On Thu, 15 Feb 2007 14:34:41 +0000 Ralf Baechle <ralf@xxxxxxxxxxxxxx> wrote: > On Wed, Feb 14, 2007 at 08:39:03PM -0800, Andrew Morton wrote: > > > Can someone please tell us how this magic works? (And it does appear to > > work). > > > > It seems to assuming that the compiler will assume that members of packed > > structures can have arbitrary alignment, even if that alignment is obvious. > > > > Which makes sense, but I'd like to see chapter-and-verse from the spec or > > from the gcc docs so we can rely upon it working on all architectures and > > compilers from now until ever more. > > > > IOW: your changlogging sucks ;) > > It was my entry for the next edition of the C Puzzle Book ;-) > > The whole union thing was only needed to get rid of a warning but Marcel's > solution does the same thing by attaching the packed keyword to the entire > structure instead, so this patch is now using his macros but using __packed > instead. How do we know this trick will work as-designed across all versions of gcc and icc (at least) and for all architectures and for all sets of compiler options? Basically, it has to be guaranteed by a C standard. Is it?
