[PATCH 07/23] powerpc/64s: Fix comment on interrupt handler prologue

[Nicholas Piggin]

On Fri Sep 16, 2022 at 3:32 PM AEST, Rohan McLure wrote:
> Interrupt handlers on 64s systems will often need to save register state
> from the interrupted process to make space for loading special purpose
> registers or for internal state.
>
> Fix a comment documenting a common code path macro in the beginning of
> interrupt handlers where r10 is saved to the PACA to afford space for
> the value of the CFAR. Comment is currently written as if r10-r12 are
> saved to PACA, but in fact only r10 is saved, with r11-r12 saved much
> later. The distance in code between these saves has grown over the many
> revisions of this macro. Fix this by signalling with a comment where
> r11-r12 are saved to the PACA.
>
> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
> Reported-by: Nicholas Piggin <npiggin at gmail.com>

Reviewed-by: Nicholas Piggin <npiggin at gmail.com>

> ---
> V1 -> V2: Given its own commit
> V2 -> V3: Annotate r11-r12 save locations with comment.
> ---
>  arch/powerpc/kernel/exceptions-64s.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index 3d0dc133a9ae..a3b51441b039 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -281,7 +281,7 @@ BEGIN_FTR_SECTION
>  	mfspr	r9,SPRN_PPR
>  END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
>  	HMT_MEDIUM
> -	std	r10,IAREA+EX_R10(r13)		/* save r10 - r12 */
> +	std	r10,IAREA+EX_R10(r13)		/* save r10 */
>  	.if ICFAR
>  BEGIN_FTR_SECTION
>  	mfspr	r10,SPRN_CFAR
> @@ -321,7 +321,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
>  	mfctr	r10
>  	std	r10,IAREA+EX_CTR(r13)
>  	mfcr	r9
> -	std	r11,IAREA+EX_R11(r13)
> +	std	r11,IAREA+EX_R11(r13)		/* save r11 - r12 */
>  	std	r12,IAREA+EX_R12(r13)
>  
>  	/*
> -- 
> 2.34.1