[Bug 1203496] Re: micompilation of autoconf stack growth test at -O > 0 on ARM

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------------------------------------------------------------------------
On 2013-09-05T10:06:26+00:00 Doko-v wrote:

seen on arm-linux-gnueabihf, as part of an autoconf test in librep:

$ cat stack.c 
#include <stdlib.h>

void inner (char *foo) {
  char bar;
  exit (!(foo >= &bar));
}

void main () {
  char foo;
  inner (&foo);
}

$ gcc-4.6 -o conftest -O2 stack.c && ./conftest ; echo $?
0
$ gcc-4.7 -o conftest -O2 stack.c && ./conftest ; echo $?
1
$ gcc-4.8 -o conftest -O2 stack.c && ./conftest ; echo $?
1
$ gcc-4.8 -o conftest -O0 stack.c && ./conftest ; echo $?
0

Reply at:
https://bugs.launchpad.net/ubuntu/+source/gcc-4.8/+bug/1203496/comments/1

------------------------------------------------------------------------
On 2013-09-05T10:36:36+00:00 Rguenth wrote:

Well, it's clearly a bogus test - you are comparing addresses of two
distinct objects which invokes undefined behavior.

Reply at:
https://bugs.launchpad.net/ubuntu/+source/gcc-4.8/+bug/1203496/comments/2


** Changed in: gcc
       Status: Unknown => Invalid

** Changed in: gcc
   Importance: Unknown => Medium

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https://bugs.launchpad.net/bugs/1203496

Title:
  micompilation of autoconf stack growth test at -O > 0 on ARM

Status in The GNU Compiler Collection:
  Invalid
Status in Linaro GCC:
  New
Status in “gcc-4.7” package in Ubuntu:
  New
Status in “gcc-4.8” package in Ubuntu:
  New

Bug description:
  This autoconf test works on x86, but appears to fail on ARM when built
  with optimisation.  It worked fine with gcc-4.6, and fails with 4.7.
  Versions here were all from current saucy:

  gcc-4.6: 4.6.4-3ubuntu1
  gcc-4.7: 4.7.3-6ubuntu1
  gcc-4.8: 4.8.1-7ubuntu1

  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ gcc-4.6 -o conftest -O2 stack.c
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ ./conftest ; echo $?
  0
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ gcc-4.7 -o conftest -O2 stack.c
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ ./conftest ; echo $?
  1
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ gcc-4.8 -o conftest -O2 stack.c
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ ./conftest ; echo $?
  1
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ gcc-4.8 -o conftest -O1 stack.c
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ ./conftest ; echo $?
  1
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ gcc-4.8 -o conftest -O0 stack.c
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ ./conftest ; echo $?
  0
  (saucy-kde)adconrad at shiva:~/librep-0.90.2$ cat stack.c 
  #include <stdlib.h>

  void inner (char *foo) {
    char bar;
    exit (!(foo >= &bar));
  }

  void main () {
    char foo;
    inner (&foo);
  }

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