cmd/link: intial skeleton of linker written in Go

R=iant
CC=golang-codereviews
https://golang.org/cl/48870044

src/cmd/link/link_test.go

@@ -0,0 +1,32 @@
+// Copyright 2014 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"bytes"
+	"debug/goobj"
+	"testing"
+)
+
+func TestLinkHello(t *testing.T) {
+	p := &Prog{
+		GOOS:   "darwin",
+		GOARCH: "amd64",
+		Error:  func(s string) { t.Error(s) },
+	}
+	var buf bytes.Buffer
+	p.link(&buf, "testdata/hello.6")
+	if p.NumError > 0 {
+		return
+	}
+	if len(p.Syms) != 2 || p.Syms[goobj.SymID{"_rt0_go", 0}] == nil || p.Syms[goobj.SymID{"hello", 1}] == nil {
+		t.Errorf("Syms = %v, want [_rt0_go hello<1>]", p.Syms)
+	}
+
+	checkGolden(t, buf.Bytes(), "testdata/link.hello.darwin.amd64")
+
+	// uncomment to leave file behind for execution:
+	// ioutil.WriteFile("a.out", buf.Bytes(), 0777)
+}