On Tue, Nov 26, 2013 at 11:49 PM, Thorsten Glaser <t...@mirbsd.de> wrote:
> I know that GCC will need the alignment attribute twice in structs, e.g.
>
> struct foo {
> int bar __attribute__((__aligned__(8)));
> int baz;
> } __attribute__((__aligned__(8)));
That's not true: the alignment of a struct is the largest alignment of any
of its members. So the explicit alignment of bar is sufficient.
#include <stdio.h>
#include <stdlib.h>
struct foo {
int bar __attribute__((__aligned__(8)));
int baz;
} __attribute__((__aligned__(8)));
struct foo2 {
int bar __attribute__((__aligned__(8)));
int baz;
};
struct foo3 {
int bar;
int baz;
};
struct foo4 {
int bar;
int baz;
} __attribute__((__aligned__(8)));
int main(int argc, char *argv[])
{
printf("__alignof__(struct foo) = %zu\n", __alignof__(struct foo));
printf("__alignof__(struct foo2) = %zu\n", __alignof__(struct foo2));
printf("__alignof__(struct foo3) = %zu\n", __alignof__(struct foo3));
printf("__alignof__(struct foo4) = %zu\n", __alignof__(struct foo4));
exit(0);
}
On m68k:
__alignof__(struct foo) = 8
__alignof__(struct foo2) = 8
__alignof__(struct foo3) = 2
__alignof__(struct foo4) = 8
On amd64:
__alignof__(struct foo) = 8
__alignof__(struct foo2) = 8
__alignof__(struct foo3) = 4
__alignof__(struct foo4) = 8
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- ge...@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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