Re: [Fastboot] [CFT] ELF Relocatable x86 and x86_64 bzImages

From: Vivek Goyal
Date: Thu Aug 10 2006 - 14:16:28 EST

On Thu, Aug 10, 2006 at 11:05:22AM -0600, Eric W. Biederman wrote:
> Vivek Goyal <vgoyal@xxxxxxxxxx> writes:
> > Apart from this I think something is still off on x86_64. I have not
> > been able to make kdump work on x86_64. Second kernel simply hangs.
> > Two different machines are showing different results.
> >
> > - On one machine, it seems to be stuck somewhere in decompress_kernel().
> > Serial console is not behaving properly even with earlyprintk(). Somehow
> > I feel it is some bss corruption even after my changes.
> >
> > - Other machines seems to be going till start_kernel() and even after
> > that (No messages on the console, all serial debugging) and then
> > either it hangs or jumps back to BIOS.
> >
> > Will look more into it.
> Thanks.
> I'm a little disappointed but at this point it isn't a great surprise,
> the code is early yet and hasn't had much testing or attention.
> I wonder if I have missed something else silly.
> As for testing, can you use plain kexec to load the kernel at a
> different address? I'm curious to know if it is something related
> to the kexec on panic path or if it is just running at a different
> location that is the problem.

Yes. This seems to be minor stuff. Parameter segment seems to be
getting stomped while I am doing decompression. Most probably should
be coming from extra space calculations (32K etc) being done at run
time to find out where should we shift the compressed image.

Kexec works because parameter segment is being loaded below the
compressed image and doest not get stomped over. :-)

I just reserved memory at non 2MB aligned location 65MB@15MB so that
kernel is loaded at 16MB and other smaller segments below the compressed
image, then I can successfully booted into the kdump kernel.

So basically kexec on panic path seems to be clean except stomping issue.
May be bzImage program header should reflect right "MemSize" which
takes into account extra memory space calculations.

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