cmd/internal/objabi: shrink SymType down to a uint8

Now that it only takes small values.

Change-Id: I08086d392529d8775b470d65afc2475f8d0e7f4a
Reviewed-on: https://go-review.googlesource.com/42030
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/internal/obj/objfile.go

@@ -283,7 +283,7 @@ func (w *objWriter) writeSym(s *LSym) {
 	}
 
 	w.wr.WriteByte(symPrefix)
-	w.writeInt(int64(s.Type))
+	w.wr.WriteByte(byte(s.Type))
 	w.writeRefIndex(s)
 	flags := int64(0)
 	if s.DuplicateOK() {

src/cmd/internal/objabi/symkind.go

@@ -31,7 +31,7 @@
 package objabi
 
 // A SymKind describes the kind of memory represented by a symbol.
-type SymKind int16
+type SymKind uint8
 
 // Defined SymKind values.
 //

src/cmd/internal/objabi/symkind_string.go

@@ -9,7 +9,7 @@ const _SymKind_name = "SxxxSTEXTSRODATASNOPTRDATASDATASBSSSNOPTRBSSSTLSBSSSDWARF
 var _SymKind_index = [...]uint8{0, 4, 9, 16, 26, 31, 35, 44, 51, 61}
 
 func (i SymKind) String() string {
-	if i < 0 || i >= SymKind(len(_SymKind_index)-1) {
+	if i >= SymKind(len(_SymKind_index)-1) {
 		return fmt.Sprintf("SymKind(%d)", i)
 	}
 	return _SymKind_name[_SymKind_index[i]:_SymKind_index[i+1]]

src/cmd/link/internal/ld/objfile.go

@@ -155,10 +155,15 @@ func (r *objReader) readSlices() {
 const symPrefix = 0xfe
 
 func (r *objReader) readSym() {
-	if c, err := r.rd.ReadByte(); c != symPrefix || err != nil {
+	var c byte
+	var err error
+	if c, err = r.rd.ReadByte(); c != symPrefix || err != nil {
 		log.Fatalln("readSym out of sync")
 	}
-	t := abiSymKindToSymKind[r.readInt()]
+	if c, err = r.rd.ReadByte(); err != nil {
+		log.Fatalln("error reading input: ", err)
+	}
+	t := abiSymKindToSymKind[c]
 	s := r.readSymIndex()
 	flags := r.readInt()
 	dupok := flags&1 != 0