[PATCH 0/8] kexec build system updates, to allow cross-kexec()ing

[Jeremy Kerr]

(resend to kexec list)

Hi Vivek,

> I got a stupid question.
>
> - What's the advantage of building a 32bit binary for powerpc64 bit
>   platforms?

So you don't need to have 64-bit libc and libz present. It's often the 
case that you have an entire 32-bit userspace environment, but still 
require 64-bit libraries just for the kexec program.

>   IOW, why do you need to build 32bit purgatory?

We build the purgatory for the $target architecture, that's all. My 
setup involves:

 build: powerpc-linux-gnu
 host: powerpc-linux-uclibc
 target: powerpc64-linux-uclibc

So I'm aiming for a 64-bit purgatory here, we generally tend to boot 
64-bit kernels on powerpc64 machines.

>   Can't we launch 32bit kernel from 64bit purgatory?

I assume so, but you wouldn't be able to do this on 32-bit machines, of 
course. I haven't been trying the case where the purgatory arch != 
kernel arch.

> > This allows us to kexec a powerpc64 kernel from a powerpc
> > userspace. x86{,_64} users might find this handy too, but I don't
> > have hardware to test.
>
> I think x86 it already happens. I think I can launch 64bit kernel
> from a 32bit kexec.

OK, this change should make this possible for all arches, just by 
specifying --host and --target - are you able to make sure that you can 
build a kexec where host=i386-linux and target=x86_64-linux ?

Cheers,


Jeremy