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From: "sherpya at netfarm dot it" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/52991] New: attribute packed broken on mingw32?
Date: Sun, 15 Apr 2012 04:21:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52991

             Bug #: 52991
           Summary: attribute packed broken on mingw32?
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: sherpya@netfarm.it


I've switched form mingw gcc 4.6.2 to 4.7.0 and I've noticed that attribute
packed does not work anymore as expected, simple testcase:

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

typedef struct st_tag
{
    uint16_t head __attribute__ ((packed));
    uint8_t type;
    uint16_t flags __attribute__ ((packed));
} st;

int main(void)
{
    st x;
    printf("Structure packing got %u offset, expected 3\n",
(unsigned)((char*)&x.flags - (char*)&x));
    return 0;
}

the generated asm is:
        movl    $4, 4(%esp)
        movl    $LC0, (%esp)
        call    _printf

the value is 3 in gcc 4.6.2

Using built-in specs.
COLLECT_GCC=c:\mingw\bin\gcc-4.7.exe
COLLECT_LTO_WRAPPER=c:/mingw/bin/../libexec/gcc/i686-pc-mingw32/4.7.0/lto-wrapper.exe
Target: i686-pc-mingw32
Configured with: ../gcc-4.7.0/configure --prefix=/mingw --disable-bootstrap
--enable-lto --with-pkgversion=Sherpya --with-bugurl=http://oss.netfarm.it/
--target=i686-pc-mingw32 --enable-targets=i686-pc-mingw32 --with-tune=generic
--with-cpu=i686 --disable-win32-registry --disable-shared --program-suffix=-4.7
--enable-version-specific-runtime-libs --enable-languages=c,c++
--disable-werror --enable-threads=win32 --with-dwarf2 --disable-nls
Thread model: win32
gcc version 4.7.0 (Sherpya)

I don't think save-temps output may be relevant