http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46488
--- Comment #26 from rguenther at suse dot de <rguenther at suse dot de> 2010-11-29 14:20:45 UTC --- On Mon, 29 Nov 2010, jorton at redhat dot com wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46488 > > --- Comment #25 from Joe Orton <jorton at redhat dot com> 2010-11-29 14:03:40 > UTC --- > (In reply to comment #22) > > APR_RING_SPLICE_HEAD does such a dereference as far I can see: > > You are right, sorry, I had forgotten exactly how this code works. > > (In reply to comment #24) > > not really. But using > > > > typedef struct elem elem_ __attribute__((may_alias)); > > #define APR_RING_SENTINEL(hp, elem, link) \ > > (struct elem_ *)((char *)(hp) - APR_OFFSETOF(struct elem, link)) > > > > would be safe wrt strict aliasing (if the pointer is only dereferenced > > directly and not casted to another pointer type before, of course). > > I don't think we can guarantee this with the API unchanged; the sentinel > pointer could well be stored in a "struct elem *" pointer. You could stick the attribute on the elem struct declaration itself then. Richard.
