[Bug 1027977] Re: strstr() function produces wrong results under valgrind callgrind

[Moritz Hassert]

Also created an upstream bug report:
https://bugs.kde.org/show_bug.cgi?id=303963

** Bug watch added: KDE Bug Tracking System #303963
   https://bugs.kde.org/show_bug.cgi?id=303963

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Title:
  strstr() function produces wrong results under valgrind callgrind

Status in “valgrind” package in Ubuntu:
  New

Bug description:
  $valgrind --version
  valgrind-3.7.0

  When an application that uses the strstr() function from the C standard library is profiled with valgrind --tool=callgrind, the strstr() function produces false results (at least) under the following conditions:
  * the string s1 to search in and the string s2 to search for are exact duplicates, that is strcmp(s1,s2)==0. s1 and s2 don't need to be pointing to the same memory object.
  * the string length (excluding terminating zero) is a multiple of 16

  Expected result: strstr(s1,s2) returns s1, indicating a match at the first charactor of s1
  What happens: strstr(s1,s2) returns NULL, indicating no matching substring was found.

  See attached minimal testcase for an example. Reproduce under Ubuntu 12.04 with the following steps:
  $gcc strstrtest.c -o strstrtest
  $./ strstrtest    # <-- should report no errors
  $valgrind --tool=callgrind ./ strstrtest  # <-- should report errors for lengths multiple of 16

  - The Problem does not show up under valgrind-3.6.0.SVN-Debian from Ubuntu 10.04 Lucid Lynx
  - The Problem does not show up under tool=memcheck.

  Some more info:
  OS: Ubuntu 12.04 Precise Pangolin
  $uname -a
  Linux mhassert 3.2.0-26-generic #41-Ubuntu SMP Thu Jun 14 17:49:24 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

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