From 3e1155ade1baab51458374efd0295bdf6db455fc Mon Sep 17 00:00:00 2001
From: Justin Hibbits <jhibbits@FreeBSD.org>
Date: Sat, 11 Mar 2023 11:30:00 -0500
Subject: [PATCH] dtrace/powerpc: "Fix" stack traces across trap frames

In function boundary tracing the link register is not yet saved to the
save stack location, so the save point contains whatever the previous
'lr' save was, or even garbage, at the time the trap is taken.  Address
this by explicitly loading the link register from the trap frame instead
of the stack, and propagate that out.
---
 sys/cddl/dev/dtrace/powerpc/dtrace_isa.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/sys/cddl/dev/dtrace/powerpc/dtrace_isa.c b/sys/cddl/dev/dtrace/powerpc/dtrace_isa.c
index cce1c907b5d8..2139be1ccec7 100644
--- a/sys/cddl/dev/dtrace/powerpc/dtrace_isa.c
+++ b/sys/cddl/dev/dtrace/powerpc/dtrace_isa.c
@@ -97,15 +97,18 @@ dtrace_sp_inkernel(uintptr_t sp)
 }
 
 static __inline void
-dtrace_next_sp_pc(uintptr_t sp, uintptr_t *nsp, uintptr_t *pc)
+dtrace_next_sp_pc(uintptr_t sp, uintptr_t *nsp, uintptr_t *pc, uintptr_t *lr)
 {
 	vm_offset_t callpc;
 	struct trapframe *frame;
 
+	if (lr != 0 && *lr != 0)
+		callpc = *lr;
+	else
 #ifdef __powerpc64__
-	callpc = *(vm_offset_t *)(sp + RETURN_OFFSET64);
+		callpc = *(vm_offset_t *)(sp + RETURN_OFFSET64);
 #else
-	callpc = *(vm_offset_t *)(sp + RETURN_OFFSET);
+		callpc = *(vm_offset_t *)(sp + RETURN_OFFSET);
 #endif
 
 	/*
@@ -121,6 +124,8 @@ dtrace_next_sp_pc(uintptr_t sp, uintptr_t *nsp, uintptr_t *pc)
 			*nsp = frame->fixreg[1];
 		if (pc != NULL)
 			*pc = frame->srr0;
+		if (lr != NULL)
+			*lr = frame->lr;
 		return;
 	}
 
@@ -128,6 +133,9 @@ dtrace_next_sp_pc(uintptr_t sp, uintptr_t *nsp, uintptr_t *pc)
 		*nsp = *(uintptr_t *)sp;
 	if (pc != NULL)
 		*pc = callpc;
+	/* lr is only valid for trap frames */
+	if (lr != NULL)
+		*lr = 0;
 }
 
 void
@@ -135,7 +143,7 @@ dtrace_getpcstack(pc_t *pcstack, int pcstack_limit, int aframes,
     uint32_t *intrpc)
 {
 	int depth = 0;
-	uintptr_t osp, sp;
+	uintptr_t osp, sp, lr = 0;
 	vm_offset_t callpc;
 	pc_t caller = (pc_t) solaris_cpu[curcpu].cpu_dtrace_caller;
 
@@ -154,7 +162,8 @@ dtrace_getpcstack(pc_t *pcstack, int pcstack_limit, int aframes,
 		if (!dtrace_sp_inkernel(sp))
 			break;
 		osp = sp;
-		dtrace_next_sp_pc(osp, &sp, &callpc);
+		dtrace_next_sp_pc(osp, &sp, &callpc, &lr);
+		//printf("sp: %#lx, pc: %#lx, lr: %#lx\n", sp, callpc, lr);
 
 		if (aframes > 0) {
 			aframes--;
@@ -513,7 +522,7 @@ dtrace_getstackdepth(int aframes)
 
 		depth++;
 		osp = sp;
-		dtrace_next_sp_pc(sp, &sp, NULL);
+		dtrace_next_sp_pc(sp, &sp, NULL, NULL);
 	}
 	if (depth < aframes)
 		return (0);