Re: [Patch v8 19/23] perf/x86: Support SSP sampling using sample_regs_* fields

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The uAPI header addition for PERF_REG_X86_SSP is not synchronized with the perf tool's copy, and the perf tool lacks support for formatting or synthesizing the new register.
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commit b3c69baea8c8d8c919d96ea56a7caf694d17f469
Author: Dapeng Mi <dapeng1.mi@linux.intel.com>

perf/x86: Support SSP sampling using sample_regs_* fields

This patch supports sampling of the CET SSP register via the sample_regs_*
fields by using spare space reclaimed from the XMM space. It updates the
register extraction logic and enables arch-PEBS-based SSP sampling on
x86_64.

> diff --git a/arch/x86/include/uapi/asm/perf_regs.h b/arch/x86/include/uapi/asm/perf_regs.h
> index 8774a1290fbef..31a025cb9dbaf 100644
> --- a/arch/x86/include/uapi/asm/perf_regs.h
> +++ b/arch/x86/include/uapi/asm/perf_regs.h

[ ... ]

> @@ -51,10 +51,11 @@ enum perf_event_x86_regs {
>  	PERF_REG_X86_R29,
>  	PERF_REG_X86_R30,
>  	PERF_REG_X86_R31,
> +	PERF_REG_X86_SSP,

[Severity: Medium]
Should the corresponding UAPI header for the perf tool in
tools/arch/x86/include/uapi/asm/perf_regs.h be updated in sync with this
change?

Also, does the perf tool require additional updates to support this new
register? Without adding a string representation mapping for SSP, the
tool might not be able to parse '--user-regs=ssp' or print the register
name.

Furthermore, tools/perf/util/intel-pt.c relies on PERF_REG_X86_64_MAX
and a hardcoded pebs_gp_regs array that does not currently include SSP.
Will this cause the SSP register to be silently dropped from synthesized
PT PEBS samples?

>  	/* These are the limits for the GPRs. */
>  	PERF_REG_X86_32_MAX = PERF_REG_X86_GS + 1,
>  	PERF_REG_X86_64_MAX = PERF_REG_X86_R15 + 1,
> -	PERF_REG_MISC_MAX = PERF_REG_X86_R31 + 1,
> +	PERF_REG_MISC_MAX = PERF_REG_X86_SSP + 1,
>  
>  	/* These all need two bits set because they are 128bit */
>  	PERF_REG_X86_XMM0  = 32,

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Sashiko AI review · https://sashiko.dev/#/patchset/20260529075645.580362-1-dapeng1.mi@linux.intel.com?part=19