cmd/link: start file-local symbols at version 10

We're going to use the linker's symbol versions to track ABIs.
Currently, version 0 is used for global symbols and version > 0 is
used for file-local symbols. This CL reserves versions 0 to 9 for
global symbols with ABIs and uses version 10 and up for file-local
symbols. To make this clean, it also introduces a method on Symbol for
querying whether it's file-local.

For #27539.

Change-Id: Id3bc7369268f35128b14318a62e86335181a80e5
Reviewed-on: https://go-review.googlesource.com/c/146859
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>

src/cmd/link/internal/arm64/asm.go

@@ -256,7 +256,7 @@ func archreloc(ctxt *ld.Link, r *sym.Reloc, s *sym.Symbol, val int64) (int64, bo
 			// (https://sourceware.org/bugzilla/show_bug.cgi?id=18270). So
 			// we convert the adrp; ld64 + R_ARM64_GOTPCREL into adrp;
 			// add + R_ADDRARM64.
-			if !(r.Sym.Version != 0 || r.Sym.Attr.VisibilityHidden() || r.Sym.Attr.Local()) && r.Sym.Type == sym.STEXT && ctxt.DynlinkingGo() {
+			if !(r.Sym.IsFileLocal() || r.Sym.Attr.VisibilityHidden() || r.Sym.Attr.Local()) && r.Sym.Type == sym.STEXT && ctxt.DynlinkingGo() {
 				if o2&0xffc00000 != 0xf9400000 {
 					ld.Errorf(s, "R_ARM64_GOTPCREL against unexpected instruction %x", o2)
 				}

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

@@ -346,10 +346,20 @@ func lookupOrDiag(ctxt *Link, n string) *sym.Symbol {
 // If the symbol does not exist, it creates it if create is true,
 // or returns nil otherwise.
 func dwarfFuncSym(ctxt *Link, s *sym.Symbol, meta string, create bool) *sym.Symbol {
-	if create {
+	// All function ABIs use symbol version 0 for the DWARF data.
-		return ctxt.Syms.Lookup(meta+s.Name, int(s.Version))
+	//
+	// TODO(austin): It may be useful to have DWARF info for ABI
+	// wrappers, in which case we may want these versions to
+	// align. Better yet, replace these name lookups with a
+	// general way to attach metadata to a symbol.
+	ver := 0
+	if s.IsFileLocal() {
+		ver = int(s.Version)
 	}
-	return ctxt.Syms.ROLookup(meta+s.Name, int(s.Version))
+	if create {
+		return ctxt.Syms.Lookup(meta+s.Name, ver)
+	}
+	return ctxt.Syms.ROLookup(meta+s.Name, ver)
 }
 
 func dotypedef(ctxt *Link, parent *dwarf.DWDie, name string, def *dwarf.DWDie) *dwarf.DWDie {
@@ -853,7 +863,7 @@ func dwarfDefineGlobal(ctxt *Link, s *sym.Symbol, str string, v int64, gotype *s
 	}
 	dv := newdie(ctxt, ctxt.compUnitByPackage[lib].dwinfo, dwarf.DW_ABRV_VARIABLE, str, int(s.Version))
 	newabslocexprattr(dv, v, s)
-	if s.Version == 0 {
+	if !s.IsFileLocal() {
 		newattr(dv, dwarf.DW_AT_external, dwarf.DW_CLS_FLAG, 1, 0)
 	}
 	dt := defgotype(ctxt, gotype)

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

@@ -2129,7 +2129,7 @@ func genasmsym(ctxt *Link, put func(*Link, *sym.Symbol, string, SymbolType, int6
 		if s.Attr.NotInSymbolTable() {
 			continue
 		}
-		if (s.Name == "" || s.Name[0] == '.') && s.Version == 0 && s.Name != ".rathole" && s.Name != ".TOC." {
+		if (s.Name == "" || s.Name[0] == '.') && !s.IsFileLocal() && s.Name != ".rathole" && s.Name != ".TOC." {
 			continue
 		}
 		switch s.Type {

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

@@ -704,7 +704,7 @@ func (f *peFile) writeSymbols(ctxt *Link) {
 			}
 		}
 		class := IMAGE_SYM_CLASS_EXTERNAL
-		if s.Version != 0 || s.Attr.VisibilityHidden() || s.Attr.Local() {
+		if s.IsFileLocal() || s.Attr.VisibilityHidden() || s.Attr.Local() {
 			class = IMAGE_SYM_CLASS_STATIC
 		}
 		f.writeSymbol(ctxt.Out, s, value, sect, typ, uint8(class))

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

@@ -128,7 +128,7 @@ func putelfsym(ctxt *Link, x *sym.Symbol, s string, t SymbolType, addr int64, go
 	// maybe one day STB_WEAK.
 	bind := STB_GLOBAL
 
-	if x.Version != 0 || x.Attr.VisibilityHidden() || x.Attr.Local() {
+	if x.IsFileLocal() || x.Attr.VisibilityHidden() || x.Attr.Local() {
 		bind = STB_LOCAL
 	}
 
@@ -224,7 +224,7 @@ func putplan9sym(ctxt *Link, x *sym.Symbol, s string, typ SymbolType, addr int64
 	t := int(typ)
 	switch typ {
 	case TextSym, DataSym, BSSSym:
-		if x.Version != 0 {
+		if x.IsFileLocal() {
 			t += 'a' - 'A'
 		}
 		fallthrough

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

@@ -51,6 +51,10 @@ type AuxSymbol struct {
 	elftype elf.SymType
 }
 
+const (
+	SymVerStatic = 10 // Minimum version used by static (file-local) syms
+)
+
 func (s *Symbol) String() string {
 	if s.Version == 0 {
 		return s.Name
@@ -58,6 +62,10 @@ func (s *Symbol) String() string {
 	return fmt.Sprintf("%s<%d>", s.Name, s.Version)
 }
 
+func (s *Symbol) IsFileLocal() bool {
+	return s.Version >= SymVerStatic
+}
+
 func (s *Symbol) ElfsymForReloc() int32 {
 	// If putelfsym created a local version of this symbol, use that in all
 	// relocations.

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

@@ -40,12 +40,11 @@ type Symbols struct {
 }
 
 func NewSymbols() *Symbols {
+	hash := make([]map[string]*Symbol, SymVerStatic)
+	// Preallocate about 2mb for hash of non static symbols
+	hash[0] = make(map[string]*Symbol, 100000)
 	return &Symbols{
-		hash: []map[string]*Symbol{
+		hash:   hash,
-			// preallocate about 2mb for hash of
-			// non static symbols
-			make(map[string]*Symbol, 100000),
-		},
 		Allsym: make([]*Symbol, 0, 100000),
 	}
 }