[SeaBIOS] vgabios testing

[Kevin O'Connor]

On Sun, Mar 04, 2012 at 07:26:58PM +0000, Julian Pidancet wrote:
> On Sun, Mar 4, 2012 at 7:04 PM, Kevin O'Connor <kevin at koconnor.net> wrote:
> > So, I guess the question is, how important is support for
> > current/legacy x86emu versions?
> 
> I've tried to replace .code16gcc with .code16 in src/code16gcc.s to
> see if gcc would be able to generate code which doesn't use 32bit
> version of the call/ret instructions. The result was quite
> disappointing, it generates functions like this:

That definitely wont work.  Gcc assumes the return address is 32bits -
it will be totally confused if it's not.  (Function parameters passed
on the stack wont be in the right spot.)  Likely other things will
break as well.

> I am going to propose a patch to xorg-devel in the next few days, but
> in the meantime, it would be nice to find a solution in SeaBIOS so the
> code can work with older versions of Xorg.

The only thing I can think of would be to post-process the assembler
and replace "retl" instructions with "retw $2" instructions.  I'm not
sure if it would work and it would be real ugly.

-Kevin