cmd/ld: restore .debug_gdb_script section after runtime reorganization

On some systems, gdb refuses to load Python plugin from arbitrary
paths, so we have to add $GOROOT/src/runtime to auto-load-safe-path
in the gdb script test.

Change-Id: Icc44baab8d04a65bd21ceac2ab8ddb13c8d083e8
Reviewed-on: https://go-review.googlesource.com/2905Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/cmd/ld/dwarf.c

@@ -1414,7 +1414,7 @@ movetomodule(DWDie *parent)
 	die->link = parent->child;
 }
 
-// If the pcln table contains runtime/string.goc, use that to set gdbscript path.
+// If the pcln table contains runtime/runtime.go, use that to set gdbscript path.
 static void
 finddebugruntimepath(LSym *s)
 {
@@ -1427,7 +1427,7 @@ finddebugruntimepath(LSym *s)
 
 	for(i=0; i<s->pcln->nfile; i++) {
 		f = s->pcln->file[i];
-		if((p = strstr(f->name, "runtime/string.goc")) != nil) {
+		if((p = strstr(f->name, "runtime/runtime.go")) != nil) {
 			*p = '\0';
 			snprint(gdbscript, sizeof gdbscript, "%sruntime/runtime-gdb.py", f->name);
 			*p = 'r';

src/runtime/runtime-gdb_test.go

 package runtime_test
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 	"testing"
 )
 
 func checkGdbPython(t *testing.T) {
-	cmd := exec.Command("gdb", "-nx", "-q", "--batch", "-ex", "python import sys; print('golang gdb python support')")
+	cmd := exec.Command("gdb", "-nx", "-q", "--batch", "-ex", "python import sys; print('go gdb python support')")
 	out, err := cmd.CombinedOutput()
 
 	if err != nil {
-		t.Skipf("skipping due to issue running gdb%v", err)
+		t.Skipf("skipping due to issue running gdb: %v", err)
 	}
-	if string(out) != "golang gdb python support\n" {
+	if string(out) != "go gdb python support\n" {
 		t.Skipf("skipping due to lack of python gdb support: %s", out)
 	}
 }
@@ -29,7 +31,6 @@ func main() {
 `
 
 func TestGdbLoadRuntimeSupport(t *testing.T) {
-
 	checkGdbPython(t)
 
 	dir, err := ioutil.TempDir("", "go-build")
@@ -51,7 +52,8 @@ func TestGdbLoadRuntimeSupport(t *testing.T) {
 		t.Fatalf("building source %v\n%s", err, out)
 	}
 
-	got, _ := exec.Command("gdb", "-nx", "-q", "--batch", "-ex", "source runtime-gdb.py",
+	got, _ := exec.Command("gdb", "-nx", "-q", "--batch", "-iex",
+		fmt.Sprintf("add-auto-load-safe-path %s/src/runtime", runtime.GOROOT()),
 		filepath.Join(dir, "a.exe")).CombinedOutput()
 	if string(got) != "Loading Go Runtime support.\n" {
 		t.Fatalf("%s", got)