Re: [Qemu-devel] Re: [PATCH] pc: e820 qemu_cfg tables need to be packed

[Arnd Bergmann]

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.

        Arnd