runtime: fix CGO traceback frame count

Without this, each additional C frame found via SetCgoTraceback will
cause a frame to be dropped from the bottom of the traceback stack.

Fixes #29034

Change-Id: I90aa6b2a1dced90c69b64c5dd565fe64a25724a3
Reviewed-on: https://go-review.googlesource.com/c/151917
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 12 insertions, 2 deletions

diff --git a/src/runtime/testdata/testprogcgo/pprof.go b/src/runtime/testdata/testprogcgo/pprof.go
index 4460b9304e..00f2c42e93 100644
--- a/src/runtime/testdata/testprogcgo/pprof.go
+++ b/src/runtime/testdata/testprogcgo/pprof.go
@@ -26,6 +26,9 @@ void cpuHog() {
 	salt2 = foo;
 }
 
+void cpuHog2() {
+}
+
 static int cpuHogCount;
 
 struct cgoTracebackArg {
@@ -37,10 +40,13 @@ struct cgoTracebackArg {
 
 // pprofCgoTraceback is passed to runtime.SetCgoTraceback.
 // For testing purposes it pretends that all CPU hits in C code are in cpuHog.
+// Issue #29034: At least 2 frames are required to verify all frames are captured
+// since runtime/pprof ignores the runtime.goexit base frame if it exists.
 void pprofCgoTraceback(void* parg) {
 	struct cgoTracebackArg* arg = (struct cgoTracebackArg*)(parg);
 	arg->buf[0] = (uintptr_t)(cpuHog) + 0x10;
-	arg->buf[1] = 0;
+	arg->buf[1] = (uintptr_t)(cpuHog2) + 0x4;
+	arg->buf[2] = 0;
 	++cpuHogCount;
 }
 
diff --git a/src/runtime/testdata/testprogcgo/threadpprof.go b/src/runtime/testdata/testprogcgo/threadpprof.go
index 3da82961b9..37a2a1ab65 100644
--- a/src/runtime/testdata/testprogcgo/threadpprof.go
+++ b/src/runtime/testdata/testprogcgo/threadpprof.go
@@ -30,6 +30,9 @@ void cpuHogThread() {
 	threadSalt2 = foo;
 }
 
+void cpuHogThread2() {
+}
+
 static int cpuHogThreadCount;
 
 struct cgoTracebackArg {
@@ -44,7 +47,8 @@ struct cgoTracebackArg {
 void pprofCgoThreadTraceback(void* parg) {
 	struct cgoTracebackArg* arg = (struct cgoTracebackArg*)(parg);
 	arg->buf[0] = (uintptr_t)(cpuHogThread) + 0x10;
-	arg->buf[1] = 0;
+	arg->buf[1] = (uintptr_t)(cpuHogThread2) + 0x4;
+	arg->buf[2] = 0;
 	__sync_add_and_fetch(&cpuHogThreadCount, 1);
 }