Bug#639818: gcc-4.6: valgrind reports "Invalid read of size 4" in legal code

[Nikos Mavrogiannopoulos <n.mavrogiannopoulos@gmail.com>]

Package: gcc-4.6
Version: 4.6.1-4
Severity: important
Tags: upstream

The attached code is being miscompiled with gcc-4.6 (works perfectly with 4.4
or 4.5). The error can be seen if valgrind is run on the resulting executable
as:

==21804== Invalid read of size 4
==21804==    at 0x400437: main (c.c:12)
==21804==  Address 0x51b1048 is 8 bytes inside a block of size 11 alloc'd
==21804==    at 0x4C2779D: malloc (in /usr/lib/valgrind/vgpreload_memcheck-
amd64-linux.so)
==21804==    by 0x40040D: main (c.c:9)

-- System Information:
Debian Release: wheezy/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 3.0.0-1-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_US.utf8, LC_CTYPE=en_US.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages gcc-4.6 depends on:
ii  binutils              2.21.52.20110606-2 The GNU assembler, linker and bina
ii  cpp-4.6               4.6.1-4            GNU C preprocessor
ii  gcc-4.6-base          4.6.1-4            GCC, the GNU Compiler Collection (
ii  libc6                 2.13-16            Embedded GNU C Library: Shared lib
ii  libcloog-ppl0         0.15.9-3           the Chunky Loop Generator (runtime
ii  libgcc1               1:4.6.1-4          GCC support library
ii  libgmp10              2:5.0.1+dfsg-7     Multiprecision arithmetic library
ii  libgmpxx4ldbl         2:5.0.1+dfsg-7     Multiprecision arithmetic library
ii  libgomp1              4.6.1-4            GCC OpenMP (GOMP) support library
ii  libmpc2               0.9-3              multiple precision complex floatin
ii  libmpfr4              3.0.1-5            multiple precision floating-point
ii  libppl-c4             0.11.2-4           Parma Polyhedra Library (C interfa
ii  libppl9               0.11.2-4           Parma Polyhedra Library (runtime l
ii  libquadmath0          4.6.1-4            GCC Quad-Precision Math Library
ii  zlib1g                1:1.2.3.4.dfsg-3   compression library - runtime

Versions of packages gcc-4.6 recommends:
ii  libc6-dev                     2.13-16    Embedded GNU C Library: Developmen

Versions of packages gcc-4.6 suggests:
pn  binutils-gold                 <none>     (no description available)
pn  gcc-4.6-doc                   <none>     (no description available)
pn  gcc-4.6-locales               <none>     (no description available)
pn  gcc-4.6-multilib              <none>     (no description available)
pn  libgcc1-dbg                   <none>     (no description available)
pn  libgomp1-dbg                  <none>     (no description available)
pn  libmudflap0-4.6-dev           <none>     (no description available)
pn  libmudflap0-dbg               <none>     (no description available)
pn  libquadmath0-dbg              <none>     (no description available)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char** argv)
{
char *z;
  
  z = malloc(11);
  
  strcpy(z, "hello ppl"); /* 9 chars */
  strcat(z, "."); /* + 1 */
  
  return 0;
}