cmd/objdump: support reading from a pipe

It is convenient if the objdump supports reading from a pipe. I modified `cmd/internal/objfile.Open`, it would check file at first, dumps it to a temporary file if it is not seekable, and open tmp file.

For golang#41051

Change-Id: I4bf47c1b9722aee03a54147a7aa8dd44529ada89

src/cmd/internal/objfile/objfile.go

@@ -10,8 +10,10 @@ import (
 	"debug/gosym"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"sort"
+	"strings"
 )
 
 type rawFile interface {
@@ -64,13 +66,40 @@ var openers = []func(io.ReaderAt) (rawFile, error){
 	openXcoff,
 }
 
+func trySeekOrDump(f *os.File) (*os.File, error) {
+	_, err := f.Seek(0, 0)
+	if err == nil {
+		return f, nil
+	}
+	if !strings.Contains(err.Error(), "illegal seek") {
+		return nil, err
+	}
+	defer f.Close()
+
+	tempFile, err := ioutil.TempFile(os.TempDir(), "go-objfile")
+	if err != nil {
+		return nil, err
+	}
+
+	if _, err := io.Copy(tempFile, f); err != nil {
+		return nil, err
+	}
+	if _, err := tempFile.Seek(0, io.SeekStart); err != nil {
+		return nil, err
+	}
+	return tempFile, nil
+}
+
 // Open opens the named file.
 // The caller must call f.Close when the file is no longer needed.
 func Open(name string) (*File, error) {
 	r, err := os.Open(name)
 	if err != nil {
 		return nil, err
 	}
+	if r, err = trySeekOrDump(r); err != nil {
+		return nil, err
+	}
 	if f, err := openGoFile(r); err == nil {
 		return f, nil
 	}

src/cmd/objdump/objdump_test.go

@@ -283,6 +283,36 @@ func TestDisasmExtld(t *testing.T) {
 	testDisasm(t, "fmthello.go", false, false, "-ldflags=-linkmode=external")
 }
 
+func buildTestData(t *testing.T) string {
+	hello := filepath.Join(tmp, "hello.o")
+	args := []string{"tool", "compile", "-o", hello}
+	args = append(args, "testdata/fmthello.go")
+	out, err := exec.Command(testenv.GoToolPath(t), args...).CombinedOutput()
+	if err != nil {
+		t.Fatalf("go tool compile fmthello.go: %v\n%s", err, out)
+	}
+	return hello
+}
+
+func validateOutput(t *testing.T, text string, need []string) {
+	ok := true
+	for _, s := range need {
+		if !strings.Contains(text, s) {
+			t.Errorf("disassembly missing '%s'", s)
+			ok = false
+		}
+	}
+	if runtime.GOARCH == "386" {
+		if strings.Contains(text, "(IP)") {
+			t.Errorf("disassembly contains PC-Relative addressing on 386")
+			ok = false
+		}
+	}
+	if !ok {
+		t.Logf("full disassembly:\n%s", text)
+	}
+}
+
 func TestDisasmGoobj(t *testing.T) {
 	switch runtime.GOARCH {
 	case "mips", "mipsle", "mips64", "mips64le":
@@ -293,43 +323,70 @@ func TestDisasmGoobj(t *testing.T) {
 		t.Skipf("skipping on %s, issue 15255", runtime.GOARCH)
 	}
 
-	hello := filepath.Join(tmp, "hello.o")
-	args := []string{"tool", "compile", "-o", hello}
-	args = append(args, "testdata/fmthello.go")
-	out, err := exec.Command(testenv.GoToolPath(t), args...).CombinedOutput()
-	if err != nil {
-		t.Fatalf("go tool compile fmthello.go: %v\n%s", err, out)
-	}
+	hello := buildTestData(t)
 	need := []string{
 		"main(SB)",
 		"fmthello.go:6",
 	}
 
-	args = []string{
+	args := []string{
 		"-s", "main",
 		hello,
 	}
 
-	out, err = exec.Command(exe, args...).CombinedOutput()
+	out, err := exec.Command(exe, args...).CombinedOutput()
 	if err != nil {
 		t.Fatalf("objdump fmthello.o: %v\n%s", err, out)
 	}
 
-	text := string(out)
-	ok := true
-	for _, s := range need {
-		if !strings.Contains(text, s) {
-			t.Errorf("disassembly missing '%s'", s)
-			ok = false
-		}
+	validateOutput(t, string(out), need)
+}
+
+func TestDisasmGoobjFromStdin(t *testing.T) {
+	switch runtime.GOARCH {
+	case "mips", "mipsle", "mips64", "mips64le":
+		t.Skipf("skipping on %s, issue 12559", runtime.GOARCH)
+	case "riscv64":
+		t.Skipf("skipping on %s, issue 36738", runtime.GOARCH)
+	case "s390x":
+		t.Skipf("skipping on %s, issue 15255", runtime.GOARCH)
 	}
-	if runtime.GOARCH == "386" {
-		if strings.Contains(text, "(IP)") {
-			t.Errorf("disassembly contains PC-Relative addressing on 386")
-			ok = false
-		}
+
+	hello := buildTestData(t)
+	need := []string{
+		"main(SB)",
+		"fmthello.go:6",
 	}
-	if !ok {
-		t.Logf("full disassembly:\n%s", text)
+
+	args := []string{
+		"-s", "main", "/dev/stdin",
+	}
+
+	cmd := exec.Command(exe, args...)
+	input, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatalf("get stdin pipe error: %v\n", err)
 	}
+	f, err := os.Open(hello)
+	if err != nil {
+		t.Fatalf("open output file error: %v\n", err)
+	}
+	bytes, err := ioutil.ReadAll(f)
+	if err != nil {
+		t.Fatalf("read output file error: %v\n", err)
+	}
+	_, err = input.Write(bytes)
+	if err != nil {
+		t.Fatalf("write stdin pipe error: %v\n", err)
+	}
+	err = input.Close()
+	if err != nil {
+		t.Fatalf("close stdin pipe error: %v\n", err)
+	}
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("objdump /dev/stdin: %v\n%s", err, out)
+	}
+
+	validateOutput(t, string(out), need)
 }