On Tue, 2008-04-15 at 17:12 +0100, David Woodhouse wrote: > On Tue, 2008-04-15 at 08:07 -0700, Harvey Harrison wrote: > > The reason I kept the byte-shifting versions around was that for > > arches that need special handling of unaligned access, > > Are there any? GCC should emit appropriate code for the packed-structure > version on all architectures, shouldn't it? > > > they could do the byteshifting manually and get the unaligned access > > 'for free' as it were. > > GCC really ought to be able to sort that out for itself. Let the dog see > the rabbit. Sorry, I didn't explain that very well, let me try again. There is also some new API along with this patch, for a reason: This type of pattern, repeat for various byteorder/widths: le32_to_cpu(get_unaligned((__le32 *)p)) For which the following has been added: get_unaligned_le32(p) Which allows BE arches that require special alignment handling to do the endianness swapping as they do the unaligned accesses. Similarly for LE arches and the get_unaligned_be* I realy think gcc will have a hard time seeing that it can fold the accesses in this way. If you grep for get/put_unaligned you'll see the majority of the current users actually are wrapping it in some kind of byteorder access as well...which prompted me to add this api. But _if_ gcc is smart enough to fold that together on arches with special alignment requirements, I'm happy to move to a wrapper approach. HPA made the suggestion to look into this method, maybe he can explain it better than I. Anyways, I hope I made myself a little clearer this time. Harvey -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
