Re: [PATCH] codetag: Avoid unused alloc_tags sections/symbols

From: Kent Overstreet
Date: Thu Mar 13 2025 - 13:19:21 EST


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@xxxxxxxx>

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

> ---
> 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
>