powerpc/64e: Clarify register saves and clears with {SAVE,ZEROIZE}_GPRS

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@linux.ibm.com>
Reported-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220921065605.1051927-7-rmclure@linux.ibm.com

arch/powerpc/kernel/exceptions-64e.S

@@ -216,17 +216,15 @@ 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_GPR(0, r1)
+	REST_GPR(1, r1)
 	mtspr	\srr0,r10
 	mtspr	\srr1,r11
 	ld	r10,\paca_ex+EX_R10(r13)
@@ -364,16 +362,15 @@ 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 */	    \
@@ -382,7 +379,7 @@ 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@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 */	    \
@@ -1048,28 +1045,27 @@ 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
 	mfxer	r12
 	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