[Qemu-devel] Re: [Bochs-developers] [PATCH v5 1/5] Add S3 state to DSDT.Handle resume event in the BIOS.

["Sebastian Herbszt" <herbszt@gmx.de>]

Gleb Natapov wrote:
> On Sat, Dec 06, 2008 at 09:57:38PM -0500, Kevin O'Connor wrote:
>> Hi Gleb,
>> 
>> On Thu, Nov 27, 2008 at 01:02:25PM +0200, Gleb Natapov wrote:
>> [...]
>> > @@ -10375,6 +10420,12 @@ normal_post:
>> >    mov  ds, ax
>> >    mov  ss, ax
>> >  
>> > +  ;; Save shutdown status
>> > +  mov 0x04b0, bl
>> > +
>> > +  cmp bl, #0xfe
>> > +  jz s3_post
>> > +
>> 
>> What sets 40:b0 to 0xfe on a resume?
>> 
> Qemu/Bochs.
> 
>> Also, wouldn't this corrupt memory used by the stack (the stack gets
>> set to 0xfffe, and s3_post has call insns in it)?

insns = instructions?

> Oh. I thought it was set to be at the top of the first page, but it has
> one extra 'f' :( We should change it to be 0xffe instead.

Can you please explain this memory corruption? Why would "this" (?) corrupt
memory used by the stack?

We set the stack to 0xfffe and then call rombios32_init. rombios32_init saves
the current ss:sp and then uses own stack, which is now located below the EBDA.
0xfffe is "user memory", same applys to 0xffe so in both cases we use "user memory".

Do you suggest 0xffe because it's in the first page (i assume 4KB pages) reserved for
BIOS use?

- Sebastian