[dev.link] cmd/link/internal/objfile: new 'Sym' type for global symbol index

First change of several to update the loader API to reflect the final
consensus version of the loader API as described in Cherry's doc.

This piece:

 - define new loader.Sym type to encapsulate a global symbol
   index (as opposed to just using 'int')

Change-Id: I6f6483e269f80abfc7d373b2856b2c0d61b9ac24
Reviewed-on: https://go-review.googlesource.com/c/go/+/200417
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

src/cmd/link/internal/objfile/objfile2.go

@@ -23,6 +23,10 @@ import (
 
 var _ = fmt.Print
 
+// Sym encapsulates a global symbol index, used to identify a specific
+// Go symbol. The 0-valued Sym is corresponds to an invalid symbol.
+type Sym int
+
 // oReader is a wrapper type of obj.Reader, along with some
 // extra information.
 // TODO: rename to objReader once the old one is gone?
@@ -35,7 +39,7 @@ type oReader struct {
 
 type objIdx struct {
 	r *oReader
-	i int // start index
+	i Sym // start index
 }
 
 type nameVer struct {
@@ -47,11 +51,11 @@ type nameVer struct {
 //
 // TODO: describe local-global index mapping.
 type Loader struct {
-	start map[*oReader]int // map from object file to its start index
+	start map[*oReader]Sym // map from object file to its start index
 	objs  []objIdx         // sorted by start index (i.e. objIdx.i)
-	max   int              // current max index
+	max   Sym              // current max index
 
-	symsByName map[nameVer]int // map symbol name to index
+	symsByName map[nameVer]Sym // map symbol name to index
 
 	objByPkg map[string]*oReader // map package path to its Go object reader
 
@@ -60,21 +64,21 @@ type Loader struct {
 
 func NewLoader() *Loader {
 	return &Loader{
-		start:      make(map[*oReader]int),
+		start:      make(map[*oReader]Sym),
 		objs:       []objIdx{{nil, 0}},
-		symsByName: make(map[nameVer]int),
+		symsByName: make(map[nameVer]Sym),
 		objByPkg:   make(map[string]*oReader),
 		Syms:       []*sym.Symbol{nil},
 	}
 }
 
 // Return the start index in the global index space for a given object file.
-func (l *Loader) StartIndex(r *oReader) int {
+func (l *Loader) StartIndex(r *oReader) Sym {
 	return l.start[r]
 }
 
 // Add object file r, return the start index.
-func (l *Loader) AddObj(pkg string, r *oReader) int {
+func (l *Loader) AddObj(pkg string, r *oReader) Sym {
 	if _, ok := l.start[r]; ok {
 		panic("already added")
 	}
@@ -85,12 +89,12 @@ func (l *Loader) AddObj(pkg string, r *oReader) int {
 	i := l.max + 1
 	l.start[r] = i
 	l.objs = append(l.objs, objIdx{r, i})
-	l.max += n
+	l.max += Sym(n)
 	return i
 }
 
 // Add a symbol with a given index, return if it is added.
-func (l *Loader) AddSym(name string, ver int, i int, dupok bool) bool {
+func (l *Loader) AddSym(name string, ver int, i Sym, dupok bool) bool {
 	nv := nameVer{name, ver}
 	if _, ok := l.symsByName[nv]; ok {
 		if dupok || true { // TODO: "true" isn't quite right. need to implement "overwrite" logic.
@@ -104,7 +108,7 @@ func (l *Loader) AddSym(name string, ver int, i int, dupok bool) bool {
 
 // Add an external symbol (without index). Return the index of newly added
 // symbol, or 0 if not added.
-func (l *Loader) AddExtSym(name string, ver int) int {
+func (l *Loader) AddExtSym(name string, ver int) Sym {
 	nv := nameVer{name, ver}
 	if _, ok := l.symsByName[nv]; ok {
 		return 0
@@ -116,23 +120,23 @@ func (l *Loader) AddExtSym(name string, ver int) int {
 }
 
 // Convert a local index to a global index.
-func (l *Loader) ToGlobal(r *oReader, i int) int {
-	return l.StartIndex(r) + i
+func (l *Loader) ToGlobal(r *oReader, i int) Sym {
+	return l.StartIndex(r) + Sym(i)
 }
 
 // Convert a global index to a local index.
-func (l *Loader) ToLocal(i int) (*oReader, int) {
-	k := sort.Search(i, func(k int) bool {
+func (l *Loader) ToLocal(i Sym) (*oReader, int) {
+	k := sort.Search(int(i), func(k int) bool {
 		return l.objs[k].i >= i
 	})
 	if k == len(l.objs) {
 		return nil, 0
 	}
-	return l.objs[k].r, i - l.objs[k].i
+	return l.objs[k].r, int(i - l.objs[k].i)
 }
 
 // Resolve a local symbol reference. Return global index.
-func (l *Loader) Resolve(r *oReader, s goobj2.SymRef) int {
+func (l *Loader) Resolve(r *oReader, s goobj2.SymRef) Sym {
 	var rr *oReader
 	switch p := s.PkgIdx; p {
 	case goobj2.PkgIdxInvalid:
@@ -163,7 +167,7 @@ func (l *Loader) Resolve(r *oReader, s goobj2.SymRef) int {
 // Look up a symbol by name, return global index, or 0 if not found.
 // This is more like Syms.ROLookup than Lookup -- it doesn't create
 // new symbol.
-func (l *Loader) Lookup(name string, ver int) int {
+func (l *Loader) Lookup(name string, ver int) Sym {
 	nv := nameVer{name, ver}
 	return l.symsByName[nv]
 }
@@ -213,10 +217,10 @@ func LoadNew(l *Loader, arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, lib *s
 		}
 		v := abiToVer(osym.ABI, localSymVersion)
 		dupok := osym.Flag&goobj2.SymFlagDupok != 0
-		if l.AddSym(name, v, istart+i, dupok) {
+		if l.AddSym(name, v, istart+Sym(i), dupok) {
 			s := syms.Newsym(name, v)
 			preprocess(arch, s) // TODO: put this at a better place
-			l.Syms[istart+i] = s
+			l.Syms[istart+Sym(i)] = s
 		}
 	}
 
@@ -244,7 +248,7 @@ func loadObjRefs(l *Loader, r *oReader, arch *sys.Arch, syms *sym.Symbols) {
 		if ii := l.AddExtSym(name, v); ii != 0 {
 			s := syms.Newsym(name, v)
 			preprocess(arch, s) // TODO: put this at a better place
-			if ii != len(l.Syms) {
+			if ii != Sym(len(l.Syms)) {
 				panic("AddExtSym returned bad index")
 			}
 			l.Syms = append(l.Syms, s)
@@ -309,7 +313,7 @@ func loadObjReloc(l *Loader, r *oReader) {
 	}
 
 	for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
-		s := l.Syms[istart+i]
+		s := l.Syms[istart+Sym(i)]
 		if s == nil || s.Name == "" {
 			continue
 		}
@@ -422,7 +426,7 @@ func loadObjFull(l *Loader, r *oReader) {
 
 	pcdataBase := r.PcdataBase()
 	for i, n := 0, r.NSym()+r.NNonpkgdef(); i < n; i++ {
-		s := l.Syms[istart+i]
+		s := l.Syms[istart+Sym(i)]
 		if s == nil || s.Name == "" {
 			continue
 		}