runtime: skip gdb goroutine backtrace test on non-x86

Gdb is not able to backtrace our non-standard stack frames on RISC
architectures without frame pointer.

Change-Id: Id62a566ce2d743602ded2da22ff77b9ae34bc5ae
Signed-off-by: Shenghou Ma <minux@golang.org>
Reviewed-on: https://go-review.googlesource.com/9456Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/runtime-gdb_test.go

@@ -64,7 +64,7 @@ func TestGdbPython(t *testing.T) {
 		t.Fatalf("building source %v\n%s", err, out)
 	}
 
-	got, _ := exec.Command("gdb", "-nx", "-q", "--batch", "-iex",
+	args := []string{"-nx", "-q", "--batch", "-iex",
 		fmt.Sprintf("add-auto-load-safe-path %s/src/runtime", runtime.GOROOT()),
 		"-ex", "br main.go:10",
 		"-ex", "run",
@@ -79,11 +79,22 @@ func TestGdbPython(t *testing.T) {
 		"-ex", "echo END\n",
 		"-ex", "echo BEGIN print ptrvar\n",
 		"-ex", "print ptrvar",
-		"-ex", "echo END\n",
+		"-ex", "echo END\n"}
+
+	// without framepointer, gdb cannot backtrace our non-standard
+	// stack frames on RISC architectures.
+	canBackTrace := false
+	switch runtime.GOARCH {
+	case "amd64", "386":
+		canBackTrace = true
+		args = append(args,
 			"-ex", "echo BEGIN goroutine 2 bt\n",
 			"-ex", "goroutine 2 bt",
-		"-ex", "echo END\n",
-		filepath.Join(dir, "a.exe")).CombinedOutput()
+			"-ex", "echo END\n")
+	}
+
+	args = append(args, filepath.Join(dir, "a.exe"))
+	got, _ := exec.Command("gdb", args...).CombinedOutput()
 
 	firstLine := bytes.SplitN(got, []byte("\n"), 2)[0]
 	if string(firstLine) != "Loading Go Runtime support." {
@@ -117,7 +128,9 @@ func TestGdbPython(t *testing.T) {
 	}
 
 	btGoroutineRe := regexp.MustCompile(`^#0\s+runtime.+at`)
-	if bl := blocks["goroutine 2 bt"]; !btGoroutineRe.MatchString(bl) {
+	if bl := blocks["goroutine 2 bt"]; canBackTrace && !btGoroutineRe.MatchString(bl) {
 		t.Fatalf("goroutine 2 bt failed: %s", bl)
+	} else if !canBackTrace {
+		t.Logf("gdb cannot backtrace for GOARCH=%s, skipped goroutine backtrace test", runtime.GOARCH)
 	}
 }