Re: [Patch v9 05/10] perf regs: Support x86 eGPRs/SSP sampling

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Reclaiming XMM register space breaks explicit XMM register selection on SIMD-capable hosts.
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commit 4a688e42468a5e89b85174c21cc87866b350369c
Author: Dapeng Mi <dapeng1.mi@linux.intel.com>

perf regs: Support x86 eGPRs/SSP sampling

This commit adds support for sampling x86 extended GP registers (R16-R31)
and the shadow stack pointer (SSP) by reclaiming the original XMM register
space. A new abi argument is introduced to distinguish the register layout,
defaulting to the new SIMD layout on supported platforms.

> diff --git a/tools/perf/util/parse-regs-options.c b/tools/perf/util/parse-regs-options.c
> --- a/tools/perf/util/parse-regs-options.c
> +++ b/tools/perf/util/parse-regs-options.c
[ ... ]
> @@ -87,14 +100,16 @@ __parse_regs(const struct option *opt, const char *str, int unset, bool intr)
>  			*p = '\0';
>  
>  		if (!strcmp(s, "?")) {
> -			list_perf_regs(stderr, mask);
> +			list_perf_regs(stderr, mask, abi);
>  			goto error;
>  		}
>  
> -		reg_mask = name_to_perf_reg_mask(s, mask);
> -		if (reg_mask == 0) {
> -			ui__warning("Unknown register \"%s\", check man page or run \"perf record %s?\"\n",
> -				s, intr ? "-I" : "--user-regs=");
> +		reg_mask = name_to_perf_reg_mask(s, mask, abi);
> +		if (reg_mask) {
> +			if (abi & PERF_SAMPLE_REGS_ABI_SIMD)
> +				opts->sample_simd_regs_enabled = 1;
> +		} else {
> +			ui__warning(warn, s, intr ? "-I" : "--user-regs=");

[Severity: Medium]
Will this change break explicit XMM register selection on SIMD-capable hosts?

Because PERF_SAMPLE_REGS_ABI_SIMD is set by default on platforms with SIMD
support, the reclaimed register space means name_to_perf_reg_mask will now map
to eGPRs instead of XMM registers. 

If a user runs an existing script that explicitly requests individual XMM
registers, such as perf record -I xmm0, won't this branch fail to match the
string, return an Unknown register warning, and break backward compatibility
for those CLI options?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260706023444.3067660-1-dapeng1.mi@linux.intel.com?part=5