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Date: Mon, 27 Jul 2015 08:24:27 +0200
From: Stefan Weil <sw@weilnetz.de>
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Subject: Re: [Qemu-devel] BIOS regression since v2.3.0 (misaligned longword
 i/o to address 0xffff)
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To: QEMU Developer <qemu-devel@nongnu.org>, Gerd Hoffmann <kraxel@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>

Am 27.07.2015 um 07:49 schrieb Stefan Weil:
> Am 26.07.2015 um 21:32 schrieb Stefan Weil:
>> Hi,
>>
>> since commit 21f5826a04d38e19488f917e1eef22751490c769
>> "seabios: update to 1.8.0 release" there is a misaligned i/o access
>> caused by the PC BIOS.
>>
>> QEMU's PC emulation (qemu-system-i386, qemu-system-x86_64)
>> with enabled trace backend reports the misaligned i/o access
>> when running the BIOS code:
>>
>> Misaligned i/o to address 0x0000ffff with size 4 for memory region io
>>
>> ("to address 0x0000ffff" was added by my debug code)
>>
>> This issue was reported by users of QEMU for Windows,
>> but it is not Windows specific.
>>
>> Regards
>> Stefan
>
>
> Sorry, I did not notice that the code which reports misaligned access is
> not part of the official QEMU code.
>
> Here is the patch for memory.c which adds it:
>
> @@ -1073,6 +1119,9 @@ bool memory_region_access_valid(MemoryRegion *mr,
>      int access_size, i;
>
>      if (!mr->ops->valid.unaligned && (addr & (size - 1))) {
> +        fprintf(stderr, "Misaligned i/o to address %08" HWADDR_PRIx
> +                        " with size %u for memory region %s\n",
> +                addr, size, mr->name);
>          return false;
>      }
>
> Is the misaligned i/o access done by the BIOS code a feature or a bug?
>
> Regards
> Stefan
>

The change (regression?) was caused by this commit (which obviously
did not intend to change generated code):

40d03128531e06b35a3836f9346790003692540e is the first bad commit
commit 40d03128531e06b35a3836f9346790003692540e
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Thu May 15 13:22:26 2014 +0200

     piix: add and use dev-piix.h

     Move all definitions for PIIX registers to a single header file,
     like there is one already for Q35, and make the naming more
     consistent.

     Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

:040000 040000 72d3a611f87106916d58e30fa1d615659fa711f6 
5bfd5601430bc5263ac0a6f8a15a131f3bc8678e M    src