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[Bug c/45317] New: struct union misalignment
- From: "sherpya at netfarm dot it" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 18 Aug 2010 03:51:54 -0000
- Subject: [Bug c/45317] New: struct union misalignment
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
Hi, bug or feature? I have this sample:
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdint.h>
int main(void)
{
union U
{
struct
{
uint32_t l;
uint32_t h;
} d;
uint64_t q;
};
struct S
{
uint32_t one;
union U two;
uint32_t three;
};
printf("sizeof(union) = %u\n", sizeof(union U));
printf("offsets %u, %u, %u\n", offsetof(struct S, one), offsetof(struct S,
two), offsetof(struct S, three));
return 0;
}
I have different results:
gcc version 4.4.5 20100816 (prerelease) (Debian 4.4.4-9) (32bit)
and gcc version 4.3.5 (Debian 4.3.5-2)
sizeof(union) = 8
offsets 0, 4, 12
----------------
gcc version 4.2.5 20090330 (prerelease) [Sherpya] (32bit latest changeset 4.2.5
on mingw)
and gcc version 4.4.3 on mingw32 (built from release tarball)
sizeof(union) = 8
offsets 0, 8, 16
---
I've discovered the problem by passing struct between a binary compiled with
msvc and my code, looks like the 'correct way' is to pad the first int32 in the
struct S with 4 byte to make union 'two' aligned to union size (8)
Something changed in gcc behavior that I don't known?
Regards
--
Summary: struct union misalignment
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: sherpya at netfarm dot it
GCC build triplet: i486-linux-gnu
GCC host triplet: i486-linux-gnu
GCC target triplet: i486-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45317