On 02/23/2014 07:02 PM, Vince Weaver wrote:
> On Sun, 23 Feb 2014, Vince Weaver wrote:
>>
>> and as far as I can tell nothing touches rbp again until the segfault.
>> Nothing in _memset_sse2 does as far as I can tell.
>
> I only know enough about ftrace to be dangerous, but here is what I think
> is the trace of the problem:
>
> perf_fuzzer-11492 [000] 197077.488420: function:
> perf_output_put_handle
> perf_fuzzer-11492 [000] 197077.488421: function:
> __do_page_fault
So we do a write to the buffer rather immediately before this happens,
and in particular that will update the head:
rb->user_page->data_head = head;
However, that doesn't explain what is going on and in particular the
write to whatever address was in %rbp. The rest pretty much seems to be
the page fault logic.
Incidentally, I doubt that this is x32-related in any way; there seems
to be absolutely no difference between x86-64 perf and x32 perf; more
likely it just makes the error more reproducible because the address
space is so much smaller.
-hpa
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