1 files changed, 108 insertions, 0 deletions
diff --git a/libgo/go/debug/elf/reader.go b/libgo/go/debug/elf/reader.go
new file mode 100644
index 00000000000..17b57165bc3
--- /dev/null
+++ b/libgo/go/debug/elf/reader.go
@@ -0,0 +1,108 @@
+// Copyright 2015 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 elf
+
+import (
+	"io"
+	"os"
+)
+
+// errorReader returns error from all operations.
+type errorReader struct {
+	error
+}
+
+func (r errorReader) Read(p []byte) (n int, err error) {
+	return 0, r.error
+}
+
+func (r errorReader) ReadAt(p []byte, off int64) (n int, err error) {
+	return 0, r.error
+}
+
+func (r errorReader) Seek(offset int64, whence int) (int64, error) {
+	return 0, r.error
+}
+
+func (r errorReader) Close() error {
+	return r.error
+}
+
+// readSeekerFromReader converts an io.Reader into an io.ReadSeeker.
+// In general Seek may not be efficient, but it is optimized for
+// common cases such as seeking to the end to find the length of the
+// data.
+type readSeekerFromReader struct {
+	reset  func() (io.Reader, error)
+	r      io.Reader
+	size   int64
+	offset int64
+}
+
+func (r *readSeekerFromReader) start() {
+	x, err := r.reset()
+	if err != nil {
+		r.r = errorReader{err}
+	} else {
+		r.r = x
+	}
+	r.offset = 0
+}
+
+func (r *readSeekerFromReader) Read(p []byte) (n int, err error) {
+	if r.r == nil {
+		r.start()
+	}
+	n, err = r.r.Read(p)
+	r.offset += int64(n)
+	return n, err
+}
+
+func (r *readSeekerFromReader) Seek(offset int64, whence int) (int64, error) {
+	var newOffset int64
+	switch whence {
+	case 0:
+		newOffset = offset
+	case 1:
+		newOffset = r.offset + offset
+	case 2:
+		newOffset = r.size + offset
+	default:
+		return 0, os.ErrInvalid
+	}
+
+	switch {
+	case newOffset == r.offset:
+		return newOffset, nil
+
+	case newOffset < 0, newOffset > r.size:
+		return 0, os.ErrInvalid
+
+	case newOffset == 0:
+		r.r = nil
+
+	case newOffset == r.size:
+		r.r = errorReader{io.EOF}
+
+	default:
+		if newOffset < r.offset {
+			// Restart at the beginning.
+			r.start()
+		}
+		// Read until we reach offset.
+		var buf [512]byte
+		for r.offset < newOffset {
+			b := buf[:]
+			if newOffset-r.offset < int64(len(buf)) {
+				b = buf[:newOffset-r.offset]
+			}
+			if _, err := r.Read(b); err != nil {
+				return 0, err
+			}
+		}
+	}
+	r.offset = newOffset
+	return r.offset, nil
+}