cmd/internal/obj: simplify filename handling

The old Go object file format used linker symbols like "gofile..foo"
to record references to the filename "foo". But the current object
file format has a dedicated section for file names, so we don't need
these useless prefixes anymore.

Also, change DWARF generation to pass around the src.Pos directly,
rather than the old file symbols, which it just turned back into a
file index before writing out anyway.

Finally, directly record the FileIndex into src.PosBase, so that we
can skip the map lookups.

Change-Id: Ia4a5ebfa95da271f2522e45befdb9f137c16d373
Reviewed-on: https://go-review.googlesource.com/c/go/+/523378
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/dwarfgen/dwinl.go

@@ -273,13 +273,11 @@ func insertInlCall(dwcalls *dwarf.InlCalls, inlIdx int, imap map[int]int) int {
 	// Create new entry for this inline
 	inlinedFn := base.Ctxt.InlTree.InlinedFunction(inlIdx)
 	callXPos := base.Ctxt.InlTree.CallPos(inlIdx)
-	callPos := base.Ctxt.PosTable.Pos(callXPos)
+	callPos := base.Ctxt.InnermostPos(callXPos)
-	callFileSym := base.Ctxt.Lookup(callPos.Base().SymFilename())
 	absFnSym := base.Ctxt.DwFixups.AbsFuncDwarfSym(inlinedFn)
 	ic := dwarf.InlCall{
 		InlIndex:  inlIdx,
-		CallFile:  callFileSym,
+		CallPos:   callPos,
-		CallLine:  uint32(callPos.RelLine()),
 		AbsFunSym: absFnSym,
 		Root:      parCallIdx == -1,
 	}

src/cmd/internal/dwarf/dwarf.go

@@ -9,6 +9,7 @@ package dwarf
 
 import (
 	"bytes"
+	"cmd/internal/src"
 	"errors"
 	"fmt"
 	"internal/buildcfg"
@@ -85,13 +86,12 @@ type Range struct {
 type FnState struct {
 	Name          string
 	Info          Sym
-	Filesym       Sym
 	Loc           Sym
 	Ranges        Sym
 	Absfn         Sym
 	StartPC       Sym
+	StartPos      src.Pos
 	Size          int64
-	StartLine     int32
 	External      bool
 	Scopes        []Scope
 	InlCalls      InlCalls
@@ -166,11 +166,8 @@ type InlCall struct {
 	// index into ctx.InlTree describing the call inlined here
 	InlIndex int
 
-	// Symbol of file containing inlined call site (really *obj.LSym).
+	// Position of the inlined call site.
-	CallFile Sym
+	CallPos src.Pos
-
-	// Line number of inlined call site.
-	CallLine uint32
 
 	// Dwarf abstract subroutine symbol (really *obj.LSym).
 	AbsFunSym Sym
@@ -202,7 +199,6 @@ type Context interface {
 	RecordDclReference(from Sym, to Sym, dclIdx int, inlIndex int)
 	RecordChildDieOffsets(s Sym, vars []*Var, offsets []int32)
 	AddString(s Sym, v string)
-	AddFileRef(s Sym, f interface{})
 	Logf(format string, args ...interface{})
 }
 
@@ -1246,7 +1242,8 @@ func PutAbstractFunc(ctxt Context, s *FnState) error {
 	// DW_AT_inlined value
 	putattr(ctxt, s.Absfn, abbrev, DW_FORM_data1, DW_CLS_CONSTANT, int64(DW_INL_inlined), nil)
 
-	putattr(ctxt, s.Absfn, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartLine), nil)
+	// TODO(mdempsky): Shouldn't we write out StartPos.FileIndex() too?
+	putattr(ctxt, s.Absfn, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartPos.RelLine()), nil)
 
 	var ev int64
 	if s.External {
@@ -1335,9 +1332,9 @@ func putInlinedFunc(ctxt Context, s *FnState, callIdx int) error {
 	}
 
 	// Emit call file, line attrs.
-	ctxt.AddFileRef(s.Info, ic.CallFile)
+	putattr(ctxt, s.Info, abbrev, DW_FORM_data4, DW_CLS_CONSTANT, int64(1+ic.CallPos.FileIndex()), nil) // 1-based file table
 	form := int(expandPseudoForm(DW_FORM_udata_pseudo))
-	putattr(ctxt, s.Info, abbrev, form, DW_CLS_CONSTANT, int64(ic.CallLine), nil)
+	putattr(ctxt, s.Info, abbrev, form, DW_CLS_CONSTANT, int64(ic.CallPos.RelLine()), nil)
 
 	// Variables associated with this inlined routine instance.
 	vars := ic.InlVars
@@ -1438,8 +1435,8 @@ func PutDefaultFunc(ctxt Context, s *FnState, isWrapper bool) error {
 	if isWrapper {
 		putattr(ctxt, s.Info, abbrev, DW_FORM_flag, DW_CLS_FLAG, int64(1), 0)
 	} else {
-		ctxt.AddFileRef(s.Info, s.Filesym)
+		putattr(ctxt, s.Info, abbrev, DW_FORM_data4, DW_CLS_CONSTANT, int64(1+s.StartPos.FileIndex()), nil) // 1-based file index
-		putattr(ctxt, s.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartLine), nil)
+		putattr(ctxt, s.Info, abbrev, DW_FORM_udata, DW_CLS_CONSTANT, int64(s.StartPos.RelLine()), nil)
 
 		var ev int64
 		if s.External {

src/cmd/internal/obj/dwarf.go

@@ -48,7 +48,7 @@ func (ctxt *Link) generateDebugLinesSymbol(s, lines *LSym) {
 	line := int64(1)
 	pc := s.Func().Text.Pc
 	var lastpc int64 // last PC written to line table, not last PC in func
-	name := ""
+	fileIndex := 1
 	prologue, wrotePrologue := false, false
 	// Walk the progs, generating the DWARF table.
 	for p := s.Func().Text; p != nil; p = p.Link {
@@ -58,15 +58,15 @@ func (ctxt *Link) generateDebugLinesSymbol(s, lines *LSym) {
 			continue
 		}
 		newStmt := p.Pos.IsStmt() != src.PosNotStmt
-		newName, newLine := ctxt.getFileSymbolAndLine(p.Pos)
+		newFileIndex, newLine := ctxt.getFileIndexAndLine(p.Pos)
+		newFileIndex++ // 1 indexing for the table
 
 		// Output debug info.
 		wrote := false
-		if name != newName {
+		if newFileIndex != fileIndex {
-			newFile := ctxt.PosTable.FileIndex(newName) + 1 // 1 indexing for the table.
 			dctxt.AddUint8(lines, dwarf.DW_LNS_set_file)
-			dwarf.Uleb128put(dctxt, lines, int64(newFile))
+			dwarf.Uleb128put(dctxt, lines, int64(newFileIndex))
-			name = newName
+			fileIndex = newFileIndex
 			wrote = true
 		}
 		if prologue && !wrotePrologue {
@@ -258,16 +258,6 @@ func (c dwCtxt) AddDWARFAddrSectionOffset(s dwarf.Sym, t interface{}, ofs int64)
 	r.Type = objabi.R_DWARFSECREF
 }
 
-func (c dwCtxt) AddFileRef(s dwarf.Sym, f interface{}) {
-	ls := s.(*LSym)
-	rsym := f.(*LSym)
-	fidx := c.Link.PosTable.FileIndex(rsym.Name)
-	// Note the +1 here -- the value we're writing is going to be an
-	// index into the DWARF line table file section, whose entries
-	// are numbered starting at 1, not 0.
-	ls.WriteInt(c.Link, ls.Size, 4, int64(fidx+1))
-}
-
 func (c dwCtxt) CurrentOffset(s dwarf.Sym) int64 {
 	ls := s.(*LSym)
 	return ls.Size
@@ -329,17 +319,13 @@ func (s *LSym) Length(dwarfContext interface{}) int64 {
 	return s.Size
 }
 
-// fileSymbol returns a symbol corresponding to the source file of the
+// textPos returns the source position of the first instruction (prog)
-// first instruction (prog) of the specified function. This will
+// of the specified function.
-// presumably be the file in which the function is defined.
+func textPos(fn *LSym) src.XPos {
-func (ctxt *Link) fileSymbol(fn *LSym) *LSym {
+	if p := fn.Func().Text; p != nil {
-	p := fn.Func().Text
+		return p.Pos
-	if p != nil {
-		f, _ := ctxt.getFileSymbolAndLine(p.Pos)
-		fsym := ctxt.Lookup(f)
-		return fsym
 	}
-	return nil
+	return src.NoXPos
 }
 
 // populateDWARF fills in the DWARF Debugging Information Entries for
@@ -362,17 +348,19 @@ func (ctxt *Link) populateDWARF(curfn Func, s *LSym) {
 	}
 	var err error
 	dwctxt := dwCtxt{ctxt}
-	filesym := ctxt.fileSymbol(s)
+	startPos := ctxt.InnermostPos(textPos(s))
+	if !startPos.IsKnown() || startPos.RelLine() != uint(s.Func().StartLine) {
+		panic("bad startPos")
+	}
 	fnstate := &dwarf.FnState{
 		Name:          s.Name,
 		Info:          info,
-		Filesym:       filesym,
 		Loc:           loc,
 		Ranges:        ranges,
 		Absfn:         absfunc,
 		StartPC:       s,
 		Size:          s.Size,
-		StartLine:     s.Func().StartLine,
+		StartPos:      startPos,
 		External:      !s.Static(),
 		Scopes:        scopes,
 		InlCalls:      inlcalls,
@@ -434,13 +422,12 @@ func (ctxt *Link) DwarfAbstractFunc(curfn Func, s *LSym) {
 		s.NewFuncInfo()
 	}
 	scopes, _ := ctxt.DebugInfo(s, absfn, curfn)
-	_, startLine := ctxt.getFileSymbolAndLine(curfn.Pos())
 	dwctxt := dwCtxt{ctxt}
 	fnstate := dwarf.FnState{
 		Name:          s.Name,
 		Info:          absfn,
 		Absfn:         absfn,
-		StartLine:     startLine,
+		StartPos:      ctxt.InnermostPos(curfn.Pos()),
 		External:      !s.Static(),
 		Scopes:        scopes,
 		UseBASEntries: ctxt.UseBASEntries,

src/cmd/internal/obj/line.go

@@ -14,22 +14,14 @@ func (ctxt *Link) AddImport(pkg string, fingerprint goobj.FingerprintType) {
 	ctxt.Imports = append(ctxt.Imports, goobj.ImportedPkg{Pkg: pkg, Fingerprint: fingerprint})
 }
 
-// getFileSymbolAndLine returns the relative file symbol and relative line
-// number for a position (i.e., as adjusted by a //line directive). This is the
-// file/line visible in the final binary (pcfile, pcln, etc).
-func (ctxt *Link) getFileSymbolAndLine(xpos src.XPos) (f string, l int32) {
-	pos := ctxt.InnermostPos(xpos)
-	if !pos.IsKnown() {
-		pos = src.Pos{}
-	}
-	return pos.SymFilename(), int32(pos.RelLine())
-}
-
 // getFileIndexAndLine returns the relative file index (local to the CU), and
 // the relative line number for a position (i.e., as adjusted by a //line
 // directive). This is the file/line visible in the final binary (pcfile, pcln,
 // etc).
 func (ctxt *Link) getFileIndexAndLine(xpos src.XPos) (int, int32) {
-	f, l := ctxt.getFileSymbolAndLine(xpos)
+	pos := ctxt.InnermostPos(xpos)
-	return ctxt.PosTable.FileIndex(f), l
+	if !pos.IsKnown() {
+		pos = src.Pos{}
+	}
+	return pos.FileIndex(), int32(pos.RelLine())
 }

src/cmd/internal/obj/line_test.go

@@ -31,9 +31,15 @@ func TestGetFileSymbolAndLine(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		f, l := ctxt.getFileSymbolAndLine(ctxt.PosTable.XPos(test.pos))
+		fileIndex, line := ctxt.getFileIndexAndLine(ctxt.PosTable.XPos(test.pos))
-		got := fmt.Sprintf("%s:%d", f, l)
+
-		if got != src.FileSymPrefix+test.want {
+		file := "??"
+		if fileIndex >= 0 {
+			file = ctxt.PosTable.FileTable()[fileIndex]
+		}
+		got := fmt.Sprintf("%s:%d", file, line)
+
+		if got != test.want {
 			t.Errorf("ctxt.getFileSymbolAndLine(%v) = %q, want %q", test.pos, got, test.want)
 		}
 	}

src/cmd/internal/obj/plist.go

@@ -198,7 +198,7 @@ func (ctxt *Link) InitTextSym(s *LSym, flag int, start src.XPos) {
 	// startLine should be the same line number that would be displayed via
 	// pcln, etc for the declaration (i.e., relative line number, as
 	// adjusted by //line).
-	_, startLine := ctxt.getFileSymbolAndLine(start)
+	_, startLine := ctxt.getFileIndexAndLine(start)
 
 	s.Func().FuncID = objabi.GetFuncID(s.Name, flag&WRAPPER != 0 || flag&ABIWRAPPER != 0)
 	s.Func().FuncFlag = ctxt.toFuncFlag(flag)

src/cmd/internal/obj/sym.go

@@ -449,10 +449,6 @@ func (ctxt *Link) traverseFuncAux(flag traverseFlag, fsym *LSym, fn func(parent
 		if call.Func != nil {
 			fn(fsym, call.Func)
 		}
-		f, _ := ctxt.getFileSymbolAndLine(call.Pos)
-		if filesym := ctxt.Lookup(f); filesym != nil {
-			fn(fsym, filesym)
-		}
 	}
 
 	auxsyms := []*LSym{fninfo.dwarfRangesSym, fninfo.dwarfLocSym, fninfo.dwarfDebugLinesSym, fninfo.dwarfInfoSym, fninfo.WasmImportSym, fninfo.sehUnwindInfoSym}

src/cmd/internal/src/pos.go

@@ -116,9 +116,9 @@ func (p Pos) RelCol() uint {
 // AbsFilename() returns the absolute filename recorded with the position's base.
 func (p Pos) AbsFilename() string { return p.base.AbsFilename() }
 
-// SymFilename() returns the absolute filename recorded with the position's base,
+// FileIndex returns the file index of the position's base's absolute
-// prefixed by FileSymPrefix to make it appropriate for use as a linker symbol.
+// filename within the PosTable that it was registered.
-func (p Pos) SymFilename() string { return p.base.SymFilename() }
+func (p Pos) FileIndex() int { return p.base.FileIndex() }
 
 func (p Pos) String() string {
 	return p.Format(true, true)
@@ -193,9 +193,9 @@ type PosBase struct {
 	pos         Pos    // position at which the relative position is (line, col)
 	filename    string // file name used to open source file, for error messages
 	absFilename string // absolute file name, for PC-Line tables
-	symFilename string // cached symbol file name, to avoid repeated string concatenation
 	line, col   uint   // relative line, column number at pos
 	inl         int    // inlining index (see cmd/internal/obj/inl.go)
+	fileIndex   int    // index of absFilename within PosTable.FileTable
 }
 
 // NewFileBase returns a new *PosBase for a file with the given (relative and
@@ -204,10 +204,10 @@ func NewFileBase(filename, absFilename string) *PosBase {
 	base := &PosBase{
 		filename:    filename,
 		absFilename: absFilename,
-		symFilename: FileSymPrefix + absFilename,
 		line:        1,
 		col:         1,
 		inl:         -1,
+		fileIndex:   -1,
 	}
 	base.pos = MakePos(base, 1, 1)
 	return base
@@ -220,24 +220,22 @@ func NewFileBase(filename, absFilename string) *PosBase {
 //
 // at position pos.
 func NewLinePragmaBase(pos Pos, filename, absFilename string, line, col uint) *PosBase {
-	return &PosBase{pos, filename, absFilename, FileSymPrefix + absFilename, line, col, -1}
+	return &PosBase{pos, filename, absFilename, line, col, -1, -1}
 }
 
-// NewInliningBase returns a copy of the old PosBase with the given inlining
+// NewInliningBase returns a copy of the orig PosBase with the given inlining
-// index. If old == nil, the resulting PosBase has no filename.
+// index. If orig == nil, NewInliningBase panics.
-func NewInliningBase(old *PosBase, inlTreeIndex int) *PosBase {
+func NewInliningBase(orig *PosBase, inlTreeIndex int) *PosBase {
-	if old == nil {
+	if orig == nil {
-		base := &PosBase{line: 1, col: 1, inl: inlTreeIndex}
+		panic("no old PosBase")
-		base.pos = MakePos(base, 1, 1)
-		return base
 	}
-	copy := *old
+	base := *orig
-	base := &copy
 	base.inl = inlTreeIndex
-	if old == old.pos.base {
+	base.fileIndex = -1
-		base.pos.base = base
+	if orig == orig.pos.base {
+		base.pos.base = &base
 	}
-	return base
+	return &base
 }
 
 var noPos Pos
@@ -269,16 +267,21 @@ func (b *PosBase) AbsFilename() string {
 	return ""
 }
 
+// FileSymPrefix is the linker symbol prefix that used to be used for
+// linker pseudo-symbols representing file names.
 const FileSymPrefix = "gofile.."
 
-// SymFilename returns the absolute filename recorded with the base,
+// FileIndex returns the index of the base's absolute filename within
-// prefixed by FileSymPrefix to make it appropriate for use as a linker symbol.
+// its PosTable's FileTable. It panics if it hasn't been registered
-// If b is nil, SymFilename returns FileSymPrefix + "??".
+// with a PosTable. If b == nil, the result is -1.
-func (b *PosBase) SymFilename() string {
+func (b *PosBase) FileIndex() int {
 	if b != nil {
-		return b.symFilename
+		if b.fileIndex < 0 {
+			panic("PosBase has no file index")
+		}
+		return b.fileIndex
 	}
-	return FileSymPrefix + "??"
+	return -1
 }
 
 // Line returns the line number recorded with the base.

src/cmd/internal/src/xpos.go

@@ -124,25 +124,40 @@ type PosTable struct {
 // XPos returns the corresponding XPos for the given pos,
 // adding pos to t if necessary.
 func (t *PosTable) XPos(pos Pos) XPos {
-	m := t.indexMap
+	return XPos{t.baseIndex(pos.base), pos.lico}
-	if m == nil {
+}
-		// Create new list and map and populate with nil
+
-		// base so that NoPos always gets index 0.
+func (t *PosTable) baseIndex(base *PosBase) int32 {
+	if base == nil {
+		return 0
+	}
+
+	if i, ok := t.indexMap[base]; ok {
+		return int32(i)
+	}
+
+	if base.fileIndex >= 0 {
+		panic("PosBase already registered with a PosTable")
+	}
+
+	if t.indexMap == nil {
 		t.baseList = append(t.baseList, nil)
-		m = map[*PosBase]int{nil: 0}
+		t.indexMap = make(map[*PosBase]int)
-		t.indexMap = m
 		t.nameMap = make(map[string]int)
 	}
-	i, ok := m[pos.base]
+
+	i := len(t.baseList)
+	t.indexMap[base] = i
+	t.baseList = append(t.baseList, base)
+
+	fileIndex, ok := t.nameMap[base.absFilename]
 	if !ok {
-		i = len(t.baseList)
+		fileIndex = len(t.nameMap)
-		t.baseList = append(t.baseList, pos.base)
+		t.nameMap[base.absFilename] = fileIndex
-		t.indexMap[pos.base] = i
-		if _, ok := t.nameMap[pos.base.symFilename]; !ok {
-			t.nameMap[pos.base.symFilename] = len(t.nameMap)
-		}
 	}
-	return XPos{int32(i), pos.lico}
+	base.fileIndex = fileIndex
+
+	return int32(i)
 }
 
 // Pos returns the corresponding Pos for the given p.
@@ -155,14 +170,6 @@ func (t *PosTable) Pos(p XPos) Pos {
 	return Pos{base, p.lico}
 }
 
-// FileIndex returns the index of the given filename(symbol) in the PosTable, or -1 if not found.
-func (t *PosTable) FileIndex(filename string) int {
-	if v, ok := t.nameMap[filename]; ok {
-		return v
-	}
-	return -1
-}
-
 // FileTable returns a slice of all files used to build this package.
 func (t *PosTable) FileTable() []string {
 	// Create a LUT of the global package level file indices. This table is what

src/cmd/internal/src/xpos_test.go

@@ -62,8 +62,8 @@ func TestConversion(t *testing.T) {
 		}
 	}
 
-	if len(tab.baseList) != len(tab.indexMap) {
+	if len(tab.baseList) != 1+len(tab.indexMap) { // indexMap omits nil
-		t.Errorf("table length discrepancy: %d != %d", len(tab.baseList), len(tab.indexMap))
+		t.Errorf("table length discrepancy: %d != 1+%d", len(tab.baseList), len(tab.indexMap))
 	}
 
 	const wantLen = 4

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

@@ -154,10 +154,6 @@ func (c dwctxt) Logf(format string, args ...interface{}) {
 
 // At the moment these interfaces are only used in the compiler.
 
-func (c dwctxt) AddFileRef(s dwarf.Sym, f interface{}) {
-	panic("should be used only in the compiler")
-}
-
 func (c dwctxt) CurrentOffset(s dwarf.Sym) int64 {
 	panic("should be used only in the compiler")
 }