[Bug c/52991] attribute packed broken on mingw32?

[mikpe at it dot uu.se]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52991

Mikael Pettersson <mikpe at it dot uu.se> changed:

           What    |Removed                     |Added
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                 CC|                            |kkojima at gcc dot gnu.org

--- Comment #4 from Mikael Pettersson <mikpe at it dot uu.se> 2012-08-19 20:56:19 UTC ---
The problem started with the PR27942 fix in r114552:
http://gcc.gnu.org/ml/gcc-patches/2006-06/msg00569.html
http://gcc.gnu.org/ml/gcc-cvs/2006-06/msg00268.html
and it affects gcc-4.2.0 up to current trunk.

The problem isn't mingw-specific, it can be reproduced natively on e.g.
x86_64-linux.  Take this C test case, reduced from #c1:

struct A {
    short s;
    struct { int i; } x;
} __attribute__((__packed__));

struct C {
    struct { int i; } x;
    short s;
} __attribute__((__packed__));

int foo(void)
{
    return sizeof(struct A) == sizeof(struct C);
}

Compiling this with -mno-ms-bitfields makes foo() return 1, but compiling with
-mms-bitfields makes foo() return 0 because sizeof(struct A) then is 8 while
sizeof(struct C) still is 6.