linux-kernel - Re: [PATCH] codetag: Avoid unused alloc

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Message-ID: <jmcazyqlkimqhswwqn2du7ik5sbm5fommonrgovy5d6knqbqcr@xebmu4akkkoy>
Date: Thu, 13 Mar 2025 13:16:13 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Petr Pavlu <petr.pavlu@...e.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>, Arnd Bergmann <arnd@...db.de>, 
	linux-arch@...r.kernel.org, linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] codetag: Avoid unused alloc_tags sections/symbols

On Thu, Mar 13, 2025 at 03:29:20PM +0100, Petr Pavlu wrote:
> With CONFIG_MEM_ALLOC_PROFILING=n, vmlinux and all modules unnecessarily
> contain the symbols __start_alloc_tags and __stop_alloc_tags, which define
> an empty range. In the case of modules, the presence of these symbols also
> forces the linker to create an empty .codetag.alloc_tags section.
> 
> Update codetag.lds.h to make the data conditional on
> CONFIG_MEM_ALLOC_PROFILING.
> 
> Signed-off-by: Petr Pavlu <petr.pavlu@...e.com>

Reviewed-by: Kent Overstreet <kent.overstreet@...ux.dev>

> ---
>  include/asm-generic/codetag.lds.h | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/include/asm-generic/codetag.lds.h b/include/asm-generic/codetag.lds.h
> index 372c320c5043..0ea1fa678405 100644
> --- a/include/asm-generic/codetag.lds.h
> +++ b/include/asm-generic/codetag.lds.h
> @@ -2,6 +2,12 @@
>  #ifndef __ASM_GENERIC_CODETAG_LDS_H
>  #define __ASM_GENERIC_CODETAG_LDS_H
>  
> +#ifdef CONFIG_MEM_ALLOC_PROFILING
> +#define IF_MEM_ALLOC_PROFILING(...) __VA_ARGS__
> +#else
> +#define IF_MEM_ALLOC_PROFILING(...)
> +#endif
> +
>  #define SECTION_WITH_BOUNDARIES(_name)	\
>  	. = ALIGN(8);			\
>  	__start_##_name = .;		\
> @@ -9,7 +15,7 @@
>  	__stop_##_name = .;
>  
>  #define CODETAG_SECTIONS()		\
> -	SECTION_WITH_BOUNDARIES(alloc_tags)
> +	IF_MEM_ALLOC_PROFILING(SECTION_WITH_BOUNDARIES(alloc_tags))
>  
>  /*
>   * Module codetags which aren't used after module unload, therefore have the
> @@ -28,6 +34,6 @@
>   * unload them individually once unused.
>   */
>  #define MOD_SEPARATE_CODETAG_SECTIONS()		\
> -	MOD_SEPARATE_CODETAG_SECTION(alloc_tags)
> +	IF_MEM_ALLOC_PROFILING(MOD_SEPARATE_CODETAG_SECTION(alloc_tags))
>  
>  #endif /* __ASM_GENERIC_CODETAG_LDS_H */
> 
> base-commit: 80e54e84911a923c40d7bee33a34c1b4be148d7a
> -- 
> 2.43.0
>