On Thu, Oct 29, 2020 at 11:20 AM 'Fangrui Song' via Clang Built Linux clang-built-linux@googlegroups.com wrote:

Commit 39d114ddc682 ("arm64: add KASAN support") added .weak directives to arch/arm64/lib/mem*.S instead of changing the existing SYM_FUNC_START_PI macros. This can lead to the assembly snippet `.weak memcpy ... .globl memcpy` which will produce a STB_WEAK memcpy with GNU as but STB_GLOBAL memcpy with LLVM's integrated assembler before LLVM 12. LLVM 12 (since https://reviews.llvm.org/D90108) will error on such an overridden symbol binding.

Use the appropriate SYM_FUNC_START_WEAK_PI instead.

Fixes: 39d114ddc682 ("arm64: add KASAN support") Reported-by: Sami Tolvanen samitolvanen@google.com Signed-off-by: Fangrui Song maskray@google.com Cc: stable@vger.kernel.org

Before your patch, with GNU `as`: $ llvm-readelf -s arch/arm64/lib/memcpy.o | grep memcpy 19: 0000000000000000 340 FUNC WEAK DEFAULT 1 memcpy 20: 0000000000000000 340 FUNC GLOBAL DEFAULT 1 __memcpy 21: 0000000000000000 340 FUNC GLOBAL DEFAULT 1 __pi_memcpy $ llvm-readelf -s arch/arm64/lib/memmove.o | grep memmove 19: 0000000000000000 340 FUNC WEAK DEFAULT 1 memmove 20: 0000000000000000 340 FUNC GLOBAL DEFAULT 1 __memmove 21: 0000000000000000 340 FUNC GLOBAL DEFAULT 1 __pi_memmove $ llvm-readelf -s arch/arm64/lib/memset.o | grep memset 19: 0000000000000000 392 FUNC WEAK DEFAULT 1 memset 20: 0000000000000000 392 FUNC GLOBAL DEFAULT 1 __memset 21: 0000000000000000 392 FUNC GLOBAL DEFAULT 1 __pi_memset After your patch, with GNU `as`: $ llvm-readelf -s arch/arm64/lib/memcpy.o | grep memcpy 19: 0000000000000000 340 FUNC GLOBAL DEFAULT 1 __memcpy 20: 0000000000000000 340 FUNC GLOBAL DEFAULT 1 __pi_memcpy 21: 0000000000000000 340 FUNC WEAK DEFAULT 1 memcpy $ llvm-readelf -s arch/arm64/lib/memmove.o | grep memmove 19: 0000000000000000 340 FUNC GLOBAL DEFAULT 1 __memmove 20: 0000000000000000 340 FUNC GLOBAL DEFAULT 1 __pi_memmove 21: 0000000000000000 340 FUNC WEAK DEFAULT 1 memmove $ llvm-readelf -s arch/arm64/lib/memset.o | grep memset 19: 0000000000000000 392 FUNC GLOBAL DEFAULT 1 __memset 20: 0000000000000000 392 FUNC GLOBAL DEFAULT 1 __pi_memset 21: 0000000000000000 392 FUNC WEAK DEFAULT 1 memset

So it didn't change any bindings (good), but it did reorder symbols. I suspect if you flip the ordering of SYM_FUNC_START_WEAK_PI relative to SYM_FUNC_START_ALIAS you can get the previous ordering back, but I also suspect that the ordering of these symbols is not important.

Reviewed-by: Nick Desaulniers ndesaulniers@google.com Tested-by: Nick Desaulniers ndesaulniers@google.com

---

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 .endm

•   .weak memcpy
  

SYM_FUNC_START_ALIAS(__memcpy) -SYM_FUNC_START_PI(memcpy) +SYM_FUNC_START_WEAK_PI(memcpy) #include "copy_template.S" ret SYM_FUNC_END_PI(memcpy) 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
  

SYM_FUNC_START_ALIAS(__memmove) -SYM_FUNC_START_PI(memmove) +SYM_FUNC_START_WEAK_PI(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
  

SYM_FUNC_START_ALIAS(__memset) -SYM_FUNC_START_PI(memset) +SYM_FUNC_START_WEAK_PI(memset) mov dst, dstin /* Preserve return value. */ and A_lw, val, #255 orr A_lw, A_lw, A_lw, lsl #8 -- 2.29.1.341.ge80a0c044ae-goog

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