powerpc: add a define for the switch frame size and regs offset

This is open-coded in process.c, ppc32 uses a different define with the
same value, and the C definition is name differently which makes it an
extra indirection to grep for.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221127124942.1665522-12-npiggin@gmail.com

arch/powerpc/include/asm/ptrace.h

@@ -97,8 +97,6 @@ struct pt_regs
 #endif
 
 
-#define STACK_FRAME_WITH_PT_REGS (STACK_FRAME_OVERHEAD + sizeof(struct pt_regs))
-
 // Always displays as "REGS" in memory dumps
 #ifdef CONFIG_CPU_BIG_ENDIAN
 #define STACK_FRAME_REGS_MARKER	ASM_CONST(0x52454753)
@@ -125,6 +123,8 @@ struct pt_regs
 #define STACK_USER_INT_FRAME_SIZE	(sizeof(struct pt_regs) + STACK_FRAME_OVERHEAD)
 #define STACK_INT_FRAME_REGS	STACK_FRAME_OVERHEAD
 #define STACK_INT_FRAME_MARKER	(STACK_FRAME_OVERHEAD - 16)
+#define STACK_SWITCH_FRAME_SIZE	(sizeof(struct pt_regs) + STACK_FRAME_OVERHEAD)
+#define STACK_SWITCH_FRAME_REGS	STACK_FRAME_OVERHEAD
 
 #ifdef CONFIG_PPC64_ELF_ABI_V2
 #define STACK_FRAME_MIN_SIZE	32
@@ -146,6 +146,8 @@ struct pt_regs
 #define STACK_INT_FRAME_REGS	STACK_FRAME_OVERHEAD
 #define STACK_INT_FRAME_MARKER	(STACK_FRAME_OVERHEAD - 8)
 #define STACK_FRAME_MIN_SIZE	STACK_FRAME_OVERHEAD
+#define STACK_SWITCH_FRAME_SIZE	(sizeof(struct pt_regs) + STACK_FRAME_OVERHEAD)
+#define STACK_SWITCH_FRAME_REGS	STACK_FRAME_OVERHEAD
 
 /* Size of stack frame allocated when calling signal handler. */
 #define __SIGNAL_FRAMESIZE	64

arch/powerpc/kernel/asm-offsets.c

@@ -260,7 +260,7 @@ int main(void)
 
 	/* Interrupt register frame */
 	DEFINE(INT_FRAME_SIZE, STACK_INT_FRAME_SIZE);
-	DEFINE(SWITCH_FRAME_SIZE, STACK_FRAME_WITH_PT_REGS);
+	DEFINE(SWITCH_FRAME_SIZE, STACK_SWITCH_FRAME_SIZE);
 	STACK_PT_REGS_OFFSET(GPR0, gpr[0]);
 	STACK_PT_REGS_OFFSET(GPR1, gpr[1]);
 	STACK_PT_REGS_OFFSET(GPR2, gpr[2]);

arch/powerpc/kernel/entry_32.S

@@ -215,9 +215,9 @@ ret_from_kernel_thread:
  * in arch/ppc/kernel/process.c
  */
 _GLOBAL(_switch)
-	stwu	r1,-INT_FRAME_SIZE(r1)
+	stwu	r1,-SWITCH_FRAME_SIZE(r1)
 	mflr	r0
-	stw	r0,INT_FRAME_SIZE+4(r1)
+	stw	r0,SWITCH_FRAME_SIZE+4(r1)
 	/* r3-r12 are caller saved -- Cort */
 	SAVE_NVGPRS(r1)
 	stw	r0,_NIP(r1)	/* Return to switch caller */
@@ -248,7 +248,7 @@ _GLOBAL(_switch)
 
 	lwz	r4,_NIP(r1)	/* Return to _switch caller in new task */
 	mtlr	r4
-	addi	r1,r1,INT_FRAME_SIZE
+	addi	r1,r1,SWITCH_FRAME_SIZE
 	blr
 
 	.globl	fast_exception_return

arch/powerpc/kernel/process.c

@@ -1808,10 +1808,10 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	 * do some house keeping and then return from the fork or clone
 	 * system call, using the stack frame created above.
 	 */
-	sp -= sizeof(struct pt_regs);
-	kregs = (struct pt_regs *) sp;
-	sp -= STACK_FRAME_OVERHEAD;
+	sp -= STACK_SWITCH_FRAME_SIZE;
+	kregs = (struct pt_regs *)(sp + STACK_SWITCH_FRAME_REGS);
 	p->thread.ksp = sp;
+
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
 	for (i = 0; i < nr_wp_slots(); i++)
 		p->thread.ptrace_bps[i] = NULL;
@@ -2261,8 +2261,12 @@ void __no_sanitize_address show_stack(struct task_struct *tsk,
 		/*
 		 * See if this is an exception frame.
 		 * We look for the "regs" marker in the current frame.
+		 *
+		 * STACK_SWITCH_FRAME_SIZE being the smallest frame that
+		 * could hold a pt_regs, if that does not fit then it can't
+		 * have regs.
 		 */
-		if (validate_sp(sp, tsk, STACK_FRAME_WITH_PT_REGS)
+		if (validate_sp(sp, tsk, STACK_SWITCH_FRAME_SIZE)
 		    && stack[STACK_INT_FRAME_MARKER_LONGS] == STACK_FRAME_REGS_MARKER) {
 			struct pt_regs *regs = (struct pt_regs *)
 				(sp + STACK_INT_FRAME_REGS);