2 files changed, 19 insertions, 3 deletions
diff --git a/src/internal/pkgbits/decoder.go b/src/internal/pkgbits/decoder.go
index 9c8ad446ca..5b4e8f69af 100644
--- a/src/internal/pkgbits/decoder.go
+++ b/src/internal/pkgbits/decoder.go
@@ -22,7 +22,7 @@ type PkgDecoder struct {
 
 	elemEndsEnds [numRelocs]uint32
 	elemEnds     []uint32
-	elemData     string
+	elemData     string // last 8 bytes are fingerprint
 }
 
 func (pr *PkgDecoder) PkgPath() string { return pr.pkgPath }
@@ -50,7 +50,7 @@ func NewPkgDecoder(pkgPath, input string) PkgDecoder {
 	assert(err == nil)
 
 	pr.elemData = input[pos:]
-	assert(len(pr.elemData) == int(pr.elemEnds[len(pr.elemEnds)-1]))
+	assert(len(pr.elemData)-8 == int(pr.elemEnds[len(pr.elemEnds)-1]))
 
 	return pr
 }
@@ -67,6 +67,12 @@ func (pr *PkgDecoder) TotalElems() int {
 	return len(pr.elemEnds)
 }
 
+func (pr *PkgDecoder) Fingerprint() [8]byte {
+	var fp [8]byte
+	copy(fp[:], pr.elemData[len(pr.elemData)-8:])
+	return fp
+}
+
 func (pr *PkgDecoder) AbsIdx(k RelocKind, idx int) int {
 	absIdx := idx
 	if k > 0 {
diff --git a/src/internal/pkgbits/encoder.go b/src/internal/pkgbits/encoder.go
index 820c707940..4780f01c39 100644
--- a/src/internal/pkgbits/encoder.go
+++ b/src/internal/pkgbits/encoder.go
@@ -8,6 +8,7 @@ package pkgbits
 
 import (
 	"bytes"
+	"crypto/md5"
 	"encoding/binary"
 	"go/constant"
 	"io"
@@ -30,7 +31,10 @@ func NewPkgEncoder(syncFrames int) PkgEncoder {
 	}
 }
 
-func (pw *PkgEncoder) DumpTo(out io.Writer) {
+func (pw *PkgEncoder) DumpTo(out0 io.Writer) (fingerprint [8]byte) {
+	h := md5.New()
+	out := io.MultiWriter(out0, h)
+
 	writeUint32 := func(x uint32) {
 		assert(binary.Write(out, binary.LittleEndian, x) == nil)
 	}
@@ -57,6 +61,12 @@ func (pw *PkgEncoder) DumpTo(out io.Writer) {
 			assert(err == nil)
 		}
 	}
+
+	copy(fingerprint[:], h.Sum(nil))
+	_, err := out0.Write(fingerprint[:])
+	assert(err == nil)
+
+	return
 }
 
 func (pw *PkgEncoder) StringIdx(s string) int {