[PATCH] powerpc: Fix HMIs on big-endian with CONFIG_RELOCATABLE=y

[Benjamin Herrenschmidt]

On Mon, 2018-10-08 at 17:04 +1000, Nicholas Piggin wrote:
> On Mon, 08 Oct 2018 15:08:31 +1100
> Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:
> 
> > HMIs will crash the kernel due to
> > 
> > 	BRANCH_LINK_TO_FAR(hmi_exception_realmode)
> > 
> > Calling into the OPD instead of the actual code.
> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> > ---
> > 
> > This hack fixes it for me, but it's not great. Nick, any better idea ?
> 
> Is it a hack because the ifdef gunk, or because there's something
> deeper wrong with using the .sym?

I'd say ifdef gunk, also the KVM use doesn't need it bcs the kvm entry
isn't an OPD.

> I guess all those handlers that load label address by hand could have
> the bug silently creep in. Can we have them use the DOTSYM() macro?

The KVM one doesnt have a dotsym does it ?

Also should we load the TOC from the OPD ?

> Thanks,
> Nick
> 
> > 
> > diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> > index ea04dfb..752709cc8 100644
> > --- a/arch/powerpc/kernel/exceptions-64s.S
> > +++ b/arch/powerpc/kernel/exceptions-64s.S
> > @@ -1119,7 +1119,11 @@ TRAMP_REAL_BEGIN(hmi_exception_early)
> >  	EXCEPTION_PROLOG_COMMON_2(PACA_EXGEN)
> >  	EXCEPTION_PROLOG_COMMON_3(0xe60)
> >  	addi	r3,r1,STACK_FRAME_OVERHEAD
> > +#ifdef PPC64_ELF_ABI_v1
> > +	BRANCH_LINK_TO_FAR(.hmi_exception_realmode) /* Function call ABI */
> > +#else
> >  	BRANCH_LINK_TO_FAR(hmi_exception_realmode) /* Function call ABI */
> > +#endif
> >  	cmpdi	cr0,r3,0
> >  
> >  	/* Windup the stack. */
> > 
> >