[PATCH 06/23] powerpc/64e: Clarify register saves and clears with {SAVE,ZEROIZE}_GPRS

[Nicholas Piggin]

On Fri Sep 16, 2022 at 3:32 PM AEST, Rohan McLure wrote:
> The common interrupt handler prologue macro and the bad_stack
> trampolines include consecutive sequences of register saves, and some
> register clears. Neaten such instances by expanding use of the SAVE_GPRS
> macro and employing the ZEROIZE_GPR macro when appropriate.
>
> Also simplify an invocation of SAVE_GPRS targetting all non-volatile
> registers to SAVE_NVGPRS.
>
> Signed-off-by: Rohan Mclure <rmclure at linux.ibm.com>
> Reported-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> V3 -> V4: New commit.
> ---
>  arch/powerpc/kernel/exceptions-64e.S | 27 +++++++++++---------------
>  1 file changed, 11 insertions(+), 16 deletions(-)
>
> diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
> index 67dc4e3179a0..48c640ca425d 100644
> --- a/arch/powerpc/kernel/exceptions-64e.S
> +++ b/arch/powerpc/kernel/exceptions-64e.S
> @@ -216,17 +216,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_EMB_HV)
>  	mtlr	r10
>  	mtcr	r11
>  
> -	ld	r10,GPR10(r1)
> -	ld	r11,GPR11(r1)
> -	ld	r12,GPR12(r1)
> +	REST_GPRS(10, 12, r1)
>  	mtspr	\scratch,r0
>  
>  	std	r10,\paca_ex+EX_R10(r13);
>  	std	r11,\paca_ex+EX_R11(r13);
>  	ld	r10,_NIP(r1)
>  	ld	r11,_MSR(r1)
> -	ld	r0,GPR0(r1)
> -	ld	r1,GPR1(r1)
> +	REST_GPRS(0, 1, r1)

I'm hesitant to have a multi reg restore that also clobbers the base
register. It works if we always restore in order, and there might never
be a good reason to change that, but it's possibly a bit easier to miss
when you're looking at the code.

Otherwise,

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

>  	mtspr	\srr0,r10
>  	mtspr	\srr1,r11
>  	ld	r10,\paca_ex+EX_R10(r13)
> @@ -372,16 +369,15 @@ ret_from_mc_except:
>  /* Core exception code for all exceptions except TLB misses. */
>  #define EXCEPTION_COMMON_LVL(n, scratch, excf)				    \
>  exc_##n##_common:							    \
> -	std	r0,GPR0(r1);		/* save r0 in stackframe */	    \
> -	std	r2,GPR2(r1);		/* save r2 in stackframe */	    \
> -	SAVE_GPRS(3, 9, r1);		/* save r3 - r9 in stackframe */    \
> +	SAVE_GPR(0, r1);		/* save r0 in stackframe */	    \
> +	SAVE_GPRS(2, 9, r1);		/* save r2 - r9 in stackframe */    \
>  	std	r10,_NIP(r1);		/* save SRR0 to stackframe */	    \
>  	std	r11,_MSR(r1);		/* save SRR1 to stackframe */	    \
>  	beq	2f;			/* if from kernel mode */	    \
>  2:	ld	r3,excf+EX_R10(r13);	/* get back r10 */		    \
>  	ld	r4,excf+EX_R11(r13);	/* get back r11 */		    \
>  	mfspr	r5,scratch;		/* get back r13 */		    \
> -	std	r12,GPR12(r1);		/* save r12 in stackframe */	    \
> +	SAVE_GPR(12, r1);		/* save r12 in stackframe */	    \
>  	ld	r2,PACATOC(r13);	/* get kernel TOC into r2 */	    \
>  	mflr	r6;			/* save LR in stackframe */	    \
>  	mfctr	r7;			/* save CTR in stackframe */	    \
> @@ -390,7 +386,7 @@ exc_##n##_common:							    \
>  	lwz	r10,excf+EX_CR(r13);	/* load orig CR back from PACA	*/  \
>  	lbz	r11,PACAIRQSOFTMASK(r13); /* get current IRQ softe */	    \
>  	ld	r12,exception_marker at toc(r2);				    \
> -	li	r0,0;							    \
> +	ZEROIZE_GPR(0);							    \
>  	std	r3,GPR10(r1);		/* save r10 to stackframe */	    \
>  	std	r4,GPR11(r1);		/* save r11 to stackframe */	    \
>  	std	r5,GPR13(r1);		/* save it to stackframe */	    \
> @@ -1056,15 +1052,14 @@ bad_stack_book3e:
>  	mfspr	r11,SPRN_ESR
>  	std	r10,_DEAR(r1)
>  	std	r11,_ESR(r1)
> -	std	r0,GPR0(r1);		/* save r0 in stackframe */	    \
> -	std	r2,GPR2(r1);		/* save r2 in stackframe */	    \
> -	SAVE_GPRS(3, 9, r1);		/* save r3 - r9 in stackframe */    \
> +	SAVE_GPR(0, r1);		/* save r0 in stackframe */	    \
> +	SAVE_GPRS(2, 9, r1);		/* save r2 - r9 in stackframe */    \
>  	ld	r3,PACA_EXGEN+EX_R10(r13);/* get back r10 */		    \
>  	ld	r4,PACA_EXGEN+EX_R11(r13);/* get back r11 */		    \
>  	mfspr	r5,SPRN_SPRG_GEN_SCRATCH;/* get back r13 XXX can be wrong */ \
>  	std	r3,GPR10(r1);		/* save r10 to stackframe */	    \
>  	std	r4,GPR11(r1);		/* save r11 to stackframe */	    \
> -	std	r12,GPR12(r1);		/* save r12 in stackframe */	    \
> +	SAVE_GPR(12, r1);		/* save r12 in stackframe */	    \
>  	std	r5,GPR13(r1);		/* save it to stackframe */	    \
>  	mflr	r10
>  	mfctr	r11
> @@ -1072,12 +1067,12 @@ bad_stack_book3e:
>  	std	r10,_LINK(r1)
>  	std	r11,_CTR(r1)
>  	std	r12,_XER(r1)
> -	SAVE_GPRS(14, 31, r1)
> +	SAVE_NVGPRS(r1)
>  	lhz	r12,PACA_TRAP_SAVE(r13)
>  	std	r12,_TRAP(r1)
>  	addi	r11,r1,INT_FRAME_SIZE
>  	std	r11,0(r1)
> -	li	r12,0
> +	ZEROIZE_GPR(12)
>  	std	r12,0(r11)
>  	ld	r2,PACATOC(r13)
>  1:	addi	r3,r1,STACK_FRAME_OVERHEAD
> -- 
> 2.34.1