Re: [PATCH v2] x86_64: Change .weak to SYM_FUNC_START_WEAK for arch/x86/lib/mem*_64.S

[Nathan Chancellor <natechancellor@gmail.com>]

On Mon, Nov 02, 2020 at 05:23:58PM -0800, 'Fangrui Song' via Clang Built Linux wrote:
> Commit 393f203f5fd5 ("x86_64: kasan: add interceptors for
> memset/memmove/memcpy functions") added .weak directives to
> arch/x86/lib/mem*_64.S instead of changing the existing ENTRY macros to
> WEAK. 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.
> 
> Commit ef1e03152cb0 ("x86/asm: Make some functions local") changed ENTRY in
> arch/x86/lib/memcpy_64.S to SYM_FUNC_START_LOCAL, which was ineffective due to
> the preceding .weak directive.
> 
> Use the appropriate SYM_FUNC_START_WEAK instead.
> 
> Fixes: 393f203f5fd5 ("x86_64: kasan: add interceptors for memset/memmove/memcpy functions")
> Fixes: ef1e03152cb0 ("x86/asm: Make some functions local")
> Reported-by: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Fangrui Song <maskray@google.com>
> Cc: <stable@vger.kernel.org>

This resolves the build error I see with LLVM_IAS=1 and ToT LLVM.

Tested-by: Nathan Chancellor <natechancellor@gmail.com>

> ---
> Changes in v2
> * Correct the message: SYM_FUNC_START_WEAK was not available at commit 393f203f5fd5.
> * Mention Fixes: ef1e03152cb0
> ---
>  arch/x86/lib/memcpy_64.S  | 4 +---
>  arch/x86/lib/memmove_64.S | 4 +---
>  arch/x86/lib/memset_64.S  | 4 +---
>  3 files changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
> index 037faac46b0c..1e299ac73c86 100644
> --- a/arch/x86/lib/memcpy_64.S
> +++ b/arch/x86/lib/memcpy_64.S
> @@ -16,8 +16,6 @@
>   * to a jmp to memcpy_erms which does the REP; MOVSB mem copy.
>   */
>  
> -.weak memcpy
> -
>  /*
>   * memcpy - Copy a memory block.
>   *
> @@ -30,7 +28,7 @@
>   * rax original destination
>   */
>  SYM_FUNC_START_ALIAS(__memcpy)
> -SYM_FUNC_START_LOCAL(memcpy)
> +SYM_FUNC_START_WEAK(memcpy)
>  	ALTERNATIVE_2 "jmp memcpy_orig", "", X86_FEATURE_REP_GOOD, \
>  		      "jmp memcpy_erms", X86_FEATURE_ERMS
>  
> diff --git a/arch/x86/lib/memmove_64.S b/arch/x86/lib/memmove_64.S
> index 7ff00ea64e4f..41902fe8b859 100644
> --- a/arch/x86/lib/memmove_64.S
> +++ b/arch/x86/lib/memmove_64.S
> @@ -24,9 +24,7 @@
>   * Output:
>   * rax: dest
>   */
> -.weak memmove
> -
> -SYM_FUNC_START_ALIAS(memmove)
> +SYM_FUNC_START_WEAK(memmove)
>  SYM_FUNC_START(__memmove)
>  
>  	mov %rdi, %rax
> diff --git a/arch/x86/lib/memset_64.S b/arch/x86/lib/memset_64.S
> index 9ff15ee404a4..0bfd26e4ca9e 100644
> --- a/arch/x86/lib/memset_64.S
> +++ b/arch/x86/lib/memset_64.S
> @@ -6,8 +6,6 @@
>  #include <asm/alternative-asm.h>
>  #include <asm/export.h>
>  
> -.weak memset
> -
>  /*
>   * ISO C memset - set a memory block to a byte value. This function uses fast
>   * string to get better performance than the original function. The code is
> @@ -19,7 +17,7 @@
>   *
>   * rax   original destination
>   */
> -SYM_FUNC_START_ALIAS(memset)
> +SYM_FUNC_START_WEAK(memset)
>  SYM_FUNC_START(__memset)
>  	/*
>  	 * Some CPUs support enhanced REP MOVSB/STOSB feature. It is recommended
> -- 
> 2.29.1.341.ge80a0c044ae-goog
> 
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