Re: [PATCH v2 1/4] perf symbols: Fix broken ELF_C_READ_MMAP fallback guard

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Sat, Sep 19, 2026 at 07:33:56PM -0700, Alireza Haghdoost via B4 Relay wrote:
> From: Alireza Haghdoost <haghdoost@uber.com>
> 
> Commit 22dd1ac91a77 ("tools: Remove feature-libelf-mmap feature
> detection") replaced perf's compile-time feature test with an #ifdef on
> ELF_C_READ_MMAP. ELF_C_READ_MMAP is an Elf_Cmd enumerator rather than a
> preprocessor macro, so the condition is always false and perf silently
> uses ELF_C_READ.
> 
> Perf already requires a sufficiently recent elfutils version that
> provides ELF_C_READ_MMAP. Use the enumerator directly instead of
> restoring a feature probe or retaining an unreachable fallback.
> 
> Fixes: 22dd1ac91a77 ("tools: Remove feature-libelf-mmap feature detection")
> Signed-off-by: Alireza Haghdoost <haghdoost@uber.com>

Reviewed-by: Namhyung Kim <namhyung@kernel.org>

Thanks,
Namhyung

> ---
>  tools/perf/util/symbol.h | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index d0bac824c79c..46b1649c64fc 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -57,15 +57,7 @@ static inline bool is_livepatch_symbol(const char *str)
>  	return strstarts(str, KLP_SYM_PREFIX);
>  }
>  
> -/*
> - * libelf 0.8.x and earlier do not support ELF_C_READ_MMAP;
> - * for newer versions we can use mmap to reduce memory usage:
> - */
> -#ifdef ELF_C_READ_MMAP
> -# define PERF_ELF_C_READ_MMAP ELF_C_READ_MMAP
> -#else
> -# define PERF_ELF_C_READ_MMAP ELF_C_READ
> -#endif
> +#define PERF_ELF_C_READ_MMAP ELF_C_READ_MMAP
>  
>  #ifdef HAVE_LIBELF_SUPPORT
>  Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
> 
> -- 
> Git-157)
> 
>