[dev.link] cmd/link: add storage and methods for read/write of Sym value

Add loader methods SymValue() and SetSymValue() to get/set the
value of a symbol by global index.

Change-Id: Ifc71480fc34c719ad00506d0828edf36c1a57119
Reviewed-on: https://go-review.googlesource.com/c/go/+/211302


Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

src/cmd/link/internal/loader/loader.go

@@ -157,6 +157,7 @@ type Loader struct {
 	overwrite     map[Sym]Sym       // overwrite[i]=j if symbol j overwrites symbol i
 
 	payloads []extSymPayload // contents of linker-materialized external syms
+	values   []int64         // symbol values, indexed by global sym index
 
 	itablink map[Sym]struct{} // itablink[j] defined if j is go.itablink.*
 
@@ -197,11 +198,10 @@ type Loader struct {
 }
 
 // extSymPayload holds the payload (data + relocations) for linker-synthesized
-// external symbols.
+// external symbols (note that symbol value is stored in a separate slice).
 type extSymPayload struct {
 	name   string // TODO: would this be better as offset into str table?
 	size   int64
-	value  int64
 	ver    int
 	kind   sym.SymKind
 	relocs []Reloc
@@ -247,6 +247,7 @@ func (l *Loader) addObj(pkg string, r *oReader) Sym {
 	l.start[r] = i
 	l.objs = append(l.objs, objIdx{r, i, i + Sym(n) - 1})
 	l.max += Sym(n)
+	l.growValues(int(l.max))
 	return i
 }
 
@@ -373,6 +374,7 @@ func (l *Loader) growSyms(i int) {
 	}
 	l.Syms = append(l.Syms, make([]*sym.Symbol, i+1-n)...)
 	l.payloads = append(l.payloads, make([]extSymPayload, i+1-n)...)
+	l.growValues(int(i) + 1)
 	l.growAttrBitmaps(int(i) + 1)
 }
 
@@ -832,6 +834,24 @@ func (l *Loader) IsItabLink(i Sym) bool {
 	return false
 }
 
+// growValues grows the slice used to store symbol values.
+func (l *Loader) growValues(reqLen int) {
+	curLen := len(l.values)
+	if reqLen > curLen {
+		l.values = append(l.values, make([]int64, reqLen+1-curLen)...)
+	}
+}
+
+// SymValue returns the value of the i-th symbol. i is global index.
+func (l *Loader) SymValue(i Sym) int64 {
+	return l.values[i]
+}
+
+// SetSymValue sets the value of the i-th symbol. i is global index.
+func (l *Loader) SetSymValue(i Sym, val int64) {
+	l.values[i] = val
+}
+
 // Returns the symbol content of the i-th symbol. i is global index.
 func (l *Loader) Data(i Sym) []byte {
 	if l.IsExternal(i) {

src/cmd/link/internal/loader/loader_test.go

@@ -32,7 +32,7 @@ func TestAddMaterializedSymbol(t *testing.T) {
 
 	// Create some syms from a dummy object file symbol to get things going.
 	addDummyObjSym(t, ldr, or, "type.uint8")
-	addDummyObjSym(t, ldr, or, "mumble")
+	ts2 := addDummyObjSym(t, ldr, or, "mumble")
 	addDummyObjSym(t, ldr, or, "type.string")
 
 	// Create some external symbols.
@@ -96,4 +96,17 @@ func TestAddMaterializedSymbol(t *testing.T) {
 	if !ldr.AttrVisibilityHidden(es3) {
 		t.Errorf("expected hidden after update")
 	}
+
+	// Test get/set symbol value.
+	toTest := []Sym{ts2, es3}
+	for i, s := range toTest {
+		if v := ldr.SymValue(s); v != 0 {
+			t.Errorf("ldr.Value(%d): expected 0 got %d\n", s, v)
+		}
+		nv := int64(i + 101)
+		ldr.SetSymValue(s, nv)
+		if v := ldr.SymValue(s); v != nv {
+			t.Errorf("ldr.SetValue(%d,%d): expected %d got %d\n", s, nv, nv, v)
+		}
+	}
 }