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

[Michael Ellerman]

Benjamin Herrenschmidt <benh at kernel.crashing.org> writes:
> 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 ?

Technically yes. But I thought because we build with mcmodel=medium
we'll never actually get multiple TOCs in the kernel itself, so it
doesn't actually matter.

So this seems to work for now:

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 301a6a86a20f..e5566e248a02 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1149,7 +1149,7 @@ TRAMP_REAL_BEGIN(hmi_exception_early)
 	EXCEPTION_PROLOG_COMMON_2(PACA_EXGEN)
 	EXCEPTION_PROLOG_COMMON_3(0xe60)
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	BRANCH_LINK_TO_FAR(hmi_exception_realmode) /* Function call ABI */
+	BRANCH_LINK_TO_FAR(DOTSYM(hmi_exception_realmode)) /* Function call ABI */
 	cmpdi	cr0,r3,0
 
 	/* Windup the stack. */


cheers