runtime: fix runtime-gdb script loading

runtime.rtype was a copy of reflect.rtype - update script to use that directly.
Introduces a basic test which will skip on systems without appropriate GDB.

Fixes #9326

Change-Id: I6ec74e947bd2e1295492ca34b3a8c1b49315a8cb
Reviewed-on: https://go-review.googlesource.com/2821Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/runtime-gdb.py

@@ -202,7 +202,7 @@ def lookup_type(name):
 	except gdb.error:
 		pass
 
-_rctp_type = gdb.lookup_type("struct runtime.rtype").pointer()
+_rctp_type = gdb.lookup_type("struct reflect.rtype").pointer()
 
 
 def iface_commontype(obj):

src/runtime/runtime-gdb_test.go

+package runtime_test
+
+import (
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+func checkGdbPython(t *testing.T) {
+	cmd := exec.Command("gdb", "-nx", "-q", "--batch", "-ex", "python import sys; print('golang gdb python support')")
+	out, err := cmd.CombinedOutput()
+
+	if err != nil {
+		t.Skipf("skipping due to issue running gdb%v", err)
+	}
+	if string(out) != "golang gdb python support\n" {
+		t.Skipf("skipping due to lack of python gdb support: %s", out)
+	}
+}
+
+const helloSource = `
+package main
+import "fmt"
+func main() {
+	fmt.Println("hi")
+}
+`
+
+func TestGdbLoadRuntimeSupport(t *testing.T) {
+
+	checkGdbPython(t)
+
+	dir, err := ioutil.TempDir("", "go-build")
+	if err != nil {
+		t.Fatalf("failed to create temp directory: %v", err)
+	}
+	defer os.RemoveAll(dir)
+
+	src := filepath.Join(dir, "main.go")
+	err = ioutil.WriteFile(src, []byte(helloSource), 0644)
+	if err != nil {
+		t.Fatalf("failed to create file: %v", err)
+	}
+
+	cmd := exec.Command("go", "build", "-o", "a.exe")
+	cmd.Dir = dir
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("building source %v\n%s", err, out)
+	}
+
+	got, _ := exec.Command("gdb", "-nx", "-q", "--batch", "-ex", "source runtime-gdb.py",
+		filepath.Join(dir, "a.exe")).CombinedOutput()
+	if string(got) != "Loading Go Runtime support.\n" {
+		t.Fatalf("%s", got)
+	}
+}