cmd/link: move Localentry field in sym.Symbol to cold section

The sym.Symbol 'Localentry' field is used only with cgo and/or
external linking on MachoPPC. Relocate it to sym.AuxSymbol since it is
infrequently used, so as to shrink the main Symbol struct.

Updates #26186

Change-Id: I5872aa3f059270c2a091016d235a1a732695e411
Reviewed-on: https://go-review.googlesource.com/125477Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/link/internal/loadelf/ldelf.go

@@ -820,7 +820,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length i
 		if elfobj.machine == ElfMachPower64 {
 			flag := int(elfsym.other) >> 5
 			if 2 <= flag && flag <= 6 {
-				s.Localentry = 1 << uint(flag-2)
+				s.SetLocalentry(1 << uint(flag-2))
 			} else if flag == 7 {
 				return errorf("%v: invalid sym.other 0x%x", s, elfsym.other)
 			}

src/cmd/link/internal/ppc64/asm.go

@@ -280,7 +280,7 @@ func adddynrel(ctxt *ld.Link, s *sym.Symbol, r *sym.Reloc) bool {
 		// callee. Hence, we need to go to the local entry
 		// point.  (If we don't do this, the callee will try
 		// to use r12 to compute r2.)
-		r.Add += int64(r.Sym.Localentry) * 4
+		r.Add += int64(r.Sym.Localentry()) * 4
 
 		if targ.Type == sym.SDYNIMPORT {
 			// Should have been handled in elfsetupplt

src/cmd/link/internal/sym/sizeof_test.go

@@ -23,7 +23,7 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Symbol{}, 124, 200},
+		{Symbol{}, 120, 192},
 	}
 
 	for _, tt := range tests {

src/cmd/link/internal/sym/symbol.go

@@ -18,7 +18,6 @@ type Symbol struct {
 	Type        SymKind
 	Version     int16
 	Attr        Attribute
-	Localentry  uint8
 	Dynid       int32
 	Plt         int32
 	Got         int32
@@ -49,6 +48,7 @@ type AuxSymbol struct {
 	extname    string
 	dynimplib  string
 	dynimpvers string
+	localentry uint8
 }
 
 func (s *Symbol) String() string {
@@ -327,6 +327,23 @@ func (s *Symbol) ResetDyninfo() {
 	}
 }
 
+func (s *Symbol) Localentry() uint8 {
+	if s.auxinfo == nil {
+		return 0
+	}
+	return s.auxinfo.localentry
+}
+
+func (s *Symbol) SetLocalentry(val uint8) {
+	if s.auxinfo == nil {
+		if val != 0 {
+			return
+		}
+		s.makeAuxInfo()
+	}
+	s.auxinfo.localentry = val
+}
+
 // SortSub sorts a linked-list (by Sub) of *Symbol by Value.
 // Used for sub-symbols when loading host objects (see e.g. ldelf.go).
 func SortSub(l *Symbol) *Symbol {