linux-kernel - Re: [PATCH] perf: Ignore stripped vmlinux and fallback to kallsyms

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Date:	Fri, 12 Sep 2014 15:33:20 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Anton Blanchard <anton@...ba.org>
Cc:	acme@...hat.com, a.p.zijlstra@...llo.nl, paulus@...ba.org,
	mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: Ignore stripped vmlinux and fallback to kallsyms

Hi Anton,

On Tue, 9 Sep 2014 08:59:29 +1000, Anton Blanchard wrote:
> If a vmlinux is stripped, perf will use it and ignore kallsyms. We
> end up with useless profiles where everything maps to a few
> runtime symbols:
>
>     63.39%       swapper  [kernel.kallsyms]   [k] hcall_real_table
>      4.90%      beam.smp  [kernel.kallsyms]   [k] hcall_real_table
>      4.44%      beam.smp  [kernel.kallsyms]   [k] __sched_text_start
>      3.72%      beam.smp  [kernel.kallsyms]   [k] __run_at_kexec
>
> Detect this case and fallback to using kallsyms. This fixes the issue:
>
>     62.81%       swapper  [kernel.kallsyms]   [k] snooze_loop
>      4.44%      beam.smp  [kernel.kallsyms]   [k] __schedule
>      0.91%      beam.smp  [kernel.kallsyms]   [k] _switch
>      0.73%      beam.smp  [kernel.kallsyms]   [k] put_prev_entity
>
> Signed-off-by: Anton Blanchard <anton@...ba.org>

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung


> ---
>
> Index: b/tools/perf/util/symbol-elf.c
> ===================================================================
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -712,6 +712,14 @@ int dso__load_sym(struct dso *dso, struc
>  		symbols__delete(&dso->symbols[map->type]);
>  
>  	if (!syms_ss->symtab) {
> +		/*
> +		 * If the vmlinux is stripped, fail so we will fall back
> +		 * to using kallsyms. The vmlinux runtime symbols aren't
> +		 * of much use.
> +		 */
> +		if (dso->kernel)
> +			goto out_elf_end;
> +
>  		syms_ss->symtab  = syms_ss->dynsym;
>  		syms_ss->symshdr = syms_ss->dynshdr;
>  	}
--
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