cmd/compile: output DWARF lexical blocks for local variables

Change compiler and linker to emit DWARF lexical blocks in .debug_info
section when compiling with -N -l.

Version of debug_info is updated from DWARF v2 to DWARF v3 since
version 2 does not allow lexical blocks with discontinuous PC ranges.

Remaining open problems:
- scope information is removed from inlined functions
- variables records 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, even before its declaration.

Updates #6913.
Updates #12899.

Change-Id: Idc6808788512ea20e7e45bcf782453acb416fb49
Reviewed-on: https://go-review.googlesource.com/40095
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

4 files changed, 40 insertions, 21 deletions

diff --git a/src/cmd/internal/obj/data.go b/src/cmd/internal/obj/data.go
index 8b1bdb1056..23d1809e0c 100644
--- a/src/cmd/internal/obj/data.go
+++ b/src/cmd/internal/obj/data.go
@@ -120,7 +120,8 @@ func (s *LSym) WriteInt(ctxt *Link, off int64, siz int, i int64) {
 // WriteAddr writes an address of size siz into s at offset off.
 // rsym and roff specify the relocation for the address.
 func (s *LSym) WriteAddr(ctxt *Link, off int64, siz int, rsym *LSym, roff int64) {
-	if siz != ctxt.Arch.PtrSize {
+	// Allow 4-byte addresses for DWARF.
+	if siz != ctxt.Arch.PtrSize && siz != 4 {
 		ctxt.Diag("WriteAddr: bad address size %d in %s", siz, s.Name)
 	}
 	s.prepwrite(ctxt, off, siz)
diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go
index 8bdc3f55e9..d49bc8c564 100644
--- a/src/cmd/internal/obj/link.go
+++ b/src/cmd/internal/obj/link.go
@@ -324,12 +324,15 @@ type LSym struct {
 
 // A FuncInfo contains extra fields for STEXT symbols.
 type FuncInfo struct {
-	Args     int32
-	Locals   int32
-	Text     *Prog
-	Autom    []*Auto
-	Pcln     Pcln
-	dwarfSym *LSym
+	Args   int32
+	Locals int32
+	Text   *Prog
+	Autom  []*Auto
+	Pcln   Pcln
+
+	dwarfSym       *LSym
+	dwarfRangesSym *LSym
+
 	GCArgs   LSym
 	GCLocals LSym
 }
@@ -490,7 +493,7 @@ type Link struct {
 	InlTree       InlTree // global inlining tree used by gc/inl.go
 	Imports       []string
 	DiagFunc      func(string, ...interface{})
-	DebugInfo     func(fn *LSym, curfn interface{}) []*dwarf.Var // if non-nil, curfn is a *gc.Node
+	DebugInfo     func(fn *LSym, curfn interface{}) []dwarf.Scope // if non-nil, curfn is a *gc.Node
 	Errors        int
 
 	Framepointer_enabled bool
diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index dc22eacdf4..e309c5f7e7 100644
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -447,10 +447,14 @@ 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)
@@ -460,27 +464,35 @@ func (c dwCtxt) AddSectionOffset(s dwarf.Sym, size int, t interface{}, ofs int64
 	r.Type = objabi.R_DWARFREF
 }
 
-// dwarfSym returns the DWARF symbol for TEXT symbol.
-func (ctxt *Link) dwarfSym(s *LSym) *LSym {
+// dwarfSym returns the DWARF symbols for TEXT symbol.
+func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfRangesSym *LSym) {
 	if s.Type != objabi.STEXT {
 		ctxt.Diag("dwarfSym of non-TEXT %v", s)
 	}
 	if s.Func.dwarfSym == nil {
 		s.Func.dwarfSym = ctxt.LookupDerived(s, dwarf.InfoPrefix+s.Name)
+		s.Func.dwarfRangesSym = ctxt.LookupDerived(s, dwarf.RangePrefix+s.Name)
 	}
-	return s.Func.dwarfSym
+	return s.Func.dwarfSym, s.Func.dwarfRangesSym
 }
 
-// populateDWARF fills in the DWARF Debugging Information Entry for TEXT symbol s.
-// The DWARF symbol must already have been initialized in InitTextSym.
+func (s *LSym) Len() int64 {
+	return s.Size
+}
+
+// populateDWARF fills in the DWARF Debugging Information Entries for TEXT symbol s.
+// The DWARFs symbol must already have been initialized in InitTextSym.
 func (ctxt *Link) populateDWARF(curfn interface{}, s *LSym) {
-	dsym := ctxt.dwarfSym(s)
+	dsym, drsym := ctxt.dwarfSym(s)
 	if dsym.Size != 0 {
 		ctxt.Diag("makeFuncDebugEntry double process %v", s)
 	}
-	var vars []*dwarf.Var
+	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.Static(), 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.Static(), s, s.Size, vars)
 }
diff --git a/src/cmd/internal/obj/plist.go b/src/cmd/internal/obj/plist.go
index 5c86c20e73..861da88703 100644
--- a/src/cmd/internal/obj/plist.go
+++ b/src/cmd/internal/obj/plist.go
@@ -135,11 +135,14 @@ func (ctxt *Link) InitTextSym(s *LSym, flag int) {
 	s.Type = objabi.STEXT
 	ctxt.Text = append(ctxt.Text, s)
 
-	// Set up DWARF entry for s.
-	dsym := ctxt.dwarfSym(s)
+	// Set up DWARF entries for s.
+	dsym, drsym := ctxt.dwarfSym(s)
 	dsym.Type = objabi.SDWARFINFO
 	dsym.Set(AttrDuplicateOK, s.DuplicateOK())
+	drsym.Type = objabi.SDWARFRANGE
+	drsym.Set(AttrDuplicateOK, s.DuplicateOK())
 	ctxt.Data = append(ctxt.Data, dsym)
+	ctxt.Data = append(ctxt.Data, drsym)
 
 	// Set up the function's gcargs and gclocals.
 	// They will be filled in later if needed.