linux-kernel - Re: [PATCH 3/3] perf: parse the .debug_frame section in case .eh_frame is not present

Open Source and information security mailing list archives

Date:	Thu, 5 Sep 2013 15:05:57 +0200
From:	Jean Pihet <jean.pihet@...oldbits.com>
To:	Will Deacon <will.deacon@....com>
Cc:	Jean Pihet <jean.pihet@...aro.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"patches@...aro.org" <patches@...aro.org>,
	Michael Hudson-Doyle <michael.hudson@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] perf: parse the .debug_frame section in case
 .eh_frame is not present

Hi Will,

On Thu, Sep 5, 2013 at 2:45 PM, Will Deacon <will.deacon@....com> wrote:
> Hi Jean,
>
> [adding Michael, since I know he was interested in this]
>
> On Wed, Sep 04, 2013 at 07:04:14PM +0100, Jean Pihet wrote:
>> On ARM the debug info is not present in the .eh_frame sections but
>> instead in .debug_frame.
>> Use libunwind to load and parse the debug info.
>
> How have you tested this? Regardless of whether or not I apply this patch, I
> get the same (broken/truncated) callchains for userspace in perf report.
Here are the commands I have been using:
 perf record -g dwarf -- <binary to profile>
 perf report --sort symbol --call-graph --stdio

>
> E.g. the following stupid program (built with -O0 -g):
>
> --->8
>
> void bar(void)
> {
>         int i;
>         for (i = 0; i < 1000000; ++i)
>                 asm volatile("nop" ::: "memory");
> }
>
> void foo(void)
> {
>         bar();
> }
>
>
> int main(void)
> {
>         foo();
>         return 0;
> }
>
> 8<---
>
> Gives me an incomplete callchain:
>
> # Overhead   Command      Shared Object                           Symbol
> # ........  ........  .................  ...............................
> #
>      0.00%  unwindme  unwindme           [.] bar
>             |
>             --- bar
I get the following with a simple stupid program with a long call chain:
     0.57%  stress_bt  stress_bt          [.] foo_115
            |
            --- foo_115
                foo_114
                foo_113
...
                foo_92
                bar
                doit
                main
                __libc_start_main

Things to check:
- compile the binaries and libraries with -g (-dbg flavor of libs are
usually ok),
- use -g dwarf in perf record

> This is the same with or without your patch.
>
> Will

Thanks for testing!
Jean

>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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