[PATCH v3 00/20] kbuild: significantly speed up kernel builds

[PATCH v3 00/20] kbuild: significantly speed up kernel builds

[Lorenzo Stoakes (ARM)]

A typical kernel build consists of a frustratingly large amount of time
spent stuck in single-threaded bottlenecks.

It turns out that there's a lot we can do about this and doing so
significantly impacts kernel build times.

This series makes allmodconfig builds up to 36% faster, incremental builds
up to ~70% faster, and noop builds up to ~90% faster.

Builds are faster across the board on every device I tested.

Machines used for perf testing:

* Threadripper -   x86, AMD Threadripper 9980X, 64 cores, 128 threads
* EPYC         -   x86, 2 socket EPYC 9754, 256 cores, 512 threads
* M2           - arm64, 2022 M2 macbook pro, 8 cores, 8 threads
                        (4 perf, 4 efficiency)

Cutting to the chase:

		== IMPORTANT NOTE on dependencies/build configuration ==

Performance numbers are based on a build which:

* Has these series applied (as these supersede changes from a previous
  version of this series):
	https://lore.kernel.org/linux-modules/20260731-module_ver_remove-v2-0-c9163858f382@linuxfoundation.org/
	https://lore.kernel.org/all/cover.1788899473.git.jpoimboe@kernel.org/
* Runs `make KRUSTFLAGS=-Zthreads=8 -j $(nproc) ...`.
* Runs with the pigz tool installed locally.

		== allmodconfig FULL build ==

                        before    after     delta
                      ----------------------------------
Threadripper, gcc       344.2s   278.6s    -65.6s (-19%)
Threadripper, clang     342.6s   266.8s    -75.8s (-22%)
EPYC, gcc               188.0s   121.1s    -66.9s (-36%)
EPYC, clang             259.5s   184.6s    -74.9s (-29%)

		== allmodconfig INCREMENTAL build ==

                        before    after     delta
                      ----------------------------------
Threadripper, gcc        40.1s    15.4s    -24.7s (-62%)
Threadripper, clang      40.3s    15.6s    -24.8s (-61%)
EPYC, gcc                70.9s    24.3s    -46.6s (-66%)
EPYC, clang              70.4s    24.3s    -46.1s (-65%)

		== allmodconfig NO-OP build ==

                        before    after     delta
                      ----------------------------------
Threadripper, gcc        15.3s     1.4s    -13.9s (-91%)
Threadripper, clang      16.2s     1.8s    -14.4s (-89%)
EPYC, gcc                30.6s     1.5s    -29.1s (-95%)
EPYC, clang              32.3s     2.2s    -30.1s (-93%)

		== defconfig FULL build ==

                        before    after     delta
                      ----------------------------------
Threadripper, gcc        32.5s    26.3s     -6.1s (-19%)
Threadripper, clang      34.5s    27.2s     -7.3s (-21%)
EPYC, gcc                28.7s    20.6s     -8.1s (-28%)
EPYC, clang              39.8s    32.2s     -7.6s (-19%)
M2, gcc                 519.3s   512.4s     -6.9s (-1%)
M2, clang               634.5s   569.4s    -65.1s (-10%)

		== defconfig INCREMENTAL build ==

                        before    after     delta
                      ----------------------------------
Threadripper, gcc        11.2s     6.0s     -5.3s (-47%)
Threadripper, clang      11.3s     5.4s     -5.9s (-52%)
EPYC, gcc                18.6s     9.2s     -9.4s (-51%)
EPYC, clang              19.6s     8.6s    -11.0s (-56%)
M2, gcc                  18.0s     9.9s     -8.1s (-45%)
M2, clang                18.1s     8.2s     -9.9s (-55%)

		== defconfig NO-OP build ==

                        before    after     delta
                      ----------------------------------
Threadripper, gcc         1.1s    0.60s    -0.50s (-45%)
Threadripper, clang       1.3s    0.66s    -0.63s (-49%)
EPYC, gcc                 1.7s    0.66s     -1.0s (-61%)
EPYC, clang               2.0s    0.80s     -1.2s (-60%)
M2, gcc                   6.4s     1.7s     -4.7s (-74%)
M2, clang                 7.1s     1.7s     -5.4s (-76%)

Further performance numbers are provided for each commit giving a sense of
what each contributes to the final result.

			== Testing ==

Beyond x86, allmodconfig was built with the series for arm64, arm, riscv,
powerpc64, s390 and loongarch, and for arm64, arm, s390 and loongarch the
System.map is identical to what the previous shell mksysmap produces for
the same vmlinux.

Also tested were parisc64 and m68k build as far as mainline lets them
(a driver's static assertion and an undefined-symbol check on parisc, gcc
16 internal compiler errors on m68k, none of it from this series).

Kernels for x86, arm64, arm, riscv, loongarch, powerpc64, s390, m68k and
parisc64 all boot under qemu, every text symbol of System.map is in
/proc/kallsyms at the relocated address, and a module loads and unloads.
The s390, arm and loongarch kernels also pass the kallsyms selftest.

An x86 kernel with CONFIG_MODVERSIONS, CONFIG_EXTENDED_MODVERSIONS and
CONFIG_MODULE_SRCVERSION_ALL boots, loads and unloads modules. External
modules build against both in-tree and O= builds, and every commit builds
on x86 defconfig.

Build times are the best of several runs, no unexpected errors or
warnings were seen.

While some aspects of the build process have been changed, all tooling
should function identically to before.

			== LLM usage ==

An LLM was used to first determine where the bottlenecks were then to
figure out how to improve them.

It generated a lot of code, much of it hideous.

I extensively audited and rewrote a lot of it, and heavily edited commit
messages, the cover letter and comments.

The LLM has also orchestrated build runs, testing, debugging and analysis.

I have manually checked for correctness in both build and running kernels
generated with this series applied.

Performance improvements were also verified manually.

Since an LLM was used extensively, each commit carries an Assisted-by tag.

			== What was changed? ==

Fundamentally the series improves build times by parallelising
single-threaded tasks as much as possible and improving the efficiency of
code used in the build process.

kbuild, kallsyms, modpost, objtool, mksysmap and the rust build system were
all updated as part of this change.

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.

			== Patches ==

   kbuild (1):       Make .modinfo an INFO section.

   kallsyms (2, 3):  Some efficiency improvements through use of a cache.

   kbuild (4, 5):    Don't sort nm output unnecessarily, do not include
                     relocations in the kallsyms trial links.

   elf-parse (6):    Section flags, symbol binding and a read-only mapping,
                     for the next patch.

   kallsyms (7):     Don't use nm, read the ELF symbol table directly.

   kbuild (8, 9):    Implement a cache to track objects, check dependency
                     timestamps more efficiently.

   kbuild (10):      Move the toolchain checks into their own Kconfig file.

   kbuild (11):      Probe compiler, linker flags once at top of build.

   modpost (12):     Improve performance through use of a cache.

   modules (13, 14): Emit module descriptors as assembly (*.mod.S) rather
                     than C (*.mod.c), reducing CPU seconds taken by 10x to
                     perform the task. Also shard module finalisation
                     rather than running 10's of thousands of tiny runs.

   objtool (15-17):  Replace reloc hash with a per-section index, size
                     the instruction hash to the code rather than hard-code
                     it, and decode large objects over multiple threads.

   rust (18, 19):    Set correct dependencies and build crates in parallel
                     with C code, retaining the requirement that rust/
                     crates are built first.

   kbuild (20):      Default to using a parallel implementation of gzip
                     (pigz) if available on the system.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
v3:
* Rebased on Linus's master branch.
* Fixed link to Josh's series, which was wrongly pointing at a single
  commit as per Andre (off-list).
* Fixed typo in 11/20 (+ fixed a couple more), as per John.
* Hardened depcheck in 9/20 against a .cmd file with an empty name as per
  Sashiko.
* Updated 14/20 so only the top-level make instance builds .module-common.o
  the chunk instances treat it as a plain prerequisite, to prevent a child
  accidentally building it as per Sashiko.
* Updated 15/20 to drop the relocation hash altogether, building one
  section at a time incrementally, falling back to linear scan for anything
  out of order (not sure that'll ever happen though?) as per Josh, Linus.
* Updated 17/20 to limit the parallelisation to the --link step only (in
  practice - objtool's processing of vmlinux.o) + updated commit msg to
  reflect, as per Kees.
* Updated the commit message in 14/20 to give clearer rationales for the
  batching of modfinal instances, as per Kees.
* Dropped what was 18/21 - the rustc front end threading patch, as the
  parallel flag name is still uncertain and a user can set
  KRUSTFLAGS=-Zthreads=8 to get the behaviour without it. Also updated
  cover letter pre-requisite section to mention this, as per Miguel.
* Updated 19/20 (was 20/21) so modules_prepare no longer builds rust/
  when a goal that builds the tree is also given, ensuring duplicate rust/
  builds do not happen, as per Kees.
* Updated 20/20 (was 21/21) to remove the reproducible build doc update,
  as per Kees.
* Updated 20/20 (was 21/21) to have pigz use the make job server and to
  define a specific kernel build variable for this - KPGZIP - also fold
  in a further suggestion which eliminates a wrapper script, as per Kees.

v2:
* Rebased on Linus's master branch.
* Removed the first 2 fix patches as they have been taken to upstream in
  commit 281b61d408d4 ("scripts/mksysmap: drop the MODULE_INFO() symbols
  from kallsyms") and commit 59351365ac27 ("scripts/mksysmap: fix escape of
  '$' in the __pi_ pattern") - thanks Nicolas!
* Fixed patch 3/21 (previously 4/23) to check error on close via ferror()
  and fclose() as per David Laight.
* Updated 21/21 to not use threads for modules, only for vmlinux, and
  updated docs to reflect this.
* Dropped patches (as was) 13 and 17 as the equivalent work is being
  performed upstream:
  https://lore.kernel.org/linux-modules/20260731-module_ver_remove-v2-0-c9163858f382@linuxfoundation.org/
* Updated the cover letter to mention the dependency on this series for
  perf numbers.
* Fixed various typos.
* Checked all of the hallucinated sashiko reports. Replied inline to emails
  to keep a record of them but not going to repeat here, unless people want
  a list.
* Fixed up 9/21 (was 11/23) to fix the bit of sashiko's report that wasn't
  hallucinated - check ferror() to bring depcheck in line with fixdep and
  kallsyms.
* Fixed up patch 13/21 (was 15/23) to emit the __this_module fields in
  offset order to handle CONFIG_RANDSTRUCT as per Sashiko.
* Fixed up patch 19/23 (now 17/21) to resolve various races. Sashiko
  hallucinated a lot of the report, and missed some stuff thread sanitizer
  found. Resolve call destinations serially to resolve most of the valid
  stuff and add a lock around pv_ops, and instruction hash freed
  properly. Tested and confirmed resolved locally, as per Sashiko.
* Fixed up patch 20/21 (was 22/23) to only build rust/ when modules_prepare
  is one of several make goals, rather than the only one. This matches the
  rest of the Makefile's behaviour on this and ensures rust components are
  built if multiple build choices are passed to make, as per Sashiko.
* Fixed up patch 5/21 (was 6/23) to test CONFIG_ARCH_VMLINUX_NEEDS_RELOCS
  directly in link-vmlinux.sh rather than plumbing a var through, for a far
  smaller patch as per Nathan.
* Moved patch 1/21 (was 9/23) to the front of the series and dropped two
  comments, as per Nathan, so it can go in ahead of the rest.
* Added patch 10/21 moving the existing toolchain checks out of
  init/Kconfig into init/Kconfig.toolchain, as per Nathan, with 11/21
  adding to it.
* In 11/21 (previously 12/23) Moved -fno-stack-clash-protection back to
  the Makefile to fix an issue with ppc32 as per Nathan.
* Updated patch 15/21 (was 18/23) to drop the dead end cache as Josh has
  one in his noreturn series:
  https://lore.kernel.org/9d4b8ccfed745ac47a954aa2e1de62a85197122d.1788899473.git.jpoimboe@kernel.org
* Also updated patch 15/21 (was 18/23) to hash relocation sections objtool
  creates itself and moved cache-to-hash copy into elf_create_reloc(), as
  per Josh.
* Split the instruction hash sizing out of patch 17/21 (was 19/23) into its
  own patch 16/21, as per Josh.
* Made the rustc parallel front end opt-in in patch 18/21 (was 20/23) via
  KBUILD_RUST_THREADS, as its output is not yet reproducible, and dropped
  the probe for the planned -j flag, as per Björn, Miguel and Nicolas.
* Tested changes to ensure any flagged issues were resolved and that
  nothing broke.
* Did a re-run of profiling numbers to reflect changes and updated cover
  letter and commit messages.
https://lore.kernel.org/r/20260914-build-speedup-v2-0-39817ec5db23@kernel.org

v1:
https://lore.kernel.org/r/20260908-build-speedup-v1-0-5dc1ac01672d@kernel.org

---
Lorenzo Stoakes (ARM) (20):
      kbuild: do not allocate .modinfo in vmlinux
      kallsyms: index symbols by token to speed up table compression
      kallsyms: output binary data to speed output and kallsyms assembly
      kbuild: do not sort nm output where the order is irrelevant
      kbuild: only emit vmlinux relocations when required
      elf-parse: add section flags, symbol binding and a read-only mapping
      kallsyms: reimplement mksysmap in C
      kbuild: cache list, composite object state per object
      kbuild: implement and use depcheck to check dependency timestamps
      kbuild: move the toolchain checks into init/Kconfig.toolchain
      kbuild: avoid re-running compiler and linker probes
      modpost: cache section relocation mismatch state
      modpost: emit module descriptors as assembly
      kbuild: batch module finalisation
      objtool: cache relocations, do less work, eliminate relocation hash
      objtool: size the instruction hash to the text
      objtool: decode instructions and resolve branch targets in parallel
      rust: make exports.o depend on the headers generated for it
      kbuild: build rust crates in parallel with the rest of the build
      kbuild: compress the kernel with pigz if available

 .gitignore                              |   1 +
 Documentation/kbuild/kbuild.rst         |  17 +
 Documentation/process/changes.rst       |   8 +
 Kbuild                                  |   5 +
 Makefile                                |  48 +-
 arch/arm64/kernel/pi/Makefile           |   2 +-
 arch/riscv/kernel/pi/Makefile           |   2 +-
 arch/x86/Kconfig                        |  17 +
 arch/x86/Makefile                       |  12 +-
 arch/x86/boot/Makefile                  |   2 +-
 arch/x86/boot/compressed/Makefile       |   2 +-
 drivers/firmware/efi/libstub/Makefile   |   2 +-
 include/asm-generic/vmlinux.lds.h       |   2 +-
 include/linux/vermagic.h                |   2 +-
 init/Kconfig                            | 197 +-------
 init/Kconfig.toolchain                  | 272 +++++++++++
 kernel/Makefile                         |   6 +-
 rust/Makefile                           |   5 +
 scripts/Makefile                        |   4 +-
 scripts/Makefile.build                  |  27 +-
 scripts/Makefile.lib                    |  11 +-
 scripts/Makefile.modfinal               |  40 +-
 scripts/Makefile.modpost                |   2 +-
 scripts/Makefile.vmlinux                |  22 +-
 scripts/Makefile.warn                   |  28 +-
 scripts/basic/.gitignore                |   1 +
 scripts/basic/Makefile                  |   2 +-
 scripts/basic/depcheck.c                | 441 ++++++++++++++++++
 scripts/check-function-names.sh         |   3 +-
 scripts/elf-parse.c                     |  48 +-
 scripts/elf-parse.h                     |  19 +
 scripts/jobserver-exec                  |   3 +-
 scripts/kallsyms-sysmap.c               | 269 +++++++++++
 scripts/kallsyms.c                      | 374 +++++++++++-----
 scripts/kallsyms.h                      |  44 ++
 scripts/link-vmlinux.sh                 |  24 +-
 scripts/mksysmap                        |  94 ----
 scripts/mod/.gitignore                  |   1 +
 scripts/mod/Makefile                    |   8 +
 scripts/mod/modpost.c                   | 703 ++++++++++++++++++++++-------
 scripts/mod/module-offsets.c            |  35 ++
 scripts/tags.sh                         |   5 +-
 tools/lib/python/jobserver.py           |  13 +
 tools/objtool/Makefile                  |   2 +-
 tools/objtool/check.c                   | 771 ++++++++++++++++++++++++--------
 tools/objtool/elf.c                     | 204 +++++++--
 tools/objtool/include/objtool/elf.h     |  10 +-
 tools/objtool/include/objtool/objtool.h |   3 +-
 tools/objtool/objtool.c                 |  15 +-
 49 files changed, 2925 insertions(+), 903 deletions(-)
---
base-commit: 238650ef6c7c7cca08e032527329424c9fbd70e5
change-id: 20260904-build-speedup-25e11a00b3d0

Best regards,
-- 
Lorenzo Stoakes (ARM) <ljs@kernel.org>

[PATCH v3 01/20] kbuild: do not allocate .modinfo in vmlinux

[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

[PATCH v3 02/20] kallsyms: index symbols by token to speed up table compression

[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

[PATCH v3 03/20] kallsyms: output binary data to speed output and kallsyms assembly

[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

[PATCH v3 04/20] kbuild: do not sort nm output where the order is irrelevant

[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

[PATCH v3 05/20] kbuild: only emit vmlinux relocations when required

[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

[PATCH v3 06/20] elf-parse: add section flags, symbol binding and a read-only mapping

[Lorenzo Stoakes (ARM)]

Extend elf-parse to be able to read the symbol table of vmlinux in
kallsyms.

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

[PATCH v3 07/20] kallsyms: reimplement mksysmap in C

[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

[PATCH v3 08/20] kbuild: cache list, composite object state per object

[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

[PATCH v3 09/20] kbuild: implement and use depcheck to check dependency timestamps

[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 | 441 +++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 457 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..622101c33650
--- /dev/null
+++ b/scripts/basic/depcheck.c
@@ -0,0 +1,441 @@
+// 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;
+	const size_t affix_len = strlen(".") + strlen(CMD_SUFFIX);
+	const size_t base_len = strlen(base);
+
+	if (base[0] != '.' || !str_ends_with(base, CMD_SUFFIX) ||
+	    base_len <= affix_len)
+		return false;
+
+	return snprintf(target, size, "%.*s%.*s", (int)dir_len, cmd_path,
+			(int)(base_len - affix_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

[PATCH v3 10/20] kbuild: move the toolchain checks into init/Kconfig.toolchain

[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

[PATCH v3 11/20] kbuild: avoid re-running compiler and linker probes

[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 subtle 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

[PATCH v3 12/20] modpost: cache section relocation mismatch state

[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 &sectioncheck[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

[PATCH v3 13/20] modpost: emit module descriptors as assembly

[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

[PATCH v3 14/20] kbuild: batch module finalisation

[Lorenzo Stoakes (ARM)]

With the .mod.S change in place, module finalisation on allmodconfig builds
consists of a large number of very short-lived jobs.

For allmodconfig x86-64 this can be on the order of ~22,000 jobs of a few
milliseconds in duration each.

Each job entails processing ~22k .cmd files, so the combination of heavy
overhead and small individual job results in a lot of unnecessary and
repeated work even with all cores being utilised.

The solution is to batch by a number of jobs. Determining which value makes
sense was done empirically.

On a 128-thread threadripper box doing an allmodconfig build, best of
2, *.ko, *.mod.o deleted each time:

    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

Wall time flattens for 16-256 module batches.

A slower/lower core machine will do better with fewer modules-per-batch, a
faster/higher core machine will do better with more modules-per-batch.

Therefore, take the midpoint which works in the most margin in either
direction - 128 modules per batch.

This naturally scales with module count too as the optimum gains are
obtained with higher module count, so fewer batches in this case costs less
overhead.

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>.

Only the top-level instance builds .module-common.o, to the chunks it is a
plain prerequisite, so no two instances ever write it.

"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 | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 75e9effdf02c..4d5e6e1a0ff9 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
@@ -29,8 +50,11 @@ quiet_cmd_as_mod_o = AS [M]  $@
 %.mod.o: %.mod.S FORCE
 	$(call if_changed,as_mod_o)
 
+# Built by the top-level instance alone, the chunks take it as a plain file.
+ifndef modfinal-first
 .module-common.o: $(srctree)/scripts/module-common.c FORCE
 	$(call if_changed_rule,cc_o_c)
+endif
 
 ifneq ($(WARN_ON_UNUSED_TRACEPOINTS),)
 cmd_check_tracepoint = $(objtree)/scripts/tracepoint-update --module $<;
@@ -58,7 +82,11 @@ ifdef CONFIG_DEBUG_INFO_BTF_MODULES
 endif
 	+$(call cmd,check_tracepoint)
 
-targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o) .module-common.o
+ifdef modfinal-first
+targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o)
+else
+targets += .module-common.o
+endif
 
 # Add FORCE to the prerequisites of a target to force it to be always rebuilt.
 # ---------------------------------------------------------------------------

-- 
2.55.0

[PATCH v3 15/20] objtool: cache relocations, do less work, eliminate relocation hash

[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.

With this in place the relocation hash is unnecessary and removed. This
saves ~90 MiB in peak memory usage for an allmodconfig build.

If anything is processed out of order, fall back to a linear scan.

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().

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 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 the gcc allmodconfig vmlinux.o goes from 10.5s to 9.0s, clang
from 9.8s to 8.3s and gcc defconfig from 2.08s to 1.79s, with peak memory
down ~90 MiB on allmodconfig.

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                 | 204 ++++++++++++++++++++++++++++--------
 tools/objtool/include/objtool/elf.h |  10 +-
 2 files changed, 162 insertions(+), 52 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index a791f4ea6ec1..8524d287621b 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -316,45 +316,165 @@ 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);
+}
+
+/* Index the first relocation at or after each 64 byte window of the base. */
+#define RELOC_CACHE_INDEX_SHIFT	6
+
+static unsigned long reloc_cache_index(unsigned long offset)
+{
+	return offset >> RELOC_CACHE_INDEX_SHIFT;
+}
+
+static void reloc_cache_free(struct section *rsec)
+{
+	free(rsec->reloc_cache);
+	rsec->reloc_cache = NULL;
+	rsec->nr_cache_windows = 0;
+	rsec->nr_indexed = 0;
+	rsec->sorted = false;
+}
+
+/* Grow the index to cover the base section, new windows start past the end. */
+static int reloc_cache_resize(struct section *rsec)
+{
+	const unsigned int nr_windows = reloc_cache_index(sec_size(rsec->base)) + 1;
+	unsigned int *cache;
+
+	if (nr_windows <= rsec->nr_cache_windows)
+		return 0;
+
+	cache = realloc(rsec->reloc_cache, nr_windows * sizeof(*cache));
+	if (!cache) {
+		ERROR_GLIBC("realloc");
+		return -1;
+	}
+
+	while (rsec->nr_cache_windows < nr_windows)
+		cache[rsec->nr_cache_windows++] = rsec->nr_indexed;
+	rsec->reloc_cache = cache;
+
+	return 0;
+}
+
+/*
+ * Index the next relocation. It must follow the previous one in position and
+ * offset, otherwise the section is scanned from now on.
+ */
+static int reloc_cache_add(struct section *rsec, unsigned int reloc_idx)
+{
+	const unsigned long offset = reloc_offset(&rsec->relocs[reloc_idx]);
+	const unsigned long window = reloc_cache_index(offset);
+	unsigned long first_window = 0;
+
+	if (reloc_idx != rsec->nr_indexed)
+		goto unsorted;
+
+	if (reloc_idx) {
+		const unsigned long prev = reloc_offset(&rsec->relocs[reloc_idx - 1]);
+
+		if (offset < prev)
+			goto unsorted;
+		first_window = reloc_cache_index(prev) + 1;
+	}
+
+	if (reloc_cache_resize(rsec))
+		return -1;
+	if (window >= rsec->nr_cache_windows)
+		goto unsorted;
+
+	while (first_window <= window)
+		rsec->reloc_cache[first_window++] = reloc_idx;
+	rsec->nr_indexed = reloc_idx + 1;
+
+	return 0;
+
+unsorted:
+	reloc_cache_free(rsec);
+	return 0;
+}
+
+static int init_reloc_cache(struct section *rsec)
+{
+	const unsigned int nr_relocs = sec_num_entries(rsec);
+	unsigned int reloc_idx;
+
+	rsec->sorted = true;
+	for (reloc_idx = 0; reloc_idx < nr_relocs; reloc_idx++) {
+		if (reloc_cache_add(rsec, reloc_idx))
+			return -1;
+		if (!rsec->sorted)
+			break;
+	}
+
+	return 0;
+}
+
+static bool reloc_in_range(struct reloc *reloc, unsigned long offset,
+			   unsigned int len)
+{
+	return reloc_offset(reloc) >= offset && reloc_offset(reloc) < offset + len;
+}
+
+/* The index gives a lower bound, scan on from there. */
+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;
+	const unsigned long cache_idx = reloc_cache_index(offset);
+	unsigned int reloc_idx;
 
-	rsec = sec->rsec;
-	if (!rsec)
+	if (cache_idx >= rsec->nr_cache_windows)
 		return NULL;
 
-	for_offset_range(o, offset, offset + len) {
-		elf_hash_for_each_possible(elf, reloc, reloc, hash,
-					   sec_offset_hash(rsec, o)) {
-			if (reloc->sec != rsec)
-				continue;
+	for (reloc_idx = rsec->reloc_cache[cache_idx];
+	     reloc_idx < rsec->nr_indexed; reloc_idx++) {
+		struct reloc *reloc = &rsec->relocs[reloc_idx];
 
-			if (reloc_offset(reloc) >= offset &&
-			    reloc_offset(reloc) < offset + len) {
-				if (!r || reloc_offset(reloc) < reloc_offset(r))
-					r = reloc;
-			}
-		}
-		if (r && (reloc_offset(r) & OFFSET_STRIDE_MASK) == o)
-			return r;
+		if (reloc_offset(reloc) >= offset)
+			return reloc_in_range(reloc, offset, len) ? reloc : NULL;
 	}
 
-	return r;
+	return NULL;
 }
 
-struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
+/* Out of order sections, only ever DWARF or one objtool grew that way. */
+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;
+
+	for_each_reloc(rsec, reloc) {
+		if (!reloc->sec || !reloc_in_range(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);
+
+	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 +1191,8 @@ 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->sorted && reloc_cache_add(rsec, reloc_idx))
+		return NULL;
 	set_sym_next_reloc(reloc, sym->relocs);
 	sym->relocs = reloc;
 
@@ -1125,16 +1246,13 @@ struct reloc *elf_init_reloc_data_sym(struct elf *elf, struct section *sec,
 
 static int read_relocs(struct elf *elf)
 {
-	unsigned long nr_reloc, max_reloc = 0;
+	unsigned long nr_reloc, max_reloc = 0, nr_linear = 0;
 	struct section *rsec;
 	struct reloc *reloc;
 	unsigned int symndx;
 	struct symbol *sym;
 	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;
@@ -1168,19 +1286,26 @@ static int read_relocs(struct elf *elf)
 				return -1;
 			}
 
-			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);
+
+		/* DWARF relocs are never looked up, so are not worth indexing. */
+		if (is_dwarf_section(rsec->base))
+			continue;
+		if (init_reloc_cache(rsec))
+			return -1;
+		if (!rsec->sorted)
+			nr_linear += nr_reloc;
 	}
 
 	if (opts.stats) {
 		printf("max_reloc: %lu\n", max_reloc);
 		printf("num_relocs: %lu\n", elf->num_relocs);
-		printf("reloc_bits: %d\n", elf->reloc_bits);
+		printf("num_relocs_linear: %lu\n", nr_linear);
 	}
 
 	return 0;
@@ -1327,8 +1452,7 @@ struct elf *elf_create_file(GElf_Ehdr *ehdr, const char *name)
 	if (!elf_alloc_hash(section,		1000) ||
 	    !elf_alloc_hash(section_name,	1000) ||
 	    !elf_alloc_hash(symbol,		10000) ||
-	    !elf_alloc_hash(symbol_name,	10000) ||
-	    !elf_alloc_hash(reloc,		100000))
+	    !elf_alloc_hash(symbol_name,	10000))
 		return NULL;
 
 	null		= elf_create_section(elf, NULL, 0, 0, SHT_NULL, 0, 0);
@@ -1508,6 +1632,8 @@ struct section *elf_create_section(struct elf *elf, const char *name,
 	sec->sh.sh_type = type;
 	sec->sh.sh_addralign = align;
 	sec->sh.sh_flags = flags;
+	/* Relocations objtool adds are indexed as they come. */
+	sec->sorted = type == SHT_RELA;
 
 	if (name) {
 		sec->name = strdup(name);
@@ -1633,16 +1759,6 @@ static int elf_alloc_reloc(struct elf *elf, struct section *rsec)
 	}
 
 	memcpy(new_relocs, old_relocs, nr_relocs_old * sizeof(struct reloc));
-
-	for (int i = 0; i < nr_relocs_old; i++) {
-		struct reloc *old = &old_relocs[i];
-		struct reloc *new = &new_relocs[i];
-		u32 key = reloc_hash(old);
-
-		elf_hash_del(reloc, &old->hash, key);
-		elf_hash_add(reloc, &new->hash, key);
-	}
-
 	free(old_relocs);
 done:
 	rsec->relocs = new_relocs;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index a82517a76a0f..ba18e188fc5f 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 sorted;
+	unsigned int *reloc_cache, nr_cache_windows, nr_indexed;
 	struct reloc *relocs;
 	unsigned long nr_alloc_relocs;
 	struct section *twin;
@@ -106,7 +108,6 @@ struct symbol {
 };
 
 struct reloc {
-	struct elf_hash_node hash;
 	struct section *sec;
 	struct symbol *sym;
 	unsigned long _sym_next_reloc;
@@ -127,13 +128,11 @@ struct elf {
 	int symbol_name_bits;
 	int section_bits;
 	int section_name_bits;
-	int reloc_bits;
 
 	struct elf_hash_node **symbol_hash;
 	struct elf_hash_node **symbol_name_hash;
 	struct elf_hash_node **section_hash;
 	struct elf_hash_node **section_name_hash;
-	struct elf_hash_node **reloc_hash;
 
 	struct section *section_data;
 	struct symbol *symbol_data;
@@ -575,9 +574,4 @@ static inline u32 sec_offset_hash(struct section *sec, unsigned long offset)
 	return ol;
 }
 
-static inline u32 reloc_hash(struct reloc *reloc)
-{
-	return sec_offset_hash(reloc->sec, reloc_offset(reloc));
-}
-
 #endif /* _OBJTOOL_ELF_H */

-- 
2.55.0

[PATCH v3 16/20] objtool: size the instruction hash to the text

[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

[PATCH v3 17/20] objtool: decode instructions and resolve branch targets in parallel

[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, but
limit this to invocations that pass --link, and only where the there is 8
MiB or more text to justify it.

In practice this limits this to processing vmlinux.o in the kernel build
and modules are processed as they were before.

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.

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   | 717 ++++++++++++++++++++++++++++++++++++------------
 tools/objtool/objtool.c |  14 +-
 3 files changed, 546 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..52af91e048a2 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 the vmlinux.o link, and only if it is this large, runs 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 +460,350 @@ 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);
+
+	/* Modules are processed inside the parallel build, on one thread. */
+	if (!opts.link || opts.module)
+		return 1;
+	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 +828,20 @@ 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 +1884,147 @@ 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 +2039,82 @@ 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 +3083,8 @@ 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

[PATCH v3 18/20] rust: make exports.o depend on the headers generated for it

[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

[PATCH v3 19/20] kbuild: build rust crates in parallel with the rest of the build

[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,
and that only one rust/ build will be performed at any one time.

External rust modules builds are unaffected - 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               | 13 ++++++++++++-
 scripts/Makefile.build |  5 ++++-
 3 files changed, 21 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 8263fc8a86b3..ede9cfeffd56 100644
--- a/Makefile
+++ b/Makefile
@@ -1425,11 +1425,14 @@ 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
@@ -1756,6 +1759,14 @@ modules: modules_prepare
 # Target to prepare building external modules
 modules_prepare: prepare
 	$(Q)$(MAKE) $(build)=scripts scripts/module.lds
+ifdef CONFIG_RUST
+# Avoid two instances of rust/ being built at any one time.
+ifneq ($(filter modules_prepare,$(MAKECMDGOALS)),)
+ifeq ($(filter all vmlinux modules %Image% dtbs rustdoc rusttest,$(MAKECMDGOALS)),)
+	$(Q)$(MAKE) $(build)=rust
+endif
+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

[PATCH v3 20/20] kbuild: compress the kernel with pigz if available

[Lorenzo Stoakes (ARM)]

The gzip step of a kernel build is very lengthy, 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.

Therefore introduce the KPGZIP build variable which specifies the
compressor to use for the kernel image and default it to pigz if available,
or KGZIP otherwise (which itself defaults to gzip).

Modules, packaging and the embedded kernel configuration (CONFIG_IKCONFIG)
continue to use KGZIP which defaults to a single-threaded gzip instance.

Module compression is run in parallel by make, so pigz offers no benefit
there, packaging sits outside the build and the embedded configuration is
too small to matter.

pigz is executed using scripts/jobserver-exec, which reserves the job slots
make has free - necessary, as otherwise pigz would just grab unbounded
CPUs.

The kernel image compression step is always performed at the end of the
build so should typically have all job slots available.

pigz always provides byte-for-byte identical output across runs regardless
of thread count, but pigz and gzip are not guaranteed to generate the same
binary output, so reproducible builds must use the same tools consistently.

Also update Documentation/kbuild/kbuild.rst to describe KPGZIP and
Documentation/process/changes.rst to list the optional pigz dependency.

While there, add entries for the other compressor programs.

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%)

Suggested-by: Kees Cook <kees@kernel.org>
Link: https://zlib.net/pigz/
Assisted-by: LLM
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 Documentation/kbuild/kbuild.rst   | 17 +++++++++++++++++
 Documentation/process/changes.rst |  8 ++++++++
 Makefile                          |  5 ++++-
 kernel/Makefile                   |  6 +++++-
 scripts/Makefile.lib              |  4 ++--
 scripts/jobserver-exec            |  3 ++-
 tools/lib/python/jobserver.py     | 13 +++++++++++++
 7 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
index 5a9013bacfb7..e71a692a559a 100644
--- a/Documentation/kbuild/kbuild.rst
+++ b/Documentation/kbuild/kbuild.rst
@@ -110,6 +110,23 @@ HOSTLDLIBS
 ----------
 Additional libraries to link against when building host programs.
 
+KGZIP
+-----
+The gzip program used for compressed modules, packaging and the embedded
+kernel configuration. Defaults to gzip.
+
+KPGZIP
+------
+The gzip program used for the compressed kernel image. Defaults to pigz (a
+parallel implementation of gzip), run under scripts/jobserver-exec so that it
+uses the job slots make has free, if pigz is installed, otherwise to
+``KGZIP``. Set ``KPGZIP=`` on the make command line to use another program.
+
+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/process/changes.rst b/Documentation/process/changes.rst
index 0aa232b117b5..28f2ca63318e 100644
--- a/Documentation/process/changes.rst
+++ b/Documentation/process/changes.rst
@@ -55,6 +55,7 @@ nfs-utils              1.0.5            showmount --version
 openssl & libcrypto    1.0.0            openssl version
 pahole                 1.26             pahole --version
 pcmciautils            004              pccardctl -V
+pigz (optional)        2.4              pigz --version
 PPP                    2.4.0            pppd --version
 procps                 3.2.0            ps --version
 Python                 3.9.x            python3 --version
@@ -206,6 +207,13 @@ GNU AWK
 GNU AWK is needed if you want kernel builds to generate address range data for
 builtin modules (CONFIG_BUILTIN_MODULE_RANGES).
 
+pigz (optional)
+---------------
+
+pigz is a parallel implementation of gzip. If it is installed the compressed
+kernel image is produced with it rather than with gzip, see ``KPGZIP`` in
+Documentation/kbuild/kbuild.rst.
+
 System utilities
 ****************
 
diff --git a/Makefile b/Makefile
index ede9cfeffd56..d50bcb480134 100644
--- a/Makefile
+++ b/Makefile
@@ -568,6 +568,9 @@ LZMA		= lzma
 LZ4		= lz4
 XZ		= xz
 ZSTD		= zstd
+# The kernel image is compressed with pigz, on the job slots make has free,
+# if it is installed. Everything else uses KGZIP.
+KPGZIP		:= $(if $(shell command -v pigz 2>/dev/null),$(PYTHON3) $(abs_srctree)/scripts/jobserver-exec pigz -p %PARALLELISM%,$(KGZIP))
 TAR		= tar
 
 CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
@@ -648,7 +651,7 @@ export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN LLVM_
 export HOSTRUSTC KBUILD_HOSTRUSTFLAGS
 export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL
 export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
-export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD TAR
+export KGZIP KPGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD TAR
 export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS KBUILD_PROCMACROLDFLAGS LDFLAGS_MODULE
 export KBUILD_USERCFLAGS KBUILD_USERLDFLAGS
 
diff --git a/kernel/Makefile b/kernel/Makefile
index 1e1a31673577..c64c82c96b40 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -153,9 +153,13 @@ obj-$(CONFIG_SCF_TORTURE_TEST) += scftorture.o
 
 $(obj)/configs.o: $(obj)/config_data.gz
 
+# .config is small, so it is compressed with gzip rather than the image compressor.
+quiet_cmd_gzip_config = GZIP    $@
+      cmd_gzip_config = cat $(real-prereqs) | $(KGZIP) -n -f -9 > $@
+
 targets += config_data config_data.gz
 $(obj)/config_data.gz: $(obj)/config_data FORCE
-	$(call if_changed,gzip)
+	$(call if_changed,gzip_config)
 
 filechk_cat = cat $<
 
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 2f447bc25e7b..8936925d4d50 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -332,11 +332,11 @@ quiet_cmd_ar = AR      $@
 quiet_cmd_objcopy = OBJCOPY $@
 cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
 
-# Gzip
+# Gzip, for the kernel image
 # ---------------------------------------------------------------------------
 
 quiet_cmd_gzip = GZIP    $@
-      cmd_gzip = cat $(real-prereqs) | $(KGZIP) -n -f -9 > $@
+      cmd_gzip = cat $(real-prereqs) | $(KPGZIP) -n -f -9 > $@
 
 # Bzip2
 # ---------------------------------------------------------------------------
diff --git a/scripts/jobserver-exec b/scripts/jobserver-exec
index 21b319e6c9a5..89119acb1b9e 100755
--- a/scripts/jobserver-exec
+++ b/scripts/jobserver-exec
@@ -4,7 +4,8 @@
 """
 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.
+with PARALLELISM environment variable set and any %PARALLELISM% in its
+arguments replaced by the count, and releases the jobs back again.
 
 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..7e94635bf7d9 100755
--- a/tools/lib/python/jobserver.py
+++ b/tools/lib/python/jobserver.py
@@ -29,6 +29,10 @@ $claim child to do the actual work.
 The end goal here is to keep the total number of build tasks under the
 limit established by the initial ``make -j$n_proc`` call.
 
+A command that takes its thread count on the command line rather than from
+the environment can use the ``%PARALLELISM%`` token in its arguments, which
+is replaced by the count, or by 1 when there is no jobserver.
+
 See:
     https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
 """
@@ -38,6 +42,8 @@ import os
 import subprocess
 import sys
 
+PARALLELISM_TOKEN = "%PARALLELISM%"
+
 def warn(text, *args):
     print(f'WARNING: {text}', *args, file = sys.stderr)
 
@@ -182,6 +188,9 @@ class JobserverExec:
         Run a command setting PARALLELISM env variable to the number of
         available job slots (claim) + 1, e.g. it will reserve claim slots
         to do the actual build work, plus one to monitor its children.
+
+        Any %PARALLELISM% in the command's arguments is replaced by the same
+        number, or by 1 when there is no jobserver.
         """
         self.open()             # Ensure that self.claim is set
 
@@ -192,4 +201,8 @@ class JobserverExec:
         if self.claim:
             os.environ["PARALLELISM"] = str(self.claim)
 
+        if not isinstance(cmd, str):
+            parallelism = str(self.claim or 1)
+            cmd = [arg.replace(PARALLELISM_TOKEN, parallelism) for arg in cmd]
+
         return subprocess.call(cmd, *args, **pwargs)

-- 
2.55.0

Re: [PATCH v3 01/20] kbuild: do not allocate .modinfo in vmlinux

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:11PM +0100, Lorenzo Stoakes (ARM) wrote:
> -# .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.

This comment still seems useful here (afaict the stripping is still
happening with the "sed"). Maybe better to leave it, or future readers
are left wondering what the sed is for?

>  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' $@

Otherwise, looks good. With the comment back (or rewritten):

Reviewed-by: Kees Cook <kees@kernel.org>

-Kees

-- 
Kees Cook

Re: [PATCH v3 20/20] kbuild: compress the kernel with pigz if available

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:30PM +0100, Lorenzo Stoakes (ARM) wrote:
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> ---
>  Documentation/kbuild/kbuild.rst   | 17 +++++++++++++++++
>  Documentation/process/changes.rst |  8 ++++++++
>  Makefile                          |  5 ++++-
>  kernel/Makefile                   |  6 +++++-
>  scripts/Makefile.lib              |  4 ++--
>  scripts/jobserver-exec            |  3 ++-
>  tools/lib/python/jobserver.py     | 13 +++++++++++++
>  7 files changed, 51 insertions(+), 5 deletions(-)

Awesome; I love it. (I may send a follow-up to improve the PARALLELISM
token so things can define the fallback instead of the hard-coded "1",
but there is only one place I found where that might be useful, and it
will be totally separate from this.)

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v3 14/20] kbuild: batch module finalisation

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:24PM +0100, Lorenzo Stoakes (ARM) wrote:
> With the .mod.S change in place, module finalisation on allmodconfig builds
> consists of a large number of very short-lived jobs.
> 
> For allmodconfig x86-64 this can be on the order of ~22,000 jobs of a few
> milliseconds in duration each.
> 
> Each job entails processing ~22k .cmd files, so the combination of heavy
> overhead and small individual job results in a lot of unnecessary and
> repeated work even with all cores being utilised.
> 
> The solution is to batch by a number of jobs. Determining which value makes
> sense was done empirically.
> 
> On a 128-thread threadripper box doing an allmodconfig build, best of
> 2, *.ko, *.mod.o deleted each time:
> 
>     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
> 
> Wall time flattens for 16-256 module batches.
> 
> A slower/lower core machine will do better with fewer modules-per-batch, a
> faster/higher core machine will do better with more modules-per-batch.
> 
> Therefore, take the midpoint which works in the most margin in either
> direction - 128 modules per batch.

This is easy to tweak, so if we get negative feedback on this for
smaller machines, it's an easy fix.

> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v3 01/20] kbuild: do not allocate .modinfo in vmlinux

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:11PM +0100, Lorenzo Stoakes (ARM) wrote:
> +      cmd_modules_builtin_modinfo = $(OBJCOPY) -O binary -j .modinfo --dump-section .modinfo=$@ $< $@.tmp; \
> +                                    rm -f $@.tmp; \
> +                                    sed -i 's/\x00\+$$/\x00/g' $@

Oh, I just noticed this. I don't think the .tmp is needed. You can just
use /dev/null for the outfile here: no need to write anything unused to
disk; seems to work for binutils and llvm's objcopy.

-- 
Kees Cook

Re: [PATCH v3 00/20] kbuild: significantly speed up kernel builds

[Linus Torvalds]

On Thu, 17 Sept 2026 at 09:06, Lorenzo Stoakes (ARM) <ljs@kernel.org> wrote:
>
>                 == defconfig FULL build ==
>
>                         before    after     delta
>                       ----------------------------------
> Threadripper, gcc        32.5s    26.3s     -6.1s (-19%)
> Threadripper, clang      34.5s    27.2s     -7.3s (-21%)
> EPYC, gcc                28.7s    20.6s     -8.1s (-28%)
> EPYC, clang              39.8s    32.2s     -7.6s (-19%)
> M2, gcc                 519.3s   512.4s     -6.9s (-1%)
> M2, clang               634.5s   569.4s    -65.1s (-10%)

There's something odd going on with that M2 gcc build. Why is it such
an odd duck?

             Linus

Re: [PATCH v3 02/20] kallsyms: index symbols by token to speed up table compression

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:12PM +0100, Lorenzo Stoakes (ARM) wrote:
> 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];

Nit: since you're refactoring too, can 0x10000 be a #define so it's not
open-coded 3 places? (find_best_token() uses the value too, though
arguably it should actually just use ARRAY_SIZE(token_profit) instead).

> [...]
> -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 */

Why drop this comment? It's a little redundant to "find_token", but I
always question comment _removal_ when it's not solving an inaccuracy.

> [...]
> @@ -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 */

Same question here: the comment is still valid?

Otherwise, looks good to me.

Reviewed-by: Kees Cook <kees@kernel.org>


-- 
Kees Cook

Re: [PATCH v3 03/20] kallsyms: output binary data to speed output and kallsyms assembly

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:13PM +0100, Lorenzo Stoakes (ARM) wrote:
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

A clear win. :)

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v3 00/20] kbuild: significantly speed up kernel builds

[Lorenzo Stoakes (ARM)]

On Thu, Sep 17, 2026 at 10:15:26AM -0700, Linus Torvalds wrote:
> On Thu, 17 Sept 2026 at 09:06, Lorenzo Stoakes (ARM) <ljs@kernel.org> wrote:
> >
> >                 == defconfig FULL build ==
> >
> >                         before    after     delta
> >                       ----------------------------------
> > Threadripper, gcc        32.5s    26.3s     -6.1s (-19%)
> > Threadripper, clang      34.5s    27.2s     -7.3s (-21%)
> > EPYC, gcc                28.7s    20.6s     -8.1s (-28%)
> > EPYC, clang              39.8s    32.2s     -7.6s (-19%)
> > M2, gcc                 519.3s   512.4s     -6.9s (-1%)
> > M2, clang               634.5s   569.4s    -65.1s (-10%)
>
> There's something odd going on with that M2 gcc build. Why is it such
> an odd duck?

Ugh dear lord I think the LLM somehow corrupted the numbers... Let me
re-run those myself locally and come back with the actual times!

(I didn't do an allmodconfig out of pure impatience but might take the time
to do that too)

>
>              Linus

--
Cheers, Lorenzo

Re: [PATCH v3 04/20] kbuild: do not sort nm output where the order is irrelevant

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:14PM +0100, Lorenzo Stoakes (ARM) wrote:
> 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.
> [...]
>                                           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>

Not a huge boost, but it's a trivial change with a deterministic improvement.

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v3 01/20] kbuild: do not allocate .modinfo in vmlinux

[Lorenzo Stoakes (ARM)]

On Thu, Sep 17, 2026 at 10:05:34AM -0700, Kees Cook wrote:
> On Thu, Sep 17, 2026 at 05:06:11PM +0100, Lorenzo Stoakes (ARM) wrote:
> > +      cmd_modules_builtin_modinfo = $(OBJCOPY) -O binary -j .modinfo --dump-section .modinfo=$@ $< $@.tmp; \
> > +                                    rm -f $@.tmp; \
> > +                                    sed -i 's/\x00\+$$/\x00/g' $@
>
> Oh, I just noticed this. I don't think the .tmp is needed. You can just
> use /dev/null for the outfile here: no need to write anything unused to
> disk; seems to work for binutils and llvm's objcopy.

Ack will fix up thanks!

>
> --
> Kees Cook

--
Cheers, Lorenzo

Re: [PATCH v3 01/20] kbuild: do not allocate .modinfo in vmlinux

[Lorenzo Stoakes (ARM)]

On Thu, Sep 17, 2026 at 09:52:32AM -0700, Kees Cook wrote:
> On Thu, Sep 17, 2026 at 05:06:11PM +0100, Lorenzo Stoakes (ARM) wrote:
> > -# .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.
>
> This comment still seems useful here (afaict the stripping is still
> happening with the "sed"). Maybe better to leave it, or future readers
> are left wondering what the sed is for?

Ack will restore!

>
> >  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' $@
>
> Otherwise, looks good. With the comment back (or rewritten):
>
> Reviewed-by: Kees Cook <kees@kernel.org>

Thanks!

>
> -Kees
>
> --
> Kees Cook

--
Cheers, Lorenzo

Re: [PATCH v3 05/20] kbuild: only emit vmlinux relocations when required

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:15PM +0100, Lorenzo Stoakes (ARM) wrote:
> 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

Nit: I think a comment here is worth adding, like in link-vmlinux.sh.
They're separate files, and it's kind of weird that ...NEEDS_RELOCS
doesn't actually add --emit-relocs here unless you go find how
--emit-relocs is used later.

>  
>  # 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

But yeah, otherwise, another "don't generate something that doesn't get
used" improvement. :)

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v3 06/20] elf-parse: add section flags, symbol binding and a read-only mapping

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:16PM +0100, Lorenzo Stoakes (ARM) wrote:
> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

LGTM

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v3 02/20] kallsyms: index symbols by token to speed up table compression

[Lorenzo Stoakes (ARM)]

On Thu, Sep 17, 2026 at 10:27:32AM -0700, Kees Cook wrote:
> On Thu, Sep 17, 2026 at 05:06:12PM +0100, Lorenzo Stoakes (ARM) wrote:
> > 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];
>
> Nit: since you're refactoring too, can 0x10000 be a #define so it's not
> open-coded 3 places? (find_best_token() uses the value too, though
> arguably it should actually just use ARRAY_SIZE(token_profit) instead).

Sure, will do!

And yeah ARRAY_SIZE() makes sense there also.

>
> > [...]
> > -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 */
>
> Why drop this comment? It's a little redundant to "find_token", but I
> always question comment _removal_ when it's not solving an inaccuracy.

Sometimes I lose track which bits are mine/the LLM's, but I don't love
comments that don't add all that much, and I also berate the LLM about
writing the literally worse comments I've ever seen in my life so could
have been either me or it...

Anyway, will restore!

>
> > [...]
> > @@ -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 */
>
> Same question here: the comment is still valid?

Ack will restore!

>
> Otherwise, looks good to me.
>
> Reviewed-by: Kees Cook <kees@kernel.org>

Thanks!

>
>
> --
> Kees Cook

--
Cheers, Lorenzo

Re: [PATCH v3 05/20] kbuild: only emit vmlinux relocations when required

[Lorenzo Stoakes (ARM)]

On Thu, Sep 17, 2026 at 10:41:50AM -0700, Kees Cook wrote:
> On Thu, Sep 17, 2026 at 05:06:15PM +0100, Lorenzo Stoakes (ARM) wrote:
> > 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
>
> Nit: I think a comment here is worth adding, like in link-vmlinux.sh.
> They're separate files, and it's kind of weird that ...NEEDS_RELOCS
> doesn't actually add --emit-relocs here unless you go find how
> --emit-relocs is used later.

Ack will add!

>
> >
> >  # 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
>
> But yeah, otherwise, another "don't generate something that doesn't get
> used" improvement. :)

Yes :) it's funny how simple a lot of these changes are

- Don't do work you don't need to
- Cache stuff so you don't have to look it up again (a variant on the first
  one)
- Do other work at the same time

>
> Reviewed-by: Kees Cook <kees@kernel.org>

Thanks!

>
> --
> Kees Cook

--
Cheers, Lorenzo

Re: [PATCH v3 07/20] kallsyms: reimplement mksysmap in C

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:17PM +0100, Lorenzo Stoakes (ARM) wrote:
> 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__",
> +};

I really think these need to be 1 per line with the comments from
scripts/mksysmap retained. It's going to be changed over time, and we
want to be able to review the rationale for entries without having to
dig through commit history.

> +static const char *const sysmap_omit_suffixes[] = {
> +	"_from_arm", "_from_thumb", "_veneer",
> +};
> +static const char *const sysmap_omit_names[] = {
> +	"L0", "_SDA_BASE_", "_SDA2_BASE_",
> +};

Same for these 2 tables.

> +
> +/* __<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;
> +}

I'm less excited about these "open coded" regular expression matches.
Having to do this feels like it'll make future exceptions annoying to
add. Can't there be another class of table that is just regular
expressions? It is probably faster to keep the prefix/suffix/exact
tables as-is, but is_range_thunk() and is_modinfo_id() just feel clunky
compared to the more expressive re, e.g. r'^__UNIQUE_ID_modinfo[0-9]*$'

> +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.");

And then mixing data-driven search with in-line patterns I don't like.
The .long_branch. and .plt_branch. matches should be in a new "any
position" table, IMO.

> +/* 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",
> +	};

I worry about maintenance overhead on this: are we going to have to
chase changes to "nm" when other debug prefixes get added here?

> +	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 '?';

And to that end: instead of "?" shouldn't this fail hard when a section
symbol type is unknown to the tool?

> +}
> +
> +/* 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 '?';

Same concerns...

> +	}
> +
> +	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);
> +}

These 2 functions kind of feel like they should live in elfparse instead?

> +
> +/* 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;
> +}

And this one too, with maybe a "maybe_omit" callback passed in so this
mksysmap could pass sysmap_omits in as?

> -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);

I realize this is just moving logic around, but traditional xrealloc
loop uses doubling. I think this was linear only because it wanted to
jump-start the initial allocation size to 10000 entries. Could be:

	table_size = table_size ? table_size * 2 : 10000;

But maybe even that initial allocation number should be bumped up?

> [...]
> +	if (optind + 1 == argc) {
> +		read_elf(in, sysmap_out);
> +		if (fclose(sysmap_out)) {

This needs to check ferror() too.

> +			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)) {

Same: this needs to check ferror() too.


-Kees

-- 
Kees Cook

Re: [PATCH v3 08/20] kbuild: cache list, composite object state per object

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:18PM +0100, Lorenzo Stoakes (ARM) wrote:
> Fix the issue by caching this data and looking it up instead of getting it
> over and over again.

Nit: I would describe this as "calculate these once". It _is_ caching,
but I think with Makefiles there is an implication the "caching" means
"write to disk". But maybe that's just me.

> This has a particularly large impact on allmodconfig builds.

Love it. :)

Reviewed-by: Kees Cook <kees@kernel.org>

-- 
Kees Cook

Re: [PATCH v3 09/20] kbuild: implement and use depcheck to check dependency timestamps

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:19PM +0100, Lorenzo Stoakes (ARM) wrote:
> 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.

Doesn't this run the risk of missing transitive deps?

C.cmd:	C.o depends on A.c and B.c and B.h
B.cmd:	B.h depends on B.data and B.script

depcheck looks at C.o and B.h's times and is happy so it drops C.cmd file,
but then see B.script has changed compared to B.h, so it keeps B.cmd,
and then the build runs and doesn't have the C.o dep list any more,
and C.o goes unbuilt?

Also, I don't think this handles if_changed commands at all? The kbuild
rebuild condition is timestamps plus if_changed's command-line check.

> diff --git a/scripts/basic/depcheck.c b/scripts/basic/depcheck.c
> new file mode 100644
> index 000000000000..622101c33650
> --- /dev/null
> +++ b/scripts/basic/depcheck.c
> @@ -0,0 +1,441 @@
> [...]
> +/* 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"
> [...]
> +static bool is_blank(char chr)
> [...]
> +static bool str_ends_with(const char *str, const char *suffix)
> [...]
> +static bool line_starts_with(const struct line *line, const char *prefix)
> [...]
> +static bool line_ends_with(const struct line *line, const char *suffix)
> [...]
> +static bool line_is_blank(const struct line *line)
> [...]
> +static bool line_is_continued(const struct line *line)
> [...]
> +static void line_strip_continuation(struct line *line)
> [...]
> +static void line_trim(struct line *line)
> [...]
> +static bool next_line(const char **pos, const char *end, struct line *line)

There is a lot of sting handling in here. I know you're going for speed,
but it just feels like a python script doing all this would be much more
readable without wrecking speed compared to C much. Yes, C will win out,
but the maintainability of this helper does not fill me with joy. :P

> [...]
> +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;

I realize you only check "mtime" after an "exists" check, but I bristle
at leaving a time-stamp uninitialized. Can we just add an "else
dep->mtime = 0" here?

-Kees

-- 
Kees Cook

Re: [PATCH v3 10/20] kbuild: move the toolchain checks into init/Kconfig.toolchain

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:20PM +0100, Lorenzo Stoakes (ARM) wrote:
> 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(-)

Yeah, totally right to move to a separate file. I think, however, I
would prefer this wasn't in init/ though. Kbuild uses scripts/ as its
Makefile.$topic dumping ground, and Kconfig.include also lives there. To
me, this new file should be scripts/Kconfig.toolchain instead. And
arguably, this should be included by the top-level Kconfig rather than
init/Kconfig...

I defer to kbuild folks, though.

-Kees

-- 
Kees Cook

Re: [PATCH v3 11/20] kbuild: avoid re-running compiler and linker probes

[Kees Cook]

On Thu, Sep 17, 2026 at 05:06:21PM +0100, Lorenzo Stoakes (ARM) wrote:
> 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.

Yeah, I agree about the rationale here.

It does, however, now drive a long-time annoyance of mine to the top of
mind: the repetition of the compiler command-line options in two places:
the Kconfig and the Makefile. I dislike that pattern so much that I really
really worked hard to use cc-option instead where ever I possibly could
(though it continued to add to my growing concern about the repetition
of running those checks all the time, so I'm motivated to see something
like what you have here actually land).

But I would really like to find a way to avoid the duplication. It's
fragile and it's weird and it's split across 2 files that don't always
have an obvious relationship. I really don't like it. And with it being
used for things that are "detected" (i.e. not part of always required
builds), that fragility means typos may go unnoticed, etc.

We've had a need for some kind of kconfig "append to a list" logic that
we've been working around in places, e.g. include/linux/lsm_count.h for
how "count the list of enabled LSMs" got dealt with. If we could have
had:

config LSM_LIST
	list
	separator " "

config SECURITY_SELINUX
	...
	append_to LSM_LIST
	...

We could just parse CONFIG_LSM_LIST directly. And I think we can do the
same with this:

config CC_OPTION_LIST
	list
	separator " "

config CC_OPTION_ZERO_INIT_PADDING_BITS
	string
	default "$(cc-option-bit,-fzero-init-padding-bits=all)"
	append_to CC_OPTION_LIST

And the dump all of it into the Makefile in one via CONFIG_CC_OPTION_LIST

(And we'd need to implement ld-option-bit. Though really I think
cc-option-bit should be renamed to cc-option-str or something)

But even without the new "list" Kconfig type, it'd be nicer to use the
cc-option-bit string default method and dump all the newly created
CC_OPTION_... strings into the makefile manually. The "append_to" idea
could be a follow-up.

-Kees

-- 
Kees Cook

Re: [PATCH v3 00/20] kbuild: significantly speed up kernel builds

[Lorenzo Stoakes (ARM)]

On Thu, Sep 17, 2026 at 06:36:18PM +0100, Lorenzo Stoakes (ARM) wrote:
> On Thu, Sep 17, 2026 at 10:15:26AM -0700, Linus Torvalds wrote:
> > On Thu, 17 Sept 2026 at 09:06, Lorenzo Stoakes (ARM) <ljs@kernel.org> wrote:
> > >
> > >                 == defconfig FULL build ==
> > >
> > >                         before    after     delta
> > >                       ----------------------------------
> > > Threadripper, gcc        32.5s    26.3s     -6.1s (-19%)
> > > Threadripper, clang      34.5s    27.2s     -7.3s (-21%)
> > > EPYC, gcc                28.7s    20.6s     -8.1s (-28%)
> > > EPYC, clang              39.8s    32.2s     -7.6s (-19%)
> > > M2, gcc                 519.3s   512.4s     -6.9s (-1%)
> > > M2, clang               634.5s   569.4s    -65.1s (-10%)
> >
> > There's something odd going on with that M2 gcc build. Why is it such
> > an odd duck?
>
> Ugh dear lord I think the LLM somehow corrupted the numbers... Let me
> re-run those myself locally and come back with the actual times!

OK numbers are in:

M2, gcc			564.7s   512.1s    -52.6s (-9%)
M2, clang		615.1s   564.1s    -51.0s (-8%)

From the v1:

M2, gcc                 564.0s   512.4s    -51.6s (-9%)
M2, clang               616.1s   569.4s    -46.7s (-8%)

(Tested as per the cover letter pre-reqs, i.e. applying dependent series
first etc.)

Not sure on the -5s delta on the clang build :) that might have been me
being more disciplined this time to not use the laptop at the same time.

But broadly in line with the original numbers.

>
> >
> >              Linus
>
> --
> Cheers, Lorenzo

--
Cheers, Lorenzo

Re: [PATCH v3 00/20] kbuild: significantly speed up kernel builds

[Nick Desaulniers]

On Thu, Sep 17, 2026 at 12:42 PM Lorenzo Stoakes (ARM) <ljs@kernel.org> wrote:
>
> On Thu, Sep 17, 2026 at 06:36:18PM +0100, Lorenzo Stoakes (ARM) wrote:
> > On Thu, Sep 17, 2026 at 10:15:26AM -0700, Linus Torvalds wrote:
> > > On Thu, 17 Sept 2026 at 09:06, Lorenzo Stoakes (ARM) <ljs@kernel.org> wrote:
> > > >
> > > >                 == defconfig FULL build ==
> > > >
> > > >                         before    after     delta
> > > >                       ----------------------------------
> > > > Threadripper, gcc        32.5s    26.3s     -6.1s (-19%)
> > > > Threadripper, clang      34.5s    27.2s     -7.3s (-21%)
> > > > EPYC, gcc                28.7s    20.6s     -8.1s (-28%)
> > > > EPYC, clang              39.8s    32.2s     -7.6s (-19%)
> > > > M2, gcc                 519.3s   512.4s     -6.9s (-1%)
> > > > M2, clang               634.5s   569.4s    -65.1s (-10%)
> > >
> > > There's something odd going on with that M2 gcc build. Why is it such
> > > an odd duck?
> >
> > Ugh dear lord I think the LLM somehow corrupted the numbers... Let me
> > re-run those myself locally and come back with the actual times!
>
> OK numbers are in:
>
> M2, gcc                 564.7s   512.1s    -52.6s (-9%)
> M2, clang               615.1s   564.1s    -51.0s (-8%)
>
> From the v1:
>
> M2, gcc                 564.0s   512.4s    -51.6s (-9%)
> M2, clang               616.1s   569.4s    -46.7s (-8%)
>
> (Tested as per the cover letter pre-reqs, i.e. applying dependent series
> first etc.)
>
> Not sure on the -5s delta on the clang build :) that might have been me

Clang is faster on Thursdays.

> being more disciplined this time to not use the laptop at the same time.
>
> But broadly in line with the original numbers.
>
> >
> > >
> > >              Linus
> >
> > --
> > Cheers, Lorenzo
>
> --
> Cheers, Lorenzo



-- 
Thanks,
~Nick Desaulniers

Re: [PATCH v3 09/20] kbuild: implement and use depcheck to check dependency timestamps

[Kees Cook]

On Thu, Sep 17, 2026 at 11:42:50AM -0700, Kees Cook wrote:
> On Thu, Sep 17, 2026 at 05:06:19PM +0100, Lorenzo Stoakes (ARM) wrote:
> > 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.
>
> Doesn't this run the risk of missing transitive deps?
>
> C.cmd:	C.o depends on A.c and B.c and B.h
> B.cmd:	B.h depends on B.data and B.script
>
> depcheck looks at C.o and B.h's times and is happy so it drops C.cmd file,
> but then see B.script has changed compared to B.h, so it keeps B.cmd,
> and then the build runs and doesn't have the C.o dep list any more,
> and C.o goes unbuilt?
>
> Also, I don't think this handles if_changed commands at all? The kbuild
> rebuild condition is timestamps plus if_changed's command-line check.

tl;dr: I spent way too long looking at this. I think my conclusion is
"Hm, this makes some cases of missed Makefile deps on generated files
harder to find, but there don't *appear* to be any obviously wrong
instances of this in the tree."

Long version:

There does appear to be a problem in the case of generated targets where
the Makefile deps are build-order correct but lack explicit deps. As
in, a clean build generates the needed dependencies due to some prior
explicit Makefile rule dependency, and a later source-level "#include"
for the generated file exists (and the build doesn't fail since the
included file got generated before the source that "#include"d it got
built), and then the normal dep tracking (-Wp,-MMD,... -> .cmd) catches
it and any direct changes to that dep would normally get noticed going
forward on incremental builds.

However, with the depcheck .cmd pruning, changes to transitive deps
(either via file contents or Kconfig options) will go unnoticed during
incremental builds without that explicit dep (but stock doesn't miss
it). Though actually it's kind of worse because it'll get noticed on
rebuild #N+1 for N level of transitive depth, so something will break,
and then you build again, and the changes from 2 builds ago suddenly
get rebuilt...

I think you maybe encountered an instance of this in your series, too,
but it got exposed due to a clean build no longer having the ordering
correct:
https://lore.kernel.org/lkml/20260917-build-speedup-v3-18-9ecf4163ff36@kernel.org/

See the trailing diff for a demo:


  git apply demo.diff
  make O=b defconfig
  # simulate a earlier-stage header generation...
  make O=b lib/byfile_anchor.o lib/byconf_anchor.o
  make O=b lib/

  # trigger 1: the header's input file changes
  echo FROMFILE-two > lib/byfile_gen.in
  make O=b lib/

  # trigger 2: a Kconfig value changes; no file is touched
  ./scripts/config --file b/.config --set-str LOCALVERSION -demo2
  make O=b lib/

  # what each object ended up holding
  strings b/lib/byfile_anchor.o | grep FROMFILE-    # FROMFILE-two   both trees
  strings b/lib/byfile_victim.o | grep FROMFILE-    # FROMFILE-two   stock
                                                    # FROMFILE-one   patched  <-- stale

  strings b/lib/byconf_anchor.o | grep CONF-        # CONF--demo2    both trees
  strings b/lib/byconf_victim.o | grep CONF-        # CONF--demo2    stock
                                                    # CONF-          patched  <-- stale


This means adding depcheck would silently expose any current (and future)
missing explicit deps on generated files where those files get generated
by either an earlier build stage or an earlier rule. :(

I went looking for the kind of missed Makefile dep for a generated file,
and while it's not a very grep-able condition, I did look at stuff that
fell into include/generated/, but it's safe due to the prepare/archprepare
ordering AFAICT. So then I looked at places where -I had $(obj) added to
it, and all of those seemed to have explicit Makefile deps too. Well, all
except for arch/x86/boot/compressed/sev-handle-vc.c which includes
"../../lib/inat.c" but that seems safe today due to ordering from
arch/x86/lib/ being needed before arch/x86/boot/compressed/.

So, yeah, it makes me nervous, and it may make incremental builds less
idempotent. But I can't really find extant problems and the demo is
slightly contrived, but not exactly an impossible situation.

-Kees


diff --git a/lib/Makefile b/lib/Makefile
index dfab958327c5c..aed0bd9eb7d6a 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -350,3 +350,36 @@ CONTEXT_ANALYSIS_test_context-analysis.o := y
 obj-$(CONFIG_CONTEXT_ANALYSIS_TEST) += test_context-analysis.o
 
 subdir-$(CONFIG_FORTIFY_SOURCE) += test_fortify
+
+# --- depcheck demo ---
+obj-y += byfile_anchor.o byfile_victim.o byconf_anchor.o byconf_victim.o
+
+quiet_cmd_byfile = GENFILE $@
+      cmd_byfile = printf '\#define BYFILE_STR "%s"\n' "$$(cat $<)" > $@
+
+quiet_cmd_byconf = GENCONF $@
+      cmd_byconf = printf '\#define BYCONF_STR "CONF-%s"\n' '$(CONFIG_LOCALVERSION)' > $@
+
+# Regenerated when its input file changes.
+$(obj)/byfile_gen.h: $(src)/byfile_gen.in FORCE
+	$(call if_changed,byfile)
+
+# No input file: regenerated only when its command line changes, which here
+# means when CONFIG_LOCALVERSION changes. No file is touched.
+$(obj)/byconf_gen.h: FORCE
+	$(call if_changed,byconf)
+
+targets += byfile_gen.h byconf_gen.h
+
+# The anchors declare the dependency. That is what generates the headers on
+# a clean build: fixdep only records a header once the object has compiled
+# successfully, so on a first build there is no .cmd file to rely on. The
+# victims include the same headers without declaring them, so the only
+# record of that edge is the deps_ list in their .cmd files.
+$(obj)/byfile_anchor.o: $(obj)/byfile_gen.h
+$(obj)/byconf_anchor.o: $(obj)/byconf_gen.h
+
+CFLAGS_byfile_anchor.o += -I$(obj)
+CFLAGS_byfile_victim.o += -I$(obj)
+CFLAGS_byconf_anchor.o += -I$(obj)
+CFLAGS_byconf_victim.o += -I$(obj)
diff --git a/lib/byconf_anchor.c b/lib/byconf_anchor.c
new file mode 100644
index 0000000000000..8035eaa352a3b
--- /dev/null
+++ b/lib/byconf_anchor.c
@@ -0,0 +1,3 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "byconf_gen.h"
+const char byconf_anchor_marker[] = BYCONF_STR;
diff --git a/lib/byconf_victim.c b/lib/byconf_victim.c
new file mode 100644
index 0000000000000..285a8de8bdf6e
--- /dev/null
+++ b/lib/byconf_victim.c
@@ -0,0 +1,3 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "byconf_gen.h"
+const char byconf_victim_marker[] = BYCONF_STR;
diff --git a/lib/byfile_anchor.c b/lib/byfile_anchor.c
new file mode 100644
index 0000000000000..9ea0b8ad55963
--- /dev/null
+++ b/lib/byfile_anchor.c
@@ -0,0 +1,3 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "byfile_gen.h"
+const char byfile_anchor_marker[] = BYFILE_STR;
diff --git a/lib/byfile_gen.in b/lib/byfile_gen.in
new file mode 100644
index 0000000000000..7da9e5e0cd83c
--- /dev/null
+++ b/lib/byfile_gen.in
@@ -0,0 +1 @@
+FROMFILE-one
diff --git a/lib/byfile_victim.c b/lib/byfile_victim.c
new file mode 100644
index 0000000000000..763c5ef8f1514
--- /dev/null
+++ b/lib/byfile_victim.c
@@ -0,0 +1,3 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "byfile_gen.h"
+const char byfile_victim_marker[] = BYFILE_STR;


-- 
Kees Cook