http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50325
--- Comment #24 from Iain Sandoe <iains at gcc dot gnu.org> 2011-12-01 10:25:33 UTC --- well.. sorry, that might be a bogus comment - it depends on whether the following can be interpreted to allow a different layout on the stack from 'normal' memory. Since the embedding alignment of bitfields doesn't seem to be specifically referenced in the struct. layout section (pp10 in the pdf) - other than saying that it's 'natural' if the first element and 4 bytes otherwise. but page14 in the pdf of the ABI doc has: 1. All nonvector parameters are aligned on 4-byte boundaries. 2. Vector parameters are aligned on 16-byte boundaries. 3. Noncomposite parameters (that is, parameters that are not arrays or data structures) smaller than 4 bytes occupy the high-order bytes of their 4-byte area. 4. Composite parameters (arrays, structures, and unions) 1 or 2 bytes in size occupy the low-order bytes of their 4-byte area. They are preceded by padding to 4 bytes. This rule is inconsistent with other 32-bit PowerPC binary inter faces. In AIX and Mac OS 9 (and earlier), padding bytes always follow the data structure even in the case of composite parameters smaller than 4 bytes. 5. Composite parameters 3 bytes or larger in size occupy the high-order bytes of their 4-byte area. They are followed by padding to make a multiple of 4 bytes, with the padding bytes being undefined. again no specific mention of bitfields ...
