cmd/compile: add new symbol for debug line numbers

This is broken out from: CL 187117

This new symbol will be populated by the compiler and contain debug line
information that's currently generated in the linker. One might say it's
sad to create a new symbol, but this symbol will replace the isStmt
symbols.

Testing: Ran go build -toolexec 'toolstash -cmp'

Change-Id: If8f7ae4b43b7247076605b6429b7d03a1fd239c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/188238
Reviewed-by: Austin Clements <[email protected]>

Author: jeremyfaller

src/cmd/internal/dwarf/dwarf.go

@@ -30,6 +30,9 @@ const RangePrefix = "go.range."
 // IsStmtPrefix is the prefix for all the symbols containing DWARF is_stmt info for the line number table.
 const IsStmtPrefix = "go.isstmt."
 
+// DebugLinesPrefix is the prefix for all the symbols containing DWARF debug_line information from the compiler.
+const DebugLinesPrefix = "go.debuglines."
+
 // ConstInfoPrefix is the prefix for all symbols containing DWARF info
 // entries that contain constants.
 const ConstInfoPrefix = "go.constinfo."

src/cmd/internal/obj/link.go

@@ -402,11 +402,12 @@ type FuncInfo struct {
 	Pcln     Pcln
 	InlMarks []InlMark
 
-	dwarfInfoSym   *LSym
-	dwarfLocSym    *LSym
-	dwarfRangesSym *LSym
-	dwarfAbsFnSym  *LSym
-	dwarfIsStmtSym *LSym
+	dwarfInfoSym       *LSym
+	dwarfLocSym        *LSym
+	dwarfRangesSym     *LSym
+	dwarfAbsFnSym      *LSym
+	dwarfIsStmtSym     *LSym
+	dwarfDebugLinesSym *LSym
 
 	GCArgs       *LSym
 	GCLocals     *LSym

src/cmd/internal/obj/objfile.go

@@ -537,7 +537,7 @@ func isDwarf64(ctxt *Link) bool {
 	return ctxt.Headtype == objabi.Haix
 }
 
-func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym, dwarfAbsFnSym, dwarfIsStmtSym *LSym) {
+func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym, dwarfAbsFnSym, dwarfIsStmtSym, dwarfDebugLines *LSym) {
 	if s.Type != objabi.STEXT {
 		ctxt.Diag("dwarfSym of non-TEXT %v", s)
 	}
@@ -551,9 +551,9 @@ func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym,
 			s.Func.dwarfAbsFnSym = ctxt.DwFixups.AbsFuncDwarfSym(s)
 		}
 		s.Func.dwarfIsStmtSym = ctxt.LookupDerived(s, dwarf.IsStmtPrefix+s.Name)
-
+		s.Func.dwarfDebugLinesSym = ctxt.LookupDerived(s, dwarf.DebugLinesPrefix+s.Name)
 	}
-	return s.Func.dwarfInfoSym, s.Func.dwarfLocSym, s.Func.dwarfRangesSym, s.Func.dwarfAbsFnSym, s.Func.dwarfIsStmtSym
+	return s.Func.dwarfInfoSym, s.Func.dwarfLocSym, s.Func.dwarfRangesSym, s.Func.dwarfAbsFnSym, s.Func.dwarfIsStmtSym, s.Func.dwarfDebugLinesSym
 }
 
 func (s *LSym) Len() int64 {
@@ -577,7 +577,7 @@ func (ctxt *Link) fileSymbol(fn *LSym) *LSym {
 // TEXT symbol 's'. The various DWARF symbols must already have been
 // initialized in InitTextSym.
 func (ctxt *Link) populateDWARF(curfn interface{}, s *LSym, myimportpath string) {
-	info, loc, ranges, absfunc, _ := ctxt.dwarfSym(s)
+	info, loc, ranges, absfunc, _, _ := ctxt.dwarfSym(s)
 	if info.Size != 0 {
 		ctxt.Diag("makeFuncDebugEntry double process %v", s)
 	}

src/cmd/internal/obj/plist.go

@@ -137,7 +137,7 @@ func (ctxt *Link) InitTextSym(s *LSym, flag int) {
 	ctxt.Text = append(ctxt.Text, s)
 
 	// Set up DWARF entries for s.
-	info, loc, ranges, _, isstmt := ctxt.dwarfSym(s)
+	info, loc, ranges, _, isstmt, _ := ctxt.dwarfSym(s)
 	info.Type = objabi.SDWARFINFO
 	info.Set(AttrDuplicateOK, s.DuplicateOK())
 	if loc != nil {

src/cmd/internal/objabi/symkind.go

@@ -60,6 +60,7 @@ const (
 	SDWARFRANGE
 	SDWARFLOC
 	SDWARFMISC
+	SDWARFLINES
 	// ABI alias. An ABI alias symbol is an empty symbol with a
 	// single relocation with 0 size that references the native
 	// function implementation symbol.

src/cmd/link/internal/sym/symkind.go

@@ -110,6 +110,7 @@ const (
 	SDWARFINFO
 	SDWARFRANGE
 	SDWARFLOC
+	SDWARFLINES
 	SDWARFMISC // Not really a section; informs/affects other DWARF section generation
 
 	// ABI aliases (these never appear in the output)
@@ -130,6 +131,7 @@ var AbiSymKindToSymKind = [...]SymKind{
 	SDWARFINFO,
 	SDWARFRANGE,
 	SDWARFLOC,
+	SDWARFLINES,
 	SDWARFMISC,
 	SABIALIAS,
 }