[kvm-unit-tests PATCH 4/5] s390x: Clear first stack frame and end backtrace early

[Janosch Frank <frankja@linux.ibm.com>]

When setting the first stack frame to 0, we can check for a 0
backchain pointer when doing backtraces to know when to stop.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
 lib/s390x/stack.c | 2 ++
 s390x/cstart64.S  | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/lib/s390x/stack.c b/lib/s390x/stack.c
index e714e07c..9f234a12 100644
--- a/lib/s390x/stack.c
+++ b/lib/s390x/stack.c
@@ -22,6 +22,8 @@ int backtrace_frame(const void *frame, const void **return_addrs, int max_depth)
 	for (depth = 0; stack && depth < max_depth; depth++) {
 		return_addrs[depth] = (void *)stack->grs[8];
 		stack = stack->back_chain;
+		if (!stack)
+			break;
 	}
 
 	return depth;
diff --git a/s390x/cstart64.S b/s390x/cstart64.S
index 666a9567..6f83da2a 100644
--- a/s390x/cstart64.S
+++ b/s390x/cstart64.S
@@ -37,6 +37,8 @@ start:
 	sam64				# Set addressing mode to 64 bit
 	/* setup stack */
 	larl	%r15, stackptr
+	/* Clear first stack frame */
+	xc      0(160,%r15), 0(%r15)
 	/* setup initial PSW mask + control registers*/
 	larl	%r1, initial_psw
 	lpswe	0(%r1)
-- 
2.34.1