Crash when recording clock_gettime

Robert O'Callahan robert at ocallahan.org
Mon Aug 28 21:38:08 UTC 2017


On Tue, Aug 29, 2017 at 9:36 AM, Robert O'Callahan <robert at ocallahan.org>
wrote:

> On Tue, Aug 29, 2017 at 8:14 AM, Benjamin King <benjaminking at web.de>
> wrote:
>
>> clock_gettime from my libc disassembles to this:
>> ----
>> 0000000000115810 <__clock_gettime@@GLIBC_PRIVATE>:
>>  115810:        55                      push   %rbp
>>  115811:        53                      push   %rbx
>>  115812:        48 89 f5                mov    %rsi,%rbp
>>  115815:        89 fb                   mov    %edi,%ebx
>>  115817:        48 83 ec 08             sub    $0x8,%rsp
>>  11581b:        48 8b 05 c6 3a 2b 00    mov    0x2b3ac6(%rip),%rax
>> # 3c92e8 <_dl_open_hook@@GLIBC_PRIVATE+0x8>
>>  115822:        48 c1 c8 11             ror    $0x11,%rax
>>  115826:        64 48 33 04 25 30 00    xor    %fs:0x30,%rax
>>  11582d:        00 00  11582f:  48 85 c0                test   %rax,%rax
>>  115832:        74 2c                   je     115860 <__clock_gettime@
>> @GLIBC_PRIVATE+0x50>
>>  115834:        ff d0                   callq  *%rax
>>  ...
>> ----
>>
>> Both commit e7b00db and the previous one are going through this, but the
>> call
>> to *%rax sends rr commit e7b00db to a bunch of instructions that are not
>> in
>> the disassembly of my libc. I also fail to understand what they are
>> supposed
>> to do and they crash, eventually.
>>
>
> Can you paste the disassembly of those instructions at *%rax in the
> failing case? Also, if you look up /proc/<pid>/maps for the process you
> should be able to see the mapping they belong to.
>

Also, try running with RR_LOG=Monkeypatcher. That should give us some
useful output.

Rob
-- 
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