debug/dwarf: compute ByteSize for more DWARF types

When AttrByteSize is not present for a type, we can still determine the
size in two more cases: when the type is a Typedef referring to another
type, and when the type is a pointer and we know the default address
size.

entry.go: return after setting an error if the offset is out of range.

Change-Id: I63a922ca4e4ad2fc9e9be3e5b47f59fae7d0eb5c
Reviewed-on: https://go-review.googlesource.com/9663Reviewed-by: Austin Clements <austin@google.com>

src/debug/dwarf/entry.go

@@ -522,6 +522,12 @@ func (d *Data) Reader() *Reader {
 	return r
 }
 
+// AddressSize returns the size in bytes of addresses in the current compilation
+// unit.
+func (r *Reader) AddressSize() int {
+	return r.d.unit[r.unit].asize
+}
+
 // Seek positions the Reader at offset off in the encoded entry stream.
 // Offset 0 can be used to denote the first entry.
 func (r *Reader) Seek(off Offset) {
@@ -541,6 +547,7 @@ func (r *Reader) Seek(off Offset) {
 	i := d.offsetToUnit(off)
 	if i == -1 {
 		r.err = errors.New("offset out of range")
+		return
 	}
 	u := &d.unit[i]
 	r.unit = i

src/debug/dwarf/type.go

@@ -268,6 +268,9 @@ type typeReader interface {
 	Next() (*Entry, error)
 	clone() typeReader
 	offset() Offset
+	// AddressSize returns the size in bytes of addresses in the current
+	// compilation unit.
+	AddressSize() int
 }
 
 // Type reads the type at off in the DWARF ``info'' section.
@@ -286,6 +289,7 @@ func (d *Data) readType(name string, r typeReader, off Offset, typeCache map[Off
 	if err != nil {
 		return nil, err
 	}
+	addressSize := r.AddressSize()
 	if e == nil || e.Offset != off {
 		return nil, DecodeError{name, off, "no type at offset"}
 	}
@@ -668,6 +672,12 @@ func (d *Data) readType(name string, r typeReader, off Offset, typeCache map[Off
 		b, ok := e.Val(AttrByteSize).(int64)
 		if !ok {
 			b = -1
+			switch t := typ.(type) {
+			case *TypedefType:
+				b = t.Type.Size()
+			case *PtrType:
+				b = int64(addressSize)
+			}
 		}
 		typ.Common().ByteSize = b
 	}

src/debug/dwarf/typeunit.go

@@ -129,6 +129,11 @@ func (tur *typeUnitReader) Seek(off Offset) {
 	tur.b = makeBuf(tur.d, tur.tu, tur.tu.name, off, tur.tu.data[doff:])
 }
 
+// AddressSize returns the size in bytes of addresses in the current type unit.
+func (tur *typeUnitReader) AddressSize() int {
+	return tur.tu.unit.asize
+}
+
 // Next reads the next Entry from the type unit.
 func (tur *typeUnitReader) Next() (*Entry, error) {
 	if tur.err != nil {