Fix unsafe usage in Decode

structs.go

@@ -13,6 +13,8 @@ type valuePointer struct {
 	Offset uint32
 }
 
+const vptrSize = unsafe.Sizeof(valuePointer{})
+
 func (p valuePointer) Less(o valuePointer) bool {
 	if p.Fid != o.Fid {
 		return p.Fid < o.Fid
@@ -27,8 +29,6 @@ func (p valuePointer) IsZero() bool {
 	return p.Fid == 0 && p.Offset == 0 && p.Len == 0
 }
 
-const vptrSize = 12
-
 // Encode encodes Pointer into byte buffer.
 func (p valuePointer) Encode() []byte {
 	b := make([]byte, vptrSize)
@@ -39,7 +39,9 @@ func (p valuePointer) Encode() []byte {
 
 // Decode decodes the value pointer into the provided byte buffer.
 func (p *valuePointer) Decode(b []byte) {
-	*p = *(*valuePointer)(unsafe.Pointer(&b[0]))
+	// Copy over data from b into p. Using *p=unsafe.pointer(...) leads to
+	// pointer alignment issues. See https://github.com/dgraph-io/badger/issues/1096
+	copy((*[vptrSize]byte)(unsafe.Pointer(p))[:], b)
 }
 
 // header is used in value log as a header before Entry.

table/builder.go

@@ -44,6 +44,8 @@ type header struct {
 	diff    uint16 // Length of the diff.
 }
 
+const headerSize = uint16(unsafe.Sizeof(header{}))
+
 // Encode encodes the header.
 func (h header) Encode() []byte {
 	var b [4]byte
@@ -52,16 +54,12 @@ func (h header) Encode() []byte {
 }
 
 // Decode decodes the header.
-func (h *header) Decode(buf []byte) int {
-	*h = *(*header)(unsafe.Pointer(&buf[0]))
-	return h.Size()
+func (h *header) Decode(buf []byte) {
+	// Copy over data from buf into h. Using *h=unsafe.pointer(...) leads to
+	// pointer alignment issues. See https://github.com/dgraph-io/badger/issues/1096
+	copy((*[headerSize]byte)(unsafe.Pointer(h))[:], buf)
 }
 
-const headerSize = 4
-
-// Size returns size of the header. Currently it's just a constant.
-func (h header) Size() int { return headerSize }
-
 // Builder is used in building a table.
 type Builder struct {
 	// Typically tens or hundreds of meg. This is for one single file.

table/iterator.go

@@ -87,7 +87,7 @@ func (itr *blockIterator) setIdx(i int) {
 		itr.key = append(itr.key[:itr.prevOverlap], itr.baseKey[itr.prevOverlap:h.overlap]...)
 	}
 	itr.prevOverlap = h.overlap
-	valueOff := headerSize + int(h.diff)
+	valueOff := headerSize + h.diff
 	diffKey := entryData[headerSize:valueOff]
 	itr.key = append(itr.key[:h.overlap], diffKey...)
 	itr.val = entryData[valueOff:]