------- Comment #23 from matz at suse dot de 2006-01-16 15:14 ------- The x86-64 ABI itself doesn't talk about zero-sized bitfields. So both behaviours are correct regarding the ABI. It talks about unnamed bitfields (which zero-sized ones must be) not influencing the overall alignment of structures or unions, but the problem here is different.
Having said that I agree with Marks mail on gcc@ that the pre-3.4 behaviour made more sense. Unfortunately I'm also no stor-layout.c expert, so can't really comment on how the best approach is to implement it. I assume Jason would be the best to comment here, as he changed that behaviour. Stevens latest patch changes the evaluation of EMPTY_FIELD_BOUNDARY vs. PCC_BITFIELD_TYPE_MATTERS, so someone needs to make sure that this is okay. Additionally I don't know how stor-layout tracks alignment, i.e. if desired_align contains the alignment for the _current_ field, or for the _next_ field. A zero-sized bitfield should influence alignment of the next field (although due to the size of zero this shouldn't make a difference). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22275
