[coreboot] GSOC USBROM linking problem

[Carl-Daniel Hailfinger]

On 17.06.2009 19:18, ron minnich wrote:
> On Wed, Jun 17, 2009 at 10:15 AM, Marc Jones<marcj303 at gmail.com> wrote:
>   
>> The code is a PCI option ROM that can be copied and run at some
>> arbitrary location between 0xC0000 and 0x100000. For 16bit code the
>> segment would be loaded and there is no problem. I don't know the
>> right way to do this for 32bit flat mode code.
>>     
>
> I think we need to seek a common solution, and after discussion with
> segher from a while back I think -fpic and -fpie as we do it in v3 are
> rather questionable.
>   

-fpic/-fpie may not be an universally preferred solution, but if GCC
developers ever decide to drop support for it, we can still move to
LLVM/clang.
v3 initram is a bit of a special case because it is PIC calling non-PIC.
As far as I can see, GDT trickery would not work for such a case.


> What we should look to do is a run command which sets a new entry in
> the gdt and does a ljmp which sets CS to that entry. Then we link with
> that code to run at 0. This is what FILO does and it works well.
>   

As long as the code does not have to call outside code, using the GDT
may indeed be the best option.

Regards,
Carl-Daniel

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