@@ -5,6 +5,7 @@ import (

 	"fmt"

 	"io"

 	"os"

+	"runtime"

 	"strings"

 	"github.com/containerd/continuity/driver"

@@ -173,6 +174,9 @@ func StatAt(remote builder.Source, path string) (os.FileInfo, error) {

 func FullPath(remote builder.Source, path string) (string, error) {

 	fullPath, err := remote.Root().ResolveScopedPath(path, true)

 	if err != nil {

+		if runtime.GOOS == "windows" {

+			return "", fmt.Errorf("failed to resolve scoped path %s (%s): %s. Possible cause is a forbidden path outside the build context", path, fullPath, err)

+		}

 		return "", fmt.Errorf("Forbidden path outside the build context: %s (%s)", path, fullPath) // backwards compat with old error

 	}

 	return fullPath, nil

@@ -3,6 +3,7 @@

 package lcow // import "github.com/docker/docker/daemon/graphdriver/lcow"

 import (

+	"bytes"

 	"errors"

 	"fmt"

 	"io"

@@ -385,7 +386,15 @@ func (svm *serviceVM) deleteUnionMount(mountName string, disks ...hcsshim.Mapped

 }

 func (svm *serviceVM) runProcess(command string, stdin io.Reader, stdout io.Writer, stderr io.Writer) error {

-	process, err := svm.config.RunProcess(command, stdin, stdout, stderr)

+	var process hcsshim.Process

+	var err error

+	errOut := &bytes.Buffer{}

+

+	if stderr != nil {

+		process, err = svm.config.RunProcess(command, stdin, stdout, stderr)

+	} else {

+		process, err = svm.config.RunProcess(command, stdin, stdout, errOut)

+	}

 	if err != nil {

 		return err

 	}

@@ -398,7 +407,12 @@ func (svm *serviceVM) runProcess(command string, stdin io.Reader, stdout io.Writ

 	}

 	if exitCode != 0 {

-		return fmt.Errorf("svm.runProcess: command %s failed with exit code %d", command, exitCode)

+		// If the caller isn't explicitly capturing stderr output, then capture it here instead.

+		e := fmt.Sprintf("svm.runProcess: command %s failed with exit code %d", command, exitCode)

+		if stderr == nil {

+			e = fmt.Sprintf("%s. (%s)", e, errOut.String())

+		}

+		return fmt.Errorf(e)

 	}

 	return nil

 }