Aligning struct member has strange impact on struct alignment

Aligning struct member has strange impact on struct alignment

[Stephan Bergmann]

Hi all.

I have a strange effect with gcc 3.2.2 on Linux x86, where the C program

#include <stdio.h>
struct S1 { double m; };
struct S2 { double m __attribute__((aligned(4))); };
int main(void) {
     printf(
         "__alignof__(S1) = %d\n__alignof__(S2) = %d\n",
         __alignof__(struct S1), __alignof__(struct S2));
}

prints

__alignof__(S1) = 4
__alignof__(S2) = 8

Why is the alignment of S2 == 8 when I align its double member on 4?  Is 
that a bug, or am I missing something?

-Stephan

Re: Aligning struct member has strange impact on struct alignment

[Jim Wilson]

Stephan Bergmann wrote:
> Why is the alignment of S2 == 8 when I align its double member on 4?  Is 
> that a bug, or am I missing something?

I can reproduce this with the RHL 8 compiler which is 3.2 plus patches. 
  I can not reproduce this with gcc-3.3 or later, so it apparently has 
already been fixed.  We aren't maintaining gcc-3.2 anymore.  Only 
gcc-3.3 and on.


-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com