cmd/internal/obj: generate function DWARF symbols early

This removes a concurrent access of ctxt.Data.

Updates #15756

Change-Id: Id017e90e47e093cd8825907f3853bb3d3bf8280d
Reviewed-on: https://go-review.googlesource.com/40507
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/internal/obj/objfile.go

@@ -555,19 +555,24 @@ func (c dwCtxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64
 	r.Type = R_DWARFREF
 }
 
-// makeFuncDebugEntry makes a DWARF Debugging Information Entry
-// for TEXT symbol s.
-func makeFuncDebugEntry(ctxt *Link, curfn interface{}, s *LSym) {
-	dsym := ctxt.Lookup(dwarf.InfoPrefix+s.Name, int(s.Version))
+// dwarfSym returns the DWARF symbol for TEXT symbol.
+func (ctxt *Link) dwarfSym(s *LSym) *LSym {
+	if s.Type != STEXT {
+		ctxt.Diag("dwarfSym of non-TEXT %v", s)
+	}
+	return ctxt.Lookup(dwarf.InfoPrefix+s.Name, int(s.Version))
+}
+
+// populateDWARF fills in the DWARF Debugging Information Entry for TEXT symbol s.
+// The DWARF symbol must already have been initialized in InitTextSym.
+func (ctxt *Link) populateDWARF(curfn interface{}, s *LSym) {
+	dsym := ctxt.dwarfSym(s)
 	if dsym.Size != 0 {
-		return
+		ctxt.Diag("makeFuncDebugEntry double process %v", s)
 	}
-	dsym.Type = SDWARFINFO
-	dsym.Set(AttrDuplicateOK, s.DuplicateOK())
 	var vars []*dwarf.Var
 	if ctxt.DebugInfo != nil {
 		vars = ctxt.DebugInfo(s, curfn)
 	}
 	dwarf.PutFunc(dwCtxt{ctxt}, dsym, s.Name, s.Version == 0, s, s.Size, vars)
-	ctxt.Data = append(ctxt.Data, dsym)
 }

src/cmd/internal/obj/plist.go

@@ -105,7 +105,7 @@ func Flushplist(ctxt *Link, plist *Plist, newprog ProgAlloc) {
 		ctxt.Arch.Preprocess(ctxt, s, newprog)
 		ctxt.Arch.Assemble(ctxt, s, newprog)
 		linkpcln(ctxt, s)
-		makeFuncDebugEntry(ctxt, plist.Curfn, s)
+		ctxt.populateDWARF(plist.Curfn, s)
 	}
 }
 
@@ -133,6 +133,12 @@ func (ctxt *Link) InitTextSym(s *LSym, flag int) {
 	s.Set(AttrNoFrame, flag&NOFRAME != 0)
 	s.Type = STEXT
 	ctxt.Text = append(ctxt.Text, s)
+
+	// Set up DWARF entry for s.
+	dsym := ctxt.dwarfSym(s)
+	dsym.Type = SDWARFINFO
+	dsym.Set(AttrDuplicateOK, s.DuplicateOK())
+	ctxt.Data = append(ctxt.Data, dsym)
 }
 
 func (ctxt *Link) Globl(s *LSym, size int64, flag int) {