[Xen-devel] Re: define BOOT_TRAMPOLINE and stack based on result of probing EBDA area by INT12

[Keir Fraser <keir@xxxxxxx>]

On 31/08/2011 09:47, "Lin-bao Zhang" <zhang.linbao@xxxxxxxxx> wrote:

> 1,define a variable named "EBDA_bottom".
> 2, get EBDA_bottom by above method.
> 3, stack should equals EBDA_bottom (or EBDA_bottom -1 safely)
> 4, mov     $(EBDA_bottom -1),%esp
> in most case , EBDA area is 1K,but we define 0x7c000(this is absolutely
> safe),but we will waste too much memory space.
> 
> I did test, it can work .Certainly, I am familiar with assembler code, I just
> hard code to test:mov     0x903ff , %esp thanks for your corrections , I have
> not read over all histories and stories about them, if I am wrong , I am sorry
> first.

If you actually tried to implement it you'd realise you're stuck. Because
you start off in protected mode and can't make the BIOS call, until you are
in real mode, which requires the trampoline to be set up.

 -- Keir



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