = \
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 09/21] kbuild: implement and use depcheck to check dependency timestamps
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (7 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 08/21] kbuild: cache list, composite object state per object Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 10/21] kbuild: move the toolchain checks into init/Kconfig.toolchain Lorenzo Stoakes (ARM)
` (12 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
Each object's .cmd file lists its header dependencies, which often
consists of over a thousand dependencies.
When little has changed in the tree, this is what make spends most of its
time doing, spending over a second, single-threaded when parsing larger
directory trees.
It performs considerably more work that is actually necessary to get the
job done.
This can be done faster in C, so implement scripts/basic/depcheck to do so.
It does as little work as possible, reading the .cmd files from a
directory's targets and running stat on each dependency only a single time.
It generates a fragment holding only the saved command line for a target
whose dependencies all exist and are older than it, and the entire .cmd
file for any other.
That way, Makefile.build simply includes the fragment and the amount of
work make has to do is significantly reduced when there is not much work to
do.
If the operation fails, kbuild falls back to using .cmd files.
The result is exactly the same as before.
For drivers/gpu/drm/amd/amdgpu in an allmodconfig tree the fragment is a
fifth of the size of the .cmd files, make reads it in 10ms instead of
380ms, and the instance goes from 2.2s to 0.4s.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, no-op make, gcc 1.1s 0.78s -0.30s (-28%)
x86 defconfig, no-op make, clang 1.3s 0.94s -0.34s (-27%)
x86 allmodconfig, no-op make, gcc 14.5s 12.9s -1.6s (-11%)
x86 allmodconfig, no-op make, clang 15.5s 14.2s -1.3s (-9%)
x86 allmodconfig, touch mm/vma.c, gcc 34.3s 33.9s -0.33s (-1%)
x86 allmodconfig, touch mm/vma.c, clang 33.2s 32.2s -0.98s (-3%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
Makefile | 1 +
scripts/Makefile.build | 14 +-
scripts/basic/.gitignore | 1 +
scripts/basic/Makefile | 2 +-
scripts/basic/depcheck.c | 443 +++++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 459 insertions(+), 2 deletions(-)
diff --git a/Makefile b/Makefile
index dd4c10afbb7f..8105123bcf4d 100644
--- a/Makefile
+++ b/Makefile
@@ -2237,6 +2237,7 @@ clean: $(clean-dirs)
$(call cmd,rmfiles)
@find . $(RCS_FIND_IGNORE) \
\( -name '*.[aios]' -o -name '*.rsi' -o -name '*.ko' -o -name '.*.cmd' \
+ -o -name '.depcheck.mk' -o -name '.depcheck.mk.tmp' \
-o -name '*.ko.*' -o -name '*.o.thinlto.bc' \
-o -name '*.dtb' -o -name '*.dtbo' \
-o -name '*.dtb.S' -o -name '*.dtbo.S' \
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 2cabfe85b798..b9093b39cc2f 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -592,7 +592,19 @@ $(obj)/: $(if $(KBUILD_BUILTIN), $(targets-for-builtin)) \
existing-targets := $(wildcard $(sort $(targets)))
--include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+cmd-files := $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+# depcheck checks timestamps first and outputs only saved command lines of
+# up-to-date targets, falling back to .cmd files if it fails.
+depcheck := $(wildcard $(objtree)/scripts/basic/depcheck)
+
+ifneq ($(and $(depcheck),$(cmd-files)),)
+ifeq ($(shell $(depcheck) $(obj)/.depcheck.mk $(cmd-files) && echo ok),ok)
+cmd-files := $(obj)/.depcheck.mk
+endif
+endif
+
+-include $(cmd-files)
# Create directories for object files if they do not exist
obj-dirs := $(sort $(patsubst %/,%, $(dir $(targets))))
diff --git a/scripts/basic/.gitignore b/scripts/basic/.gitignore
index 07c195f605a1..761ee14f9477 100644
--- a/scripts/basic/.gitignore
+++ b/scripts/basic/.gitignore
@@ -1,3 +1,4 @@
# SPDX-License-Identifier: GPL-2.0-only
+/depcheck
/fixdep
/randstruct.seed
diff --git a/scripts/basic/Makefile b/scripts/basic/Makefile
index fb8e2c38fbc7..ff98780e474d 100644
--- a/scripts/basic/Makefile
+++ b/scripts/basic/Makefile
@@ -2,7 +2,7 @@
#
# fixdep: used to generate dependency information during build process
-hostprogs-always-y += fixdep
+hostprogs-always-y += fixdep depcheck
# randstruct: the seed is needed before building the gcc-plugin or
# before running a Clang kernel build.
diff --git a/scripts/basic/depcheck.c b/scripts/basic/depcheck.c
new file mode 100644
index 000000000000..ce5c4565ae31
--- /dev/null
+++ b/scripts/basic/depcheck.c
@@ -0,0 +1,443 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * depcheck - check the dependency timestamps of a directory's targets so that
+ * make reads only what it needs from their .cmd files.
+ *
+ * fixdep writes a .cmd file as:
+ *
+ * savedcmd_dir/foo.o := <command line>
+ *
+ * source_dir/foo.o := dir/foo.c
+ *
+ * deps_dir/foo.o := \
+ * include/linux/bar.h \
+ * $(wildcard include/config/BAZ) \
+ *
+ * dir/foo.o: $(deps_dir/foo.o)
+ *
+ * $(deps_dir/foo.o):
+ *
+ * and kbuild may append rules of its own after that, such as one making the
+ * target depend on objtool.
+ *
+ * For a target that exists and is newer than every dependency listed, make can
+ * have nothing to do with the list, so it is left out and only what precedes
+ * and follows it is passed on; for anything else the .cmd file is passed on in
+ * full.
+ *
+ * Usage: depcheck <output> <.cmd files...>
+ *
+ * The output is a makefile fragment to include in place of the .cmd files; a
+ * non-zero exit status means the caller should include those instead.
+ */
+#include <limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <time.h>
+#include <unistd.h>
+
+#include <hash.h>
+#include <hashtable.h>
+#include <xalloc.h>
+
+/* What fixdep writes, see above. */
+#define DEPS_PREFIX "deps_"
+#define DEPS_RULE_PREFIX "$(" DEPS_PREFIX
+#define RULE_SUFFIX ":"
+#define LINE_CONTINUATION " \\"
+#define WILDCARD_OPEN "$(wildcard "
+#define WILDCARD_CLOSE ")"
+#define CMD_SUFFIX ".cmd"
+
+/* A line of a .cmd file, without its newline. */
+struct line {
+ const char *text;
+ size_t len;
+};
+
+static bool is_blank(char chr)
+{
+ return chr == ' ' || chr == '\t';
+}
+
+static bool str_ends_with(const char *str, const char *suffix)
+{
+ const size_t len = strlen(str), suffix_len = strlen(suffix);
+
+ return len >= suffix_len && !strcmp(str + len - suffix_len, suffix);
+}
+
+static bool line_starts_with(const struct line *line, const char *prefix)
+{
+ const size_t len = strlen(prefix);
+
+ return line->len >= len && !memcmp(line->text, prefix, len);
+}
+
+static bool line_ends_with(const struct line *line, const char *suffix)
+{
+ const size_t len = strlen(suffix);
+
+ return line->len >= len &&
+ !memcmp(line->text + line->len - len, suffix, len);
+}
+
+static bool line_is_blank(const struct line *line)
+{
+ size_t i;
+
+ for (i = 0; i < line->len; i++)
+ if (!is_blank(line->text[i]))
+ return false;
+
+ return true;
+}
+
+/* Whether the line ends in " \", continuing the list on the next line. */
+static bool line_is_continued(const struct line *line)
+{
+ return line_ends_with(line, LINE_CONTINUATION);
+}
+
+static void line_strip_continuation(struct line *line)
+{
+ if (line_is_continued(line))
+ line->len -= strlen(LINE_CONTINUATION);
+}
+
+static void line_trim(struct line *line)
+{
+ while (line->len && is_blank(line->text[0])) {
+ line->text++;
+ line->len--;
+ }
+ while (line->len && is_blank(line->text[line->len - 1]))
+ line->len--;
+}
+
+/* Take the next line out of [*pos, end); false once there are none left. */
+static bool next_line(const char **pos, const char *end, struct line *line)
+{
+ const char *newline;
+
+ if (*pos >= end)
+ return false;
+
+ newline = memchr(*pos, '\n', end - *pos);
+ line->text = *pos;
+ line->len = (newline ? newline : end) - *pos;
+ *pos = newline ? newline + 1 : end;
+
+ return true;
+}
+
+/* Describes a dependency file. */
+struct dep {
+ struct hlist_node hnode;
+ struct timespec mtime;
+ bool exists;
+ char path[];
+};
+
+static HASHTABLE_DEFINE(dep_table, 1U << 16);
+
+static const struct dep *lookup_dep(const char *path)
+{
+ const unsigned int key = hash_str(path);
+ struct dep *dep;
+ struct stat st;
+
+ hash_for_each_possible(dep_table, dep, hnode, key) {
+ if (!strcmp(dep->path, path))
+ return dep;
+ }
+
+ dep = xmalloc(sizeof(*dep) + strlen(path) + 1);
+ strcpy(dep->path, path);
+ dep->exists = !stat(path, &st);
+ if (dep->exists)
+ dep->mtime = st.st_mtim;
+ hash_add(dep_table, &dep->hnode, key);
+
+ return dep;
+}
+
+/* Strictly newer, as make compares timestamps. */
+static bool newer(const struct timespec *time_a, const struct timespec *time_b)
+{
+ if (time_a->tv_sec != time_b->tv_sec)
+ return time_a->tv_sec > time_b->tv_sec;
+
+ return time_a->tv_nsec > time_b->tv_nsec;
+}
+
+/*
+ * $(wildcard include/config/FOO) is a prerequisite only while FOO is set:
+ * unwrap it and say that it is optional.
+ */
+static bool line_unwrap_wildcard(struct line *line)
+{
+ if (!line_starts_with(line, WILDCARD_OPEN) ||
+ !line_ends_with(line, WILDCARD_CLOSE))
+ return false;
+
+ line->text += strlen(WILDCARD_OPEN);
+ line->len -= strlen(WILDCARD_OPEN) + strlen(WILDCARD_CLOSE);
+
+ return true;
+}
+
+/* fixdep doubles '$' and escapes '#' in a path: undo that into path[]. */
+static bool unescape_path(const struct line *line, char *path, size_t size)
+{
+ size_t i, out_len = 0;
+
+ if (line->len >= size)
+ return false;
+
+ for (i = 0; i < line->len; i++) {
+ const char chr = line->text[i];
+ const char next_chr = i + 1 < line->len ? line->text[i + 1] : '\0';
+
+ if ((chr == '$' && next_chr == '$') || (chr == '\\' && next_chr == '#'))
+ i++;
+ path[out_len++] = line->text[i];
+ }
+ path[out_len] = '\0';
+
+ return true;
+}
+
+/* Is the path contained in line older than the target? */
+static bool dep_is_fresh(struct line line, const struct timespec *target)
+{
+ char path[PATH_MAX];
+ const struct dep *dep;
+ bool optional;
+
+ line_strip_continuation(&line);
+ line_trim(&line);
+ if (!line.len)
+ return false;
+
+ optional = line_unwrap_wildcard(&line);
+ if (!line.len || !unescape_path(&line, path, sizeof(path)))
+ return false;
+
+ dep = lookup_dep(path);
+ if (!dep->exists)
+ return optional;
+
+ return !newer(&dep->mtime, target);
+}
+
+/*
+ * Parse a dependency list which consists of one file per line and determine if
+ * all dependencies are 'fresh', i.e. older than the target.
+ */
+static bool deps_are_fresh(const char *pos, const char *end,
+ const struct timespec *target)
+{
+ struct line line;
+
+ while (next_line(&pos, end, &line)) {
+ if (line_is_blank(&line))
+ return true;
+ if (!dep_is_fresh(line, target))
+ return false;
+ if (!line_is_continued(&line))
+ return true;
+ }
+
+ return true;
+}
+
+/*
+ * Find the "deps_" line in the input.
+ *
+ * On success returns true and *deps_off is set to its offset and *list is set
+ * to the list's own lines start or NULL if the line is not continued.
+ *
+ * Otherwise returns false if the prefix cannot be found.
+ */
+static bool find_deps(const char *buf, size_t len, size_t *deps_off,
+ const char **list)
+{
+ const char *pos = buf, *end = buf + len;
+ struct line line;
+
+ while (next_line(&pos, end, &line)) {
+ if (!line_starts_with(&line, DEPS_PREFIX))
+ continue;
+
+ *deps_off = line.text - buf;
+ *list = line_is_continued(&line) ? pos : NULL;
+ return true;
+ }
+
+ return false;
+}
+
+/*
+ * Is this the target of a .cmd file, i.e. 'dir/.name.cmd names dir/name.'?
+ */
+static bool target_of(const char *cmd_path, char *target, size_t size)
+{
+ const char *slash = strrchr(cmd_path, '/');
+ const char *base = slash ? slash + 1 : cmd_path;
+ const size_t dir_len = base - cmd_path;
+ size_t name_len;
+
+ if (base[0] != '.' || !str_ends_with(base, CMD_SUFFIX))
+ return false;
+
+ name_len = strlen(base) - strlen(".") - strlen(CMD_SUFFIX);
+ if (!name_len)
+ return false;
+
+ return snprintf(target, size, "%.*s%.*s", (int)dir_len, cmd_path,
+ (int)name_len, base + 1) < (int)size;
+}
+
+/*
+ * Does the .cmd file's target exists and is it newer than everything in its
+ * dependency list?
+ *
+ * Returns true if so and sets *deps_off to the start of the list, otherwise
+ * returns false.
+ */
+static bool target_is_fresh(const char *cmd_path, const char *buf, size_t len,
+ size_t *deps_off)
+{
+ char target[PATH_MAX];
+ struct stat st;
+ const char *list;
+
+ if (!target_of(cmd_path, target, sizeof(target)) || stat(target, &st))
+ return false;
+ if (!find_deps(buf, len, deps_off, &list))
+ return false;
+ if (!list)
+ return true;
+
+ return deps_are_fresh(list, buf + len, &st.st_mtim);
+}
+
+static char *read_file(const char *path, size_t *len)
+{
+ FILE *file = fopen(path, "r");
+ struct stat st;
+ char *buf;
+ size_t nr_read = 0;
+
+ if (!file)
+ return NULL;
+ if (fstat(fileno(file), &st)) {
+ fclose(file);
+ return NULL;
+ }
+
+ buf = xmalloc(st.st_size + 1);
+ while (nr_read < (size_t)st.st_size) {
+ const size_t chunk = fread(buf + nr_read, 1, st.st_size - nr_read, file);
+
+ if (!chunk)
+ break;
+ nr_read += chunk;
+ }
+ fclose(file);
+
+ buf[nr_read] = '\0';
+ *len = nr_read;
+ return buf;
+}
+
+/*
+ * Find the end of the dependency block: the offset just past its closing
+ * "$(deps_x):" line. Anything after that was appended by kbuild and is not for
+ * us to judge. Returns len if the line cannot be found.
+ */
+static size_t deps_block_end(const char *buf, size_t len, size_t deps_off)
+{
+ const char *pos = buf + deps_off, *end = buf + len;
+ struct line line;
+
+ while (next_line(&pos, end, &line)) {
+ if (line_starts_with(&line, DEPS_RULE_PREFIX) &&
+ line_ends_with(&line, RULE_SUFFIX))
+ return pos - buf;
+ }
+
+ return len;
+}
+
+/* The target is fresh: pass on everything but the dependency block. */
+static void write_without_deps(FILE *out, const char *buf, size_t len,
+ size_t deps_off)
+{
+ const size_t tail_off = deps_block_end(buf, len, deps_off);
+
+ fwrite(buf, 1, deps_off, out);
+ fputc('\n', out);
+ fwrite(buf + tail_off, 1, len - tail_off, out);
+}
+
+/*
+ * Generate a fragment for make from one .cmd file - without the dependency
+ * block if the target is fresh, otherwise all of it.
+ */
+static void process(FILE *out, const char *cmd_path)
+{
+ size_t len, deps_off;
+ char *buf;
+
+ buf = read_file(cmd_path, &len);
+ if (!buf)
+ return;
+
+ if (target_is_fresh(cmd_path, buf, len, &deps_off))
+ write_without_deps(out, buf, len, deps_off);
+ else
+ fwrite(buf, 1, len, out);
+
+ free(buf);
+}
+
+int main(int argc, char **argv)
+{
+ char tmp_path[PATH_MAX];
+ FILE *out;
+ int i;
+
+ if (argc < 2) {
+ fprintf(stderr, "usage: %s <output> <.cmd files...>\n", argv[0]);
+ return 1;
+ }
+
+ if (snprintf(tmp_path, sizeof(tmp_path), "%s.tmp", argv[1]) >=
+ (int)sizeof(tmp_path)) {
+ fprintf(stderr, "%s: path too long\n", argv[1]);
+ return 1;
+ }
+
+ out = fopen(tmp_path, "w");
+ if (!out) {
+ perror(tmp_path);
+ return 1;
+ }
+
+ for (i = 2; i < argc; i++)
+ process(out, argv[i]);
+
+ /* Write errors are latched in the stream, so one check at the end covers them all. */
+ if (ferror(out) || fclose(out) || rename(tmp_path, argv[1])) {
+ perror(argv[1]);
+ unlink(tmp_path);
+ return 1;
+ }
+
+ return 0;
+}
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 10/21] kbuild: move the toolchain checks into init/Kconfig.toolchain
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (8 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 09/21] kbuild: implement and use depcheck to check dependency timestamps Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 11/21] kbuild: avoid re-running compiler and linker probes Lorenzo Stoakes (ARM)
` (11 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
init/Kconfig opens with two hundred lines identifying the compiler,
assembler, linker and rustc and probing which options they support, none of
it to do with init.
Move them into their own file, sourced from the top of init/Kconfig, so
that the next commit can add to them without growing init/Kconfig further.
No functional change.
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
init/Kconfig | 197 +-----------------------------------------------
init/Kconfig.toolchain | 198 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 199 insertions(+), 196 deletions(-)
diff --git a/init/Kconfig b/init/Kconfig
index 8583d9f06c52..b44a9482cdc9 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1,201 +1,6 @@
# SPDX-License-Identifier: GPL-2.0-only
-config CC_VERSION_TEXT
- string
- default "$(CC_VERSION_TEXT)"
- help
- This is used in unclear ways:
-
- - Re-run Kconfig when the compiler is updated
- The 'default' property references the environment variable,
- CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd.
- When the compiler is updated, Kconfig will be invoked.
-
- - Ensure full rebuild when the compiler is updated
- include/linux/compiler-version.h contains this option in the comment
- line so fixdep adds include/config/CC_VERSION_TEXT into the
- auto-generated dependency. When the compiler is updated, syncconfig
- will touch it and then every file will be rebuilt.
-
-config CC_IS_GCC
- def_bool $(success,test "$(cc-name)" = GCC)
-
-config GCC_VERSION
- int
- default $(cc-version) if CC_IS_GCC
- default 0
-
-config CC_IS_CLANG
- def_bool $(success,test "$(cc-name)" = Clang)
-
-config CLANG_VERSION
- int
- default $(cc-version) if CC_IS_CLANG
- default 0
-
-config AS_IS_GNU
- def_bool $(success,test "$(as-name)" = GNU)
-
-config AS_IS_LLVM
- def_bool $(success,test "$(as-name)" = LLVM)
-
-config AS_VERSION
- int
- # Use clang version if this is the integrated assembler
- default CLANG_VERSION if AS_IS_LLVM
- default $(as-version)
-
-config LD_IS_BFD
- def_bool $(success,test "$(ld-name)" = BFD)
-
-config LD_VERSION
- int
- default $(ld-version) if LD_IS_BFD
- default 0
-
-config LD_IS_LLD
- def_bool $(success,test "$(ld-name)" = LLD)
-
-config LLD_VERSION
- int
- default $(ld-version) if LD_IS_LLD
- default 0
-
-config RUSTC_VERSION
- int
- default $(rustc-version)
- help
- It does not depend on `RUST` since that one may need to use the version
- in a `depends on`.
-
-config RUST_IS_AVAILABLE
- def_bool $(success,$(srctree)/scripts/rust_is_available.sh)
- help
- This shows whether a suitable Rust toolchain is available (found).
-
- Please see Documentation/rust/quick-start.rst for instructions on how
- to satisfy the build requirements of Rust support.
-
- In particular, the Makefile target 'rustavailable' is useful to check
- why the Rust toolchain is not being detected.
-
-config RUSTC_LLVM_VERSION
- int
- default $(rustc-llvm-version)
-
-config RUSTC_LLVM_MAJOR_VERSION
- int
- default $(shell,expr $(rustc-llvm-version) / 10000)
-config RUSTC_CLANG_LLVM_COMPATIBLE
- bool
- default y if CC_IS_CLANG && RUSTC_LLVM_MAJOR_VERSION = $(shell,expr $(cc-version) / 10000)
- help
- This indicates whether Rust and Clang use LLVM of the same major
- version.
-
- Operations involving handling LLVM IR or bitcode (e.g. cross-language
- LTO) require the same LLVM major version to work properly. For best
- compatibility it is recommended that the exact same LLVM is used.
-
-config ARCH_HAS_CC_CAN_LINK
- bool
-
-config CC_CAN_LINK
- bool
- default ARCH_CC_CAN_LINK if ARCH_HAS_CC_CAN_LINK
- default $(cc_can_link_user,$(m64-flag)) if 64BIT
- default $(cc_can_link_user,$(m32-flag))
-
-# Fixed in GCC 14, 13.3, 12.4 and 11.5
-# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921
-config GCC_ASM_GOTO_OUTPUT_BROKEN
- bool
- depends on CC_IS_GCC
- default y if GCC_VERSION < 110500
- default y if GCC_VERSION >= 120000 && GCC_VERSION < 120400
- default y if GCC_VERSION >= 130000 && GCC_VERSION < 130300
-
-config CC_HAS_ASM_GOTO_OUTPUT
- def_bool y
- depends on !GCC_ASM_GOTO_OUTPUT_BROKEN
- depends on $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
-
-config CC_HAS_ASM_GOTO_TIED_OUTPUT
- depends on CC_HAS_ASM_GOTO_OUTPUT
- # Detect buggy gcc and clang, fixed in gcc-11 clang-14.
- def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null)
-
-config TOOLS_SUPPORT_RELR
- def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
-
-config CC_HAS_ASM_INLINE
- def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
-
-config CC_HAS_ASSUME
- bool
- # clang needs to be at least 19.1.0 since the meaning of the assume
- # attribute changed:
- # https://github.com/llvm/llvm-project/commit/c44fa3e8a9a44c2e9a575768a3c185354b9f6c17
- default y if CC_IS_CLANG && CLANG_VERSION >= 190100
- # supported since gcc 13.1.0
- # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106654
- default y if CC_IS_GCC && GCC_VERSION >= 130100
-
-config CC_HAS_NO_PROFILE_FN_ATTR
- def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)
-
-config CC_HAS_COUNTED_BY
- bool
- # clang needs to be at least 20.1.0 to avoid potential crashes
- # when building structures that contain __counted_by
- # https://github.com/ClangBuiltLinux/linux/issues/2114
- # https://github.com/llvm/llvm-project/commit/160fb1121cdf703c3ef5e61fb26c5659eb581489
- default y if CC_IS_CLANG && CLANG_VERSION >= 200100
- # supported since gcc 15.1.0
- # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
- default y if CC_IS_GCC && GCC_VERSION >= 150100
-
-config CC_HAS_COUNTED_BY_PTR
- bool
- # supported since clang 22
- default y if CC_IS_CLANG && CLANG_VERSION >= 220100
- # supported since gcc 16.0.0
- default y if CC_IS_GCC && GCC_VERSION >= 160000
-
-config CC_HAS_BROKEN_COUNTED_BY_REF
- bool
- # https://github.com/llvm/llvm-project/issues/182575
- default y if CC_IS_CLANG && CLANG_VERSION < 220100
-
-config CC_HAS_ALLOC_TOKEN
- def_bool $(cc-option,-falloc-token-max=123)
-
-config CC_HAS_MULTIDIMENSIONAL_NONSTRING
- def_bool $(success,echo 'char tag[][4] __attribute__((__nonstring__)) = { };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)
-
-config LD_CAN_USE_KEEP_IN_OVERLAY
- # ld.lld prior to 21.0.0 did not support KEEP within an overlay description
- # https://github.com/llvm/llvm-project/pull/130661
- def_bool LD_IS_BFD || LLD_VERSION >= 210000
-
-config RUSTC_HAS_SPAN_FILE
- def_bool RUSTC_VERSION >= 108800
-
-config RUSTC_HAS_UNNECESSARY_TRANSMUTES
- def_bool RUSTC_VERSION >= 108800
-
-config RUSTC_HAS_FILE_WITH_NUL
- def_bool RUSTC_VERSION >= 108900
-
-config RUSTC_HAS_FILE_AS_C_STR
- def_bool RUSTC_VERSION >= 109100
-
-config RUSTC_HAS_SUSPICIOUS_RUNTIME_SYMBOL_DEFINITIONS
- def_bool RUSTC_VERSION >= 109800
-
-config PAHOLE_VERSION
- int
- default "$(PAHOLE_VERSION)"
+source "init/Kconfig.toolchain"
config CONSTRUCTORS
bool
diff --git a/init/Kconfig.toolchain b/init/Kconfig.toolchain
new file mode 100644
index 000000000000..fac36246451f
--- /dev/null
+++ b/init/Kconfig.toolchain
@@ -0,0 +1,198 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config CC_VERSION_TEXT
+ string
+ default "$(CC_VERSION_TEXT)"
+ help
+ This is used in unclear ways:
+
+ - Re-run Kconfig when the compiler is updated
+ The 'default' property references the environment variable,
+ CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd.
+ When the compiler is updated, Kconfig will be invoked.
+
+ - Ensure full rebuild when the compiler is updated
+ include/linux/compiler-version.h contains this option in the comment
+ line so fixdep adds include/config/CC_VERSION_TEXT into the
+ auto-generated dependency. When the compiler is updated, syncconfig
+ will touch it and then every file will be rebuilt.
+
+config CC_IS_GCC
+ def_bool $(success,test "$(cc-name)" = GCC)
+
+config GCC_VERSION
+ int
+ default $(cc-version) if CC_IS_GCC
+ default 0
+
+config CC_IS_CLANG
+ def_bool $(success,test "$(cc-name)" = Clang)
+
+config CLANG_VERSION
+ int
+ default $(cc-version) if CC_IS_CLANG
+ default 0
+
+config AS_IS_GNU
+ def_bool $(success,test "$(as-name)" = GNU)
+
+config AS_IS_LLVM
+ def_bool $(success,test "$(as-name)" = LLVM)
+
+config AS_VERSION
+ int
+ # Use clang version if this is the integrated assembler
+ default CLANG_VERSION if AS_IS_LLVM
+ default $(as-version)
+
+config LD_IS_BFD
+ def_bool $(success,test "$(ld-name)" = BFD)
+
+config LD_VERSION
+ int
+ default $(ld-version) if LD_IS_BFD
+ default 0
+
+config LD_IS_LLD
+ def_bool $(success,test "$(ld-name)" = LLD)
+
+config LLD_VERSION
+ int
+ default $(ld-version) if LD_IS_LLD
+ default 0
+
+config RUSTC_VERSION
+ int
+ default $(rustc-version)
+ help
+ It does not depend on `RUST` since that one may need to use the version
+ in a `depends on`.
+
+config RUST_IS_AVAILABLE
+ def_bool $(success,$(srctree)/scripts/rust_is_available.sh)
+ help
+ This shows whether a suitable Rust toolchain is available (found).
+
+ Please see Documentation/rust/quick-start.rst for instructions on how
+ to satisfy the build requirements of Rust support.
+
+ In particular, the Makefile target 'rustavailable' is useful to check
+ why the Rust toolchain is not being detected.
+
+config RUSTC_LLVM_VERSION
+ int
+ default $(rustc-llvm-version)
+
+config RUSTC_LLVM_MAJOR_VERSION
+ int
+ default $(shell,expr $(rustc-llvm-version) / 10000)
+
+config RUSTC_CLANG_LLVM_COMPATIBLE
+ bool
+ default y if CC_IS_CLANG && RUSTC_LLVM_MAJOR_VERSION = $(shell,expr $(cc-version) / 10000)
+ help
+ This indicates whether Rust and Clang use LLVM of the same major
+ version.
+
+ Operations involving handling LLVM IR or bitcode (e.g. cross-language
+ LTO) require the same LLVM major version to work properly. For best
+ compatibility it is recommended that the exact same LLVM is used.
+
+config ARCH_HAS_CC_CAN_LINK
+ bool
+
+config CC_CAN_LINK
+ bool
+ default ARCH_CC_CAN_LINK if ARCH_HAS_CC_CAN_LINK
+ default $(cc_can_link_user,$(m64-flag)) if 64BIT
+ default $(cc_can_link_user,$(m32-flag))
+
+# Fixed in GCC 14, 13.3, 12.4 and 11.5
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921
+config GCC_ASM_GOTO_OUTPUT_BROKEN
+ bool
+ depends on CC_IS_GCC
+ default y if GCC_VERSION < 110500
+ default y if GCC_VERSION >= 120000 && GCC_VERSION < 120400
+ default y if GCC_VERSION >= 130000 && GCC_VERSION < 130300
+
+config CC_HAS_ASM_GOTO_OUTPUT
+ def_bool y
+ depends on !GCC_ASM_GOTO_OUTPUT_BROKEN
+ depends on $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
+
+config CC_HAS_ASM_GOTO_TIED_OUTPUT
+ depends on CC_HAS_ASM_GOTO_OUTPUT
+ # Detect buggy gcc and clang, fixed in gcc-11 clang-14.
+ def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null)
+
+config TOOLS_SUPPORT_RELR
+ def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
+
+config CC_HAS_ASM_INLINE
+ def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
+
+config CC_HAS_ASSUME
+ bool
+ # clang needs to be at least 19.1.0 since the meaning of the assume
+ # attribute changed:
+ # https://github.com/llvm/llvm-project/commit/c44fa3e8a9a44c2e9a575768a3c185354b9f6c17
+ default y if CC_IS_CLANG && CLANG_VERSION >= 190100
+ # supported since gcc 13.1.0
+ # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106654
+ default y if CC_IS_GCC && GCC_VERSION >= 130100
+
+config CC_HAS_NO_PROFILE_FN_ATTR
+ def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)
+
+config CC_HAS_COUNTED_BY
+ bool
+ # clang needs to be at least 20.1.0 to avoid potential crashes
+ # when building structures that contain __counted_by
+ # https://github.com/ClangBuiltLinux/linux/issues/2114
+ # https://github.com/llvm/llvm-project/commit/160fb1121cdf703c3ef5e61fb26c5659eb581489
+ default y if CC_IS_CLANG && CLANG_VERSION >= 200100
+ # supported since gcc 15.1.0
+ # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896
+ default y if CC_IS_GCC && GCC_VERSION >= 150100
+
+config CC_HAS_COUNTED_BY_PTR
+ bool
+ # supported since clang 22
+ default y if CC_IS_CLANG && CLANG_VERSION >= 220100
+ # supported since gcc 16.0.0
+ default y if CC_IS_GCC && GCC_VERSION >= 160000
+
+config CC_HAS_BROKEN_COUNTED_BY_REF
+ bool
+ # https://github.com/llvm/llvm-project/issues/182575
+ default y if CC_IS_CLANG && CLANG_VERSION < 220100
+
+config CC_HAS_ALLOC_TOKEN
+ def_bool $(cc-option,-falloc-token-max=123)
+
+config CC_HAS_MULTIDIMENSIONAL_NONSTRING
+ def_bool $(success,echo 'char tag[][4] __attribute__((__nonstring__)) = { };' | $(CC) $(CLANG_FLAGS) -x c - -c -o /dev/null -Werror)
+
+config LD_CAN_USE_KEEP_IN_OVERLAY
+ # ld.lld prior to 21.0.0 did not support KEEP within an overlay description
+ # https://github.com/llvm/llvm-project/pull/130661
+ def_bool LD_IS_BFD || LLD_VERSION >= 210000
+
+config RUSTC_HAS_SPAN_FILE
+ def_bool RUSTC_VERSION >= 108800
+
+config RUSTC_HAS_UNNECESSARY_TRANSMUTES
+ def_bool RUSTC_VERSION >= 108800
+
+config RUSTC_HAS_FILE_WITH_NUL
+ def_bool RUSTC_VERSION >= 108900
+
+config RUSTC_HAS_FILE_AS_C_STR
+ def_bool RUSTC_VERSION >= 109100
+
+config RUSTC_HAS_SUSPICIOUS_RUNTIME_SYMBOL_DEFINITIONS
+ def_bool RUSTC_VERSION >= 109800
+
+config PAHOLE_VERSION
+ int
+ default "$(PAHOLE_VERSION)"
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 11/21] kbuild: avoid re-running compiler and linker probes
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (9 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 10/21] kbuild: move the toolchain checks into init/Kconfig.toolchain Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 15:02 ` John Stoffel
2026-09-14 9:22 ` [PATCH v2 12/21] modpost: cache section relocation mismatch state Lorenzo Stoakes (ARM)
` (10 subsequent siblings)
21 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
Each kernel make invocation begins with ~30 compiler and linker runs each
of which performs duplicate probe for a number of compiler and linker
options.
This is useless work - the compiler and its version is known, so use these
to determine which options are available, once.
A convention already exists for this - CC_HAS_xxx, LD_HAS_xxx in Kconfig
files (for example, CC_HAS_COUNTED_BY), so convert these probes to Kconfig
options where appropriate.
This change avoids a sublte issue with ppc32 (big endian) - clang doesn't
accept -fno-stack-clash-protection on this sub-target, so keep this option
in the Makefile.
With gcc and clang, defconfig and allmodconfig, the recorded command
lines are unchanged, a build with nothing to do rebuilds nothing and W=1
continues to function correctly.
Doing this improves all builds, but has a particularly positive impact on
no-op builds (builds where nothing has changed).
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, no-op make, gcc 0.78s 0.60s -0.18s (-23%)
x86 defconfig, no-op make, clang 0.94s 0.66s -0.28s (-30%)
x86 defconfig, touch mm/vma.c, gcc 8.6s 8.5s -0.16s (-2%)
x86 defconfig, touch mm/vma.c, clang 8.0s 7.7s -0.24s (-3%)
x86 defconfig, clean, clang 29.8s 29.4s -0.37s (-1%)
x86 allmodconfig, no-op make, gcc 12.9s 12.7s -0.23s (-2%)
x86 allmodconfig, no-op make, clang 14.2s 13.9s -0.29s (-2%)
x86 allmodconfig, touch mm/vma.c, clang 32.2s 31.9s -0.30s (-1%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
Makefile | 23 +++++------
arch/arm64/kernel/pi/Makefile | 2 +-
arch/riscv/kernel/pi/Makefile | 2 +-
arch/x86/Kconfig | 17 ++++++++
arch/x86/Makefile | 12 +++---
drivers/firmware/efi/libstub/Makefile | 2 +-
init/Kconfig.toolchain | 74 +++++++++++++++++++++++++++++++++++
scripts/Makefile.warn | 28 ++++++-------
8 files changed, 126 insertions(+), 34 deletions(-)
diff --git a/Makefile b/Makefile
index 8105123bcf4d..68df3446d111 100644
--- a/Makefile
+++ b/Makefile
@@ -946,8 +946,8 @@ KBUILD_RUSTFLAGS += -Coverflow-checks=$(if $(CONFIG_RUST_OVERFLOW_CHECKS),y,n)
ifdef CONFIG_CC_IS_GCC
# gcc-10 renamed --param=allow-store-data-races=0 to
# -fno-allow-store-data-races.
-KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0)
-KBUILD_CFLAGS += $(call cc-option,-fno-allow-store-data-races)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_ALLOW_STORE_DATA_RACES_PARAM),--param=allow-store-data-races=0)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_NO_ALLOW_STORE_DATA_RACES),-fno-allow-store-data-races)
endif
ifdef CONFIG_READABLE_ASM
@@ -1011,18 +1011,20 @@ endif
endif
# Explicitly clear padding bits during variable initialization
-KBUILD_CFLAGS += $(call cc-option,-fzero-init-padding-bits=all)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_ZERO_INIT_PADDING_BITS),-fzero-init-padding-bits=all)
# While VLAs have been removed, GCC produces unreachable stack probes
# for the randomize_kstack_offset feature. Disable it for all compilers.
+# Probed here rather than in Kconfig as clang only accepts it for some
+# sub-targets, so the architecture's flags matter.
KBUILD_CFLAGS += $(call cc-option, -fno-stack-clash-protection)
# Get details on warnings generated due to GCC value tracking.
-KBUILD_CFLAGS += $(call cc-option, -fdiagnostics-show-context=2)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_DIAGNOSTICS_SHOW_CONTEXT),-fdiagnostics-show-context=2)
# Show inlining notes for __attribute__((warning/error)) call chains.
# GCC supports this unconditionally while Clang 23+ provides a flag.
-KBUILD_CFLAGS += $(call cc-option, -fdiagnostics-show-inlining-chain)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_DIAGNOSTICS_SHOW_INLINING_CHAIN),-fdiagnostics-show-inlining-chain)
# Clear used registers at func exit (to reduce data lifetime and ROP gadgets).
ifdef CONFIG_ZERO_CALL_USED_REGS
@@ -1033,7 +1035,7 @@ ifdef CONFIG_FUNCTION_TRACER
ifdef CONFIG_FTRACE_MCOUNT_USE_CC
CC_FLAGS_FTRACE += -mrecord-mcount
ifdef CONFIG_HAVE_NOP_MCOUNT
- ifeq ($(call cc-option-yn, -mnop-mcount),y)
+ ifdef CONFIG_CC_HAS_MNOP_MCOUNT
CC_FLAGS_FTRACE += -mnop-mcount
CC_FLAGS_USING += -DCC_USING_NOP_MCOUNT
endif
@@ -1051,8 +1053,7 @@ ifdef CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
endif
endif
ifdef CONFIG_HAVE_FENTRY
- # s390-linux-gnu-gcc did not support -mfentry until gcc-9.
- ifeq ($(call cc-option-yn, -mfentry),y)
+ ifdef CONFIG_CC_HAS_MFENTRY
CC_FLAGS_FTRACE += -mfentry
CC_FLAGS_USING += -DCC_USING_FENTRY
endif
@@ -1160,7 +1161,7 @@ NOSTDINC_FLAGS += -nostdinc
# the kernel uses only C99 flexible arrays for dynamically sized trailing
# arrays. Enforce this for everything that may examine structure sizes and
# perform bounds checking.
-KBUILD_CFLAGS += $(call cc-option, -fstrict-flex-arrays=3)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_STRICT_FLEX_ARRAYS),-fstrict-flex-arrays=3)
# disable invalid "can't wrap" optimizations for signed / pointers
KBUILD_CFLAGS += -fno-strict-overflow
@@ -1240,11 +1241,11 @@ LDFLAGS_vmlinux += --build-id=sha1
# COMDAT-deduplicated sections. Use --force-group-allocation to resolve these
# groups when linking modules. The option is available from ld.bfd 2.29 and
# ld.lld 19.1.0.
-KBUILD_LDFLAGS_MODULE += $(call ld-option,--force-group-allocation)
+KBUILD_LDFLAGS_MODULE += $(if $(CONFIG_LD_HAS_FORCE_GROUP_ALLOCATION),--force-group-allocation)
KBUILD_LDFLAGS += -z noexecstack
ifeq ($(CONFIG_LD_IS_BFD),y)
-KBUILD_LDFLAGS += $(call ld-option,--no-warn-rwx-segments)
+KBUILD_LDFLAGS += $(if $(CONFIG_LD_HAS_NO_WARN_RWX_SEGMENTS),--no-warn-rwx-segments)
endif
ifeq ($(CONFIG_STRIP_ASM_SYMS),y)
diff --git a/arch/arm64/kernel/pi/Makefile b/arch/arm64/kernel/pi/Makefile
index be92d73c25b2..5aa8dffe492b 100644
--- a/arch/arm64/kernel/pi/Makefile
+++ b/arch/arm64/kernel/pi/Makefile
@@ -9,7 +9,7 @@ KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) -fpie \
-include $(srctree)/include/linux/hidden.h \
-D__DISABLE_EXPORTS -ffreestanding -D__NO_FORTIFY \
-fno-asynchronous-unwind-tables -fno-unwind-tables \
- $(call cc-option,-fno-addrsig)
+ $(if $(CONFIG_CC_HAS_NO_ADDRSIG),-fno-addrsig)
# this code may run with the MMU off so disable unaligned accesses
CFLAGS_map_range.o += -mstrict-align
diff --git a/arch/riscv/kernel/pi/Makefile b/arch/riscv/kernel/pi/Makefile
index bc098edac898..e0ed7ca7e347 100644
--- a/arch/riscv/kernel/pi/Makefile
+++ b/arch/riscv/kernel/pi/Makefile
@@ -8,7 +8,7 @@ KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) -fpie \
-include $(srctree)/include/linux/hidden.h \
-D__DISABLE_EXPORTS -ffreestanding \
-fno-asynchronous-unwind-tables -fno-unwind-tables \
- $(call cc-option,-fno-addrsig)
+ $(if $(CONFIG_CC_HAS_NO_ADDRSIG),-fno-addrsig)
# Disable LTO
KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 15fd9ec5ecac..be0624fee27a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2364,6 +2364,23 @@ config CC_HAS_KCFI_ARITY
def_bool $(cc-option,-fsanitize=kcfi -fsanitize-kcfi-arity)
depends on CC_IS_CLANG && !RUST
+config CC_HAS_INDIRECT_BRANCH_CS_PREFIX
+ def_bool $(cc-option,-mindirect-branch-cs-prefix)
+
+config CC_HAS_CF_PROTECTION_NONE
+ def_bool $(cc-option,-fcf-protection=none)
+
+# with jump tables off: the compilers use NOTRACK for them, which kernel IBT
+# does not allow
+config CC_HAS_CF_PROTECTION_BRANCH
+ def_bool $(cc-option,-fcf-protection=branch -fno-jump-tables)
+
+config CC_HAS_FALIGN_JUMPS
+ def_bool $(cc-option,-falign-jumps=1)
+
+config CC_HAS_FALIGN_LOOPS
+ def_bool $(cc-option,-falign-loops=1)
+
config FUNCTION_PADDING_CFI
int
default 59 if FUNCTION_ALIGNMENT_64B
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 598f178102ee..29bb515df9f6 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -20,7 +20,7 @@ ifdef CONFIG_CC_IS_CLANG
RETPOLINE_CFLAGS := -mretpoline-external-thunk
RETPOLINE_VDSO_CFLAGS := -mretpoline
endif
-RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch-cs-prefix)
+RETPOLINE_CFLAGS += $(if $(CONFIG_CC_HAS_INDIRECT_BRANCH_CS_PREFIX),-mindirect-branch-cs-prefix)
ifdef CONFIG_MITIGATION_RETHUNK
RETHUNK_CFLAGS := -mfunction-return=thunk-extern
@@ -52,7 +52,7 @@ REALMODE_CFLAGS := $(CC_FLAGS_DIALECT) -m16 -g -Os \
-DDISABLE_BRANCH_PROFILING -D__DISABLE_EXPORTS \
-Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
-fno-strict-aliasing -fomit-frame-pointer -fno-pic \
- -mno-mmx -mno-sse $(call cc-option,-fcf-protection=none)
+ -mno-mmx -mno-sse $(if $(CONFIG_CC_HAS_CF_PROTECTION_NONE),-fcf-protection=none)
REALMODE_CFLAGS += -ffreestanding
REALMODE_CFLAGS += -fno-stack-protector
@@ -99,10 +99,10 @@ ifeq ($(CONFIG_X86_KERNEL_IBT),y)
#
# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104816
#
-KBUILD_CFLAGS += $(call cc-option,-fcf-protection=branch -fno-jump-tables)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_CF_PROTECTION_BRANCH),-fcf-protection=branch -fno-jump-tables)
KBUILD_RUSTFLAGS += -Zcf-protection=branch $(if $(call rustc-min-version,109300),-Cjump-tables=n,-Zno-jump-tables)
else
-KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_CF_PROTECTION_NONE),-fcf-protection=none)
endif
ifeq ($(CONFIG_X86_32),y)
@@ -138,10 +138,10 @@ else
KBUILD_CFLAGS += -m64
# Align jump targets to 1 byte, not the default 16 bytes:
- KBUILD_CFLAGS += $(call cc-option,-falign-jumps=1)
+ KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_FALIGN_JUMPS),-falign-jumps=1)
# Pack loops tightly as well:
- KBUILD_CFLAGS += $(call cc-option,-falign-loops=1)
+ KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_FALIGN_LOOPS),-falign-loops=1)
# Don't autogenerate traditional x87 instructions
KBUILD_CFLAGS += -mno-80387
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 77a2b2d74f3f..80058bbddaf5 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -40,7 +40,7 @@ KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
-D__NO_FORTIFY \
-ffreestanding \
-fno-stack-protector \
- $(call cc-option,-fno-addrsig) \
+ $(if $(CONFIG_CC_HAS_NO_ADDRSIG),-fno-addrsig) \
-D__DISABLE_EXPORTS
#
diff --git a/init/Kconfig.toolchain b/init/Kconfig.toolchain
index fac36246451f..7a0438f0eb86 100644
--- a/init/Kconfig.toolchain
+++ b/init/Kconfig.toolchain
@@ -144,6 +144,80 @@ config CC_HAS_ASSUME
config CC_HAS_NO_PROFILE_FN_ATTR
def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)
+config CC_HAS_ZERO_INIT_PADDING_BITS
+ def_bool $(cc-option,-fzero-init-padding-bits=all)
+
+config CC_HAS_NO_ADDRSIG
+ def_bool $(cc-option,-fno-addrsig)
+
+config CC_HAS_DIAGNOSTICS_SHOW_CONTEXT
+ def_bool $(cc-option,-fdiagnostics-show-context=2)
+
+config CC_HAS_DIAGNOSTICS_SHOW_INLINING_CHAIN
+ def_bool $(cc-option,-fdiagnostics-show-inlining-chain)
+
+config CC_HAS_STRICT_FLEX_ARRAYS
+ def_bool $(cc-option,-fstrict-flex-arrays=3)
+
+# gcc-10 renamed --param=allow-store-data-races=0 to -fno-allow-store-data-races
+config CC_HAS_ALLOW_STORE_DATA_RACES_PARAM
+ def_bool CC_IS_GCC && $(cc-option,--param=allow-store-data-races=0)
+
+config CC_HAS_NO_ALLOW_STORE_DATA_RACES
+ def_bool CC_IS_GCC && $(cc-option,-fno-allow-store-data-races)
+
+config CC_HAS_MNOP_MCOUNT
+ def_bool $(cc-option,-mnop-mcount)
+
+# s390-linux-gnu-gcc did not support -mfentry until gcc-9.
+config CC_HAS_MFENTRY
+ def_bool $(cc-option,-mfentry)
+
+config LD_HAS_FORCE_GROUP_ALLOCATION
+ def_bool $(ld-option,--force-group-allocation)
+
+config LD_HAS_NO_WARN_RWX_SEGMENTS
+ def_bool $(ld-option,--no-warn-rwx-segments)
+
+config CC_HAS_WNO_ADDRESS_OF_PACKED_MEMBER
+ def_bool $(cc-option,-Wno-address-of-packed-member)
+
+config CC_HAS_WNO_FORMAT_OVERFLOW_NON_KPRINTF
+ def_bool CC_IS_CLANG && $(cc-option,-Wno-format-overflow-non-kprintf)
+
+config CC_HAS_WNO_FORMAT_TRUNCATION_NON_KPRINTF
+ def_bool CC_IS_CLANG && $(cc-option,-Wno-format-truncation-non-kprintf)
+
+config CC_HAS_WNO_DEFAULT_CONST_INIT_UNSAFE
+ def_bool CC_IS_CLANG && $(cc-option,-Wno-default-const-init-unsafe)
+
+config CC_HAS_WNO_DANGLING_POINTER
+ def_bool $(cc-option,-Wno-dangling-pointer)
+
+config CC_HAS_WVLA_LARGER_THAN
+ def_bool $(cc-option,-Wvla-larger-than=1)
+
+config CC_HAS_WSTRINGOP_OVERFLOW
+ def_bool $(cc-option,-Wstringop-overflow)
+
+config CC_HAS_WNO_UNTERMINATED_STRING_INITIALIZATION
+ def_bool $(cc-option,-Wno-unterminated-string-initialization)
+
+config CC_HAS_WERROR_DESIGNATED_INIT
+ def_bool $(cc-option,-Werror=designated-init)
+
+config CC_HAS_WENUM_CONVERSION
+ def_bool $(cc-option,-Wenum-conversion)
+
+config CC_HAS_WNO_PACKED_NOT_ALIGNED
+ def_bool $(cc-option,-Wno-packed-not-aligned)
+
+config CC_HAS_WNO_FORMAT_OVERFLOW
+ def_bool $(cc-option,-Wno-format-overflow)
+
+config CC_HAS_WNO_STRINGOP_TRUNCATION
+ def_bool $(cc-option,-Wno-stringop-truncation)
+
config CC_HAS_COUNTED_BY
bool
# clang needs to be at least 20.1.0 to avoid potential crashes
diff --git a/scripts/Makefile.warn b/scripts/Makefile.warn
index 35af7d6c6d18..83d274fcbfaf 100644
--- a/scripts/Makefile.warn
+++ b/scripts/Makefile.warn
@@ -17,7 +17,7 @@ KBUILD_CFLAGS += -Werror=strict-prototypes
KBUILD_CFLAGS += -Wno-format-security
KBUILD_CFLAGS += -Wno-trigraphs
KBUILD_CFLAGS += -Wno-frame-address
-KBUILD_CFLAGS += $(call cc-option, -Wno-address-of-packed-member)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WNO_ADDRESS_OF_PACKED_MEMBER),-Wno-address-of-packed-member)
KBUILD_CFLAGS += -Wmissing-declarations
KBUILD_CFLAGS += -Wmissing-prototypes
@@ -30,8 +30,8 @@ KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
ifdef CONFIG_CC_IS_CLANG
# Clang checks for overflow/truncation with '%p', while GCC does not:
# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219
-KBUILD_CFLAGS += $(call cc-option, -Wno-format-overflow-non-kprintf)
-KBUILD_CFLAGS += $(call cc-option, -Wno-format-truncation-non-kprintf)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WNO_FORMAT_OVERFLOW_NON_KPRINTF),-Wno-format-overflow-non-kprintf)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WNO_FORMAT_TRUNCATION_NON_KPRINTF),-Wno-format-truncation-non-kprintf)
# Clang may emit a warning when a const variable, such as the dummy variables
# in typecheck(), or const member of an aggregate type are not initialized,
@@ -43,7 +43,7 @@ KBUILD_CFLAGS += $(call cc-option, -Wno-format-truncation-non-kprintf)
# disabled with this same switch, there should not be too much coverage lost
# because -Wuninitialized will still flag when an uninitialized const variable
# is used.
-KBUILD_CFLAGS += $(call cc-option, -Wno-default-const-init-unsafe)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WNO_DEFAULT_CONST_INIT_UNSAFE),-Wno-default-const-init-unsafe)
else
# gcc inanely warns about local variables called 'main'
@@ -54,7 +54,7 @@ endif
KBUILD_CFLAGS += -Wno-type-limits
# These result in bogus false positives
-KBUILD_CFLAGS += $(call cc-option, -Wno-dangling-pointer)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WNO_DANGLING_POINTER),-Wno-dangling-pointer)
# Stack Variable Length Arrays (VLAs) must not be used in the kernel.
# Function array parameters should, however, be usable, but -Wvla will
@@ -62,7 +62,7 @@ KBUILD_CFLAGS += $(call cc-option, -Wno-dangling-pointer)
# types, so depend on GCC for now to keep stack VLAs out of the tree.
# https://github.com/llvm/llvm-project/issues/57098
# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98217
-KBUILD_CFLAGS += $(call cc-option,-Wvla-larger-than=1)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WVLA_LARGER_THAN),-Wvla-larger-than=1)
# disable pointer signed / unsigned warnings in gcc 4.0
KBUILD_CFLAGS += -Wno-pointer-sign
@@ -73,11 +73,11 @@ KBUILD_CFLAGS += -Wno-pointer-sign
KBUILD_CFLAGS += -Wcast-function-type
# Currently, disable -Wstringop-overflow for GCC 11, globally.
-KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-option, -Wno-stringop-overflow)
-KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow)
+KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(if $(CONFIG_CC_HAS_WSTRINGOP_OVERFLOW),-Wno-stringop-overflow)
+KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(if $(CONFIG_CC_HAS_WSTRINGOP_OVERFLOW),-Wstringop-overflow)
# Currently, disable -Wunterminated-string-initialization as broken
-KBUILD_CFLAGS += $(call cc-option, -Wno-unterminated-string-initialization)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WNO_UNTERMINATED_STRING_INITIALIZATION),-Wno-unterminated-string-initialization)
# The allocators already balk at large sizes, so silence the compiler
# warnings for bounds checks involving those possible values. While
@@ -100,10 +100,10 @@ KBUILD_CFLAGS += -Werror=date-time
KBUILD_CFLAGS += -Werror=incompatible-pointer-types
# Require designated initializers for all marked structures
-KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WERROR_DESIGNATED_INIT),-Werror=designated-init)
# Warn if there is an enum types mismatch
-KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WENUM_CONVERSION),-Wenum-conversion)
KBUILD_CFLAGS += -Wunused
@@ -125,12 +125,12 @@ else
# Suppress them by using -Wno... except for W=1.
KBUILD_CFLAGS += -Wno-unused-but-set-variable
KBUILD_CFLAGS += -Wno-unused-const-variable
-KBUILD_CFLAGS += $(call cc-option, -Wno-packed-not-aligned)
-KBUILD_CFLAGS += $(call cc-option, -Wno-format-overflow)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WNO_PACKED_NOT_ALIGNED),-Wno-packed-not-aligned)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WNO_FORMAT_OVERFLOW),-Wno-format-overflow)
ifdef CONFIG_CC_IS_GCC
KBUILD_CFLAGS += -Wno-format-truncation
endif
-KBUILD_CFLAGS += $(call cc-option, -Wno-stringop-truncation)
+KBUILD_CFLAGS += $(if $(CONFIG_CC_HAS_WNO_STRINGOP_TRUNCATION),-Wno-stringop-truncation)
KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 11/21] kbuild: avoid re-running compiler and linker probes
2026-09-14 9:22 ` [PATCH v2 11/21] kbuild: avoid re-running compiler and linker probes Lorenzo Stoakes (ARM)
@ 2026-09-14 15:02 ` John Stoffel
2026-09-14 15:24 ` Lorenzo Stoakes (ARM)
0 siblings, 1 reply; 58+ messages in thread
From: John Stoffel @ 2026-09-14 15:02 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva,
linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening
>>>>> "Lorenzo" == Lorenzo Stoakes (ARM) <ljs@kernel.org> writes:
> Each kernel make invocation begins with ~30 compiler and linker runs each
> of which performs duplicate probe for a number of compiler and linker
> options.
> This is useless work - the compiler and its version is known, so use these
> to determine which options are available, once.
> A convention already exists for this - CC_HAS_xxx, LD_HAS_xxx in Kconfig
> files (for example, CC_HAS_COUNTED_BY), so convert these probes to Kconfig
> options where appropriate.
> This change avoids a sublte issue with ppc32 (big endian) - clang doesn't
^^^^^^
subtle
> accept -fno-stack-clash-protection on this sub-target, so keep this option
> in the Makefile.
> With gcc and clang, defconfig and allmodconfig, the recorded command
> lines are unchanged, a build with nothing to do rebuilds nothing and W=1
> continues to function correctly.
> Doing this improves all builds, but has a particularly positive impact on
> no-op builds (builds where nothing has changed).
> Whole build, 128-thread Threadripper 9980X, best of N runs:
> before after delta
> -------------------------------
> x86 defconfig, no-op make, gcc 0.78s 0.60s -0.18s (-23%)
> x86 defconfig, no-op make, clang 0.94s 0.66s -0.28s (-30%)
> x86 defconfig, touch mm/vma.c, gcc 8.6s 8.5s -0.16s (-2%)
> x86 defconfig, touch mm/vma.c, clang 8.0s 7.7s -0.24s (-3%)
> x86 defconfig, clean, clang 29.8s 29.4s -0.37s (-1%)
> x86 allmodconfig, no-op make, gcc 12.9s 12.7s -0.23s (-2%)
> x86 allmodconfig, no-op make, clang 14.2s 13.9s -0.29s (-2%)
> x86 allmodconfig, touch mm/vma.c, clang 32.2s 31.9s -0.30s (-1%)
Are these deltas just per-patch, but cumulative with all the previous
patches applied?
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 11/21] kbuild: avoid re-running compiler and linker probes
2026-09-14 15:02 ` John Stoffel
@ 2026-09-14 15:24 ` Lorenzo Stoakes (ARM)
2026-09-15 11:01 ` Lorenzo Stoakes (ARM)
0 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 15:24 UTC (permalink / raw)
To: John Stoffel
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva,
linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening
On Mon, Sep 14, 2026 at 11:02:22AM -0400, John Stoffel wrote:
> >>>>> "Lorenzo" == Lorenzo Stoakes (ARM) <ljs@kernel.org> writes:
>
> > Each kernel make invocation begins with ~30 compiler and linker runs each
> > of which performs duplicate probe for a number of compiler and linker
> > options.
>
> > This is useless work - the compiler and its version is known, so use these
> > to determine which options are available, once.
>
> > A convention already exists for this - CC_HAS_xxx, LD_HAS_xxx in Kconfig
> > files (for example, CC_HAS_COUNTED_BY), so convert these probes to Kconfig
> > options where appropriate.
>
> > This change avoids a sublte issue with ppc32 (big endian) - clang doesn't
> ^^^^^^
>
> subtle
Oops!
I love that I ran this through AI review several times and it missed
something as simple as this :)
>
> > accept -fno-stack-clash-protection on this sub-target, so keep this option
> > in the Makefile.
>
> > With gcc and clang, defconfig and allmodconfig, the recorded command
> > lines are unchanged, a build with nothing to do rebuilds nothing and W=1
> > continues to function correctly.
>
> > Doing this improves all builds, but has a particularly positive impact on
> > no-op builds (builds where nothing has changed).
>
> > Whole build, 128-thread Threadripper 9980X, best of N runs:
>
> > before after delta
> > -------------------------------
> > x86 defconfig, no-op make, gcc 0.78s 0.60s -0.18s (-23%)
> > x86 defconfig, no-op make, clang 0.94s 0.66s -0.28s (-30%)
> > x86 defconfig, touch mm/vma.c, gcc 8.6s 8.5s -0.16s (-2%)
> > x86 defconfig, touch mm/vma.c, clang 8.0s 7.7s -0.24s (-3%)
> > x86 defconfig, clean, clang 29.8s 29.4s -0.37s (-1%)
> > x86 allmodconfig, no-op make, gcc 12.9s 12.7s -0.23s (-2%)
> > x86 allmodconfig, no-op make, clang 14.2s 13.9s -0.29s (-2%)
> > x86 allmodconfig, touch mm/vma.c, clang 32.2s 31.9s -0.30s (-1%)
>
> Are these deltas just per-patch, but cumulative with all the previous
> patches applied?
>
Per-patch. I let the threadripper do builds for a LONG time to accumulate
these... :)
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* Re: [PATCH v2 11/21] kbuild: avoid re-running compiler and linker probes
2026-09-14 15:24 ` Lorenzo Stoakes (ARM)
@ 2026-09-15 11:01 ` Lorenzo Stoakes (ARM)
0 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 11:01 UTC (permalink / raw)
To: John Stoffel
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva,
linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening
> On Mon, Sep 14, 2026 at 11:02:22AM -0400, John Stoffel wrote:
> > > This change avoids a sublte issue with ppc32 (big endian) - clang doesn't
> > ^^^^^^
> >
> > subtle
>
> Oops!
>
> I love that I ran this through AI review several times and it missed
> something as simple as this :)
(Fixed for v3 along with a few other typos :)
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* [PATCH v2 12/21] modpost: cache section relocation mismatch state
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (10 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 11/21] kbuild: avoid re-running compiler and linker probes Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 13/21] modpost: emit module descriptors as assembly Lorenzo Stoakes (ARM)
` (9 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
For every relocation modpost invokes check_section_mismatch() to determine
whether there is any kind of mismatch between the source and destination,
and if so which classification applies.
Each time it does this it invokes section_mismatch() which iterates
through the sectioncheck[] array every time it's called.
When walked a relocation section the source is fixed and there aren't many
targets, so the same names are looked up over and over again.
Therefore cache not only mismatch categorisation but also whether a
mismatch even exists for a given section and look up the sections in the
cache.
Special indices (undefined, absolute, common) take the uncached path as
before.
This results in very significant speed ups for allmodconfig incremental
builds.
modpost is on the serial tail of every build that links vmlinux.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 8.5s 8.3s -0.14s (-2%)
x86 defconfig, touch mm/vma.c, clang 7.7s 7.6s -0.13s (-2%)
x86 allmodconfig, touch mm/vma.c, gcc 33.9s 29.4s -4.5s (-13%)
x86 allmodconfig, touch mm/vma.c, clang 31.9s 27.9s -4.0s (-13%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
scripts/mod/modpost.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 64 insertions(+), 2 deletions(-)
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 75374c64b8cc..0fd43c8a89ea 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1155,12 +1155,67 @@ static void check_export_symbol(struct module *mod, struct elf_info *elf,
name);
}
+/*
+ * mismatch_cache[section index] ->
+ * 0 - uncached.
+ * -1 - no mismatch.
+ * >0 - mismatch index + 1.
+ */
+static int *mismatch_cache;
+
+static void init_mismatch_cache(unsigned int num_sections)
+{
+ mismatch_cache = xcalloc(num_sections, sizeof(*mismatch_cache));
+}
+
+static void reset_mismatch_cache(unsigned int num_sections)
+{
+ memset(mismatch_cache, 0, num_sections * sizeof(*mismatch_cache));
+}
+
+static void free_mismatch_cache(void)
+{
+ free(mismatch_cache);
+ mismatch_cache = NULL;
+}
+
+static const struct sectioncheck
+*cache_mismatch(unsigned int secndx, const struct sectioncheck *mismatch)
+{
+ if (!mismatch) {
+ mismatch_cache[secndx] = -1;
+ return NULL;
+ }
+
+ mismatch_cache[secndx] = (mismatch - sectioncheck) + 1;
+ return mismatch;
+}
+
+static const struct sectioncheck *get_section_mismatch(const char *fromsec,
+ const struct elf_info *elf, unsigned int secndx)
+{
+ int cached;
+
+ if (secndx >= elf->num_sections)
+ return section_mismatch(fromsec, sec_name(elf, secndx));
+
+ cached = mismatch_cache[secndx];
+ if (cached < 0)
+ return NULL;
+ if (cached > 0)
+ return §ioncheck[cached - 1];
+
+ return cache_mismatch(secndx,
+ section_mismatch(fromsec, sec_name(elf, secndx)));
+}
+
static void check_section_mismatch(struct module *mod, struct elf_info *elf,
Elf_Sym *sym,
unsigned int fsecndx, const char *fromsec,
Elf_Addr faddr, Elf_Addr taddr)
{
- const char *tosec = sec_name(elf, get_secindex(elf, sym));
+ const unsigned int to_secndx = get_secindex(elf, sym);
+ const char *tosec = sec_name(elf, to_secndx);
const struct sectioncheck *mismatch;
if (module_enabled && elf->export_symbol_secndx == fsecndx) {
@@ -1168,7 +1223,7 @@ static void check_section_mismatch(struct module *mod, struct elf_info *elf,
return;
}
- mismatch = section_mismatch(fromsec, tosec);
+ mismatch = get_section_mismatch(fromsec, elf, to_secndx);
if (!mismatch)
return;
@@ -1445,6 +1500,8 @@ static void check_sec_ref(struct module *mod, struct elf_info *elf)
{
int i;
+ init_mismatch_cache(elf->num_sections);
+
/* Walk through all sections */
for (i = 0; i < elf->num_sections; i++) {
Elf_Shdr *sechdr = &elf->sechdrs[i];
@@ -1461,6 +1518,9 @@ static void check_sec_ref(struct module *mod, struct elf_info *elf)
if (match(secname, section_white_list))
continue;
+ /* Reset cache per-section. */
+ reset_mismatch_cache(elf->num_sections);
+
start = sym_get_data_by_offset(elf, i, 0);
stop = start + sechdr->sh_size;
@@ -1472,6 +1532,8 @@ static void check_sec_ref(struct module *mod, struct elf_info *elf)
start, stop);
}
}
+
+ free_mismatch_cache();
}
static char *remove_dot(char *s)
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 13/21] modpost: emit module descriptors as assembly
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (11 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 12/21] modpost: cache section relocation mismatch state Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 14/21] kbuild: batch module finalisation Lorenzo Stoakes (ARM)
` (8 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
modpost generates a descriptor for every module in the form of a
<module>.mod.c file with .modinfo strings, the __this_module descriptor,
exported symbol tables and (with CONFIG_MODVERSIONS set), the CRC of
imported symbols.
These files are compiled like any other kernel C file with all of the
-include preamble, as well as including linux/module.h, header dependencies
generated by fixdep of a few hundred headers, an objtool run and if LTO is
being performed, a link is performed to generate native code.
On an x86-64 allmodconfig build 11,189 *.mod.c files are built, each
taking ~0.24s of CPU time to compile, and module finalisation as a whole
6,300 CPU seconds, or 64 seconds of wall time when run over 128 threads.
It also generates ~1.3 GiB of *.mod.o.cmd files that every subsequent build
has to read back.
Avoid all this by emitting the descriptors as assembly instead.
The layout required (size and alignment of struct module, struct
modversion_info, the module's name offsets, init, and exit fields and
whether the architecture uses PREL32 ksymtab references) can all be derived
from scripts/mod/module-offsets.h.
The fields of __this_module are emitted in offset order rather than
declaration order, as CONFIG_RANDSTRUCT shuffles struct module so the name,
init and exit fields can land anywhere.
An assembly file avoids all of the issues previously mentioned so this
conversion results in a very significant performance win on kernel build.
As a consequence of this change, since module-offsets.c includes
linux/module.h, scripts/mod is now built after the generated headers in
prepare0, rather than before.
Also update .gitignore and make clean to handle .mod.S files, but keep
.mod.c files there to ensure that users do not end up with untracked
changes/dirty trees after the change takes effect.
The sections were confirmed to be byte-for-byte identical to the C version
produced - each of .modinfo, .gnu.linkonce.this_module, __ksymtab*,
__ksymtab_strings, __kcrctab*, __kflagstab*, __versions,
__version_ext_crcs, __version_ext_names and their relocations - for all
8,135 modules of a clang allmodconfig build with CONFIG_COMPILE_TEST off
and CONFIG_MODVERSIONS, CONFIG_EXTENDED_MODVERSIONS and
CONFIG_MODULE_SRCVERSION_ALL on, and for a sample built with gcc.
What differs is what the compiler added around them: the __UNIQUE_ID_*
locals, the KASAN constructor for the .mod.c globals, and on x86 a
.note.gnu.property that the linker already drops from any module containing
an assembly file and the loader never reads.
None of these have any impact on the build, however.
x86_64 kernels built with gcc and clang, with CONFIG_MODVERSIONS,
CONFIG_EXTENDED_MODVERSIONS and CONFIG_MODULE_SRCVERSION_ALL, were booted,
every module and an external one loaded and unloaded, and the srcversions
checked against modinfo, i386 and arm64 defconfigs (gcc and clang) and a
ThinLTO build were also built as part of testing.
An x86_64 CONFIG_RANDSTRUCT_FULL build with clang, which places the name
field after init and exit, was checked the same way and produces the same
.gnu.linkonce.this_module sections and relocations as the C version.
On the x86_64 allmodconfig with clang 22, "make modules" with every
*.mod.o and *.ko deleted goes from 64.5s (6,306 CPU-s) to 28.5s (518
CPU-s).
A consequence of this change is that the make jobs are now so small that
make cannot dispatch them quick enough, however the next commit in the
series addresses this issue.
This impacts clean and no-op builds with a large number of modules most
noticeably.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 allmodconfig, no-op make, gcc 12.7s 2.3s -10.4s (-82%)
x86 allmodconfig, no-op make, clang 13.9s 2.8s -11.2s (-80%)
x86 allmodconfig, clean, gcc 342.6s 306.6s -36.0s (-11%)
x86 allmodconfig, clean, clang 340.1s 290.2s -49.8s (-15%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
.gitignore | 1 +
Makefile | 4 +-
include/linux/vermagic.h | 2 +-
scripts/Makefile.modfinal | 10 +-
scripts/Makefile.modpost | 2 +-
scripts/mod/.gitignore | 1 +
scripts/mod/Makefile | 8 +
scripts/mod/modpost.c | 637 ++++++++++++++++++++++++++++++++-----------
scripts/mod/module-offsets.c | 35 +++
scripts/tags.sh | 5 +-
10 files changed, 530 insertions(+), 175 deletions(-)
diff --git a/.gitignore b/.gitignore
index 9875120ea7bd..00fc262b894b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -38,6 +38,7 @@
*.lzo
*.mod
*.mod.c
+*.mod.S
*.o
*.o.*
*.patch
diff --git a/Makefile b/Makefile
index 68df3446d111..8263fc8a86b3 100644
--- a/Makefile
+++ b/Makefile
@@ -1422,8 +1422,8 @@ archprepare: outputmakefile archheaders archscripts scripts include/config/kerne
include/generated/rustc_cfg remove-stale-files
prepare0: archprepare
- $(Q)$(MAKE) $(build)=scripts/mod
$(Q)$(MAKE) $(build)=. prepare
+ $(Q)$(MAKE) $(build)=scripts/mod
# All the preparing..
prepare: prepare0
@@ -2245,7 +2245,7 @@ clean: $(clean-dirs)
-o -name '*.dt.yaml' -o -name 'dtbs-list' \
-o -name '*.dwo' -o -name '*.lst' \
-o -name '*.su' -o -name '*.mod' \
- -o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
+ -o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' -o -name '*.mod.S' \
-o -name '*.lex.c' -o -name '*.tab.[ch]' \
-o -name '*.asn1.[ch]' \
-o -name '*.symtypes' -o -name 'modules.order' \
diff --git a/include/linux/vermagic.h b/include/linux/vermagic.h
index 335c360d4f9b..09f05d02664c 100644
--- a/include/linux/vermagic.h
+++ b/include/linux/vermagic.h
@@ -3,7 +3,7 @@
#define _LINUX_VERMAGIC_H
#ifndef INCLUDE_VERMAGIC
-#error "This header can be included from kernel/module.c or *.mod.c only"
+#error "This header can be included from kernel/module.c or scripts/module-common.c only"
#endif
#include <generated/utsrelease.h>
diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 01a37ec872b9..75e9effdf02c 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -20,10 +20,14 @@ __modfinal: $(modules:%.o=%.ko)
modname = $(notdir $(@:.mod.o=))
part-of-module = y
GCOV_PROFILE := n
-ccflags-remove-y := $(CC_FLAGS_CFI)
-%.mod.o: %.mod.c FORCE
- $(call if_changed_rule,cc_o_c)
+# modpost lays the <module>.mod.S out completely (write_mod_S_file()), so it
+# needs only the assembler and no dependency tracking.
+quiet_cmd_as_mod_o = AS [M] $@
+ cmd_as_mod_o = $(CC) $(_a_flags) $(modkern_aflags) -c -o $@ $<
+
+%.mod.o: %.mod.S FORCE
+ $(call if_changed,as_mod_o)
.module-common.o: $(srctree)/scripts/module-common.c FORCE
$(call if_changed_rule,cc_o_c)
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index d7d45067d08b..eecf5f5c99b4 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -13,7 +13,7 @@
# Stage 2 is handled by this file and does the following
# 1) Find all modules listed in modules.order
# 2) modpost is then used to
-# 3) create one <module>.mod.c file per module
+# 3) create one <module>.mod.S file per module
# 4) create one Module.symvers file with CRC for all exported symbols
# Step 3 is used to place certain information in the module's ELF
diff --git a/scripts/mod/.gitignore b/scripts/mod/.gitignore
index 0465ec33c9bf..620ab4362094 100644
--- a/scripts/mod/.gitignore
+++ b/scripts/mod/.gitignore
@@ -1,5 +1,6 @@
# SPDX-License-Identifier: GPL-2.0-only
/devicetable-offsets.h
+/module-offsets.h
/elfconfig.h
/mk_elfconfig
/modpost
diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
index c729bc936bae..fbd5099e0441 100644
--- a/scripts/mod/Makefile
+++ b/scripts/mod/Makefile
@@ -13,10 +13,18 @@ $(obj)/$(devicetable-offsets-file): $(obj)/devicetable-offsets.s FORCE
targets += $(devicetable-offsets-file) devicetable-offsets.s
+module-offsets-file := module-offsets.h
+
+$(obj)/$(module-offsets-file): $(obj)/module-offsets.s FORCE
+ $(call filechk,offsets,__MODULE_OFFSETS_H__)
+
+targets += $(module-offsets-file) module-offsets.s
+
# dependencies on generated files need to be listed explicitly
$(obj)/modpost.o $(obj)/file2alias.o $(obj)/sumversion.o $(obj)/symsearch.o: $(obj)/elfconfig.h
$(obj)/file2alias.o: $(obj)/$(devicetable-offsets-file)
+$(obj)/modpost.o: $(obj)/$(module-offsets-file)
quiet_cmd_elfconfig = MKELF $@
cmd_elfconfig = $(obj)/mk_elfconfig < $< > $@
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 0fd43c8a89ea..b4550b545330 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -26,6 +26,7 @@
#include <list.h>
#include <xalloc.h>
#include "modpost.h"
+#include "module-offsets.h"
#include "../../include/linux/license.h"
#define MODULE_NS_PREFIX "module:"
@@ -1920,39 +1921,6 @@ static void check_modname_len(struct module *mod)
mod_error(mod, "module name is too long\n");
}
-/**
- * Header for the generated file
- **/
-static void add_header(struct buffer *b, struct module *mod)
-{
- buf_printf(b, "#include <linux/module.h>\n");
- buf_printf(b, "#include <linux/export-internal.h>\n");
- buf_printf(b, "#include <linux/compiler.h>\n");
- buf_printf(b, "\n");
- buf_printf(b, "MODULE_INFO(name, KBUILD_MODNAME);\n");
- buf_printf(b, "\n");
- buf_printf(b, "__visible struct module __this_module\n");
- buf_printf(b, "__section(\".gnu.linkonce.this_module\") = {\n");
- buf_printf(b, "\t.name = KBUILD_MODNAME,\n");
- if (mod->has_init)
- buf_printf(b, "\t.init = init_module,\n");
- if (mod->has_cleanup)
- buf_printf(b, "#ifdef CONFIG_MODULE_UNLOAD\n"
- "\t.exit = cleanup_module,\n"
- "#endif\n");
- buf_printf(b, "\t.arch = MODULE_ARCH_INIT,\n");
- buf_printf(b, "};\n");
-
- if (!external_module)
- buf_printf(b, "\nMODULE_INFO(intree, \"Y\");\n");
-
- if (strstarts(mod->name, "drivers/staging"))
- buf_printf(b, "\nMODULE_INFO(staging, \"Y\");\n");
-
- if (strstarts(mod->name, "tools/testing"))
- buf_printf(b, "\nMODULE_INFO(test, \"Y\");\n");
-}
-
static void add_exported_symbols(struct buffer *buf, struct module *mod)
{
struct symbol *sym;
@@ -1990,123 +1958,6 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
}
}
-/**
- * Record CRCs for unresolved symbols, supporting long names
- */
-static void add_extended_versions(struct buffer *b, struct module *mod)
-{
- struct symbol *s;
-
- if (!extended_modversions)
- return;
-
- buf_printf(b, "\n");
- buf_printf(b, "static const u32 ____version_ext_crcs[]\n");
- buf_printf(b, "__used __section(\"__version_ext_crcs\") = {\n");
- list_for_each_entry(s, &mod->unresolved_symbols, list) {
- if (!s->module)
- continue;
- if (!s->crc_valid) {
- mod_warn(mod, "symbol '%s' has no CRC!\n", s->name);
- continue;
- }
- buf_printf(b, "\t0x%08x,\n", s->crc);
- }
- buf_printf(b, "};\n");
-
- buf_printf(b, "static const char ____version_ext_names[]\n");
- buf_printf(b, "__used __section(\"__version_ext_names\") =\n");
- list_for_each_entry(s, &mod->unresolved_symbols, list) {
- if (!s->module)
- continue;
- if (!s->crc_valid)
- /*
- * We already warned on this when producing the crc
- * table.
- * We need to skip its name too, as the indexes in
- * both tables need to align.
- */
- continue;
- buf_printf(b, "\t\"%s\\0\"\n", s->name);
- }
- buf_printf(b, ";\n");
-}
-
-/**
- * Record CRCs for unresolved symbols
- **/
-static void add_versions(struct buffer *b, struct module *mod)
-{
- struct symbol *s;
-
- if (!basic_modversions)
- return;
-
- buf_printf(b, "\n");
- buf_printf(b, "static const struct modversion_info ____versions[]\n");
- buf_printf(b, "__used __section(\"__versions\") = {\n");
-
- list_for_each_entry(s, &mod->unresolved_symbols, list) {
- if (!s->module)
- continue;
- if (!s->crc_valid) {
- mod_warn(mod, "symbol '%s' has no CRC!\n", s->name);
- continue;
- }
- if (strlen(s->name) >= MODULE_NAME_LEN) {
- if (extended_modversions) {
- /* this symbol will only be in the extended info */
- continue;
- } else {
- mod_error(mod, "too long symbol '%s'\n", s->name);
- break;
- }
- }
- buf_printf(b, "\t{ 0x%08x, \"%s\" },\n",
- s->crc, s->name);
- }
-
- buf_printf(b, "};\n");
-}
-
-static void add_depends(struct buffer *b, struct module *mod)
-{
- struct symbol *s;
- int first = 1;
-
- /* Clear ->seen flag of modules that own symbols needed by this. */
- list_for_each_entry(s, &mod->unresolved_symbols, list) {
- if (s->module)
- s->module->seen = s->module->is_vmlinux;
- }
-
- buf_printf(b, "\n");
- buf_printf(b, "MODULE_INFO(depends, \"");
- list_for_each_entry(s, &mod->unresolved_symbols, list) {
- const char *p;
- if (!s->module)
- continue;
-
- if (s->module->seen)
- continue;
-
- s->module->seen = true;
- p = get_basename(s->module->name);
- buf_printf(b, "%s%s", first ? "" : ",", p);
- first = 0;
- }
- buf_printf(b, "\");\n");
-}
-
-static void add_srcversion(struct buffer *b, struct module *mod)
-{
- if (mod->srcversion[0]) {
- buf_printf(b, "\n");
- buf_printf(b, "MODULE_INFO(srcversion, \"%s\");\n",
- mod->srcversion);
- }
-}
-
static void write_buf(struct buffer *b, const char *fname)
{
FILE *file;
@@ -2191,30 +2042,483 @@ static void write_vmlinux_export_c_file(struct module *mod)
free(buf.p);
}
-/* do sanity checks, and generate *.mod.c file */
-static void write_mod_c_file(struct module *mod)
+#if MOD_SIZEOF_LONG == 8
+#define MOD_PTR_DIRECTIVE ".quad"
+#else
+#define MOD_PTR_DIRECTIVE ".long"
+#endif
+
+/* See KSYM_FUNC() in include/linux/export-internal.h. */
+#if MOD_FUNC_PLABEL
+#define MOD_FUNC_PREFIX "P%"
+#else
+#define MOD_FUNC_PREFIX ""
+#endif
+
+/* See __KSYM_ALIGN in include/linux/export-internal.h. */
+#if MOD_PREL32_RELOCATIONS || MOD_SIZEOF_LONG == 4
+#define KSYM_ALIGN 4
+#else
+#define KSYM_ALIGN 8
+#endif
+
+/* Append the body of an assembler string literal, escaped as needed. */
+static void buf_escaped(struct buffer *buf, const char *str)
+{
+ unsigned char chr;
+
+ while ((chr = *str++)) {
+ if (chr == '"' || chr == '\\')
+ buf_printf(buf, "\\%c", chr);
+ else if (isprint(chr))
+ buf_printf(buf, "%c", chr);
+ else
+ buf_printf(buf, "\\%03o", chr);
+ }
+}
+
+static void buf_asciz(struct buffer *buf, const char *str)
{
- struct buffer buf = { };
- struct module_alias *alias, *next;
- char fname[PATH_MAX];
- int ret;
+ buf_printf(buf, "\t.asciz \"");
+ buf_escaped(buf, str);
+ buf_printf(buf, "\"\n");
+}
- add_header(&buf, mod);
- add_exported_symbols(&buf, mod);
- add_versions(&buf, mod);
- add_extended_versions(&buf, mod);
- add_depends(&buf, mod);
+/* The equivalent of MODULE_INFO(tag, info). */
+static void add_asm_modinfo(struct buffer *buf, const char *tag,
+ const char *info)
+{
+ buf_printf(buf, "\t.section .modinfo,\"a\",%%progbits\n");
+ buf_printf(buf, "\t.asciz \"%s=", tag);
+ buf_escaped(buf, info);
+ buf_printf(buf, "\"\n");
+}
- buf_printf(&buf, "\n");
+/* See __KSYM_REF() in include/linux/export-internal.h. */
+static void add_asm_ksym_ref(struct buffer *buf, const char *prefix,
+ const char *sym)
+{
+#if MOD_PREL32_RELOCATIONS
+ buf_printf(buf, "\t.long %s%s - .\n", prefix, sym);
+#else
+ buf_printf(buf, "\t" MOD_PTR_DIRECTIVE " %s%s\n", prefix, sym);
+#endif
+}
+
+/* The name and namespace strings a ksymtab entry refers to. */
+static void add_asm_kstrtab(struct buffer *buf, const struct symbol *sym)
+{
+ buf_printf(buf, "\t.section \"__ksymtab_strings\",\"aMS\",%%progbits,1\n");
+ buf_printf(buf, "__kstrtab_%s:\n", sym->name);
+ buf_asciz(buf, sym->name);
+ buf_printf(buf, "__kstrtabns_%s:\n", sym->name);
+ buf_asciz(buf, sym->namespace);
+ buf_printf(buf, "\t.previous\n");
+}
+
+/* The equivalent of SYMBOL_FLAGS(). */
+static void add_asm_kflagstab(struct buffer *buf, const struct symbol *sym)
+{
+ buf_printf(buf, "\t.section \"___kflagstab+%s\", \"a\"\n", sym->name);
+ buf_printf(buf, "__flags_%s:\n", sym->name);
+ buf_printf(buf, "\t.byte 0x%02x\n", get_symbol_flags(sym));
+ buf_printf(buf, "\t.previous\n");
+}
+
+/* The equivalent of KSYMTAB_FUNC()/KSYMTAB_DATA(). */
+static void add_asm_ksymtab(struct buffer *buf, const struct symbol *sym)
+{
+ const char *name = sym->name;
+
+ add_asm_kstrtab(buf, sym);
+
+ buf_printf(buf, "\t.section \"___ksymtab+%s\", \"a\"\n", name);
+ buf_printf(buf, "\t.balign %d\n", KSYM_ALIGN);
+ buf_printf(buf, "__ksymtab_%s:\n", name);
+ add_asm_ksym_ref(buf, sym->is_func ? MOD_FUNC_PREFIX : "", name);
+ add_asm_ksym_ref(buf, "__kstrtab_", name);
+ add_asm_ksym_ref(buf, "__kstrtabns_", name);
+ buf_printf(buf, "\t.previous\n");
+
+ add_asm_kflagstab(buf, sym);
+}
+
+/* The equivalent of SYMBOL_CRC(). */
+static void add_asm_crc(struct buffer *buf, const struct symbol *sym)
+{
+ buf_printf(buf, "\t.section \"___kcrctab+%s\",\"a\"\n", sym->name);
+ buf_printf(buf, "\t.balign 4\n");
+ buf_printf(buf, "__crc_%s:\n", sym->name);
+ buf_printf(buf, "\t.long 0x%08x\n", sym->crc);
+ buf_printf(buf, "\t.previous\n");
+}
+
+static bool export_is_kept(const struct symbol *sym)
+{
+ return !trim_unused_exports || sym->used;
+}
+
+/* Record the CRCs of the exported symbols. */
+static void add_asm_crcs(struct buffer *buf, struct module *mod)
+{
+ struct symbol *sym;
+
+ list_for_each_entry(sym, &mod->exported_symbols, list) {
+ if (!export_is_kept(sym))
+ continue;
+
+ if (!sym->crc_valid)
+ mod_warn(mod, "EXPORT symbol '%s' version generation failed, symbol will not be versioned.\n"
+ "Is '%s' prototyped in <asm/asm-prototypes.h>?\n",
+ sym->name, sym->name);
+ add_asm_crc(buf, sym);
+ }
+}
+
+static void add_asm_exported_symbols(struct buffer *buf, struct module *mod)
+{
+ struct symbol *sym;
+
+ list_for_each_entry(sym, &mod->exported_symbols, list) {
+ if (export_is_kept(sym))
+ add_asm_ksymtab(buf, sym);
+ }
+
+ if (modversions)
+ add_asm_crcs(buf, mod);
+}
+
+/* Zero fill up to the offset. */
+static void asm_skip_to(struct buffer *buf, unsigned int *pos,
+ unsigned int offset)
+{
+ if (offset < *pos)
+ fatal("__this_module field at offset %u overlaps the previous one\n",
+ offset);
+ if (offset > *pos)
+ buf_printf(buf, "\t.skip %u\n", offset - *pos);
+
+ *pos = offset;
+}
+
+/* A non-zero field of __this_module: its offset and the name or symbol in it. */
+struct this_module_field {
+ unsigned int offset;
+ bool is_name;
+ const char *value;
+};
+
+#define THIS_MODULE_MAX_FIELDS 5
+
+static int compare_field_offsets(const void *ptr_a, const void *ptr_b)
+{
+ const struct this_module_field *field_a = ptr_a, *field_b = ptr_b;
+
+ if (field_a->offset != field_b->offset)
+ return field_a->offset < field_b->offset ? -1 : 1;
+
+ return 0;
+}
+
+/*
+ * The fields of __this_module which are not zero, in offset order. The order
+ * is only known from module-offsets.h, CONFIG_RANDSTRUCT shuffles struct module.
+ */
+static unsigned int get_this_module_fields(const struct module *mod,
+ const char *modname,
+ struct this_module_field *fields)
+{
+ unsigned int nr_fields = 0;
+
+ fields[nr_fields++] = (struct this_module_field)
+ { MOD_OFF_module_name, true, modname };
+ if (mod->has_init)
+ fields[nr_fields++] = (struct this_module_field)
+ { MOD_OFF_module_init, false, MOD_FUNC_PREFIX "init_module" };
+#ifdef MOD_OFF_module_exit
+ if (mod->has_cleanup)
+ fields[nr_fields++] = (struct this_module_field)
+ { MOD_OFF_module_exit, false, MOD_FUNC_PREFIX "cleanup_module" };
+#endif
+#ifdef MOD_OFF_module_arch_fixup_start
+ fields[nr_fields++] = (struct this_module_field)
+ { MOD_OFF_module_arch_fixup_start, false, "__start_fixup" };
+ fields[nr_fields++] = (struct this_module_field)
+ { MOD_OFF_module_arch_fixup_end, false, "__stop_fixup" };
+#endif
+ qsort(fields, nr_fields, sizeof(*fields), compare_field_offsets);
+
+ return nr_fields;
+}
+
+/* Emit one field of __this_module, returning its size. */
+static unsigned int add_asm_this_module_field(struct buffer *buf,
+ const struct this_module_field *field)
+{
+ if (field->is_name) {
+ buf_printf(buf, "\t.ascii \"%s\"\n", field->value);
+ return strlen(field->value);
+ }
+
+ buf_printf(buf, "\t" MOD_PTR_DIRECTIVE " %s\n", field->value);
+ return MOD_SIZEOF_LONG;
+}
+
+/*
+ * The equivalent of:
+ *
+ * __visible struct module __this_module __section(".gnu.linkonce.this_module")
+ * = { .name = KBUILD_MODNAME, .init = init_module, .exit = cleanup_module,
+ * .arch = MODULE_ARCH_INIT };
+ *
+ * Everything not listed is zero, MODULE_ARCH_INIT included, except on m68k.
+ */
+static void add_asm_this_module(struct buffer *buf, const struct module *mod,
+ const char *modname)
+{
+ struct this_module_field fields[THIS_MODULE_MAX_FIELDS];
+ const unsigned int nr_fields = get_this_module_fields(mod, modname, fields);
+ unsigned int pos = 0, i;
+
+ buf_printf(buf, "\n\t.section .gnu.linkonce.this_module,\"aw\",%%progbits\n");
+ buf_printf(buf, "\t.balign %d\n", MOD_ALIGNOF_struct_module);
+ buf_printf(buf, "\t.globl __this_module\n");
+ buf_printf(buf, "\t.type __this_module, %%object\n");
+ buf_printf(buf, "\t.size __this_module, %d\n", MOD_SIZEOF_struct_module);
+ buf_printf(buf, "__this_module:\n");
+
+ for (i = 0; i < nr_fields; i++) {
+ asm_skip_to(buf, &pos, fields[i].offset);
+ pos += add_asm_this_module_field(buf, &fields[i]);
+ }
+
+ asm_skip_to(buf, &pos, MOD_SIZEOF_struct_module);
+}
+
+/*
+ * An unresolved symbol without a module is not versioned; one without a CRC
+ * cannot be, so warn about it.
+ */
+static bool skip_unversioned(struct module *mod, const struct symbol *sym)
+{
+ if (!sym->module)
+ return true;
+ if (sym->crc_valid)
+ return false;
+
+ mod_warn(mod, "symbol '%s' has no CRC!\n", sym->name);
+ return true;
+}
+
+/* One struct modversion_info: the CRC, then the name padded to the end. */
+static void add_asm_version(struct buffer *buf, const struct symbol *sym)
+{
+ buf_printf(buf, "\t" MOD_PTR_DIRECTIVE " 0x%08x\n", sym->crc);
+ buf_printf(buf, "\t.ascii \"%s\"\n", sym->name);
+ buf_printf(buf, "\t.skip %zu\n", MOD_SIZEOF_struct_modversion_info -
+ MOD_OFF_modversion_info_name - strlen(sym->name));
+}
+
+/*
+ * The equivalent of:
+ *
+ * static const struct modversion_info ____versions[]
+ * __used __section("__versions") = { { crc, "name" }, ... };
+ *
+ * for unresolved symbols.
+ */
+static void add_asm_versions(struct buffer *buf, struct module *mod)
+{
+ struct symbol *sym;
+
+ if (!basic_modversions)
+ return;
+
+ buf_printf(buf, "\n\t.section __versions,\"a\",%%progbits\n");
+ buf_printf(buf, "\t.balign %d\n", MOD_ALIGNOF_struct_modversion_info);
+ list_for_each_entry(sym, &mod->unresolved_symbols, list) {
+ if (skip_unversioned(mod, sym))
+ continue;
+
+ if (strlen(sym->name) >= MOD_NAME_LEN) {
+ /* Only the extended table can hold it. */
+ if (extended_modversions)
+ continue;
+
+ mod_error(mod, "too long symbol '%s'\n", sym->name);
+ break;
+ }
+
+ add_asm_version(buf, sym);
+ }
+}
+
+static void add_asm_version_ext_crcs(struct buffer *buf, struct module *mod)
+{
+ struct symbol *sym;
+
+ buf_printf(buf, "\n\t.section __version_ext_crcs,\"a\",%%progbits\n");
+ buf_printf(buf, "\t.balign 4\n");
+ list_for_each_entry(sym, &mod->unresolved_symbols, list) {
+ if (skip_unversioned(mod, sym))
+ continue;
+
+ buf_printf(buf, "\t.long 0x%08x\n", sym->crc);
+ }
+}
+
+/*
+ * A symbol without a CRC was warned about with the CRCs, and is skipped here
+ * too so that the names line up with them.
+ */
+static void add_asm_version_ext_names(struct buffer *buf, struct module *mod)
+{
+ struct symbol *sym;
+
+ buf_printf(buf, "\t.section __version_ext_names,\"a\",%%progbits\n");
+ list_for_each_entry(sym, &mod->unresolved_symbols, list) {
+ if (!sym->module || !sym->crc_valid)
+ continue;
+
+ buf_asciz(buf, sym->name);
+ }
+ /* The terminator of the string literal this used to be. */
+ buf_printf(buf, "\t.byte 0\n");
+}
+
+/*
+ * The equivalent of:
+ * static const u32 ____version_ext_crcs[] __section("__version_ext_crcs") = { crc, ... };
+ * static const char ____version_ext_names[] __section("__version_ext_names") = "name\0" ...;
+ *
+ * for unresolved symbols.
+ */
+static void add_asm_extended_versions(struct buffer *buf, struct module *mod)
+{
+ if (!extended_modversions)
+ return;
+
+ add_asm_version_ext_crcs(buf, mod);
+ add_asm_version_ext_names(buf, mod);
+}
+
+/* Clear ->seen of the modules that own symbols this one needs. */
+static void clear_seen_dependencies(struct module *mod)
+{
+ struct symbol *sym;
+
+ list_for_each_entry(sym, &mod->unresolved_symbols, list) {
+ if (sym->module)
+ sym->module->seen = sym->module->is_vmlinux;
+ }
+}
+
+/* The modules this one depends on, each once, comma separated. */
+static void collect_dependencies(struct module *mod, struct buffer *deps)
+{
+ struct symbol *sym;
+ bool first = true;
+
+ clear_seen_dependencies(mod);
+
+ list_for_each_entry(sym, &mod->unresolved_symbols, list) {
+ struct module *owner = sym->module;
+
+ if (!owner || owner->seen)
+ continue;
+
+ owner->seen = true;
+ buf_printf(deps, "%s%s", first ? "" : ",",
+ get_basename(owner->name));
+ first = false;
+ }
+ buf_write(deps, "", 1);
+}
+
+static void add_asm_depends(struct buffer *buf, struct module *mod)
+{
+ struct buffer deps = { };
+
+ collect_dependencies(mod, &deps);
+ buf_printf(buf, "\n");
+ add_asm_modinfo(buf, "depends", deps.p);
+ free(deps.p);
+}
+
+/*
+ * KBUILD_MODNAME: the basename of the module with '-' and ',' replaced by
+ * '_' (see name-fix in scripts/Makefile.lib).
+ */
+static char *get_kbuild_modname(const struct module *mod)
+{
+ char *name = xstrdup(get_basename(mod->name));
+ char *curr;
+
+ for (curr = name; *curr; curr++) {
+ if (*curr == '-' || *curr == ',')
+ *curr = '_';
+ }
+
+ return name;
+}
+
+/* The module's name, its descriptor, and where it comes from. */
+static void add_asm_header(struct buffer *buf, const struct module *mod,
+ const char *modname)
+{
+ buf_printf(buf, "/* Generated by modpost, see scripts/Makefile.modfinal */\n\n");
+
+ add_asm_modinfo(buf, "name", modname);
+ add_asm_this_module(buf, mod, modname);
+ buf_printf(buf, "\n");
+
+ if (!external_module)
+ add_asm_modinfo(buf, "intree", "Y");
+ if (strstarts(mod->name, "drivers/staging"))
+ add_asm_modinfo(buf, "staging", "Y");
+ if (strstarts(mod->name, "tools/testing"))
+ add_asm_modinfo(buf, "test", "Y");
+}
+
+static void add_asm_aliases(struct buffer *buf, struct module *mod)
+{
+ struct module_alias *alias, *next;
+
+ buf_printf(buf, "\n");
list_for_each_entry_safe(alias, next, &mod->aliases, node) {
- buf_printf(&buf, "MODULE_ALIAS(\"%s\");\n", alias->str);
+ add_asm_modinfo(buf, "alias", alias->str);
list_del(&alias->node);
free(alias);
}
+}
- add_srcversion(&buf, mod);
+static void add_asm_srcversion(struct buffer *buf, const struct module *mod)
+{
+ if (!mod->srcversion[0])
+ return;
- ret = snprintf(fname, sizeof(fname), "%s.mod.c", mod->name);
+ buf_printf(buf, "\n");
+ add_asm_modinfo(buf, "srcversion", mod->srcversion);
+}
+
+static void write_mod_S_file(struct module *mod)
+{
+ struct buffer buf = { };
+ char fname[PATH_MAX];
+ char *modname = get_kbuild_modname(mod);
+ int ret;
+
+ add_asm_header(&buf, mod, modname);
+ buf_printf(&buf, "\n");
+ add_asm_exported_symbols(&buf, mod);
+ add_asm_versions(&buf, mod);
+ add_asm_extended_versions(&buf, mod);
+ add_asm_depends(&buf, mod);
+ add_asm_aliases(&buf, mod);
+ add_asm_srcversion(&buf, mod);
+ buf_printf(&buf, "\n\t.section .note.GNU-stack,\"\",%%progbits\n");
+
+ ret = snprintf(fname, sizeof(fname), "%s.mod.S", mod->name);
if (ret >= sizeof(fname)) {
error("%s: too long path was truncated\n", fname);
goto free;
@@ -2223,6 +2527,7 @@ static void write_mod_c_file(struct module *mod)
write_if_changed(&buf, fname);
free:
+ free(modname);
free(buf.p);
}
@@ -2462,7 +2767,7 @@ int main(int argc, char **argv)
if (mod->is_vmlinux)
write_vmlinux_export_c_file(mod);
else
- write_mod_c_file(mod);
+ write_mod_S_file(mod);
}
if (missing_namespace_deps)
diff --git a/scripts/mod/module-offsets.c b/scripts/mod/module-offsets.c
new file mode 100644
index 000000000000..a336dd47aa33
--- /dev/null
+++ b/scripts/mod/module-offsets.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Layout of the structures modpost emits into *.mod.S, extracted from the
+ * target headers as devicetable-offsets.c does for the device tables.
+ */
+#define COMPILE_OFFSETS
+#include <linux/kbuild.h>
+#include <linux/module.h>
+
+int main(void)
+{
+ DEFINE(MOD_SIZEOF_LONG, sizeof(long));
+ DEFINE(MOD_PREL32_RELOCATIONS, IS_ENABLED(CONFIG_HAVE_ARCH_PREL32_RELOCATIONS));
+ DEFINE(MOD_FUNC_PLABEL, IS_ENABLED(CONFIG_PARISC) && IS_ENABLED(CONFIG_64BIT));
+
+ DEFINE(MOD_SIZEOF_struct_module, sizeof(struct module));
+ DEFINE(MOD_ALIGNOF_struct_module, __alignof__(struct module));
+ OFFSET(MOD_OFF_module_name, module, name);
+ OFFSET(MOD_OFF_module_init, module, init);
+#ifdef CONFIG_MODULE_UNLOAD
+ OFFSET(MOD_OFF_module_exit, module, exit);
+#endif
+#if defined(CONFIG_M68K) && defined(CONFIG_MMU)
+ /* MODULE_ARCH_INIT: the only architecture where it is not all zeroes. */
+ OFFSET(MOD_OFF_module_arch_fixup_start, module, arch.fixup_start);
+ OFFSET(MOD_OFF_module_arch_fixup_end, module, arch.fixup_end);
+#endif
+ DEFINE(MOD_NAME_LEN, MODULE_NAME_LEN);
+
+ DEFINE(MOD_SIZEOF_struct_modversion_info, sizeof(struct modversion_info));
+ DEFINE(MOD_ALIGNOF_struct_modversion_info, __alignof__(struct modversion_info));
+ OFFSET(MOD_OFF_modversion_info_name, modversion_info, name);
+
+ return 0;
+}
diff --git a/scripts/tags.sh b/scripts/tags.sh
index 41e38df96984..c33d0f58a9d4 100755
--- a/scripts/tags.sh
+++ b/scripts/tags.sh
@@ -14,8 +14,9 @@ fi
# RCS_FIND_IGNORE has escaped ()s -- remove them.
ignore="$(echo "$RCS_FIND_IGNORE" | sed 's|\\||g' )"
-# tags and cscope files should also ignore MODVERSION *.mod.c files
-ignore="$ignore ( -name *.mod.c ) -prune -o"
+# tags and cscope files should also ignore the modpost-generated *.mod.S files
+# and any *.mod.c left behind from before they were assembly
+ignore="$ignore ( -name *.mod.c -o -name *.mod.S ) -prune -o"
# ignore arbitrary directories
if [ -n "${IGNORE_DIRS}" ]; then
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 14/21] kbuild: batch module finalisation
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (12 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 13/21] modpost: emit module descriptors as assembly Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 18:00 ` Kees Cook
2026-09-14 9:22 ` [PATCH v2 15/21] objtool: cache relocations, do less work Lorenzo Stoakes (ARM)
` (7 subsequent siblings)
21 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
Module finalisation on allmodconfig builds consists of a large number of
very short-lived jobs, and the make job dispatcher cannot possibly dispatch
jobs fast enough.
For allmodconfig x86-64 this can be on the order of ~22,000 jobs of a few
milliseconds in duration each.
However per-job cost grows with the variables the instance holds, here the
savedcmd_* of every .mod.o and .ko read back from the .cmd files, since it
walks them all to build each child's environment.
This makes module finalisation very inefficient when large numbers of
modules are being built.
Fix this by splitting modules.order into chunks of 128 at a time, run in
parallel.
Each instance holds only its own modules' variables and the top-level one
reads no per-module .cmd files at all, the same rules serve both levels,
and an instance is told its chunk with modfinal-first=<index>.
"make modules" with every *.mod.o and *.ko deleted goes from 28.9s to 15.9s
with clang 22. No-op "make modules" goes from 5.6s to 4.8s, as checking the
22,000 targets is spread over the chunks too.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 allmodconfig, no-op make, gcc 2.3s 1.4s -0.85s (-38%)
x86 allmodconfig, no-op make, clang 2.8s 1.8s -0.94s (-34%)
x86 allmodconfig, clean, gcc 306.6s 294.1s -12.6s (-4%)
x86 allmodconfig, clean, clang 290.2s 283.9s -6.4s (-2%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
scripts/Makefile.modfinal | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 75e9effdf02c..858fa798090b 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -13,9 +13,30 @@ include $(srctree)/scripts/Makefile.lib
# find all modules listed in modules.order
modules := $(call read-file, modules.order)
+modfinal-chunk-size := 128
+
+ifdef modfinal-first
+
+# this instance handles the chunk of modules.order starting at $(modfinal-first)
+modules := $(wordlist $(modfinal-first), $(words $(modules)), $(modules))
+modules := $(wordlist 1, $(modfinal-chunk-size), $(modules))
+
__modfinal: $(modules:%.o=%.ko)
@:
+else
+
+modfinal-chunks := $(addprefix chunk-, $(shell seq 1 $(modfinal-chunk-size) $(words $(modules))))
+
+PHONY += $(modfinal-chunks)
+$(modfinal-chunks): .module-common.o
+ $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modfinal modfinal-first=$(@:chunk-%=%)
+
+__modfinal: $(modfinal-chunks)
+ @:
+
+endif
+
# modname and part-of-module are set to make c_flags define proper module flags
modname = $(notdir $(@:.mod.o=))
part-of-module = y
@@ -58,7 +79,10 @@ ifdef CONFIG_DEBUG_INFO_BTF_MODULES
endif
+$(call cmd,check_tracepoint)
-targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o) .module-common.o
+targets += .module-common.o
+ifdef modfinal-first
+targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o)
+endif
# Add FORCE to the prerequisites of a target to force it to be always rebuilt.
# ---------------------------------------------------------------------------
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 14/21] kbuild: batch module finalisation
2026-09-14 9:22 ` [PATCH v2 14/21] kbuild: batch module finalisation Lorenzo Stoakes (ARM)
@ 2026-09-14 18:00 ` Kees Cook
2026-09-15 10:44 ` Lorenzo Stoakes (ARM)
0 siblings, 1 reply; 58+ messages in thread
From: Kees Cook @ 2026-09-14 18:00 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 10:22:13AM +0100, Lorenzo Stoakes (ARM) wrote:
> Module finalisation on allmodconfig builds consists of a large number of
> very short-lived jobs, and the make job dispatcher cannot possibly dispatch
> jobs fast enough.
This "cannot possibly" sounds like a weird LLM language intensifier. I'd
rather a concrete description of the problem, not this kind of
(redundant?) vagueness.
> [...]
> Fix this by splitting modules.order into chunks of 128 at a time, run in
> parallel.
Why "128"? This seems tied to the 128-thread test machine, but ends up
getting hard-coded, but this choice of value needs some rationale, IMO.
--
Kees Cook
^ permalink raw reply [flat|nested] 58+ messages in thread
* Re: [PATCH v2 14/21] kbuild: batch module finalisation
2026-09-14 18:00 ` Kees Cook
@ 2026-09-15 10:44 ` Lorenzo Stoakes (ARM)
0 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 10:44 UTC (permalink / raw)
To: Kees Cook
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 11:00:27AM -0700, Kees Cook wrote:
> On Mon, Sep 14, 2026 at 10:22:13AM +0100, Lorenzo Stoakes (ARM) wrote:
> > Module finalisation on allmodconfig builds consists of a large number of
> > very short-lived jobs, and the make job dispatcher cannot possibly dispatch
> > jobs fast enough.
>
> This "cannot possibly" sounds like a weird LLM language intensifier. I'd
Again that's my writing actually, probably best to stop assuming LLM now ;)
> rather a concrete description of the problem, not this kind of
> (redundant?) vagueness.
In the very next paragraph I say:
For allmodconfig x86-64 this can be on the order of ~22,000 jobs of
a few milliseconds in duration each.
You did also say that the commit messages were over-long, so there's a
trade-off here :)
But I think best to expand it a bit if it's not clear.
The general idea is that each job is so short (ms) that the work of
dispatching them exceeds the time doing the work, so you need to shard
things.
And the work of dispatching is heavy - each modfinal instance means it has
to process ~22k .cmd files of every .mod.o and .ko.
I will update the commit message to reflect this.
As a result, we need to batch these (see below).
>
> > [...]
> > Fix this by splitting modules.order into chunks of 128 at a time, run in
> > parallel.
>
> Why "128"? This seems tied to the 128-thread test machine, but ends up
Honestly Kees :) you really think I'd let a hardcoded-to-my-machine
variable through to the point of being called out in the commit msg? :P
No, that's not what this is.
> getting hard-coded, but this choice of value needs some rationale, IMO.
The rationale bit is fair enough, I thought it was somewhat implied but
it's a heuristically-determined value which determines how best to shard
the jobs.
So, it's about both getting parallelism and batching up to offset this job
dispatch overhead, there's naturally an equilibrium.
Emperically:
modules per chunk 32 64 128 256 512
wall time 4.05s 4.07s 4.05s 4.03s 4.18s
But in more detail, allmodconfig tree (~11k modules on x86-64), best of 2,
make modules with *.ko *.mod.o deleted:
modules per chunk instances wall
----------------- --------- ------
1 11171 10.22s
2 5586 6.72s
4 2793 4.97s
8 1397 4.26s
16 699 4.05s
32 350 4.05s
64 175 4.07s
128 88 4.05s
256 44 4.03s
512 22 4.18s
which I think makes things clearer.
So realistically 32 - 256 is the right sort of range. You also have to take
into account the fact that you might be building fewer modules.
The argument for 128 is that this is the mid-point of where the graph
flattens off for a larger number of modules.
For a smaller number, you're going to have a single dispatch or less and
the delta won't be that much anyway.
So it's very much a sensibly derived empirical value.
I'll update the commit message to give this rationale there.
>
> --
> Kees Cook
And for avoidance of doubt, it's ME replying to things :P I deal with a LOT
of AI slop in mm so am quite sensitive to doing things right here (TM).
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* [PATCH v2 15/21] objtool: cache relocations, do less work
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (13 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 14/21] kbuild: batch module finalisation Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 19:44 ` Josh Poimboeuf
2026-09-14 9:22 ` [PATCH v2 16/21] objtool: size the instruction hash to the text Lorenzo Stoakes (ARM)
` (6 subsequent siblings)
21 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
Instruction relocations are looked up by destination in objtool via a hash
which is keyed on a 16-byte (OFFSET_STRIDE) window within the section being
walked.
It iterates through each 16-byte window, looking up relocations over
several passes, before moving on to the next 16-byte window, caching only
when a relocation is not found saving further lookups in this case.
Improve upon this by introducing a per-section relocation cache storing the
first relocation at or after each 64-byte window of data (an empirically
determined index range), indexed by chunk.
The lookup is implemented an array lookup and touches no shared state, so
can be used from multiple threads.
This relies upon the entries within a section being sorted, which is the
case for all sections supplied to objtool by the link step during the
kernel build.
For cases where sections are supplied out of order, grown one relocation
at a time (e.g. livepatch) or created by objtool itself, fall back to using
the existing hash mechanism.
DWARF sections are a special case - their relocations are never looked up
by destination at all and only need to be on their symbol's list for
elf_update_sym_relocs().
So do not index or hash DWARF relocations at all - however add a mechanism
such that if one were ever looked up, a linear scan will be used.
This is meaningful in practice as on an x86-64 kernel build with
CONFIG_DEBUG_INFO set objtool processing of vmlinux.o is dominated by DWARF
section processing.
For an allmodconfig build ~9 million relocations were hashed, and ~8.2
million of those were DWARF sections, which added overhead on cache miss
and pollution of the hash table. This is now eliminated.
The hash, when used, is read-mostly (every jump, call and memory operand)
and several relocations share a key due to the 16-byte stride, so keep the
hash sparse by scaling the hash by the number of objects to be hashed.
The output of objtool before and after this change was confirmed to be
byte-for-byte identical both for x86_64 defconfig and allmodconfig with
gcc and clang.
objtool on vmlinux.o is on the serial tail of every build that links
vmlinux, no-op builds are unchanged.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 8.3s 8.2s -0.14s (-2%)
x86 defconfig, touch mm/vma.c, clang 7.6s 7.3s -0.25s (-3%)
x86 defconfig, clean, gcc 28.9s 28.6s -0.22s (-1%)
x86 defconfig, clean, clang 29.4s 29.1s -0.28s (-1%)
x86 allmodconfig, touch mm/vma.c, gcc 29.4s 28.0s -1.4s (-5%)
x86 allmodconfig, touch mm/vma.c, clang 27.9s 26.2s -1.7s (-6%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
tools/objtool/elf.c | 246 +++++++++++++++++++++++++++++++++---
tools/objtool/include/objtool/elf.h | 2 +
2 files changed, 231 insertions(+), 17 deletions(-)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index a791f4ea6ec1..5ee11301a5a3 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -316,18 +316,117 @@ struct symbol *find_global_symbol_by_name(const struct elf *elf, const char *nam
return NULL;
}
-/* If there are multiple matches, return the first one in the range */
-struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
+static bool is_dwarf_section(struct section *sec)
+{
+ return !strncmp(sec->name, ".debug_", 7);
+}
+
+/* Cache relocations at a 64 byte granularity. */
+#define RELOC_CACHE_INDEX_SHIFT 6
+
+static unsigned long reloc_cache_index(unsigned long offset)
+{
+ return offset >> RELOC_CACHE_INDEX_SHIFT;
+}
+
+static unsigned int reloc_cache_nr_windows(const struct section *rsec)
+{
+ const unsigned long size = sec_size(rsec->base);
+
+ return (size >> RELOC_CACHE_INDEX_SHIFT) + 1;
+}
+
+static int init_reloc_cache(struct section *rsec)
+{
+ const unsigned int nr_relocs = sec_num_entries(rsec);
+ const unsigned int nr_windows = reloc_cache_nr_windows(rsec);
+ unsigned int reloc_idx, next_cache_idx = 0;
+
+ rsec->reloc_cache = malloc(nr_windows * sizeof(unsigned int));
+ if (!rsec->reloc_cache) {
+ ERROR_GLIBC("malloc");
+ return -1;
+ }
+
+ /* Populate relocation indexes reloc cache index -> reloc index. */
+ for (reloc_idx = 0; reloc_idx < nr_relocs; reloc_idx++) {
+ struct reloc *reloc = &rsec->relocs[reloc_idx];
+ const unsigned long offset = reloc_offset(reloc);
+ const unsigned long cache_idx = reloc_cache_index(offset);
+
+ if (cache_idx >= nr_windows)
+ break;
+
+ while (next_cache_idx <= cache_idx)
+ rsec->reloc_cache[next_cache_idx++] = reloc_idx;
+ }
+
+ while (next_cache_idx < nr_windows)
+ rsec->reloc_cache[next_cache_idx++] = nr_relocs;
+
+ rsec->sorted = true;
+ return 0;
+}
+
+static void free_reloc_cache(struct section *rsec)
+{
+ free(rsec->reloc_cache);
+ rsec->reloc_cache = NULL;
+ rsec->sorted = false;
+}
+
+static struct reloc *find_reloc_sorted(struct section *rsec,
unsigned long offset, unsigned int len)
{
- struct reloc *reloc, *r = NULL;
- struct section *rsec;
- unsigned long o;
+ struct reloc *relocs = rsec->relocs;
+ const unsigned int nr_relocs = sec_num_entries(rsec);
+ const unsigned long cache_idx = reloc_cache_index(offset);
+ unsigned int reloc_idx, i;
- rsec = sec->rsec;
- if (!rsec)
+ if (cache_idx >= reloc_cache_nr_windows(rsec))
+ return NULL;
+
+ reloc_idx = rsec->reloc_cache[cache_idx];
+
+ /*
+ * Scan through all relocations covered by cache entry to find the
+ * first at or after offset. Relocations are sorted by offset.
+ */
+ for (i = reloc_idx; i < nr_relocs; i++) {
+ struct reloc *reloc = &relocs[i];
+ const unsigned long curr_offset = reloc_offset(reloc);
+
+ if (curr_offset >= offset)
+ break;
+
+ reloc_idx++;
+ }
+
+ /* Nothing found, or the first candidate lies beyond the range. */
+ if (reloc_idx >= nr_relocs ||
+ reloc_offset(&relocs[reloc_idx]) >= offset + len)
return NULL;
+ /* If there are duplicate entries, return the last. */
+ for (i = reloc_idx; i < nr_relocs - 1; i++) {
+ struct reloc *reloc = &relocs[i];
+ struct reloc *next_reloc = &relocs[i + 1];
+
+ if (reloc_offset(next_reloc) != reloc_offset(reloc))
+ break;
+ reloc_idx++;
+ }
+
+ return &relocs[reloc_idx];
+}
+
+/* Not indexed, so look it up in the hash. */
+static struct reloc *find_reloc_hash(const struct elf *elf, struct section *rsec,
+ unsigned long offset, unsigned int len)
+{
+ unsigned long o;
+ struct reloc *reloc, *r = NULL;
+
for_offset_range(o, offset, offset + len) {
elf_hash_for_each_possible(elf, reloc, reloc, hash,
sec_offset_hash(rsec, o)) {
@@ -347,14 +446,48 @@ struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *se
return r;
}
-struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
+/* Should never be invoked, provided as a backstop. */
+static struct reloc *find_reloc_linear(struct section *rsec,
+ unsigned long offset, unsigned int len)
{
- return find_reloc_by_dest_range(elf, sec, offset, 1);
+ struct reloc *reloc, *first = NULL;
+
+ WARN("%s: linear scan for sec %s with %u relocs at offset %lu len %u",
+ __func__, rsec->name, sec_num_entries(rsec), offset, len);
+
+ for_each_reloc(rsec, reloc) {
+ if (reloc_offset(reloc) < offset ||
+ reloc_offset(reloc) >= offset + len)
+ continue;
+
+ if (!first || reloc_offset(reloc) < reloc_offset(first))
+ first = reloc;
+ }
+
+ return first;
}
-static bool is_dwarf_section(struct section *sec)
+/* If there are multiple matches, return the first one in the range. */
+struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
+ unsigned long offset, unsigned int len)
{
- return !strncmp(sec->name, ".debug_", 7);
+ struct section *rsec = sec->rsec;
+
+ if (!rsec)
+ return NULL;
+
+ if (rsec->sorted)
+ return find_reloc_sorted(rsec, offset, len);
+
+ if (rsec->hashed)
+ return find_reloc_hash(elf, rsec, offset, len);
+
+ return find_reloc_linear(rsec, offset, len);
+}
+
+struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
+{
+ return find_reloc_by_dest_range(elf, sec, offset, 1);
}
static int read_sections(struct elf *elf)
@@ -1071,7 +1204,8 @@ struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec,
set_reloc_type(elf, reloc, type);
set_reloc_addend(elf, reloc, addend);
- elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
+ if (rsec->hashed)
+ elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
set_sym_next_reloc(reloc, sym->relocs);
sym->relocs = reloc;
@@ -1123,18 +1257,44 @@ struct reloc *elf_init_reloc_data_sym(struct elf *elf, struct section *sec,
elf_data_rela_type(elf));
}
+static u64 raw_reloc_offset(const struct section *rsec, unsigned int idx)
+{
+ const void *entry = rsec->data->d_buf + idx * rsec->sh.sh_entsize;
+
+ if (rsec->sh.sh_entsize < sizeof(Elf64_Rel))
+ return ((const Elf32_Rela *)entry)->r_offset;
+
+ return ((const Elf64_Rela *)entry)->r_offset;
+}
+
+static bool reloc_sec_in_order(struct section *rsec)
+{
+ const unsigned int nr_relocs = sec_num_entries(rsec);
+ u64 prev_offset = 0;
+ unsigned int i;
+
+ for (i = 0; i < nr_relocs; i++) {
+ /* Called before relocs exist, so look at raw entry. */
+ const u64 offset = raw_reloc_offset(rsec, i);
+
+ if (offset < prev_offset)
+ return false;
+ prev_offset = offset;
+ }
+
+ return true;
+}
+
static int read_relocs(struct elf *elf)
{
- unsigned long nr_reloc, max_reloc = 0;
+ unsigned long nr_reloc, max_reloc = 0, nr_hashed = 0;
struct section *rsec;
struct reloc *reloc;
unsigned int symndx;
struct symbol *sym;
+ bool hashed;
int i;
- if (!elf_alloc_hash(reloc, elf->num_relocs))
- return -1;
-
list_for_each_entry(rsec, &elf->sections, list) {
if (!is_reloc_sec(rsec))
continue;
@@ -1147,6 +1307,28 @@ static int read_relocs(struct elf *elf)
rsec->base->rsec = rsec;
+ /* DWARF relocs are never looked up. */
+ if (is_dwarf_section(rsec->base))
+ continue;
+ if (reloc_sec_in_order(rsec)) {
+ rsec->sorted = true;
+ continue;
+ }
+
+ rsec->hashed = true;
+ nr_hashed += sec_num_entries(rsec);
+ }
+
+ /* Read mostly, so avoid collisions and keep the hash sparse. */
+ if (!elf_alloc_hash(reloc, nr_hashed * OFFSET_STRIDE))
+ return -1;
+
+ list_for_each_entry(rsec, &elf->sections, list) {
+ if (!is_reloc_sec(rsec))
+ continue;
+
+ hashed = rsec->hashed;
+
/* nr_alloc_relocs=0: libelf owns d_buf */
rsec->nr_alloc_relocs = 0;
@@ -1168,18 +1350,23 @@ static int read_relocs(struct elf *elf)
return -1;
}
- elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
+ if (hashed)
+ elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
set_sym_next_reloc(reloc, sym->relocs);
sym->relocs = reloc;
nr_reloc++;
}
max_reloc = max(max_reloc, nr_reloc);
+
+ if (rsec->sorted && init_reloc_cache(rsec))
+ return -1;
}
if (opts.stats) {
printf("max_reloc: %lu\n", max_reloc);
printf("num_relocs: %lu\n", elf->num_relocs);
+ printf("num_relocs_hashed: %lu\n", nr_hashed);
printf("reloc_bits: %d\n", elf->reloc_bits);
}
@@ -1541,6 +1728,26 @@ struct section *elf_create_section(struct elf *elf, const char *name,
return sec;
}
+/* A relocation was appended, abandon relocation cache and use hash instead. */
+static void copy_reloc_cache_to_hash(struct elf *elf, struct section *rsec,
+ unsigned int nr_relocs)
+{
+ unsigned int i;
+
+ if (rsec->hashed)
+ return;
+
+ if (rsec->sorted)
+ free_reloc_cache(rsec);
+
+ for (i = 0; i < nr_relocs; i++) {
+ struct reloc *reloc = &rsec->relocs[i];
+
+ elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
+ }
+ rsec->hashed = true;
+}
+
static int elf_alloc_reloc(struct elf *elf, struct section *rsec)
{
struct reloc *old_relocs, *old_relocs_end, *new_relocs;
@@ -1686,6 +1893,8 @@ struct section *elf_create_rela_section(struct elf *elf, struct section *sec,
sec->rsec = rsec;
rsec->base = sec;
+ /* Relocations objtool creates are looked up through the hash. */
+ rsec->hashed = true;
return rsec;
}
@@ -1708,6 +1917,9 @@ struct reloc *elf_create_reloc(struct elf *elf, struct section *sec,
return NULL;
}
+ /* A section read from the file is indexed, once grown it is hashed. */
+ copy_reloc_cache_to_hash(elf, rsec, sec_num_entries(rsec));
+
if (elf_alloc_reloc(elf, rsec))
return NULL;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index a82517a76a0f..946b411ff1b9 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -59,6 +59,8 @@ struct section {
const char *name;
int idx;
bool _changed, text, rodata, noinstr, init, truncate;
+ bool hashed, sorted;
+ unsigned int *reloc_cache;
struct reloc *relocs;
unsigned long nr_alloc_relocs;
struct section *twin;
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 15/21] objtool: cache relocations, do less work
2026-09-14 9:22 ` [PATCH v2 15/21] objtool: cache relocations, do less work Lorenzo Stoakes (ARM)
@ 2026-09-14 19:44 ` Josh Poimboeuf
2026-09-14 20:06 ` Linus Torvalds
2026-09-15 12:19 ` Lorenzo Stoakes (ARM)
0 siblings, 2 replies; 58+ messages in thread
From: Josh Poimboeuf @ 2026-09-14 19:44 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Peter Zijlstra, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl,
Trevor Gross, Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Kees Cook, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 10:22:14AM +0100, Lorenzo Stoakes (ARM) wrote:
> +static struct reloc *find_reloc_sorted(struct section *rsec,
> unsigned long offset, unsigned int len)
> {
> - struct reloc *reloc, *r = NULL;
> - struct section *rsec;
> - unsigned long o;
> + struct reloc *relocs = rsec->relocs;
> + const unsigned int nr_relocs = sec_num_entries(rsec);
> + const unsigned long cache_idx = reloc_cache_index(offset);
> + unsigned int reloc_idx, i;
>
> - rsec = sec->rsec;
> - if (!rsec)
> + if (cache_idx >= reloc_cache_nr_windows(rsec))
> + return NULL;
> +
> + reloc_idx = rsec->reloc_cache[cache_idx];
> +
> + /*
> + * Scan through all relocations covered by cache entry to find the
> + * first at or after offset. Relocations are sorted by offset.
> + */
> + for (i = reloc_idx; i < nr_relocs; i++) {
> + struct reloc *reloc = &relocs[i];
> + const unsigned long curr_offset = reloc_offset(reloc);
> +
> + if (curr_offset >= offset)
> + break;
> +
> + reloc_idx++;
> + }
> +
> + /* Nothing found, or the first candidate lies beyond the range. */
> + if (reloc_idx >= nr_relocs ||
> + reloc_offset(&relocs[reloc_idx]) >= offset + len)
> return NULL;
>
> + /* If there are duplicate entries, return the last. */
Hm, for consistency with the others, shouldn't this be returning the
*first* match?
> +/* If there are multiple matches, return the first one in the range. */
> +struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
> + unsigned long offset, unsigned int len)
> {
> - return !strncmp(sec->name, ".debug_", 7);
> + struct section *rsec = sec->rsec;
> +
> + if (!rsec)
> + return NULL;
> +
> + if (rsec->sorted)
> + return find_reloc_sorted(rsec, offset, len);
> +
> + if (rsec->hashed)
> + return find_reloc_hash(elf, rsec, offset, len);
> +
> + return find_reloc_linear(rsec, offset, len);
I'm not sure there's much benefit in having two fallbacks (hashed +
linear) instead of one. If the vast majority of reloc sections are
sorted, then hopefully a single (linear) fallback would be fine,
assuming no major performance regressions. That would help contain the
complexity.
BTW, I found another initialization bug: klp-post-link.c uses
elf_create_section() to create a reloc section, so it missing the
initialization of rsec->hashed in elf_create_rela_section(). But that's
moot if we just get rid of the hashing.
--
Josh
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 15/21] objtool: cache relocations, do less work
2026-09-14 19:44 ` Josh Poimboeuf
@ 2026-09-14 20:06 ` Linus Torvalds
2026-09-14 22:23 ` Josh Poimboeuf
2026-09-15 12:19 ` Lorenzo Stoakes (ARM)
1 sibling, 1 reply; 58+ messages in thread
From: Linus Torvalds @ 2026-09-14 20:06 UTC (permalink / raw)
To: Josh Poimboeuf
Cc: Lorenzo Stoakes (ARM),
Nathan Chancellor, Nicolas Schier, Nick Desaulniers,
Bill Wendling, Justin Stitt, Masahiro Yamada, Alexey Gladkov,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Paul Walmsley, Palmer Dabbelt, Albert Ou,
Alexandre Ghiti, Arnd Bergmann, Catalin Marinas, Will Deacon,
Mark Rutland, Ard Biesheuvel, Ilias Apalodimas, Peter Zijlstra,
Miguel Ojeda, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Kees Cook, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, 14 Sept 2026 at 12:44, Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> BTW, I found another initialization bug: klp-post-link.c uses
> elf_create_section() to create a reloc section, so it missing the
> initialization of rsec->hashed in elf_create_rela_section(). But that's
> moot if we just get rid of the hashing.
Talking about "getting rid of the hashing": the instruction hashing is
obviously a big deal judging by the hash size expansion in that other
patch.
Do we actually look up all instructions by hash in the first place?
From a quick glance, it looks like almost every user of "find_insn()"
is looking for just certain *kinds* of instructions: calls, branches,
returns, endbr. And branch targets.
Maybe stack updates? I didn't check.
Yet we seem to hash them all - even if they are just some random
ALU-only instruction that is in the middle of a function and never a
target of anything and has no impact on any code flow.
So the question becomes: do we actually need to hash those
instructions at all? Are they ever actually looked up?
I don't know this codebase at all, so maybe that's just a really
stupid question. Feel free to look at me condescendinly, shake your
head and say "Poor Linus has lost the plot".
[ And yes, I see that whole "next_insn_same_sec()" thing, which
obviously *does* look up all the instructions when you iterate over
that function, but it strikes me that using a hash table for that is a
bit strange when the natural way to do it would be with juyst a
"struct instruction *next" field instead.. ]
So if hashing was such a big deal that it showed up clearly on
profiles, maybe the answer isn't just a "make the hash table larger".
If a "next" field were to not only make the hash table much smaller,
but also mean that next_insn_same_{func,sec}() would become a "follow
one pointer", mayeb hashing would become rather cheaper?
Stupid? Or maybe "not completely stupid, but too painful to change"?
Linus
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 15/21] objtool: cache relocations, do less work
2026-09-14 20:06 ` Linus Torvalds
@ 2026-09-14 22:23 ` Josh Poimboeuf
2026-09-14 22:30 ` Linus Torvalds
0 siblings, 1 reply; 58+ messages in thread
From: Josh Poimboeuf @ 2026-09-14 22:23 UTC (permalink / raw)
To: Linus Torvalds
Cc: Lorenzo Stoakes (ARM),
Nathan Chancellor, Nicolas Schier, Nick Desaulniers,
Bill Wendling, Justin Stitt, Masahiro Yamada, Alexey Gladkov,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Paul Walmsley, Palmer Dabbelt, Albert Ou,
Alexandre Ghiti, Arnd Bergmann, Catalin Marinas, Will Deacon,
Mark Rutland, Ard Biesheuvel, Ilias Apalodimas, Peter Zijlstra,
Miguel Ojeda, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Kees Cook, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 01:06:37PM -0700, Linus Torvalds wrote:
> Talking about "getting rid of the hashing": the instruction hashing is
> obviously a big deal judging by the hash size expansion in that other
> patch.
>
> Do we actually look up all instructions by hash in the first place?
> From a quick glance, it looks like almost every user of "find_insn()"
> is looking for just certain *kinds* of instructions: calls, branches,
> returns, endbr. And branch targets.
>
> Maybe stack updates? I didn't check.
>
> Yet we seem to hash them all - even if they are just some random
> ALU-only instruction that is in the middle of a function and never a
> target of anything and has no impact on any code flow.
>
> So the question becomes: do we actually need to hash those
> instructions at all? Are they ever actually looked up?
>
> I don't know this codebase at all, so maybe that's just a really
> stupid question. Feel free to look at me condescendinly, shake your
> head and say "Poor Linus has lost the plot".
>
> [ And yes, I see that whole "next_insn_same_sec()" thing, which
> obviously *does* look up all the instructions when you iterate over
> that function, but it strikes me that using a hash table for that is a
> bit strange when the natural way to do it would be with juyst a
> "struct instruction *next" field instead.. ]
>
> So if hashing was such a big deal that it showed up clearly on
> profiles, maybe the answer isn't just a "make the hash table larger".
> If a "next" field were to not only make the hash table much smaller,
> but also mean that next_insn_same_{func,sec}() would become a "follow
> one pointer", mayeb hashing would become rather cheaper?
>
> Stupid? Or maybe "not completely stupid, but too painful to change"?
The find_insn() in next_insn_same_sec() is a bit odd, that was itself
part of a performance optimization, but yes, a 'next' pointer could be
used instead. Though, IIRC, that instruction struct is the biggest
overall user of memory, and it just barely fits inside a cache line
boundary, which we do take advantage of by putting them in adjacent
blocks.
But as you alluded to, find_insn() has a lot more users beyond just
next_insn_same_sec(), like finding jump targets, alternatives, annotated
instructions, and quite a bit more. Determining in advance which subset
of instructions need to be hashed is likely somewhere between "too
painful to change" and "not feasible" IMO.
There might be more efficient ways to structure the considerable amount
of data, like replacing "struct instruction" with "struct basic_block"
or so, but it's hard to know whether that would be a net positive.
At least the current design is a somewhat tolerable balance of
CPU/memory usage and maintainability. Peter and I already fixed most of
the major performance issues, so I'm not overly motivated to squeeze the
last remaining juice of performance, especially if it's going to hurt
maintainability (maintainer bandwidth is also a precious resource).
--
Josh
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 15/21] objtool: cache relocations, do less work
2026-09-14 22:23 ` Josh Poimboeuf
@ 2026-09-14 22:30 ` Linus Torvalds
2026-09-15 12:24 ` Lorenzo Stoakes (ARM)
0 siblings, 1 reply; 58+ messages in thread
From: Linus Torvalds @ 2026-09-14 22:30 UTC (permalink / raw)
To: Josh Poimboeuf
Cc: Lorenzo Stoakes (ARM),
Nathan Chancellor, Nicolas Schier, Nick Desaulniers,
Bill Wendling, Justin Stitt, Masahiro Yamada, Alexey Gladkov,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Paul Walmsley, Palmer Dabbelt, Albert Ou,
Alexandre Ghiti, Arnd Bergmann, Catalin Marinas, Will Deacon,
Mark Rutland, Ard Biesheuvel, Ilias Apalodimas, Peter Zijlstra,
Miguel Ojeda, Boqun Feng, Gary Guo, Björn Roy Baron,
Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross,
Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Kees Cook, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, 14 Sept 2026 at 15:23, Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> There might be more efficient ways to structure the considerable amount
> of data, like replacing "struct instruction" with "struct basic_block"
> or so, but it's hard to know whether that would be a net positive.
Yeah, I was thinking that you'd only hash instructions as you find
them if they are obvious "I need this instruction", and then try to
hash them *again* if they are branch targets (and just have a "already
hashed" flag).
That way random number instructions would not be on the hash - unless
they become branch targets.
And you wouldn't ever really have to track any complicated decisions
(like that whole "basic block" thing - I agree that it's painful,
because the shape of a basic block will change over time as you find
branch targets).
But not a big deal. More an idle thought brought on by that other
patch that changed the hash table size, and this discussion that was
talking about the hashing - or not hashing - of sections.
So more of a "if it is easy and straightforward" kind of thing.
Linus
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 15/21] objtool: cache relocations, do less work
2026-09-14 22:30 ` Linus Torvalds
@ 2026-09-15 12:24 ` Lorenzo Stoakes (ARM)
0 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 12:24 UTC (permalink / raw)
To: Linus Torvalds
Cc: Josh Poimboeuf, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Peter Zijlstra, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl,
Trevor Gross, Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Kees Cook, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 03:30:19PM -0700, Linus Torvalds wrote:
> On Mon, 14 Sept 2026 at 15:23, Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> >
> > There might be more efficient ways to structure the considerable amount
> > of data, like replacing "struct instruction" with "struct basic_block"
> > or so, but it's hard to know whether that would be a net positive.
>
> Yeah, I was thinking that you'd only hash instructions as you find
> them if they are obvious "I need this instruction", and then try to
> hash them *again* if they are branch targets (and just have a "already
> hashed" flag).
>
> That way random number instructions would not be on the hash - unless
> they become branch targets.
>
> And you wouldn't ever really have to track any complicated decisions
> (like that whole "basic block" thing - I agree that it's painful,
> because the shape of a basic block will change over time as you find
> branch targets).
>
> But not a big deal. More an idle thought brought on by that other
> patch that changed the hash table size, and this discussion that was
> talking about the hashing - or not hashing - of sections.
>
> So more of a "if it is easy and straightforward" kind of thing.
Obviously I defer to Josh on this, but it seems from what he said it's
probably a little involved and maybe tricky to figure out how much impact
it might have.
Anyway v3 drops the relocation hash altogether so 1 out of 2 ain't bad ;)
>
> Linus
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* Re: [PATCH v2 15/21] objtool: cache relocations, do less work
2026-09-14 19:44 ` Josh Poimboeuf
2026-09-14 20:06 ` Linus Torvalds
@ 2026-09-15 12:19 ` Lorenzo Stoakes (ARM)
1 sibling, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 12:19 UTC (permalink / raw)
To: Josh Poimboeuf
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Peter Zijlstra, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl,
Trevor Gross, Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Kees Cook, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 12:44:13PM -0700, Josh Poimboeuf wrote:
> On Mon, Sep 14, 2026 at 10:22:14AM +0100, Lorenzo Stoakes (ARM) wrote:
> > +static struct reloc *find_reloc_sorted(struct section *rsec,
> > unsigned long offset, unsigned int len)
> > {
> > - struct reloc *reloc, *r = NULL;
> > - struct section *rsec;
> > - unsigned long o;
> > + struct reloc *relocs = rsec->relocs;
> > + const unsigned int nr_relocs = sec_num_entries(rsec);
> > + const unsigned long cache_idx = reloc_cache_index(offset);
> > + unsigned int reloc_idx, i;
> >
> > - rsec = sec->rsec;
> > - if (!rsec)
> > + if (cache_idx >= reloc_cache_nr_windows(rsec))
> > + return NULL;
> > +
> > + reloc_idx = rsec->reloc_cache[cache_idx];
> > +
> > + /*
> > + * Scan through all relocations covered by cache entry to find the
> > + * first at or after offset. Relocations are sorted by offset.
> > + */
> > + for (i = reloc_idx; i < nr_relocs; i++) {
> > + struct reloc *reloc = &relocs[i];
> > + const unsigned long curr_offset = reloc_offset(reloc);
> > +
> > + if (curr_offset >= offset)
> > + break;
> > +
> > + reloc_idx++;
> > + }
> > +
> > + /* Nothing found, or the first candidate lies beyond the range. */
> > + if (reloc_idx >= nr_relocs ||
> > + reloc_offset(&relocs[reloc_idx]) >= offset + len)
> > return NULL;
> >
> > + /* If there are duplicate entries, return the last. */
>
> Hm, for consistency with the others, shouldn't this be returning the
> *first* match?
Ack you're right.
It was pedantically trying to recreate what the hash did exactly but no section
has two relocations at one offset anyway, so have updated to return the first
and removed the special casing.
>
> > +/* If there are multiple matches, return the first one in the range. */
> > +struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
> > + unsigned long offset, unsigned int len)
> > {
> > - return !strncmp(sec->name, ".debug_", 7);
> > + struct section *rsec = sec->rsec;
> > +
> > + if (!rsec)
> > + return NULL;
> > +
> > + if (rsec->sorted)
> > + return find_reloc_sorted(rsec, offset, len);
> > +
> > + if (rsec->hashed)
> > + return find_reloc_hash(elf, rsec, offset, len);
> > +
> > + return find_reloc_linear(rsec, offset, len);
>
> I'm not sure there's much benefit in having two fallbacks (hashed +
> linear) instead of one. If the vast majority of reloc sections are
> sorted, then hopefully a single (linear) fallback would be fine,
> assuming no major performance regressions. That would help contain the
> complexity.
Ack, and it turns out we don't even need to fallback for growth either after all
- relocations objtool appends actually arrive in offset order anyway.
So we can indeed just get rid of the hash entirely :)
So now v3 fallbacks to linear if there's anything out of order (belts + braces
I'm not sure anything will do that now actually but good to have to be safe),
annnd no hash :)
Have tested locally and confirmed output is byte-identical for vmlinux.o for
gcc/clang allmodconfig and defconfig, also tested klp-build and that's all
working too for livepatch stuff.
>
> BTW, I found another initialization bug: klp-post-link.c uses
> elf_create_section() to create a reloc section, so it missing the
> initialization of rsec->hashed in elf_create_rela_section(). But that's
> moot if we just get rid of the hashing.
Thanks, with the hash gone that's now moot as you say :)
>
> --
> Josh
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* [PATCH v2 16/21] objtool: size the instruction hash to the text
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (14 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 15/21] objtool: cache relocations, do less work Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 17/21] objtool: decode instructions and resolve branch targets in parallel Lorenzo Stoakes (ARM)
` (5 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
The instruction hash is a fixed 2^20 buckets, which for an x86-64
allmodconfig vmlinux.o of ~16 million instructions leaves find_insn()
walking chains of four or more entries.
Size it by the amount of text to be decoded instead, at one bucket per
OFFSET_STRIDE window, as sec_offset_hash() keys on those and anything
finer would sit empty.
This gives 2^20 buckets (8 MiB) for a defconfig vmlinux.o and 2^22 (32 MiB)
for allmodconfig, so it is not an egregious use of memory.
The output of objtool before and after this change was confirmed to be
byte-for-byte identical for x86_64 defconfig and allmodconfig.
On a 128-thread machine, objtool on the gcc allmodconfig vmlinux.o goes
from 9.0s to 6.8s. A defconfig vmlinux.o already had 2^20 buckets and is
unchanged.
objtool on vmlinux.o is on the serial tail of every build that links
vmlinux, no-op builds are unchanged.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 allmodconfig, touch mm/vma.c, gcc 28.0s 25.7s -2.4s (-8%)
x86 allmodconfig, touch mm/vma.c, clang 26.2s 24.1s -2.0s (-8%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
tools/objtool/check.c | 58 +++++++++++++++++++++++++++++++--
tools/objtool/include/objtool/objtool.h | 3 +-
tools/objtool/objtool.c | 1 -
3 files changed, 58 insertions(+), 4 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 464f6c9d9ff0..62a3e1d4e9e5 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -38,12 +38,22 @@ struct disas_context *objtool_disas_ctx;
size_t sym_name_max_len;
+static struct hlist_head *insn_hash_head(struct objtool_file *file,
+ struct section *sec, unsigned long offset)
+{
+ /* Determine instruction hash based on section index and offset. */
+ const u32 sec_hash = sec_offset_hash(sec, offset);
+ const u32 hash = hash_min(sec_hash, file->insn_hash_bits);
+
+ return &file->insn_hash[hash];
+}
+
struct instruction *find_insn(struct objtool_file *file,
struct section *sec, unsigned long offset)
{
struct instruction *insn;
- hash_for_each_possible(file->insn_hash, insn, hash, sec_offset_hash(sec, offset)) {
+ hlist_for_each_entry(insn, insn_hash_head(file, sec, offset), hash) {
if (insn->sec == sec && insn->offset == offset)
return insn;
}
@@ -403,6 +413,44 @@ static void *cfi_hash_alloc(unsigned long size)
static unsigned long nr_insns;
static unsigned long nr_insns_visited;
+/*
+ * sec_offset_hash() keys on OFFSET_STRIDE windows, so the instructions of a
+ * window share a chain and buckets beyond one per window would sit empty.
+ */
+#define INSN_HASH_BYTES_PER_BUCKET OFFSET_STRIDE
+#define INSN_HASH_MIN_BITS 10
+
+static unsigned long total_text_size(struct objtool_file *file)
+{
+ unsigned long size = 0;
+ struct section *sec;
+
+ for_each_sec(file->elf, sec)
+ if (is_text_sec(sec))
+ size += sec_size(sec);
+
+ return size;
+}
+
+static int alloc_insn_hash(struct objtool_file *file, unsigned long text_size)
+{
+ const unsigned long nr_buckets = text_size / INSN_HASH_BYTES_PER_BUCKET;
+ const int bits = ilog2(nr_buckets);
+
+ file->insn_hash_bits = max(INSN_HASH_MIN_BITS, bits);
+ file->insn_hash = calloc(1UL << file->insn_hash_bits,
+ sizeof(*file->insn_hash));
+ if (!file->insn_hash) {
+ ERROR_GLIBC("calloc");
+ return -1;
+ }
+
+ if (opts.stats)
+ printf("insn_hash_bits: %d\n", file->insn_hash_bits);
+
+ return 0;
+}
+
/*
* Call the arch-specific instruction decoder for all the instructions and add
* them to the global instruction list.
@@ -414,6 +462,9 @@ static int decode_instructions(struct objtool_file *file)
unsigned long offset;
struct instruction *insn;
+ if (alloc_insn_hash(file, total_text_size(file)))
+ return -1;
+
for_each_sec(file->elf, sec) {
struct instruction *insns = NULL;
u8 prev_len = 0;
@@ -474,7 +525,7 @@ static int decode_instructions(struct objtool_file *file)
if (insn->type == INSN_BUG)
insn->dead_end = true;
- hash_add(file->insn_hash, &insn->hash, sec_offset_hash(sec, insn->offset));
+ hlist_add_head(&insn->hash, insn_hash_head(file, sec, insn->offset));
nr_insns++;
}
@@ -4802,6 +4853,9 @@ void free_insns(struct objtool_file *file)
for (chunk = chunks; chunk; chunk = chunk->next)
free(chunk->addr);
+
+ free(file->insn_hash);
+ file->insn_hash = NULL;
}
const char *objtool_disas_insn(struct instruction *insn)
diff --git a/tools/objtool/include/objtool/objtool.h b/tools/objtool/include/objtool/objtool.h
index 6dc12a59ad00..79fe82b7397e 100644
--- a/tools/objtool/include/objtool/objtool.h
+++ b/tools/objtool/include/objtool/objtool.h
@@ -21,7 +21,8 @@ struct pv_state {
struct objtool_file {
struct elf *elf;
- DECLARE_HASHTABLE(insn_hash, 20);
+ struct hlist_head *insn_hash;
+ int insn_hash_bits;
struct list_head retpoline_call_list;
struct list_head return_thunk_list;
struct list_head static_call_list;
diff --git a/tools/objtool/objtool.c b/tools/objtool/objtool.c
index a4e139dee7e9..71e048f8582a 100644
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -29,7 +29,6 @@ struct objtool_file *objtool_open_read(const char *filename)
if (!file.elf)
return NULL;
- hash_init(file.insn_hash);
INIT_LIST_HEAD(&file.retpoline_call_list);
INIT_LIST_HEAD(&file.return_thunk_list);
INIT_LIST_HEAD(&file.static_call_list);
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 17/21] objtool: decode instructions and resolve branch targets in parallel
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (15 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 16/21] objtool: size the instruction hash to the text Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 18:20 ` Kees Cook
2026-09-14 9:22 ` [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end Lorenzo Stoakes (ARM)
` (4 subsequent siblings)
21 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
During a kernel build objtool is used to decode vmlinux.o's instructions
and resolve every jump and call destination.
This forms a large part of the work objtool does during the build process,
and it is all done in serial.
Decode these in parallel at a function granularity to speed things up.
Only the instruction hash is shared between the threads and nothing is ever
removed from it, so an insertion is a compare-and-swap on the bucket head.
Threads are only created for objects with 8 MiB or more of text, meaning
that runs involving smaller objects remain unaffected.
Threading is limited to decoding and the jump pass, so the gain flattens
out at 16 threads and any further threads were found to only add overhead.
When performing an allmodconfig build, the clang invocation of objtool when
processing vmlinux.o took 5.93s on 1 thread, 4.56s on 8, 4.51s on
16 and 4.63s on 128.
Therefore cap the thread count at 16 or the number of CPUs, whichever is
fewer.
The output of objtool before and after this change was confirmed to be
byte-for-byte identical for x86_64 defconfig and allmodconfig with gcc and
clang, and for a loongarch defconfig, where objtool runs on every object.
On a 128-thread machine, objtool on the clang allmodconfig vmlinux.o goes
from 5.2s to 4.4s (6.5s to 4.4s together with the previous two patches),
and on defconfig from 1.99s to 1.38s.
objtool on vmlinux.o is on the serial tail of every build that links
vmlinux, no-op builds are unchanged.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 8.2s 7.7s -0.55s (-7%)
x86 defconfig, touch mm/vma.c, clang 7.3s 6.9s -0.44s (-6%)
x86 defconfig, clean, gcc 28.6s 28.2s -0.47s (-2%)
x86 defconfig, clean, clang 29.1s 28.7s -0.45s (-2%)
x86 allmodconfig, touch mm/vma.c, gcc 25.7s 23.7s -2.0s (-8%)
x86 allmodconfig, touch mm/vma.c, clang 24.1s 22.5s -1.6s (-7%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
tools/objtool/Makefile | 2 +-
tools/objtool/check.c | 714 ++++++++++++++++++++++++++++++++++++------------
tools/objtool/objtool.c | 14 +-
3 files changed, 543 insertions(+), 187 deletions(-)
diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index a4484fd22a96..2de50c3917ba 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -63,7 +63,7 @@ INCLUDES := -I$(srctree)/tools/include \
OBJTOOL_CFLAGS := -std=gnu11 -fomit-frame-pointer -O2 -g $(WARNINGS) \
$(INCLUDES) $(LIBELF_FLAGS) $(LIBXXHASH_CFLAGS) $(HOSTCFLAGS)
-OBJTOOL_LDFLAGS := $(LIBSUBCMD) $(LIBELF_LIBS) $(LIBXXHASH_LIBS) $(HOSTLDFLAGS)
+OBJTOOL_LDFLAGS := $(LIBSUBCMD) $(LIBELF_LIBS) $(LIBXXHASH_LIBS) -lpthread $(HOSTLDFLAGS)
# Allow old libelf to be used:
elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(HOSTCC) $(OBJTOOL_CFLAGS) -x c -E - 2>/dev/null | grep elf_getshdr)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 62a3e1d4e9e5..a7499f247818 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -7,6 +7,9 @@
#include <fnmatch.h>
#include <string.h>
#include <stdlib.h>
+#include <pthread.h>
+#include <stddef.h>
+#include <unistd.h>
#include <inttypes.h>
#include <sys/mman.h>
@@ -24,6 +27,7 @@
#include <linux/objtool_types.h>
#include <linux/hashtable.h>
#include <linux/kernel.h>
+#include <linux/sizes.h>
#include <linux/static_call_types.h>
#include <linux/string.h>
@@ -64,14 +68,13 @@ struct instruction *find_insn(struct objtool_file *file,
struct instruction *next_insn_same_sec(struct objtool_file *file,
struct instruction *insn)
{
- if (insn->idx == INSN_CHUNK_MAX)
- return find_insn(file, insn->sec, insn->offset + insn->len);
+ const unsigned long next_offset = insn->offset + insn->len;
- insn++;
- if (!insn->len)
- return NULL;
+ /* A chunk ends at its last slot or an empty one, so look the next up. */
+ if (insn->idx == INSN_CHUNK_MAX || !insn[1].len)
+ return find_insn(file, insn->sec, next_offset);
- return insn;
+ return insn + 1;
}
struct instruction *next_insn_same_func(struct objtool_file *file,
@@ -413,6 +416,12 @@ static void *cfi_hash_alloc(unsigned long size)
static unsigned long nr_insns;
static unsigned long nr_insns_visited;
+/* Only an object this large, e.g. vmlinux.o, is decoded on several threads. */
+#define DECODE_THREADED_MIN_TEXT SZ_8M
+/* Only decoding and the branch passes are threaded, so more gains nothing. */
+#define DECODE_MAX_THREADS 16
+#define DECODE_RANGES_PER_THREAD 4
+
/*
* sec_offset_hash() keys on OFFSET_STRIDE windows, so the instructions of a
* window share a chain and buckets beyond one per window would sit empty.
@@ -451,24 +460,347 @@ static int alloc_insn_hash(struct objtool_file *file, unsigned long text_size)
return 0;
}
+/* Per-thread state, only instruction hash is shared. */
+struct insn_range {
+ struct section *sec;
+ unsigned long start, end;
+ struct instruction *first, *last;
+ unsigned long nr_insns;
+ int ret;
+
+ /*
+ * Each thread writes to its own copy of an objtool file, which are
+ * combined upon completion.
+ */
+ struct objtool_file shadow;
+};
+
+#define range_for_each_insn(file, range, insn) \
+ for (insn = (range)->first; \
+ insn && insn->offset < (range)->end; \
+ insn = next_insn_same_sec(file, insn))
+
+typedef int (*range_fn_t)(struct objtool_file *file, struct insn_range *range);
+
+struct range_work {
+ range_fn_t fn;
+};
+
+static struct insn_range *decode_ranges;
+static unsigned int nr_decode_ranges, next_decode_range, nr_decode_threads;
+
+/* The kernel's try_cmpxchg(); the tools' cmpxchg() is host-arch only. */
+static bool hlist_try_cmpxchg(struct hlist_node **ptr, struct hlist_node **old,
+ struct hlist_node *new)
+{
+ struct hlist_node *seen = __sync_val_compare_and_swap(ptr, *old, new);
+
+ if (seen == *old)
+ return true;
+
+ *old = seen;
+ return false;
+}
+
+/* Nothing is ever removed, so push onto the bucket as llist_add() does. */
+static void insn_hash_add(struct objtool_file *file, struct instruction *insn)
+{
+ struct hlist_head *head = insn_hash_head(file, insn->sec, insn->offset);
+ struct hlist_node *first = READ_ONCE(head->first);
+
+ insn->hash.pprev = &head->first;
+ do {
+ insn->hash.next = first;
+ } while (!hlist_try_cmpxchg(&head->first, &first, &insn->hash));
+}
+
+/* The slot after prev in its chunk, or the first of a new chunk. */
+static struct instruction *next_insn_slot(struct instruction *prev)
+{
+ struct instruction *insn;
+
+ if (prev && prev->idx < INSN_CHUNK_MAX) {
+ insn = prev + 1;
+ insn->idx = prev->idx + 1;
+ return insn;
+ }
+
+ insn = calloc(INSN_CHUNK_SIZE, sizeof(*insn));
+ if (!insn)
+ ERROR_GLIBC("calloc");
+
+ return insn;
+}
+
+static int decode_range(struct objtool_file *file, struct insn_range *range)
+{
+ struct instruction *insn = NULL;
+ struct section *sec = range->sec;
+ unsigned long offset;
+ u8 prev_len = 0;
+
+ for (offset = range->start; offset < range->end; offset += insn->len) {
+ const unsigned long remaining = sec_size(sec) - offset;
+
+ insn = next_insn_slot(insn);
+ if (!insn)
+ return -1;
+
+ INIT_LIST_HEAD(&insn->call_node);
+ insn->sec = sec;
+ insn->offset = offset;
+ insn->prev_len = prev_len;
+
+ if (arch_decode_instruction(file, sec, offset, remaining, insn))
+ return -1;
+
+ prev_len = insn->len;
+
+ if (insn->type == INSN_BUG)
+ insn->dead_end = true;
+
+ insn_hash_add(file, insn);
+ if (!range->first)
+ range->first = insn;
+ range->nr_insns++;
+ }
+ range->last = insn;
+
+ /* The range ends at a function symbol, so decoding must land on it. */
+ if (offset != range->end) {
+ ERROR("%s: no instruction boundary at %s", sec->name,
+ offstr(sec, range->end));
+ return -1;
+ }
+
+ return 0;
+}
+
+static int run_threads(void *(*fn)(void *), void *arg, unsigned int nr_threads)
+{
+ unsigned int nr_started, i;
+ pthread_t *threads;
+ int ret = 0;
+
+ if (nr_threads <= 1) {
+ fn(arg);
+ return 0;
+ }
+
+ threads = calloc(nr_threads, sizeof(*threads));
+ if (!threads) {
+ ERROR_GLIBC("calloc");
+ return -1;
+ }
+
+ for (nr_started = 0; nr_started < nr_threads; nr_started++) {
+ if (pthread_create(&threads[nr_started], NULL, fn, arg)) {
+ ERROR_GLIBC("pthread_create");
+ ret = -1;
+ break;
+ }
+ }
+
+ for (i = 0; i < nr_started; i++)
+ pthread_join(threads[i], NULL);
+
+ free(threads);
+ return ret;
+}
+
+/* Hand out the ranges one at a time, or NULL once they are all taken. */
+static struct insn_range *claim_decode_range(void)
+{
+ const unsigned int idx = __sync_fetch_and_add(&next_decode_range, 1);
+
+ return idx < nr_decode_ranges ? &decode_ranges[idx] : NULL;
+}
+
+static void *range_worker(void *arg)
+{
+ const struct range_work *work = arg;
+ struct insn_range *range;
+
+ while ((range = claim_decode_range()))
+ range->ret = work->fn(&range->shadow, range);
+
+ return NULL;
+}
+
+/* The lists in the objtool_file that the passes add instructions to. */
+static const size_t shadow_list_offsets[] = {
+ offsetof(struct objtool_file, retpoline_call_list),
+ offsetof(struct objtool_file, return_thunk_list),
+ offsetof(struct objtool_file, static_call_list),
+ offsetof(struct objtool_file, mcount_loc_list),
+ offsetof(struct objtool_file, endbr_list),
+ offsetof(struct objtool_file, call_list),
+};
+
+static struct list_head *shadow_list(struct objtool_file *file,
+ unsigned int idx)
+{
+ return (void *)file + shadow_list_offsets[idx];
+}
+
+static void init_range_shadow(struct objtool_file *file,
+ struct insn_range *range)
+{
+ unsigned int i;
+
+ range->shadow = *file;
+ range->ret = 0;
+ for (i = 0; i < ARRAY_SIZE(shadow_list_offsets); i++)
+ INIT_LIST_HEAD(shadow_list(&range->shadow, i));
+}
+
+/* Joined in range order, which is the order a single walk would produce. */
+static int join_range_shadow(struct objtool_file *file,
+ struct insn_range *range)
+{
+ unsigned int i;
+
+ for (i = 0; i < ARRAY_SIZE(shadow_list_offsets); i++)
+ list_splice_tail(shadow_list(&range->shadow, i),
+ shadow_list(file, i));
+
+ return range->ret;
+}
+
+/* Run a pass over the instructions, one range per thread at a time. */
+static int run_insn_ranges(struct objtool_file *file, range_fn_t fn)
+{
+ struct range_work work = { .fn = fn };
+ unsigned int i;
+ int ret = 0;
+
+ for (i = 0; i < nr_decode_ranges; i++)
+ init_range_shadow(file, &decode_ranges[i]);
+ next_decode_range = 0;
+
+ if (run_threads(range_worker, &work, nr_decode_threads))
+ return -1;
+
+ for (i = 0; i < nr_decode_ranges; i++) {
+ if (join_range_shadow(file, &decode_ranges[i]))
+ ret = -1;
+ }
+
+ return ret;
+}
+
+static int add_decode_range(struct section *sec, unsigned long start,
+ unsigned long end)
+{
+ const size_t size = (nr_decode_ranges + 1) * sizeof(*decode_ranges);
+ struct insn_range *range;
+
+ decode_ranges = realloc(decode_ranges, size);
+ if (!decode_ranges) {
+ ERROR_GLIBC("realloc");
+ return -1;
+ }
+
+ range = &decode_ranges[nr_decode_ranges++];
+ memset(range, 0, sizeof(*range));
+ range->sec = sec;
+ range->start = start;
+ range->end = end;
+
+ return 0;
+}
+
+/* Split a section into ranges of roughly range_size, at function starts. */
+static int add_decode_ranges(struct section *sec, unsigned long range_size)
+{
+ const unsigned long size = sec_size(sec);
+ unsigned long start = 0;
+ struct symbol *sym;
+
+ if (!range_size)
+ return add_decode_range(sec, 0, size);
+
+ sec_for_each_sym(sec, sym) {
+ if (!is_func_sym(sym) || sym->offset <= start ||
+ sym->offset >= size)
+ continue;
+ if (sym->offset - start < range_size)
+ continue;
+
+ if (add_decode_range(sec, start, sym->offset))
+ return -1;
+ start = sym->offset;
+ }
+
+ return add_decode_range(sec, start, size);
+}
+
+static void free_decode_ranges(void)
+{
+ free(decode_ranges);
+ decode_ranges = NULL;
+ nr_decode_ranges = 0;
+ next_decode_range = 0;
+}
+
+/* A range's first instruction follows the last of the range before it. */
+static void link_decode_ranges(void)
+{
+ unsigned int i;
+
+ for (i = 1; i < nr_decode_ranges; i++) {
+ const struct insn_range *prev = &decode_ranges[i - 1];
+ struct insn_range *range = &decode_ranges[i];
+
+ if (prev->sec != range->sec || !prev->last || !range->first)
+ continue;
+
+ range->first->prev_len = prev->last->len;
+ }
+}
+
+static unsigned int decode_threads(unsigned long text_size)
+{
+ const long nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
+
+ if (text_size < DECODE_THREADED_MIN_TEXT || nr_cpus < 2)
+ return 1;
+
+ return min_t(unsigned int, nr_cpus, DECODE_MAX_THREADS);
+}
+
+/* Several ranges per thread so uneven ones balance out; 0 means per section. */
+static unsigned long decode_range_size(unsigned long text_size,
+ unsigned int nr_threads)
+{
+ const unsigned int nr_ranges = nr_threads * DECODE_RANGES_PER_THREAD;
+
+ if (nr_threads <= 1)
+ return 0;
+
+ return text_size / nr_ranges;
+}
+
/*
* Call the arch-specific instruction decoder for all the instructions and add
* them to the global instruction list.
*/
static int decode_instructions(struct objtool_file *file)
{
+ const unsigned long text_size = total_text_size(file);
+ unsigned long range_size;
+ struct instruction *insn;
struct section *sec;
struct symbol *func;
- unsigned long offset;
- struct instruction *insn;
+ unsigned int i;
- if (alloc_insn_hash(file, total_text_size(file)))
+ if (alloc_insn_hash(file, text_size))
return -1;
+ nr_decode_threads = decode_threads(text_size);
+ range_size = decode_range_size(text_size, nr_decode_threads);
+
for_each_sec(file->elf, sec) {
- struct instruction *insns = NULL;
- u8 prev_len = 0;
- u8 idx = 0;
if (!is_text_sec(sec))
continue;
@@ -493,41 +825,20 @@ static int decode_instructions(struct objtool_file *file)
if (!strcmp(sec->name, ".init.text") && !opts.module)
sec->init = true;
- for (offset = 0; offset < sec_size(sec); offset += insn->len) {
- if (!insns || idx == INSN_CHUNK_MAX) {
- insns = calloc(INSN_CHUNK_SIZE, sizeof(*insn));
- if (!insns) {
- ERROR_GLIBC("calloc");
- return -1;
- }
- idx = 0;
- } else {
- idx++;
- }
- insn = &insns[idx];
- insn->idx = idx;
-
- INIT_LIST_HEAD(&insn->call_node);
- insn->sec = sec;
- insn->offset = offset;
- insn->prev_len = prev_len;
+ if (add_decode_ranges(sec, range_size))
+ return -1;
+ }
- if (arch_decode_instruction(file, sec, offset, sec_size(sec) - offset, insn))
- return -1;
+ if (run_insn_ranges(file, decode_range))
+ return -1;
- prev_len = insn->len;
+ for (i = 0; i < nr_decode_ranges; i++)
+ nr_insns += decode_ranges[i].nr_insns;
+ link_decode_ranges();
- /*
- * By default, "ud2" is a dead end unless otherwise
- * annotated, because GCC 7 inserts it for certain
- * divide-by-zero cases.
- */
- if (insn->type == INSN_BUG)
- insn->dead_end = true;
-
- hlist_add_head(&insn->hash, insn_hash_head(file, sec, insn->offset));
- nr_insns++;
- }
+ for_each_sec(file->elf, sec) {
+ if (!is_text_sec(sec))
+ continue;
sec_for_each_sym(sec, func) {
if (!is_notype_sym(func) && !is_func_sym(func))
@@ -1570,133 +1881,147 @@ static bool is_first_func_insn(struct objtool_file *file,
/*
* Find the destination instructions for all jumps.
*/
-static int add_jump_destinations(struct objtool_file *file)
+static int add_jump_destination(struct objtool_file *file, struct instruction *insn)
{
- struct instruction *insn;
struct reloc *reloc;
+ struct symbol *func = insn_func(insn);
+ struct instruction *dest_insn;
+ struct section *dest_sec;
+ struct symbol *dest_sym;
+ unsigned long dest_off;
- for_each_insn(file, insn) {
- struct symbol *func = insn_func(insn);
- struct instruction *dest_insn;
- struct section *dest_sec;
- struct symbol *dest_sym;
- unsigned long dest_off;
+ if (!is_static_jump(insn))
+ return 0;
- if (!is_static_jump(insn))
- continue;
+ if (insn->jump_dest) {
+ /*
+ * handle_group_alt() may have previously set
+ * 'jump_dest' for some alternatives.
+ */
+ return 0;
+ }
- if (insn->jump_dest) {
- /*
- * handle_group_alt() may have previously set
- * 'jump_dest' for some alternatives.
- */
- continue;
- }
+ reloc = insn_reloc(file, insn);
+ if (!reloc) {
+ dest_sec = insn->sec;
+ dest_off = arch_jump_destination(insn);
+ dest_sym = dest_sec->sym;
+ } else {
+ dest_sym = reloc->sym;
+ if (is_undef_sym(dest_sym)) {
+ if (dest_sym->retpoline_thunk) {
+ if (add_retpoline_call(file, insn))
+ return -1;
+ return 0;
+ }
- reloc = insn_reloc(file, insn);
- if (!reloc) {
- dest_sec = insn->sec;
- dest_off = arch_jump_destination(insn);
- dest_sym = dest_sec->sym;
- } else {
- dest_sym = reloc->sym;
- if (is_undef_sym(dest_sym)) {
- if (dest_sym->retpoline_thunk) {
- if (add_retpoline_call(file, insn))
- return -1;
- continue;
- }
+ if (dest_sym->return_thunk) {
+ add_return_call(file, insn, true);
+ return 0;
+ }
- if (dest_sym->return_thunk) {
- add_return_call(file, insn, true);
- continue;
- }
+ /* External symbol */
+ if (func) {
+ /* External sibling call */
+ if (add_call_dest(file, insn, dest_sym, true))
+ return -1;
+ return 0;
+ }
- /* External symbol */
- if (func) {
- /* External sibling call */
- if (add_call_dest(file, insn, dest_sym, true))
- return -1;
- continue;
- }
+ /* Non-func asm code jumping to external symbol */
+ return 0;
+ }
- /* Non-func asm code jumping to external symbol */
- continue;
- }
+ dest_sec = dest_sym->sec;
+ dest_off = dest_sym->offset + arch_insn_adjusted_addend(insn, reloc);
+ }
- dest_sec = dest_sym->sec;
- dest_off = dest_sym->offset + arch_insn_adjusted_addend(insn, reloc);
+ dest_insn = find_insn(file, dest_sec, dest_off);
+ if (!dest_insn) {
+ struct symbol *sym = find_symbol_by_offset(dest_sec, dest_off);
+
+ /*
+ * retbleed_untrain_ret() jumps to
+ * __x86_return_thunk(), but objtool can't find
+ * the thunk's starting RET instruction,
+ * because the RET is also in the middle of
+ * another instruction. Objtool only knows
+ * about the outer instruction.
+ */
+ if (sym && sym->embedded_insn) {
+ add_return_call(file, insn, false);
+ return 0;
}
- dest_insn = find_insn(file, dest_sec, dest_off);
- if (!dest_insn) {
- struct symbol *sym = find_symbol_by_offset(dest_sec, dest_off);
+ /*
+ * GCOV/KCOV dead code can jump to the end of
+ * the function/section.
+ */
+ if (file->ignore_unreachables && func &&
+ dest_sec == insn->sec &&
+ dest_off == func->offset + func->len)
+ return 0;
- /*
- * retbleed_untrain_ret() jumps to
- * __x86_return_thunk(), but objtool can't find
- * the thunk's starting RET instruction,
- * because the RET is also in the middle of
- * another instruction. Objtool only knows
- * about the outer instruction.
- */
- if (sym && sym->embedded_insn) {
- add_return_call(file, insn, false);
- continue;
- }
+ ERROR_INSN(insn, "can't find jump dest instruction at %s",
+ offstr(dest_sec, dest_off));
+ return -1;
+ }
- /*
- * GCOV/KCOV dead code can jump to the end of
- * the function/section.
- */
- if (file->ignore_unreachables && func &&
- dest_sec == insn->sec &&
- dest_off == func->offset + func->len)
- continue;
+ if (!dest_sym || is_sec_sym(dest_sym)) {
+ dest_sym = insn_sym(dest_insn);
+ if (!dest_sym)
+ goto set_jump_dest;
+ }
- ERROR_INSN(insn, "can't find jump dest instruction at %s",
- offstr(dest_sec, dest_off));
+ if (dest_sym->retpoline_thunk && dest_insn->offset == dest_sym->offset) {
+ if (add_retpoline_call(file, insn))
return -1;
- }
+ return 0;
+ }
- if (!dest_sym || is_sec_sym(dest_sym)) {
- dest_sym = insn_sym(dest_insn);
- if (!dest_sym)
- goto set_jump_dest;
- }
+ if (dest_sym->return_thunk && dest_insn->offset == dest_sym->offset) {
+ add_return_call(file, insn, true);
+ return 0;
+ }
- if (dest_sym->retpoline_thunk && dest_insn->offset == dest_sym->offset) {
- if (add_retpoline_call(file, insn))
- return -1;
- continue;
- }
+ if (!insn_sym(insn) || insn_sym(insn)->pfunc == dest_sym->pfunc)
+ goto set_jump_dest;
- if (dest_sym->return_thunk && dest_insn->offset == dest_sym->offset) {
- add_return_call(file, insn, true);
- continue;
- }
+ /*
+ * Internal cross-function jump.
+ */
- if (!insn_sym(insn) || insn_sym(insn)->pfunc == dest_sym->pfunc)
- goto set_jump_dest;
+ if (is_first_func_insn(file, dest_insn)) {
+ /* Internal sibling call */
+ if (add_call_dest(file, insn, dest_sym, true))
+ return -1;
+ return 0;
+ }
- /*
- * Internal cross-function jump.
- */
+set_jump_dest:
+ insn->jump_dest = dest_insn;
- if (is_first_func_insn(file, dest_insn)) {
- /* Internal sibling call */
- if (add_call_dest(file, insn, dest_sym, true))
- return -1;
- continue;
- }
+ return 0;
+}
-set_jump_dest:
- insn->jump_dest = dest_insn;
+static int add_jump_destinations_range(struct objtool_file *file,
+ struct insn_range *range)
+{
+ struct instruction *insn;
+
+ range_for_each_insn(file, range, insn) {
+ if (add_jump_destination(file, insn))
+ return -1;
}
return 0;
}
+static int add_jump_destinations(struct objtool_file *file)
+{
+ return run_insn_ranges(file, add_jump_destinations_range);
+}
+
static struct symbol *find_call_destination(struct section *sec, unsigned long offset)
{
struct symbol *call_dest;
@@ -1711,59 +2036,82 @@ static struct symbol *find_call_destination(struct section *sec, unsigned long o
/*
* Find the destination instructions for all calls.
*/
-static int add_call_destinations(struct objtool_file *file)
+static int add_call_destination(struct objtool_file *file, struct instruction *insn)
{
- struct instruction *insn;
unsigned long dest_off;
struct symbol *dest;
struct reloc *reloc;
+ struct symbol *func = insn_func(insn);
- for_each_insn(file, insn) {
- struct symbol *func = insn_func(insn);
- if (insn->type != INSN_CALL)
- continue;
+ if (insn->type != INSN_CALL)
+ return 0;
- reloc = insn_reloc(file, insn);
- if (!reloc) {
- dest_off = arch_jump_destination(insn);
- dest = find_call_destination(insn->sec, dest_off);
+ reloc = insn_reloc(file, insn);
+ if (!reloc) {
+ dest_off = arch_jump_destination(insn);
+ dest = find_call_destination(insn->sec, dest_off);
- if (add_call_dest(file, insn, dest, false))
- return -1;
+ if (add_call_dest(file, insn, dest, false))
+ return -1;
- if (func && func->ignore)
- continue;
+ if (func && func->ignore)
+ return 0;
- if (!insn_call_dest(insn)) {
- ERROR_INSN(insn, "unannotated intra-function call");
- return -1;
- }
+ if (!insn_call_dest(insn)) {
+ ERROR_INSN(insn, "unannotated intra-function call");
+ return -1;
+ }
- if (func && !is_func_sym(insn_call_dest(insn))) {
- ERROR_INSN(insn, "unsupported call to non-function");
- return -1;
- }
+ if (func && !is_func_sym(insn_call_dest(insn))) {
+ ERROR_INSN(insn, "unsupported call to non-function");
+ return -1;
+ }
- } else if (is_sec_sym(reloc->sym)) {
- dest_off = arch_insn_adjusted_addend(insn, reloc);
- dest = find_call_destination(reloc->sym->sec, dest_off);
- if (!dest) {
- ERROR_INSN(insn, "can't find call dest symbol at %s+0x%lx",
- reloc->sym->sec->name, dest_off);
- return -1;
- }
+ } else if (is_sec_sym(reloc->sym)) {
+ dest_off = arch_insn_adjusted_addend(insn, reloc);
+ dest = find_call_destination(reloc->sym->sec, dest_off);
+ if (!dest) {
+ ERROR_INSN(insn, "can't find call dest symbol at %s+0x%lx",
+ reloc->sym->sec->name, dest_off);
+ return -1;
+ }
- if (add_call_dest(file, insn, dest, false))
- return -1;
+ if (add_call_dest(file, insn, dest, false))
+ return -1;
- } else if (reloc->sym->retpoline_thunk) {
- if (add_retpoline_call(file, insn))
- return -1;
+ } else if (reloc->sym->retpoline_thunk) {
+ if (add_retpoline_call(file, insn))
+ return -1;
- } else {
- if (add_call_dest(file, insn, reloc->sym, false))
- return -1;
- }
+ } else {
+ if (add_call_dest(file, insn, reloc->sym, false))
+ return -1;
+ }
+
+ return 0;
+}
+
+static int add_call_destinations_range(struct objtool_file *file,
+ struct insn_range *range)
+{
+ struct instruction *insn;
+
+ range_for_each_insn(file, range, insn) {
+ if (add_call_destination(file, insn))
+ return -1;
+ }
+
+ return 0;
+}
+
+/* Serial: annotating a call site rewrites instructions the dead end walks read. */
+static int add_call_destinations(struct objtool_file *file)
+{
+ unsigned int i;
+
+ for (i = 0; i < nr_decode_ranges; i++) {
+ if (add_call_destinations_range(file, &decode_ranges[i]))
+ return -1;
}
return 0;
@@ -2732,6 +3080,8 @@ int decode_file(struct objtool_file *file)
if (read_annotate(file, __annotate_late))
return -1;
+ free_decode_ranges();
+
return 0;
}
diff --git a/tools/objtool/objtool.c b/tools/objtool/objtool.c
index 71e048f8582a..f472dfe7a773 100644
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -8,6 +8,7 @@
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
+#include <pthread.h>
#include <subcmd/exec-cmd.h>
#include <subcmd/pager.h>
#include <linux/kernel.h>
@@ -41,6 +42,8 @@ struct objtool_file *objtool_open_read(const char *filename)
return &file;
}
+static pthread_mutex_t pv_ops_lock = PTHREAD_MUTEX_INITIALIZER;
+
int objtool_pv_add(struct objtool_file *f, int idx, struct symbol *func)
{
if (!opts.noinstr)
@@ -59,12 +62,15 @@ int objtool_pv_add(struct objtool_file *f, int idx, struct symbol *func)
!strcmp(func->name, "_paravirt_ident_64"))
return 0;
+ pthread_mutex_lock(&pv_ops_lock);
+
/* already added this function */
- if (!list_empty(&func->pv_target))
- return 0;
+ if (list_empty(&func->pv_target)) {
+ list_add(&func->pv_target, &f->pv_ops[idx].targets);
+ f->pv_ops[idx].clean = false;
+ }
- list_add(&func->pv_target, &f->pv_ops[idx].targets);
- f->pv_ops[idx].clean = false;
+ pthread_mutex_unlock(&pv_ops_lock);
return 0;
}
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 17/21] objtool: decode instructions and resolve branch targets in parallel
2026-09-14 9:22 ` [PATCH v2 17/21] objtool: decode instructions and resolve branch targets in parallel Lorenzo Stoakes (ARM)
@ 2026-09-14 18:20 ` Kees Cook
2026-09-15 10:09 ` Lorenzo Stoakes (ARM)
0 siblings, 1 reply; 58+ messages in thread
From: Kees Cook @ 2026-09-14 18:20 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 10:22:16AM +0100, Lorenzo Stoakes (ARM) wrote:
> Threads are only created for objects with 8 MiB or more of text, meaning
> that runs involving smaller objects remain unaffected.
> [...]
> objtool on vmlinux.o is on the serial tail of every build that links
> vmlinux, no-op builds are unchanged.
This isn't limited to vmlinux.o, though? With CONFIG_X86_KERNEL_IBT
(default y on x86_64), delay-objtool is set in scripts/Makefile.lib, and
objtool then runs on every multi-object module, in the middle of the
parallel part of the build. In an x86_64 allmodconfig build here,
amdgpu.o has 46.2 MiB of executable text and i915.o has 10.2 MiB, so
each of those objtool runs gets 16 threads on top of the -jN jobs that
are already running.
Any parallelism added need to be handled by the make jobserver, not
hard-coded anyway.
> [...]
> +/* Only an object this large, e.g. vmlinux.o, is decoded on several threads. */
> +#define DECODE_THREADED_MIN_TEXT SZ_8M
> +/* Only decoding and the branch passes are threaded, so more gains nothing. */
> +#define DECODE_MAX_THREADS 16
> +#define DECODE_RANGES_PER_THREAD 4
I just don't think a size-based approach is going to work. And any max
parallelism needs a rationale.
> +static unsigned int decode_threads(unsigned long text_size)
> +{
> + const long nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
> +
> + if (text_size < DECODE_THREADED_MIN_TEXT || nr_cpus < 2)
> + return 1;
> +
> + return min_t(unsigned int, nr_cpus, DECODE_MAX_THREADS);
> +}
No, anything using _SC_NPROCESSORS_ONLN internally is wrong, whether its
pigz or objtool.
> [...]
> +static int add_jump_destinations(struct objtool_file *file)
> +{
> + return run_insn_ranges(file, add_jump_destinations_range);
> +}
I haven't examined this myself yet, but my LLM doesn't like this,
saying:
For an internal sibling call, add_jump_destination() calls
add_call_dest(file, insn, dest_sym, true), and add_call_dest() calls
annotate_call_site(), which for --hack-noinstr profiling calls, and for
__fentry__ calls with --mcount --mnop, does set_reloc_type() and
elf_write_insn() on file->elf. The per-range shadow gives each thread
its own lists, but the struct elf is shared, and both helpers write to
the section and mark it changed without any locking.
add_call_destinations() is kept serial because "annotating a call site
rewrites instructions the dead end walks read", so it looks like this
path needs the same care: a lock, or deferring those writes until the
threads have been joined. This is from reading the code; I haven't hit
a failure. Was the thread sanitizer run mentioned in the cover letter
done with those objtool options enabled?
So, take it with a grain of salt. ;)
-Kees
--
Kees Cook
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 17/21] objtool: decode instructions and resolve branch targets in parallel
2026-09-14 18:20 ` Kees Cook
@ 2026-09-15 10:09 ` Lorenzo Stoakes (ARM)
2026-09-15 11:29 ` David Laight
0 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 10:09 UTC (permalink / raw)
To: Kees Cook
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 11:20:37AM -0700, Kees Cook wrote:
> On Mon, Sep 14, 2026 at 10:22:16AM +0100, Lorenzo Stoakes (ARM) wrote:
> > Threads are only created for objects with 8 MiB or more of text, meaning
> > that runs involving smaller objects remain unaffected.
> > [...]
> > objtool on vmlinux.o is on the serial tail of every build that links
> > vmlinux, no-op builds are unchanged.
>
> This isn't limited to vmlinux.o, though? With CONFIG_X86_KERNEL_IBT
> (default y on x86_64), delay-objtool is set in scripts/Makefile.lib, and
> objtool then runs on every multi-object module, in the middle of the
> parallel part of the build. In an x86_64 allmodconfig build here,
> amdgpu.o has 46.2 MiB of executable text and i915.o has 10.2 MiB, so
> each of those objtool runs gets 16 threads on top of the -jN jobs that
> are already running.
Ack, will fix in v3 to limit to only the --link run without --module, which
is how vmlinux.o is processed, leaves modules as they are.
>
> Any parallelism added need to be handled by the make jobserver, not
> hard-coded anyway.
I'm not sure that really gains us anything - at the point of doing the
vmlinux.o processing (which with the above change is all that is being done
now) everything's idle so the jobserver would just hand over the same 16
threads.
It'd need quite a bit of work to interact with it too with added complexity
+ some overhead so would have to check impact on perf here.
You did complain about added complexity also ;) if you insist I can try.
>
> > [...]
> > +/* Only an object this large, e.g. vmlinux.o, is decoded on several threads. */
> > +#define DECODE_THREADED_MIN_TEXT SZ_8M
> > +/* Only decoding and the branch passes are threaded, so more gains nothing. */
> > +#define DECODE_MAX_THREADS 16
> > +#define DECODE_RANGES_PER_THREAD 4
>
> I just don't think a size-based approach is going to work. And any max
> parallelism needs a rationale.
A rationale was provided:
Threading is limited to decoding and the jump pass, so the gain
flattens out at 16 threads and any further threads were found to
only add overhead.
When performing an allmodconfig build, the clang invocation of
objtool when processing vmlinux.o took 5.93s on 1 thread, 4.56s on
8, 4.51s on 16 and 4.63s on 128.
Let me know what you feel was missing there? These things inevitably have
to be somewhat heuristic.
The size threshold is about paying for too many threads for no real gain,
and now (for v3) the code is limited to a --link operation only, that'll
only really stop a tinyconfig vmlinux.o :)
>
> > +static unsigned int decode_threads(unsigned long text_size)
> > +{
> > + const long nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
> > +
> > + if (text_size < DECODE_THREADED_MIN_TEXT || nr_cpus < 2)
> > + return 1;
> > +
> > + return min_t(unsigned int, nr_cpus, DECODE_MAX_THREADS);
> > +}
>
> No, anything using _SC_NPROCESSORS_ONLN internally is wrong, whether its
> pigz or objtool.
Why? We shouldn't cap a 4 CPU box to 4 CPUs?
The idea is that the empirically obtained 16 core limit should naturally be
capped to the number of CPUs.
I guess in a world where make hands jobs off this could be dropped, though,
if the complexity there seems worthwhile.
>
> > [...]
> > +static int add_jump_destinations(struct objtool_file *file)
> > +{
> > + return run_insn_ranges(file, add_jump_destinations_range);
> > +}
>
> I haven't examined this myself yet, but my LLM doesn't like this,
> saying:
>
> For an internal sibling call, add_jump_destination() calls
> add_call_dest(file, insn, dest_sym, true), and add_call_dest() calls
> annotate_call_site(), which for --hack-noinstr profiling calls, and for
> __fentry__ calls with --mcount --mnop, does set_reloc_type() and
> elf_write_insn() on file->elf. The per-range shadow gives each thread
> its own lists, but the struct elf is shared, and both helpers write to
> the section and mark it changed without any locking.
> add_call_destinations() is kept serial because "annotating a call site
> rewrites instructions the dead end walks read", so it looks like this
> path needs the same care: a lock, or deferring those writes until the
> threads have been joined. This is from reading the code; I haven't hit
> a failure. Was the thread sanitizer run mentioned in the cover letter
> done with those objtool options enabled?
>
> So, take it with a grain of salt. ;)
I mean sashiko is hallucinating at a rate >50% on this series, so pinches
of salt all round :) I do think frontier models with a good amount of
checking + e.g. Chris Mason's review-prompts are helpful to rein in stuff.
Anyway I had mine check it ;) and I also have a beefy threadripper sitting
around for bounding reality on this stuff and it all came back clean:
Those writes go to the thread's own instruction bytes and its own
relocation, the only shared state touched is the section and elf
"changed" flags, which every writer sets to true, and the mcount
case for a sibling call is a warning path. The v2 sanitizer run
used the gcc allmodconfig options, which lack
--mcount/--mnop/--cfi/--fineibt, so I reran it on the clang
allmodconfig vmlinux.o with its full option set: zero reports, the
jump pass included.
>
> -Kees
>
> --
> Kees Cook
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 17/21] objtool: decode instructions and resolve branch targets in parallel
2026-09-15 10:09 ` Lorenzo Stoakes (ARM)
@ 2026-09-15 11:29 ` David Laight
0 siblings, 0 replies; 58+ messages in thread
From: David Laight @ 2026-09-15 11:29 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Kees Cook, Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Tue, 15 Sep 2026 11:09:25 +0100
"Lorenzo Stoakes (ARM)" <ljs@kernel.org> wrote:
> > > +static unsigned int decode_threads(unsigned long text_size)
> > > +{
> > > + const long nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
> > > +
> > > + if (text_size < DECODE_THREADED_MIN_TEXT || nr_cpus < 2)
> > > + return 1;
The text_size check ought to be before the sysconf() call.
> > > +
> > > + return min_t(unsigned int, nr_cpus, DECODE_MAX_THREADS);
Why min_t() - you might as well make nr_cpus 'unsigned int'.
> > > +}
> >
> > No, anything using _SC_NPROCESSORS_ONLN internally is wrong, whether its
> > pigz or objtool.
>
> Why? We shouldn't cap a 4 CPU box to 4 CPUs?
You almost certainly don't want to use more...
(Unless they end up waiting for disk)
>
> The idea is that the empirically obtained 16 core limit should naturally be
> capped to the number of CPUs.
The 'empirical' limit is very likely to be system dependant.
There might also be situations where you don't want the build to run as fast
as possible because the system is performing other workloads.
(Not to mention if you have had to add tracing to find a bug.)
>
> I guess in a world where make hands jobs off this could be dropped, though,
> if the complexity there seems worthwhile.
You need to pull tokens out of the make pipe :-)
David
^ permalink raw reply [flat|nested] 58+ messages in thread
* [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (16 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 17/21] objtool: decode instructions and resolve branch targets in parallel Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 18:32 ` Kees Cook
2026-09-15 6:32 ` Miguel Ojeda
2026-09-14 9:22 ` [PATCH v2 19/21] rust: make exports.o depend on the headers generated for it Lorenzo Stoakes (ARM)
` (3 subsequent siblings)
21 siblings, 2 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
Rust crates are compiled in a serial chain on the critical path - core,
bindings, kernel crates and then the drivers - each a rustc invocation.
With CONFIG_RUST set and every rust driver enabled, the entire chain takes
around 25 seconds on a 128-thread machine, with the associated C code
taking 24 seconds.
Each time a change is made to any of the bindings, it triggers a rebuild.
rustc has a parallel front end, enabled with -Zthreads, available since
rust 1.84 [0] and therefore on every rustc the kernel supports.
It is not yet stable and its output is not reproducible, so it cannot be
used by default - stabilisation is being worked on [1].
Add optional build parameter KBUILD_RUST_THREADS, which when set passes
that many threads to rustc.
The threads are taken from make's jobserver, so a parallel build is not
oversubscribed. It was found that benefits level off at 8 threads (16 was
found to be around the same, and 32 slower).
Generated output was confirmed byte-for-byte identical.
Observed build time changes with KBUILD_RUST_THREADS=8 (rustc 1.98, clang):
before after
core.o 7.7s 4.9s
bindings.o 4.3s 3.1s
kernel.o 2.0s 1.4s
clean build 39.3s 34.6s
touch rust/kernel/lib.rs 12.9s 12.1s
touch rust/bindings/bindings_helper.h 19.5s 17.5s
Whole build, 128-thread Threadripper 9980X, KBUILD_RUST_THREADS=8, best of
N runs:
before after delta
-------------------------------
x86 defconfig+RUST, clean 41.0s 36.4s -4.6s (-11%)
x86 defconfig+RUST, touch lib.rs 8.3s 7.7s -0.56s (-7%)
Link: https://github.com/rust-lang/rust/pull/132282 [0]
Link: https://github.com/rust-lang/compiler-team/issues/1005 [1]
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
Documentation/kbuild/kbuild.rst | 7 +++++++
Makefile | 4 ++++
2 files changed, 11 insertions(+)
diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
index 5a9013bacfb7..9b2b127676c3 100644
--- a/Documentation/kbuild/kbuild.rst
+++ b/Documentation/kbuild/kbuild.rst
@@ -134,6 +134,13 @@ See make help for the full list.
Setting "V=..." takes precedence over KBUILD_VERBOSE.
+KBUILD_RUST_THREADS
+-------------------
+The number of threads rustc's parallel front end may use, passed to it as
+``-Zthreads``. Unset by default, as the parallel front end is not yet
+stable and its output is not reproducible. The gain levels off at 8
+threads.
+
KBUILD_EXTMOD
-------------
Set the directory to look for the kernel source when building external
diff --git a/Makefile b/Makefile
index 8263fc8a86b3..4ef504c1ace2 100644
--- a/Makefile
+++ b/Makefile
@@ -1206,6 +1206,10 @@ KBUILD_RUSTFLAGS += --remap-path-prefix=$(srcroot)/= --remap-path-scope=macro
endif
endif
+ifneq ($(KBUILD_RUST_THREADS),)
+KBUILD_RUSTFLAGS += -Zthreads=$(KBUILD_RUST_THREADS)
+endif
+
# include additional Makefiles when needed
include-y := scripts/Makefile.warn
include-$(CONFIG_DEBUG_INFO) += scripts/Makefile.debug
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end
2026-09-14 9:22 ` [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end Lorenzo Stoakes (ARM)
@ 2026-09-14 18:32 ` Kees Cook
2026-09-15 11:09 ` Lorenzo Stoakes (ARM)
2026-09-15 6:32 ` Miguel Ojeda
1 sibling, 1 reply; 58+ messages in thread
From: Kees Cook @ 2026-09-14 18:32 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 10:22:17AM +0100, Lorenzo Stoakes (ARM) wrote:
> The threads are taken from make's jobserver, so a parallel build is not
> oversubscribed. It was found that benefits level off at 8 threads (16 was
> found to be around the same, and 32 slower).
I think it's worth noting that this comes from rustc itself (it has
built-in support for the make jobserver). See commit ecab4115c44c
("kbuild: mark `rustc` (and others) invocations as recursive").
What happens when there is no jobserver, e.g. "make" without -j, or
"make -j1"?
> [...]
> rustc has a parallel front end, enabled with -Zthreads, available since
> rust 1.84 [0] and therefore on every rustc the kernel supports.
>
> It is not yet stable and its output is not reproducible, so it cannot be
> [...]
> +The number of threads rustc's parallel front end may use, passed to it as
> +``-Zthreads``. Unset by default, as the parallel front end is not yet
> +stable and its output is not reproducible. The gain levels off at 8
> +threads.
Okay, unstable, not reproducible.
> Generated output was confirmed byte-for-byte identical.
But this says otherwise? I am confused. Reproducible or not?
--
Kees Cook
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end
2026-09-14 18:32 ` Kees Cook
@ 2026-09-15 11:09 ` Lorenzo Stoakes (ARM)
2026-09-15 11:16 ` Lorenzo Stoakes (ARM)
0 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 11:09 UTC (permalink / raw)
To: Kees Cook
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 11:32:14AM -0700, Kees Cook wrote:
> On Mon, Sep 14, 2026 at 10:22:17AM +0100, Lorenzo Stoakes (ARM) wrote:
> > The threads are taken from make's jobserver, so a parallel build is not
> > oversubscribed. It was found that benefits level off at 8 threads (16 was
> > found to be around the same, and 32 slower).
>
> I think it's worth noting that this comes from rustc itself (it has
> built-in support for the make jobserver). See commit ecab4115c44c
> ("kbuild: mark `rustc` (and others) invocations as recursive").
>
> What happens when there is no jobserver, e.g. "make" without -j, or
> "make -j1"?
>
> > [...]
> > rustc has a parallel front end, enabled with -Zthreads, available since
> > rust 1.84 [0] and therefore on every rustc the kernel supports.
> >
> > It is not yet stable and its output is not reproducible, so it cannot be
> > [...]
> > +The number of threads rustc's parallel front end may use, passed to it as
> > +``-Zthreads``. Unset by default, as the parallel front end is not yet
> > +stable and its output is not reproducible. The gain levels off at 8
> > +threads.
>
> Okay, unstable, not reproducible.
>
> > Generated output was confirmed byte-for-byte identical.
>
> But this says otherwise? I am confused. Reproducible or not?
Well, we can set all of this aside as, based on Miguel's feedback, I think
dropping this commit is best :)
>
> --
> Kees Cook
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end
2026-09-15 11:09 ` Lorenzo Stoakes (ARM)
@ 2026-09-15 11:16 ` Lorenzo Stoakes (ARM)
0 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 11:16 UTC (permalink / raw)
To: Kees Cook
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Tue, Sep 15, 2026 at 12:09:04PM +0100, Lorenzo Stoakes (ARM) wrote:
> On Mon, Sep 14, 2026 at 11:32:14AM -0700, Kees Cook wrote:
> > On Mon, Sep 14, 2026 at 10:22:17AM +0100, Lorenzo Stoakes (ARM) wrote:
> > > The threads are taken from make's jobserver, so a parallel build is not
> > > oversubscribed. It was found that benefits level off at 8 threads (16 was
> > > found to be around the same, and 32 slower).
> >
> > I think it's worth noting that this comes from rustc itself (it has
> > built-in support for the make jobserver). See commit ecab4115c44c
> > ("kbuild: mark `rustc` (and others) invocations as recursive").
> >
> > What happens when there is no jobserver, e.g. "make" without -j, or
> > "make -j1"?
> >
> > > [...]
> > > rustc has a parallel front end, enabled with -Zthreads, available since
> > > rust 1.84 [0] and therefore on every rustc the kernel supports.
> > >
> > > It is not yet stable and its output is not reproducible, so it cannot be
> > > [...]
> > > +The number of threads rustc's parallel front end may use, passed to it as
> > > +``-Zthreads``. Unset by default, as the parallel front end is not yet
> > > +stable and its output is not reproducible. The gain levels off at 8
> > > +threads.
> >
> > Okay, unstable, not reproducible.
> >
> > > Generated output was confirmed byte-for-byte identical.
> >
> > But this says otherwise? I am confused. Reproducible or not?
On this though - the lack of reproducibility was the reports in the rust world
of the -Zthreads flag sometimes resulting in that.
I never observed that locally at all, and so locally it was all byte-for-byte
identical.
It could have been worded better :)
>
> Well, we can set all of this aside as, based on Miguel's feedback, I think
> dropping this commit is best :)
>
> >
> > --
> > Kees Cook
>
> --
> Cheers, Lorenzo
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* Re: [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end
2026-09-14 9:22 ` [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end Lorenzo Stoakes (ARM)
2026-09-14 18:32 ` Kees Cook
@ 2026-09-15 6:32 ` Miguel Ojeda
2026-09-15 11:15 ` Lorenzo Stoakes (ARM)
1 sibling, 1 reply; 58+ messages in thread
From: Miguel Ojeda @ 2026-09-15 6:32 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva,
linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening
On Mon, Sep 14, 2026 at 10:24 AM Lorenzo Stoakes (ARM) <ljs@kernel.org> wrote:
>
> Rust crates are compiled in a serial chain on the critical path - core,
> bindings, kernel crates and then the drivers - each a rustc invocation.
This confused the LWN article... :)
There is a critical path in the graph, indeed, and doing it in
`prepare` is painful, but to clarify: each crate is already built in
parallel with others where possible, and the fact that each crate is
built by one `rustc` is unrelated, plus the flag this patch proposes
is also unrelated to that.
I guess the LLM was trying to add context to the numbers below, but it
looks like it will easily confuse readers.
> Each time a change is made to any of the bindings, it triggers a rebuild.
This seems oddly focused (i.e. not sure why `bindings` is mentioned in
particular). It is also at least independent of this patch, i.e. it
will remain true regardless of the patch.
> rustc has a parallel front end, enabled with -Zthreads, available since
> rust 1.84 [0] and therefore on every rustc the kernel supports.
>
> It is not yet stable and its output is not reproducible, so it cannot be
> used by default - stabilisation is being worked on [1].
Not sure what it means by "by default". In any case, the main issue
with the flag is that it has had issues recently, not so much the fact
that it is unstable.
> Add optional build parameter KBUILD_RUST_THREADS, which when set passes
> that many threads to rustc.
>
> Observed build time changes with KBUILD_RUST_THREADS=8 (rustc 1.98, clang):
I assume the improvements are most notable due to the work being on
`prepare`, i.e. there is no other work available. When that is
relaxed, this should be way less needed. Though it will be still very
nice to have for full Rust rebuilds, like when changing the compiler
versions often, due to `core` mainly (e.g. I have to do that often, so
I would like it :).
In any case, I am not sure about adding a Kbuild variable already for
this at the moment, especially with that name, i.e. it is not really
"threads" but "frontend jobs" and the flag will not be called that in
the future anyway.
And if someone wants to risk their kernel builds, then they can
already pass the flag today...
(We probably also want to know what the flag will finally do before
committing to particular names, e.g. whether it affects
codegen/reproducibility in any way. But perhaps Kbuild doesn't mind
having new variables that may be replaced soon.)
Thanks!
Cheers,
Miguel
^ permalink raw reply [flat|nested] 58+ messages in thread
* Re: [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end
2026-09-15 6:32 ` Miguel Ojeda
@ 2026-09-15 11:15 ` Lorenzo Stoakes (ARM)
0 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 11:15 UTC (permalink / raw)
To: Miguel Ojeda
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva,
linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening
On Tue, Sep 15, 2026 at 07:32:02AM +0100, Miguel Ojeda wrote:
> On Mon, Sep 14, 2026 at 10:24 AM Lorenzo Stoakes (ARM) <ljs@kernel.org> wrote:
> >
> > Rust crates are compiled in a serial chain on the critical path - core,
> > bindings, kernel crates and then the drivers - each a rustc invocation.
>
> This confused the LWN article... :)
Sorry :)
>
> There is a critical path in the graph, indeed, and doing it in
> `prepare` is painful, but to clarify: each crate is already built in
> parallel with others where possible, and the fact that each crate is
> built by one `rustc` is unrelated, plus the flag this patch proposes
> is also unrelated to that.
Ack. And the other rust changes help maximise the parallelisation
that exists :)
>
> I guess the LLM was trying to add context to the numbers below, but it
> looks like it will easily confuse readers.
>
> > Each time a change is made to any of the bindings, it triggers a rebuild.
>
> This seems oddly focused (i.e. not sure why `bindings` is mentioned in
> particular). It is also at least independent of this patch, i.e. it
> will remain true regardless of the patch.
>
> > rustc has a parallel front end, enabled with -Zthreads, available since
> > rust 1.84 [0] and therefore on every rustc the kernel supports.
> >
> > It is not yet stable and its output is not reproducible, so it cannot be
> > used by default - stabilisation is being worked on [1].
>
> Not sure what it means by "by default". In any case, the main issue
> with the flag is that it has had issues recently, not so much the fact
> that it is unstable.
>
> > Add optional build parameter KBUILD_RUST_THREADS, which when set passes
> > that many threads to rustc.
> >
> > Observed build time changes with KBUILD_RUST_THREADS=8 (rustc 1.98, clang):
>
> I assume the improvements are most notable due to the work being on
> `prepare`, i.e. there is no other work available. When that is
> relaxed, this should be way less needed. Though it will be still very
> nice to have for full Rust rebuilds, like when changing the compiler
> versions often, due to `core` mainly (e.g. I have to do that often, so
> I would like it :).
Yup that stalling is the key issue.
I mean KRUSTFLAGS=-Zthreads=8 gives you a way to achieve that, I'll stick
that into my scripts locally for now too I think as I've found it to be
completely stable at least on my machine (TM).
But definitely a TODO to pin for you guys once this is stabilised - it
makes a big difference so when a. stabilised and b. kernel required minimum
version has the stabilised feature -> easy to switch on :)
>
> In any case, I am not sure about adding a Kbuild variable already for
> this at the moment, especially with that name, i.e. it is not really
> "threads" but "frontend jobs" and the flag will not be called that in
> the future anyway.
>
> And if someone wants to risk their kernel builds, then they can
> already pass the flag today...
I agree, best to drop this in general, done for v3 already. I've updated
the cover letter to say that KRUSTFLAGS=-Zthreads=8 is what was done with
the build.
>
> (We probably also want to know what the flag will finally do before
> committing to particular names, e.g. whether it affects
> codegen/reproducibility in any way. But perhaps Kbuild doesn't mind
> having new variables that may be replaced soon.)
I don't think it's too egregious either way tbh, but in any case dropping
this for now is the way to go.
>
> Thanks!
>
> Cheers,
> Miguel
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* [PATCH v2 19/21] rust: make exports.o depend on the headers generated for it
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (17 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 18/21] kbuild: rust: optionally parallelise rustc front end Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 9:22 ` [PATCH v2 20/21] kbuild: build rust crates in parallel with the rest of the build Lorenzo Stoakes (ARM)
` (2 subsequent siblings)
21 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
rust/exports.c includes the exports_*_generated.h listing the symbols of
the core, bindings, kernel and helpers objects, but this is not expressed
in its Makefile.
This worked previously because the headers are always-y targets, and make
prepare built all of the rust crates first, which is an implicit
dependency.
Fix this as it is a dependency of the subsequent commit.
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
rust/Makefile | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/rust/Makefile b/rust/Makefile
index da1a7409d984..74d21ae6f383 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -728,6 +728,11 @@ endef
$(obj)/helpers/helpers.o: $(src)/helpers/helpers.c $(recordmcount_source) FORCE
+$(call if_changed_rule,rust_cc_library)
+# The exported symbol lists are generated from the crates' objects.
+$(obj)/exports.o: $(obj)/exports_core_generated.h \
+ $(obj)/exports_bindings_generated.h $(obj)/exports_kernel_generated.h \
+ $(if $(CONFIG_RUST_INLINE_HELPERS),,$(obj)/exports_helpers_generated.h)
+
# Disable symbol versioning for exports.o to avoid conflicts with the actual
# symbol versions generated from Rust objects.
$(obj)/exports.o: private skip_gendwarfksyms = 1
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* [PATCH v2 20/21] kbuild: build rust crates in parallel with the rest of the build
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (18 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 19/21] rust: make exports.o depend on the headers generated for it Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 18:37 ` Kees Cook
2026-09-14 9:22 ` [PATCH v2 21/21] kbuild: use pigz for gzip compression if available Lorenzo Stoakes (ARM)
2026-09-14 15:41 ` [PATCH v2 00/21] kbuild: significantly speed up kernel builds Kees Cook
21 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
When CONFIG_RUST is specified make prepare builds all of the rust
components before descending into the tree.
This means nothing can be done until all of these are compiled, resulting
in a stall at the start of every clean CONFIG_RUST build.
This also implicitly slows down every rust-capable LLVM allmodconfig build
as this enables the CONFIG_RUST option.
Fix this by allowing rust crates to be built alongside the C code.
Remove the rust build from the make prepare step, then establish a
dependency between rust code located elsewhere in the tree upon rust
components contained in rust/.
Do this by establishing a top-level list of directories containing rust
code, KBUILD_RUST_DIRS, upon which the dependency is expressed.
Finally, ensure that no rust code is located elsewhere and fail the build
if any is found to ensure that nothing is missed in future.
Care is taken to ensure the rust/ dependency is also established for any
module being built to account for external rust modules which rely upon it.
Care is taken to ensure that external rust modules can still be built
against the tree - make modules_prepare ... (where ... are other goals)
will build rust/ first.
Every Rust and C object was confirmed to be byte-for-byte identical after
this change.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig+RUST, clean 36.5s 32.6s -3.9s (-11%)
x86 allmodconfig, clean 297.0s 278.3s -18.7s (-6%)
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
Kbuild | 5 +++++
Makefile | 11 ++++++++++-
scripts/Makefile.build | 5 ++++-
3 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/Kbuild b/Kbuild
index a6a0192dea08..9670556059dd 100644
--- a/Kbuild
+++ b/Kbuild
@@ -115,3 +115,8 @@ obj-$(CONFIG_NET) += net/
obj-y += virt/
obj-y += $(ARCH_DRIVERS)
obj-$(CONFIG_DRM_HEADER_TEST) += include/
+
+# Rust code elsewhere in the tree depends upon rust/.
+ifdef CONFIG_RUST
+$(KBUILD_RUST_DIRS): | rust
+endif
diff --git a/Makefile b/Makefile
index 4ef504c1ace2..790ef23c5e8a 100644
--- a/Makefile
+++ b/Makefile
@@ -1429,11 +1429,14 @@ prepare0: archprepare
$(Q)$(MAKE) $(build)=. prepare
$(Q)$(MAKE) $(build)=scripts/mod
+ifdef CONFIG_RUST
+export KBUILD_RUST_DIRS := drivers lib mm samples
+endif
+
# All the preparing..
prepare: prepare0
ifdef CONFIG_RUST
+$(Q)$(CONFIG_SHELL) $(srctree)/scripts/rust_is_available.sh
- $(Q)$(MAKE) $(build)=rust
endif
PHONY += remove-stale-files
@@ -1760,6 +1763,12 @@ modules: modules_prepare
# Target to prepare building external modules
modules_prepare: prepare
$(Q)$(MAKE) $(build)=scripts scripts/module.lds
+ifdef CONFIG_RUST
+# Ensure rust/ is built before any external rust module which will rely upon it.
+ifneq ($(filter modules_prepare,$(MAKECMDGOALS)),)
+ $(Q)$(MAKE) $(build)=rust
+endif
+endif
endif # CONFIG_MODULES
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index b9093b39cc2f..77351d6006fa 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -360,8 +360,11 @@ quiet_cmd_rustc_o_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
$(cmd_ld_single)) \
$(cmd_objtool)
+rust-dir-ok = $(or $(KBUILD_EXTMOD),$(filter rust $(KBUILD_RUST_DIRS),$(firstword $(subst /, ,$@))))
+
+# Ensure that any rust code located elsewhere from rust/ is listed in KBUILD_RUST_DIRS.
define rule_rustc_o_rs
- $(call cmd_and_fixdep,rustc_o_rs)
+ $(if $(rust-dir-ok),,$(error $@: Rust code in a directory not listed in KBUILD_RUST_DIRS, see the top Makefile))$(call cmd_and_fixdep,rustc_o_rs)
$(call cmd,gen_objtooldep)
endef
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 20/21] kbuild: build rust crates in parallel with the rest of the build
2026-09-14 9:22 ` [PATCH v2 20/21] kbuild: build rust crates in parallel with the rest of the build Lorenzo Stoakes (ARM)
@ 2026-09-14 18:37 ` Kees Cook
2026-09-15 11:58 ` Lorenzo Stoakes (ARM)
0 siblings, 1 reply; 58+ messages in thread
From: Kees Cook @ 2026-09-14 18:37 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 10:22:19AM +0100, Lorenzo Stoakes (ARM) wrote:
> Care is taken to ensure that external rust modules can still be built
> against the tree - make modules_prepare ... (where ... are other goals)
> will build rust/ first.
> [...]
> prepare: prepare0
> ifdef CONFIG_RUST
> +$(Q)$(CONFIG_SHELL) $(srctree)/scripts/rust_is_available.sh
> - $(Q)$(MAKE) $(build)=rust
> endif
>
> PHONY += remove-stale-files
> @@ -1760,6 +1763,12 @@ modules: modules_prepare
> # Target to prepare building external modules
> modules_prepare: prepare
> $(Q)$(MAKE) $(build)=scripts scripts/module.lds
> +ifdef CONFIG_RUST
> +# Ensure rust/ is built before any external rust module which will rely upon it.
> +ifneq ($(filter modules_prepare,$(MAKECMDGOALS)),)
> + $(Q)$(MAKE) $(build)=rust
> +endif
> +endif
As far as I can see, nothing orders this recipe against the tree build,
which also descends into rust/ through "obj-$(CONFIG_RUST) += rust/"
in Kbuild, while $(build-dir) only depends on prepare. Before this
patch that was fine, because prepare had already built rust/ by the
time either of them ran. Now "make -jN modules_prepare all" can have
two make processes building rust/ at the same time, and so can
"make -jN rustdoc all" or "make -jN rusttest all", whose recipes also
run "$(MAKE) $(build)=rust". That means two rustc runs writing the same
objects in rust/ ...
> +# Rust code elsewhere in the tree depends upon rust/.
> +ifdef CONFIG_RUST
> +$(KBUILD_RUST_DIRS): | rust
> +endif
> [...]
> +export KBUILD_RUST_DIRS := drivers lib mm samples
Doesn't this make all of drivers/, lib/, mm/ and samples/ wait for rust/?
That's a lot of stall: drivers/ is most of the tree. I think then a
CONFIG_RUST build has most of its C work waiting on the rust chain;
only the other top-level directories start early? This didn't create new
build delays for those configurations?
--
Kees Cook
^ permalink raw reply [flat|nested] 58+ messages in thread
* Re: [PATCH v2 20/21] kbuild: build rust crates in parallel with the rest of the build
2026-09-14 18:37 ` Kees Cook
@ 2026-09-15 11:58 ` Lorenzo Stoakes (ARM)
0 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 11:58 UTC (permalink / raw)
To: Kees Cook
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 11:37:54AM -0700, Kees Cook wrote:
> On Mon, Sep 14, 2026 at 10:22:19AM +0100, Lorenzo Stoakes (ARM) wrote:
> > Care is taken to ensure that external rust modules can still be built
> > against the tree - make modules_prepare ... (where ... are other goals)
> > will build rust/ first.
> > [...]
> > prepare: prepare0
> > ifdef CONFIG_RUST
> > +$(Q)$(CONFIG_SHELL) $(srctree)/scripts/rust_is_available.sh
> > - $(Q)$(MAKE) $(build)=rust
> > endif
> >
> > PHONY += remove-stale-files
> > @@ -1760,6 +1763,12 @@ modules: modules_prepare
> > # Target to prepare building external modules
> > modules_prepare: prepare
> > $(Q)$(MAKE) $(build)=scripts scripts/module.lds
> > +ifdef CONFIG_RUST
> > +# Ensure rust/ is built before any external rust module which will rely upon it.
> > +ifneq ($(filter modules_prepare,$(MAKECMDGOALS)),)
> > + $(Q)$(MAKE) $(build)=rust
> > +endif
> > +endif
>
> As far as I can see, nothing orders this recipe against the tree build,
> which also descends into rust/ through "obj-$(CONFIG_RUST) += rust/"
> in Kbuild, while $(build-dir) only depends on prepare. Before this
> patch that was fine, because prepare had already built rust/ by the
> time either of them ran. Now "make -jN modules_prepare all" can have
> two make processes building rust/ at the same time, and so can
> "make -jN rustdoc all" or "make -jN rusttest all", whose recipes also
> run "$(MAKE) $(build)=rust". That means two rustc runs writing the same
> objects in rust/ ...
Ack.
It seems make can't order two independent sub-makes, so will change the patch so
it skips the modules_prepare rust build when a goal that builds the tree* is
present, as they all descend into rust/ themselves.
I checked the change against:
$ make modules_prepare
$ make modules_prepare scripts
$ make -j128 modules_prepare all
+ confirmed they all built rust/ once only for each.
* LLM says: all, vmlinux, modules, image targets, dtbs, rustdoc, rusttest
So, fixed in v3 :)
>
> > +# Rust code elsewhere in the tree depends upon rust/.
> > +ifdef CONFIG_RUST
> > +$(KBUILD_RUST_DIRS): | rust
> > +endif
> > [...]
> > +export KBUILD_RUST_DIRS := drivers lib mm samples
>
> Doesn't this make all of drivers/, lib/, mm/ and samples/ wait for rust/?
> That's a lot of stall: drivers/ is most of the tree. I think then a
> CONFIG_RUST build has most of its C work waiting on the rust chain;
> only the other top-level directories start early? This didn't create new
> build delays for those configurations?
Yeah good point.
For a defconfig+rust clean build on 128 threads the other top-level directories
were done at ~14s while rust ran to ~18.6s, so there was 4-5 of idle.
However the patch improves things by net -3.9s regardless.
This is really only a big box issue though. With fewer threads the rest of the
tree takes longer so it has no impact on the build.
(An aside - this kind of trade-off is what the series is all about really - the
'serial tail' - i.e. the single threaded stuff that _overlaps_ the end of the
build is what slows you down.)
Since this _still_ gives you a significant speed up on bigger boxes, I think
it's fine as-is.
The LLM says a fix for this would need significant work - a cross-instance lock
and an on-demand rust/ build. So I think best as a follow-up?
>
> --
> Kees Cook
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* [PATCH v2 21/21] kbuild: use pigz for gzip compression if available
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (19 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 20/21] kbuild: build rust crates in parallel with the rest of the build Lorenzo Stoakes (ARM)
@ 2026-09-14 9:22 ` Lorenzo Stoakes (ARM)
2026-09-14 16:39 ` Kees Cook
2026-09-14 15:41 ` [PATCH v2 00/21] kbuild: significantly speed up kernel builds Kees Cook
21 siblings, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 9:22 UTC (permalink / raw)
To: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Kees Cook, Gustavo A. R. Silva
Cc: linux-kbuild, linux-kernel, llvm, linux-riscv, linux-arch,
linux-arm-kernel, linux-efi, rust-for-linux, linux-doc,
Jens Axboe, linux-hardening, Lorenzo Stoakes (ARM)
The gzip step of a kernel build is very lengthily, especially for larger
builds such as allmodconfig.
gzip itself cannot be run in parallel, however an alternative tool exists
that can, providing the same feature set as gzip itself - pigz - which
works as a drop-in replacement.
On a 128-core Threadripper, gzip -9 of a 36 MiB x86-64 vmlinux.bin takes
1.6s, and with pigz it takes 0.09s, so the performance increase is
significant.
It is already possible to specify KGZIP on the make command line to make
use of pigz, however it seems sensible to make use of pigz if it is
available.
Therefore default to using pigz if it is available on the system upon which
the kernel is being built, otherwise fall back to gzip.
Modules are compressed one per make job at install time, so a parallel
compressor gains nothing there and with -jN would run N times the core
count in threads. Limit pigz to a single thread for module compression.
The output is byte-for-byte identical between pigz/gzip invocations, but
gzip and pigz do not produce the same stream as one another.
Therefore, for reproducible builds, the same set of tools should be used.
This seems to already be an implicit requirement in any case, but update
the reproducible build documentation to make this clear.
Also update the kbuild documentation to reflect the change.
Every x86 build ends with the compression of vmlinux.bin, 36MB for
defconfig and over 200MB for allmodconfig, no-op builds are unchanged.
Whole build, 128-thread Threadripper 9980X, best of N runs:
before after delta
-------------------------------
x86 defconfig, touch mm/vma.c, gcc 7.7s 6.0s -1.7s (-22%)
x86 defconfig, touch mm/vma.c, clang 6.9s 5.4s -1.5s (-21%)
x86 defconfig, clean, gcc 28.2s 26.3s -1.8s (-6%)
x86 defconfig, clean, clang 28.7s 27.2s -1.5s (-5%)
x86 allmodconfig, touch mm/vma.c, gcc 23.7s 15.4s -8.3s (-35%)
x86 allmodconfig, touch mm/vma.c, clang 22.5s 15.6s -7.0s (-31%)
x86 allmodconfig, clean, gcc 294.1s 278.6s -15.5s (-5%)
x86 allmodconfig, clean, clang 283.9s 266.8s -17.1s (-6%)
Link: https://zlib.net/pigz/
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
Documentation/kbuild/kbuild.rst | 15 +++++++++++++++
Documentation/kbuild/reproducible-builds.rst | 16 ++++++++++++++++
Makefile | 2 +-
scripts/Makefile.modinst | 4 +++-
4 files changed, 35 insertions(+), 2 deletions(-)
diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
index 9b2b127676c3..ebfc2945ac03 100644
--- a/Documentation/kbuild/kbuild.rst
+++ b/Documentation/kbuild/kbuild.rst
@@ -110,6 +110,21 @@ HOSTLDLIBS
----------
Additional libraries to link against when building host programs.
+KGZIP
+-----
+The gzip compressor used for the compressed kernel image, compressed
+modules and packaging.
+
+Defaults to pigz (a parallel implementation of gzip) if it is available,
+otherwise gzip. Set ``KGZIP=`` on the make command line to use another
+program. Modules are compressed one per make job, so pigz is limited to a
+single thread there.
+
+KBZIP2, KLZOP, LZMA, LZ4, XZ, ZSTD
+----------------------------------
+The compressor programs for the other formats. Each defaults to the program
+of the same name.
+
.. _userkbuildflags:
USERCFLAGS
diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst
index bc1eb82211df..ec0135da4464 100644
--- a/Documentation/kbuild/reproducible-builds.rst
+++ b/Documentation/kbuild/reproducible-builds.rst
@@ -76,6 +76,22 @@ include generated files. You should ensure the source tree is
pristine by running ``make mrproper`` or ``git clean -d -f -x`` before
building a source package.
+Compression tools
+-----------------
+
+The compressed kernel image, compressed modules and packages are produced
+using the program named by the make variable ``KGZIP`` (described in
+Documentation/kbuild/kbuild.rst).
+
+It defaults to ``pigz`` if installed (a parallel implementation of gzip),
+or ``gzip`` otherwise.
+
+The generated output between two invocations of identical builds with
+either of the default tools will be byte-for-byte equivalent.
+
+However, for reproducible builds, ensure the same tool is used on all build
+hosts, as different tools may generate different output from one another.
+
Module signing
--------------
diff --git a/Makefile b/Makefile
index 790ef23c5e8a..38c0cdc9f591 100644
--- a/Makefile
+++ b/Makefile
@@ -561,7 +561,7 @@ PERL = perl
PYTHON3 = python3
CHECK = sparse
BASH = bash
-KGZIP = gzip
+KGZIP := $(if $(shell command -v pigz 2>/dev/null),pigz,gzip)
KBZIP2 = bzip2
KLZOP = lzop
LZMA = lzma
diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
index 9ba45e5b32b1..58dafec8f910 100644
--- a/scripts/Makefile.modinst
+++ b/scripts/Makefile.modinst
@@ -145,8 +145,10 @@ endif
#
# Compression
#
+# Modules are compressed in parallel by make itself, so keep the compressor
+# single-threaded when it is pigz.
quiet_cmd_gzip = GZIP $@
- cmd_gzip = $(KGZIP) -n -f $<
+ cmd_gzip = $(KGZIP) $(if $(filter pigz,$(notdir $(firstword $(KGZIP)))),-p 1) -n -f $<
quiet_cmd_xz = XZ $@
cmd_xz = $(XZ) --check=crc32 --lzma2=dict=1MiB -f $<
quiet_cmd_zstd = ZSTD $@
--
2.55.0
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 21/21] kbuild: use pigz for gzip compression if available
2026-09-14 9:22 ` [PATCH v2 21/21] kbuild: use pigz for gzip compression if available Lorenzo Stoakes (ARM)
@ 2026-09-14 16:39 ` Kees Cook
2026-09-14 16:49 ` H. Peter Anvin
0 siblings, 1 reply; 58+ messages in thread
From: Kees Cook @ 2026-09-14 16:39 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 10:22:20AM +0100, Lorenzo Stoakes (ARM) wrote:
> On a 128-core Threadripper, gzip -9 of a 36 MiB x86-64 vmlinux.bin takes
> 1.6s, and with pigz it takes 0.09s, so the performance increase is
> significant.
Neat! I wanna go learn how pigz accomplishes this -- I thought the
problem with gzip was a common lookup table. Anyway...
> --- a/Documentation/kbuild/reproducible-builds.rst
> +++ b/Documentation/kbuild/reproducible-builds.rst
> @@ -76,6 +76,22 @@ include generated files. You should ensure the source tree is
> pristine by running ``make mrproper`` or ``git clean -d -f -x`` before
> building a source package.
>
> +Compression tools
> +-----------------
> +
> +The compressed kernel image, compressed modules and packages are produced
> +using the program named by the make variable ``KGZIP`` (described in
> +Documentation/kbuild/kbuild.rst).
> +
> +It defaults to ``pigz`` if installed (a parallel implementation of gzip),
> +or ``gzip`` otherwise.
> +
> +The generated output between two invocations of identical builds with
> +either of the default tools will be byte-for-byte equivalent.
> +
> +However, for reproducible builds, ensure the same tool is used on all build
> +hosts, as different tools may generate different output from one another.
> +
> Module signing
> --------------
>
This doc update seems totally unneeded? Having the same build tools for RB
is already a known requirement. I don't think anything new is added here?
> diff --git a/Makefile b/Makefile
> index 790ef23c5e8a..38c0cdc9f591 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -561,7 +561,7 @@ PERL = perl
> PYTHON3 = python3
> CHECK = sparse
> BASH = bash
> -KGZIP = gzip
> +KGZIP := $(if $(shell command -v pigz 2>/dev/null),pigz,gzip)
I think the more idiomatic way to do this is:
KGZIP := $(call try-run,command -v pigz,pigz,gzip)
However, parallelism needs to be set. We can't let it eat all CPUs: it
needs to respect the -j make option (and make its CPU reservation known
to "make"), which we already have a solution for in
scripts/jobserver-exec.
However, I would actually argue that given such an improvement we should just
make pigz explicitly required and not optional. It is packaged everywhere:
│ Debian / Ubuntu │ ✅ │ pigz (main)
│ Fedora │ ✅ │ pigz 2.8 (current)
│ RHEL / CentOS / Rocky / Alma │ ✅ via EPEL │ pigz — not in base/AppStream
│ openSUSE / SLE │ ✅ │ pigz
│ Arch Linux │ ✅ │ pigz (extra)
│ Alpine │ ✅ │ pigz
│ Gentoo │ ✅ │ app-arch/pigz 2.8
Only RHEL appears a little glitchy, but likely they would trivially move
it to base since it's already packaged, but off in EPEL.
So, I would say that pigz would be best run as something like:
KGZIP := $(PYTHON3) $(abs_srctree)/scripts/jobserver-exec $(abs_srctree)/scripts/parallel-pigz
with scripts/parallel-pigz being something like:
#!/bin/sh
exec pigz -p ${PARALLELISM:-1} "$@"
> --- a/scripts/Makefile.modinst
> +++ b/scripts/Makefile.modinst
> @@ -145,8 +145,10 @@ endif
> #
> # Compression
> #
> +# Modules are compressed in parallel by make itself, so keep the compressor
> +# single-threaded when it is pigz.
> quiet_cmd_gzip = GZIP $@
> - cmd_gzip = $(KGZIP) -n -f $<
> + cmd_gzip = $(KGZIP) $(if $(filter pigz,$(notdir $(firstword $(KGZIP)))),-p 1) -n -f $<
> quiet_cmd_xz = XZ $@
Then this could be:
cmd_gzip = SINGLE_THREADED=1 $(KGZIP) -n -f $<
and we patch scripts/jobserver-exec:
diff --git a/scripts/jobserver-exec b/scripts/jobserver-exec
index 21b319e6c9a5..8b953148ee9f 100755
--- a/scripts/jobserver-exec
+++ b/scripts/jobserver-exec
@@ -5,6 +5,7 @@
Determines how many parallel tasks "make" is expecting, as it is
not exposed via any special variables, reserves them all, runs a subprocess
with PARALLELISM environment variable set, and releases the jobs back again.
+If SINGLE_THREADED is set, nothing is reserved and PARALLELISM is 1.
See:
https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
diff --git a/tools/lib/python/jobserver.py b/tools/lib/python/jobserver.py
index 0b1ffdf9f7a3..fc38c5020b22 100755
--- a/tools/lib/python/jobserver.py
+++ b/tools/lib/python/jobserver.py
@@ -29,6 +29,11 @@ $claim child to do the actual work.
The end goal here is to keep the total number of build tasks under the
limit established by the initial ``make -j$n_proc`` call.
+Setting the ``SINGLE_THREADED`` environment variable skips the reservation
+entirely and runs the command with ``PARALLELISM=1``. This is meant for callers
+that run many short commands in parallel themselves, where each one should use
+only the job slot it already holds.
+
See:
https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
"""
@@ -68,6 +73,13 @@ class JobserverExec:
self.is_open = True # We only try once
self.claim = None
#
+ # SINGLE_THREADED asks for no reservation at all: the command runs
+ # with PARALLELISM=1, using only the slot its caller already holds.
+ #
+ if os.environ.get('SINGLE_THREADED'):
+ self.claim = 1
+ return
+ #
# Check the make flags for "--jobserver=R,W"
# Note that GNU Make has used --jobserver-fds and --jobserver-auth
# so this handles all of them.
--
Kees Cook
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 21/21] kbuild: use pigz for gzip compression if available
2026-09-14 16:39 ` Kees Cook
@ 2026-09-14 16:49 ` H. Peter Anvin
2026-09-14 17:50 ` Kees Cook
0 siblings, 1 reply; 58+ messages in thread
From: H. Peter Anvin @ 2026-09-14 16:49 UTC (permalink / raw)
To: Kees Cook, Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, Paul Walmsley, Palmer Dabbelt, Albert Ou,
Alexandre Ghiti, Arnd Bergmann, Catalin Marinas, Will Deacon,
Mark Rutland, Ard Biesheuvel, Ilias Apalodimas, Josh Poimboeuf,
Peter Zijlstra, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl,
Trevor Gross, Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Gustavo A. R. Silva, linux-kbuild, linux-kernel,
llvm, linux-riscv, linux-arch, linux-arm-kernel, linux-efi,
rust-for-linux, linux-doc, Jens Axboe, linux-hardening
On September 14, 2026 9:39:07 AM PDT, Kees Cook <kees@kernel.org> wrote:
>On Mon, Sep 14, 2026 at 10:22:20AM +0100, Lorenzo Stoakes (ARM) wrote:
>> On a 128-core Threadripper, gzip -9 of a 36 MiB x86-64 vmlinux.bin takes
>> 1.6s, and with pigz it takes 0.09s, so the performance increase is
>> significant.
>
>Neat! I wanna go learn how pigz accomplishes this -- I thought the
>problem with gzip was a common lookup table. Anyway...
>
>> --- a/Documentation/kbuild/reproducible-builds.rst
>> +++ b/Documentation/kbuild/reproducible-builds.rst
>> @@ -76,6 +76,22 @@ include generated files. You should ensure the source tree is
>> pristine by running ``make mrproper`` or ``git clean -d -f -x`` before
>> building a source package.
>>
>> +Compression tools
>> +-----------------
>> +
>> +The compressed kernel image, compressed modules and packages are produced
>> +using the program named by the make variable ``KGZIP`` (described in
>> +Documentation/kbuild/kbuild.rst).
>> +
>> +It defaults to ``pigz`` if installed (a parallel implementation of gzip),
>> +or ``gzip`` otherwise.
>> +
>> +The generated output between two invocations of identical builds with
>> +either of the default tools will be byte-for-byte equivalent.
>> +
>> +However, for reproducible builds, ensure the same tool is used on all build
>> +hosts, as different tools may generate different output from one another.
>> +
>> Module signing
>> --------------
>>
>
>This doc update seems totally unneeded? Having the same build tools for RB
>is already a known requirement. I don't think anything new is added here?
>
>> diff --git a/Makefile b/Makefile
>> index 790ef23c5e8a..38c0cdc9f591 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -561,7 +561,7 @@ PERL = perl
>> PYTHON3 = python3
>> CHECK = sparse
>> BASH = bash
>> -KGZIP = gzip
>> +KGZIP := $(if $(shell command -v pigz 2>/dev/null),pigz,gzip)
>
>I think the more idiomatic way to do this is:
>
>KGZIP := $(call try-run,command -v pigz,pigz,gzip)
>
>However, parallelism needs to be set. We can't let it eat all CPUs: it
>needs to respect the -j make option (and make its CPU reservation known
>to "make"), which we already have a solution for in
>scripts/jobserver-exec.
>
>However, I would actually argue that given such an improvement we should just
>make pigz explicitly required and not optional. It is packaged everywhere:
>
> │ Debian / Ubuntu │ ✅ │ pigz (main)
> │ Fedora │ ✅ │ pigz 2.8 (current)
> │ RHEL / CentOS / Rocky / Alma │ ✅ via EPEL │ pigz — not in base/AppStream
> │ openSUSE / SLE │ ✅ │ pigz
> │ Arch Linux │ ✅ │ pigz (extra)
> │ Alpine │ ✅ │ pigz
> │ Gentoo │ ✅ │ app-arch/pigz 2.8
>
>Only RHEL appears a little glitchy, but likely they would trivially move
>it to base since it's already packaged, but off in EPEL.
>
>So, I would say that pigz would be best run as something like:
>
> KGZIP := $(PYTHON3) $(abs_srctree)/scripts/jobserver-exec $(abs_srctree)/scripts/parallel-pigz
>
>with scripts/parallel-pigz being something like:
>
> #!/bin/sh
> exec pigz -p ${PARALLELISM:-1} "$@"
>
>> --- a/scripts/Makefile.modinst
>> +++ b/scripts/Makefile.modinst
>> @@ -145,8 +145,10 @@ endif
>> #
>> # Compression
>> #
>> +# Modules are compressed in parallel by make itself, so keep the compressor
>> +# single-threaded when it is pigz.
>> quiet_cmd_gzip = GZIP $@
>> - cmd_gzip = $(KGZIP) -n -f $<
>> + cmd_gzip = $(KGZIP) $(if $(filter pigz,$(notdir $(firstword $(KGZIP)))),-p 1) -n -f $<
>> quiet_cmd_xz = XZ $@
>
>Then this could be:
>
> cmd_gzip = SINGLE_THREADED=1 $(KGZIP) -n -f $<
>
>and we patch scripts/jobserver-exec:
>
>diff --git a/scripts/jobserver-exec b/scripts/jobserver-exec
>index 21b319e6c9a5..8b953148ee9f 100755
>--- a/scripts/jobserver-exec
>+++ b/scripts/jobserver-exec
>@@ -5,6 +5,7 @@
> Determines how many parallel tasks "make" is expecting, as it is
> not exposed via any special variables, reserves them all, runs a subprocess
> with PARALLELISM environment variable set, and releases the jobs back again.
>+If SINGLE_THREADED is set, nothing is reserved and PARALLELISM is 1.
>
> See:
> https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
>diff --git a/tools/lib/python/jobserver.py b/tools/lib/python/jobserver.py
>index 0b1ffdf9f7a3..fc38c5020b22 100755
>--- a/tools/lib/python/jobserver.py
>+++ b/tools/lib/python/jobserver.py
>@@ -29,6 +29,11 @@ $claim child to do the actual work.
> The end goal here is to keep the total number of build tasks under the
> limit established by the initial ``make -j$n_proc`` call.
>
>+Setting the ``SINGLE_THREADED`` environment variable skips the reservation
>+entirely and runs the command with ``PARALLELISM=1``. This is meant for callers
>+that run many short commands in parallel themselves, where each one should use
>+only the job slot it already holds.
>+
> See:
> https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
> """
>@@ -68,6 +73,13 @@ class JobserverExec:
> self.is_open = True # We only try once
> self.claim = None
> #
>+ # SINGLE_THREADED asks for no reservation at all: the command runs
>+ # with PARALLELISM=1, using only the slot its caller already holds.
>+ #
>+ if os.environ.get('SINGLE_THREADED'):
>+ self.claim = 1
>+ return
>+ #
> # Check the make flags for "--jobserver=R,W"
> # Note that GNU Make has used --jobserver-fds and --jobserver-auth
> # so this handles all of them.
>
If we are going to add dependencies, can we add *any* scripting language that is less stone tablet than POSIX awk?
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 21/21] kbuild: use pigz for gzip compression if available
2026-09-14 16:49 ` H. Peter Anvin
@ 2026-09-14 17:50 ` Kees Cook
0 siblings, 0 replies; 58+ messages in thread
From: Kees Cook @ 2026-09-14 17:50 UTC (permalink / raw)
To: H. Peter Anvin
Cc: Lorenzo Stoakes (ARM),
Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, Paul Walmsley, Palmer Dabbelt, Albert Ou,
Alexandre Ghiti, Arnd Bergmann, Catalin Marinas, Will Deacon,
Mark Rutland, Ard Biesheuvel, Ilias Apalodimas, Josh Poimboeuf,
Peter Zijlstra, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl,
Trevor Gross, Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Gustavo A. R. Silva, linux-kbuild, linux-kernel,
llvm, linux-riscv, linux-arch, linux-arm-kernel, linux-efi,
rust-for-linux, linux-doc, Jens Axboe, linux-hardening
On Mon, Sep 14, 2026 at 09:49:50AM -0700, H. Peter Anvin wrote:
> On September 14, 2026 9:39:07 AM PDT, Kees Cook <kees@kernel.org> wrote:
> [...]
> >diff --git a/tools/lib/python/jobserver.py b/tools/lib/python/jobserver.py
> >index 0b1ffdf9f7a3..fc38c5020b22 100755
> >--- a/tools/lib/python/jobserver.py
> >+++ b/tools/lib/python/jobserver.py
> >@@ -29,6 +29,11 @@ $claim child to do the actual work.
> > The end goal here is to keep the total number of build tasks under the
> > limit established by the initial ``make -j$n_proc`` call.
> >
> >+Setting the ``SINGLE_THREADED`` environment variable skips the reservation
> >+entirely and runs the command with ``PARALLELISM=1``. This is meant for callers
> >+that run many short commands in parallel themselves, where each one should use
> >+only the job slot it already holds.
> >+
> > See:
> > https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
> > """
> >@@ -68,6 +73,13 @@ class JobserverExec:
> > self.is_open = True # We only try once
> > self.claim = None
> > #
> >+ # SINGLE_THREADED asks for no reservation at all: the command runs
> >+ # with PARALLELISM=1, using only the slot its caller already holds.
> >+ #
> >+ if os.environ.get('SINGLE_THREADED'):
> >+ self.claim = 1
> >+ return
> >+ #
> > # Check the make flags for "--jobserver=R,W"
> > # Note that GNU Make has used --jobserver-fds and --jobserver-auth
> > # so this handles all of them.
> >
>
> If we are going to add dependencies, can we add *any* scripting language that is less stone tablet than POSIX awk?
What are you referring to here? The jobserver logic is all Python.
--
Kees Cook
^ permalink raw reply [flat|nested] 58+ messages in thread
* Re: [PATCH v2 00/21] kbuild: significantly speed up kernel builds
2026-09-14 9:21 [PATCH v2 00/21] kbuild: significantly speed up kernel builds Lorenzo Stoakes (ARM)
` (20 preceding siblings ...)
2026-09-14 9:22 ` [PATCH v2 21/21] kbuild: use pigz for gzip compression if available Lorenzo Stoakes (ARM)
@ 2026-09-14 15:41 ` Kees Cook
2026-09-14 15:53 ` Linus Torvalds
2026-09-14 18:25 ` Lorenzo Stoakes (ARM)
21 siblings, 2 replies; 58+ messages in thread
From: Kees Cook @ 2026-09-14 15:41 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 10:21:59AM +0100, Lorenzo Stoakes (ARM) wrote:
> This series makes allmodconfig builds up to 36% faster, ...
This is very nice!
> incremental builds
> up to ~70% faster, and noop builds up to ~90% faster.
Some of the changes for this seem to add complexity that I'm not sure
is balanced against the gain? I am still looking through the series,
though, maybe I'll change my opinion. ;)
> == allmodconfig FULL build ==
Did you try Clang CONFIG_LTO=y builds?
> == LLM usage ==
> [...]
> I extensively audited and rewrote a lot of it, and heavily edited commit
> messages, the cover letter and comments.
I feel like the commit logs still need a lot of work. The LLM verbosity
problem appears in many of them, for example spending 80% of the commit
log describing every step of some process as background before getting
to the actual change. I think a human writing this would be much more
terse about the background. I have, however, been known to be too terse
in my own commit logs. :P
> [...]
> Nothing too controversial was included. There are further improvements that
> could be made, but they would either by very invasive (large scale C header
> changes) or generate diminishing returns.
One area I think might solved via an LLM is the 3-pass kallsyms stuff.
If we could get a deterministic kallsyms build in 1 pass, that would be
very nice. A lot of people have tried, but it has eluded upstreaming.
-Kees
--
Kees Cook
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 00/21] kbuild: significantly speed up kernel builds
2026-09-14 15:41 ` [PATCH v2 00/21] kbuild: significantly speed up kernel builds Kees Cook
@ 2026-09-14 15:53 ` Linus Torvalds
2026-09-15 8:53 ` Arnd Bergmann
2026-09-14 18:25 ` Lorenzo Stoakes (ARM)
1 sibling, 1 reply; 58+ messages in thread
From: Linus Torvalds @ 2026-09-14 15:53 UTC (permalink / raw)
To: Kees Cook
Cc: Lorenzo Stoakes (ARM),
Nathan Chancellor, Nicolas Schier, Nick Desaulniers,
Bill Wendling, Justin Stitt, Masahiro Yamada, Alexey Gladkov,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Paul Walmsley, Palmer Dabbelt, Albert Ou,
Alexandre Ghiti, Arnd Bergmann, Catalin Marinas, Will Deacon,
Mark Rutland, Ard Biesheuvel, Ilias Apalodimas, Josh Poimboeuf,
Peter Zijlstra, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl,
Trevor Gross, Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Gustavo A. R. Silva, linux-kbuild, linux-kernel,
llvm, linux-riscv, linux-arch, linux-arm-kernel, linux-efi,
rust-for-linux, linux-doc, Jens Axboe, linux-hardening
On Mon, 14 Sept 2026 at 08:41, Kees Cook <kees@kernel.org> wrote:
>
> One area I think might solved via an LLM is the 3-pass kallsyms stuff.
> If we could get a deterministic kallsyms build in 1 pass, that would be
> very nice. A lot of people have tried, but it has eluded upstreaming.
Even the three-pass one hasn't apparently always been entirely
deterministic. We've had random reports over the years of it failing
in some circumstances.
Maybe we've fixed it all, or maybe the failures just go imperceptibly
rare. Regardless, it has definitely been fragile.
Linus
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 00/21] kbuild: significantly speed up kernel builds
2026-09-14 15:53 ` Linus Torvalds
@ 2026-09-15 8:53 ` Arnd Bergmann
2026-09-15 11:35 ` Lorenzo Stoakes (ARM)
0 siblings, 1 reply; 58+ messages in thread
From: Arnd Bergmann @ 2026-09-15 8:53 UTC (permalink / raw)
To: Linus Torvalds, Kees Cook
Cc: Lorenzo Stoakes, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Catalin Marinas, Will Deacon,
Mark Rutland, Ard Biesheuvel, Ilias Apalodimas, Josh Poimboeuf,
Peter Zijlstra, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl,
Trevor Gross, Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Gustavo A. R. Silva, linux-kbuild, linux-kernel,
llvm, linux-riscv, Linux-Arch, linux-arm-kernel, linux-efi,
rust-for-linux, linux-doc, Jens Axboe, linux-hardening
On Mon, Sep 14, 2026, at 17:53, Linus Torvalds wrote:
> On Mon, 14 Sept 2026 at 08:41, Kees Cook <kees@kernel.org> wrote:
>>
>> One area I think might solved via an LLM is the 3-pass kallsyms stuff.
>> If we could get a deterministic kallsyms build in 1 pass, that would be
>> very nice. A lot of people have tried, but it has eluded upstreaming.
>
> Even the three-pass one hasn't apparently always been entirely
> deterministic. We've had random reports over the years of it failing
> in some circumstances.
This tends to break whenever a linker (rather than the compiler) starts
creating a new type of symbols that show up in pass 2.
> Maybe we've fixed it all, or maybe the failures just go imperceptibly
> rare. Regardless, it has definitely been fragile.
The rate seems to be once every few years, looking at the list
of exceptions added to scripts/kallsyms.c (now scripts/mksysmap):
efe6e3068067 ("kallsyms: fix nonconverging kallsyms table with lld")
516d980f8541 ("scripts/kallsyms: skip ppc compiler stub *.long_branch.* / *.plt_branch.*")
b9b74be163a2 ("ARM: 8555/1: kallsyms: ignore ARM mode switching veneers")
I'm sure there are other instances on architectures that get less
build coverage.
Arnd
^ permalink raw reply [flat|nested] 58+ messages in thread* Re: [PATCH v2 00/21] kbuild: significantly speed up kernel builds
2026-09-15 8:53 ` Arnd Bergmann
@ 2026-09-15 11:35 ` Lorenzo Stoakes (ARM)
0 siblings, 0 replies; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-15 11:35 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Linus Torvalds, Kees Cook, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Catalin Marinas, Will Deacon,
Mark Rutland, Ard Biesheuvel, Ilias Apalodimas, Josh Poimboeuf,
Peter Zijlstra, Miguel Ojeda, Boqun Feng, Gary Guo,
Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl,
Trevor Gross, Danilo Krummrich, Daniel Almeida, Tamir Duberstein,
Alexandre Courbot, Onur Özkan, Jonathan Corbet,
Randy Dunlap, Gustavo A. R. Silva, linux-kbuild, linux-kernel,
llvm, linux-riscv, Linux-Arch, linux-arm-kernel, linux-efi,
rust-for-linux, linux-doc, Jens Axboe, linux-hardening
On Tue, Sep 15, 2026 at 10:53:51AM +0200, Arnd Bergmann wrote:
> On Mon, Sep 14, 2026, at 17:53, Linus Torvalds wrote:
> > On Mon, 14 Sept 2026 at 08:41, Kees Cook <kees@kernel.org> wrote:
> >>
> >> One area I think might solved via an LLM is the 3-pass kallsyms stuff.
> >> If we could get a deterministic kallsyms build in 1 pass, that would be
> >> very nice. A lot of people have tried, but it has eluded upstreaming.
> >
> > Even the three-pass one hasn't apparently always been entirely
> > deterministic. We've had random reports over the years of it failing
> > in some circumstances.
>
> This tends to break whenever a linker (rather than the compiler) starts
> creating a new type of symbols that show up in pass 2.
>
> > Maybe we've fixed it all, or maybe the failures just go imperceptibly
> > rare. Regardless, it has definitely been fragile.
>
> The rate seems to be once every few years, looking at the list
> of exceptions added to scripts/kallsyms.c (now scripts/mksysmap):
>
> efe6e3068067 ("kallsyms: fix nonconverging kallsyms table with lld")
> 516d980f8541 ("scripts/kallsyms: skip ppc compiler stub *.long_branch.* / *.plt_branch.*")
> b9b74be163a2 ("ARM: 8555/1: kallsyms: ignore ARM mode switching veneers")
>
> I'm sure there are other instances on architectures that get less
> build coverage.
Yeah, it's stuff like this that makes it more sensible in general to use
existing tooling where that makes sense, e.g. also the .mod.S stuff.
Though I also think dropping some of these arches would be a good idea ;)
*ahem*.
In any case, I think the bigger picture ideas like a single pass kallsyms is
stuff for the future.
The way I see it: grab the really low-hanging fruit (this series), then the
medium-hanging fruit, and only then enter the pits of hell to fight the
satanic hordes which clasp on to what remains.
>
> Arnd
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* Re: [PATCH v2 00/21] kbuild: significantly speed up kernel builds
2026-09-14 15:41 ` [PATCH v2 00/21] kbuild: significantly speed up kernel builds Kees Cook
2026-09-14 15:53 ` Linus Torvalds
@ 2026-09-14 18:25 ` Lorenzo Stoakes (ARM)
2026-09-14 18:43 ` Kees Cook
1 sibling, 1 reply; 58+ messages in thread
From: Lorenzo Stoakes (ARM) @ 2026-09-14 18:25 UTC (permalink / raw)
To: Kees Cook
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 08:41:39AM -0700, Kees Cook wrote:
> On Mon, Sep 14, 2026 at 10:21:59AM +0100, Lorenzo Stoakes (ARM) wrote:
> > This series makes allmodconfig builds up to 36% faster, ...
>
> This is very nice!
Thanks :)
>
> > incremental builds
> > up to ~70% faster, and noop builds up to ~90% faster.
>
> Some of the changes for this seem to add complexity that I'm not sure
> is balanced against the gain? I am still looking through the series,
> though, maybe I'll change my opinion. ;)
Well, I aggressively stripped all the commits that had a bad RoI on that.
And a lot of these are additive over 21 commits.
So, unfortunately, hacking away at what seem like low cost commits will eat
away at the overall result.
I really did work hard to cut the fat where I could, believe me going
through what remained and a. figuring out what it did, b. rewriting a lot
of the code and c. rewriting commit messages (ahem ;) was NOT fun :)
So I was happy to swing the axe as it saved me in terms of what little
sanity remains ;)
>
> > == allmodconfig FULL build ==
>
> Did you try Clang CONFIG_LTO=y builds?
I tried a CONFIG_LTO_CLANG_THIN in order to check that the *.mod.S stuff
worked correctly, all working correctly.
I can try to get some profiling numbers for thin and full if you want?
>
> > == LLM usage ==
> > [...]
> > I extensively audited and rewrote a lot of it, and heavily edited commit
> > messages, the cover letter and comments.
>
> I feel like the commit logs still need a lot of work. The LLM verbosity
> problem appears in many of them, for example spending 80% of the commit
Well I rewrote the majority of them, so this is a stinging critique of my
commit message writing I guess :)
> log describing every step of some process as background before getting
> to the actual change. I think a human writing this would be much more
> terse about the background. I have, however, been known to be too terse
> in my own commit logs. :P
I mean no, I did write nearly all of them. So I guess err... yeah :)
The testing results and perf numbers are generated and maybe I missed some
bits but generally this is so.
Anyway, I am known to be critical on-list on occasion, so if you dish it
out you have to take it - if you point out specific commit messages that
need work then I can try to put commit msgs on a diet :)
(N.B. I have had feedback like that on a fair few human-written commit
messages of mine lately so there might be some validity to that ;)
>
> > [...]
> > Nothing too controversial was included. There are further improvements that
> > could be made, but they would either by very invasive (large scale C header
> > changes) or generate diminishing returns.
>
> One area I think might solved via an LLM is the 3-pass kallsyms stuff.
> If we could get a deterministic kallsyms build in 1 pass, that would be
> very nice. A lot of people have tried, but it has eluded upstreaming.
"going from three passes to one would save around 8s on an allmodconfig
build and 2 to 3s on defconfig, out of tails that are currently roughly 25s
and 8s." says the LLM :) so that actually does seem worthwhile.
But I think best as a follow up?
I'd like to land the really low-hanging fruit before maybe digging in to
what else we can cut out :)
>
> -Kees
>
> --
> Kees Cook
--
Cheers, Lorenzo
^ permalink raw reply [flat|nested] 58+ messages in thread
* Re: [PATCH v2 00/21] kbuild: significantly speed up kernel builds
2026-09-14 18:25 ` Lorenzo Stoakes (ARM)
@ 2026-09-14 18:43 ` Kees Cook
0 siblings, 0 replies; 58+ messages in thread
From: Kees Cook @ 2026-09-14 18:43 UTC (permalink / raw)
To: Lorenzo Stoakes (ARM)
Cc: Linus Torvalds, Nathan Chancellor, Nicolas Schier,
Nick Desaulniers, Bill Wendling, Justin Stitt, Masahiro Yamada,
Alexey Gladkov, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Paul Walmsley, Palmer Dabbelt,
Albert Ou, Alexandre Ghiti, Arnd Bergmann, Catalin Marinas,
Will Deacon, Mark Rutland, Ard Biesheuvel, Ilias Apalodimas,
Josh Poimboeuf, Peter Zijlstra, Miguel Ojeda, Boqun Feng,
Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg,
Alice Ryhl, Trevor Gross, Danilo Krummrich, Daniel Almeida,
Tamir Duberstein, Alexandre Courbot, Onur Özkan,
Jonathan Corbet, Randy Dunlap, Gustavo A. R. Silva, linux-kbuild,
linux-kernel, llvm, linux-riscv, linux-arch, linux-arm-kernel,
linux-efi, rust-for-linux, linux-doc, Jens Axboe,
linux-hardening
On Mon, Sep 14, 2026 at 07:25:28PM +0100, Lorenzo Stoakes (ARM) wrote:
> On Mon, Sep 14, 2026 at 08:41:39AM -0700, Kees Cook wrote:
> > Did you try Clang CONFIG_LTO=y builds?
>
> I tried a CONFIG_LTO_CLANG_THIN in order to check that the *.mod.S stuff
> worked correctly, all working correctly.
Okay, thanks! I did the same just now too. It seems to be just fine.
> I can try to get some profiling numbers for thin and full if you want?
Mostly I wanted to know if it worked still, and I guess for profiling,
I'd want to make sure it didn't regress how long it took to build. :)
> Well I rewrote the majority of them, so this is a stinging critique of my
> commit message writing I guess :)
Oops! Sorry. I'll go through them again, but I felt like the objtool
commit logs were very long, but perhaps it is justified. ;)
> (N.B. I have had feedback like that on a fair few human-written commit
> messages of mine lately so there might be some validity to that ;)
And as I said, I get told I'm often too terse, so perhaps my sensing
here is broken. :P
> > One area I think might solved via an LLM is the 3-pass kallsyms stuff.
> > If we could get a deterministic kallsyms build in 1 pass, that would be
> > very nice. A lot of people have tried, but it has eluded upstreaming.
>
> "going from three passes to one would save around 8s on an allmodconfig
> build and 2 to 3s on defconfig, out of tails that are currently roughly 25s
> and 8s." says the LLM :) so that actually does seem worthwhile.
It's what I'm always staring at when I do incrementals. ;)
> But I think best as a follow up?
Yeah, I would imagine it'd be separate. (I think a few of these sets of
changes could be landed separately too, like the pigz work.)
--
Kees Cook
^ permalink raw reply [flat|nested] 58+ messages in thread