On Wed, Aug 21, 2013 at 01:45:12AM -0400, Behdad Esfahbod wrote:
> On 13-08-21 12:44 AM, Albert Chin wrote:
> > On AIX 32-bit and 64-bit, alignof(double) == 4. This isn't a
> > problem for 32-bit builds of fontconfig but for 64-bit builds, the
> > following assert in src/fcarch.c fails:
> > FC_ASSERT_STATIC (0x08 + 1*FC_MAX(4,ALIGNOF_DOUBLE) == sizeof (FcValue));
>
> So, what *is* sizeof(FcValue)? If alignof(double) is 4, double
> itself is 8, and enum is 4, then sizeof(FcValue) should be 12 which
> is exactly what the assertion is trying to ensure.
This is the offending line above compiled with -E:
typedef int _static_assert_on_line_59_failed[(((0x08 + 1*((4) > (4) ? (4) : (4)) == sizeof (FcValue))))?1:-1];
sizeof (FcValue) == 16.
typedef struct _FcValue { // sizeof(type)
FcType type; 4
union {
const FcChar8 *s; 8
int i; 4
FcBool b; 4
double d; 8
const FcMatrix *m; 8
const FcCharSet *c; 8
void *f; 8
const FcLangSet *l; 8
} u;
} FcValue; 16
AIX has some oddity when it comes to the alignment of aggregates
involving doubles:
http://pic.dhe.ibm.com/infocenter/comphelp/v111v131/topic/com.ibm.xlcpp111.aix.doc/proguide/aggregate_align.html
http://peeterjoot.wordpress.com/2009/11/11/c-structure-alignment-padding/
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10645
>From one of the comments in
http://peeterjoot.wordpress.com/2009/11/11/c-structure-alignment-padding/:
We don’t see the effects of this much anymore since 64-bit AIX
defaults to -qalign=natural, and we stopped shipping a 32-bit server
on AIX (32-bit client only).
However, we're using the v11 version of the compiler and it doesn't
seem to default to -qalign=natural:
$ cat >e.c <<_EOT_
#include <stdio.h>
struct {
char c1;
double d1;
} s1;
struct {
double d1;
char c1;
} s2;
int
main (void) {
printf ("sizeof (s1): %ld\n", sizeof (s1));
printf ("sizeof (s2): %ld\n", sizeof (s2));
}
_EOT_
$ xlc -q64 e.c && ./a.out
sizeof (s1): 12
sizeof (s2): 16
$ xlc -q64 -qalign=natural e.c && ./a.out
sizeof (s1): 16
sizeof (s2): 16
--
albert chin (china@xxxxxxxxxxxxxxxxxx)
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