linux-kernel - Re: [PATCH] linkage: Fix issue with missing symbol size

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Date:   Tue, 3 May 2022 15:30:28 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, jpoimboe@...hat.com, linux-kernel@...r.kernel.org,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH] linkage: Fix issue with missing symbol size

On Fri, Apr 29, 2022 at 11:18:59AM +0200, Peter Zijlstra wrote:
> 
> Occasionally, typically when a function doesn't end with 'ret', an
> alias on that function will have 0 size.
> 
> The difference between what GCC generates and our linkage magic, is
> that GCC doesn't appear to provide .size for the alias'ed symbol at
> all. And indeed, removing this directive cures the issue.
> 
> Additionally, GCC also doesn't emit .type for alias symbols either, so
> also omit that.
> 
> Fixes: e0891269a8c2 ("linkage: add SYM_FUNC_ALIAS{,_LOCAL,_WEAK}()")
> Suggested-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Sorry about this!

FWIW:

Reviewed-by: Mark Rutland <mark.rutland@....com>

Thanks,
Mark.

> ---
>  include/linux/linkage.h |   15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> --- a/include/linux/linkage.h
> +++ b/include/linux/linkage.h
> @@ -171,12 +171,9 @@
>  
>  /* SYM_ALIAS -- use only if you have to */
>  #ifndef SYM_ALIAS
> -#define SYM_ALIAS(alias, name, sym_type, linkage)			\
> -	linkage(alias) ASM_NL						\
> -	.set alias, name ASM_NL						\
> -	.type alias sym_type ASM_NL					\
> -	.set .L__sym_size_##alias, .L__sym_size_##name ASM_NL		\
> -	.size alias, .L__sym_size_##alias
> +#define SYM_ALIAS(alias, name, linkage)			\
> +	linkage(alias) ASM_NL				\
> +	.set alias, name ASM_NL
>  #endif
>  
>  /* === code annotations === */
> @@ -261,7 +258,7 @@
>   */
>  #ifndef SYM_FUNC_ALIAS
>  #define SYM_FUNC_ALIAS(alias, name)					\
> -	SYM_ALIAS(alias, name, SYM_T_FUNC, SYM_L_GLOBAL)
> +	SYM_ALIAS(alias, name, SYM_L_GLOBAL)
>  #endif
>  
>  /*
> @@ -269,7 +266,7 @@
>   */
>  #ifndef SYM_FUNC_ALIAS_LOCAL
>  #define SYM_FUNC_ALIAS_LOCAL(alias, name)				\
> -	SYM_ALIAS(alias, name, SYM_T_FUNC, SYM_L_LOCAL)
> +	SYM_ALIAS(alias, name, SYM_L_LOCAL)
>  #endif
>  
>  /*
> @@ -277,7 +274,7 @@
>   */
>  #ifndef SYM_FUNC_ALIAS_WEAK
>  #define SYM_FUNC_ALIAS_WEAK(alias, name)				\
> -	SYM_ALIAS(alias, name, SYM_T_FUNC, SYM_L_WEAK)
> +	SYM_ALIAS(alias, name, SYM_L_WEAK)
>  #endif
>  
>  /* SYM_CODE_START -- use for non-C (special) functions */
>