[dev.link] cmd/link: expand set of symbol attributes in loader

Add in a collection of new loader interfaces for getting/setting
symbol attributes, e.g. properties that would normally be part of the
sym.Symbol "Attr" field. This change also moves references to the
loaders 'reachable' bitmap behind a pair of loader methods, so that we
a consistent way of accessing symbol attributes overall. It is worth
noting that not every symbol attribute is backed by a bitmap; for some
infrequently used attributes, a map[Sym]struct{} is used instead.

Change-Id: I0010c9cd928d41b4bb6cdf45db4581e11c3c5db3
Reviewed-on: https://go-review.googlesource.com/c/go/+/210778
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_test.go

@@ -6,6 +6,7 @@ package loader
 
 import (
 	"cmd/link/internal/sym"
+	"fmt"
 	"testing"
 )
 
@@ -52,4 +53,47 @@ func TestAddMaterializedSymbol(t *testing.T) {
 	if es3 == 0 {
 		t.Fatalf("CreateExtSym failed for nameless sym")
 	}
+
+	// New symbols should not initially be reachable.
+	if ldr.AttrReachable(es1) || ldr.AttrReachable(es2) || ldr.AttrReachable(es3) {
+		t.Errorf("newly materialized symbols should not be reachable")
+	}
+
+	// ... however it should be possible to set/unset their reachability.
+	ldr.SetAttrReachable(es3, true)
+	if !ldr.AttrReachable(es3) {
+		t.Errorf("expected reachable symbol after update")
+	}
+	ldr.SetAttrReachable(es3, false)
+	if ldr.AttrReachable(es3) {
+		t.Errorf("expected unreachable symbol after update")
+	}
+
+	// Test expansion of attr bitmaps
+	for idx := 0; idx < 36; idx++ {
+		es := ldr.AddExtSym(fmt.Sprintf("zext%d", idx), 0)
+		if ldr.AttrOnList(es) {
+			t.Errorf("expected OnList after creation")
+		}
+		ldr.SetAttrOnList(es, true)
+		if !ldr.AttrOnList(es) {
+			t.Errorf("expected !OnList after update")
+		}
+		if ldr.AttrDuplicateOK(es) {
+			t.Errorf("expected DupOK after creation")
+		}
+		ldr.SetAttrDuplicateOK(es, true)
+		if !ldr.AttrDuplicateOK(es) {
+			t.Errorf("expected !DupOK after update")
+		}
+	}
+
+	// Get/set a few other attributes
+	if ldr.AttrVisibilityHidden(es3) {
+		t.Errorf("expected initially not hidden")
+	}
+	ldr.SetAttrVisibilityHidden(es3, true)
+	if !ldr.AttrVisibilityHidden(es3) {
+		t.Errorf("expected hidden after update")
+	}
 }