[PATCH v2 0/3] tools/nolibc: clang LTO compatibility

[PATCH v2 0/3] tools/nolibc: clang LTO compatibility

[Thomas Weißschuh]

A few tiny bugfixes and refactoring to provide compatibility with
clangs -flto.

$ CFLAGS_EXTRA=-flto ./run-tests.sh -m user -l       
i386:          195 test(s): 193 passed,   2 skipped,   0 failed => status: warning
x86_64:        195 test(s): 193 passed,   2 skipped,   0 failed => status: warning
arm64:         195 test(s): 193 passed,   2 skipped,   0 failed => status: warning
arm:           195 test(s): 193 passed,   2 skipped,   0 failed => status: warning
mips32le:      195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
mips32be:      195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
ppc:           195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
ppc64:         195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
ppc64le:       195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
riscv:         195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
s390:          195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
loongarch:     195 test(s): 192 passed,   3 skipped,   0 failed => status: warning

GCC is not supported, for details read the discussion in v1 of the
series.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Changes in v2:
- Drop GCC support
- arch-x86_64.h: Don't try to wrap the asm functions in C functions,
  Instead just replace the local symbol with a local label.
- Link to v1: https://lore.kernel.org/r/20240810-nolibc-lto-v1-0-a86e514c7fc1@weissschuh.net

---
Thomas Weißschuh (3):
      tools/nolibc: crt: mark _start_c() as used
      tools/nolibc: stackprotector: mark implicitly used symbols as used
      tools/nolibc: x86_64: use local label in memcpy/memmove

 tools/include/nolibc/arch-x86_64.h    | 4 ++--
 tools/include/nolibc/crt.h            | 2 +-
 tools/include/nolibc/stackprotector.h | 4 ++--
 3 files changed, 5 insertions(+), 5 deletions(-)
---
base-commit: 22ba81c50a49468d80055674d8d6f78afb1c92c4
change-id: 20240728-nolibc-lto-331813b72a0b

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

[PATCH v2 1/3] tools/nolibc: crt: mark _start_c() as used

[Thomas Weißschuh]

During LTO the reference from the asm startup code to the _start_c()
function is not visible and _start_c() is removed.
This will then lead to errors during linking.
As _start_c() is indeed always used, mark it as such.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/include/nolibc/crt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/include/nolibc/crt.h b/tools/include/nolibc/crt.h
index ac291574f6c0..bbcd5fd09806 100644
--- a/tools/include/nolibc/crt.h
+++ b/tools/include/nolibc/crt.h
@@ -22,7 +22,7 @@ extern void (*const __init_array_end[])(int, char **, char**) __attribute__((wea
 extern void (*const __fini_array_start[])(void) __attribute__((weak));
 extern void (*const __fini_array_end[])(void) __attribute__((weak));
 
-__attribute__((weak))
+__attribute__((weak,used))
 void _start_c(long *sp)
 {
 	long argc;

-- 
2.46.0

[PATCH v2 2/3] tools/nolibc: stackprotector: mark implicitly used symbols as used

[Thomas Weißschuh]

During LTO the references from the compiler-generated prologue and
epilogues to the stack protector symbols are not visible and the symbols
are removed.
This will then lead to errors during linking.
As those symbols are already #ifdeffed-out if unused mark them as "used"
to prevent their removal.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/include/nolibc/stackprotector.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/include/nolibc/stackprotector.h b/tools/include/nolibc/stackprotector.h
index 13f1d0e60387..1d0d5259ec41 100644
--- a/tools/include/nolibc/stackprotector.h
+++ b/tools/include/nolibc/stackprotector.h
@@ -18,7 +18,7 @@
  * triggering stack protector errors themselves
  */
 
-__attribute__((weak,noreturn,section(".text.nolibc_stack_chk")))
+__attribute__((weak,used,noreturn,section(".text.nolibc_stack_chk")))
 void __stack_chk_fail(void)
 {
 	pid_t pid;
@@ -34,7 +34,7 @@ void __stack_chk_fail_local(void)
 	__stack_chk_fail();
 }
 
-__attribute__((weak,section(".data.nolibc_stack_chk")))
+__attribute__((weak,used,section(".data.nolibc_stack_chk")))
 uintptr_t __stack_chk_guard;
 
 static __no_stack_protector void __stack_chk_init(void)

-- 
2.46.0

[PATCH v2 3/3] tools/nolibc: x86_64: use local label in memcpy/memmove

[Thomas Weißschuh]

Compiling arch-x86_64.h with clang and binutils LD yields
duplicate label errors:

.../gcc-13.2.0-nolibc/x86_64-linux/bin/x86_64-linux-ld: error: LLVM gold plugin: <inline asm>:44:1: symbol '.Lbackward_copy' is already defined
.Lbackward_copy:leaq -1(%rdi, %rcx, 1), %rdi

Instead of a local symbol use a local label which can be defined
multiple times and therefore avoids the error.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/include/nolibc/arch-x86_64.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/include/nolibc/arch-x86_64.h b/tools/include/nolibc/arch-x86_64.h
index 65252c005a30..1e40620a2b33 100644
--- a/tools/include/nolibc/arch-x86_64.h
+++ b/tools/include/nolibc/arch-x86_64.h
@@ -193,10 +193,10 @@ __asm__ (
 	"movq %rdi, %rdx\n\t"
 	"subq %rsi, %rdx\n\t"
 	"cmpq %rcx, %rdx\n\t"
-	"jb   .Lbackward_copy\n\t"
+	"jb   1f\n\t"
 	"rep movsb\n\t"
 	"retq\n"
-".Lbackward_copy:"
+"1:" /* backward copy */
 	"leaq -1(%rdi, %rcx, 1), %rdi\n\t"
 	"leaq -1(%rsi, %rcx, 1), %rsi\n\t"
 	"std\n\t"

-- 
2.46.0

Re: [PATCH v2 0/3] tools/nolibc: clang LTO compatibility

[Willy Tarreau]

On Mon, Aug 12, 2024 at 10:50:16PM +0200, Thomas Weißschuh wrote:
> A few tiny bugfixes and refactoring to provide compatibility with
> clangs -flto.
> 
> $ CFLAGS_EXTRA=-flto ./run-tests.sh -m user -l       
> i386:          195 test(s): 193 passed,   2 skipped,   0 failed => status: warning
> x86_64:        195 test(s): 193 passed,   2 skipped,   0 failed => status: warning
> arm64:         195 test(s): 193 passed,   2 skipped,   0 failed => status: warning
> arm:           195 test(s): 193 passed,   2 skipped,   0 failed => status: warning
> mips32le:      195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
> mips32be:      195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
> ppc:           195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
> ppc64:         195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
> ppc64le:       195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
> riscv:         195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
> s390:          195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
> loongarch:     195 test(s): 192 passed,   3 skipped,   0 failed => status: warning
> 
> GCC is not supported, for details read the discussion in v1 of the
> series.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
> Changes in v2:
> - Drop GCC support
> - arch-x86_64.h: Don't try to wrap the asm functions in C functions,
>   Instead just replace the local symbol with a local label.
> - Link to v1: https://lore.kernel.org/r/20240810-nolibc-lto-v1-0-a86e514c7fc1@weissschuh.net

For the whole series:

Acked-by: Willy Tarreau <w@1wt.eu>

Thanks Thoams!
Willy

Re: [PATCH v2 3/3] tools/nolibc: x86_64: use local label in memcpy/memmove

[Ammar Faizi]

On Mon, Aug 12, 2024 at 10:50:19PM +0200, Thomas Weißschuh wrote:
> Compiling arch-x86_64.h with clang and binutils LD yields
> duplicate label errors:
> 
> .../gcc-13.2.0-nolibc/x86_64-linux/bin/x86_64-linux-ld: error: LLVM gold plugin: <inline asm>:44:1: symbol '.Lbackward_copy' is already defined
> .Lbackward_copy:leaq -1(%rdi, %rcx, 1), %rdi
> 
> Instead of a local symbol use a local label which can be defined
> multiple times and therefore avoids the error.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---

Reviewed-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>

-- 
Ammar Faizi