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

[Nicholas Piggin <npiggin@gmail.com>]

On Mon, 08 Oct 2018 15:08:31 +1100
Benjamin Herrenschmidt <benh@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@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 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?

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. */
> 
>