linux-kernel - Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling taken at 'callq' instruction

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Date:	Wed, 18 Nov 2015 09:20:33 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	David Ahern <dsahern@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Milian Wolff <milian.wolff@...b.com>,
	linux-kernel@...r.kernel.org, pi3orama <pi3orama@....com>,
	lizefan 00213767 <lizefan@...wei.com>
Subject: Re: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling
 taken at 'callq' instruction


* Wangnan (F) <wangnan0@...wei.com> wrote:

> On 2015/11/18 15:20, Wangnan (F) wrote:
> >Hi all,
> >
> >When analysising Jiri's patchset [1] I found a dwarf unwind problem.
> >On x86 platform, when sample is at a 'callq' instruction, dwarf based
> >stack unwind always fail.
> >
> >I compile a small C source file with debug information, turn off
> >frame pointer and disable optimization:
> >
> >$ gcc -g -O0 -fomit-frame-pointer ./test_dwarf_unwind.c -o
> >./test_dwarf_unwind
> 
> For whom want to test it: here is the test code I used.
> 
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/time.h>
> 
> static volatile int x = 0;
> 
> int funcc(void)
> {
>     struct timeval tv1, tv2;
>     unsigned long us1, us2;
> 
>     gettimeofday(&tv1, NULL);
> 
>     us1 = tv1.tv_sec * 1000000 + tv1.tv_usec;
> 
>     while(1) {
>         x = x + 100;
>         gettimeofday(&tv2, NULL);
>         us2 = tv2.tv_sec * 1000000 + tv2.tv_usec;
>         if (us2 - us1 >= 3000000)
>             break;
>     }
>     return x;
> }
> int funcb(void) { return funcc();}
> int funca(void) { return funcb();}
> int main() { funca(); return 0;}

What CPU model is this, and what event was used - PEBS perhaps? This might be some 
sort of PMU sampling bug/quirk/misfeature - or perhaps a kernel side fixup that 
went bad?

Thanks,

	Ingo
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