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

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] perf: build failure on non-elfutils systems due to removed ELF_C_READ_MMAP fallback
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commit 85681e93b31655f473355c4d4ba6288016a5ebcd
Author: Alireza Haghdoost <haghdoost@uber.com>

perf symbols: Fix broken ELF_C_READ_MMAP fallback guard

This commit removes the compile-time fallback guard for ELF_C_READ_MMAP,
relying on the assumption that perf already requires a recent elfutils version
that provides this enumerator. It replaces the conditional definition with an
unconditional one.

> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index d0bac824c79c8..46b1649c64fc7 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

[Severity: Low]
Does this unconditional reference cause a build failure on systems using
alternative libelf implementations?

ELF_C_READ_MMAP is an elfutils-specific extension and is undefined in
alternative implementations like elftoolchain, or in older libelf releases.

The perf build system verifies basic libelf support via test-libelf.c, which
only probes for ELF_C_READ. If a non-elfutils libelf is installed, the feature
test successfully passes and sets HAVE_LIBELF_SUPPORT.

When the compiler then evaluates symbol.h, the unconditional reference to
ELF_C_READ_MMAP will trigger an 'undeclared identifier' error.

Should this optional library extension be dynamically probed (e.g., via 
test-libelf-mmap.c) and safely guarded with fallbacks to avoid breaking builds 
on non-elfutils systems?

>  
>  #ifdef HAVE_LIBELF_SUPPORT
>  Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,

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Sashiko AI review · https://sashiko.dev/#/patchset/20260919-perf-symbol-memory-send-v2-0-495b8f00ad7c@uber.com?part=1