On Wed, May 27, 2020 at 1:57 PM Bill Wendling morbo@google.com wrote:
On Wed, May 27, 2020 at 11:04 AM Nick Desaulniers ndesaulniers@google.com wrote:
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.
I think that would be this patch by Fangrui:
https://prodkernel-review.git.corp.google.com/c/kernel/release/9xx/+/292011
Thanks. That patch references this discussion: https://lore.kernel.org/linuxppc-dev/20200325164257.170229-1-maskray@google....
-bw
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, %raxdiff --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
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-- Thanks, ~Nick Desaulniers