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Re: [Xen-devel] Re: define BOOT_TRAMPOLINE and stack based on result of probing EBDA area by INT12
- To: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
- From: Keir Fraser <keir.xen@xxxxxxxxx>
- Date: Wed, 31 Aug 2011 20:57:50 +0100
- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Lin-bao Zhang <zhang.linbao@xxxxxxxxx>
- Delivery-date: Wed, 31 Aug 2011 13:00:47 -0700
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- Thread-topic: [Xen-devel] Re: define BOOT_TRAMPOLINE and stack based on result of probing EBDA area by INT12
On 31/08/2011 20:25, "Alan Cox" <alan@xxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 31 Aug 2011 09:55:10 +0100
> Keir Fraser <keir@xxxxxxx> wrote:
>> 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
>>> hard code to test:mov 0x903ff , %esp thanks for your corrections , I
>>> not read over all histories and stories about them, if I am wrong , I am
>> If you actually tried to implement it you'd realise you're stuck.
> Re-read the original. The EBDA is accessible at BIOS segment offset 0E.
> You don't need to make a BIOS call to read it, just load the location and
> check it against 0.W in which case one isn't present.
> At that point you know where to put your bits.
> Obviously once you get into the world of EFI and the like there are
> different ways all this should occur, but for good old BIOS stuff it
> works fine.
Ah, makes sense. And our real-mode code is now relocatable, which was
implemented as part of support for EFI. That could be used to dynamically
relocate below EBDA for legacy BIOS too.
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