runtime: add test for systemstack frame pointer adjustment

Add TestSystemstackFramePointerAdjust as a regression test for CL
489015.

By turning stackPoisonCopy into a var instead of const and introducing
the ShrinkStackAndVerifyFramePointers() helper function, we are able to
trigger the exact combination of events that can crash traceEvent() if
systemstack restores a frame pointer that is pointing into the old
stack.

Updates #59692

Change-Id: I60fc6940638077e3b60a81d923b5f5b4f6d8a44c
Reviewed-on: https://go-review.googlesource.com/c/go/+/489115
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Felix Geisendörfer <felix.geisendoerfer@datadoghq.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/src/runtime/stack_test.go b/src/runtime/stack_test.go
index 4e3f369f2f..042289aa58 100644
--- a/src/runtime/stack_test.go
+++ b/src/runtime/stack_test.go
@@ -939,3 +939,22 @@ func TestFramePointerAdjust(t *testing.T) {
 		t.Errorf("output:\n%s\n\nwant no output", output)
 	}
 }
+
+// TestSystemstackFramePointerAdjust is a regression test for issue 59692 that
+// ensures that the frame pointer of systemstack is correctly adjusted. See CL
+// 489015 for more details.
+func TestSystemstackFramePointerAdjust(t *testing.T) {
+	growAndShrinkStack(512, [1024]byte{})
+}
+
+// growAndShrinkStack grows the stack of the current goroutine in order to
+// shrink it again and verify that all frame pointers on the new stack have
+// been correctly adjusted. stackBallast is used to ensure we're not depending
+// on the current heuristics of stack shrinking too much.
+func growAndShrinkStack(n int, stackBallast [1024]byte) {
+	if n <= 0 {
+		return
+	}
+	growAndShrinkStack(n-1, stackBallast)
+	ShrinkStackAndVerifyFramePointers()
+}