On Thu, 2010-10-14 at 22:20 +0200, Arnd Bergmann wrote: > On Thursday 14 October 2010 21:58:08 Alex Williamson wrote: > > If it works anywhere (I assume it works on 32bit), then it's only > > because it happened to get the alignment right. This just makes 64bit > > hosts get it right too. I don't see any compatibility issues, > > non-packed + 64bit = broken. Thanks, > > I would actually assume that only x86-32 hosts got it right, because > all 32 bit hosts I've seen other than x86 also define 8 byte alignment > for uint64_t. > > You might however consider making it > > __attribute((__packed__, __aligned__(4))) > > instead of just packed, because otherwise you make the alignment one byte, > which is not only different from what it used to be on x86-32 but also > will cause inefficient compiler outpout on platforms that don't have unaligned > word accesses in hardware. The structs in question only contain 4 & 8 byte elements, so there shouldn't be any change on x86-32 using one-byte aligned packing. AFAIK, e820 is x86-only, so we don't need to worry about breaking anyone else. Performance isn't much of a consideration for this type of interface since it's only used pre-boot. In fact, the channel between qemu and the bios is only one byte wide, so wider alignment can cost extra emulated I/O accesses. Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
