Re: [Qemu-devel] [PATCH 0/7] Fix packing for MinGW with -mms-bitfields

[Stefan Weil <weil@mail.berlios.de>]

Am 28.08.2011 23:43, schrieb Blue Swirl:
> On Sun, Aug 28, 2011 at 8:43 PM, Stefan Weil <weil@mail.berlios.de> wrote:
>> These patches fix the packing of structures which were affected by
>> the new compiler attribute -mms-bitfields (which is needed for glib-2.0).
>>
>> I compiled qemu.exe with and without -mms-bitfields and compared
>> the resulting struct alignment using pahole and codiff.
>
> If a structure is only used internally by QEMU (not used in network,
> disk or guest interfaces), changes in padding don't matter. In fact,
> in those cases it may be better to remove the packing, because then
> the fields may be naturally aligned and that gives better performance
> on most architectures. Could you please check if this is the case for
> any of the structs?

I did this already, but also forward your question to the maintainers.
Here is my result:

[PATCH 2/7] block/vvfat: Fix packing for w32: needs packing (disk)
[PATCH 3/7] acpi: Fix packing for w32: needs packing (bios interface)
[PATCH 4/7] hpet: Fix packing for w32: needs packing (bios interface)
[PATCH 5/7] usb: Fix packing for w32: needs packing (usb interface)
[PATCH 6/7] virtio: Fix packing for w32: needs packing? (guest interface?)
[PATCH 7/7] slirp: Fix packing for w32: needs packing (network interface)

All those struct statements need the pack attribute (otherwise the code
would have to be rewritten which is of course always possible).