Benjamin Herrenschmidt <b...@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 <b...@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 <b...@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
