cmd/compile: output DWARF lexical blocks for local variables

Change compiler and linker to emit DWARF lexical blocks in debug_info.
Version of debug_info is updated from DWARF v.2 to DWARF v.3 since version 2
does not allow lexical blocks with discontinuous ranges.

Second attempt at https://go-review.googlesource.com/#/c/29591/

Remaining open problems:
- scope information is removed from inlined functions
- variables in debug_info do not have DW_AT_start_scope attributes so a
variable will shadow other variables with the same name as soon as its
containing scope begins, before its declaration.

Updates golang/go#12899, golang/go#6913

Change-Id: I0e260a45b564d14a87b88974eb16c5387cb410a5
Reviewed-on: https://go-review.googlesource.com/36879
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 25 insertions, 6 deletions

diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index 6858143674..314c7a9de6 100644
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -542,10 +542,14 @@ func (c dwCtxt) SymValue(s dwarf.Sym) int64 {
 	return 0
 }
 func (c dwCtxt) AddAddress(s dwarf.Sym, data interface{}, value int64) {
-	rsym := data.(*LSym)
 	ls := s.(*LSym)
 	size := c.PtrSize()
-	ls.WriteAddr(c.Link, ls.Size, size, rsym, value)
+	if data != nil {
+		rsym := data.(*LSym)
+		ls.WriteAddr(c.Link, ls.Size, size, rsym, value)
+	} else {
+		ls.WriteInt(c.Link, ls.Size, size, value)
+	}
 }
 func (c dwCtxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64) {
 	ls := s.(*LSym)
@@ -555,6 +559,10 @@ func (c dwCtxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64
 	r.Type = R_DWARFREF
 }
 
+func (s *LSym) Len() int64 {
+	return s.Size
+}
+
 // makeFuncDebugEntry makes a DWARF Debugging Information Entry
 // for TEXT symbol s.
 func makeFuncDebugEntry(ctxt *Link, curfn interface{}, s *LSym) {
@@ -564,10 +572,21 @@ func makeFuncDebugEntry(ctxt *Link, curfn interface{}, s *LSym) {
 	}
 	dsym.Type = SDWARFINFO
 	dsym.Set(AttrDuplicateOK, s.DuplicateOK())
-	var vars []*dwarf.Var
+
+	drsym := ctxt.Lookup(dwarf.RangePrefix+s.Name, int(s.Version))
+	if drsym.Size != 0 {
+		return
+	}
+	drsym.Type = SDWARFRANGE
+	drsym.Set(AttrDuplicateOK, s.DuplicateOK())
+
+	var scopes []dwarf.Scope
 	if ctxt.DebugInfo != nil {
-		vars = ctxt.DebugInfo(s, curfn)
+		scopes = ctxt.DebugInfo(s, curfn)
+	}
+	err := dwarf.PutFunc(dwCtxt{ctxt}, dsym, drsym, s.Name, s.Version == 0, s, s.Size, scopes)
+	if err != nil {
+		ctxt.Diag("emitting DWARF for %s failed: %v", s.Name, err)
 	}
-	dwarf.PutFunc(dwCtxt{ctxt}, dsym, s.Name, s.Version == 0, s, s.Size, vars)
-	ctxt.Data = append(ctxt.Data, dsym)
+	ctxt.Data = append(ctxt.Data, dsym, drsym)
 }