Re: [PATCH] arm64: fix clang integrated assembler build

From: Fangrui Song
Date: Wed May 27 2020 - 14:47:46 EST

On 2020-05-27, 'Nick Desaulniers' via Clang Built Linux wrote:
On Wed, May 27, 2020 at 7:14 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:

clang and gas seem to interpret the symbols in memmove.S and
memset.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.

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

This may be another instance of

I haven't checked but there may be both a .globl directive and a .weak

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
arch/arm64/lib/memcpy.S | 3 +--
arch/arm64/lib/memmove.S | 3 +--
arch/arm64/lib/memset.S | 3 +--
3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/lib/memcpy.S b/arch/arm64/lib/memcpy.S
index e0bf83d556f2..dc8d2a216a6e 100644
--- a/arch/arm64/lib/memcpy.S
+++ b/arch/arm64/lib/memcpy.S
@@ -56,9 +56,8 @@
stp \reg1, \reg2, [\ptr], \val

- .weak memcpy
#include "copy_template.S"
diff --git a/arch/arm64/lib/memmove.S b/arch/arm64/lib/memmove.S
index 02cda2e33bde..1035dce4bdaf 100644
--- a/arch/arm64/lib/memmove.S
+++ b/arch/arm64/lib/memmove.S
@@ -45,9 +45,8 @@ C_h .req x12
D_l .req x13
D_h .req x14

- .weak memmove
cmp dstin, src
b.lo __memcpy
add tmp1, src, count
diff --git a/arch/arm64/lib/memset.S b/arch/arm64/lib/memset.S
index 77c3c7ba0084..a9c1c9a01ea9 100644
--- a/arch/arm64/lib/memset.S
+++ b/arch/arm64/lib/memset.S
@@ -42,9 +42,8 @@ dst .req x8
tmp3w .req w9
tmp3 .req x9

- .weak memset
mov dst, dstin /* Preserve return value. */
and A_lw, val, #255
orr A_lw, A_lw, A_lw, lsl #8

~Nick Desaulniers

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