Mark the return address of the call to ast() in the generic trap

handling code so the stack trace unwinders don't start trying to
go into user-space.

Found by trying to create core dumps with a KTR_COMPILE/KTR_GEOM
kernel, which results in a stack_save() call in the ast() coredump
path - this created a panic, and then calling 'trace' in ddb resulted
in the black screen of death after printing out most of the backtrace.

3 files changed, 13 insertions, 5 deletions

diff --git a/sys/powerpc/aim/trap_subr.S b/sys/powerpc/aim/trap_subr.S
index c719917..06ed891 100644
--- a/sys/powerpc/aim/trap_subr.S
+++ b/sys/powerpc/aim/trap_subr.S
@@ -438,6 +438,8 @@ CNAME(trapexit):
 	isync
 	addi	%r3,%r1,8
 	bl	CNAME(ast)
+	.globl	CNAME(asttrapexit)	/* backtrace code sentinel #2 */
+CNAME(asttrapexit):
 	b	trapexit		/* test ast ret value ? */
 1:
 	FRAME_LEAVE(PC_TEMPSAVE)
diff --git a/sys/powerpc/powerpc/db_trace.c b/sys/powerpc/powerpc/db_trace.c
index 131beef..e70f5e1 100644
--- a/sys/powerpc/powerpc/db_trace.c
+++ b/sys/powerpc/powerpc/db_trace.c
@@ -97,6 +97,7 @@ struct db_variable db_regs[] = {
 struct db_variable *db_eregs = db_regs + sizeof (db_regs)/sizeof (db_regs[0]);
 
 extern int trapexit[];
+extern int asttrapexit[];
 extern int end[];
 
 /*
@@ -186,11 +187,13 @@ db_backtrace(struct thread *td, db_addr_t fp, int count)
 		db_printf("0x%08x: ", stackframe);
 
 		/*
-		 * The trap code labels the return address from the
-		 * call to C code as 'trapexit'. Use this to determine
-		 * if the callframe has to traverse a saved trap context
+		 * The trap code labels the return addresses from the
+		 * call to C code as 'trapexit' and 'asttrapexit. Use this
+		 * to determine if the callframe has to traverse a saved
+		 * trap context
 		 */
-		if (lr + 4 == (db_addr_t) &trapexit) {
+		if ((lr + 4 == (db_addr_t) &trapexit) ||
+		    (lr + 4 == (db_addr_t) &asttrapexit)) {
 			const char *trapstr;
 			struct trapframe *tf = (struct trapframe *)
 				(stackframe+8);
@@ -312,7 +315,8 @@ stack_save(struct stack *st)
 		 * things are going wrong. Plus, prevents this shortened
 		 * version of code from accessing user-space frames
 		 */
-		if (callpc + 4 == (db_addr_t) &trapexit)
+		if (callpc + 4 == (db_addr_t) &trapexit ||
+		    callpc + 4 == (db_addr_t) &asttrapexit)
 			break;
 
 		if (stack_put(st, callpc) == -1)
diff --git a/sys/powerpc/powerpc/trap_subr.S b/sys/powerpc/powerpc/trap_subr.S
index c719917..06ed891 100644
--- a/sys/powerpc/powerpc/trap_subr.S
+++ b/sys/powerpc/powerpc/trap_subr.S
@@ -438,6 +438,8 @@ CNAME(trapexit):
 	isync
 	addi	%r3,%r1,8
 	bl	CNAME(ast)
+	.globl	CNAME(asttrapexit)	/* backtrace code sentinel #2 */
+CNAME(asttrapexit):
 	b	trapexit		/* test ast ret value ? */
 1:
 	FRAME_LEAVE(PC_TEMPSAVE)