linux-kernel - Re: [PATCH v2 07/10] perf annotate: Invalidate register states for unsupported instructions

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Message-ID: <aLKlDp6bl9Qjiziy@google.com>
Date: Sat, 30 Aug 2025 00:15:26 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Zecheng Li <zecheng@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Xu Liu <xliuprof@...gle.com>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 07/10] perf annotate: Invalidate register states for
 unsupported instructions

On Mon, Aug 25, 2025 at 07:57:48PM +0000, Zecheng Li wrote:
> Invalidate register states when encountering unsupported instructions
> that modify pointers, to prevent propagating incorrect pointer types.
> 
> On x86, the 'xor' instruction may appear in a predecessor basic block
> and zero out a register that invalidates the target register state. This
> sometimes relates to tagged pointers and normal programs should not
> dereference NULL pointers, so we assume such execution paths are invalid
> and do not invalidate states for 'xor' instructions.

Probably we can set it to 0 with TSR_KIND_CONST.

Thanks,
Namhyung

> 
> Signed-off-by: Zecheng Li <zecheng@...gle.com>
> ---
>  tools/perf/arch/x86/annotate/instructions.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/tools/perf/arch/x86/annotate/instructions.c b/tools/perf/arch/x86/annotate/instructions.c
> index 540b4d0a01af..03df52a5266d 100644
> --- a/tools/perf/arch/x86/annotate/instructions.c
> +++ b/tools/perf/arch/x86/annotate/instructions.c
> @@ -413,6 +413,23 @@ static void update_insn_state_x86(struct type_state *state,
>  		return;
>  	}
>  
> +	/* Invalidate register states for other ops which may change pointers */
> +	if (has_reg_type(state, dst->reg1) && !dst->mem_ref &&
> +	    dwarf_tag(&state->regs[dst->reg1].type) == DW_TAG_pointer_type) {
> +		if (!strncmp(dl->ins.name, "imul", 4) || !strncmp(dl->ins.name, "mul", 3) ||
> +		    !strncmp(dl->ins.name, "idiv", 4) || !strncmp(dl->ins.name, "div", 3) ||
> +		    !strncmp(dl->ins.name, "shl", 3)  || !strncmp(dl->ins.name, "shr", 3) ||
> +		    !strncmp(dl->ins.name, "sar", 3)  || !strncmp(dl->ins.name, "and", 3) ||
> +		    !strncmp(dl->ins.name, "or", 2)   || !strncmp(dl->ins.name, "neg", 3) ||
> +		    !strncmp(dl->ins.name, "inc", 3)  || !strncmp(dl->ins.name, "dec", 3)) {
> +			pr_debug_dtp("%s [%x] invalidate reg%d\n",
> +						dl->ins.name, insn_offset, dst->reg1);
> +			state->regs[dst->reg1].ok = false;
> +			state->regs[dst->reg1].copied_from = -1;
> +			return;
> +		}
> +	}
> +
>  	if (strncmp(dl->ins.name, "mov", 3))
>  		return;
>  
> -- 
> 2.51.0.261.g7ce5a0a67e-goog
>