2 files changed, 32 insertions, 4 deletions
diff --git a/src/internal/coverage/slicereader/slicereader.go b/src/internal/coverage/slicereader/slicereader.go
index 3d117bae37..d9f2a7eac4 100644
--- a/src/internal/coverage/slicereader/slicereader.go
+++ b/src/internal/coverage/slicereader/slicereader.go
@@ -6,6 +6,8 @@ package slicereader
 
 import (
 	"encoding/binary"
+	"fmt"
+	"io"
 	"unsafe"
 )
 
@@ -38,8 +40,31 @@ func (r *Reader) Read(b []byte) (int, error) {
 	return amt, nil
 }
 
-func (r *Reader) SeekTo(off int64) {
-	r.off = off
+func (r *Reader) Seek(offset int64, whence int) (ret int64, err error) {
+	switch whence {
+	case io.SeekStart:
+		if offset < 0 || offset > int64(len(r.b)) {
+			return 0, fmt.Errorf("invalid seek: new offset %d (out of range [0 %d]", offset, len(r.b))
+		}
+		r.off = offset
+		return offset, nil
+	case io.SeekCurrent:
+		newoff := r.off + offset
+		if newoff < 0 || newoff > int64(len(r.b)) {
+			return 0, fmt.Errorf("invalid seek: new offset %d (out of range [0 %d]", newoff, len(r.b))
+		}
+		r.off = newoff
+		return r.off, nil
+	case io.SeekEnd:
+		newoff := int64(len(r.b)) + offset
+		if newoff < 0 || newoff > int64(len(r.b)) {
+			return 0, fmt.Errorf("invalid seek: new offset %d (out of range [0 %d]", newoff, len(r.b))
+		}
+		r.off = newoff
+		return r.off, nil
+	}
+	// other modes are not supported
+	return 0, fmt.Errorf("unsupported seek mode %d", whence)
 }
 
 func (r *Reader) Offset() int64 {
diff --git a/src/internal/coverage/slicereader/slr_test.go b/src/internal/coverage/slicereader/slr_test.go
index 2f7cef00f8..461436d5f5 100644
--- a/src/internal/coverage/slicereader/slr_test.go
+++ b/src/internal/coverage/slicereader/slr_test.go
@@ -6,6 +6,7 @@ package slicereader
 
 import (
 	"encoding/binary"
+	"io"
 	"testing"
 )
 
@@ -64,10 +65,12 @@ func TestSliceReader(t *testing.T) {
 		if gs2 != s2 {
 			t.Fatalf("readStr got %s want %s", gs2, s2)
 		}
-		slr.SeekTo(4)
+		if _, err := slr.Seek(4, io.SeekStart); err != nil {
+			t.Fatal(err)
+		}
 		off := slr.Offset()
 		if off != 4 {
-			t.Fatalf("Offset(0 returned %d wanted 4", off)
+			t.Fatalf("Offset() returned %d wanted 4", off)
 		}
 		g64 = slr.ReadUint64()
 		if g64 != e64 {