[PATCH] x86: fix clang integrated assembler build

From: Arnd Bergmann
Date: Wed May 27 2020 - 10:17:03 EST

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@xxxxxxxxxxxxxxx
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
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


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
* Some CPUs support enhanced REP MOVSB/STOSB feature. It is recommended
* to use it when possible. If not available, use fast string instructions.