linux-kernel - Re: EFI Boot Stub Early Console

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Message-ID: <4F68B3A6.4080404@zytor.com>
Date:	Tue, 20 Mar 2012 09:43:18 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Maarten Lankhorst <m.b.lankhorst@...il.com>
CC:	Matt Fleming <matt.fleming@...el.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Shea Levy <shea@...alevy.com>, linux-kernel@...r.kernel.org
Subject: Re: EFI Boot Stub Early Console

On 03/20/2012 08:45 AM, Maarten Lankhorst wrote:
> Hey Matt,
> 
> Op 19-03-12 17:03, Matt Fleming schreef:
>> On Mon, 2012-03-19 at 15:56 +0000, Alan Cox wrote:
>>>>> any bootloader (including the bootstub) will call ExitBootServices() 
>>>>> before any printk'ing actually happens?? Or am I misunderstanding the 
>>>>> spec somehow? I suppose I could just try it and see what happens...
>>>> Oops. Good point, that isn't going to work.
>>> Surely it works fine if you are using bootstub directly from EFI ?
>> Yeah, up until the point you call ExitBootServices(), which is very
>> early in the boot process. After that you can't rely on the validity of
>> the console pointers in the system table.
>>
> I think my system spontaneously rebooted when I tried to
> do some output right after ExitBootServices when debugging
> the efi stub, so not only is this unreliable, it will fail to boot for
> at least some systems out there.
> 

I would expect it to fail for just about any system.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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