Re: [PATCH v6 25/26] perf annotate-arm64: Support per-cpu variable access tracking

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] perf: retry mechanism fails for per-cpu variable loads
--

commit 0a8000b94df79930832d6fd4535fbe42f682b339
Author: Tengda Wu <wutengda@huaweicloud.com>

perf annotate-arm64: Support per-cpu variable access tracking

This commit extends update_insn_state_arm64() to handle per-cpu variable
addressing. It detects pairs resolving to the '__per_cpu_offset' symbol
and marks the destination register as TSR_KIND_PERCPU_BASE to propagate
type information during subsequent instructions.

> diff --git a/tools/perf/util/annotate-arch/annotate-arm64.c b/tools/perf/util/annotate-arch/annotate-arm64.c
> index b25a3c70675c1..f4b7b0eb44f42 100644
> --- a/tools/perf/util/annotate-arch/annotate-arm64.c
> +++ b/tools/perf/util/annotate-arch/annotate-arm64.c
[ ... ]
> @@ -666,6 +677,12 @@ static int propagate_load_reg_state(struct type_state *state,
>  	}
>  
>  load_non_regoff:
> +	/*
> +	 * If src_tsr->kind is TSR_KIND_PERCPU_BASE, treat it as an array.
> +	 * No special handling is needed here; just fall through to retry
> +	 * and resolve the type from the second register.
> +	 */
> +
>  	/* Try another register if any */
>  	if (src->multi_regs && src->reg1 != src->reg2 && sreg != src->reg2 &&
>  	    !(src->extend_type || src->shift_type)) {

[Severity: Medium]
Will this retry logic actually succeed for per-cpu variable loads?

Since both registers in the per-cpu load are non-constant
(TSR_KIND_PERCPU_BASE and TSR_KIND_GLOBAL_ADDR), arch_get_reg_offset()
returns -1 for both the initial attempt and the retry pass because it
requires the 'other' register in a multi-register operand to be
TSR_KIND_CONST.

Does this break the intended fallback logic here in
propagate_load_reg_state(), resulting in an unhandled -1 return and
silent type propagation failure?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1789521520.git.wutengda@huaweicloud.com?part=25