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SubjectRe: [BUG REPORT] perf tools: x86_64: Broken calllchain when sampling taken at 'callq' instruction

* Wangnan (F) <wangnan0@huawei.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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