Regression in 5.1.0-rc2: PowerBook G4 Aluminum fails to boot - bisected to commit 0df977eafc792

Christophe Leroy christophe.leroy at
Mon Mar 25 19:46:39 AEDT 2019

Le 25/03/2019 à 01:49, Larry Finger a écrit :
> A build of kernel 5.1.0-rc2 resulted in a failure to boot on my 
> PowerBook G4 Aluminum. The bootstrap loads the initial kernel and issues 
> the appropriate start, but the machine hangs at that point.
> The problem does not depend on the choice of PPC32 processor type. This 
> machine has a 7447A according to /proc/cpuinfo.
> The problem was bisected to the following:
> commit 0df977eafc792a5365a7f81d8d5920132e03afad
> Author: Christophe Leroy <christophe.leroy at>
> Date:   Thu Feb 21 10:37:54 2019 +0000
>      powerpc/6xx: Don't use SPRN_SPRG2 for storing stack pointer while 
> in RTAS
>      When calling RTAS, the stack pointer is stored in SPRN_SPRG2
>      in order to be able to restore it in case of machine check in RTAS.
>      As machine check is not a perfomance critical path, this patch
>      frees SPRN_SPRG2 by using a field in thread struct instead.
>      Signed-off-by: Christophe Leroy <christophe.leroy at>
>      Signed-off-by: Michael Ellerman <mpe at>
> I reverted this patch and found that the system began execution, and 
> then failed, likely due to the reassignment of SPRN_SPRG2.
> I had found this problem with 5.1.0-rc1, but -rc2 was out by the time I 
> finished the bisection. Unfortunately, none of the changes in -rc2 fixed 
> the problem.

I think I identified the issue, see

It is now booting properly under QEMU with your .config

Could you please test it on your target ?


> Attached is the .config that I used.
> Thanks,
> Larry

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