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

The sym.Symbol 'ElfType' field is used only for symbols corresponding
to things in imported shared libraries, hence is not needed in the
common case. Relocate it to sym.AuxSymbol so as to shrink the main
Symbol struct.

Updates #26186

Change-Id: I803efc561c31a0ca1d93eca434fda1c862a7b2c5
Reviewed-on: https://go-review.googlesource.com/125479
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/link/internal/amd64/asm.go

@@ -410,7 +410,7 @@ func elfreloc1(ctxt *ld.Link, r *sym.Reloc, sectoff int64) bool {
 		}
 	case objabi.R_PCREL:
 		if r.Siz == 4 {
-			if r.Xsym.Type == sym.SDYNIMPORT && r.Xsym.ElfType == elf.STT_FUNC {
+			if r.Xsym.Type == sym.SDYNIMPORT && r.Xsym.ElfType() == elf.STT_FUNC {
 				ctxt.Out.Write64(uint64(elf.R_X86_64_PLT32) | uint64(elfsym)<<32)
 			} else {
 				ctxt.Out.Write64(uint64(elf.R_X86_64_PC32) | uint64(elfsym)<<32)

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

@@ -1706,7 +1706,7 @@ func ldshlibsyms(ctxt *Link, shlib string) {
 			continue
 		}
 		lsym.Type = sym.SDYNIMPORT
-		lsym.ElfType = elf.ST_TYPE(elfsym.Info)
+		lsym.SetElfType(elf.ST_TYPE(elfsym.Info))
 		lsym.Size = int64(elfsym.Size)
 		if elfsym.Section != elf.SHN_UNDEF {
 			// Set .File for the library that actually defines the symbol.

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

@@ -93,7 +93,7 @@ func putelfsym(ctxt *Link, x *sym.Symbol, s string, t SymbolType, addr int64, go
 	case UndefinedSym:
 		// ElfType is only set for symbols read from Go shared libraries, but
 		// for other symbols it is left as STT_NOTYPE which is fine.
-		typ = int(x.ElfType)
+		typ = int(x.ElfType())
 
 	case TLSSym:
 		typ = STT_TLS

src/cmd/link/internal/s390x/asm.go

@@ -285,7 +285,7 @@ func elfreloc1(ctxt *ld.Link, r *sym.Reloc, sectoff int64) bool {
 		case objabi.R_PCRELDBL, objabi.R_CALL:
 			isdbl = true
 		}
-		if r.Xsym.Type == sym.SDYNIMPORT && (r.Xsym.ElfType == elf.STT_FUNC || r.Type == objabi.R_CALL) {
+		if r.Xsym.Type == sym.SDYNIMPORT && (r.Xsym.ElfType() == elf.STT_FUNC || r.Type == objabi.R_CALL) {
 			if isdbl {
 				switch r.Siz {
 				case 2:

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{}, 112, 184},
+		{Symbol{}, 108, 176},
 	}
 
 	for _, tt := range tests {

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

@@ -24,18 +24,14 @@ type Symbol struct {
 	LocalElfsym int32
 	Value       int64
 	Size        int64
-	// ElfType is set for symbols read from shared libraries by ldshlibsyms. It
-	// is not set for symbols defined by the packages being linked or by symbols
-	// read by ldelf (and so is left as elf.STT_NOTYPE).
-	ElfType  elf.SymType
-	Sub      *Symbol
-	Outer    *Symbol
-	Gotype   *Symbol
-	File     string
-	auxinfo  *AuxSymbol
-	Sect     *Section
-	FuncInfo *FuncInfo
-	Lib      *Library // Package defining this symbol
+	Sub         *Symbol
+	Outer       *Symbol
+	Gotype      *Symbol
+	File        string
+	auxinfo     *AuxSymbol
+	Sect        *Section
+	FuncInfo    *FuncInfo
+	Lib         *Library // Package defining this symbol
 	// P contains the raw symbol data.
 	P []byte
 	R []Reloc
@@ -49,6 +45,10 @@ type AuxSymbol struct {
 	localentry uint8
 	plt        int32
 	got        int32
+	// ElfType is set for symbols read from shared libraries by ldshlibsyms. It
+	// is not set for symbols defined by the packages being linked or by symbols
+	// read by ldelf (and so is left as elf.STT_NOTYPE).
+	elftype elf.SymType
 }
 
 func (s *Symbol) String() string {
@@ -378,6 +378,23 @@ func (s *Symbol) SetGot(val int32) {
 	s.auxinfo.got = val
 }
 
+func (s *Symbol) ElfType() elf.SymType {
+	if s.auxinfo == nil {
+		return elf.STT_NOTYPE
+	}
+	return s.auxinfo.elftype
+}
+
+func (s *Symbol) SetElfType(val elf.SymType) {
+	if s.auxinfo == nil {
+		if val == elf.STT_NOTYPE {
+			return
+		}
+		s.makeAuxInfo()
+	}
+	s.auxinfo.elftype = 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 {