go/gccgoexportdata: correctly handle archive files containing string tables

If the name of an archive member is longer than 16 bytes, an ELF archive
file contains a string table of file names under the name "//", and this
member has no mode.  Skip such members.

+ Test.

Change-Id: Ib10db1cc42816c9002433be6176240e490678560
Reviewed-on: https://go-review.googlesource.com/32973
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/go/gccgoexportdata/gccgoexportdata_test.go b/go/gccgoexportdata/gccgoexportdata_test.go
index 131f413..1aa114c 100644
--- a/go/gccgoexportdata/gccgoexportdata_test.go
+++ b/go/gccgoexportdata/gccgoexportdata_test.go
@@ -9,28 +9,59 @@
 )
 
 // Test ensures this package can read gccgo export data from the
-// .go_export section of an ELF file.
+// .go_export from a standalone ELF file or such a file in an archive
+// library.
+//
+// The testdata/{short,long}.a ELF archive files were produced by:
+//
+//   $ echo 'package foo; func F()' > foo.go
+//   $ gccgo -c -fgo-pkgpath blah foo.go
+//   $ objcopy -j .go_export foo.o foo.gox
+//   $ ar q short.a foo.gox
+//   $ objcopy -j .go_export foo.o name-longer-than-16-bytes.gox
+//   $ ar q long.a name-longer-than-16-bytes.gox
+//
+// The file long.a contains an archive string table.
+//
+// The errors.gox file (an ELF object file) comes from the toolchain's
+// standard library.
 func Test(t *testing.T) {
-	f, err := os.Open("testdata/errors.gox")
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer f.Close()
-	r, err := gccgoexportdata.NewReader(f)
-	if err != nil {
-		t.Fatal(err)
-	}
-	imports := make(map[string]*types.Package)
-	pkg, err := gccgoexportdata.Read(r, nil, imports, "errors")
-	if err != nil {
+	for _, test := range []struct {
+		filename, path, member, wantType string
+	}{
+		{"testdata/errors.gox", "errors", "New", "func(text string) error"},
+		{"testdata/short.a", "short", "F", "func()"},
+		{"testdata/long.a", "long", "F", "func()"},
+	} {
+		t.Logf("filename = %s", test.filename)
+		f, err := os.Open(test.filename)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		defer f.Close()
+		r, err := gccgoexportdata.NewReader(f)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
 
-		t.Fatal(err)
-	}
+		imports := make(map[string]*types.Package)
+		pkg, err := gccgoexportdata.Read(r, nil, imports, test.path)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
 
-	// Check type of errors.New.
-	got := pkg.Scope().Lookup("New").Type().String()
-	want := "func(text string) error"
-	if got != want {
-		t.Errorf("New.Type = %s, want %s", got, want)
+		// Check type of designated package member.
+		obj := pkg.Scope().Lookup(test.member)
+		if obj == nil {
+			t.Errorf("%s.%s not found", test.path, test.member)
+			continue
+		}
+		if obj.Type().String() != test.wantType {
+			t.Errorf("%s.%s.Type = %s, want %s",
+				test.path, test.member, obj.Type(), test.wantType)
+		}
 	}
 }