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Date: Mon, 27 Jul 2015 07:49:29 +0200
From: Stefan Weil <stefan.weil@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>

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