Ensure runner notices post-main stderr output.

If LeakSanitizer fires something on a test that's expected to fail, runner will
swallow it. Have stderr output always end in a "--- DONE ---" marker and treat
all output following that as a test failure.

Change-Id: Ia8fd9dfcaf48dd23972ab8f906d240bcb6badfe2
Reviewed-on: https://boringssl-review.googlesource.com/7281
Reviewed-by: Adam Langley <agl@google.com>

ssl/test/bssl_shim.cc

@@ -1485,7 +1485,16 @@ static bool DoExchange(ScopedSSL_SESSION *out_session, SSL_CTX *ssl_ctx,
   return true;
 }
 
+class StderrDelimiter {
+ public:
+  ~StderrDelimiter() { fprintf(stderr, "--- DONE ---\n"); }
+};
+
 int main(int argc, char **argv) {
+  // To distinguish ASan's output from ours, add a trailing message to stderr.
+  // Anything following this line will be considered an error.
+  StderrDelimiter delimiter;
+
 #if defined(OPENSSL_WINDOWS)
   /* Initialize Winsock. */
   WORD wsa_version = MAKEWORD(2, 2);

ssl/test/runner/runner.go

@@ -738,6 +738,15 @@ func runTest(test *testCase, shimPath string, mallocNumToFail int64) error {
 
 	stdout := string(stdoutBuf.Bytes())
 	stderr := string(stderrBuf.Bytes())
+
+	// Separate the errors from the shim and those from tools like
+	// AddressSanitizer.
+	var extraStderr string
+	if stderrParts := strings.SplitN(stderr, "--- DONE ---\n", 2); len(stderrParts) == 2 {
+		stderr = stderrParts[0]
+		extraStderr = stderrParts[1]
+	}
+
 	failed := err != nil || childErr != nil
 	correctFailure := len(test.expectedError) == 0 || strings.Contains(stderr, test.expectedError)
 	localError := "none"
@@ -769,8 +778,8 @@ func runTest(test *testCase, shimPath string, mallocNumToFail int64) error {
 		return fmt.Errorf("%s: local error '%s', child error '%s', stdout:\n%s\nstderr:\n%s", msg, localError, childError, stdout, stderr)
 	}
 
-	if !*useValgrind && !failed && len(stderr) > 0 {
-		println(stderr)
+	if !*useValgrind && (len(extraStderr) > 0 || (!failed && len(stderr) > 0)) {
+		return fmt.Errorf("unexpected error output:\n%s\n%s", stderr, extraStderr)
 	}
 
 	return nil