[PATCH v2] x86emu: Correctly handle 0x66 prefix for some instructions

Julian Pidancet julian.pidancet at gmail.com
Thu Mar 15 15:45:56 PDT 2012

On Thu, Mar 15, 2012 at 10:39 PM, Julian Pidancet
<julian.pidancet at gmail.com> wrote:
> On Fri, Mar 9, 2012 at 2:08 AM, Guillem Jover <guillem at hadrons.org> wrote:
>> On Fri, 2012-03-09 at 00:02:55 +0000, Julian Pidancet wrote:
>>> Some instructions are not emulated correctly by x86emu when they
>>> are prefixed by the 0x66 opcode.
>>> I've identified problems in the emulation of these intructions: ret,
>>> enter, leave, iret and some forms of call.
>>> Most of the time, the problem is that these instructions should push or
>>> pop 32-bit values to/from the stack, instead of 16bit, when they are
>>> prefixed by the 0x66 special opcode.
>>> The SeaBIOS project aims to produce a complete legacy BIOS
>>> implementation as well as a VGA option ROM, entirely written in C and
>>> using the GCC compiler.
>>> In 16bit code produced by the GCC compiler, the 0x66 prefix is used
>>> almost everywhere. This patch is necessary to allow the SeaBIOS VGA
>>> option ROM to function with Xorg when using the vesa driver.
>>> v2: - Decrement BP instead of EBP in accordance with the Intel Manual
>>>     - Assign EIP instead of IP when poping the return address from the
>>>     stack in 32-bit operand size mode in ret_far_IMM, ret_far, and iret
>>>     - When poping EFLAGS from the stack in iret in 32-bit operand size
>>>     mode, apply some mask to preserve Read-only flags.
>>> Signed-off-by: Julian Pidancet <julian.pidancet at gmail.com>
>> Looks good to me:
>> Reviewed-by: Guillem Jover <guillem at hadrons.org>
>> thanks,
>> guillem
> Anyone interested in this ? Is there a maintainer for x86emu ? The
> MAINTAINERS file in xorg-docs doesn't mention anything about it.

CCed: Adam Jackson

Adam, you seem to be the maintainer of the xorg vesa driver. I think
this patch is closely related. Would you mind taking a look at it ?



More information about the xorg-devel mailing list