cmd/internal/obj: avoid duplicate file name symbols

The meaning of Version=1 was overloaded: it was reserved for file name
symbols (to avoid conflicts with non-file name symbols), but was also
used to mean "give me a fresh version number for this symbol."

With the new inlining tree, the same file name symbol can appear in
multiple entries, but each one would become a distinct symbol with its
own version number.

Now, we avoid duplicating symbols by using Version=0 for file name
symbols and we avoid conflicts with other symbols by prefixing the
symbol name with "gofile..".

Change-Id: I8d0374053b8cdb6a9ca7fb71871b69b4dd369a9c
Reviewed-on: https://go-review.googlesource.com/37234
Run-TryBot: David Lazar <lazard@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/internal/obj/line.go

@@ -74,14 +74,16 @@ func (ctxt *Link) AddImport(pkg string) {
 	ctxt.Imports = append(ctxt.Imports, pkg)
 }
 
+const FileSymPrefix = "gofile.."
+
 func linkgetlineFromPos(ctxt *Link, xpos src.XPos) (f *LSym, l int32) {
 	pos := ctxt.PosTable.Pos(xpos)
 	filename := pos.AbsFilename()
 	if !pos.IsKnown() || filename == "" {
-		return Linklookup(ctxt, "??", HistVersion), 0
+		return Linklookup(ctxt, FileSymPrefix+"??", 0), 0
 	}
 	// TODO(gri) Should this use relative or absolute line number?
-	return Linklookup(ctxt, filename, HistVersion), int32(pos.RelLine())
+	return Linklookup(ctxt, FileSymPrefix+filename, 0), int32(pos.RelLine())
 }
 
 func fieldtrack(ctxt *Link, cursym *LSym) {

src/cmd/internal/obj/line_test.go

@@ -32,7 +32,7 @@ func TestLinkgetlineFromPos(t *testing.T) {
 	for _, test := range tests {
 		f, l := linkgetlineFromPos(ctxt, ctxt.PosTable.XPos(test.pos))
 		got := fmt.Sprintf("%s:%d", f.Name, l)
-		if got != test.want {
+		if got != FileSymPrefix+test.want {
 			t.Errorf("linkgetline(%v) = %q, want %q", test.pos, got, test.want)
 		}
 	}

src/cmd/internal/obj/link.go

@@ -708,12 +708,6 @@ type Pcdata struct {
 	P []byte
 }
 
-// symbol version, incremented each time a file is loaded.
-// version==1 is reserved for savehist.
-const (
-	HistVersion = 1
-)
-
 // Link holds the context for writing object code from a compiler
 // to be linker input or for reading that input into the linker.
 type Link struct {

src/cmd/internal/obj/sym.go

@@ -53,7 +53,7 @@ func Linknew(arch *LinkArch) *Link {
 	ctxt := new(Link)
 	ctxt.Hash = make(map[SymVer]*LSym)
 	ctxt.Arch = arch
-	ctxt.Version = HistVersion
+	ctxt.Version = 0
 	ctxt.Pathname = WorkingDir()
 
 	ctxt.Headtype.Set(GOOS)

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

@@ -114,7 +114,8 @@ func numberfile(ctxt *Link, file *Symbol) {
 		ctxt.Filesyms = append(ctxt.Filesyms, file)
 		file.Value = int64(len(ctxt.Filesyms))
 		file.Type = obj.SFILEPATH
-		file.Name = expandGoroot(file.Name)
+		path := file.Name[len(obj.FileSymPrefix):]
+		file.Name = expandGoroot(path)
 	}
 }