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

[Christophe Leroy]

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.

Can you please be more explicit ? What do you mean by "issues the 
appropriate start" ? What is "that point" ? Any messages on the console ?

Thanks
Christophe


> 
> 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 c-s.fr>
> 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 c-s.fr>
>      Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> 
> 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.
> 
> Attached is the .config that I used.
> 
> Thanks,
> 
> Larry