restoring x86 BIOS state before reboot

restoring x86 BIOS state before reboot

[Bart Trojanowski]

Hi all,

I am looking at a two stage boot where linux is loaded to do some system
initialization before booting to Windows, which needs BIOS.

I am interested in bypassing the BIOS on the second boot.

I wanted to know if anyone has attempted to restore the BIOS memory such 
that this could be attempted.  If not, I would love to get some pointers
:)

My plan right now is to backup the 128k of memory under 0x10000 to some
staging memory under 0x90000, temporarily while in real mode, and then
move it up somewhere higher once the kernel is running.

Then on reboot I hope to undo the above and jump to 0x00007c00.

Does this approach have any merit?

Cheers,

-Bart

Re: restoring x86 BIOS state before reboot

[Jan Engelhardt]

On Apr 6 2007 11:46, Bart Trojanowski wrote:
>Hi all,
>
>I am looking at a two stage boot where linux is loaded to do some system
>initialization before booting to Windows, which needs BIOS.
>
>I am interested in bypassing the BIOS on the second boot.
>
>I wanted to know if anyone has attempted to restore the BIOS memory such 
>that this could be attempted.  If not, I would love to get some pointers
>:)

Hmm.... minix3's "boot monitor" seems to be something in that direction.
When typing "halt" on minix, the system is 'shut down' and control is
passed to the boot monitor where you can select minix again.


Jan
-- 

Re: [Fastboot] restoring x86 BIOS state before reboot

[Eric W. Biederman]

Bart Trojanowski <bart@jukie.net> writes:

> Hi all,
>
> I am looking at a two stage boot where linux is loaded to do some system
> initialization before booting to Windows, which needs BIOS.
>
> I am interested in bypassing the BIOS on the second boot.
>
> I wanted to know if anyone has attempted to restore the BIOS memory such 
> that this could be attempted.  If not, I would love to get some pointers
> :)
>
> My plan right now is to backup the 128k of memory under 0x10000 to some
> staging memory under 0x90000, temporarily while in real mode, and then
> move it up somewhere higher once the kernel is running.
>
> Then on reboot I hope to undo the above and jump to 0x00007c00.
>
> Does this approach have any merit?

The primary problem isn't so much the BIOS memory.  That is usually
preserved.  But rather the BIOS gets confused at the massive change
in hardware state.  At least I think that is what happens.

On some BIOS/kernel configuration it isn't a problem I think I
got maybe a 20% success rate trying to use the 16bit linux entry
point that starts the new kernel from kexec when I was investigating
it.

You might get a little more success if you backup the BIOS memory
I don't know.

As long as you are not coming out of a panic situation there is
no theoretical reason why you shouldn't get the BIOS back and
working again, but the how of it is a challenge.

The possibility I keep playing with is to load the Bochs BIOS or
some other implementation of the basic boot services that I have
control over so that if it doesn't work the code can be fixed.
There has been some limited success with this technique in the
context of LinuxBIOS.

The ACPI tables should be reusable as is.

It may also be worth investigating if it is possible to bypass
the part of windows that uses BIOS calls.  I really don't have
a clue how a modern windows systems boots.

Eric

Re: [Fastboot] restoring x86 BIOS state before reboot

[Eric W. Biederman]

Bart Trojanowski <bart@jukie.net> writes:

> Hi all,
>
> I am looking at a two stage boot where linux is loaded to do some system
> initialization before booting to Windows, which needs BIOS.
>
> I am interested in bypassing the BIOS on the second boot.
>
> I wanted to know if anyone has attempted to restore the BIOS memory such 
> that this could be attempted.  If not, I would love to get some pointers
> :)
>
> My plan right now is to backup the 128k of memory under 0x10000 to some
> staging memory under 0x90000, temporarily while in real mode, and then
> move it up somewhere higher once the kernel is running.
>
> Then on reboot I hope to undo the above and jump to 0x00007c00.
>
> Does this approach have any merit?

The primary problem isn't so much the BIOS memory.  That is usually
preserved.  But rather the BIOS gets confused at the massive change
in hardware state.  At least I think that is what happens.

On some BIOS/kernel configuration it isn't a problem I think I
got maybe a 20% success rate trying to use the 16bit linux entry
point that starts the new kernel from kexec when I was investigating
it.

You might get a little more success if you backup the BIOS memory
I don't know.

As long as you are not coming out of a panic situation there is
no theoretical reason why you shouldn't get the BIOS back and
working again, but the how of it is a challenge.

The possibility I keep playing with is to load the Bochs BIOS or
some other implementation of the basic boot services that I have
control over so that if it doesn't work the code can be fixed.
There has been some limited success with this technique in the
context of LinuxBIOS.

The ACPI tables should be reusable as is.

It may also be worth investigating if it is possible to bypass
the part of windows that uses BIOS calls.  I really don't have
a clue how a modern windows systems boots.

Eric

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Re: [Fastboot] restoring x86 BIOS state before reboot

[Bernhard Walle]

* Eric W. Biederman <ebiederm@xmission.com> [2007-04-29 08:51]:
> 
> It may also be worth investigating if it is possible to bypass
> the part of windows that uses BIOS calls.  I really don't have
> a clue how a modern windows systems boots.

I think ReactOS has a bootlader that can also boot Windows, or at
least they are close to booting the Windows kernel. That bootloader
could be then used for booting Windows without BIOS calls.

I also heard that the 100-$-Laptop should now be able to use Windows.
As it's using LinuxBIOS, this could also be interesting. However,
maybe Microsoft simply modifies a special Windows for this, or they
integrate a ClosedSource part in that LinuxBIOS, I don't know ... :-(


Thanks,
   Bernhard

Re: [Fastboot] restoring x86 BIOS state before reboot

[Bernhard Walle]

* Eric W. Biederman <ebiederm@xmission.com> [2007-04-29 08:51]:
> 
> It may also be worth investigating if it is possible to bypass
> the part of windows that uses BIOS calls.  I really don't have
> a clue how a modern windows systems boots.

I think ReactOS has a bootlader that can also boot Windows, or at
least they are close to booting the Windows kernel. That bootloader
could be then used for booting Windows without BIOS calls.

I also heard that the 100-$-Laptop should now be able to use Windows.
As it's using LinuxBIOS, this could also be interesting. However,
maybe Microsoft simply modifies a special Windows for this, or they
integrate a ClosedSource part in that LinuxBIOS, I don't know ... :-(


Thanks,
   Bernhard

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Re: [Fastboot] restoring x86 BIOS state before reboot

[Eric W. Biederman]

Bernhard Walle <bwalle@suse.de> writes:

> * Eric W. Biederman <ebiederm@xmission.com> [2007-04-29 08:51]:
>> 
>> It may also be worth investigating if it is possible to bypass
>> the part of windows that uses BIOS calls.  I really don't have
>> a clue how a modern windows systems boots.
>
> I think ReactOS has a bootlader that can also boot Windows, or at
> least they are close to booting the Windows kernel. That bootloader
> could be then used for booting Windows without BIOS calls.
>
> I also heard that the 100-$-Laptop should now be able to use Windows.
> As it's using LinuxBIOS, this could also be interesting. However,
> maybe Microsoft simply modifies a special Windows for this, or they
> integrate a ClosedSource part in that LinuxBIOS, I don't know ... :-(

I know it isn't a ClosedSource part in LinuxBIOS.

In any particular case you can work through the details, and
make it work.

The hard part is making the general case work.

Eric

Re: [Fastboot] restoring x86 BIOS state before reboot

[Eric W. Biederman]

Bernhard Walle <bwalle@suse.de> writes:

> * Eric W. Biederman <ebiederm@xmission.com> [2007-04-29 08:51]:
>> 
>> It may also be worth investigating if it is possible to bypass
>> the part of windows that uses BIOS calls.  I really don't have
>> a clue how a modern windows systems boots.
>
> I think ReactOS has a bootlader that can also boot Windows, or at
> least they are close to booting the Windows kernel. That bootloader
> could be then used for booting Windows without BIOS calls.
>
> I also heard that the 100-$-Laptop should now be able to use Windows.
> As it's using LinuxBIOS, this could also be interesting. However,
> maybe Microsoft simply modifies a special Windows for this, or they
> integrate a ClosedSource part in that LinuxBIOS, I don't know ... :-(

I know it isn't a ClosedSource part in LinuxBIOS.

In any particular case you can work through the details, and
make it work.

The hard part is making the general case work.

Eric

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Re: [Fastboot] restoring x86 BIOS state before reboot

[David Woodhouse]

On Sun, 2007-04-29 at 11:41 +0200, Bernhard Walle wrote:
> I also heard that the 100-$-Laptop should now be able to use Windows.
> As it's using LinuxBIOS, this could also be interesting. However,
> maybe Microsoft simply modifies a special Windows for this, or they
> integrate a ClosedSource part in that LinuxBIOS, I don't know ... :-(

You heard wrong. Microsoft have a few early test units and are trying to
get Windows to boot on it. I believe their plan involves replacing
LinuxBIOS with a 'normal' PC BIOS.

-- 
dwmw2

Re: [Fastboot] restoring x86 BIOS state before reboot

[David Woodhouse]

On Sun, 2007-04-29 at 11:41 +0200, Bernhard Walle wrote:
> I also heard that the 100-$-Laptop should now be able to use Windows.
> As it's using LinuxBIOS, this could also be interesting. However,
> maybe Microsoft simply modifies a special Windows for this, or they
> integrate a ClosedSource part in that LinuxBIOS, I don't know ... :-(

You heard wrong. Microsoft have a few early test units and are trying to
get Windows to boot on it. I believe their plan involves replacing
LinuxBIOS with a 'normal' PC BIOS.

-- 
dwmw2


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Re: [Fastboot] restoring x86 BIOS state before reboot

[Pavel Machek]

Hi!

> > It may also be worth investigating if it is possible to bypass
> > the part of windows that uses BIOS calls.  I really don't have
> > a clue how a modern windows systems boots.
> 
> I think ReactOS has a bootlader that can also boot Windows, or at
> least they are close to booting the Windows kernel. That bootloader
> could be then used for booting Windows without BIOS calls.
> 
> I also heard that the 100-$-Laptop should now be able to use Windows.
> As it's using LinuxBIOS, this could also be interesting. However,
> maybe Microsoft simply modifies a special Windows for this, or they
> integrate a ClosedSource part in that LinuxBIOS, I don't know ... :-(

I do not think OLPC is using linuxBIOS these days. What they have
certainly looks like Sun's ROM monitor.

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [Fastboot] restoring x86 BIOS state before reboot

[Pavel Machek]

Hi!

> > It may also be worth investigating if it is possible to bypass
> > the part of windows that uses BIOS calls.  I really don't have
> > a clue how a modern windows systems boots.
> 
> I think ReactOS has a bootlader that can also boot Windows, or at
> least they are close to booting the Windows kernel. That bootloader
> could be then used for booting Windows without BIOS calls.
> 
> I also heard that the 100-$-Laptop should now be able to use Windows.
> As it's using LinuxBIOS, this could also be interesting. However,
> maybe Microsoft simply modifies a special Windows for this, or they
> integrate a ClosedSource part in that LinuxBIOS, I don't know ... :-(

I do not think OLPC is using linuxBIOS these days. What they have
certainly looks like Sun's ROM monitor.

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Re: [Fastboot] restoring x86 BIOS state before reboot

[Jeremy Fitzhardinge]

Pavel Machek wrote:
> I do not think OLPC is using linuxBIOS these days. What they have
> certainly looks like Sun's ROM monitor.

Yep, looks like they've got Mitch Bradley, (ex?) of Firmworks, doing
their firmware.  That means its pretty much exactly OpenFirmware.  Lots
of yummy, delicious Forth.

    J

Re: [Fastboot] restoring x86 BIOS state before reboot

[Jeremy Fitzhardinge]

Pavel Machek wrote:
> I do not think OLPC is using linuxBIOS these days. What they have
> certainly looks like Sun's ROM monitor.

Yep, looks like they've got Mitch Bradley, (ex?) of Firmworks, doing
their firmware.  That means its pretty much exactly OpenFirmware.  Lots
of yummy, delicious Forth.

    J

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Re: [Fastboot] restoring x86 BIOS state before reboot

[H. Peter Anvin]

Pavel Machek wrote:
> 
> I do not think OLPC is using linuxBIOS these days. What they have
> certainly looks like Sun's ROM monitor.
> 

That would be OpenFirmware, then.

	-hpa

Re: [Fastboot] restoring x86 BIOS state before reboot

[H. Peter Anvin]

Pavel Machek wrote:
> 
> I do not think OLPC is using linuxBIOS these days. What they have
> certainly looks like Sun's ROM monitor.
> 

That would be OpenFirmware, then.

	-hpa

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Re: [Fastboot] restoring x86 BIOS state before reboot

[yhlu]

On 5/11/07, H. Peter Anvin <hpa@zytor.com> wrote:
> Pavel Machek wrote:
> >
> > I do not think OLPC is using linuxBIOS these days. What they have
> > certainly looks like Sun's ROM monitor.
> >
>
> That would be OpenFirmware, then.
>
current kernel for x86 support OFW boot patch?

YH

Re: [Fastboot] restoring x86 BIOS state before reboot

[yhlu]

On 5/11/07, H. Peter Anvin <hpa@zytor.com> wrote:
> Pavel Machek wrote:
> >
> > I do not think OLPC is using linuxBIOS these days. What they have
> > certainly looks like Sun's ROM monitor.
> >
>
> That would be OpenFirmware, then.
>
current kernel for x86 support OFW boot patch?

YH

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