cmd/compile,cmd/link: remove statictmp variables from symbol table.

Removes statictmp variables from debug_info and the final symbol table.

Fixes #27800

Change-Id: I302c59a04bc3f460e7085fef241f937bbf30421d
Reviewed-on: https://go-review.googlesource.com/c/142577
Run-TryBot: Alessandro Arzilli <alessandro.arzilli@gmail.com>
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

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

@@ -863,7 +863,9 @@ func defdwsymb(ctxt *Link, s *sym.Symbol, str string, t SymbolType, v int64, got
 		default:
 			return
 		}
-
+		if ctxt.LinkMode != LinkExternal && isStaticTemp(s.Name) {
+			return
+		}
 		dwarfDefineGlobal(ctxt, s, str, v, gotype)
 
 	case AutoSym, ParamSym, DeletedAutoSym:

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

@@ -1062,3 +1062,76 @@ func main() {
 		}
 	}
 }
+
+func TestStaticTmp(t *testing.T) {
+	// Checks that statictmp variables do not appear in debug_info or the
+	// symbol table.
+	// Also checks that statictmp variables do not collide with user defined
+	// variables (issue #25113)
+
+	testenv.MustHaveGoBuild(t)
+
+	if runtime.GOOS == "plan9" {
+		t.Skip("skipping on plan9; no DWARF symbol table in executables")
+	}
+
+	dir, err := ioutil.TempDir("", "go-build")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	const prog = `package main
+
+var stmp_0 string
+var a []int
+
+func init() {
+	a = []int{ 7 }
+}
+
+func main() {
+	println(a[0])
+}
+`
+
+	f := gobuild(t, dir, prog, NoOpt)
+
+	defer f.Close()
+
+	d, err := f.DWARF()
+	if err != nil {
+		t.Fatalf("error reading DWARF: %v", err)
+	}
+
+	rdr := d.Reader()
+	for {
+		e, err := rdr.Next()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if e == nil {
+			break
+		}
+		if e.Tag != dwarf.TagVariable {
+			continue
+		}
+		name, ok := e.Val(dwarf.AttrName).(string)
+		if !ok {
+			continue
+		}
+		if strings.Contains(name, "stmp") {
+			t.Errorf("statictmp variable found in debug_info: %s at %x", name, e.Offset)
+		}
+	}
+
+	syms, err := f.Symbols()
+	if err != nil {
+		t.Fatalf("error reading symbols: %v", err)
+	}
+	for _, sym := range syms {
+		if strings.Contains(sym.Name, "stmp") {
+			t.Errorf("statictmp variable found in symbol table: %s", sym.Name)
+		}
+	}
+}

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

@@ -432,6 +432,10 @@ func (ctxt *Link) symtab() {
 	// just defined above will be first.
 	// hide the specific symbols.
 	for _, s := range ctxt.Syms.Allsym {
+		if ctxt.LinkMode != LinkExternal && isStaticTemp(s.Name) {
+			s.Attr |= sym.AttrNotInSymbolTable
+		}
+
 		if !s.Attr.Reachable() || s.Attr.Special() || s.Type != sym.SRODATA {
 			continue
 		}
@@ -676,3 +680,10 @@ func (ctxt *Link) symtab() {
 		lastmoduledatap.AddAddr(ctxt.Arch, moduledata)
 	}
 }
+
+func isStaticTemp(name string) bool {
+	if i := strings.LastIndex(name, "/"); i >= 0 {
+		name = name[i:]
+	}
+	return strings.Contains(name, "..stmp_")
+}