Re: [Qemu-devel] BIOS regression since v2.3.0 (misaligned longword i/o to address 0xffff)

[Stefan Weil]

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 <address@hidden>
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 <address@hidden>

:040000 040000 72d3a611f87106916d58e30fa1d615659fa711f6 
5bfd5601430bc5263ac0a6f8a15a131f3bc8678e M    src