powerpc/64: use 32-bit immediate for STACK_FRAME_REGS_MARKER

Using a 32-bit constant for this marker allows it to be loaded with
two ALU instructions, like 32-bit. This avoids a TOC entry and a
TOC load that depends on the r2 value that has just been loaded from
the PACA.

This changes the value for 32-bit as well, so both have the same
value in the low 4 bytes and 64-bit has 0 in the top bytes.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220926034057.2360083-2-npiggin@gmail.com

arch/powerpc/include/asm/ptrace.h

@@ -99,6 +99,8 @@ struct pt_regs
 
 #define STACK_FRAME_WITH_PT_REGS (STACK_FRAME_OVERHEAD + sizeof(struct pt_regs))
 
+#define STACK_FRAME_REGS_MARKER	ASM_CONST(0x72656773)
+
 #ifdef __powerpc64__
 
 /*
@@ -115,7 +117,6 @@ struct pt_regs
 
 #define STACK_FRAME_OVERHEAD	112	/* size of minimum stack frame */
 #define STACK_FRAME_LR_SAVE	2	/* Location of LR in stack frame */
-#define STACK_FRAME_REGS_MARKER	ASM_CONST(0x7265677368657265)
 #define STACK_INT_FRAME_SIZE	(sizeof(struct pt_regs) + \
 				 STACK_FRAME_OVERHEAD + KERNEL_REDZONE_SIZE)
 #define STACK_FRAME_MARKER	12
@@ -136,7 +137,6 @@ struct pt_regs
 #define KERNEL_REDZONE_SIZE	0
 #define STACK_FRAME_OVERHEAD	16	/* size of minimum stack frame */
 #define STACK_FRAME_LR_SAVE	1	/* Location of LR in stack frame */
-#define STACK_FRAME_REGS_MARKER	ASM_CONST(0x72656773)
 #define STACK_INT_FRAME_SIZE	(sizeof(struct pt_regs) + STACK_FRAME_OVERHEAD)
 #define STACK_FRAME_MARKER	2
 #define STACK_FRAME_MIN_SIZE	STACK_FRAME_OVERHEAD

arch/powerpc/kernel/entry_32.S

@@ -263,7 +263,7 @@ fast_exception_return:
 	mtcr	r10
 	lwz	r10,_LINK(r11)
 	mtlr	r10
-	/* Clear the exception_marker on the stack to avoid confusing stacktrace */
+	/* Clear the exception marker on the stack to avoid confusing stacktrace */
 	li	r10, 0
 	stw	r10, 8(r11)
 	REST_GPR(10, r11)
@@ -320,7 +320,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
 	li	r0,0
 
 	/*
-	 * Leaving a stale exception_marker on the stack can confuse
+	 * Leaving a stale exception marker on the stack can confuse
 	 * the reliable stack unwinder later on. Clear it.
 	 */
 	stw	r0,8(r1)
@@ -372,7 +372,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
 	mtspr	SPRN_XER,r5
 
 	/*
-	 * Leaving a stale exception_marker on the stack can confuse
+	 * Leaving a stale exception marker on the stack can confuse
 	 * the reliable stack unwinder later on. Clear it.
 	 */
 	stw	r0,8(r1)

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

@@ -378,7 +378,7 @@ exc_##n##_common:							    \
 	ld	r9,excf+EX_R1(r13);	/* load orig r1 back from PACA */   \
 	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);				    \
+	LOAD_REG_IMMEDIATE(r12, STACK_FRAME_REGS_MARKER);		    \
 	ZEROIZE_GPR(0);							    \
 	std	r3,GPR10(r1);		/* save r10 to stackframe */	    \
 	std	r4,GPR11(r1);		/* save r11 to stackframe */	    \
@@ -459,12 +459,6 @@ exc_##n##_bad_stack:							    \
 	bl	hdlr;							\
 	b	interrupt_return
 
-/* This value is used to mark exception frames on the stack. */
-	.section	".toc","aw"
-exception_marker:
-	.tc	ID_EXC_MARKER[TC],STACK_FRAME_REGS_MARKER
-
-
 /*
  * And here we have the exception vectors !
  */

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

@@ -589,7 +589,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
 	li	r9,IVEC
 	std	r9,_TRAP(r1)		/* set trap number		*/
 	li	r10,0
-	ld	r11,exception_marker@toc(r2)
+	LOAD_REG_IMMEDIATE(r11, STACK_FRAME_REGS_MARKER)
 	std	r10,RESULT(r1)		/* clear regs->result		*/
 	std	r11,STACK_FRAME_OVERHEAD-16(r1) /* mark the frame	*/
 .endm

arch/powerpc/kernel/head_64.S

@@ -192,13 +192,6 @@ __secondary_hold:
 #endif
 CLOSE_FIXED_SECTION(first_256B)
 
-/* This value is used to mark exception frames on the stack. */
-	.section ".toc","aw"
-/* This value is used to mark exception frames on the stack. */
-exception_marker:
-	.tc	ID_EXC_MARKER[TC],STACK_FRAME_REGS_MARKER
-	.previous
-
 /*
  * On server, we include the exception vectors code here as it
  * relies on absolute addressing which is only possible within

arch/powerpc/kernel/interrupt_64.S

@@ -80,7 +80,7 @@ _ASM_NOKPROBE_SYMBOL(system_call_vectored_\name)
 	/* Calling convention has r3 = regs, r4 = orig r0 */
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	mr	r4,r0
-	ld	r11,exception_marker@toc(r2)
+	LOAD_REG_IMMEDIATE(r11, STACK_FRAME_REGS_MARKER)
 	std	r11,-16(r3)		/* "regshere" marker */
 
 BEGIN_FTR_SECTION
@@ -253,7 +253,7 @@ END_BTB_FLUSH_SECTION
 	/* Calling convention has r3 = regs, r4 = orig r0 */
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	mr	r4,r0
-	ld	r11,exception_marker@toc(r2)
+	LOAD_REG_IMMEDIATE(r11, STACK_FRAME_REGS_MARKER)
 	std	r11,-16(r3)		/* "regshere" marker */
 
 #ifdef CONFIG_PPC_BOOK3S
@@ -614,7 +614,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
 	mtspr	SPRN_XER,r5
 
 	/*
-	 * Leaving a stale exception_marker on the stack can confuse
+	 * Leaving a stale STACK_FRAME_REGS_MARKER on the stack can confuse
 	 * the reliable stack unwinder later on. Clear it.
 	 */
 	std	r0,STACK_FRAME_OVERHEAD-16(r1)