Re: [Qemu-devel] [PATCH]bug fix for softmmu slow_st unaligned access

[TeLeMan <geleman@gmail.com>]

andrzej zaborowski wrote:
> 
> Hi,
> 
> On 28/10/2007, TeLeMan <geleman@gmail.com> wrote:
>> For example, the memory address 0x10008000 is on an unwritable page.When
>> the
>> instruction "add dword ptr [0x10007FFF],0x12345678" is executed,the OS
>> will
>> set 0x10008000 page be a writable page and re-execute this instruction.
>> But
>> softmmu has modifed the value of 0x10007FFF,so after re-executing this
>> instruction, the final result is wrong(double-added on 0x10007FFF).
>> Reversing the stored byte order can fix this bug.
> 
> I'm not sure I understand, but what happens if now the 10008000 page
> is writable and 10007fff isn't, thus the OS needs to make it writable
> and re-execute? I guess reversing the accesses order is not a
> solution?
> 
> Regards,
> Andrew
> 
> 

If the 0x10008000 page is writable and 0x10007FFF isn't, softmmu can raise
this exception before modifing 0x10007FFF-0x10008002 because softmmu checks
0x10007FFF at first. I don't know if reversing the order is an exact
solution,but its simple and working.

btw, I found this bug because I found the some windows dll reloc offset are
calculated incorrectly by the guest OS. If you need a sample, I can give it
to you.
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