Merge "cmd: merge branch 'dev.link' into master"

src/cmd/asm/internal/flags/flags.go

@@ -23,6 +23,7 @@ var (
 	Dynlink    = flag.Bool("dynlink", false, "support references to Go symbols defined in other shared libraries")
 	AllErrors  = flag.Bool("e", false, "no limit on number of errors reported")
 	SymABIs    = flag.Bool("gensymabis", false, "write symbol ABI information to output file, don't assemble")
+	Newobj     = flag.Bool("newobj", false, "use new object file format")
 )
 
 var (

src/cmd/asm/main.go

@@ -40,18 +40,18 @@ func main() {
 	}
 	ctxt.Flag_dynlink = *flags.Dynlink
 	ctxt.Flag_shared = *flags.Shared || *flags.Dynlink
+	ctxt.Flag_newobj = *flags.Newobj
 	ctxt.Bso = bufio.NewWriter(os.Stdout)
 	defer ctxt.Bso.Flush()
 
 	architecture.Init(ctxt)
 
 	// Create object file, write header.
-	out, err := os.Create(*flags.OutputFile)
+	buf, err := bio.Create(*flags.OutputFile)
 	if err != nil {
 		log.Fatal(err)
 	}
-	defer bio.MustClose(out)
-	buf := bufio.NewWriter(bio.MustWriter(out))
+	defer buf.Close()
 
 	if !*flags.SymABIs {
 		fmt.Fprintf(buf, "go object %s %s %s\n", objabi.GOOS, objabi.GOARCH, objabi.Version)
@@ -83,6 +83,7 @@ func main() {
 		}
 	}
 	if ok && !*flags.SymABIs {
+		ctxt.NumberSyms(true)
 		obj.WriteObjFile(ctxt, buf, "")
 	}
 	if !ok || diag {
@@ -91,9 +92,8 @@ func main() {
 		} else {
 			log.Print("assembly failed")
 		}
-		out.Close()
+		buf.Close()
 		os.Remove(*flags.OutputFile)
 		os.Exit(1)
 	}
-	buf.Flush()
 }

src/cmd/compile/internal/gc/iexport.go

@@ -203,6 +203,7 @@ import (
 	"bufio"
 	"bytes"
 	"cmd/compile/internal/types"
+	"cmd/internal/goobj2"
 	"cmd/internal/src"
 	"encoding/binary"
 	"fmt"
@@ -945,10 +946,12 @@ func (w *exportWriter) string(s string) { w.uint64(w.p.stringOff(s)) }
 
 func (w *exportWriter) varExt(n *Node) {
 	w.linkname(n.Sym)
+	w.symIdx(n.Sym)
 }
 
 func (w *exportWriter) funcExt(n *Node) {
 	w.linkname(n.Sym)
+	w.symIdx(n.Sym)
 
 	// Escape analysis.
 	for _, fs := range types.RecvsParams {
@@ -987,6 +990,22 @@ func (w *exportWriter) linkname(s *types.Sym) {
 	w.string(s.Linkname)
 }
 
+func (w *exportWriter) symIdx(s *types.Sym) {
+	if Ctxt.Flag_newobj {
+		lsym := s.Linksym()
+		if lsym.PkgIdx > goobj2.PkgIdxSelf || (lsym.PkgIdx == goobj2.PkgIdxInvalid && !lsym.Indexed()) || s.Linkname != "" {
+			// Don't export index for non-package symbols, linkname'd symbols,
+			// and symbols without an index. They can only be referenced by
+			// name.
+			w.int64(-1)
+		} else {
+			// For a defined symbol, export its index.
+			// For re-exporting an imported symbol, pass its index through.
+			w.int64(int64(lsym.SymIdx))
+		}
+	}
+}
+
 // Inline bodies.
 
 func (w *exportWriter) stmtList(list Nodes) {

src/cmd/compile/internal/gc/iimport.go

@@ -10,6 +10,7 @@ package gc
 import (
 	"cmd/compile/internal/types"
 	"cmd/internal/bio"
+	"cmd/internal/obj"
 	"cmd/internal/src"
 	"encoding/binary"
 	"fmt"
@@ -651,10 +652,12 @@ func (r *importReader) byte() byte {
 
 func (r *importReader) varExt(n *Node) {
 	r.linkname(n.Sym)
+	r.symIdx(n.Sym)
 }
 
 func (r *importReader) funcExt(n *Node) {
 	r.linkname(n.Sym)
+	r.symIdx(n.Sym)
 
 	// Escape analysis.
 	for _, fs := range types.RecvsParams {
@@ -683,6 +686,20 @@ func (r *importReader) linkname(s *types.Sym) {
 	s.Linkname = r.string()
 }
 
+func (r *importReader) symIdx(s *types.Sym) {
+	if Ctxt.Flag_newobj {
+		lsym := s.Linksym()
+		idx := int32(r.int64())
+		if idx != -1 {
+			if s.Linkname != "" {
+				Fatalf("bad index for linknamed symbol: %v %d\n", lsym, idx)
+			}
+			lsym.SymIdx = idx
+			lsym.Set(obj.AttrIndexed, true)
+		}
+	}
+}
+
 func (r *importReader) doInline(n *Node) {
 	if len(n.Func.Inl.Body) != 0 {
 		Fatalf("%v already has inline body", n)

src/cmd/compile/internal/gc/main.go

@@ -260,6 +260,7 @@ func Main(archInit func(*Arch)) {
 	if supportsDynlink(thearch.LinkArch.Arch) {
 		flag.BoolVar(&flag_shared, "shared", false, "generate code that can be linked into a shared library")
 		flag.BoolVar(&flag_dynlink, "dynlink", false, "support references to Go symbols defined in other shared libraries")
+		flag.BoolVar(&Ctxt.Flag_linkshared, "linkshared", false, "generate code that will be linked against Go shared libraries")
 	}
 	flag.StringVar(&cpuprofile, "cpuprofile", "", "write cpu profile to `file`")
 	flag.StringVar(&memprofile, "memprofile", "", "write memory profile to `file`")
@@ -274,12 +275,14 @@ func Main(archInit func(*Arch)) {
 	flag.StringVar(&benchfile, "bench", "", "append benchmark times to `file`")
 	flag.BoolVar(&smallFrames, "smallframes", false, "reduce the size limit for stack allocated objects")
 	flag.BoolVar(&Ctxt.UseBASEntries, "dwarfbasentries", Ctxt.UseBASEntries, "use base address selection entries in DWARF")
+	flag.BoolVar(&Ctxt.Flag_newobj, "newobj", false, "use new object file format")
+
 	objabi.Flagparse(usage)
 
 	// Record flags that affect the build result. (And don't
 	// record flags that don't, since that would cause spurious
 	// changes in the binary.)
-	recordFlags("B", "N", "l", "msan", "race", "shared", "dynlink", "dwarflocationlists", "dwarfbasentries", "smallframes")
+	recordFlags("B", "N", "l", "msan", "race", "shared", "dynlink", "dwarflocationlists", "dwarfbasentries", "smallframes", "newobj")
 
 	if smallFrames {
 		maxStackVarSize = 128 * 1024
@@ -746,6 +749,8 @@ func Main(archInit func(*Arch)) {
 
 	// Write object data to disk.
 	timings.Start("be", "dumpobj")
+	dumpdata()
+	Ctxt.NumberSyms(false)
 	dumpobj()
 	if asmhdr != "" {
 		dumpasmhdr()

src/cmd/compile/internal/gc/obj.go

@@ -111,21 +111,7 @@ func dumpCompilerObj(bout *bio.Writer) {
 	dumpexport(bout)
 }
 
-func dumpLinkerObj(bout *bio.Writer) {
-	printObjHeader(bout)
-
-	if len(pragcgobuf) != 0 {
-		// write empty export section; must be before cgo section
-		fmt.Fprintf(bout, "\n$$\n\n$$\n\n")
-		fmt.Fprintf(bout, "\n$$  // cgo\n")
-		if err := json.NewEncoder(bout).Encode(pragcgobuf); err != nil {
-			Fatalf("serializing pragcgobuf: %v", err)
-		}
-		fmt.Fprintf(bout, "\n$$\n\n")
-	}
-
-	fmt.Fprintf(bout, "\n!\n")
-
+func dumpdata() {
 	externs := len(externdcl)
 
 	dumpglobls()
@@ -163,8 +149,24 @@ func dumpLinkerObj(bout *bio.Writer) {
 	}
 
 	addGCLocals()
+}
 
-	obj.WriteObjFile(Ctxt, bout.Writer, myimportpath)
+func dumpLinkerObj(bout *bio.Writer) {
+	printObjHeader(bout)
+
+	if len(pragcgobuf) != 0 {
+		// write empty export section; must be before cgo section
+		fmt.Fprintf(bout, "\n$$\n\n$$\n\n")
+		fmt.Fprintf(bout, "\n$$  // cgo\n")
+		if err := json.NewEncoder(bout).Encode(pragcgobuf); err != nil {
+			Fatalf("serializing pragcgobuf: %v", err)
+		}
+		fmt.Fprintf(bout, "\n$$\n\n")
+	}
+
+	fmt.Fprintf(bout, "\n!\n")
+
+	obj.WriteObjFile(Ctxt, bout, myimportpath)
 }
 
 func addptabs() {

src/cmd/compile/internal/types/sym.go

@@ -80,11 +80,18 @@ func (sym *Sym) Linksym() *obj.LSym {
 	if sym == nil {
 		return nil
 	}
+	initPkg := func(r *obj.LSym) {
+		if sym.Linkname != "" {
+			r.Pkg = "_"
+		} else {
+			r.Pkg = sym.Pkg.Prefix
+		}
+	}
 	if sym.Func() {
 		// This is a function symbol. Mark it as "internal ABI".
-		return Ctxt.LookupABI(sym.LinksymName(), obj.ABIInternal)
+		return Ctxt.LookupABIInit(sym.LinksymName(), obj.ABIInternal, initPkg)
 	}
-	return Ctxt.Lookup(sym.LinksymName())
+	return Ctxt.LookupInit(sym.LinksymName(), initPkg)
 }
 
 // Less reports whether symbol a is ordered before symbol b.

src/cmd/dist/buildtool.go

@@ -54,6 +54,7 @@ var bootstrapDirs = []string{
 	"cmd/internal/gcprog",
 	"cmd/internal/dwarf",
 	"cmd/internal/edit",
+	"cmd/internal/goobj2",
 	"cmd/internal/objabi",
 	"cmd/internal/obj",
 	"cmd/internal/obj/arm",
@@ -72,6 +73,7 @@ var bootstrapDirs = []string{
 	"cmd/link/internal/arm64",
 	"cmd/link/internal/ld",
 	"cmd/link/internal/loadelf",
+	"cmd/link/internal/loader",
 	"cmd/link/internal/loadmacho",
 	"cmd/link/internal/loadpe",
 	"cmd/link/internal/loadxcoff",

src/cmd/dist/test.go

@@ -585,7 +585,7 @@ func (t *tester) registerTests() {
 			},
 		})
 		// Also test a cgo package.
-		if t.cgoEnabled {
+		if t.cgoEnabled && t.internalLink() {
 			t.tests = append(t.tests, distTest{
 				name:    "pie_internal_cgo",
 				heading: "internal linking of -buildmode=pie",

src/cmd/go/alldocs.go

@@ -145,8 +145,8 @@
 // 	-ldflags '[pattern=]arg list'
 // 		arguments to pass on each go tool link invocation.
 // 	-linkshared
-// 		link against shared libraries previously created with
-// 		-buildmode=shared.
+// 		build code that will be linked against shared libraries previously
+// 		created with -buildmode=shared.
 // 	-mod mode
 // 		module download mode to use: readonly or vendor.
 // 		See 'go help modules' for more.

src/cmd/go/internal/work/build.go

@@ -97,8 +97,8 @@ and test commands:
 	-ldflags '[pattern=]arg list'
 		arguments to pass on each go tool link invocation.
 	-linkshared
-		link against shared libraries previously created with
-		-buildmode=shared.
+		build code that will be linked against shared libraries previously
+		created with -buildmode=shared.
 	-mod mode
 		module download mode to use: readonly or vendor.
 		See 'go help modules' for more.

src/cmd/go/internal/work/init.go

@@ -224,6 +224,7 @@ func buildModeInit() {
 				base.Fatalf("-linkshared not supported on %s\n", platform)
 			}
 			codegenArg = "-dynlink"
+			forcedGcflags = append(forcedGcflags, "-linkshared")
 			// TODO(mwhudson): remove -w when that gets fixed in linker.
 			forcedLdflags = append(forcedLdflags, "-linkshared", "-w")
 		}

src/cmd/internal/dwarf/dwarf.go

@@ -1372,7 +1372,13 @@ func PutDefaultFunc(ctxt Context, s *FnState) error {
 	abbrev := DW_ABRV_FUNCTION
 	Uleb128put(ctxt, s.Info, int64(abbrev))
 
-	putattr(ctxt, s.Info, DW_ABRV_FUNCTION, DW_FORM_string, DW_CLS_STRING, int64(len(s.Name)), s.Name)
+	// Expand '"".' to import path.
+	name := s.Name
+	if s.Importpath != "" {
+		name = strings.Replace(name, "\"\".", objabi.PathToPrefix(s.Importpath)+".", -1)
+	}
+
+	putattr(ctxt, s.Info, DW_ABRV_FUNCTION, DW_FORM_string, DW_CLS_STRING, int64(len(name)), name)
 	putattr(ctxt, s.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, 0, s.StartPC)
 	putattr(ctxt, s.Info, abbrev, DW_FORM_addr, DW_CLS_ADDRESS, s.Size, s.StartPC)
 	putattr(ctxt, s.Info, abbrev, DW_FORM_block1, DW_CLS_BLOCK, 1, []byte{DW_OP_call_frame_cfa})

src/cmd/internal/goobj/read.go

@@ -502,6 +502,14 @@ func (r *objReader) parseObject(prefix []byte) error {
 	}
 	// TODO: extract OS + build ID if/when we need it
 
+	p, err := r.peek(8)
+	if err != nil {
+		return err
+	}
+	if bytes.Equal(p, []byte("\x00go114LD")) {
+		r.readNew()
+		return nil
+	}
 	r.readFull(r.tmp[:8])
 	if !bytes.Equal(r.tmp[:8], []byte("\x00go114ld")) {
 		return r.error(errCorruptObject)

src/cmd/internal/goobj/readnew.go

@@ -0,0 +1,187 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package goobj
+
+import (
+	"cmd/internal/goobj2"
+	"cmd/internal/objabi"
+	"fmt"
+	"strings"
+)
+
+// Read object file in new format. For now we still fill
+// the data to the current goobj API.
+func (r *objReader) readNew() {
+	start := uint32(r.offset)
+
+	length := r.limit - r.offset
+	objbytes := make([]byte, length)
+	r.readFull(objbytes)
+	rr := goobj2.NewReaderFromBytes(objbytes, false)
+	if rr == nil {
+		panic("cannot read object file")
+	}
+
+	// Imports
+	r.p.Imports = rr.Autolib()
+
+	pkglist := rr.Pkglist()
+
+	abiToVer := func(abi uint16) int64 {
+		var vers int64
+		if abi == goobj2.SymABIstatic {
+			// Static symbol
+			vers = r.p.MaxVersion
+		}
+		return vers
+	}
+
+	resolveSymRef := func(s goobj2.SymRef) SymID {
+		var i int
+		switch p := s.PkgIdx; p {
+		case goobj2.PkgIdxInvalid:
+			if s.SymIdx != 0 {
+				panic("bad sym ref")
+			}
+			return SymID{}
+		case goobj2.PkgIdxNone:
+			i = int(s.SymIdx) + rr.NSym()
+		case goobj2.PkgIdxBuiltin:
+			name, abi := goobj2.BuiltinName(int(s.SymIdx))
+			return SymID{name, int64(abi)}
+		case goobj2.PkgIdxSelf:
+			i = int(s.SymIdx)
+		default:
+			pkg := pkglist[p]
+			return SymID{fmt.Sprintf("%s.<#%d>", pkg, s.SymIdx), 0}
+		}
+		sym := goobj2.Sym{}
+		sym.Read(rr, rr.SymOff(i))
+		return SymID{sym.Name, abiToVer(sym.ABI)}
+	}
+
+	// Read things for the current goobj API for now.
+
+	// Symbols
+	pcdataBase := start + rr.PcdataBase()
+	n := rr.NSym() + rr.NNonpkgdef() + rr.NNonpkgref()
+	ndef := rr.NSym() + rr.NNonpkgdef()
+	for i := 0; i < n; i++ {
+		osym := goobj2.Sym{}
+		osym.Read(rr, rr.SymOff(i))
+		if osym.Name == "" {
+			continue // not a real symbol
+		}
+		// In a symbol name in an object file, "". denotes the
+		// prefix for the package in which the object file has been found.
+		// Expand it.
+		name := strings.ReplaceAll(osym.Name, `"".`, r.pkgprefix)
+		symID := SymID{Name: name, Version: abiToVer(osym.ABI)}
+		r.p.SymRefs = append(r.p.SymRefs, symID)
+
+		if i >= ndef {
+			continue // not a defined symbol from here
+		}
+
+		// Symbol data
+		dataOff := rr.DataOff(i)
+		siz := int64(rr.DataSize(i))
+
+		sym := Sym{
+			SymID: symID,
+			Kind:  objabi.SymKind(osym.Type),
+			DupOK: osym.Dupok(),
+			Size:  int64(osym.Siz),
+			Data:  Data{int64(start + dataOff), siz},
+		}
+		r.p.Syms = append(r.p.Syms, &sym)
+
+		// Reloc
+		nreloc := rr.NReloc(i)
+		sym.Reloc = make([]Reloc, nreloc)
+		for j := 0; j < nreloc; j++ {
+			rel := goobj2.Reloc{}
+			rel.Read(rr, rr.RelocOff(i, j))
+			sym.Reloc[j] = Reloc{
+				Offset: int64(rel.Off),
+				Size:   int64(rel.Siz),
+				Type:   objabi.RelocType(rel.Type),
+				Add:    rel.Add,
+				Sym:    resolveSymRef(rel.Sym),
+			}
+		}
+
+		// Aux symbol info
+		isym := -1
+		funcdata := make([]goobj2.SymRef, 0, 4)
+		naux := rr.NAux(i)
+		for j := 0; j < naux; j++ {
+			a := goobj2.Aux{}
+			a.Read(rr, rr.AuxOff(i, j))
+			switch a.Type {
+			case goobj2.AuxGotype:
+				sym.Type = resolveSymRef(a.Sym)
+			case goobj2.AuxFuncInfo:
+				if a.Sym.PkgIdx != goobj2.PkgIdxSelf {
+					panic("funcinfo symbol not defined in current package")
+				}
+				isym = int(a.Sym.SymIdx)
+			case goobj2.AuxFuncdata:
+				funcdata = append(funcdata, a.Sym)
+			case goobj2.AuxDwarfInfo, goobj2.AuxDwarfLoc, goobj2.AuxDwarfRanges, goobj2.AuxDwarfLines:
+				// nothing to do
+			default:
+				panic("unknown aux type")
+			}
+		}
+
+		// Symbol Info
+		if isym == -1 {
+			continue
+		}
+		b := rr.BytesAt(rr.DataOff(isym), rr.DataSize(isym))
+		info := goobj2.FuncInfo{}
+		info.Read(b)
+
+		info.Pcdata = append(info.Pcdata, info.PcdataEnd) // for the ease of knowing where it ends
+		f := &Func{
+			Args:     int64(info.Args),
+			Frame:    int64(info.Locals),
+			NoSplit:  info.NoSplit != 0,
+			Leaf:     osym.Leaf(),
+			TopFrame: osym.TopFrame(),
+			PCSP:     Data{int64(pcdataBase + info.Pcsp), int64(info.Pcfile - info.Pcsp)},
+			PCFile:   Data{int64(pcdataBase + info.Pcfile), int64(info.Pcline - info.Pcfile)},
+			PCLine:   Data{int64(pcdataBase + info.Pcline), int64(info.Pcinline - info.Pcline)},
+			PCInline: Data{int64(pcdataBase + info.Pcinline), int64(info.Pcdata[0] - info.Pcinline)},
+			PCData:   make([]Data, len(info.Pcdata)-1), // -1 as we appended one above
+			FuncData: make([]FuncData, len(info.Funcdataoff)),
+			File:     make([]string, len(info.File)),
+			InlTree:  make([]InlinedCall, len(info.InlTree)),
+		}
+		sym.Func = f
+		for k := range f.PCData {
+			f.PCData[k] = Data{int64(pcdataBase + info.Pcdata[k]), int64(info.Pcdata[k+1] - info.Pcdata[k])}
+		}
+		for k := range f.FuncData {
+			symID := resolveSymRef(funcdata[k])
+			f.FuncData[k] = FuncData{symID, int64(info.Funcdataoff[k])}
+		}
+		for k := range f.File {
+			symID := resolveSymRef(info.File[k])
+			f.File[k] = symID.Name
+		}
+		for k := range f.InlTree {
+			inl := &info.InlTree[k]
+			f.InlTree[k] = InlinedCall{
+				Parent:   int64(inl.Parent),
+				File:     resolveSymRef(inl.File).Name,
+				Line:     int64(inl.Line),
+				Func:     resolveSymRef(inl.Func),
+				ParentPC: int64(inl.ParentPC),
+			}
+		}
+	}
+}

src/cmd/internal/goobj2/builtin.go

@@ -0,0 +1,45 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package goobj2
+
+// Builtin (compiler-generated) function references appear
+// frequently. We assign special indices for them, so they
+// don't need to be referenced by name.
+
+// NBuiltin returns the number of listed builtin
+// symbols.
+func NBuiltin() int {
+	return len(builtins)
+}
+
+// BuiltinName returns the name and ABI of the i-th
+// builtin symbol.
+func BuiltinName(i int) (string, int) {
+	return builtins[i].name, builtins[i].abi
+}
+
+// BuiltinIdx returns the index of the builtin with the
+// given name and abi, or -1 if it is not a builtin.
+func BuiltinIdx(name string, abi int) int {
+	i, ok := builtinMap[name]
+	if !ok {
+		return -1
+	}
+	if builtins[i].abi != abi {
+		return -1
+	}
+	return i
+}
+
+//go:generate go run mkbuiltin.go
+
+var builtinMap map[string]int
+
+func init() {
+	builtinMap = make(map[string]int, len(builtins))
+	for i, b := range builtins {
+		builtinMap[b.name] = i
+	}
+}

src/cmd/internal/goobj2/builtinlist.go

@@ -0,0 +1,194 @@
+// Code generated by mkbuiltin.go. DO NOT EDIT.
+
+package goobj2
+
+var builtins = [...]struct {
+	name string
+	abi  int
+}{
+	{"runtime.newobject", 1},
+	{"runtime.panicdivide", 1},
+	{"runtime.panicshift", 1},
+	{"runtime.panicmakeslicelen", 1},
+	{"runtime.throwinit", 1},
+	{"runtime.panicwrap", 1},
+	{"runtime.gopanic", 1},
+	{"runtime.gorecover", 1},
+	{"runtime.goschedguarded", 1},
+	{"runtime.goPanicIndex", 1},
+	{"runtime.goPanicIndexU", 1},
+	{"runtime.goPanicSliceAlen", 1},
+	{"runtime.goPanicSliceAlenU", 1},
+	{"runtime.goPanicSliceAcap", 1},
+	{"runtime.goPanicSliceAcapU", 1},
+	{"runtime.goPanicSliceB", 1},
+	{"runtime.goPanicSliceBU", 1},
+	{"runtime.goPanicSlice3Alen", 1},
+	{"runtime.goPanicSlice3AlenU", 1},
+	{"runtime.goPanicSlice3Acap", 1},
+	{"runtime.goPanicSlice3AcapU", 1},
+	{"runtime.goPanicSlice3B", 1},
+	{"runtime.goPanicSlice3BU", 1},
+	{"runtime.goPanicSlice3C", 1},
+	{"runtime.goPanicSlice3CU", 1},
+	{"runtime.printbool", 1},
+	{"runtime.printfloat", 1},
+	{"runtime.printint", 1},
+	{"runtime.printhex", 1},
+	{"runtime.printuint", 1},
+	{"runtime.printcomplex", 1},
+	{"runtime.printstring", 1},
+	{"runtime.printpointer", 1},
+	{"runtime.printiface", 1},
+	{"runtime.printeface", 1},
+	{"runtime.printslice", 1},
+	{"runtime.printnl", 1},
+	{"runtime.printsp", 1},
+	{"runtime.printlock", 1},
+	{"runtime.printunlock", 1},
+	{"runtime.concatstring2", 1},
+	{"runtime.concatstring3", 1},
+	{"runtime.concatstring4", 1},
+	{"runtime.concatstring5", 1},
+	{"runtime.concatstrings", 1},
+	{"runtime.cmpstring", 1},
+	{"runtime.intstring", 1},
+	{"runtime.slicebytetostring", 1},
+	{"runtime.slicebytetostringtmp", 1},
+	{"runtime.slicerunetostring", 1},
+	{"runtime.stringtoslicebyte", 1},
+	{"runtime.stringtoslicerune", 1},
+	{"runtime.slicecopy", 1},
+	{"runtime.slicestringcopy", 1},
+	{"runtime.decoderune", 1},
+	{"runtime.countrunes", 1},
+	{"runtime.convI2I", 1},
+	{"runtime.convT16", 1},
+	{"runtime.convT32", 1},
+	{"runtime.convT64", 1},
+	{"runtime.convTstring", 1},
+	{"runtime.convTslice", 1},
+	{"runtime.convT2E", 1},
+	{"runtime.convT2Enoptr", 1},
+	{"runtime.convT2I", 1},
+	{"runtime.convT2Inoptr", 1},
+	{"runtime.assertE2I", 1},
+	{"runtime.assertE2I2", 1},
+	{"runtime.assertI2I", 1},
+	{"runtime.assertI2I2", 1},
+	{"runtime.panicdottypeE", 1},
+	{"runtime.panicdottypeI", 1},
+	{"runtime.panicnildottype", 1},
+	{"runtime.ifaceeq", 1},
+	{"runtime.efaceeq", 1},
+	{"runtime.fastrand", 1},
+	{"runtime.makemap64", 1},
+	{"runtime.makemap", 1},
+	{"runtime.makemap_small", 1},
+	{"runtime.mapaccess1", 1},
+	{"runtime.mapaccess1_fast32", 1},
+	{"runtime.mapaccess1_fast64", 1},
+	{"runtime.mapaccess1_faststr", 1},
+	{"runtime.mapaccess1_fat", 1},
+	{"runtime.mapaccess2", 1},
+	{"runtime.mapaccess2_fast32", 1},
+	{"runtime.mapaccess2_fast64", 1},
+	{"runtime.mapaccess2_faststr", 1},
+	{"runtime.mapaccess2_fat", 1},
+	{"runtime.mapassign", 1},
+	{"runtime.mapassign_fast32", 1},
+	{"runtime.mapassign_fast32ptr", 1},
+	{"runtime.mapassign_fast64", 1},
+	{"runtime.mapassign_fast64ptr", 1},
+	{"runtime.mapassign_faststr", 1},
+	{"runtime.mapiterinit", 1},
+	{"runtime.mapdelete", 1},
+	{"runtime.mapdelete_fast32", 1},
+	{"runtime.mapdelete_fast64", 1},
+	{"runtime.mapdelete_faststr", 1},
+	{"runtime.mapiternext", 1},
+	{"runtime.mapclear", 1},
+	{"runtime.makechan64", 1},
+	{"runtime.makechan", 1},
+	{"runtime.chanrecv1", 1},
+	{"runtime.chanrecv2", 1},
+	{"runtime.chansend1", 1},
+	{"runtime.closechan", 1},
+	{"runtime.writeBarrier", 0},
+	{"runtime.typedmemmove", 1},
+	{"runtime.typedmemclr", 1},
+	{"runtime.typedslicecopy", 1},
+	{"runtime.selectnbsend", 1},
+	{"runtime.selectnbrecv", 1},
+	{"runtime.selectnbrecv2", 1},
+	{"runtime.selectsetpc", 1},
+	{"runtime.selectgo", 1},
+	{"runtime.block", 1},
+	{"runtime.makeslice", 1},
+	{"runtime.makeslice64", 1},
+	{"runtime.growslice", 1},
+	{"runtime.memmove", 1},
+	{"runtime.memclrNoHeapPointers", 1},
+	{"runtime.memclrHasPointers", 1},
+	{"runtime.memequal", 1},
+	{"runtime.memequal0", 1},
+	{"runtime.memequal8", 1},
+	{"runtime.memequal16", 1},
+	{"runtime.memequal32", 1},
+	{"runtime.memequal64", 1},
+	{"runtime.memequal128", 1},
+	{"runtime.f32equal", 1},
+	{"runtime.f64equal", 1},
+	{"runtime.c64equal", 1},
+	{"runtime.c128equal", 1},
+	{"runtime.strequal", 1},
+	{"runtime.interequal", 1},
+	{"runtime.nilinterequal", 1},
+	{"runtime.memhash", 1},
+	{"runtime.memhash0", 1},
+	{"runtime.memhash8", 1},
+	{"runtime.memhash16", 1},
+	{"runtime.memhash32", 1},
+	{"runtime.memhash64", 1},
+	{"runtime.memhash128", 1},
+	{"runtime.f32hash", 1},
+	{"runtime.f64hash", 1},
+	{"runtime.c64hash", 1},
+	{"runtime.c128hash", 1},
+	{"runtime.strhash", 1},
+	{"runtime.interhash", 1},
+	{"runtime.nilinterhash", 1},
+	{"runtime.int64div", 1},
+	{"runtime.uint64div", 1},
+	{"runtime.int64mod", 1},
+	{"runtime.uint64mod", 1},
+	{"runtime.float64toint64", 1},
+	{"runtime.float64touint64", 1},
+	{"runtime.float64touint32", 1},
+	{"runtime.int64tofloat64", 1},
+	{"runtime.uint64tofloat64", 1},
+	{"runtime.uint32tofloat64", 1},
+	{"runtime.complex128div", 1},
+	{"runtime.racefuncenter", 1},
+	{"runtime.racefuncenterfp", 1},
+	{"runtime.racefuncexit", 1},
+	{"runtime.raceread", 1},
+	{"runtime.racewrite", 1},
+	{"runtime.racereadrange", 1},
+	{"runtime.racewriterange", 1},
+	{"runtime.msanread", 1},
+	{"runtime.msanwrite", 1},
+	{"runtime.checkptrAlignment", 1},
+	{"runtime.checkptrArithmetic", 1},
+	{"runtime.x86HasPOPCNT", 0},
+	{"runtime.x86HasSSE41", 0},
+	{"runtime.arm64HasATOMICS", 0},
+	{"runtime.gcWriteBarrier", 0},
+	{"runtime.deferproc", 1},
+	{"runtime.deferprocStack", 1},
+	{"runtime.deferreturn", 1},
+	{"runtime.newproc", 1},
+	{"runtime.morestack", 0},
+	{"runtime.morestackc", 0},
+	{"runtime.morestack_noctxt", 0},
+}

src/cmd/internal/goobj2/funcinfo.go

@@ -0,0 +1,147 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package goobj2
+
+import (
+	"bytes"
+	"encoding/binary"
+)
+
+// FuncInfo is serialized as a symbol (aux symbol). The symbol data is
+// the binary encoding of the struct below.
+//
+// TODO: make each pcdata a separate symbol?
+type FuncInfo struct {
+	NoSplit uint8
+
+	Args   uint32
+	Locals uint32
+
+	Pcsp        uint32
+	Pcfile      uint32
+	Pcline      uint32
+	Pcinline    uint32
+	Pcdata      []uint32
+	PcdataEnd   uint32
+	Funcdataoff []uint32
+	File        []SymRef // TODO: just use string?
+
+	InlTree []InlTreeNode
+}
+
+func (a *FuncInfo) Write(w *bytes.Buffer) {
+	w.WriteByte(a.NoSplit)
+
+	var b [4]byte
+	writeUint32 := func(x uint32) {
+		binary.LittleEndian.PutUint32(b[:], x)
+		w.Write(b[:])
+	}
+
+	writeUint32(a.Args)
+	writeUint32(a.Locals)
+
+	writeUint32(a.Pcsp)
+	writeUint32(a.Pcfile)
+	writeUint32(a.Pcline)
+	writeUint32(a.Pcinline)
+	writeUint32(uint32(len(a.Pcdata)))
+	for _, x := range a.Pcdata {
+		writeUint32(x)
+	}
+	writeUint32(a.PcdataEnd)
+	writeUint32(uint32(len(a.Funcdataoff)))
+	for _, x := range a.Funcdataoff {
+		writeUint32(x)
+	}
+	writeUint32(uint32(len(a.File)))
+	for _, f := range a.File {
+		writeUint32(f.PkgIdx)
+		writeUint32(f.SymIdx)
+	}
+	writeUint32(uint32(len(a.InlTree)))
+	for i := range a.InlTree {
+		a.InlTree[i].Write(w)
+	}
+}
+
+func (a *FuncInfo) Read(b []byte) {
+	a.NoSplit = b[0]
+	b = b[1:]
+
+	readUint32 := func() uint32 {
+		x := binary.LittleEndian.Uint32(b)
+		b = b[4:]
+		return x
+	}
+
+	a.Args = readUint32()
+	a.Locals = readUint32()
+
+	a.Pcsp = readUint32()
+	a.Pcfile = readUint32()
+	a.Pcline = readUint32()
+	a.Pcinline = readUint32()
+	pcdatalen := readUint32()
+	a.Pcdata = make([]uint32, pcdatalen)
+	for i := range a.Pcdata {
+		a.Pcdata[i] = readUint32()
+	}
+	a.PcdataEnd = readUint32()
+	funcdataofflen := readUint32()
+	a.Funcdataoff = make([]uint32, funcdataofflen)
+	for i := range a.Funcdataoff {
+		a.Funcdataoff[i] = readUint32()
+	}
+	filelen := readUint32()
+	a.File = make([]SymRef, filelen)
+	for i := range a.File {
+		a.File[i] = SymRef{readUint32(), readUint32()}
+	}
+	inltreelen := readUint32()
+	a.InlTree = make([]InlTreeNode, inltreelen)
+	for i := range a.InlTree {
+		b = a.InlTree[i].Read(b)
+	}
+}
+
+// InlTreeNode is the serialized form of FileInfo.InlTree.
+type InlTreeNode struct {
+	Parent   int32
+	File     SymRef
+	Line     int32
+	Func     SymRef
+	ParentPC int32
+}
+
+func (inl *InlTreeNode) Write(w *bytes.Buffer) {
+	var b [4]byte
+	writeUint32 := func(x uint32) {
+		binary.LittleEndian.PutUint32(b[:], x)
+		w.Write(b[:])
+	}
+	writeUint32(uint32(inl.Parent))
+	writeUint32(inl.File.PkgIdx)
+	writeUint32(inl.File.SymIdx)
+	writeUint32(uint32(inl.Line))
+	writeUint32(inl.Func.PkgIdx)
+	writeUint32(inl.Func.SymIdx)
+	writeUint32(uint32(inl.ParentPC))
+}
+
+// Read an InlTreeNode from b, return the remaining bytes.
+func (inl *InlTreeNode) Read(b []byte) []byte {
+	readUint32 := func() uint32 {
+		x := binary.LittleEndian.Uint32(b)
+		b = b[4:]
+		return x
+	}
+	inl.Parent = int32(readUint32())
+	inl.File = SymRef{readUint32(), readUint32()}
+	inl.Line = int32(readUint32())
+	inl.Func = SymRef{readUint32(), readUint32()}
+	inl.ParentPC = int32(readUint32())
+	return b
+}

src/cmd/internal/goobj2/mkbuiltin.go

@@ -0,0 +1,124 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+// Generate builtinlist.go from cmd/compile/internal/gc/builtin/runtime.go.
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/format"
+	"go/parser"
+	"go/token"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+)
+
+var stdout = flag.Bool("stdout", false, "write to stdout instead of builtinlist.go")
+
+func main() {
+	flag.Parse()
+
+	var b bytes.Buffer
+	fmt.Fprintln(&b, "// Code generated by mkbuiltin.go. DO NOT EDIT.")
+	fmt.Fprintln(&b)
+	fmt.Fprintln(&b, "package goobj2")
+
+	mkbuiltin(&b)
+
+	out, err := format.Source(b.Bytes())
+	if err != nil {
+		log.Fatal(err)
+	}
+	if *stdout {
+		_, err = os.Stdout.Write(out)
+	} else {
+		err = ioutil.WriteFile("builtinlist.go", out, 0666)
+	}
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func mkbuiltin(w io.Writer) {
+	pkg := "runtime"
+	fset := token.NewFileSet()
+	path := filepath.Join("..", "..", "compile", "internal", "gc", "builtin", "runtime.go")
+	f, err := parser.ParseFile(fset, path, nil, 0)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	decls := make(map[string]bool)
+
+	fmt.Fprintf(w, "var builtins = [...]struct{ name string; abi int }{\n")
+	for _, decl := range f.Decls {
+		switch decl := decl.(type) {
+		case *ast.FuncDecl:
+			if decl.Recv != nil {
+				log.Fatal("methods unsupported")
+			}
+			if decl.Body != nil {
+				log.Fatal("unexpected function body")
+			}
+			declName := pkg + "." + decl.Name.Name
+			decls[declName] = true
+			fmt.Fprintf(w, "{%q, 1},\n", declName) // functions are ABIInternal (1)
+		case *ast.GenDecl:
+			if decl.Tok == token.IMPORT {
+				continue
+			}
+			if decl.Tok != token.VAR {
+				log.Fatal("unhandled declaration kind", decl.Tok)
+			}
+			for _, spec := range decl.Specs {
+				spec := spec.(*ast.ValueSpec)
+				if len(spec.Values) != 0 {
+					log.Fatal("unexpected values")
+				}
+				for _, name := range spec.Names {
+					declName := pkg + "." + name.Name
+					decls[declName] = true
+					fmt.Fprintf(w, "{%q, 0},\n", declName) // variables are ABI0
+				}
+			}
+		default:
+			log.Fatal("unhandled decl type", decl)
+		}
+	}
+
+	// The list above only contains ones that are used by the frontend.
+	// The backend may create more references of builtin functions.
+	// Add them.
+	for _, b := range extra {
+		name := pkg + "." + b.name
+		if decls[name] {
+			log.Fatalf("%q already added -- mkbuiltin.go out of sync?", name)
+		}
+		fmt.Fprintf(w, "{%q, %d},\n", name, b.abi)
+	}
+	fmt.Fprintln(w, "}")
+}
+
+var extra = [...]struct {
+	name string
+	abi  int
+}{
+	{"gcWriteBarrier", 0}, // asm function, ABI0
+	{"deferproc", 1},
+	{"deferprocStack", 1},
+	{"deferreturn", 1},
+	{"newproc", 1},
+	{"morestack", 0},        // asm function, ABI0
+	{"morestackc", 0},       // asm function, ABI0
+	{"morestack_noctxt", 0}, // asm function, ABI0
+}

src/cmd/internal/goobj2/objfile.go

@@ -0,0 +1,587 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Go new object file format, reading and writing.
+
+package goobj2 // TODO: replace the goobj package?
+
+import (
+	"bytes"
+	"cmd/internal/bio"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"unsafe"
+)
+
+// New object file format.
+//
+//    Header struct {
+//       Magic   [...]byte   // "\x00go114LD"
+//       Flags   uint32
+//       // TODO: Fingerprint
+//       Offsets [...]uint32 // byte offset of each block below
+//    }
+//
+//    Strings [...]struct {
+//       Len  uint32
+//       Data [...]byte
+//    }
+//
+//    Autolib  [...]stringOff // imported packages (for file loading) // TODO: add fingerprints
+//    PkgIndex [...]stringOff // referenced packages by index
+//
+//    DwarfFiles [...]stringOff
+//
+//    SymbolDefs [...]struct {
+//       Name stringOff
+//       ABI  uint16
+//       Type uint8
+//       Flag uint8
+//       Size uint32
+//    }
+//    NonPkgDefs [...]struct { // non-pkg symbol definitions
+//       ... // same as SymbolDefs
+//    }
+//    NonPkgRefs [...]struct { // non-pkg symbol references
+//       ... // same as SymbolDefs
+//    }
+//
+//    RelocIndex [...]uint32 // index to Relocs
+//    AuxIndex   [...]uint32 // index to Aux
+//    DataIndex  [...]uint32 // offset to Data
+//
+//    Relocs [...]struct {
+//       Off  int32
+//       Size uint8
+//       Type uint8
+//       Add  int64
+//       Sym  symRef
+//    }
+//
+//    Aux [...]struct {
+//       Type uint8
+//       Sym  symRef
+//    }
+//
+//    Data   [...]byte
+//    Pcdata [...]byte
+//
+// stringOff is a uint32 (?) offset that points to the corresponding
+// string, which is a uint32 length followed by that number of bytes.
+//
+// symRef is struct { PkgIdx, SymIdx uint32 }.
+//
+// Slice type (e.g. []symRef) is encoded as a length prefix (uint32)
+// followed by that number of elements.
+//
+// The types below correspond to the encoded data structure in the
+// object file.
+
+// Symbol indexing.
+//
+// Each symbol is referenced with a pair of indices, { PkgIdx, SymIdx },
+// as the symRef struct above.
+//
+// PkgIdx is either a predeclared index (see PkgIdxNone below) or
+// an index of an imported package. For the latter case, PkgIdx is the
+// index of the package in the PkgIndex array. 0 is an invalid index.
+//
+// SymIdx is the index of the symbol in the given package.
+// - If PkgIdx is PkgIdxSelf, SymIdx is the index of the symbol in the
+//   SymbolDefs array.
+// - If PkgIdx is PkgIdxNone, SymIdx is the index of the symbol in the
+//   NonPkgDefs array (could natually overflow to NonPkgRefs array).
+// - Otherwise, SymIdx is the index of the symbol in some other package's
+//   SymbolDefs array.
+//
+// {0, 0} represents a nil symbol. Otherwise PkgIdx should not be 0.
+//
+// RelocIndex, AuxIndex, and DataIndex contains indices/offsets to
+// Relocs/Aux/Data blocks, one element per symbol, first for all the
+// defined symbols, then all the defined non-package symbols, in the
+// same order of SymbolDefs/NonPkgDefs arrays. For N total defined
+// symbols, the array is of length N+1. The last element is the total
+// number of relocations (aux symbols, data blocks, etc.).
+//
+// They can be accessed by index. For the i-th symbol, its relocations
+// are the RelocIndex[i]-th (inclusive) to RelocIndex[i+1]-th (exclusive)
+// elements in the Relocs array. Aux/Data are likewise. (The index is
+// 0-based.)
+
+// Auxiliary symbols.
+//
+// Each symbol may (or may not) be associated with a number of auxiliary
+// symbols. They are described in the Aux block. See Aux struct below.
+// Currently a symbol's Gotype and FuncInfo are auxiliary symbols. We
+// may make use of aux symbols in more cases, e.g. DWARF symbols.
+
+// Package Index.
+const (
+	PkgIdxNone    = (1<<31 - 1) - iota // Non-package symbols
+	PkgIdxBuiltin                      // Predefined symbols // TODO: not used for now, we could use it for compiler-generated symbols like runtime.newobject
+	PkgIdxSelf                         // Symbols defined in the current package
+	PkgIdxInvalid = 0
+	// The index of other referenced packages starts from 1.
+)
+
+// Blocks
+const (
+	BlkAutolib = iota
+	BlkPkgIdx
+	BlkDwarfFile
+	BlkSymdef
+	BlkNonpkgdef
+	BlkNonpkgref
+	BlkRelocIdx
+	BlkAuxIdx
+	BlkDataIdx
+	BlkReloc
+	BlkAux
+	BlkData
+	BlkPcdata
+	NBlk
+)
+
+// File header.
+// TODO: probably no need to export this.
+type Header struct {
+	Magic   string
+	Flags   uint32
+	Offsets [NBlk]uint32
+}
+
+const Magic = "\x00go114LD"
+
+func (h *Header) Write(w *Writer) {
+	w.RawString(h.Magic)
+	w.Uint32(h.Flags)
+	for _, x := range h.Offsets {
+		w.Uint32(x)
+	}
+}
+
+func (h *Header) Read(r *Reader) error {
+	b := r.BytesAt(0, len(Magic))
+	h.Magic = string(b)
+	if h.Magic != Magic {
+		return errors.New("wrong magic, not a Go object file")
+	}
+	off := uint32(len(h.Magic))
+	h.Flags = r.uint32At(off)
+	off += 4
+	for i := range h.Offsets {
+		h.Offsets[i] = r.uint32At(off)
+		off += 4
+	}
+	return nil
+}
+
+func (h *Header) Size() int {
+	return len(h.Magic) + 4 + 4*len(h.Offsets)
+}
+
+// Symbol definition.
+type Sym struct {
+	Name string
+	ABI  uint16
+	Type uint8
+	Flag uint8
+	Siz  uint32
+}
+
+const SymABIstatic = ^uint16(0)
+
+const (
+	ObjFlagShared = 1 << iota
+)
+
+const (
+	SymFlagDupok = 1 << iota
+	SymFlagLocal
+	SymFlagTypelink
+	SymFlagLeaf
+	SymFlagCFunc
+	SymFlagReflectMethod
+	SymFlagGoType
+	SymFlagTopFrame
+)
+
+func (s *Sym) Write(w *Writer) {
+	w.StringRef(s.Name)
+	w.Uint16(s.ABI)
+	w.Uint8(s.Type)
+	w.Uint8(s.Flag)
+	w.Uint32(s.Siz)
+}
+
+func (s *Sym) Read(r *Reader, off uint32) {
+	s.Name = r.StringRef(off)
+	s.ABI = r.uint16At(off + 4)
+	s.Type = r.uint8At(off + 6)
+	s.Flag = r.uint8At(off + 7)
+	s.Siz = r.uint32At(off + 8)
+}
+
+func (s *Sym) Size() int {
+	return 4 + 2 + 1 + 1 + 4
+}
+
+func (s *Sym) Dupok() bool         { return s.Flag&SymFlagDupok != 0 }
+func (s *Sym) Local() bool         { return s.Flag&SymFlagLocal != 0 }
+func (s *Sym) Typelink() bool      { return s.Flag&SymFlagTypelink != 0 }
+func (s *Sym) Leaf() bool          { return s.Flag&SymFlagLeaf != 0 }
+func (s *Sym) CFunc() bool         { return s.Flag&SymFlagCFunc != 0 }
+func (s *Sym) ReflectMethod() bool { return s.Flag&SymFlagReflectMethod != 0 }
+func (s *Sym) IsGoType() bool      { return s.Flag&SymFlagGoType != 0 }
+func (s *Sym) TopFrame() bool      { return s.Flag&SymFlagTopFrame != 0 }
+
+// Symbol reference.
+type SymRef struct {
+	PkgIdx uint32
+	SymIdx uint32
+}
+
+func (s *SymRef) Write(w *Writer) {
+	w.Uint32(s.PkgIdx)
+	w.Uint32(s.SymIdx)
+}
+
+func (s *SymRef) Read(r *Reader, off uint32) {
+	s.PkgIdx = r.uint32At(off)
+	s.SymIdx = r.uint32At(off + 4)
+}
+
+func (s *SymRef) Size() int {
+	return 4 + 4
+}
+
+// Relocation.
+type Reloc struct {
+	Off  int32
+	Siz  uint8
+	Type uint8
+	Add  int64
+	Sym  SymRef
+}
+
+func (r *Reloc) Write(w *Writer) {
+	w.Uint32(uint32(r.Off))
+	w.Uint8(r.Siz)
+	w.Uint8(r.Type)
+	w.Uint64(uint64(r.Add))
+	r.Sym.Write(w)
+}
+
+func (o *Reloc) Read(r *Reader, off uint32) {
+	o.Off = r.int32At(off)
+	o.Siz = r.uint8At(off + 4)
+	o.Type = r.uint8At(off + 5)
+	o.Add = r.int64At(off + 6)
+	o.Sym.Read(r, off+14)
+}
+
+func (r *Reloc) Size() int {
+	return 4 + 1 + 1 + 8 + r.Sym.Size()
+}
+
+// Aux symbol info.
+type Aux struct {
+	Type uint8
+	Sym  SymRef
+}
+
+// Aux Type
+const (
+	AuxGotype = iota
+	AuxFuncInfo
+	AuxFuncdata
+	AuxDwarfInfo
+	AuxDwarfLoc
+	AuxDwarfRanges
+	AuxDwarfLines
+
+	// TODO: more. Pcdata?
+)
+
+func (a *Aux) Write(w *Writer) {
+	w.Uint8(a.Type)
+	a.Sym.Write(w)
+}
+
+func (a *Aux) Read(r *Reader, off uint32) {
+	a.Type = r.uint8At(off)
+	a.Sym.Read(r, off+1)
+}
+
+func (a *Aux) Size() int {
+	return 1 + a.Sym.Size()
+}
+
+type Writer struct {
+	wr        *bio.Writer
+	stringMap map[string]uint32
+	off       uint32 // running offset
+}
+
+func NewWriter(wr *bio.Writer) *Writer {
+	return &Writer{wr: wr, stringMap: make(map[string]uint32)}
+}
+
+func (w *Writer) AddString(s string) {
+	if _, ok := w.stringMap[s]; ok {
+		return
+	}
+	w.stringMap[s] = w.off
+	w.Uint32(uint32(len(s)))
+	w.RawString(s)
+}
+
+func (w *Writer) StringRef(s string) {
+	off, ok := w.stringMap[s]
+	if !ok {
+		panic(fmt.Sprintf("writeStringRef: string not added: %q", s))
+	}
+	w.Uint32(off)
+}
+
+func (w *Writer) RawString(s string) {
+	w.wr.WriteString(s)
+	w.off += uint32(len(s))
+}
+
+func (w *Writer) Bytes(s []byte) {
+	w.wr.Write(s)
+	w.off += uint32(len(s))
+}
+
+func (w *Writer) Uint64(x uint64) {
+	var b [8]byte
+	binary.LittleEndian.PutUint64(b[:], x)
+	w.wr.Write(b[:])
+	w.off += 8
+}
+
+func (w *Writer) Uint32(x uint32) {
+	var b [4]byte
+	binary.LittleEndian.PutUint32(b[:], x)
+	w.wr.Write(b[:])
+	w.off += 4
+}
+
+func (w *Writer) Uint16(x uint16) {
+	var b [2]byte
+	binary.LittleEndian.PutUint16(b[:], x)
+	w.wr.Write(b[:])
+	w.off += 2
+}
+
+func (w *Writer) Uint8(x uint8) {
+	w.wr.WriteByte(x)
+	w.off++
+}
+
+func (w *Writer) Offset() uint32 {
+	return w.off
+}
+
+type Reader struct {
+	b        []byte // mmapped bytes, if not nil
+	readonly bool   // whether b is backed with read-only memory
+
+	rd    io.ReaderAt
+	start uint32
+	h     Header // keep block offsets
+}
+
+func NewReaderFromBytes(b []byte, readonly bool) *Reader {
+	r := &Reader{b: b, readonly: readonly, rd: bytes.NewReader(b), start: 0}
+	err := r.h.Read(r)
+	if err != nil {
+		return nil
+	}
+	return r
+}
+
+func (r *Reader) BytesAt(off uint32, len int) []byte {
+	if len == 0 {
+		return nil
+	}
+	end := int(off) + len
+	return r.b[int(off):end:end]
+}
+
+func (r *Reader) uint64At(off uint32) uint64 {
+	b := r.BytesAt(off, 8)
+	return binary.LittleEndian.Uint64(b)
+}
+
+func (r *Reader) int64At(off uint32) int64 {
+	return int64(r.uint64At(off))
+}
+
+func (r *Reader) uint32At(off uint32) uint32 {
+	b := r.BytesAt(off, 4)
+	return binary.LittleEndian.Uint32(b)
+}
+
+func (r *Reader) int32At(off uint32) int32 {
+	return int32(r.uint32At(off))
+}
+
+func (r *Reader) uint16At(off uint32) uint16 {
+	b := r.BytesAt(off, 2)
+	return binary.LittleEndian.Uint16(b)
+}
+
+func (r *Reader) uint8At(off uint32) uint8 {
+	b := r.BytesAt(off, 1)
+	return b[0]
+}
+
+func (r *Reader) StringAt(off uint32) string {
+	l := r.uint32At(off)
+	b := r.b[off+4 : off+4+l]
+	if r.readonly {
+		return toString(b) // backed by RO memory, ok to make unsafe string
+	}
+	return string(b)
+}
+
+func toString(b []byte) string {
+	type stringHeader struct {
+		str unsafe.Pointer
+		len int
+	}
+
+	if len(b) == 0 {
+		return ""
+	}
+	ss := stringHeader{str: unsafe.Pointer(&b[0]), len: len(b)}
+	s := *(*string)(unsafe.Pointer(&ss))
+	return s
+}
+
+func (r *Reader) StringRef(off uint32) string {
+	return r.StringAt(r.uint32At(off))
+}
+
+func (r *Reader) Autolib() []string {
+	n := (r.h.Offsets[BlkAutolib+1] - r.h.Offsets[BlkAutolib]) / 4
+	s := make([]string, n)
+	for i := range s {
+		off := r.h.Offsets[BlkAutolib] + uint32(i)*4
+		s[i] = r.StringRef(off)
+	}
+	return s
+}
+
+func (r *Reader) Pkglist() []string {
+	n := (r.h.Offsets[BlkPkgIdx+1] - r.h.Offsets[BlkPkgIdx]) / 4
+	s := make([]string, n)
+	for i := range s {
+		off := r.h.Offsets[BlkPkgIdx] + uint32(i)*4
+		s[i] = r.StringRef(off)
+	}
+	return s
+}
+
+func (r *Reader) NPkg() int {
+	return int(r.h.Offsets[BlkPkgIdx+1]-r.h.Offsets[BlkPkgIdx]) / 4
+}
+
+func (r *Reader) Pkg(i int) string {
+	off := r.h.Offsets[BlkPkgIdx] + uint32(i)*4
+	return r.StringRef(off)
+}
+
+func (r *Reader) NDwarfFile() int {
+	return int(r.h.Offsets[BlkDwarfFile+1]-r.h.Offsets[BlkDwarfFile]) / 4
+}
+
+func (r *Reader) DwarfFile(i int) string {
+	off := r.h.Offsets[BlkDwarfFile] + uint32(i)*4
+	return r.StringRef(off)
+}
+
+func (r *Reader) NSym() int {
+	symsiz := (&Sym{}).Size()
+	return int(r.h.Offsets[BlkSymdef+1]-r.h.Offsets[BlkSymdef]) / symsiz
+}
+
+func (r *Reader) NNonpkgdef() int {
+	symsiz := (&Sym{}).Size()
+	return int(r.h.Offsets[BlkNonpkgdef+1]-r.h.Offsets[BlkNonpkgdef]) / symsiz
+}
+
+func (r *Reader) NNonpkgref() int {
+	symsiz := (&Sym{}).Size()
+	return int(r.h.Offsets[BlkNonpkgref+1]-r.h.Offsets[BlkNonpkgref]) / symsiz
+}
+
+// SymOff returns the offset of the i-th symbol.
+func (r *Reader) SymOff(i int) uint32 {
+	symsiz := (&Sym{}).Size()
+	return r.h.Offsets[BlkSymdef] + uint32(i*symsiz)
+}
+
+// NReloc returns the number of relocations of the i-th symbol.
+func (r *Reader) NReloc(i int) int {
+	relocIdxOff := r.h.Offsets[BlkRelocIdx] + uint32(i*4)
+	return int(r.uint32At(relocIdxOff+4) - r.uint32At(relocIdxOff))
+}
+
+// RelocOff returns the offset of the j-th relocation of the i-th symbol.
+func (r *Reader) RelocOff(i int, j int) uint32 {
+	relocIdxOff := r.h.Offsets[BlkRelocIdx] + uint32(i*4)
+	relocIdx := r.uint32At(relocIdxOff)
+	relocsiz := (&Reloc{}).Size()
+	return r.h.Offsets[BlkReloc] + (relocIdx+uint32(j))*uint32(relocsiz)
+}
+
+// NAux returns the number of aux symbols of the i-th symbol.
+func (r *Reader) NAux(i int) int {
+	auxIdxOff := r.h.Offsets[BlkAuxIdx] + uint32(i*4)
+	return int(r.uint32At(auxIdxOff+4) - r.uint32At(auxIdxOff))
+}
+
+// AuxOff returns the offset of the j-th aux symbol of the i-th symbol.
+func (r *Reader) AuxOff(i int, j int) uint32 {
+	auxIdxOff := r.h.Offsets[BlkAuxIdx] + uint32(i*4)
+	auxIdx := r.uint32At(auxIdxOff)
+	auxsiz := (&Aux{}).Size()
+	return r.h.Offsets[BlkAux] + (auxIdx+uint32(j))*uint32(auxsiz)
+}
+
+// DataOff returns the offset of the i-th symbol's data.
+func (r *Reader) DataOff(i int) uint32 {
+	dataIdxOff := r.h.Offsets[BlkDataIdx] + uint32(i*4)
+	return r.h.Offsets[BlkData] + r.uint32At(dataIdxOff)
+}
+
+// DataSize returns the size of the i-th symbol's data.
+func (r *Reader) DataSize(i int) int {
+	return int(r.DataOff(i+1) - r.DataOff(i))
+}
+
+// Data returns the i-th symbol's data.
+func (r *Reader) Data(i int) []byte {
+	return r.BytesAt(r.DataOff(i), r.DataSize(i))
+}
+
+// AuxDataBase returns the base offset of the aux data block.
+func (r *Reader) PcdataBase() uint32 {
+	return r.h.Offsets[BlkPcdata]
+}
+
+// ReadOnly returns whether r.BytesAt returns read-only bytes.
+func (r *Reader) ReadOnly() bool {
+	return r.readonly
+}
+
+// Flags returns the flag bits read from the object file header.
+func (r *Reader) Flags() uint32 {
+	return r.h.Flags
+}

src/cmd/internal/obj/link.go

@@ -388,6 +388,10 @@ type LSym struct {
 	R      []Reloc
 
 	Func *FuncInfo
+
+	Pkg    string
+	PkgIdx int32
+	SymIdx int32 // TODO: replace RefIdx
 }
 
 // A FuncInfo contains extra fields for STEXT symbols.
@@ -410,6 +414,8 @@ type FuncInfo struct {
 	GCRegs             *LSym
 	StackObjects       *LSym
 	OpenCodedDeferInfo *LSym
+
+	FuncInfoSym *LSym
 }
 
 type InlMark struct {
@@ -461,7 +467,7 @@ const (
 )
 
 // Attribute is a set of symbol attributes.
-type Attribute uint16
+type Attribute uint32
 
 const (
 	AttrDuplicateOK Attribute = 1 << iota
@@ -502,6 +508,10 @@ const (
 	// keep unwinding beyond this frame.
 	AttrTopFrame
 
+	// Indexed indicates this symbol has been assigned with an index (when using the
+	// new object file format).
+	AttrIndexed
+
 	// attrABIBase is the value at which the ABI is encoded in
 	// Attribute. This must be last; all bits after this are
 	// assumed to be an ABI value.
@@ -525,6 +535,7 @@ func (a Attribute) NoFrame() bool       { return a&AttrNoFrame != 0 }
 func (a Attribute) Static() bool        { return a&AttrStatic != 0 }
 func (a Attribute) WasInlined() bool    { return a&AttrWasInlined != 0 }
 func (a Attribute) TopFrame() bool      { return a&AttrTopFrame != 0 }
+func (a Attribute) Indexed() bool       { return a&AttrIndexed != 0 }
 
 func (a *Attribute) Set(flag Attribute, value bool) {
 	if value {
@@ -559,6 +570,7 @@ var textAttrStrings = [...]struct {
 	{bit: AttrStatic, s: "STATIC"},
 	{bit: AttrWasInlined, s: ""},
 	{bit: AttrTopFrame, s: "TOPFRAME"},
+	{bit: AttrIndexed, s: ""},
 }
 
 // TextAttrString formats a for printing in as part of a TEXT prog.
@@ -637,8 +649,10 @@ type Link struct {
 	Debugpcln          string
 	Flag_shared        bool
 	Flag_dynlink       bool
+	Flag_linkshared    bool
 	Flag_optimize      bool
 	Flag_locationlists bool
+	Flag_newobj        bool // use new object file format
 	Bso                *bufio.Writer
 	Pathname           string
 	hashmu             sync.Mutex       // protects hash, funchash
@@ -672,6 +686,14 @@ type Link struct {
 	// TODO(austin): Replace this with ABI wrappers once the ABIs
 	// actually diverge.
 	ABIAliases []*LSym
+
+	// pkgIdx maps package path to index. The index is used for
+	// symbol reference in the object file.
+	pkgIdx map[string]int32
+
+	defs       []*LSym // list of defined symbols in the current package
+	nonpkgdefs []*LSym // list of defined non-package symbols
+	nonpkgrefs []*LSym // list of referenced non-package symbols
 }
 
 func (ctxt *Link) Diag(format string, args ...interface{}) {

src/cmd/internal/obj/objfile.go

@@ -8,6 +8,7 @@ package obj
 
 import (
 	"bufio"
+	"cmd/internal/bio"
 	"cmd/internal/dwarf"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
@@ -80,7 +81,13 @@ func newObjWriter(ctxt *Link, b *bufio.Writer, pkgpath string) *objWriter {
 	}
 }
 
-func WriteObjFile(ctxt *Link, b *bufio.Writer, pkgpath string) {
+func WriteObjFile(ctxt *Link, bout *bio.Writer, pkgpath string) {
+	if ctxt.Flag_newobj {
+		WriteObjFile2(ctxt, bout, pkgpath)
+		return
+	}
+
+	b := bout.Writer
 	w := newObjWriter(ctxt, b, pkgpath)
 
 	// Magic header
@@ -221,8 +228,7 @@ func (w *objWriter) writeRefs(s *LSym) {
 	}
 }
 
-func (w *objWriter) writeSymDebug(s *LSym) {
-	ctxt := w.ctxt
+func (ctxt *Link) writeSymDebug(s *LSym) {
 	fmt.Fprintf(ctxt.Bso, "%s ", s.Name)
 	if s.Type != 0 {
 		fmt.Fprintf(ctxt.Bso, "%v ", s.Type)
@@ -302,7 +308,7 @@ func (w *objWriter) writeSymDebug(s *LSym) {
 func (w *objWriter) writeSym(s *LSym) {
 	ctxt := w.ctxt
 	if ctxt.Debugasm > 0 {
-		w.writeSymDebug(s)
+		w.ctxt.writeSymDebug(s)
 	}
 
 	w.wr.WriteByte(symPrefix)

src/cmd/internal/obj/objfile2.go

@@ -0,0 +1,429 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Writing Go object files.
+
+package obj
+
+import (
+	"bytes"
+	"cmd/internal/bio"
+	"cmd/internal/goobj2"
+	"cmd/internal/objabi"
+	"fmt"
+	"path/filepath"
+	"strings"
+)
+
+// Entry point of writing new object file.
+func WriteObjFile2(ctxt *Link, b *bio.Writer, pkgpath string) {
+	if ctxt.Debugasm > 0 {
+		ctxt.traverseSyms(traverseDefs, ctxt.writeSymDebug)
+	}
+
+	genFuncInfoSyms(ctxt)
+
+	w := writer{
+		Writer:  goobj2.NewWriter(b),
+		ctxt:    ctxt,
+		pkgpath: objabi.PathToPrefix(pkgpath),
+	}
+
+	start := b.Offset()
+	w.init()
+
+	// Header
+	// We just reserve the space. We'll fill in the offsets later.
+	flags := uint32(0)
+	if ctxt.Flag_shared {
+		flags |= goobj2.ObjFlagShared
+	}
+	h := goobj2.Header{Magic: goobj2.Magic, Flags: flags}
+	h.Write(w.Writer)
+
+	// String table
+	w.StringTable()
+
+	// Autolib
+	h.Offsets[goobj2.BlkAutolib] = w.Offset()
+	for _, pkg := range ctxt.Imports {
+		w.StringRef(pkg)
+	}
+
+	// Package references
+	h.Offsets[goobj2.BlkPkgIdx] = w.Offset()
+	for _, pkg := range w.pkglist {
+		w.StringRef(pkg)
+	}
+
+	// DWARF file table
+	h.Offsets[goobj2.BlkDwarfFile] = w.Offset()
+	for _, f := range ctxt.PosTable.DebugLinesFileTable() {
+		w.StringRef(f)
+	}
+
+	// Symbol definitions
+	h.Offsets[goobj2.BlkSymdef] = w.Offset()
+	for _, s := range ctxt.defs {
+		w.Sym(s)
+	}
+
+	// Non-pkg symbol definitions
+	h.Offsets[goobj2.BlkNonpkgdef] = w.Offset()
+	for _, s := range ctxt.nonpkgdefs {
+		w.Sym(s)
+	}
+
+	// Non-pkg symbol references
+	h.Offsets[goobj2.BlkNonpkgref] = w.Offset()
+	for _, s := range ctxt.nonpkgrefs {
+		w.Sym(s)
+	}
+
+	// Reloc indexes
+	h.Offsets[goobj2.BlkRelocIdx] = w.Offset()
+	nreloc := uint32(0)
+	lists := [][]*LSym{ctxt.defs, ctxt.nonpkgdefs}
+	for _, list := range lists {
+		for _, s := range list {
+			w.Uint32(nreloc)
+			nreloc += uint32(len(s.R))
+		}
+	}
+	w.Uint32(nreloc)
+
+	// Symbol Info indexes
+	h.Offsets[goobj2.BlkAuxIdx] = w.Offset()
+	naux := uint32(0)
+	for _, list := range lists {
+		for _, s := range list {
+			w.Uint32(naux)
+			naux += uint32(nAuxSym(s))
+		}
+	}
+	w.Uint32(naux)
+
+	// Data indexes
+	h.Offsets[goobj2.BlkDataIdx] = w.Offset()
+	dataOff := uint32(0)
+	for _, list := range lists {
+		for _, s := range list {
+			w.Uint32(dataOff)
+			dataOff += uint32(len(s.P))
+		}
+	}
+	w.Uint32(dataOff)
+
+	// Relocs
+	h.Offsets[goobj2.BlkReloc] = w.Offset()
+	for _, list := range lists {
+		for _, s := range list {
+			for i := range s.R {
+				w.Reloc(&s.R[i])
+			}
+		}
+	}
+
+	// Aux symbol info
+	h.Offsets[goobj2.BlkAux] = w.Offset()
+	for _, list := range lists {
+		for _, s := range list {
+			w.Aux(s)
+		}
+	}
+
+	// Data
+	h.Offsets[goobj2.BlkData] = w.Offset()
+	for _, list := range lists {
+		for _, s := range list {
+			w.Bytes(s.P)
+		}
+	}
+
+	// Pcdata
+	h.Offsets[goobj2.BlkPcdata] = w.Offset()
+	for _, s := range ctxt.Text { // iteration order must match genFuncInfoSyms
+		if s.Func != nil {
+			pc := &s.Func.Pcln
+			w.Bytes(pc.Pcsp.P)
+			w.Bytes(pc.Pcfile.P)
+			w.Bytes(pc.Pcline.P)
+			w.Bytes(pc.Pcinline.P)
+			for i := range pc.Pcdata {
+				w.Bytes(pc.Pcdata[i].P)
+			}
+		}
+	}
+
+	// Fix up block offsets in the header
+	end := start + int64(w.Offset())
+	b.MustSeek(start, 0)
+	h.Write(w.Writer)
+	b.MustSeek(end, 0)
+}
+
+type writer struct {
+	*goobj2.Writer
+	ctxt    *Link
+	pkgpath string   // the package import path (escaped), "" if unknown
+	pkglist []string // list of packages referenced, indexed by ctxt.pkgIdx
+}
+
+// prepare package index list
+func (w *writer) init() {
+	w.pkglist = make([]string, len(w.ctxt.pkgIdx)+1)
+	w.pkglist[0] = "" // dummy invalid package for index 0
+	for pkg, i := range w.ctxt.pkgIdx {
+		w.pkglist[i] = pkg
+	}
+}
+
+func (w *writer) StringTable() {
+	w.AddString("")
+	for _, pkg := range w.ctxt.Imports {
+		w.AddString(pkg)
+	}
+	for _, pkg := range w.pkglist {
+		w.AddString(pkg)
+	}
+	w.ctxt.traverseSyms(traverseAll, func(s *LSym) {
+		if w.pkgpath != "" {
+			s.Name = strings.Replace(s.Name, "\"\".", w.pkgpath+".", -1)
+		}
+		w.AddString(s.Name)
+	})
+	w.ctxt.traverseSyms(traverseDefs, func(s *LSym) {
+		if s.Type != objabi.STEXT {
+			return
+		}
+		pc := &s.Func.Pcln
+		for _, f := range pc.File {
+			w.AddString(filepath.ToSlash(f))
+		}
+		for _, call := range pc.InlTree.nodes {
+			f, _ := linkgetlineFromPos(w.ctxt, call.Pos)
+			w.AddString(filepath.ToSlash(f))
+		}
+	})
+	for _, f := range w.ctxt.PosTable.DebugLinesFileTable() {
+		w.AddString(f)
+	}
+}
+
+func (w *writer) Sym(s *LSym) {
+	abi := uint16(s.ABI())
+	if s.Static() {
+		abi = goobj2.SymABIstatic
+	}
+	flag := uint8(0)
+	if s.DuplicateOK() {
+		flag |= goobj2.SymFlagDupok
+	}
+	if s.Local() {
+		flag |= goobj2.SymFlagLocal
+	}
+	if s.MakeTypelink() {
+		flag |= goobj2.SymFlagTypelink
+	}
+	if s.Leaf() {
+		flag |= goobj2.SymFlagLeaf
+	}
+	if s.CFunc() {
+		flag |= goobj2.SymFlagCFunc
+	}
+	if s.ReflectMethod() {
+		flag |= goobj2.SymFlagReflectMethod
+	}
+	if s.TopFrame() {
+		flag |= goobj2.SymFlagTopFrame
+	}
+	if strings.HasPrefix(s.Name, "type.") && s.Name[5] != '.' && s.Type == objabi.SRODATA {
+		flag |= goobj2.SymFlagGoType
+	}
+	name := s.Name
+	if strings.HasPrefix(name, "gofile..") {
+		name = filepath.ToSlash(name)
+	}
+	o := goobj2.Sym{
+		Name: name,
+		ABI:  abi,
+		Type: uint8(s.Type),
+		Flag: flag,
+		Siz:  uint32(s.Size),
+	}
+	o.Write(w.Writer)
+}
+
+func makeSymRef(s *LSym) goobj2.SymRef {
+	if s == nil {
+		return goobj2.SymRef{}
+	}
+	if s.PkgIdx == 0 || !s.Indexed() {
+		fmt.Printf("unindexed symbol reference: %v\n", s)
+		panic("unindexed symbol reference")
+	}
+	return goobj2.SymRef{PkgIdx: uint32(s.PkgIdx), SymIdx: uint32(s.SymIdx)}
+}
+
+func (w *writer) Reloc(r *Reloc) {
+	o := goobj2.Reloc{
+		Off:  r.Off,
+		Siz:  r.Siz,
+		Type: uint8(r.Type),
+		Add:  r.Add,
+		Sym:  makeSymRef(r.Sym),
+	}
+	o.Write(w.Writer)
+}
+
+func (w *writer) Aux(s *LSym) {
+	if s.Gotype != nil {
+		o := goobj2.Aux{
+			Type: goobj2.AuxGotype,
+			Sym:  makeSymRef(s.Gotype),
+		}
+		o.Write(w.Writer)
+	}
+	if s.Func != nil {
+		o := goobj2.Aux{
+			Type: goobj2.AuxFuncInfo,
+			Sym:  makeSymRef(s.Func.FuncInfoSym),
+		}
+		o.Write(w.Writer)
+
+		for _, d := range s.Func.Pcln.Funcdata {
+			o := goobj2.Aux{
+				Type: goobj2.AuxFuncdata,
+				Sym:  makeSymRef(d),
+			}
+			o.Write(w.Writer)
+		}
+
+		if s.Func.dwarfInfoSym != nil {
+			o := goobj2.Aux{
+				Type: goobj2.AuxDwarfInfo,
+				Sym:  makeSymRef(s.Func.dwarfInfoSym),
+			}
+			o.Write(w.Writer)
+		}
+		if s.Func.dwarfLocSym != nil {
+			o := goobj2.Aux{
+				Type: goobj2.AuxDwarfLoc,
+				Sym:  makeSymRef(s.Func.dwarfLocSym),
+			}
+			o.Write(w.Writer)
+		}
+		if s.Func.dwarfRangesSym != nil {
+			o := goobj2.Aux{
+				Type: goobj2.AuxDwarfRanges,
+				Sym:  makeSymRef(s.Func.dwarfRangesSym),
+			}
+			o.Write(w.Writer)
+		}
+		if s.Func.dwarfDebugLinesSym != nil {
+			o := goobj2.Aux{
+				Type: goobj2.AuxDwarfLines,
+				Sym:  makeSymRef(s.Func.dwarfDebugLinesSym),
+			}
+			o.Write(w.Writer)
+		}
+	}
+}
+
+// return the number of aux symbols s have.
+func nAuxSym(s *LSym) int {
+	n := 0
+	if s.Gotype != nil {
+		n++
+	}
+	if s.Func != nil {
+		// FuncInfo is an aux symbol, each Funcdata is an aux symbol
+		n += 1 + len(s.Func.Pcln.Funcdata)
+		if s.Func.dwarfInfoSym != nil {
+			n++
+		}
+		if s.Func.dwarfLocSym != nil {
+			n++
+		}
+		if s.Func.dwarfRangesSym != nil {
+			n++
+		}
+		if s.Func.dwarfDebugLinesSym != nil {
+			n++
+		}
+	}
+	return n
+}
+
+// generate symbols for FuncInfo.
+func genFuncInfoSyms(ctxt *Link) {
+	infosyms := make([]*LSym, 0, len(ctxt.Text))
+	var pcdataoff uint32
+	var b bytes.Buffer
+	symidx := int32(len(ctxt.defs))
+	for _, s := range ctxt.Text {
+		if s.Func == nil {
+			continue
+		}
+		nosplit := uint8(0)
+		if s.NoSplit() {
+			nosplit = 1
+		}
+		o := goobj2.FuncInfo{
+			NoSplit: nosplit,
+			Args:    uint32(s.Func.Args),
+			Locals:  uint32(s.Func.Locals),
+		}
+		pc := &s.Func.Pcln
+		o.Pcsp = pcdataoff
+		pcdataoff += uint32(len(pc.Pcsp.P))
+		o.Pcfile = pcdataoff
+		pcdataoff += uint32(len(pc.Pcfile.P))
+		o.Pcline = pcdataoff
+		pcdataoff += uint32(len(pc.Pcline.P))
+		o.Pcinline = pcdataoff
+		pcdataoff += uint32(len(pc.Pcinline.P))
+		o.Pcdata = make([]uint32, len(pc.Pcdata))
+		for i, pcd := range pc.Pcdata {
+			o.Pcdata[i] = pcdataoff
+			pcdataoff += uint32(len(pcd.P))
+		}
+		o.PcdataEnd = pcdataoff
+		o.Funcdataoff = make([]uint32, len(pc.Funcdataoff))
+		for i, x := range pc.Funcdataoff {
+			o.Funcdataoff[i] = uint32(x)
+		}
+		o.File = make([]goobj2.SymRef, len(pc.File))
+		for i, f := range pc.File {
+			fsym := ctxt.Lookup(f)
+			o.File[i] = makeSymRef(fsym)
+		}
+		o.InlTree = make([]goobj2.InlTreeNode, len(pc.InlTree.nodes))
+		for i, inl := range pc.InlTree.nodes {
+			f, l := linkgetlineFromPos(ctxt, inl.Pos)
+			fsym := ctxt.Lookup(f)
+			o.InlTree[i] = goobj2.InlTreeNode{
+				Parent:   int32(inl.Parent),
+				File:     makeSymRef(fsym),
+				Line:     l,
+				Func:     makeSymRef(inl.Func),
+				ParentPC: inl.ParentPC,
+			}
+		}
+
+		o.Write(&b)
+		isym := &LSym{
+			Type:   objabi.SDATA, // for now, I don't think it matters
+			PkgIdx: goobj2.PkgIdxSelf,
+			SymIdx: symidx,
+			P:      append([]byte(nil), b.Bytes()...),
+		}
+		isym.Set(AttrIndexed, true)
+		symidx++
+		infosyms = append(infosyms, isym)
+		s.Func.FuncInfoSym = isym
+		b.Reset()
+	}
+	ctxt.defs = append(ctxt.defs, infosyms...)
+}

src/cmd/internal/obj/sizeof_test.go

@@ -21,7 +21,7 @@ func TestSizeof(t *testing.T) {
 		_64bit uintptr     // size on 64bit platforms
 	}{
 		{Addr{}, 32, 48},
-		{LSym{}, 56, 104},
+		{LSym{}, 76, 128},
 		{Prog{}, 132, 200},
 	}
 

src/cmd/internal/obj/sym.go

@@ -32,10 +32,12 @@
 package obj
 
 import (
+	"cmd/internal/goobj2"
 	"cmd/internal/objabi"
 	"fmt"
 	"log"
 	"math"
+	"sort"
 )
 
 func Linknew(arch *LinkArch) *Link {
@@ -78,6 +80,13 @@ func (ctxt *Link) LookupStatic(name string) *LSym {
 // LookupABI looks up a symbol with the given ABI.
 // If it does not exist, it creates it.
 func (ctxt *Link) LookupABI(name string, abi ABI) *LSym {
+	return ctxt.LookupABIInit(name, abi, nil)
+}
+
+// LookupABI looks up a symbol with the given ABI.
+// If it does not exist, it creates it and
+// passes it to init for one-time initialization.
+func (ctxt *Link) LookupABIInit(name string, abi ABI, init func(s *LSym)) *LSym {
 	var hash map[string]*LSym
 	switch abi {
 	case ABI0:
@@ -94,6 +103,9 @@ func (ctxt *Link) LookupABI(name string, abi ABI) *LSym {
 		s = &LSym{Name: name}
 		s.SetABI(abi)
 		hash[name] = s
+		if init != nil {
+			init(s)
+		}
 	}
 	ctxt.hashmu.Unlock()
 	return s
@@ -147,3 +159,167 @@ func (ctxt *Link) Int64Sym(i int64) *LSym {
 		s.Set(AttrLocal, true)
 	})
 }
+
+// Assign index to symbols.
+// asm is set to true if this is called by the assembler (i.e. not the compiler),
+// in which case all the symbols are non-package (for now).
+func (ctxt *Link) NumberSyms(asm bool) {
+	if !ctxt.Flag_newobj {
+		return
+	}
+
+	if ctxt.Headtype == objabi.Haix {
+		// Data must be sorted to keep a constant order in TOC symbols.
+		// As they are created during Progedit, two symbols can be switched between
+		// two different compilations. Therefore, BuildID will be different.
+		// TODO: find a better place and optimize to only sort TOC symbols
+		sort.Slice(ctxt.Data, func(i, j int) bool {
+			return ctxt.Data[i].Name < ctxt.Data[j].Name
+		})
+	}
+
+	ctxt.pkgIdx = make(map[string]int32)
+	ctxt.defs = []*LSym{}
+	ctxt.nonpkgdefs = []*LSym{}
+
+	var idx, nonpkgidx int32 = 0, 0
+	ctxt.traverseSyms(traverseDefs, func(s *LSym) {
+		if isNonPkgSym(ctxt, asm, s) {
+			s.PkgIdx = goobj2.PkgIdxNone
+			s.SymIdx = nonpkgidx
+			if nonpkgidx != int32(len(ctxt.nonpkgdefs)) {
+				panic("bad index")
+			}
+			ctxt.nonpkgdefs = append(ctxt.nonpkgdefs, s)
+			nonpkgidx++
+		} else {
+			s.PkgIdx = goobj2.PkgIdxSelf
+			s.SymIdx = idx
+			if idx != int32(len(ctxt.defs)) {
+				panic("bad index")
+			}
+			ctxt.defs = append(ctxt.defs, s)
+			idx++
+		}
+		s.Set(AttrIndexed, true)
+	})
+
+	ipkg := int32(1) // 0 is invalid index
+	nonpkgdef := nonpkgidx
+	ctxt.traverseSyms(traverseRefs|traverseAux, func(rs *LSym) {
+		if rs.PkgIdx != goobj2.PkgIdxInvalid {
+			return
+		}
+		if !ctxt.Flag_linkshared {
+			// Assign special index for builtin symbols.
+			// Don't do it when linking against shared libraries, as the runtime
+			// may be in a different library.
+			if i := goobj2.BuiltinIdx(rs.Name, int(rs.ABI())); i != -1 {
+				rs.PkgIdx = goobj2.PkgIdxBuiltin
+				rs.SymIdx = int32(i)
+				rs.Set(AttrIndexed, true)
+				return
+			}
+		}
+		pkg := rs.Pkg
+		if pkg == "" || pkg == "\"\"" || pkg == "_" || !rs.Indexed() {
+			rs.PkgIdx = goobj2.PkgIdxNone
+			rs.SymIdx = nonpkgidx
+			rs.Set(AttrIndexed, true)
+			if nonpkgidx != nonpkgdef+int32(len(ctxt.nonpkgrefs)) {
+				panic("bad index")
+			}
+			ctxt.nonpkgrefs = append(ctxt.nonpkgrefs, rs)
+			nonpkgidx++
+			return
+		}
+		if k, ok := ctxt.pkgIdx[pkg]; ok {
+			rs.PkgIdx = k
+			return
+		}
+		rs.PkgIdx = ipkg
+		ctxt.pkgIdx[pkg] = ipkg
+		ipkg++
+	})
+}
+
+// Returns whether s is a non-package symbol, which needs to be referenced
+// by name instead of by index.
+func isNonPkgSym(ctxt *Link, asm bool, s *LSym) bool {
+	if asm && !s.Static() {
+		// asm symbols are referenced by name only, except static symbols
+		// which are file-local and can be referenced by index.
+		return true
+	}
+	if ctxt.Flag_linkshared {
+		// The referenced symbol may be in a different shared library so
+		// the linker cannot see its index.
+		return true
+	}
+	if s.Pkg == "_" {
+		// The frontend uses package "_" to mark symbols that should not
+		// be referenced by index, e.g. linkname'd symbols.
+		return true
+	}
+	if s.DuplicateOK() {
+		// Dupok symbol needs to be dedup'd by name.
+		return true
+	}
+	return false
+}
+
+type traverseFlag uint32
+
+const (
+	traverseDefs traverseFlag = 1 << iota
+	traverseRefs
+	traverseAux
+
+	traverseAll = traverseDefs | traverseRefs | traverseAux
+)
+
+// Traverse symbols based on flag, call fn for each symbol.
+func (ctxt *Link) traverseSyms(flag traverseFlag, fn func(*LSym)) {
+	lists := [][]*LSym{ctxt.Text, ctxt.Data, ctxt.ABIAliases}
+	for _, list := range lists {
+		for _, s := range list {
+			if flag&traverseDefs != 0 {
+				fn(s)
+			}
+			if flag&traverseRefs != 0 {
+				for _, r := range s.R {
+					if r.Sym != nil {
+						fn(r.Sym)
+					}
+				}
+			}
+			if flag&traverseAux != 0 {
+				if s.Gotype != nil {
+					fn(s.Gotype)
+				}
+				if s.Type == objabi.STEXT {
+					pc := &s.Func.Pcln
+					for _, d := range pc.Funcdata {
+						if d != nil {
+							fn(d)
+						}
+					}
+					for _, f := range pc.File {
+						if fsym := ctxt.Lookup(f); fsym != nil {
+							fn(fsym)
+						}
+					}
+					for _, call := range pc.InlTree.nodes {
+						if call.Func != nil {
+							fn(call.Func)
+						}
+						f, _ := linkgetlineFromPos(ctxt, call.Pos)
+						if fsym := ctxt.Lookup(f); fsym != nil {
+							fn(fsym)
+						}
+					}
+				}
+			}
+		}
+	}
+}

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

@@ -402,7 +402,7 @@ func relocsym(ctxt *Link, s *sym.Symbol) {
 		case objabi.R_ADDRCUOFF:
 			// debug_range and debug_loc elements use this relocation type to get an
 			// offset from the start of the compile unit.
-			o = Symaddr(r.Sym) + r.Add - Symaddr(r.Sym.Unit.Lib.Textp[0])
+			o = Symaddr(r.Sym) + r.Add - Symaddr(r.Sym.Unit.Textp[0])
 
 			// r->sym can be null when CALL $(constant) is transformed from absolute PC to relative PC call.
 		case objabi.R_GOTPCREL:
@@ -1086,13 +1086,13 @@ func (p *GCProg) AddSym(s *sym.Symbol) {
 	}
 
 	ptrsize := int64(p.ctxt.Arch.PtrSize)
-	nptr := decodetypePtrdata(p.ctxt.Arch, typ) / ptrsize
+	nptr := decodetypePtrdata(p.ctxt.Arch, typ.P) / ptrsize
 
 	if debugGCProg {
 		fmt.Fprintf(os.Stderr, "gcprog sym: %s at %d (ptr=%d+%d)\n", s.Name, s.Value, s.Value/ptrsize, nptr)
 	}
 
-	if decodetypeUsegcprog(p.ctxt.Arch, typ) == 0 {
+	if decodetypeUsegcprog(p.ctxt.Arch, typ.P) == 0 {
 		// Copy pointers from mask into program.
 		mask := decodetypeGcmask(p.ctxt, typ)
 		for i := int64(0); i < nptr; i++ {

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

@@ -46,6 +46,15 @@ import (
 //
 // Any unreached text symbols are removed from ctxt.Textp.
 func deadcode(ctxt *Link) {
+	if ctxt.Debugvlog != 0 {
+		ctxt.Logf("deadcode\n")
+	}
+
+	if *flagNewobj {
+		deadcode2(ctxt)
+		return
+	}
+
 	d := &deadcodepass{
 		ctxt:        ctxt,
 		ifaceMethod: make(map[methodsig]bool),
@@ -114,22 +123,70 @@ func deadcode(ctxt *Link) {
 		}
 	}
 
-	for _, lib := range ctxt.Library {
-		lib.Textp = lib.Textp[:0]
-	}
+	addToTextp(ctxt)
+}
 
+func addToTextp(ctxt *Link) {
 	// Remove dead text but keep file information (z symbols).
-	textp := make([]*sym.Symbol, 0, len(ctxt.Textp))
+	textp := []*sym.Symbol{}
 	for _, s := range ctxt.Textp {
 		if s.Attr.Reachable() {
-			if s.Unit != nil {
-				s.Unit.Lib.Textp = append(s.Unit.Lib.Textp, s)
-				s.Unit.Textp = append(s.Unit.Textp, s)
-			}
 			textp = append(textp, s)
 		}
 	}
+
+	// Put reachable text symbols into Textp.
+	// do it in postorder so that packages are laid down in dependency order
+	// internal first, then everything else
+	ctxt.Library = postorder(ctxt.Library)
+	for _, doInternal := range [2]bool{true, false} {
+		for _, lib := range ctxt.Library {
+			if isRuntimeDepPkg(lib.Pkg) != doInternal {
+				continue
+			}
+			libtextp := lib.Textp[:0]
+			for _, s := range lib.Textp {
+				if s.Attr.Reachable() {
+					textp = append(textp, s)
+					libtextp = append(libtextp, s)
+					if s.Unit != nil {
+						s.Unit.Textp = append(s.Unit.Textp, s)
+					}
+				}
+			}
+			for _, s := range lib.DupTextSyms {
+				if s.Attr.Reachable() && !s.Attr.OnList() {
+					textp = append(textp, s)
+					libtextp = append(libtextp, s)
+					if s.Unit != nil {
+						s.Unit.Textp = append(s.Unit.Textp, s)
+					}
+					s.Attr |= sym.AttrOnList
+					// dupok symbols may be defined in multiple packages. its
+					// associated package is chosen sort of arbitrarily (the
+					// first containing package that the linker loads). canonicalize
+					// it here to the package with which it will be laid down
+					// in text.
+					s.File = objabi.PathToPrefix(lib.Pkg)
+				}
+			}
+			lib.Textp = libtextp
+		}
+	}
 	ctxt.Textp = textp
+
+	if len(ctxt.Shlibs) > 0 {
+		// We might have overwritten some functions above (this tends to happen for the
+		// autogenerated type equality/hashing functions) and we don't want to generated
+		// pcln table entries for these any more so remove them from Textp.
+		textp := make([]*sym.Symbol, 0, len(ctxt.Textp))
+		for _, s := range ctxt.Textp {
+			if s.Type != sym.SDYNIMPORT {
+				textp = append(textp, s)
+			}
+		}
+		ctxt.Textp = textp
+	}
 }
 
 // methodref holds the relocations from a receiver type symbol to its
@@ -274,7 +331,7 @@ func (d *deadcodepass) flood() {
 				// later will give a better error than deadcode.
 				continue
 			}
-			if decodetypeKind(d.ctxt.Arch, s)&kindMask == kindInterface {
+			if decodetypeKind(d.ctxt.Arch, s.P)&kindMask == kindInterface {
 				for _, sig := range decodeIfaceMethods(d.ctxt.Arch, s) {
 					if d.ctxt.Debugvlog > 1 {
 						d.ctxt.Logf("reached iface method: %s\n", sig)

src/cmd/link/internal/ld/deadcode2.go

@@ -0,0 +1,441 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ld
+
+import (
+	"bytes"
+	"cmd/internal/dwarf"
+	"cmd/internal/objabi"
+	"cmd/internal/sys"
+	"cmd/link/internal/loader"
+	"cmd/link/internal/sym"
+	"container/heap"
+	"fmt"
+	"unicode"
+)
+
+var _ = fmt.Print
+
+type workQueue []loader.Sym
+
+// Implement container/heap.Interface.
+func (q *workQueue) Len() int           { return len(*q) }
+func (q *workQueue) Less(i, j int) bool { return (*q)[i] < (*q)[j] }
+func (q *workQueue) Swap(i, j int)      { (*q)[i], (*q)[j] = (*q)[j], (*q)[i] }
+func (q *workQueue) Push(i interface{}) { *q = append(*q, i.(loader.Sym)) }
+func (q *workQueue) Pop() interface{}   { i := (*q)[len(*q)-1]; *q = (*q)[:len(*q)-1]; return i }
+
+// Functions for deadcode pass to use.
+// Deadcode pass should call push/pop, not Push/Pop.
+func (q *workQueue) push(i loader.Sym) { heap.Push(q, i) }
+func (q *workQueue) pop() loader.Sym   { return heap.Pop(q).(loader.Sym) }
+func (q *workQueue) empty() bool       { return len(*q) == 0 }
+
+type deadcodePass2 struct {
+	ctxt *Link
+	ldr  *loader.Loader
+	wq   workQueue
+	rtmp []loader.Reloc
+
+	ifaceMethod     map[methodsig]bool // methods declared in reached interfaces
+	markableMethods []methodref2       // methods of reached types
+	reflectSeen     bool               // whether we have seen a reflect method call
+}
+
+func (d *deadcodePass2) init() {
+	d.ldr.InitReachable()
+	d.ifaceMethod = make(map[methodsig]bool)
+	if d.ctxt.Reachparent != nil {
+		d.ldr.Reachparent = make([]loader.Sym, d.ldr.NSym())
+	}
+	heap.Init(&d.wq)
+
+	if d.ctxt.BuildMode == BuildModeShared {
+		// Mark all symbols defined in this library as reachable when
+		// building a shared library.
+		n := d.ldr.NDef()
+		for i := 1; i < n; i++ {
+			s := loader.Sym(i)
+			if !d.ldr.IsDup(s) {
+				d.mark(s, 0)
+			}
+		}
+		return
+	}
+
+	var names []string
+
+	// In a normal binary, start at main.main and the init
+	// functions and mark what is reachable from there.
+	if d.ctxt.linkShared && (d.ctxt.BuildMode == BuildModeExe || d.ctxt.BuildMode == BuildModePIE) {
+		names = append(names, "main.main", "main..inittask")
+	} else {
+		// The external linker refers main symbol directly.
+		if d.ctxt.LinkMode == LinkExternal && (d.ctxt.BuildMode == BuildModeExe || d.ctxt.BuildMode == BuildModePIE) {
+			if d.ctxt.HeadType == objabi.Hwindows && d.ctxt.Arch.Family == sys.I386 {
+				*flagEntrySymbol = "_main"
+			} else {
+				*flagEntrySymbol = "main"
+			}
+		}
+		names = append(names, *flagEntrySymbol)
+		if d.ctxt.BuildMode == BuildModePlugin {
+			names = append(names, objabi.PathToPrefix(*flagPluginPath)+"..inittask", objabi.PathToPrefix(*flagPluginPath)+".main", "go.plugin.tabs")
+
+			// We don't keep the go.plugin.exports symbol,
+			// but we do keep the symbols it refers to.
+			exportsIdx := d.ldr.Lookup("go.plugin.exports", 0)
+			if exportsIdx != 0 {
+				d.ReadRelocs(exportsIdx)
+				for i := 0; i < len(d.rtmp); i++ {
+					d.mark(d.rtmp[i].Sym, 0)
+				}
+			}
+		}
+	}
+
+	dynexpMap := d.ctxt.cgo_export_dynamic
+	if d.ctxt.LinkMode == LinkExternal {
+		dynexpMap = d.ctxt.cgo_export_static
+	}
+	for exp := range dynexpMap {
+		names = append(names, exp)
+	}
+
+	// DWARF constant DIE symbols are not referenced, but needed by
+	// the dwarf pass.
+	if !*FlagW {
+		for _, lib := range d.ctxt.Library {
+			names = append(names, dwarf.ConstInfoPrefix+lib.Pkg)
+		}
+	}
+
+	for _, name := range names {
+		// Mark symbol as an data/ABI0 symbol.
+		d.mark(d.ldr.Lookup(name, 0), 0)
+		// Also mark any Go functions (internal ABI).
+		d.mark(d.ldr.Lookup(name, sym.SymVerABIInternal), 0)
+	}
+}
+
+func (d *deadcodePass2) flood() {
+	symRelocs := []loader.Reloc{}
+	auxSyms := []loader.Sym{}
+	for !d.wq.empty() {
+		symIdx := d.wq.pop()
+
+		d.reflectSeen = d.reflectSeen || d.ldr.IsReflectMethod(symIdx)
+
+		relocs := d.ldr.Relocs(symIdx)
+		symRelocs = relocs.ReadAll(symRelocs)
+
+		if d.ldr.IsGoType(symIdx) {
+			p := d.ldr.Data(symIdx)
+			if len(p) != 0 && decodetypeKind(d.ctxt.Arch, p)&kindMask == kindInterface {
+				for _, sig := range d.decodeIfaceMethods2(d.ldr, d.ctxt.Arch, symIdx, symRelocs) {
+					if d.ctxt.Debugvlog > 1 {
+						d.ctxt.Logf("reached iface method: %s\n", sig)
+					}
+					d.ifaceMethod[sig] = true
+				}
+			}
+		}
+
+		var methods []methodref2
+		for i := 0; i < relocs.Count; i++ {
+			r := symRelocs[i]
+			if r.Type == objabi.R_WEAKADDROFF {
+				continue
+			}
+			if r.Type == objabi.R_METHODOFF {
+				if i+2 >= relocs.Count {
+					panic("expect three consecutive R_METHODOFF relocs")
+				}
+				methods = append(methods, methodref2{src: symIdx, r: i})
+				i += 2
+				continue
+			}
+			if r.Type == objabi.R_USETYPE {
+				// type symbol used for DWARF. we need to load the symbol but it may not
+				// be otherwise reachable in the program.
+				// do nothing for now as we still load all type symbols.
+				continue
+			}
+			d.mark(r.Sym, symIdx)
+		}
+		auxSyms = d.ldr.ReadAuxSyms(symIdx, auxSyms)
+		for i := 0; i < len(auxSyms); i++ {
+			d.mark(auxSyms[i], symIdx)
+		}
+		// Some host object symbols have an outer object, which acts like a
+		// "carrier" symbol, or it holds all the symbols for a particular
+		// section. We need to mark all "referenced" symbols from that carrier,
+		// so we make sure we're pulling in all outer symbols, and their sub
+		// symbols. This is not ideal, and these carrier/section symbols could
+		// be removed.
+		d.mark(d.ldr.OuterSym(symIdx), symIdx)
+		d.mark(d.ldr.SubSym(symIdx), symIdx)
+
+		if len(methods) != 0 {
+			// Decode runtime type information for type methods
+			// to help work out which methods can be called
+			// dynamically via interfaces.
+			methodsigs := d.decodetypeMethods2(d.ldr, d.ctxt.Arch, symIdx, symRelocs)
+			if len(methods) != len(methodsigs) {
+				panic(fmt.Sprintf("%q has %d method relocations for %d methods", d.ldr.SymName(symIdx), len(methods), len(methodsigs)))
+			}
+			for i, m := range methodsigs {
+				methods[i].m = m
+			}
+			d.markableMethods = append(d.markableMethods, methods...)
+		}
+	}
+}
+
+func (d *deadcodePass2) mark(symIdx, parent loader.Sym) {
+	if symIdx != 0 && !d.ldr.Reachable.Has(symIdx) {
+		d.wq.push(symIdx)
+		d.ldr.Reachable.Set(symIdx)
+		if d.ctxt.Reachparent != nil {
+			d.ldr.Reachparent[symIdx] = parent
+		}
+		if *flagDumpDep {
+			to := d.ldr.SymName(symIdx)
+			if to != "" {
+				from := "_"
+				if parent != 0 {
+					from = d.ldr.SymName(parent)
+				}
+				fmt.Printf("%s -> %s\n", from, to)
+			}
+		}
+	}
+}
+
+func (d *deadcodePass2) markMethod(m methodref2) {
+	d.ReadRelocs(m.src)
+	d.mark(d.rtmp[m.r].Sym, m.src)
+	d.mark(d.rtmp[m.r+1].Sym, m.src)
+	d.mark(d.rtmp[m.r+2].Sym, m.src)
+}
+
+func deadcode2(ctxt *Link) {
+	ldr := ctxt.loader
+	d := deadcodePass2{ctxt: ctxt, ldr: ldr}
+	d.init()
+	d.flood()
+
+	callSym := ldr.Lookup("reflect.Value.Call", sym.SymVerABIInternal)
+	methSym := ldr.Lookup("reflect.Value.Method", sym.SymVerABIInternal)
+	if ctxt.DynlinkingGo() {
+		// Exported methods may satisfy interfaces we don't know
+		// about yet when dynamically linking.
+		d.reflectSeen = true
+	}
+
+	for {
+		// Methods might be called via reflection. Give up on
+		// static analysis, mark all exported methods of
+		// all reachable types as reachable.
+		d.reflectSeen = d.reflectSeen || (callSym != 0 && ldr.Reachable.Has(callSym)) || (methSym != 0 && ldr.Reachable.Has(methSym))
+
+		// Mark all methods that could satisfy a discovered
+		// interface as reachable. We recheck old marked interfaces
+		// as new types (with new methods) may have been discovered
+		// in the last pass.
+		rem := d.markableMethods[:0]
+		for _, m := range d.markableMethods {
+			if (d.reflectSeen && m.isExported()) || d.ifaceMethod[m.m] {
+				d.markMethod(m)
+			} else {
+				rem = append(rem, m)
+			}
+		}
+		d.markableMethods = rem
+
+		if d.wq.empty() {
+			// No new work was discovered. Done.
+			break
+		}
+		d.flood()
+	}
+
+	n := ldr.NSym()
+
+	if ctxt.BuildMode != BuildModeShared {
+		// Keep a itablink if the symbol it points at is being kept.
+		// (When BuildModeShared, always keep itablinks.)
+		for i := 1; i < n; i++ {
+			s := loader.Sym(i)
+			if ldr.IsItabLink(s) {
+				relocs := ldr.Relocs(s)
+				if relocs.Count > 0 && ldr.Reachable.Has(relocs.At(0).Sym) {
+					ldr.Reachable.Set(s)
+				}
+			}
+		}
+	}
+}
+
+// methodref2 holds the relocations from a receiver type symbol to its
+// method. There are three relocations, one for each of the fields in
+// the reflect.method struct: mtyp, ifn, and tfn.
+type methodref2 struct {
+	m   methodsig
+	src loader.Sym // receiver type symbol
+	r   int        // the index of R_METHODOFF relocations
+}
+
+func (m methodref2) isExported() bool {
+	for _, r := range m.m {
+		return unicode.IsUpper(r)
+	}
+	panic("methodref has no signature")
+}
+
+// decodeMethodSig2 decodes an array of method signature information.
+// Each element of the array is size bytes. The first 4 bytes is a
+// nameOff for the method name, and the next 4 bytes is a typeOff for
+// the function type.
+//
+// Conveniently this is the layout of both runtime.method and runtime.imethod.
+func (d *deadcodePass2) decodeMethodSig2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc, off, size, count int) []methodsig {
+	var buf bytes.Buffer
+	var methods []methodsig
+	for i := 0; i < count; i++ {
+		buf.WriteString(decodetypeName2(ldr, symIdx, symRelocs, off))
+		mtypSym := decodeRelocSym2(ldr, symIdx, symRelocs, int32(off+4))
+		// FIXME: add some sort of caching here, since we may see some of the
+		// same symbols over time for param types.
+		d.ReadRelocs(mtypSym)
+		mp := ldr.Data(mtypSym)
+
+		buf.WriteRune('(')
+		inCount := decodetypeFuncInCount(arch, mp)
+		for i := 0; i < inCount; i++ {
+			if i > 0 {
+				buf.WriteString(", ")
+			}
+			a := d.decodetypeFuncInType2(ldr, arch, mtypSym, d.rtmp, i)
+			buf.WriteString(ldr.SymName(a))
+		}
+		buf.WriteString(") (")
+		outCount := decodetypeFuncOutCount(arch, mp)
+		for i := 0; i < outCount; i++ {
+			if i > 0 {
+				buf.WriteString(", ")
+			}
+			a := d.decodetypeFuncOutType2(ldr, arch, mtypSym, d.rtmp, i)
+			buf.WriteString(ldr.SymName(a))
+		}
+		buf.WriteRune(')')
+
+		off += size
+		methods = append(methods, methodsig(buf.String()))
+		buf.Reset()
+	}
+	return methods
+}
+
+func (d *deadcodePass2) decodeIfaceMethods2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc) []methodsig {
+	p := ldr.Data(symIdx)
+	if decodetypeKind(arch, p)&kindMask != kindInterface {
+		panic(fmt.Sprintf("symbol %q is not an interface", ldr.SymName(symIdx)))
+	}
+	rel := decodeReloc2(ldr, symIdx, symRelocs, int32(commonsize(arch)+arch.PtrSize))
+	if rel.Sym == 0 {
+		return nil
+	}
+	if rel.Sym != symIdx {
+		panic(fmt.Sprintf("imethod slice pointer in %q leads to a different symbol", ldr.SymName(symIdx)))
+	}
+	off := int(rel.Add) // array of reflect.imethod values
+	numMethods := int(decodetypeIfaceMethodCount(arch, p))
+	sizeofIMethod := 4 + 4
+	return d.decodeMethodSig2(ldr, arch, symIdx, symRelocs, off, sizeofIMethod, numMethods)
+}
+
+func (d *deadcodePass2) decodetypeMethods2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc) []methodsig {
+	p := ldr.Data(symIdx)
+	if !decodetypeHasUncommon(arch, p) {
+		panic(fmt.Sprintf("no methods on %q", ldr.SymName(symIdx)))
+	}
+	off := commonsize(arch) // reflect.rtype
+	switch decodetypeKind(arch, p) & kindMask {
+	case kindStruct: // reflect.structType
+		off += 4 * arch.PtrSize
+	case kindPtr: // reflect.ptrType
+		off += arch.PtrSize
+	case kindFunc: // reflect.funcType
+		off += arch.PtrSize // 4 bytes, pointer aligned
+	case kindSlice: // reflect.sliceType
+		off += arch.PtrSize
+	case kindArray: // reflect.arrayType
+		off += 3 * arch.PtrSize
+	case kindChan: // reflect.chanType
+		off += 2 * arch.PtrSize
+	case kindMap: // reflect.mapType
+		off += 4*arch.PtrSize + 8
+	case kindInterface: // reflect.interfaceType
+		off += 3 * arch.PtrSize
+	default:
+		// just Sizeof(rtype)
+	}
+
+	mcount := int(decodeInuxi(arch, p[off+4:], 2))
+	moff := int(decodeInuxi(arch, p[off+4+2+2:], 4))
+	off += moff                // offset to array of reflect.method values
+	const sizeofMethod = 4 * 4 // sizeof reflect.method in program
+	return d.decodeMethodSig2(ldr, arch, symIdx, symRelocs, off, sizeofMethod, mcount)
+}
+
+func decodeReloc2(ldr *loader.Loader, symIdx loader.Sym, symRelocs []loader.Reloc, off int32) loader.Reloc {
+	for j := 0; j < len(symRelocs); j++ {
+		rel := symRelocs[j]
+		if rel.Off == off {
+			return rel
+		}
+	}
+	return loader.Reloc{}
+}
+
+func decodeRelocSym2(ldr *loader.Loader, symIdx loader.Sym, symRelocs []loader.Reloc, off int32) loader.Sym {
+	return decodeReloc2(ldr, symIdx, symRelocs, off).Sym
+}
+
+// decodetypeName2 decodes the name from a reflect.name.
+func decodetypeName2(ldr *loader.Loader, symIdx loader.Sym, symRelocs []loader.Reloc, off int) string {
+	r := decodeRelocSym2(ldr, symIdx, symRelocs, int32(off))
+	if r == 0 {
+		return ""
+	}
+
+	data := ldr.Data(r)
+	namelen := int(uint16(data[1])<<8 | uint16(data[2]))
+	return string(data[3 : 3+namelen])
+}
+
+func (d *deadcodePass2) decodetypeFuncInType2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc, i int) loader.Sym {
+	uadd := commonsize(arch) + 4
+	if arch.PtrSize == 8 {
+		uadd += 4
+	}
+	if decodetypeHasUncommon(arch, ldr.Data(symIdx)) {
+		uadd += uncommonSize()
+	}
+	return decodeRelocSym2(ldr, symIdx, symRelocs, int32(uadd+i*arch.PtrSize))
+}
+
+func (d *deadcodePass2) decodetypeFuncOutType2(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, symRelocs []loader.Reloc, i int) loader.Sym {
+	return d.decodetypeFuncInType2(ldr, arch, symIdx, symRelocs, i+decodetypeFuncInCount(arch, ldr.Data(symIdx)))
+}
+
+// readRelocs reads the relocations for the specified symbol into the
+// deadcode relocs work array. Use with care, since the work array
+// is a singleton.
+func (d *deadcodePass2) ReadRelocs(symIdx loader.Sym) {
+	relocs := d.ldr.Relocs(symIdx)
+	d.rtmp = relocs.ReadAll(d.rtmp)
+}

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

@@ -65,28 +65,28 @@ func structfieldSize(arch *sys.Arch) int { return 3 * arch.PtrSize }       // ru
 func uncommonSize() int                  { return 4 + 2 + 2 + 4 + 4 }      // runtime.uncommontype
 
 // Type.commonType.kind
-func decodetypeKind(arch *sys.Arch, s *sym.Symbol) uint8 {
-	return s.P[2*arch.PtrSize+7] & objabi.KindMask //  0x13 / 0x1f
+func decodetypeKind(arch *sys.Arch, p []byte) uint8 {
+	return p[2*arch.PtrSize+7] & objabi.KindMask //  0x13 / 0x1f
 }
 
 // Type.commonType.kind
-func decodetypeUsegcprog(arch *sys.Arch, s *sym.Symbol) uint8 {
-	return s.P[2*arch.PtrSize+7] & objabi.KindGCProg //  0x13 / 0x1f
+func decodetypeUsegcprog(arch *sys.Arch, p []byte) uint8 {
+	return p[2*arch.PtrSize+7] & objabi.KindGCProg //  0x13 / 0x1f
 }
 
 // Type.commonType.size
-func decodetypeSize(arch *sys.Arch, s *sym.Symbol) int64 {
-	return int64(decodeInuxi(arch, s.P, arch.PtrSize)) // 0x8 / 0x10
+func decodetypeSize(arch *sys.Arch, p []byte) int64 {
+	return int64(decodeInuxi(arch, p, arch.PtrSize)) // 0x8 / 0x10
 }
 
 // Type.commonType.ptrdata
-func decodetypePtrdata(arch *sys.Arch, s *sym.Symbol) int64 {
-	return int64(decodeInuxi(arch, s.P[arch.PtrSize:], arch.PtrSize)) // 0x8 / 0x10
+func decodetypePtrdata(arch *sys.Arch, p []byte) int64 {
+	return int64(decodeInuxi(arch, p[arch.PtrSize:], arch.PtrSize)) // 0x8 / 0x10
 }
 
 // Type.commonType.tflag
-func decodetypeHasUncommon(arch *sys.Arch, s *sym.Symbol) bool {
-	return s.P[2*arch.PtrSize+4]&tflagUncommon != 0
+func decodetypeHasUncommon(arch *sys.Arch, p []byte) bool {
+	return p[2*arch.PtrSize+4]&tflagUncommon != 0
 }
 
 // Find the elf.Section of a given shared library that contains a given address.
@@ -138,7 +138,7 @@ func decodetypeGcprogShlib(ctxt *Link, s *sym.Symbol) uint64 {
 func decodetypeGcmask(ctxt *Link, s *sym.Symbol) []byte {
 	if s.Type == sym.SDYNIMPORT {
 		addr := decodetypeGcprogShlib(ctxt, s)
-		ptrdata := decodetypePtrdata(ctxt.Arch, s)
+		ptrdata := decodetypePtrdata(ctxt.Arch, s.P)
 		sect := findShlibSection(ctxt, s.File, addr)
 		if sect != nil {
 			r := make([]byte, ptrdata/int64(ctxt.Arch.PtrSize))
@@ -181,17 +181,17 @@ func decodetypeChanElem(arch *sys.Arch, s *sym.Symbol) *sym.Symbol {
 }
 
 // Type.FuncType.dotdotdot
-func decodetypeFuncDotdotdot(arch *sys.Arch, s *sym.Symbol) bool {
-	return uint16(decodeInuxi(arch, s.P[commonsize(arch)+2:], 2))&(1<<15) != 0
+func decodetypeFuncDotdotdot(arch *sys.Arch, p []byte) bool {
+	return uint16(decodeInuxi(arch, p[commonsize(arch)+2:], 2))&(1<<15) != 0
 }
 
 // Type.FuncType.inCount
-func decodetypeFuncInCount(arch *sys.Arch, s *sym.Symbol) int {
-	return int(decodeInuxi(arch, s.P[commonsize(arch):], 2))
+func decodetypeFuncInCount(arch *sys.Arch, p []byte) int {
+	return int(decodeInuxi(arch, p[commonsize(arch):], 2))
 }
 
-func decodetypeFuncOutCount(arch *sys.Arch, s *sym.Symbol) int {
-	return int(uint16(decodeInuxi(arch, s.P[commonsize(arch)+2:], 2)) & (1<<15 - 1))
+func decodetypeFuncOutCount(arch *sys.Arch, p []byte) int {
+	return int(uint16(decodeInuxi(arch, p[commonsize(arch)+2:], 2)) & (1<<15 - 1))
 }
 
 func decodetypeFuncInType(arch *sys.Arch, s *sym.Symbol, i int) *sym.Symbol {
@@ -199,14 +199,14 @@ func decodetypeFuncInType(arch *sys.Arch, s *sym.Symbol, i int) *sym.Symbol {
 	if arch.PtrSize == 8 {
 		uadd += 4
 	}
-	if decodetypeHasUncommon(arch, s) {
+	if decodetypeHasUncommon(arch, s.P) {
 		uadd += uncommonSize()
 	}
 	return decodeRelocSym(s, int32(uadd+i*arch.PtrSize))
 }
 
 func decodetypeFuncOutType(arch *sys.Arch, s *sym.Symbol, i int) *sym.Symbol {
-	return decodetypeFuncInType(arch, s, i+decodetypeFuncInCount(arch, s))
+	return decodetypeFuncInType(arch, s, i+decodetypeFuncInCount(arch, s.P))
 }
 
 // Type.StructType.fields.Slice::length
@@ -216,7 +216,7 @@ func decodetypeStructFieldCount(arch *sys.Arch, s *sym.Symbol) int {
 
 func decodetypeStructFieldArrayOff(arch *sys.Arch, s *sym.Symbol, i int) int {
 	off := commonsize(arch) + 4*arch.PtrSize
-	if decodetypeHasUncommon(arch, s) {
+	if decodetypeHasUncommon(arch, s.P) {
 		off += uncommonSize()
 	}
 	off += i * structfieldSize(arch)
@@ -264,8 +264,8 @@ func decodetypeStructFieldOffsAnon(arch *sys.Arch, s *sym.Symbol, i int) int64 {
 }
 
 // InterfaceType.methods.length
-func decodetypeIfaceMethodCount(arch *sys.Arch, s *sym.Symbol) int64 {
-	return int64(decodeInuxi(arch, s.P[commonsize(arch)+2*arch.PtrSize:], arch.PtrSize))
+func decodetypeIfaceMethodCount(arch *sys.Arch, p []byte) int64 {
+	return int64(decodeInuxi(arch, p[commonsize(arch)+2*arch.PtrSize:], arch.PtrSize))
 }
 
 // methodsig is a fully qualified typed method signature, like
@@ -299,7 +299,7 @@ func decodeMethodSig(arch *sys.Arch, s *sym.Symbol, off, size, count int) []meth
 		mtypSym := decodeRelocSym(s, int32(off+4))
 
 		buf.WriteRune('(')
-		inCount := decodetypeFuncInCount(arch, mtypSym)
+		inCount := decodetypeFuncInCount(arch, mtypSym.P)
 		for i := 0; i < inCount; i++ {
 			if i > 0 {
 				buf.WriteString(", ")
@@ -307,7 +307,7 @@ func decodeMethodSig(arch *sys.Arch, s *sym.Symbol, off, size, count int) []meth
 			buf.WriteString(decodetypeFuncInType(arch, mtypSym, i).Name)
 		}
 		buf.WriteString(") (")
-		outCount := decodetypeFuncOutCount(arch, mtypSym)
+		outCount := decodetypeFuncOutCount(arch, mtypSym.P)
 		for i := 0; i < outCount; i++ {
 			if i > 0 {
 				buf.WriteString(", ")
@@ -324,7 +324,7 @@ func decodeMethodSig(arch *sys.Arch, s *sym.Symbol, off, size, count int) []meth
 }
 
 func decodeIfaceMethods(arch *sys.Arch, s *sym.Symbol) []methodsig {
-	if decodetypeKind(arch, s)&kindMask != kindInterface {
+	if decodetypeKind(arch, s.P)&kindMask != kindInterface {
 		panic(fmt.Sprintf("symbol %q is not an interface", s.Name))
 	}
 	r := decodeReloc(s, int32(commonsize(arch)+arch.PtrSize))
@@ -335,17 +335,17 @@ func decodeIfaceMethods(arch *sys.Arch, s *sym.Symbol) []methodsig {
 		panic(fmt.Sprintf("imethod slice pointer in %q leads to a different symbol", s.Name))
 	}
 	off := int(r.Add) // array of reflect.imethod values
-	numMethods := int(decodetypeIfaceMethodCount(arch, s))
+	numMethods := int(decodetypeIfaceMethodCount(arch, s.P))
 	sizeofIMethod := 4 + 4
 	return decodeMethodSig(arch, s, off, sizeofIMethod, numMethods)
 }
 
 func decodetypeMethods(arch *sys.Arch, s *sym.Symbol) []methodsig {
-	if !decodetypeHasUncommon(arch, s) {
+	if !decodetypeHasUncommon(arch, s.P) {
 		panic(fmt.Sprintf("no methods on %q", s.Name))
 	}
 	off := commonsize(arch) // reflect.rtype
-	switch decodetypeKind(arch, s) & kindMask {
+	switch decodetypeKind(arch, s.P) & kindMask {
 	case kindStruct: // reflect.structType
 		off += 4 * arch.PtrSize
 	case kindPtr: // reflect.ptrType

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

@@ -422,8 +422,8 @@ func defgotype(ctxt *Link, gotype *sym.Symbol) *sym.Symbol {
 
 func newtype(ctxt *Link, gotype *sym.Symbol) *dwarf.DWDie {
 	name := gotype.Name[5:] // could also decode from Type.string
-	kind := decodetypeKind(ctxt.Arch, gotype)
-	bytesize := decodetypeSize(ctxt.Arch, gotype)
+	kind := decodetypeKind(ctxt.Arch, gotype.P)
+	bytesize := decodetypeSize(ctxt.Arch, gotype.P)
 
 	var die, typedefdie *dwarf.DWDie
 	switch kind {
@@ -488,17 +488,17 @@ func newtype(ctxt *Link, gotype *sym.Symbol) *dwarf.DWDie {
 		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_FUNCTYPE, name, 0)
 		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
 		typedefdie = dotypedef(ctxt, &dwtypes, name, die)
-		nfields := decodetypeFuncInCount(ctxt.Arch, gotype)
+		nfields := decodetypeFuncInCount(ctxt.Arch, gotype.P)
 		for i := 0; i < nfields; i++ {
 			s := decodetypeFuncInType(ctxt.Arch, gotype, i)
 			fld := newdie(ctxt, die, dwarf.DW_ABRV_FUNCTYPEPARAM, s.Name[5:], 0)
 			newrefattr(fld, dwarf.DW_AT_type, defgotype(ctxt, s))
 		}
 
-		if decodetypeFuncDotdotdot(ctxt.Arch, gotype) {
+		if decodetypeFuncDotdotdot(ctxt.Arch, gotype.P) {
 			newdie(ctxt, die, dwarf.DW_ABRV_DOTDOTDOT, "...", 0)
 		}
-		nfields = decodetypeFuncOutCount(ctxt.Arch, gotype)
+		nfields = decodetypeFuncOutCount(ctxt.Arch, gotype.P)
 		for i := 0; i < nfields; i++ {
 			s := decodetypeFuncOutType(ctxt.Arch, gotype, i)
 			fld := newdie(ctxt, die, dwarf.DW_ABRV_FUNCTYPEPARAM, s.Name[5:], 0)
@@ -508,7 +508,7 @@ func newtype(ctxt *Link, gotype *sym.Symbol) *dwarf.DWDie {
 	case objabi.KindInterface:
 		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_IFACETYPE, name, 0)
 		typedefdie = dotypedef(ctxt, &dwtypes, name, die)
-		nfields := int(decodetypeIfaceMethodCount(ctxt.Arch, gotype))
+		nfields := int(decodetypeIfaceMethodCount(ctxt.Arch, gotype.P))
 		var s *sym.Symbol
 		if nfields == 0 {
 			s = lookupOrDiag(ctxt, "type.runtime.eface")
@@ -733,7 +733,7 @@ func synthesizemaptypes(ctxt *Link, die *dwarf.DWDie) {
 		gotype := getattr(die, dwarf.DW_AT_type).Data.(*sym.Symbol)
 		keytype := decodetypeMapKey(ctxt.Arch, gotype)
 		valtype := decodetypeMapValue(ctxt.Arch, gotype)
-		keysize, valsize := decodetypeSize(ctxt.Arch, keytype), decodetypeSize(ctxt.Arch, valtype)
+		keysize, valsize := decodetypeSize(ctxt.Arch, keytype.P), decodetypeSize(ctxt.Arch, valtype.P)
 		keytype, valtype = walksymtypedef(ctxt, defgotype(ctxt, keytype)), walksymtypedef(ctxt, defgotype(ctxt, valtype))
 
 		// compute size info like hashmap.c does.

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

@@ -110,7 +110,6 @@ func ldpkg(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, filename s
 			return
 		}
 		p1 += p0
-
 		loadcgo(ctxt, filename, objabi.PathToPrefix(lib.Pkg), data[p0:p1])
 	}
 }
@@ -123,6 +122,39 @@ func loadcgo(ctxt *Link, file string, pkg string, p string) {
 		return
 	}
 
+	// Find cgo_export symbols. They are roots in the deadcode pass.
+	for _, f := range directives {
+		switch f[0] {
+		case "cgo_export_static", "cgo_export_dynamic":
+			if len(f) < 2 || len(f) > 3 {
+				continue
+			}
+			local := f[1]
+			switch ctxt.BuildMode {
+			case BuildModeCShared, BuildModeCArchive, BuildModePlugin:
+				if local == "main" {
+					continue
+				}
+			}
+			local = expandpkg(local, pkg)
+			if f[0] == "cgo_export_static" {
+				ctxt.cgo_export_static[local] = true
+			} else {
+				ctxt.cgo_export_dynamic[local] = true
+			}
+		}
+	}
+
+	if *flagNewobj {
+		// Record the directives. We'll process them later after Symbols are created.
+		ctxt.cgodata = append(ctxt.cgodata, cgodata{file, pkg, directives})
+	} else {
+		setCgoAttr(ctxt, ctxt.Syms.Lookup, file, pkg, directives)
+	}
+}
+
+// Set symbol attributes or flags based on cgo directives.
+func setCgoAttr(ctxt *Link, lookup func(string, int) *sym.Symbol, file string, pkg string, directives [][]string) {
 	for _, f := range directives {
 		switch f[0] {
 		case "cgo_import_dynamic":
@@ -164,8 +196,8 @@ func loadcgo(ctxt *Link, file string, pkg string, p string) {
 			if i := strings.Index(remote, "#"); i >= 0 {
 				remote, q = remote[:i], remote[i+1:]
 			}
-			s := ctxt.Syms.Lookup(local, 0)
-			if s.Type == 0 || s.Type == sym.SXREF || s.Type == sym.SHOSTOBJ {
+			s := lookup(local, 0)
+			if s.Type == 0 || s.Type == sym.SXREF || s.Type == sym.SBSS || s.Type == sym.SNOPTRBSS || s.Type == sym.SHOSTOBJ {
 				s.SetDynimplib(lib)
 				s.SetExtname(remote)
 				s.SetDynimpvers(q)
@@ -183,7 +215,7 @@ func loadcgo(ctxt *Link, file string, pkg string, p string) {
 			}
 			local := f[1]
 
-			s := ctxt.Syms.Lookup(local, 0)
+			s := lookup(local, 0)
 			s.Type = sym.SHOSTOBJ
 			s.Size = 0
 			continue
@@ -204,11 +236,11 @@ func loadcgo(ctxt *Link, file string, pkg string, p string) {
 			// functions. Link.loadlib will resolve any
 			// ABI aliases we find here (since we may not
 			// yet know it's an alias).
-			s := ctxt.Syms.Lookup(local, 0)
+			s := lookup(local, 0)
 
 			switch ctxt.BuildMode {
 			case BuildModeCShared, BuildModeCArchive, BuildModePlugin:
-				if s == ctxt.Syms.Lookup("main", 0) {
+				if s == lookup("main", 0) {
 					continue
 				}
 			}
@@ -223,7 +255,6 @@ func loadcgo(ctxt *Link, file string, pkg string, p string) {
 
 			if !s.Attr.CgoExport() {
 				s.SetExtname(remote)
-				dynexp = append(dynexp, s)
 			} else if s.Extname() != remote {
 				fmt.Fprintf(os.Stderr, "%s: conflicting cgo_export directives: %s as %s and %s\n", os.Args[0], s.Name, s.Extname(), remote)
 				nerrors++

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

@@ -38,6 +38,7 @@ import (
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
 	"cmd/link/internal/loadelf"
+	"cmd/link/internal/loader"
 	"cmd/link/internal/loadmacho"
 	"cmd/link/internal/loadpe"
 	"cmd/link/internal/loadxcoff"
@@ -57,6 +58,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"sort"
 	"strings"
 	"sync"
 )
@@ -378,30 +380,25 @@ func (ctxt *Link) findLibPath(libname string) string {
 }
 
 func (ctxt *Link) loadlib() {
-	switch ctxt.BuildMode {
-	case BuildModeCShared, BuildModePlugin:
-		s := ctxt.Syms.Lookup("runtime.islibrary", 0)
-		s.Attr |= sym.AttrDuplicateOK
-		s.AddUint8(1)
-	case BuildModeCArchive:
-		s := ctxt.Syms.Lookup("runtime.isarchive", 0)
-		s.Attr |= sym.AttrDuplicateOK
-		s.AddUint8(1)
+	if *flagNewobj {
+		var flags uint32
+		switch *FlagStrictDups {
+		case 0:
+			// nothing to do
+		case 1, 2:
+			flags = loader.FlagStrictDups
+		default:
+			log.Fatalf("invalid -strictdups flag value %d", *FlagStrictDups)
+		}
+		ctxt.loader = loader.NewLoader(flags)
 	}
 
-	loadinternal(ctxt, "runtime")
-	if ctxt.Arch.Family == sys.ARM {
-		loadinternal(ctxt, "math")
-	}
-	if *flagRace {
-		loadinternal(ctxt, "runtime/race")
-	}
-	if *flagMsan {
-		loadinternal(ctxt, "runtime/msan")
-	}
+	ctxt.cgo_export_static = make(map[string]bool)
+	ctxt.cgo_export_dynamic = make(map[string]bool)
 
 	// ctxt.Library grows during the loop, so not a range loop.
-	for i := 0; i < len(ctxt.Library); i++ {
+	i := 0
+	for ; i < len(ctxt.Library); i++ {
 		lib := ctxt.Library[i]
 		if lib.Shlib == "" {
 			if ctxt.Debugvlog > 1 {
@@ -411,34 +408,35 @@ func (ctxt *Link) loadlib() {
 		}
 	}
 
-	for _, lib := range ctxt.Library {
-		if lib.Shlib != "" {
-			if ctxt.Debugvlog > 1 {
-				ctxt.Logf("autolib: %s (from %s)\n", lib.Shlib, lib.Objref)
-			}
-			ldshlibsyms(ctxt, lib.Shlib)
+	// load internal packages, if not already
+	if ctxt.Arch.Family == sys.ARM {
+		loadinternal(ctxt, "math")
+	}
+	if *flagRace {
+		loadinternal(ctxt, "runtime/race")
+	}
+	if *flagMsan {
+		loadinternal(ctxt, "runtime/msan")
+	}
+	loadinternal(ctxt, "runtime")
+	for ; i < len(ctxt.Library); i++ {
+		lib := ctxt.Library[i]
+		if lib.Shlib == "" {
+			loadobjfile(ctxt, lib)
 		}
 	}
 
-	iscgo = ctxt.Syms.ROLookup("x_cgo_init", 0) != nil
+	if *flagNewobj {
+		iscgo = ctxt.loader.Lookup("x_cgo_init", 0) != 0
+		ctxt.canUsePlugins = ctxt.loader.Lookup("plugin.Open", sym.SymVerABIInternal) != 0
+	} else {
+		iscgo = ctxt.Syms.ROLookup("x_cgo_init", 0) != nil
+		ctxt.canUsePlugins = ctxt.Syms.ROLookup("plugin.Open", sym.SymVerABIInternal) != nil
+	}
 
 	// We now have enough information to determine the link mode.
 	determineLinkMode(ctxt)
 
-	// Recalculate pe parameters now that we have ctxt.LinkMode set.
-	if ctxt.HeadType == objabi.Hwindows {
-		Peinit(ctxt)
-	}
-
-	if ctxt.HeadType == objabi.Hdarwin && ctxt.LinkMode == LinkExternal {
-		*FlagTextAddr = 0
-	}
-
-	if ctxt.LinkMode == LinkExternal && ctxt.Arch.Family == sys.PPC64 && objabi.GOOS != "aix" {
-		toc := ctxt.Syms.Lookup(".TOC.", 0)
-		toc.Type = sym.SDYNIMPORT
-	}
-
 	if ctxt.LinkMode == LinkExternal && !iscgo && ctxt.LibraryByPkg["runtime/cgo"] == nil && !(objabi.GOOS == "darwin" && (ctxt.Arch.Family == sys.AMD64 || ctxt.Arch.Family == sys.I386)) {
 		// This indicates a user requested -linkmode=external.
 		// The startup code uses an import of runtime/cgo to decide
@@ -456,7 +454,29 @@ func (ctxt *Link) loadlib() {
 		}
 	}
 
-	if ctxt.LinkMode == LinkInternal {
+	for _, lib := range ctxt.Library {
+		if lib.Shlib != "" {
+			if ctxt.Debugvlog > 1 {
+				ctxt.Logf("autolib: %s (from %s)\n", lib.Shlib, lib.Objref)
+			}
+			ldshlibsyms(ctxt, lib.Shlib)
+		}
+	}
+
+	if ctxt.LinkMode == LinkInternal && len(hostobj) != 0 {
+		if *flagNewobj {
+			// In newobj mode, we typically create sym.Symbols later therefore
+			// also set cgo attributes later. However, for internal cgo linking,
+			// the host object loaders still work with sym.Symbols (for now),
+			// and they need cgo attributes set to work properly. So process
+			// them now.
+			lookup := func(name string, ver int) *sym.Symbol { return ctxt.loader.LookupOrCreate(name, ver, ctxt.Syms) }
+			for _, d := range ctxt.cgodata {
+				setCgoAttr(ctxt, lookup, d.file, d.pkg, d.directives)
+			}
+			ctxt.cgodata = nil
+		}
+
 		// Drop all the cgo_import_static declarations.
 		// Turns out we won't be needing them.
 		for _, s := range ctxt.Syms.Allsym {
@@ -474,6 +494,155 @@ func (ctxt *Link) loadlib() {
 		}
 	}
 
+	// Conditionally load host objects, or setup for external linking.
+	hostobjs(ctxt)
+	hostlinksetup(ctxt)
+
+	if *flagNewobj {
+		// Add references of externally defined symbols.
+		ctxt.loader.LoadRefs(ctxt.Arch, ctxt.Syms)
+	}
+
+	// Now that we know the link mode, set the dynexp list.
+	if !*flagNewobj { // set this later in newobj mode
+		setupdynexp(ctxt)
+	}
+
+	if ctxt.LinkMode == LinkInternal && len(hostobj) != 0 {
+		// If we have any undefined symbols in external
+		// objects, try to read them from the libgcc file.
+		any := false
+		for _, s := range ctxt.Syms.Allsym {
+			for i := range s.R {
+				r := &s.R[i] // Copying sym.Reloc has measurable impact on performance
+				if r.Sym != nil && r.Sym.Type == sym.SXREF && r.Sym.Name != ".got" {
+					any = true
+					break
+				}
+			}
+		}
+		if any {
+			if *flagLibGCC == "" {
+				*flagLibGCC = ctxt.findLibPathCmd("--print-libgcc-file-name", "libgcc")
+			}
+			if runtime.GOOS == "openbsd" && *flagLibGCC == "libgcc.a" {
+				// On OpenBSD `clang --print-libgcc-file-name` returns "libgcc.a".
+				// In this case we fail to load libgcc.a and can encounter link
+				// errors - see if we can find libcompiler_rt.a instead.
+				*flagLibGCC = ctxt.findLibPathCmd("--print-file-name=libcompiler_rt.a", "libcompiler_rt")
+			}
+			if *flagLibGCC != "none" {
+				hostArchive(ctxt, *flagLibGCC)
+			}
+			if ctxt.HeadType == objabi.Hwindows {
+				if p := ctxt.findLibPath("libmingwex.a"); p != "none" {
+					hostArchive(ctxt, p)
+				}
+				if p := ctxt.findLibPath("libmingw32.a"); p != "none" {
+					hostArchive(ctxt, p)
+				}
+				// Link libmsvcrt.a to resolve '__acrt_iob_func' symbol
+				// (see https://golang.org/issue/23649 for details).
+				if p := ctxt.findLibPath("libmsvcrt.a"); p != "none" {
+					hostArchive(ctxt, p)
+				}
+				// TODO: maybe do something similar to peimporteddlls to collect all lib names
+				// and try link them all to final exe just like libmingwex.a and libmingw32.a:
+				/*
+					for:
+					#cgo windows LDFLAGS: -lmsvcrt -lm
+					import:
+					libmsvcrt.a libm.a
+				*/
+			}
+		}
+	}
+
+	// We've loaded all the code now.
+	ctxt.Loaded = true
+
+	importcycles()
+
+	if *flagNewobj {
+		strictDupMsgCount = ctxt.loader.NStrictDupMsgs()
+	}
+}
+
+// Set up dynexp list.
+func setupdynexp(ctxt *Link) {
+	dynexpMap := ctxt.cgo_export_dynamic
+	if ctxt.LinkMode == LinkExternal {
+		dynexpMap = ctxt.cgo_export_static
+	}
+	dynexp = make([]*sym.Symbol, 0, len(dynexpMap))
+	for exp := range dynexpMap {
+		s := ctxt.Syms.Lookup(exp, 0)
+		dynexp = append(dynexp, s)
+	}
+	sort.Sort(byName(dynexp))
+
+	// Resolve ABI aliases in the list of cgo-exported functions.
+	// This is necessary because we load the ABI0 symbol for all
+	// cgo exports.
+	for i, s := range dynexp {
+		if s.Type != sym.SABIALIAS {
+			continue
+		}
+		t := resolveABIAlias(s)
+		t.Attr |= s.Attr
+		t.SetExtname(s.Extname())
+		dynexp[i] = t
+	}
+
+	ctxt.cgo_export_static = nil
+	ctxt.cgo_export_dynamic = nil
+}
+
+// Set up flags and special symbols depending on the platform build mode.
+func (ctxt *Link) linksetup() {
+	switch ctxt.BuildMode {
+	case BuildModeCShared, BuildModePlugin:
+		s := ctxt.Syms.Lookup("runtime.islibrary", 0)
+		s.Type = sym.SNOPTRDATA
+		s.Attr |= sym.AttrDuplicateOK
+		s.AddUint8(1)
+	case BuildModeCArchive:
+		s := ctxt.Syms.Lookup("runtime.isarchive", 0)
+		s.Type = sym.SNOPTRDATA
+		s.Attr |= sym.AttrDuplicateOK
+		s.AddUint8(1)
+	}
+
+	// Recalculate pe parameters now that we have ctxt.LinkMode set.
+	if ctxt.HeadType == objabi.Hwindows {
+		Peinit(ctxt)
+	}
+
+	if ctxt.HeadType == objabi.Hdarwin && ctxt.LinkMode == LinkExternal {
+		*FlagTextAddr = 0
+	}
+
+	// If there are no dynamic libraries needed, gcc disables dynamic linking.
+	// Because of this, glibc's dynamic ELF loader occasionally (like in version 2.13)
+	// assumes that a dynamic binary always refers to at least one dynamic library.
+	// Rather than be a source of test cases for glibc, disable dynamic linking
+	// the same way that gcc would.
+	//
+	// Exception: on OS X, programs such as Shark only work with dynamic
+	// binaries, so leave it enabled on OS X (Mach-O) binaries.
+	// Also leave it enabled on Solaris which doesn't support
+	// statically linked binaries.
+	if ctxt.BuildMode == BuildModeExe {
+		if havedynamic == 0 && ctxt.HeadType != objabi.Hdarwin && ctxt.HeadType != objabi.Hsolaris {
+			*FlagD = true
+		}
+	}
+
+	if ctxt.LinkMode == LinkExternal && ctxt.Arch.Family == sys.PPC64 && objabi.GOOS != "aix" {
+		toc := ctxt.Syms.Lookup(".TOC.", 0)
+		toc.Type = sym.SDYNIMPORT
+	}
+
 	// The Android Q linker started to complain about underalignment of the our TLS
 	// section. We don't actually use the section on android, so dont't
 	// generate it.
@@ -534,98 +703,6 @@ func (ctxt *Link) loadlib() {
 	moduledata.Attr |= sym.AttrReachable
 	ctxt.Moduledata = moduledata
 
-	// Now that we know the link mode, trim the dynexp list.
-	x := sym.AttrCgoExportDynamic
-
-	if ctxt.LinkMode == LinkExternal {
-		x = sym.AttrCgoExportStatic
-	}
-	w := 0
-	for i := range dynexp {
-		if dynexp[i].Attr&x != 0 {
-			dynexp[w] = dynexp[i]
-			w++
-		}
-	}
-	dynexp = dynexp[:w]
-
-	// In internal link mode, read the host object files.
-	if ctxt.LinkMode == LinkInternal {
-		hostobjs(ctxt)
-
-		// If we have any undefined symbols in external
-		// objects, try to read them from the libgcc file.
-		any := false
-		for _, s := range ctxt.Syms.Allsym {
-			for i := range s.R {
-				r := &s.R[i] // Copying sym.Reloc has measurable impact on performance
-				if r.Sym != nil && r.Sym.Type == sym.SXREF && r.Sym.Name != ".got" {
-					any = true
-					break
-				}
-			}
-		}
-		if any {
-			if *flagLibGCC == "" {
-				*flagLibGCC = ctxt.findLibPathCmd("--print-libgcc-file-name", "libgcc")
-			}
-			if runtime.GOOS == "openbsd" && *flagLibGCC == "libgcc.a" {
-				// On OpenBSD `clang --print-libgcc-file-name` returns "libgcc.a".
-				// In this case we fail to load libgcc.a and can encounter link
-				// errors - see if we can find libcompiler_rt.a instead.
-				*flagLibGCC = ctxt.findLibPathCmd("--print-file-name=libcompiler_rt.a", "libcompiler_rt")
-			}
-			if *flagLibGCC != "none" {
-				hostArchive(ctxt, *flagLibGCC)
-			}
-			if ctxt.HeadType == objabi.Hwindows {
-				if p := ctxt.findLibPath("libmingwex.a"); p != "none" {
-					hostArchive(ctxt, p)
-				}
-				if p := ctxt.findLibPath("libmingw32.a"); p != "none" {
-					hostArchive(ctxt, p)
-				}
-				// Link libmsvcrt.a to resolve '__acrt_iob_func' symbol
-				// (see https://golang.org/issue/23649 for details).
-				if p := ctxt.findLibPath("libmsvcrt.a"); p != "none" {
-					hostArchive(ctxt, p)
-				}
-				// TODO: maybe do something similar to peimporteddlls to collect all lib names
-				// and try link them all to final exe just like libmingwex.a and libmingw32.a:
-				/*
-					for:
-					#cgo windows LDFLAGS: -lmsvcrt -lm
-					import:
-					libmsvcrt.a libm.a
-				*/
-			}
-		}
-	} else {
-		hostlinksetup(ctxt)
-	}
-
-	// We've loaded all the code now.
-	ctxt.Loaded = true
-
-	// Record whether we can use plugins.
-	ctxt.canUsePlugins = (ctxt.Syms.ROLookup("plugin.Open", sym.SymVerABIInternal) != nil)
-
-	// If there are no dynamic libraries needed, gcc disables dynamic linking.
-	// Because of this, glibc's dynamic ELF loader occasionally (like in version 2.13)
-	// assumes that a dynamic binary always refers to at least one dynamic library.
-	// Rather than be a source of test cases for glibc, disable dynamic linking
-	// the same way that gcc would.
-	//
-	// Exception: on OS X, programs such as Shark only work with dynamic
-	// binaries, so leave it enabled on OS X (Mach-O) binaries.
-	// Also leave it enabled on Solaris which doesn't support
-	// statically linked binaries.
-	if ctxt.BuildMode == BuildModeExe {
-		if havedynamic == 0 && ctxt.HeadType != objabi.Hdarwin && ctxt.HeadType != objabi.Hsolaris {
-			*FlagD = true
-		}
-	}
-
 	// If package versioning is required, generate a hash of the
 	// packages used in the link.
 	if ctxt.BuildMode == BuildModeShared || ctxt.BuildMode == BuildModePlugin || ctxt.CanUsePlugins() {
@@ -643,59 +720,6 @@ func (ctxt *Link) loadlib() {
 			got.Attr |= sym.AttrReachable
 		}
 	}
-
-	importcycles()
-
-	// put symbols into Textp
-	// do it in postorder so that packages are laid down in dependency order
-	// internal first, then everything else
-	ctxt.Library = postorder(ctxt.Library)
-	for _, doInternal := range [2]bool{true, false} {
-		for _, lib := range ctxt.Library {
-			if isRuntimeDepPkg(lib.Pkg) != doInternal {
-				continue
-			}
-			ctxt.Textp = append(ctxt.Textp, lib.Textp...)
-			for _, s := range lib.DupTextSyms {
-				if !s.Attr.OnList() {
-					ctxt.Textp = append(ctxt.Textp, s)
-					s.Attr |= sym.AttrOnList
-					// dupok symbols may be defined in multiple packages. its
-					// associated package is chosen sort of arbitrarily (the
-					// first containing package that the linker loads). canonicalize
-					// it here to the package with which it will be laid down
-					// in text.
-					s.File = objabi.PathToPrefix(lib.Pkg)
-				}
-			}
-		}
-	}
-
-	if len(ctxt.Shlibs) > 0 {
-		// We might have overwritten some functions above (this tends to happen for the
-		// autogenerated type equality/hashing functions) and we don't want to generated
-		// pcln table entries for these any more so remove them from Textp.
-		textp := make([]*sym.Symbol, 0, len(ctxt.Textp))
-		for _, s := range ctxt.Textp {
-			if s.Type != sym.SDYNIMPORT {
-				textp = append(textp, s)
-			}
-		}
-		ctxt.Textp = textp
-	}
-
-	// Resolve ABI aliases in the list of cgo-exported functions.
-	// This is necessary because we load the ABI0 symbol for all
-	// cgo exports.
-	for i, s := range dynexp {
-		if s.Type != sym.SABIALIAS {
-			continue
-		}
-		t := resolveABIAlias(s)
-		t.Attr |= s.Attr
-		t.SetExtname(s.Extname())
-		dynexp[i] = t
-	}
 }
 
 // mangleTypeSym shortens the names of symbols that represent Go types
@@ -991,6 +1015,9 @@ func ldhostobj(ld func(*Link, *bio.Reader, string, int64, string), headType obja
 }
 
 func hostobjs(ctxt *Link) {
+	if ctxt.LinkMode != LinkInternal {
+		return
+	}
 	var h *Hostobj
 
 	for i := 0; i < len(hostobj); i++ {
@@ -1665,55 +1692,107 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
 
 	magic := uint32(c1)<<24 | uint32(c2)<<16 | uint32(c3)<<8 | uint32(c4)
 	if magic == 0x7f454c46 { // \x7F E L F
-		ldelf := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
-			textp, flags, err := loadelf.Load(ctxt.Arch, ctxt.Syms, f, pkg, length, pn, ehdr.flags)
-			if err != nil {
-				Errorf(nil, "%v", err)
-				return
+		if *flagNewobj {
+			ldelf := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
+				textp, flags, err := loadelf.Load(ctxt.loader, ctxt.Arch, ctxt.Syms, f, pkg, length, pn, ehdr.flags)
+				if err != nil {
+					Errorf(nil, "%v", err)
+					return
+				}
+				ehdr.flags = flags
+				ctxt.Textp = append(ctxt.Textp, textp...)
 			}
-			ehdr.flags = flags
-			ctxt.Textp = append(ctxt.Textp, textp...)
+			return ldhostobj(ldelf, ctxt.HeadType, f, pkg, length, pn, file)
+		} else {
+			ldelf := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
+				textp, flags, err := loadelf.LoadOld(ctxt.Arch, ctxt.Syms, f, pkg, length, pn, ehdr.flags)
+				if err != nil {
+					Errorf(nil, "%v", err)
+					return
+				}
+				ehdr.flags = flags
+				ctxt.Textp = append(ctxt.Textp, textp...)
+			}
+			return ldhostobj(ldelf, ctxt.HeadType, f, pkg, length, pn, file)
 		}
-		return ldhostobj(ldelf, ctxt.HeadType, f, pkg, length, pn, file)
 	}
 
 	if magic&^1 == 0xfeedface || magic&^0x01000000 == 0xcefaedfe {
-		ldmacho := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
-			textp, err := loadmacho.Load(ctxt.Arch, ctxt.Syms, f, pkg, length, pn)
-			if err != nil {
-				Errorf(nil, "%v", err)
-				return
+		if *flagNewobj {
+			ldmacho := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
+				textp, err := loadmacho.Load(ctxt.loader, ctxt.Arch, ctxt.Syms, f, pkg, length, pn)
+				if err != nil {
+					Errorf(nil, "%v", err)
+					return
+				}
+				ctxt.Textp = append(ctxt.Textp, textp...)
 			}
-			ctxt.Textp = append(ctxt.Textp, textp...)
+			return ldhostobj(ldmacho, ctxt.HeadType, f, pkg, length, pn, file)
+		} else {
+			ldmacho := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
+				textp, err := loadmacho.LoadOld(ctxt.Arch, ctxt.Syms, f, pkg, length, pn)
+				if err != nil {
+					Errorf(nil, "%v", err)
+					return
+				}
+				ctxt.Textp = append(ctxt.Textp, textp...)
+			}
+			return ldhostobj(ldmacho, ctxt.HeadType, f, pkg, length, pn, file)
 		}
-		return ldhostobj(ldmacho, ctxt.HeadType, f, pkg, length, pn, file)
 	}
 
 	if c1 == 0x4c && c2 == 0x01 || c1 == 0x64 && c2 == 0x86 {
-		ldpe := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
-			textp, rsrc, err := loadpe.Load(ctxt.Arch, ctxt.Syms, f, pkg, length, pn)
-			if err != nil {
-				Errorf(nil, "%v", err)
-				return
+		if *flagNewobj {
+			ldpe := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
+				textp, rsrc, err := loadpe.Load(ctxt.loader, ctxt.Arch, ctxt.Syms, f, pkg, length, pn)
+				if err != nil {
+					Errorf(nil, "%v", err)
+					return
+				}
+				if rsrc != nil {
+					setpersrc(ctxt, rsrc)
+				}
+				ctxt.Textp = append(ctxt.Textp, textp...)
 			}
-			if rsrc != nil {
-				setpersrc(ctxt, rsrc)
+			return ldhostobj(ldpe, ctxt.HeadType, f, pkg, length, pn, file)
+		} else {
+			ldpe := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
+				textp, rsrc, err := loadpe.LoadOld(ctxt.Arch, ctxt.Syms, f, pkg, length, pn)
+				if err != nil {
+					Errorf(nil, "%v", err)
+					return
+				}
+				if rsrc != nil {
+					setpersrc(ctxt, rsrc)
+				}
+				ctxt.Textp = append(ctxt.Textp, textp...)
 			}
-			ctxt.Textp = append(ctxt.Textp, textp...)
+			return ldhostobj(ldpe, ctxt.HeadType, f, pkg, length, pn, file)
 		}
-		return ldhostobj(ldpe, ctxt.HeadType, f, pkg, length, pn, file)
 	}
 
 	if c1 == 0x01 && (c2 == 0xD7 || c2 == 0xF7) {
-		ldxcoff := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
-			textp, err := loadxcoff.Load(ctxt.Arch, ctxt.Syms, f, pkg, length, pn)
-			if err != nil {
-				Errorf(nil, "%v", err)
-				return
+		if *flagNewobj {
+			ldxcoff := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
+				textp, err := loadxcoff.Load(ctxt.loader, ctxt.Arch, ctxt.Syms, f, pkg, length, pn)
+				if err != nil {
+					Errorf(nil, "%v", err)
+					return
+				}
+				ctxt.Textp = append(ctxt.Textp, textp...)
 			}
-			ctxt.Textp = append(ctxt.Textp, textp...)
+			return ldhostobj(ldxcoff, ctxt.HeadType, f, pkg, length, pn, file)
+		} else {
+			ldxcoff := func(ctxt *Link, f *bio.Reader, pkg string, length int64, pn string) {
+				textp, err := loadxcoff.LoadOld(ctxt.Arch, ctxt.Syms, f, pkg, length, pn)
+				if err != nil {
+					Errorf(nil, "%v", err)
+					return
+				}
+				ctxt.Textp = append(ctxt.Textp, textp...)
+			}
+			return ldhostobj(ldxcoff, ctxt.HeadType, f, pkg, length, pn, file)
 		}
-		return ldhostobj(ldxcoff, ctxt.HeadType, f, pkg, length, pn, file)
 	}
 
 	/* check the header */
@@ -1809,7 +1888,12 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
 	default:
 		log.Fatalf("invalid -strictdups flag value %d", *FlagStrictDups)
 	}
-	c := objfile.Load(ctxt.Arch, ctxt.Syms, f, lib, unit, eof-f.Offset(), pn, flags)
+	var c int
+	if *flagNewobj {
+		ctxt.loader.Preload(ctxt.Arch, ctxt.Syms, f, lib, unit, eof-f.Offset(), pn, flags)
+	} else {
+		c = objfile.Load(ctxt.Arch, ctxt.Syms, f, lib, unit, eof-f.Offset(), pn, flags)
+	}
 	strictDupMsgCount += c
 	addImports(ctxt, lib, pn)
 	return nil
@@ -1964,7 +2048,17 @@ func ldshlibsyms(ctxt *Link, shlib string) {
 			ver = sym.SymVerABIInternal
 		}
 
-		lsym := ctxt.Syms.Lookup(elfsym.Name, ver)
+		var lsym *sym.Symbol
+		if *flagNewobj {
+			i := ctxt.loader.AddExtSym(elfsym.Name, ver)
+			if i == 0 {
+				continue
+			}
+			lsym = ctxt.Syms.Newsym(elfsym.Name, ver)
+			ctxt.loader.Syms[i] = lsym
+		} else {
+			lsym = ctxt.Syms.Lookup(elfsym.Name, ver)
+		}
 		// Because loadlib above loads all .a files before loading any shared
 		// libraries, any non-dynimport symbols we find that duplicate symbols
 		// already loaded should be ignored (the symbols from the .a files
@@ -1993,7 +2087,17 @@ func ldshlibsyms(ctxt *Link, shlib string) {
 		// mangle Go function names in the .so to include the
 		// ABI.
 		if elf.ST_TYPE(elfsym.Info) == elf.STT_FUNC && ver == 0 {
-			alias := ctxt.Syms.Lookup(elfsym.Name, sym.SymVerABIInternal)
+			var alias *sym.Symbol
+			if *flagNewobj {
+				i := ctxt.loader.AddExtSym(elfsym.Name, sym.SymVerABIInternal)
+				if i == 0 {
+					continue
+				}
+				alias = ctxt.Syms.Newsym(elfsym.Name, sym.SymVerABIInternal)
+				ctxt.loader.Syms[i] = alias
+			} else {
+				alias = ctxt.Syms.Lookup(elfsym.Name, sym.SymVerABIInternal)
+			}
 			if alias.Type != 0 {
 				continue
 			}
@@ -2388,6 +2492,9 @@ func genasmsym(ctxt *Link, put func(*Link, *sym.Symbol, string, SymbolType, int6
 			}
 
 		case sym.SHOSTOBJ:
+			if !s.Attr.Reachable() {
+				continue
+			}
 			if ctxt.HeadType == objabi.Hwindows || ctxt.IsELF {
 				put(ctxt, s, s.Name, UndefinedSym, s.Value, nil)
 			}
@@ -2584,3 +2691,49 @@ func dfs(lib *sym.Library, mark map[*sym.Library]markKind, order *[]*sym.Library
 	mark[lib] = visited
 	*order = append(*order, lib)
 }
+
+func (ctxt *Link) loadlibfull() {
+	// Load full symbol contents, resolve indexed references.
+	ctxt.loader.LoadFull(ctxt.Arch, ctxt.Syms)
+
+	// Pull the symbols out.
+	ctxt.loader.ExtractSymbols(ctxt.Syms)
+
+	// Load cgo directives.
+	for _, d := range ctxt.cgodata {
+		setCgoAttr(ctxt, ctxt.Syms.Lookup, d.file, d.pkg, d.directives)
+	}
+
+	setupdynexp(ctxt)
+
+	// Populate ctxt.Reachparent if appropriate.
+	if ctxt.Reachparent != nil {
+		for i := 0; i < len(ctxt.loader.Reachparent); i++ {
+			p := ctxt.loader.Reachparent[i]
+			if p == 0 {
+				continue
+			}
+			if p == loader.Sym(i) {
+				panic("self-cycle in reachparent")
+			}
+			sym := ctxt.loader.Syms[i]
+			psym := ctxt.loader.Syms[p]
+			ctxt.Reachparent[sym] = psym
+		}
+	}
+
+	// Drop the reference.
+	ctxt.loader = nil
+	ctxt.cgodata = nil
+
+	addToTextp(ctxt)
+}
+
+func (ctxt *Link) dumpsyms() {
+	for _, s := range ctxt.Syms.Allsym {
+		fmt.Printf("%s %s %p %v %v\n", s, s.Type, s, s.Attr.Reachable(), s.Attr.OnList())
+		for i := range s.R {
+			fmt.Println("\t", s.R[i].Type, s.R[i].Sym)
+		}
+	}
+}

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

@@ -35,6 +35,7 @@ import (
 	"cmd/internal/obj"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
+	"cmd/link/internal/loader"
 	"cmd/link/internal/sym"
 	"debug/elf"
 	"fmt"
@@ -96,6 +97,18 @@ type Link struct {
 	runtimeCU *sym.CompilationUnit   // One of the runtime CUs, the last one seen.
 
 	relocbuf []byte // temporary buffer for applying relocations
+
+	loader  *loader.Loader
+	cgodata []cgodata // cgo directives to load, three strings are args for loadcgo
+
+	cgo_export_static  map[string]bool
+	cgo_export_dynamic map[string]bool
+}
+
+type cgodata struct {
+	file       string
+	pkg        string
+	directives [][]string
 }
 
 type unresolvedSymKey struct {

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

@@ -87,6 +87,7 @@ var (
 	flagInterpreter = flag.String("I", "", "use `linker` as ELF dynamic linker")
 	FlagDebugTramp  = flag.Int("debugtramp", 0, "debug trampolines")
 	FlagStrictDups  = flag.Int("strictdups", 0, "sanity check duplicate symbol contents during object file reading (1=warn 2=err).")
+	flagNewobj      = flag.Bool("newobj", false, "use new object file format")
 
 	FlagRound       = flag.Int("R", -1, "set address rounding `quantum`")
 	FlagTextAddr    = flag.Int64("T", -1, "set text segment `address`")
@@ -208,8 +209,13 @@ func Main(arch *sys.Arch, theArch Arch) {
 	}
 	ctxt.loadlib()
 
-	ctxt.dostrdata()
 	deadcode(ctxt)
+	if *flagNewobj {
+		ctxt.loadlibfull() // XXX do it here for now
+	}
+	ctxt.linksetup()
+	ctxt.dostrdata()
+
 	dwarfGenerateDebugInfo(ctxt)
 	if objabi.Fieldtrack_enabled != 0 {
 		fieldtrack(ctxt)

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

@@ -305,10 +305,10 @@ func (ctxt *Link) pclntab() {
 				// appears in the Pcfile table. In that case, this assigns
 				// the outer file a number.
 				numberfile(ctxt, call.File)
-				nameoff := nameToOffset(call.Func.Name)
+				nameoff := nameToOffset(call.Func)
 
 				inlTreeSym.SetUint16(ctxt.Arch, int64(i*20+0), uint16(call.Parent))
-				inlTreeSym.SetUint8(ctxt.Arch, int64(i*20+2), uint8(objabi.GetFuncID(call.Func.Name, call.Func.File)))
+				inlTreeSym.SetUint8(ctxt.Arch, int64(i*20+2), uint8(objabi.GetFuncID(call.Func, "")))
 				// byte 3 is unused
 				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+4), uint32(call.File.Value))
 				inlTreeSym.SetUint32(ctxt.Arch, int64(i*20+8), uint32(call.Line))

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

@@ -694,7 +694,7 @@ func (ctxt *Link) symtab() {
 	// creating the moduledata from scratch and it does not have a
 	// compiler-provided size, so read it from the type data.
 	moduledatatype := ctxt.Syms.ROLookup("type.runtime.moduledata", 0)
-	moduledata.Size = decodetypeSize(ctxt.Arch, moduledatatype)
+	moduledata.Size = decodetypeSize(ctxt.Arch, moduledatatype.P)
 	moduledata.Grow(moduledata.Size)
 
 	lastmoduledatap := ctxt.Syms.Lookup("runtime.lastmoduledatap", 0)

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

@@ -88,3 +88,10 @@ func contains(s []string, v string) bool {
 	}
 	return false
 }
+
+// implements sort.Interface, for sorting symbols by name.
+type byName []*sym.Symbol
+
+func (s byName) Len() int           { return len(s) }
+func (s byName) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s byName) Less(i, j int) bool { return s[i].Name < s[j].Name }

src/cmd/link/internal/loadelf/ldelf.go

@@ -10,6 +10,7 @@ import (
 	"cmd/internal/bio"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
+	"cmd/link/internal/loader"
 	"cmd/link/internal/sym"
 	"debug/elf"
 	"encoding/binary"
@@ -451,7 +452,20 @@ func parseArmAttributes(e binary.ByteOrder, data []byte) (found bool, ehdrFlags
 	return found, ehdrFlags, nil
 }
 
-// Load loads the ELF file pn from f.
+func Load(l *loader.Loader, arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length int64, pn string, flags uint32) ([]*sym.Symbol, uint32, error) {
+	newSym := func(name string, version int) *sym.Symbol {
+		return l.LookupOrCreate(name, version, syms)
+	}
+	return load(arch, syms.IncVersion(), newSym, newSym, f, pkg, length, pn, flags)
+}
+
+func LoadOld(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length int64, pn string, flags uint32) ([]*sym.Symbol, uint32, error) {
+	return load(arch, syms.IncVersion(), syms.Newsym, syms.Lookup, f, pkg, length, pn, flags)
+}
+
+type lookupFunc func(string, int) *sym.Symbol
+
+// load loads the ELF file pn from f.
 // Symbols are written into syms, and a slice of the text symbols is returned.
 //
 // On ARM systems, Load will attempt to determine what ELF header flags to
@@ -459,12 +473,11 @@ func parseArmAttributes(e binary.ByteOrder, data []byte) (found bool, ehdrFlags
 // parameter initEhdrFlags contains the current header flags for the output
 // object, and the returned ehdrFlags contains what this Load function computes.
 // TODO: find a better place for this logic.
-func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length int64, pn string, initEhdrFlags uint32) (textp []*sym.Symbol, ehdrFlags uint32, err error) {
+func load(arch *sys.Arch, localSymVersion int, newSym, lookup lookupFunc, f *bio.Reader, pkg string, length int64, pn string, initEhdrFlags uint32) (textp []*sym.Symbol, ehdrFlags uint32, err error) {
 	errorf := func(str string, args ...interface{}) ([]*sym.Symbol, uint32, error) {
 		return nil, 0, fmt.Errorf("loadelf: %s: %v", pn, fmt.Sprintf(str, args...))
 	}
 
-	localSymVersion := syms.IncVersion()
 	base := f.Offset()
 
 	var hdrbuf [64]uint8
@@ -715,7 +728,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length i
 		}
 		sectsymNames[name] = true
 
-		s := syms.Lookup(name, localSymVersion)
+		s := lookup(name, localSymVersion)
 
 		switch int(sect.flags) & (ElfSectFlagAlloc | ElfSectFlagWrite | ElfSectFlagExec) {
 		default:
@@ -754,7 +767,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length i
 
 	for i := 1; i < elfobj.nsymtab; i++ {
 		var elfsym ElfSym
-		if err := readelfsym(arch, syms, elfobj, i, &elfsym, 1, localSymVersion); err != nil {
+		if err := readelfsym(newSym, lookup, arch, elfobj, i, &elfsym, 1, localSymVersion); err != nil {
 			return errorf("%s: malformed elf file: %v", pn, err)
 		}
 		symbols[i] = elfsym.sym
@@ -925,7 +938,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length i
 				rp.Sym = nil
 			} else {
 				var elfsym ElfSym
-				if err := readelfsym(arch, syms, elfobj, int(info>>32), &elfsym, 0, 0); err != nil {
+				if err := readelfsym(newSym, lookup, arch, elfobj, int(info>>32), &elfsym, 0, 0); err != nil {
 					return errorf("malformed elf file: %v", err)
 				}
 				elfsym.sym = symbols[info>>32]
@@ -1002,7 +1015,7 @@ func elfmap(elfobj *ElfObj, sect *ElfSect) (err error) {
 	return nil
 }
 
-func readelfsym(arch *sys.Arch, syms *sym.Symbols, elfobj *ElfObj, i int, elfsym *ElfSym, needSym int, localSymVersion int) (err error) {
+func readelfsym(newSym, lookup lookupFunc, arch *sys.Arch, elfobj *ElfObj, i int, elfsym *ElfSym, needSym int, localSymVersion int) (err error) {
 	if i >= elfobj.nsymtab || i < 0 {
 		err = fmt.Errorf("invalid elf symbol index")
 		return err
@@ -1052,7 +1065,7 @@ func readelfsym(arch *sys.Arch, syms *sym.Symbols, elfobj *ElfObj, i int, elfsym
 		switch elfsym.bind {
 		case ElfSymBindGlobal:
 			if needSym != 0 {
-				s = syms.Lookup(elfsym.name, 0)
+				s = lookup(elfsym.name, 0)
 
 				// for global scoped hidden symbols we should insert it into
 				// symbol hash table, but mark them as hidden.
@@ -1077,7 +1090,7 @@ func readelfsym(arch *sys.Arch, syms *sym.Symbols, elfobj *ElfObj, i int, elfsym
 				// We need to be able to look this up,
 				// so put it in the hash table.
 				if needSym != 0 {
-					s = syms.Lookup(elfsym.name, localSymVersion)
+					s = lookup(elfsym.name, localSymVersion)
 					s.Attr |= sym.AttrVisibilityHidden
 				}
 
@@ -1088,14 +1101,14 @@ func readelfsym(arch *sys.Arch, syms *sym.Symbols, elfobj *ElfObj, i int, elfsym
 				// local names and hidden global names are unique
 				// and should only be referenced by their index, not name, so we
 				// don't bother to add them into the hash table
-				s = syms.Newsym(elfsym.name, localSymVersion)
+				s = newSym(elfsym.name, localSymVersion)
 
 				s.Attr |= sym.AttrVisibilityHidden
 			}
 
 		case ElfSymBindWeak:
 			if needSym != 0 {
-				s = syms.Lookup(elfsym.name, 0)
+				s = lookup(elfsym.name, 0)
 				if elfsym.other == 2 {
 					s.Attr |= sym.AttrVisibilityHidden
 				}

src/cmd/link/internal/loadmacho/ldmacho.go

@@ -10,6 +10,7 @@ import (
 	"cmd/internal/bio"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
+	"cmd/link/internal/loader"
 	"cmd/link/internal/sym"
 	"encoding/binary"
 	"fmt"
@@ -423,14 +424,24 @@ func macholoadsym(m *ldMachoObj, symtab *ldMachoSymtab) int {
 	return 0
 }
 
-// Load loads the Mach-O file pn from f.
+func Load(l *loader.Loader, arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length int64, pn string) ([]*sym.Symbol, error) {
+	newSym := func(name string, version int) *sym.Symbol {
+		return l.LookupOrCreate(name, version, syms)
+	}
+	return load(arch, syms.IncVersion(), newSym, f, pkg, length, pn)
+}
+
+func LoadOld(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, err error) {
+	return load(arch, syms.IncVersion(), syms.Lookup, f, pkg, length, pn)
+}
+
+// load the Mach-O file pn from f.
 // Symbols are written into syms, and a slice of the text symbols is returned.
-func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, err error) {
+func load(arch *sys.Arch, localSymVersion int, lookup func(string, int) *sym.Symbol, f *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, err error) {
 	errorf := func(str string, args ...interface{}) ([]*sym.Symbol, error) {
 		return nil, fmt.Errorf("loadmacho: %v: %v", pn, fmt.Sprintf(str, args...))
 	}
 
-	localSymVersion := syms.IncVersion()
 	base := f.Offset()
 
 	var hdr [7 * 4]uint8
@@ -562,7 +573,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length i
 			continue
 		}
 		name := fmt.Sprintf("%s(%s/%s)", pkg, sect.segname, sect.name)
-		s := syms.Lookup(name, localSymVersion)
+		s := lookup(name, localSymVersion)
 		if s.Type != 0 {
 			return errorf("duplicate %s/%s", sect.segname, sect.name)
 		}
@@ -610,7 +621,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, f *bio.Reader, pkg string, length i
 		if machsym.type_&N_EXT == 0 {
 			v = localSymVersion
 		}
-		s := syms.Lookup(name, v)
+		s := lookup(name, v)
 		if machsym.type_&N_EXT == 0 {
 			s.Attr |= sym.AttrDuplicateOK
 		}

src/cmd/link/internal/loadpe/ldpe.go

@@ -9,6 +9,7 @@ import (
 	"cmd/internal/bio"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
+	"cmd/link/internal/loader"
 	"cmd/link/internal/sym"
 	"debug/pe"
 	"encoding/binary"
@@ -144,12 +145,21 @@ func (f *peBiobuf) ReadAt(p []byte, off int64) (int, error) {
 	return n, nil
 }
 
-// Load loads the PE file pn from input.
+func Load(l *loader.Loader, arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, rsrc *sym.Symbol, err error) {
+	lookup := func(name string, version int) *sym.Symbol {
+		return l.LookupOrCreate(name, version, syms)
+	}
+	return load(arch, lookup, syms.IncVersion(), input, pkg, length, pn)
+}
+
+func LoadOld(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, rsrc *sym.Symbol, err error) {
+	return load(arch, syms.Lookup, syms.IncVersion(), input, pkg, length, pn)
+}
+
+// load loads the PE file pn from input.
 // Symbols are written into syms, and a slice of the text symbols is returned.
 // If an .rsrc section is found, its symbol is returned as rsrc.
-func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, rsrc *sym.Symbol, err error) {
-	localSymVersion := syms.IncVersion()
-
+func load(arch *sys.Arch, lookup func(string, int) *sym.Symbol, localSymVersion int, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, rsrc *sym.Symbol, err error) {
 	sectsyms := make(map[*pe.Section]*sym.Symbol)
 	sectdata := make(map[*pe.Section][]byte)
 
@@ -181,7 +191,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, leng
 		}
 
 		name := fmt.Sprintf("%s(%s)", pkg, sect.Name)
-		s := syms.Lookup(name, localSymVersion)
+		s := lookup(name, localSymVersion)
 
 		switch sect.Characteristics & (IMAGE_SCN_CNT_UNINITIALIZED_DATA | IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE | IMAGE_SCN_CNT_CODE | IMAGE_SCN_MEM_EXECUTE) {
 		case IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ: //.rdata
@@ -239,7 +249,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, leng
 				return nil, nil, fmt.Errorf("relocation number %d symbol index idx=%d cannot be large then number of symbols %d", j, r.SymbolTableIndex, len(f.COFFSymbols))
 			}
 			pesym := &f.COFFSymbols[r.SymbolTableIndex]
-			gosym, err := readpesym(arch, syms, f, pesym, sectsyms, localSymVersion)
+			gosym, err := readpesym(arch, lookup, f, pesym, sectsyms, localSymVersion)
 			if err != nil {
 				return nil, nil, err
 			}
@@ -351,7 +361,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, leng
 			}
 		}
 
-		s, err := readpesym(arch, syms, f, pesym, sectsyms, localSymVersion)
+		s, err := readpesym(arch, lookup, f, pesym, sectsyms, localSymVersion)
 		if err != nil {
 			return nil, nil, err
 		}
@@ -435,7 +445,7 @@ func issect(s *pe.COFFSymbol) bool {
 	return s.StorageClass == IMAGE_SYM_CLASS_STATIC && s.Type == 0 && s.Name[0] == '.'
 }
 
-func readpesym(arch *sys.Arch, syms *sym.Symbols, f *pe.File, pesym *pe.COFFSymbol, sectsyms map[*pe.Section]*sym.Symbol, localSymVersion int) (*sym.Symbol, error) {
+func readpesym(arch *sys.Arch, lookup func(string, int) *sym.Symbol, f *pe.File, pesym *pe.COFFSymbol, sectsyms map[*pe.Section]*sym.Symbol, localSymVersion int) (*sym.Symbol, error) {
 	symname, err := pesym.FullName(f.StringTable)
 	if err != nil {
 		return nil, err
@@ -481,10 +491,10 @@ func readpesym(arch *sys.Arch, syms *sym.Symbols, f *pe.File, pesym *pe.COFFSymb
 	case IMAGE_SYM_DTYPE_FUNCTION, IMAGE_SYM_DTYPE_NULL:
 		switch pesym.StorageClass {
 		case IMAGE_SYM_CLASS_EXTERNAL: //global
-			s = syms.Lookup(name, 0)
+			s = lookup(name, 0)
 
 		case IMAGE_SYM_CLASS_NULL, IMAGE_SYM_CLASS_STATIC, IMAGE_SYM_CLASS_LABEL:
-			s = syms.Lookup(name, localSymVersion)
+			s = lookup(name, localSymVersion)
 			s.Attr |= sym.AttrDuplicateOK
 
 		default:

src/cmd/link/internal/loadxcoff/ldxcoff.go

@@ -9,6 +9,7 @@ import (
 	"cmd/internal/bio"
 	"cmd/internal/objabi"
 	"cmd/internal/sys"
+	"cmd/link/internal/loader"
 	"cmd/link/internal/sym"
 	"errors"
 	"fmt"
@@ -38,13 +39,25 @@ func (f *xcoffBiobuf) ReadAt(p []byte, off int64) (int, error) {
 	return n, nil
 }
 
-// Load loads the Xcoff file pn from f.
+// Load loads xcoff files with the indexed object files.
+func Load(l *loader.Loader, arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, err error) {
+	lookup := func(name string, version int) *sym.Symbol {
+		return l.LookupOrCreate(name, version, syms)
+	}
+	return load(arch, lookup, syms.IncVersion(), input, pkg, length, pn)
+}
+
+// LoadOld uses the old version of object loading.
+func LoadOld(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, err error) {
+	return load(arch, syms.Lookup, syms.IncVersion(), input, pkg, length, pn)
+}
+
+// loads the Xcoff file pn from f.
 // Symbols are written into syms, and a slice of the text symbols is returned.
-func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, err error) {
+func load(arch *sys.Arch, lookup func(string, int) *sym.Symbol, localSymVersion int, input *bio.Reader, pkg string, length int64, pn string) (textp []*sym.Symbol, err error) {
 	errorf := func(str string, args ...interface{}) ([]*sym.Symbol, error) {
 		return nil, fmt.Errorf("loadxcoff: %v: %v", pn, fmt.Sprintf(str, args...))
 	}
-	localSymVersion := syms.IncVersion()
 
 	var ldSections []*ldSection
 
@@ -62,7 +75,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, leng
 		lds := new(ldSection)
 		lds.Section = *sect
 		name := fmt.Sprintf("%s(%s)", pkg, lds.Name)
-		s := syms.Lookup(name, localSymVersion)
+		s := lookup(name, localSymVersion)
 
 		switch lds.Type {
 		default:
@@ -100,7 +113,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, leng
 			continue
 		}
 
-		s := syms.Lookup(sx.Name, 0)
+		s := lookup(sx.Name, 0)
 
 		// Text symbol
 		if s.Type == sym.STEXT {
@@ -122,7 +135,7 @@ func Load(arch *sys.Arch, syms *sym.Symbols, input *bio.Reader, pkg string, leng
 		for i, rx := range sect.Relocs {
 			r := &rs[i]
 
-			r.Sym = syms.Lookup(rx.Symbol.Name, 0)
+			r.Sym = lookup(rx.Symbol.Name, 0)
 			if uint64(int32(rx.VirtualAddress)) != rx.VirtualAddress {
 				return errorf("virtual address of a relocation is too big: 0x%x", rx.VirtualAddress)
 			}

src/cmd/link/internal/objfile/objfile.go

@@ -369,7 +369,7 @@ overwrite:
 			pc.InlTree[i].Parent = r.readInt32()
 			pc.InlTree[i].File = r.readSymIndex()
 			pc.InlTree[i].Line = r.readInt32()
-			pc.InlTree[i].Func = r.readSymIndex()
+			pc.InlTree[i].Func = r.readSymIndex().Name
 			pc.InlTree[i].ParentPC = r.readInt32()
 		}
 

src/cmd/link/internal/ppc64/asm.go

@@ -550,7 +550,7 @@ func archreloctoc(ctxt *ld.Link, r *sym.Reloc, s *sym.Symbol, val int64) int64 {
 	const prefix = "TOC."
 	var tarSym *sym.Symbol
 	if strings.HasPrefix(r.Sym.Name, prefix) {
-		tarSym = ctxt.Syms.ROLookup(strings.TrimPrefix(r.Sym.Name, prefix), 0)
+		tarSym = r.Sym.R[0].Sym
 	} else {
 		ld.Errorf(s, "archreloctoc called for a symbol without TOC anchor")
 	}

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

@@ -534,7 +534,7 @@ type InlinedCall struct {
 	Parent   int32   // index of parent in InlTree
 	File     *Symbol // file of the inlined call
 	Line     int32   // line number of the inlined call
-	Func     *Symbol // function that was inlined
+	Func     string  // name of the function that was inlined
 	ParentPC int32   // PC of the instruction just before the inlined body (offset from function start)
 }
 

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

@@ -86,6 +86,17 @@ func (syms *Symbols) ROLookup(name string, v int) *Symbol {
 	return syms.hash[v][name]
 }
 
+// Add an existing symbol to the symbol table.
+func (syms *Symbols) Add(s *Symbol) {
+	name := s.Name
+	v := int(s.Version)
+	m := syms.hash[v]
+	if _, ok := m[name]; ok {
+		panic(name + " already added")
+	}
+	m[name] = s
+}
+
 // Allocate a new version (i.e. symbol namespace).
 func (syms *Symbols) IncVersion() int {
 	syms.hash = append(syms.hash, make(map[string]*Symbol))

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

@@ -161,3 +161,8 @@ var RelROMap = map[SymKind]SymKind{
 	SRODATA:   SRODATARELRO,
 	SFUNCTAB:  SFUNCTABRELRO,
 }
+
+// IsData returns true if the type is a data type.
+func (t SymKind) IsData() bool {
+	return t == SDATA || t == SNOPTRDATA || t == SBSS || t == SNOPTRBSS
+}

src/cmd/link/link_test.go

@@ -376,3 +376,68 @@ func TestIssue34788Android386TLSSequence(t *testing.T) {
 		}
 	}
 }
+
+const testStrictDupGoSrc = `
+package main
+func f()
+func main() { f() }
+`
+
+const testStrictDupAsmSrc1 = `
+#include "textflag.h"
+TEXT	·f(SB), NOSPLIT|DUPOK, $0-0
+	RET
+`
+
+const testStrictDupAsmSrc2 = `
+#include "textflag.h"
+TEXT	·f(SB), NOSPLIT|DUPOK, $0-0
+	JMP	0(PC)
+`
+
+func TestStrictDup(t *testing.T) {
+	// Check that -strictdups flag works.
+	testenv.MustHaveGoBuild(t)
+
+	tmpdir, err := ioutil.TempDir("", "TestStrictDup")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpdir)
+
+	src := filepath.Join(tmpdir, "x.go")
+	err = ioutil.WriteFile(src, []byte(testStrictDupGoSrc), 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+	src = filepath.Join(tmpdir, "a.s")
+	err = ioutil.WriteFile(src, []byte(testStrictDupAsmSrc1), 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+	src = filepath.Join(tmpdir, "b.s")
+	err = ioutil.WriteFile(src, []byte(testStrictDupAsmSrc2), 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	cmd := exec.Command(testenv.GoToolPath(t), "build", "-ldflags=-strictdups=1")
+	cmd.Dir = tmpdir
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Errorf("linking with -strictdups=1 failed: %v", err)
+	}
+	if !bytes.Contains(out, []byte("mismatched payload")) {
+		t.Errorf("unexpected output:\n%s", out)
+	}
+
+	cmd = exec.Command(testenv.GoToolPath(t), "build", "-ldflags=-strictdups=2")
+	cmd.Dir = tmpdir
+	out, err = cmd.CombinedOutput()
+	if err == nil {
+		t.Errorf("linking with -strictdups=2 did not fail")
+	}
+	if !bytes.Contains(out, []byte("mismatched payload")) {
+		t.Errorf("unexpected output:\n%s", out)
+	}
+}

src/runtime/internal/atomic/sys_linux_arm.s

@@ -29,9 +29,9 @@ TEXT runtime∕internal∕atomic·Cas(SB),NOSPLIT|NOFRAME,$0
 	CMP	$7, R11
 	BLT	2(PC)
 	JMP	·armcas(SB)
-	JMP	·kernelcas<>(SB)
+	JMP	kernelcas<>(SB)
 
-TEXT runtime∕internal∕atomic·kernelcas<>(SB),NOSPLIT,$0
+TEXT kernelcas<>(SB),NOSPLIT,$0
 	MOVW	ptr+0(FP), R2
 	// trigger potential paging fault here,
 	// because we don't know how to traceback through __kuser_cmpxchg

test/linkx.go

@@ -29,4 +29,10 @@ func main() {
 	fmt.Println(overwrite)
 	fmt.Println(overwritecopy)
 	fmt.Println(arraycopy[1])
+
+	// Check non-string symbols are not overwritten.
+	// This also make them used.
+	if b || x != 0 {
+		panic("b or x overwritten")
+	}
 }