powerpc/32: add a macro to get and/or save DAR and DSISR on stack.

Refactor reading and saving of DAR and DSISR in exception vectors.

This will ease the implementation of VMAP stack.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1286b3e51b07727c6b4b05f2df9af3f9b1717fb5.1576916812.git.christophe.leroy@c-s.fr

arch/powerpc/kernel/head_32.S

@@ -339,10 +339,7 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_HPTE_TABLE)
 	DO_KVM  0x600
 Alignment:
 	EXCEPTION_PROLOG
-	mfspr	r4,SPRN_DAR
-	stw	r4,_DAR(r11)
-	mfspr	r5,SPRN_DSISR
-	stw	r5,_DSISR(r11)
+	save_dar_dsisr_on_stack r4, r5, r11
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	EXC_XFER_STD(0x600, alignment_exception)
 

arch/powerpc/kernel/head_32.h

@@ -144,6 +144,17 @@
 	RFI				/* jump to handler, enable MMU */
 .endm
 
+.macro save_dar_dsisr_on_stack reg1, reg2, sp
+	mfspr	\reg1, SPRN_DAR
+	mfspr	\reg2, SPRN_DSISR
+	stw	\reg1, _DAR(\sp)
+	stw	\reg2, _DSISR(\sp)
+.endm
+
+.macro get_and_save_dar_dsisr_on_stack reg1, reg2, sp
+	save_dar_dsisr_on_stack \reg1, \reg2, \sp
+.endm
+
 /*
  * Note: code which follows this uses cr0.eq (set if from kernel),
  * r11, r12 (SRR0), and r9 (SRR1).

arch/powerpc/kernel/head_8xx.S

@@ -128,12 +128,9 @@ instruction_counter:
 	. = 0x200
 MachineCheck:
 	EXCEPTION_PROLOG
-	mfspr r4,SPRN_DAR
-	stw r4,_DAR(r11)
-	li r5,RPN_PATTERN
-	mtspr SPRN_DAR,r5	/* Tag DAR, to be used in DTLB Error */
-	mfspr r5,SPRN_DSISR
-	stw r5,_DSISR(r11)
+	save_dar_dsisr_on_stack r4, r5, r11
+	li	r6, RPN_PATTERN
+	mtspr	SPRN_DAR, r6	/* Tag DAR, to be used in DTLB Error */
 	addi r3,r1,STACK_FRAME_OVERHEAD
 	EXC_XFER_STD(0x200, machine_check_exception)
 
@@ -156,12 +153,9 @@ InstructionAccess:
 	. = 0x600
 Alignment:
 	EXCEPTION_PROLOG
-	mfspr	r4,SPRN_DAR
-	stw	r4,_DAR(r11)
-	li	r5,RPN_PATTERN
-	mtspr	SPRN_DAR,r5	/* Tag DAR, to be used in DTLB Error */
-	mfspr	r5,SPRN_DSISR
-	stw	r5,_DSISR(r11)
+	save_dar_dsisr_on_stack r4, r5, r11
+	li	r6, RPN_PATTERN
+	mtspr	SPRN_DAR, r6	/* Tag DAR, to be used in DTLB Error */
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	EXC_XFER_STD(0x600, alignment_exception)
 
@@ -502,10 +496,7 @@ DataTLBError:
 DARFixed:/* Return from dcbx instruction bug workaround */
 	EXCEPTION_PROLOG_1
 	EXCEPTION_PROLOG_2
-	mfspr	r5,SPRN_DSISR
-	stw	r5,_DSISR(r11)
-	mfspr	r4,SPRN_DAR
-	stw	r4, _DAR(r11)
+	get_and_save_dar_dsisr_on_stack r4, r5, r11
 	andis.	r10,r5,DSISR_NOHPTE@h
 	beq+	.Ldtlbie
 	tlbie	r4