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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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