linux-kernel - Re: [PATCH v1]: perf/x86: store user space frame-pointer value on a sample

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Date:   Fri, 6 Apr 2018 08:31:44 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1]: perf/x86: store user space frame-pointer value on a
 sample

> diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
> index e47b2dbbdef3..9284048cf5b0 100644
> --- a/arch/x86/kernel/perf_regs.c
> +++ b/arch/x86/kernel/perf_regs.c
> @@ -157,6 +157,15 @@ void perf_get_regs_user(struct perf_regs *regs_user,
>  	 */
>  	regs_user_copy->bx = -1;
>  	regs_user_copy->bp = -1;
> +	if (user_64bit_mode(user_regs)) {

Why is it 64bit only? Should work on 32bit too.

-Andi

> +		/*
> +		 * Store user space frame-pointer value on sample
> +		 * to facilitate stack unwinding for cases when
> +		 * user space x86_64 executable code has such
> +		 * support enabled at compile time;
> +		 */
> +		regs_user_copy->bp = user_regs->bp;
> +	}
>  	regs_user_copy->r12 = -1;
>  	regs_user_copy->r13 = -1;
>  	regs_user_copy->r14 = -1;