Bug#538019: gcc-4.2: -f no-strict-overflow causes bad code generation

[Henrique de Moraes Holschuh <hmh@debian.org>]

Package: gcc-4.2
Version: 4.2.4-6
Severity: important
Tags: fixed-upstream

gcc 4.2.4-6 generates bad code when -f no-strict-overflow is used.

This causes kernel 2.6.27.27 and 2.6.30.2 to be miscompiled and hang. It
may be a cause of suble errors elsewhere in the kernel, too.

I don't know if the pattern of code that triggers the problem is common
in userspace.

gcc 4.3.2-1.1 doesn't exibit the bug, so it is already fixed upstream,
but probably not in the 4.2 branch.

Refer to http://lkml.org/lkml/2009/7/21/493 for details.
Refer to http://lkml.org/lkml/2009/7/22/181 for a minimal test case.

--- Test case by Krzysztof Oledzki, from the link above: ---

--- fno-strict-overflow-fixed-bug.c ---
#include <stdio.h>
int main() {
         unsigned char i;

         for (i = 0; i < 128; i++)
                 printf("loop %u\n", i);

         return 0;
}
--- cut here ---

The code should be compiled with:

  cc -o fno-strict-overflow-fixed-bug -Os -fno-strict-overflow fno-strict-overflow-fixed-bug.c

or:

  cc -o fno-strict-overflow-fixed-bug -O2 -fno-strict-overflow fno-strict-overflow-fixed-bug.c

This bug does not exist with -O1 or if the loop is controlled by
"i < 127" or "i < 129".

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

-- System Information:
Debian Release: 5.0.2
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: i386 (i686)

Kernel: Linux 2.6.29.6-t43 (PREEMPT)
Locale: LANG=pt_BR.ISO-8859-1, LC_CTYPE=pt_BR.ISO-8859-1 (charmap=ISO-8859-1)
Shell: /bin/sh linked to /bin/dash

Versions of packages gcc-4.2 depends on:
ii  binutils            2.18.1~cvs20080103-7 The GNU assembler, linker and bina
ii  cpp-4.2             4.2.4-6              The GNU C preprocessor
ii  gcc-4.2-base        4.2.4-6              The GNU Compiler Collection (base 
ii  libc6               2.7-18               GNU C Library: Shared libraries
ii  libgcc1             1:4.3.2-1.1          GCC support library

Versions of packages gcc-4.2 recommends:
ii  libc6-dev                     2.7-18     GNU C Library: Development Librari

Versions of packages gcc-4.2 suggests:
ii  gcc-4.2-doc                  4.2.4.nf1-3 documentation for the GNU compiler
pn  gcc-4.2-locales              <none>      (no description available)
pn  gcc-4.2-multilib             <none>      (no description available)
pn  libgcc1-dbg                  <none>      (no description available)
pn  libgomp1-dbg                 <none>      (no description available)
pn  libmudflap0-4.2-dev          <none>      (no description available)
pn  libmudflap0-dbg              <none>      (no description available)

-- no debconf information