[Bug c/82105] unexpected padding in a struct

["egallager at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82105

Eric Gallager <egallager at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |egallager at gcc dot gnu.org

--- Comment #5 from Eric Gallager <egallager at gcc dot gnu.org> ---
I combined these all into a single testcase:

$ cat 82105.c
typedef struct {
        unsigned int x:16;
        unsigned int y:17;
        unsigned short z0; /* -Wpadded 1 */
} XXX; /* -Wpadded 2 */

typedef struct __attribute__((packed,aligned(4))) {
    unsigned int x:16;
    unsigned int y:17;
    unsigned short z1; /* -Wpadded 3 */
} XXY; /* -Wpadded 4 */

typedef struct {
        unsigned int x:1;
        unsigned int y:1;
        unsigned short z2; /* -Wpadded 5 */
} XYX; /* silent, good */

typedef struct {
        unsigned int x:16;
        unsigned int y:16;
        unsigned short z3; /* silent, good */
} XYY; /* -Wpadded 6 */
$ /usr/local/bin/gcc -c -Wall -Wextra -pedantic -Wpadded -Wpacked -O2 82105.c
82105.c:4:17: warning: padding struct to align ‘z0’ [-Wpadded]
  unsigned short z0; /* -Wpadded 1 */
                 ^~
82105.c:5:1: warning: padding struct size to alignment boundary [-Wpadded]
 } XXX; /* -Wpadded 2 */
 ^
82105.c:10:20: warning: padding struct to align ‘z1’ [-Wpadded]
     unsigned short z1; /* -Wpadded 3 */
                    ^~
82105.c:11:1: warning: padding struct size to alignment boundary [-Wpadded]
 } XXY; /* -Wpadded 4 */
 ^
82105.c:16:17: warning: padding struct to align ‘z2’ [-Wpadded]
  unsigned short z2; /* -Wpadded 5 */
                 ^~
82105.c:23:1: warning: padding struct size to alignment boundary [-Wpadded]
 } XYY; /* -Wpadded 6 */
 ^
$ 

(In reply to Richard Biener from comment #1)
> This is how bitfields work.  You can use
> 
> typedef struct __attribute__((packed,aligned(4))) {
>     unsigned int x:16;
>     unsigned int y:17;
>     unsigned short z;
> } XXX;
> 
> to get what you want.

It still prints -Wpadded warnings despite the attributes though.