[Bug 810739] Re: strcpy output incorrect if src and dst overlap

[Adam Conrad]

Does this bug still affect precise?  If it's the sse3 memcpy bug, it
should have been fixed in git before 2.15 was cut, so precise and
quantal should be fine.  Can anyone confirm?

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https://bugs.launchpad.net/bugs/810739

Title:
  strcpy output incorrect if src and dst overlap

Status in “eglibc” package in Ubuntu:
  Confirmed

Bug description:
  A commercial application (Cadence) that runs with an older libc gives
  incorrect results with the current libc.  I've tracked down the
  problem to strcpy. If I make my own strcopy, following the template of
  https://bugzilla.redhat.com/show_bug.cgi?id=638477#c38, the tool gives
  correct results.  Here is mystrcpy.c:

  $ cat mystrcpy.c

  char *strcpy(char *dest, const char *src){
    char *destcopy=dest;
    while(*dest++ = *src++) 
          ;
    return destcopy;
  }

  I've traced through the application and see that it
  is calling strcpy with overlapping source and destination,
  and that the execution goes through __strcpy_ssse3,
  which seems to cause the problem.

  I made a small testcase to replicate the behavior. 
  Following http://forums.gentoo.org/viewtopic-t-840983-start-0.html,
  here is my test case:
  ------------
  $ cat strcopytest.c
  char *strcpy(char *,char *);
  int main(){ 
          char buf[80]; 
          strcpy(buf, "012345678\n"); 
          strcpy(buf, buf+1); 
          puts(buf); 
          return 0; 
  }

  $ gcc -O2 -c mystrcpy.c
  $ ld -G mystrcpy.o -o mystrcpy.so
  $ gcc strcopytest.c -o strcopytest
  $ ./strcopytest 
  12345688

  $ LD_PRELOAD=./mystrcpy.so ./strcopytest
  12345678

  ----------------

  I know that I can make my testcase work with #include "string.h",
  but the I cannot recompile the commercial application, so that's not
  a workable solution.

  ProblemType: Bug
  DistroRelease: Ubuntu 11.04
  Package: libc6 2.13-0ubuntu13
  ProcVersionSignature: Ubuntu 2.6.39-3.10-generic 2.6.39
  Uname: Linux 2.6.39-3-generic x86_64
  Architecture: amd64
  Date: Thu Jul 14 13:43:36 2011
  InstallationMedia: Ubuntu 10.04 "Lucid Lynx" - Beta amd64 (20100317.1)
  ProcEnviron:
   LANGUAGE=en_US:en
   PATH=(custom, user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: eglibc
  UpgradeStatus: Upgraded to natty on 2011-04-29 (76 days ago)

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