cmd/link: split out Extname into cold portion of sym.Symbol

Create a new "AuxSymbol" struct into which 'cold' or 'infrequently
set' symbol fields are located. Move the Extname field from the
main Symbol struct to AuxSymbol.

Updates #26186

Change-Id: I9e795fb0cc48f978e2818475fa073ed9f2db202d
Reviewed-on: https://go-review.googlesource.com/125476Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -1034,7 +1034,7 @@ func elfdynhash(ctxt *Link) {
 			need[sy.Dynid] = addelflib(&needlib, sy.Dynimplib(), sy.Dynimpvers())
 		}
 
-		name := sy.Extname
+		name := sy.Extname()
 		hc := elfhash(name)
 
 		b := hc % uint32(nbucket)
@@ -2254,7 +2254,7 @@ func elfadddynsym(ctxt *Link, s *sym.Symbol) {
 
 		d := ctxt.Syms.Lookup(".dynsym", 0)
 
-		name := s.Extname
+		name := s.Extname()
 		d.AddUint32(ctxt.Arch, uint32(Addstring(ctxt.Syms.Lookup(".dynstr", 0), name)))
 
 		/* type */
@@ -2297,7 +2297,7 @@ func elfadddynsym(ctxt *Link, s *sym.Symbol) {
 		d := ctxt.Syms.Lookup(".dynsym", 0)
 
 		/* name */
-		name := s.Extname
+		name := s.Extname()
 
 		d.AddUint32(ctxt.Arch, uint32(Addstring(ctxt.Syms.Lookup(".dynstr", 0), name)))
 

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

@@ -156,7 +156,7 @@ func loadcgo(ctxt *Link, file string, pkg string, p string) {
 			s := ctxt.Syms.Lookup(local, 0)
 			if s.Type == 0 || s.Type == sym.SXREF || s.Type == sym.SHOSTOBJ {
 				s.SetDynimplib(lib)
-				s.Extname = remote
+				s.SetExtname(remote)
 				s.SetDynimpvers(q)
 				if s.Type != sym.SHOSTOBJ {
 					s.Type = sym.SDYNIMPORT
@@ -200,15 +200,15 @@ func loadcgo(ctxt *Link, file string, pkg string, p string) {
 			// see issue 4878.
 			if s.Dynimplib() != "" {
 				s.ResetDyninfo()
-				s.Extname = ""
+				s.SetExtname("")
 				s.Type = 0
 			}
 
 			if !s.Attr.CgoExport() {
-				s.Extname = remote
+				s.SetExtname(remote)
 				dynexp = append(dynexp, s)
-			} else if s.Extname != remote {
-				fmt.Fprintf(os.Stderr, "%s: conflicting cgo_export directives: %s as %s and %s\n", os.Args[0], s.Name, s.Extname, remote)
+			} else if s.Extname() != remote {
+				fmt.Fprintf(os.Stderr, "%s: conflicting cgo_export directives: %s as %s and %s\n", os.Args[0], s.Name, s.Extname(), remote)
 				nerrors++
 				return
 			}
@@ -276,7 +276,7 @@ func Adddynsym(ctxt *Link, s *sym.Symbol) {
 	if ctxt.IsELF {
 		elfadddynsym(ctxt, s)
 	} else if ctxt.HeadType == objabi.Hdarwin {
-		Errorf(s, "adddynsym: missed symbol (Extname=%s)", s.Extname)
+		Errorf(s, "adddynsym: missed symbol (Extname=%s)", s.Extname())
 	} else if ctxt.HeadType == objabi.Hwindows {
 		// already taken care of
 	} else {

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

@@ -435,7 +435,7 @@ func (ctxt *Link) loadlib() {
 				// cgo_import_static and cgo_import_dynamic,
 				// then we want to make it cgo_import_dynamic
 				// now.
-				if s.Extname != "" && s.Dynimplib() != "" && !s.Attr.CgoExport() {
+				if s.Extname() != "" && s.Dynimplib() != "" && !s.Attr.CgoExport() {
 					s.Type = sym.SDYNIMPORT
 				} else {
 					s.Type = 0
@@ -2116,7 +2116,7 @@ func genasmsym(ctxt *Link, put func(*Link, *sym.Symbol, string, SymbolType, int6
 			if !s.Attr.Reachable() {
 				continue
 			}
-			put(ctxt, s, s.Extname, UndefinedSym, 0, nil)
+			put(ctxt, s, s.Extname(), UndefinedSym, 0, nil)
 
 		case sym.STLSBSS:
 			if ctxt.LinkMode == LinkExternal {

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

@@ -724,7 +724,7 @@ func (x machoscmp) Less(i, j int) bool {
 		return k1 < k2
 	}
 
-	return s1.Extname < s2.Extname
+	return s1.Extname() < s2.Extname()
 }
 
 func machogenasmsym(ctxt *Link) {
@@ -763,7 +763,7 @@ func machoShouldExport(ctxt *Link, s *sym.Symbol) bool {
 	if !ctxt.DynlinkingGo() || s.Attr.Local() {
 		return false
 	}
-	if ctxt.BuildMode == BuildModePlugin && strings.HasPrefix(s.Extname, objabi.PathToPrefix(*flagPluginPath)) {
+	if ctxt.BuildMode == BuildModePlugin && strings.HasPrefix(s.Extname(), objabi.PathToPrefix(*flagPluginPath)) {
 		return true
 	}
 	if strings.HasPrefix(s.Name, "go.itab.") {
@@ -798,13 +798,13 @@ func machosymtab(ctxt *Link) {
 		// symbols like crosscall2 are in pclntab and end up
 		// pointing at the host binary, breaking unwinding.
 		// See Issue #18190.
-		cexport := !strings.Contains(s.Extname, ".") && (ctxt.BuildMode != BuildModePlugin || onlycsymbol(s))
+		cexport := !strings.Contains(s.Extname(), ".") && (ctxt.BuildMode != BuildModePlugin || onlycsymbol(s))
 		if cexport || export {
 			symstr.AddUint8('_')
 		}
 
 		// replace "·" as ".", because DTrace cannot handle it.
-		Addstring(symstr, strings.Replace(s.Extname, "·", ".", -1))
+		Addstring(symstr, strings.Replace(s.Extname(), "·", ".", -1))
 
 		if s.Type == sym.SDYNIMPORT || s.Type == sym.SHOSTOBJ {
 			symtab.AddUint8(0x01)                             // type N_EXT, external symbol

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

@@ -1040,14 +1040,15 @@ func initdynimport(ctxt *Link) *Dll {
 		// of uinptrs this function consumes. Store the argsize and discard
 		// the %n suffix if any.
 		m.argsize = -1
-		if i := strings.IndexByte(s.Extname, '%'); i >= 0 {
+		extName := s.Extname()
+		if i := strings.IndexByte(extName, '%'); i >= 0 {
 			var err error
-			m.argsize, err = strconv.Atoi(s.Extname[i+1:])
+			m.argsize, err = strconv.Atoi(extName[i+1:])
 			if err != nil {
 				Errorf(s, "failed to parse stdcall decoration: %v", err)
 			}
 			m.argsize *= ctxt.Arch.PtrSize
-			s.Extname = s.Extname[:i]
+			s.SetExtname(extName[:i])
 		}
 
 		m.s = s
@@ -1061,7 +1062,7 @@ func initdynimport(ctxt *Link) *Dll {
 			for m = d.ms; m != nil; m = m.next {
 				m.s.Type = sym.SDATA
 				m.s.Grow(int64(ctxt.Arch.PtrSize))
-				dynName := m.s.Extname
+				dynName := m.s.Extname()
 				// only windows/386 requires stdcall decoration
 				if ctxt.Arch.Family == sys.I386 && m.argsize >= 0 {
 					dynName += fmt.Sprintf("@%d", m.argsize)
@@ -1132,7 +1133,7 @@ func addimports(ctxt *Link, datsect *peSection) {
 		for m := d.ms; m != nil; m = m.next {
 			m.off = uint64(pefile.nextSectOffset) + uint64(ctxt.Out.Offset()) - uint64(startoff)
 			ctxt.Out.Write16(0) // hint
-			strput(ctxt.Out, m.s.Extname)
+			strput(ctxt.Out, m.s.Extname())
 		}
 	}
 
@@ -1217,7 +1218,7 @@ type byExtname []*sym.Symbol
 
 func (s byExtname) Len() int           { return len(s) }
 func (s byExtname) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
-func (s byExtname) Less(i, j int) bool { return s[i].Extname < s[j].Extname }
+func (s byExtname) Less(i, j int) bool { return s[i].Extname() < s[j].Extname() }
 
 func initdynexport(ctxt *Link) {
 	nexport = 0
@@ -1242,7 +1243,7 @@ func addexports(ctxt *Link) {
 
 	size := binary.Size(&e) + 10*nexport + len(*flagOutfile) + 1
 	for i := 0; i < nexport; i++ {
-		size += len(dexport[i].Extname) + 1
+		size += len(dexport[i].Extname()) + 1
 	}
 
 	if nexport == 0 {
@@ -1286,7 +1287,7 @@ func addexports(ctxt *Link) {
 
 	for i := 0; i < nexport; i++ {
 		out.Write32(uint32(v))
-		v += len(dexport[i].Extname) + 1
+		v += len(dexport[i].Extname()) + 1
 	}
 
 	// put EXPORT Ordinal Table
@@ -1298,7 +1299,7 @@ func addexports(ctxt *Link) {
 	out.WriteStringN(*flagOutfile, len(*flagOutfile)+1)
 
 	for i := 0; i < nexport; i++ {
-		out.WriteStringN(dexport[i].Extname, len(dexport[i].Extname)+1)
+		out.WriteStringN(dexport[i].Extname(), len(dexport[i].Extname())+1)
 	}
 	sect.pad(out, uint32(size))
 }

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{}, 132, 216},
+		{Symbol{}, 124, 200},
 	}
 
 	for _, tt := range tests {

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

@@ -15,7 +15,6 @@ import (
 // Symbol is an entry in the symbol table.
 type Symbol struct {
 	Name        string
-	Extname     string
 	Type        SymKind
 	Version     int16
 	Attr        Attribute
@@ -36,7 +35,7 @@ type Symbol struct {
 	Outer    *Symbol
 	Gotype   *Symbol
 	File     string
-	dyninfo  *dynimp
+	auxinfo  *AuxSymbol
 	Sect     *Section
 	FuncInfo *FuncInfo
 	Lib      *Library // Package defining this symbol
@@ -45,7 +44,9 @@ type Symbol struct {
 	R []Reloc
 }
 
-type dynimp struct {
+// AuxSymbol contains less-frequently used sym.Symbol fields.
+type AuxSymbol struct {
+	extname    string
 	dynimplib  string
 	dynimpvers string
 }
@@ -268,38 +269,62 @@ func (s *Symbol) setUintXX(arch *sys.Arch, off int64, v uint64, wid int64) int64
 	return off + wid
 }
 
+func (s *Symbol) makeAuxInfo() {
+	if s.auxinfo == nil {
+		s.auxinfo = &AuxSymbol{extname: s.Name}
+	}
+}
+
+func (s *Symbol) Extname() string {
+	if s.auxinfo == nil {
+		return s.Name
+	}
+	return s.auxinfo.extname
+}
+
+func (s *Symbol) SetExtname(n string) {
+	if s.auxinfo == nil {
+		if s.Name == n {
+			return
+		}
+		s.makeAuxInfo()
+	}
+	s.auxinfo.extname = n
+}
+
 func (s *Symbol) Dynimplib() string {
-	if s.dyninfo == nil {
+	if s.auxinfo == nil {
 		return ""
 	}
-	return s.dyninfo.dynimplib
+	return s.auxinfo.dynimplib
 }
 
 func (s *Symbol) Dynimpvers() string {
-	if s.dyninfo == nil {
+	if s.auxinfo == nil {
 		return ""
 	}
-	return s.dyninfo.dynimpvers
+	return s.auxinfo.dynimpvers
 }
 
 func (s *Symbol) SetDynimplib(lib string) {
-	if s.dyninfo == nil {
-		s.dyninfo = &dynimp{dynimplib: lib}
-	} else {
-		s.dyninfo.dynimplib = lib
+	if s.auxinfo == nil {
+		s.makeAuxInfo()
 	}
+	s.auxinfo.dynimplib = lib
 }
 
 func (s *Symbol) SetDynimpvers(vers string) {
-	if s.dyninfo == nil {
-		s.dyninfo = &dynimp{dynimpvers: vers}
-	} else {
-		s.dyninfo.dynimpvers = vers
+	if s.auxinfo == nil {
+		s.makeAuxInfo()
 	}
+	s.auxinfo.dynimpvers = vers
 }
 
 func (s *Symbol) ResetDyninfo() {
-	s.dyninfo = nil
+	if s.auxinfo != nil {
+		s.auxinfo.dynimplib = ""
+		s.auxinfo.dynimpvers = ""
+	}
 }
 
 // SortSub sorts a linked-list (by Sub) of *Symbol by Value.

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

@@ -77,7 +77,6 @@ func (syms *Symbols) Lookup(name string, v int) *Symbol {
 		return s
 	}
 	s = syms.Newsym(name, v)
-	s.Extname = s.Name
 	m[name] = s
 	return s
 }
@@ -97,9 +96,10 @@ func (syms *Symbols) IncVersion() int {
 // Rename renames a symbol.
 func (syms *Symbols) Rename(old, new string, v int, reachparent map[*Symbol]*Symbol) {
 	s := syms.hash[v][old]
+	oldExtName := s.Extname()
 	s.Name = new
-	if s.Extname == old {
-		s.Extname = new
+	if oldExtName == old {
+		s.SetExtname(new)
 	}
 	delete(syms.hash[v], old)