cmd/link: avoid name collision with DWARF .def suffix

Adding a .def suffix for DWARF info collided with the DWARF info,
without the suffix, for a method named def. Change the suffix to ..def
instead.

Fixes #15926.

Change-Id: If1bf1bcb5dff1d7f7b79f78e3f7a3bbfcd2201bb
Reviewed-on: https://go-review.googlesource.com/23733
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

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

@@ -529,7 +529,7 @@ func walktypedef(die *DWDie) *DWDie {
 }
 
 func walksymtypedef(s *LSym) *LSym {
-	if t := Linkrlookup(Ctxt, s.Name+".def", int(s.Version)); t != nil {
+	if t := Linkrlookup(Ctxt, s.Name+"..def", int(s.Version)); t != nil {
 		return t
 	}
 	return s
@@ -819,7 +819,7 @@ func dotypedef(parent *DWDie, name string, def *DWDie) {
 		Diag("dwarf: bad def in dotypedef")
 	}
 
-	def.sym = Linklookup(Ctxt, def.sym.Name+".def", 0)
+	def.sym = Linklookup(Ctxt, def.sym.Name+"..def", 0)
 	def.sym.Attr |= AttrHidden
 	def.sym.Type = obj.SDWARFINFO
 
@@ -1021,7 +1021,7 @@ func newtype(gotype *LSym) *DWDie {
 }
 
 func nameFromDIESym(dwtype *LSym) string {
-	return strings.TrimSuffix(dwtype.Name[len(infoprefix):], ".def")
+	return strings.TrimSuffix(dwtype.Name[len(infoprefix):], "..def")
 }
 
 // Find or construct *T given T.

test/fixedbugs/issue15926.go

+// build
+
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 15926: linker was adding .def to the end of symbols, causing
+// a name collision with a method actually named def.
+
+package main
+
+type S struct{}
+
+func (s S) def() {}
+
+var I = S.def
+
+func main() {
+    I(S{})
+}