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SubjectRe: [rft] s2ram wakeup moves to .c, could fix few machines
On Fri 2008-02-08 13:02:57, H. Peter Anvin wrote:
> Pavel Machek wrote:
>> On Fri 2008-02-08 17:23:15, Rafael J. Wysocki wrote:
>>> On Friday, 8 of February 2008, Pavel Machek wrote:
>>>> Hi!
>>> Hi,
>>>>>> I really need the entry point to be at offset 0, so that I can get
>>>>>> pointers to my data. I could not figure out how to do it any other
>>>>>> way. And if 0 is taken, I thought I'd put header at the end.
>>>>> Why not just put the structure at 0, and put pointers in the structure
>>>>> to everything else you need?
>>>> segments:offsets rear its ugly head here. I need %ds to point to my
>>>> data, and the way to do it is copy it from %cs; that needs start to be
>>>> at 0.
>>> Hm, why exactly is that necessay?
>> It is not _neccessary_. Try to come up with another method that gets
>> relocations right. I could not :-(.
>> (Actually, putting table at the offset 0 and short jump at beggining
>> of the table would probably do the trick. But that still keeps code at
>> offset 0 :-).
> Why not just put a pointer to the start of the code in the table, and make
> an indirect call to it?

Indirect call from where?

BIOS jumps to address you provide.

> Where is this code?


BIOS jumps to wakeup_code. With CS=something, IP=0. If wakeup code is
at other address than zero, I'll not be able to easily address data
below it.

.globl wakeup_header
realmode_flags: .long 0
signature: .long 0x51ee1111
.globl _start

/* Set up segments */
movw %cs,%ax
movw %ax,%ds
movw %ax,%es
movw %ax,%ss

/* Check header signature... */
movl signature, %eax
cmpl $0x51ee1111, %eax
jne bogus_real_magic

(cesky, pictures)

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