[coreboot] Fwd: SimNOW VGA int 1a

[ron minnich]

On Thu, Oct 16, 2008 at 3:07 PM, Carl-Daniel Hailfinger
<c-d.hailfinger.devel.2006 at gmx.net> wrote:
> On 16.10.2008 23:54, ron minnich wrote:
>> On Thu, Oct 16, 2008 at 2:52 PM, Carl-Daniel Hailfinger
>> <c-d.hailfinger.devel.2006 at gmx.net> wrote:
>>
>>
>>> If that's it, the solution is absolutely simple. And I mean totally simple.
>>> 1. Backup old content
>>> 2. Write ffffffff
>>>
>>
>> at this point it is game over.
>> The code that does this is in rom.
>>
>
> Hm. Unshare only this function, maybe with another name?

printk?

>
>
>>> 3. Read back and save in a variable
>>> 4. Restore old content.
>>> Make sure no code blacked out by the decode is executed between 1 and 4
>>> and you're safe. If you're feeling paranoid, do it as inline asm. Make
>>> sure that short sequence is never ever run as XIP code in ROM (I can do
>>> that checking right now).
>>>
>>> What am I missing?
>>>
>>>
>>
>> the big thing is that the problem code is a binary vga bios over which
>> we have zero control. :-(
>>
>
> Hmmm. Is it running in vm86? If yes, we can trap I/O port writes and
> reads, so this is solvable. Same should apply to x86emu.
>

this is getting kind of hideously complex. Let's think on it some more.

ron