[Qemu-devel] PCI Bios fixup

[Qemu-devel] PCI Bios fixup

[Samuel Thibault]

Hi,

The patch that qemu applies to bochs bios is a bit bugged:

 pci_pro_fail:
   pop edi
   pop esi
-  sti
   popf
   stc
+  and dword ptr[esp+4],0xfffffffc ;; reset CS.RPL for kqemu
   retf

The and operation clears carry... So that pci functions always leave
carry clear, and hence tell operating systems that they always work...
This should rather be:

 pci_pro_fail:
   pop edi
   pop esi
-  sti
   popf
+  and dword ptr[esp+4],0xfffffffc ;; reset CS.RPL for kqemu
   stc
   retf

Samuel

Re: [Qemu-devel] PCI Bios fixup

[Fabrice Bellard]

Right, this is better. An even better fix would be to clear CS.RPL 
before the popf.

Regards,

Fabrice.

Samuel Thibault wrote:
> Hi,
> 
> The patch that qemu applies to bochs bios is a bit bugged:
> 
>  pci_pro_fail:
>    pop edi
>    pop esi
> -  sti
>    popf
>    stc
> +  and dword ptr[esp+4],0xfffffffc ;; reset CS.RPL for kqemu
>    retf
> 
> The and operation clears carry... So that pci functions always leave
> carry clear, and hence tell operating systems that they always work...
> This should rather be:
> 
>  pci_pro_fail:
>    pop edi
>    pop esi
> -  sti
>    popf
> +  and dword ptr[esp+4],0xfffffffc ;; reset CS.RPL for kqemu
>    stc
>    retf
> 
> Samuel
> 
> 
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