Re: [PATCH 03/15] perf symbols: Use fixed buffer in sysfs__read_build_id() for no-libelf build

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Type punning via pointer casting from a declared character array to a struct pointer violates strict aliasing rules required for `tools/` code.
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commit 712f0fc91e35c55d2c2445bb412251f7934f7642
Author: Arnaldo Carvalho de Melo <acme@redhat.com>

perf symbols: Use fixed buffer in sysfs__read_build_id() for no-libelf build

This commit replaces an fstat() and malloc() approach with a fixed stack
buffer and a single read() in sysfs__read_build_id(). This ensures proper
handling of sysfs pseudo-files that report a size of 0 or 4096 regardless
of actual content.

> diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
> index 0a71d14639527..ea2de3d50d33c 100644
> --- a/tools/perf/util/symbol-minimal.c
> +++ b/tools/perf/util/symbol-minimal.c
> @@ -220,29 +220,36 @@ int sysfs__read_build_id(const char *filename, struct build_id *bid)
>  {

[ ... ]

> +	/*
> +	 * read_build_id() casts this buffer to a u32 note header pointer,
> +	 * so it must be aligned for u32 access.
> +	 *
> +	 * Accessing a char[] through a u32* is technically type-punning
> +	 * under C strict aliasing rules, but perf unconditionally builds
> +	 * with -fno-strict-aliasing (Makefile.config), so this is safe.
> +	 *
> +	 * This file is only compiled when libelf is not available — the
> +	 * common case uses the libelf-based path in symbol-elf.c instead.
> +	 */
> +	char buf[BUFSIZ] __aligned(4);

[Severity: Low]
While the comment notes that perf currently builds with -fno-strict-aliasing,
the tools directory guidelines require assuming standard -fstrict-aliasing
for all tools code.

Does casting this character array to an incompatible u32 struct pointer
inside read_build_id() violate the strict aliasing rules expected for this
subsystem?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260612003444.50723-1-acme@kernel.org?part=3