Re: [RFC] x86 ELF bootable kernels/Linux booting Linux/LinuxBIOS

[ebiederm@xmission.com (Eric W. Biederman)]

"H. Peter Anvin" <hpa@zytor.com> writes:

> Followup to:  <m1elk7d37d.fsf@frodo.biederman.org>
> By author:    ebiederm@xmission.com (Eric W. Biederman)
> In newsgroup: linux.dev.kernel
> > 
> > - Code at that entry point to query from the firmware/BIOS the
> >   information the kernel needs.
> > 
> 
> How do you query from the 16-bit firmware/BIOS at the 32-bit
> entrypoint?  Or is it that you have a table, fixed by protocol, of
> what information is available (so we're basically fucked when
> something needs to change)?

I drop back into real mode.  Run the existing query code, (I had to factor
setup.S but the queries are 100% the same) and then I climb back to
32bit mode.  But I do it from setup_arch() so if I don't have a
pcbios, I can skip all that nasty busyness.

I did it the wrong way (fixed table) initially and after some
conversations with you and some thinking I changed it around.

There is nothing outside the ELF specification that needs to be used.
All I depend on is having flat 32bit code and data segments, initially
loaded in %cs and %ds.  So basically anyones x86 ELF bootloader should
work.

I have defined a fully optional table of tagged elements, so the
bootloader can tell me what kind of firmware I have.  All it passes
besides that is the bootloader name and the bootloader version.  So
you must do the bios queries yourself.

Eric