[Bug c/56341] New: GCC produces unaligned data access

[bernd.edlinger at hotmail dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56341

             Bug #: 56341
           Summary: GCC produces unaligned data access
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: bernd.edlinger@hotmail.de


Created attachment 29464
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29464
test program produces alignment faults

Hello,

The attached test program causes two problems when compiled with GCC 4.6.3 for
ARM:

1. test() fails to write the high word of an unaligned volatile struct member.

2. test1() crashes because it uses an unaligned word access.

This code did compile and execute correctly with GCC 4.3.2

As a workaround, the bug goes away if the code is compiled with
-fno-strict-volatile-bitfields,
but this is probably less efficient code.


The attached patch is a backport of the following patch, and seems to resolve
this issue:

http://gcc.gnu.org/ml/gcc-patches/2012-08/msg01449.html

the original patch ignored the alignment of the target, and fixed only the
first test case, but not the crash in the second test case.

Regards
Bernd Edlinger