Re: [Etherboot-developers] Q: does xstart work?

[Eric W B. <ebi...@ln...>]

ke...@us... (Ken Yap) writes:

> >>	ADDR32	LJMPI(_execaddr-_start)
> 
> Incidentally if you feel motivated to convert this bit of data
> segment-modifying code to a push onto the stack followed by a ret,
> please do.

I will or something similiar, accessing the 32bit data segment
from 16bit is a fairly bad thing to do.

After staring at the problem of relocating the part of etherboot
that must run in 16bit real mode I have finally come up with
a clean design, that will be easy to convert to.

- The 16bit code will normally live above 1MB.
- The 16bit code will be pushed on the 16bit stack just before use.
- _prot_to_real && _real_to_prot will be replaced by _real_call
  which preservs all registers except %esp, and %eax. _real_call
  pushes the 16bit code onto the real mode stack.

An example from my test code.
	pushl	$ 1f
	pushl	$ 2f - 1f
	call	_real_call
1:
	.code16
	movl	$0x88880000, %ebp
	shll	$16, %ebx
	shll	$16, %ecx
	shll	$16, %edx
	shll	$16, %esi
	shll	$16, %edi
	ret
	.code32
2:


Eric