diff --git a/src/cmd/go/test.go b/src/cmd/go/test.go
index 1ff02a68e1..f477a4a253 100644
--- a/src/cmd/go/test.go
+++ b/src/cmd/go/test.go
@@ -1531,6 +1531,10 @@ func coverRegisterFile(fileName string, counter []uint32, pos []uint32, numStmts
 
 func main() {
 {{if .IsIOS}}
+	// Send a SIGUSR2, which will be intercepted by LLDB to
+	// tell the test harness that installation was successful,
+	// and to give the exec script a chance set the current
+	// working directory. See misc/ios/go_darwin_arm_exec.go.
 	signal.Notify(make(chan os.Signal), syscall.SIGUSR2)
 	syscall.Kill(0, syscall.SIGUSR2)
 	signal.Reset(syscall.SIGUSR2)