proc: detect when Launching non-executable files

This provides a better error message when the user tries to run dlv
debug on a directory that does not contain a main package, when `dlv
exec` is used with a source file.

Additionally the architecture of the executable is checked as suggested
by @alexbrainman in #443.

Fixes #509

_fixtures/nomaindir/file.go

@@ -0,0 +1,4 @@
+package nomaindir
+
+func AFunction() {
+}

cmd/dlv/cmds/commands.go

@@ -151,7 +151,7 @@ consider compiling debugging binaries with -gcflags="-N -l".`,
 			return nil
 		},
 		Run: func(cmd *cobra.Command, args []string) {
-			os.Exit(execute(0, args, conf))
+			os.Exit(execute(0, args, conf, executingExistingFile))
 		},
 	}
 	RootCommand.AddCommand(execCommand)
@@ -231,7 +231,7 @@ func debugCmd(cmd *cobra.Command, args []string) {
 		defer os.Remove(fp)
 
 		processArgs := append([]string{"./" + debugname}, targetArgs...)
-		return execute(0, processArgs, conf)
+		return execute(0, processArgs, conf, executingGeneratedFile)
 	}()
 	os.Exit(status)
 }
@@ -318,7 +318,7 @@ func testCmd(cmd *cobra.Command, args []string) {
 		defer os.Remove("./" + testdebugname)
 		processArgs := append([]string{"./" + testdebugname}, targetArgs...)
 
-		return execute(0, processArgs, conf)
+		return execute(0, processArgs, conf, executingOther)
 	}()
 	os.Exit(status)
 }
@@ -329,7 +329,7 @@ func attachCmd(cmd *cobra.Command, args []string) {
 		fmt.Fprintf(os.Stderr, "Invalid pid: %s\n", args[0])
 		os.Exit(1)
 	}
-	os.Exit(execute(pid, nil, conf))
+	os.Exit(execute(pid, nil, conf, executingOther))
 }
 
 func connectCmd(cmd *cobra.Command, args []string) {
@@ -360,7 +360,15 @@ func connect(addr string, conf *config.Config) int {
 	return status
 }
 
-func execute(attachPid int, processArgs []string, conf *config.Config) int {
+type executeKind int
+
+const (
+	executingExistingFile = executeKind(iota)
+	executingGeneratedFile
+	executingOther
+)
+
+func execute(attachPid int, processArgs []string, conf *config.Config, kind executeKind) int {
 	// Make a TCP listener
 	listener, err := net.Listen("tcp", Addr)
 	if err != nil {
@@ -404,6 +412,18 @@ func execute(attachPid int, processArgs []string, conf *config.Config) int {
 	}
 
 	if err := server.Run(); err != nil {
+		if err == api.NotExecutableErr {
+			switch kind {
+			case executingGeneratedFile:
+				fmt.Fprintln(os.Stderr, "Can not debug non-main package")
+				return 1
+			case executingExistingFile:
+				fmt.Fprintf(os.Stderr, "%s is not executable\n", processArgs[0])
+				return 1
+			default:
+				// fallthrough
+			}
+		}
 		fmt.Fprintln(os.Stderr, err)
 		return 1
 	}

proc/proc.go

@@ -63,6 +63,8 @@ type Process struct {
 	moduleData         []moduleData
 }
 
+var NotExecutableErr = errors.New("not an executable file")
+
 // New returns an initialized Process struct. Before returning,
 // it will also launch a goroutine in order to handle ptrace(2)
 // functions. For more information, see the documentation on

proc/proc_darwin.go

@@ -38,6 +38,11 @@ type OSProcessDetails struct {
 // PT_SIGEXC on Darwin which will turn Unix signals into
 // Mach exceptions.
 func Launch(cmd []string) (*Process, error) {
+	// check that the argument to Launch is an executable file
+	if fi, staterr := os.Stat(cmd[0]); staterr == nil && (fi.Mode()&0111) == 0 {
+		return nil, NotExecutableErr
+	}
+
 	argv0Go, err := filepath.Abs(cmd[0])
 	if err != nil {
 		return nil, err
@@ -266,6 +271,8 @@ func (dbp *Process) parseDebugLineInfo(exe *macho.File, wg *sync.WaitGroup) {
 	}
 }
 
+var UnsupportedArchErr = errors.New("unsupported architecture - only darwin/amd64 is supported")
+
 func (dbp *Process) findExecutable(path string) (*macho.File, error) {
 	if path == "" {
 		path = C.GoString(C.find_executable(C.int(dbp.Pid)))
@@ -274,6 +281,9 @@ func (dbp *Process) findExecutable(path string) (*macho.File, error) {
 	if err != nil {
 		return nil, err
 	}
+	if exe.Cpu != macho.CpuAmd64 {
+		return nil, UnsupportedArchErr
+	}
 	dbp.dwarf, err = exe.DWARF()
 	if err != nil {
 		return nil, err

proc/proc_linux.go

@@ -49,6 +49,10 @@ func Launch(cmd []string) (*Process, error) {
 		proc *exec.Cmd
 		err  error
 	)
+	// check that the argument to Launch is an executable file
+	if fi, staterr := os.Stat(cmd[0]); staterr == nil && (fi.Mode()&0111) == 0 {
+		return nil, NotExecutableErr
+	}
 	dbp := New(0)
 	dbp.execPtraceFunc(func() {
 		proc = exec.Command(cmd[0])
@@ -162,6 +166,8 @@ func (dbp *Process) updateThreadList() error {
 	return nil
 }
 
+var UnsupportedArchErr = errors.New("unsupported architecture - only linux/amd64 is supported")
+
 func (dbp *Process) findExecutable(path string) (*elf.File, error) {
 	if path == "" {
 		path = fmt.Sprintf("/proc/%d/exe", dbp.Pid)
@@ -174,6 +180,9 @@ func (dbp *Process) findExecutable(path string) (*elf.File, error) {
 	if err != nil {
 		return nil, err
 	}
+	if elfFile.Machine != elf.EM_X86_64 {
+		return nil, UnsupportedArchErr
+	}
 	dbp.dwarf, err = elfFile.DWARF()
 	if err != nil {
 		return nil, err

proc/proc_test.go

@@ -9,6 +9,7 @@ import (
 	"net"
 	"net/http"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"reflect"
 	"runtime"
@@ -1826,3 +1827,57 @@ func TestStepParked(t *testing.T) {
 		}
 	})
 }
+
+func TestIssue509(t *testing.T) {
+	fixturesDir := protest.FindFixturesDir()
+	nomaindir := filepath.Join(fixturesDir, "nomaindir")
+	cmd := exec.Command("go", "build", "-gcflags=-N -l", "-o", "debug")
+	cmd.Dir = nomaindir
+	assertNoError(cmd.Run(), t, "go build")
+	exepath := filepath.Join(nomaindir, "debug")
+	_, err := Launch([]string{exepath})
+	if err == nil {
+		t.Fatalf("expected error but none was generated")
+	}
+	if err != NotExecutableErr {
+		t.Fatalf("expected error \"%v\" got \"%v\"", NotExecutableErr, err)
+	}
+	os.Remove(exepath)
+}
+
+func TestUnsupportedArch(t *testing.T) {
+	ver, _ := ParseVersionString(runtime.Version())
+	if ver.Major < 0 || !ver.AfterOrEqual(GoVersion{1, 6, -1, 0, 0}) {
+		// cross compile (with -N?) works only on select versions of go
+		return
+	}
+	
+	fixturesDir := protest.FindFixturesDir()
+	infile := filepath.Join(fixturesDir, "math.go")
+	outfile := filepath.Join(fixturesDir, "_math_debug_386")
+	
+	cmd := exec.Command("go", "build", "-gcflags=-N -l", "-o", outfile, infile)
+	for _, v := range os.Environ() {
+		if !strings.HasPrefix(v, "GOARCH=") {
+			cmd.Env = append(cmd.Env, v)
+		}
+	}
+	cmd.Env = append(cmd.Env, "GOARCH=386")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("go build failed: %v: %v", err, string(out))
+	}
+	defer os.Remove(outfile)
+	
+	p, err := Launch([]string{outfile})
+	switch err {
+	case UnsupportedArchErr:
+		// all good
+	case nil:
+		p.Halt()
+		p.Kill()
+		t.Fatal("Launch is expected to fail, but succeeded")
+	default:
+		t.Fatal(err)
+	}
+}

proc/proc_windows.go

@@ -37,15 +37,20 @@ func Launch(cmd []string) (*Process, error) {
 	if err != nil {
 		return nil, err
 	}
-	// Make sure the binary exists.
+
+	// Make sure the binary exists and is an executable file
 	if filepath.Base(cmd[0]) == cmd[0] {
 		if _, err := exec.LookPath(cmd[0]); err != nil {
 			return nil, err
 		}
 	}
-	if _, err := os.Stat(argv0Go); err != nil {
-		return nil, err
+
+	peFile, err := openExecutablePath(argv0Go)
+	if err != nil {
+		return nil, NotExecutableErr
 	}
+	peFile.Close()
+
 	// Duplicate the stdin/stdout/stderr handles
 	files := []uintptr{uintptr(syscall.Stdin), uintptr(syscall.Stdout), uintptr(syscall.Stderr)}
 	p, _ := syscall.GetCurrentProcess()
@@ -308,19 +313,20 @@ func (dbp *Process) parseDebugLineInfo(exe *pe.File, wg *sync.WaitGroup) {
 	}
 }
 
+var UnsupportedArchErr = errors.New("unsupported architecture of windows/386 - only windows/amd64 is supported")
+
 func (dbp *Process) findExecutable(path string) (*pe.File, error) {
 	if path == "" {
 		// TODO: Find executable path from PID/handle on Windows:
 		// https://msdn.microsoft.com/en-us/library/aa366789(VS.85).aspx
 		return nil, fmt.Errorf("not yet implemented")
 	}
-	f, err := os.OpenFile(path, 0, os.ModePerm)
+	peFile, err := openExecutablePath(path)
 	if err != nil {
 		return nil, err
 	}
-	peFile, err := pe.NewFile(f)
-	if err != nil {
-		return nil, err
+	if peFile.Machine != pe.IMAGE_FILE_MACHINE_AMD64 {
+		return nil, UnsupportedArchErr
 	}
 	dbp.dwarf, err = dwarfFromPE(peFile)
 	if err != nil {
@@ -329,6 +335,14 @@ func (dbp *Process) findExecutable(path string) (*pe.File, error) {
 	return peFile, nil
 }
 
+func openExecutablePath(path string) (*pe.File, error) {
+	f, err := os.OpenFile(path, 0, os.ModePerm)
+ 	if err != nil {
+ 		return nil, err
+ 	}
+	return pe.NewFile(f)
+}
+
 // Adapted from src/debug/pe/file.go: pe.(*File).DWARF()
 func dwarfFromPE(f *pe.File) (*dwarf.Data, error) {
 	// There are many other DWARF sections, but these

service/api/types.go

@@ -10,6 +10,8 @@ import (
 	"github.com/derekparker/delve/proc"
 )
 
+var NotExecutableErr = proc.NotExecutableErr
+
 // DebuggerState represents the current context of the debugger.
 type DebuggerState struct {
 	// CurrentThread is the currently selected debugger thread.

service/debugger/debugger.go

@@ -61,7 +61,10 @@ func New(config *Config) (*Debugger, error) {
 		log.Printf("launching process with args: %v", d.config.ProcessArgs)
 		p, err := proc.Launch(d.config.ProcessArgs)
 		if err != nil {
-			return nil, fmt.Errorf("could not launch process: %s", err)
+			if err != proc.NotExecutableErr && err != proc.UnsupportedArchErr {
+				err = fmt.Errorf("could not launch process: %s", err)
+			}
+			return nil, err
 		}
 		d.process = p
 	}