lkml.org 
[lkml]   [2020]   [May]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] x86: fix clang integrated assembler build
On Wed, May 27, 2020 at 7:16 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> clang and gas seem to interpret the symbols in memmove_64.S and
> memset_64.S differently, such that clang does not make them
> 'weak' as expected, which leads to a linker error, with both
> ld.bfd and ld.lld:
>
> ld.lld: error: duplicate symbol: memmove
> >>> defined at common.c
> >>> kasan/common.o:(memmove) in archive mm/built-in.a
> >>> defined at memmove.o:(__memmove) in archive arch/arm64/lib/lib.a
>
> ld.lld: error: duplicate symbol: memset
> >>> defined at common.c
> >>> kasan/common.o:(memset) in archive mm/built-in.a
> >>> defined at memset.o:(__memset) in archive arch/arm64/lib/lib.a
>
> Copy the exact way these are written in memcpy_64.S, which does
> not have the same problem.
>
> I don't know why this makes a difference, and it would be good
> to have someone with a better understanding of assembler internals
> review it.
>
> It might be either a bug in the kernel or a bug in the assembler,
> no idea which one. My patch makes it work with all versions of
> clang and gcc, which is probably helpful even if it's a workaround
> for a clang bug.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

+ Bill, Fangrui, Jian
I think we saw this bug or a very similar bug internally around the
ordering of .weak to .global.

> ---
> arch/x86/lib/memmove_64.S | 4 ++--
> arch/x86/lib/memset_64.S | 4 ++--
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/lib/memmove_64.S b/arch/x86/lib/memmove_64.S
> index 7ff00ea64e4f..dcca01434be8 100644
> --- a/arch/x86/lib/memmove_64.S
> +++ b/arch/x86/lib/memmove_64.S
> @@ -26,8 +26,8 @@
> */
> .weak memmove
>
> -SYM_FUNC_START_ALIAS(memmove)
> -SYM_FUNC_START(__memmove)
> +SYM_FUNC_START_ALIAS(__memmove)
> +SYM_FUNC_START_LOCAL(memmove)
>
> mov %rdi, %rax
>
> diff --git a/arch/x86/lib/memset_64.S b/arch/x86/lib/memset_64.S
> index 9ff15ee404a4..a97f2ea4e0b2 100644
> --- a/arch/x86/lib/memset_64.S
> +++ b/arch/x86/lib/memset_64.S
> @@ -19,8 +19,8 @@
> *
> * rax original destination
> */
> -SYM_FUNC_START_ALIAS(memset)
> -SYM_FUNC_START(__memset)
> +SYM_FUNC_START_ALIAS(__memset)
> +SYM_FUNC_START_LOCAL(memset)
> /*
> * Some CPUs support enhanced REP MOVSB/STOSB feature. It is recommended
> * to use it when possible. If not available, use fast string instructions.
> --
> 2.26.2
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200527141553.1768675-1-arnd%40arndb.de.



--
Thanks,
~Nick Desaulniers

\
 
 \ /
  Last update: 2020-05-27 20:05    [W:0.045 / U:2.644 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site