diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index 833b3eb9db..bf95745d8d 100644
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -1820,7 +1820,7 @@ func ldobj(ctxt *Link, f *bio.Reader, lib *sym.Library, length int64, pn string,
 				Errorf(nil, "%v", err)
 				return
 			}
-			if rsrc != 0 {
+			if len(rsrc) != 0 {
 				setpersrc(ctxt, rsrc)
 			}
 			ctxt.Textp = append(ctxt.Textp, textp...)
diff --git a/src/cmd/link/internal/ld/pe.go b/src/cmd/link/internal/ld/pe.go
index adbf516d5c..5edaf54dd2 100644
--- a/src/cmd/link/internal/ld/pe.go
+++ b/src/cmd/link/internal/ld/pe.go
@@ -253,7 +253,7 @@ type Dll struct {
 }
 
 var (
-	rsrcsym     loader.Sym
+	rsrcsyms    []loader.Sym
 	PESECTHEADR int32
 	PEFILEHEADR int32
 	pe64        int
@@ -1508,46 +1508,56 @@ func (ctxt *Link) dope() {
 	initdynexport(ctxt)
 }
 
-func setpersrc(ctxt *Link, sym loader.Sym) {
-	if rsrcsym != 0 {
+func setpersrc(ctxt *Link, syms []loader.Sym) {
+	if len(rsrcsyms) != 0 {
 		Errorf(nil, "too many .rsrc sections")
 	}
-
-	rsrcsym = sym
+	rsrcsyms = syms
 }
 
 func addpersrc(ctxt *Link) {
-	if rsrcsym == 0 {
+	if len(rsrcsyms) == 0 {
 		return
 	}
 
-	data := ctxt.loader.Data(rsrcsym)
-	size := len(data)
-	h := pefile.addSection(".rsrc", size, size)
+	var size int64
+	for _, rsrcsym := range rsrcsyms {
+		size += ctxt.loader.SymSize(rsrcsym)
+	}
+	h := pefile.addSection(".rsrc", int(size), int(size))
 	h.characteristics = IMAGE_SCN_MEM_READ | IMAGE_SCN_CNT_INITIALIZED_DATA
 	h.checkOffset(ctxt.Out.Offset())
 
-	// relocation
-	relocs := ctxt.loader.Relocs(rsrcsym)
-	for i := 0; i < relocs.Count(); i++ {
-		r := relocs.At(i)
-		p := data[r.Off():]
-		val := uint32(int64(h.virtualAddress) + r.Add())
-
-		// 32-bit little-endian
-		p[0] = byte(val)
-
-		p[1] = byte(val >> 8)
-		p[2] = byte(val >> 16)
-		p[3] = byte(val >> 24)
+	for _, rsrcsym := range rsrcsyms {
+		// A split resource happens when the actual resource data and its relocations are
+		// split across multiple sections, denoted by a $01 or $02 at the end of the .rsrc
+		// section name.
+		splitResources := strings.Contains(ctxt.loader.SymName(rsrcsym), ".rsrc$")
+		relocs := ctxt.loader.Relocs(rsrcsym)
+		data := ctxt.loader.Data(rsrcsym)
+		for ri := 0; ri < relocs.Count(); ri++ {
+			r := relocs.At(ri)
+			p := data[r.Off():]
+			val := uint32(int64(h.virtualAddress) + r.Add())
+			if splitResources {
+				// If we're a split resource section, and that section has relocation
+				// symbols, then the data that it points to doesn't actually begin at
+				// the virtual address listed in this current section, but rather
+				// begins at the section immediately after this one. So, in order to
+				// calculate the proper virtual address of the data it's pointing to,
+				// we have to add the length of this section to the virtual address.
+				// This works because .rsrc sections are divided into two (but not more)
+				// of these sections.
+				val += uint32(len(data))
+			}
+			binary.LittleEndian.PutUint32(p, val)
+		}
+		ctxt.Out.Write(data)
 	}
-
-	ctxt.Out.Write(data)
 	h.pad(ctxt.Out, uint32(size))
 
 	// update data directory
 	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_RESOURCE].VirtualAddress = h.virtualAddress
-
 	pefile.dataDirectory[pe.IMAGE_DIRECTORY_ENTRY_RESOURCE].Size = h.virtualSize
 }
 
diff --git a/src/cmd/link/internal/loadpe/ldpe.go b/src/cmd/link/internal/loadpe/ldpe.go
index 1e6f978531..a5c025de8f 100644
--- a/src/cmd/link/internal/loadpe/ldpe.go
+++ b/src/cmd/link/internal/loadpe/ldpe.go
@@ -157,8 +157,9 @@ func makeUpdater(l *loader.Loader, bld *loader.SymbolBuilder, s loader.Sym) *loa
 
 // 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(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Reader, pkg string, length int64, pn string) (textp []loader.Sym, rsrc loader.Sym, err error) {
+// If an .rsrc section or set of .rsrc$xx sections is found, its symbols are
+// returned as rsrc.
+func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Reader, pkg string, length int64, pn string) (textp []loader.Sym, rsrc []loader.Sym, err error) {
 	lookup := func(name string, version int) (*loader.SymbolBuilder, loader.Sym) {
 		s := l.LookupOrCreateSym(name, version)
 		sb := l.MakeSymbolUpdater(s)
@@ -176,7 +177,7 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 	// TODO: replace pe.NewFile with pe.Load (grep for "add Load function" in debug/pe for details)
 	f, err := pe.NewFile(sr)
 	if err != nil {
-		return nil, 0, err
+		return nil, nil, err
 	}
 	defer f.Close()
 
@@ -211,21 +212,21 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 			bld.SetType(sym.STEXT)
 
 		default:
-			return nil, 0, fmt.Errorf("unexpected flags %#06x for PE section %s", sect.Characteristics, sect.Name)
+			return nil, nil, fmt.Errorf("unexpected flags %#06x for PE section %s", sect.Characteristics, sect.Name)
 		}
 
 		if bld.Type() != sym.SNOPTRBSS {
 			data, err := sect.Data()
 			if err != nil {
-				return nil, 0, err
+				return nil, nil, err
 			}
 			sectdata[sect] = data
 			bld.SetData(data)
 		}
 		bld.SetSize(int64(sect.Size))
 		sectsyms[sect] = s
-		if sect.Name == ".rsrc" {
-			rsrc = s
+		if sect.Name == ".rsrc" || strings.HasPrefix(sect.Name, ".rsrc$") {
+			rsrc = append(rsrc, s)
 		}
 	}
 
@@ -246,22 +247,23 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 			continue
 		}
 
+		splitResources := strings.HasPrefix(rsect.Name, ".rsrc$")
 		sb := l.MakeSymbolUpdater(sectsyms[rsect])
 		for j, r := range rsect.Relocs {
 			if int(r.SymbolTableIndex) >= len(f.COFFSymbols) {
-				return nil, 0, fmt.Errorf("relocation number %d symbol index idx=%d cannot be large then number of symbols %d", j, r.SymbolTableIndex, len(f.COFFSymbols))
+				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(l, arch, l.LookupOrCreateSym, f, pesym, sectsyms, localSymVersion)
 			if err != nil {
-				return nil, 0, err
+				return nil, nil, err
 			}
 			if gosym == 0 {
 				name, err := pesym.FullName(f.StringTable)
 				if err != nil {
 					name = string(pesym.Name[:])
 				}
-				return nil, 0, fmt.Errorf("reloc of invalid sym %s idx=%d type=%d", name, r.SymbolTableIndex, pesym.Type)
+				return nil, nil, fmt.Errorf("reloc of invalid sym %s idx=%d type=%d", name, r.SymbolTableIndex, pesym.Type)
 			}
 
 			rSym := gosym
@@ -271,11 +273,11 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 			var rType objabi.RelocType
 			switch arch.Family {
 			default:
-				return nil, 0, fmt.Errorf("%s: unsupported arch %v", pn, arch.Family)
+				return nil, nil, fmt.Errorf("%s: unsupported arch %v", pn, arch.Family)
 			case sys.I386, sys.AMD64:
 				switch r.Type {
 				default:
-					return nil, 0, fmt.Errorf("%s: %v: unknown relocation type %v", pn, sectsyms[rsect], r.Type)
+					return nil, nil, fmt.Errorf("%s: %v: unknown relocation type %v", pn, sectsyms[rsect], r.Type)
 
 				case IMAGE_REL_I386_REL32, IMAGE_REL_AMD64_REL32,
 					IMAGE_REL_AMD64_ADDR32, // R_X86_64_PC32
@@ -302,7 +304,7 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 			case sys.ARM:
 				switch r.Type {
 				default:
-					return nil, 0, fmt.Errorf("%s: %v: unknown ARM relocation type %v", pn, sectsyms[rsect], r.Type)
+					return nil, nil, fmt.Errorf("%s: %v: unknown ARM relocation type %v", pn, sectsyms[rsect], r.Type)
 
 				case IMAGE_REL_ARM_SECREL:
 					rType = objabi.R_PCREL
@@ -323,8 +325,9 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 
 			// ld -r could generate multiple section symbols for the
 			// same section but with different values, we have to take
-			// that into account
-			if issect(pesym) {
+			// that into account, or in the case of split resources,
+			// the section and its symbols are split into two sections.
+			if issect(pesym) || splitResources {
 				rAdd += int64(pesym.Value)
 			}
 
@@ -346,7 +349,7 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 
 		name, err := pesym.FullName(f.StringTable)
 		if err != nil {
-			return nil, 0, err
+			return nil, nil, err
 		}
 		if name == "" {
 			continue
@@ -384,7 +387,7 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 
 		bld, s, err := readpesym(l, arch, l.LookupOrCreateSym, f, pesym, sectsyms, localSymVersion)
 		if err != nil {
-			return nil, 0, err
+			return nil, nil, err
 		}
 
 		if pesym.SectionNumber == 0 { // extern
@@ -402,14 +405,14 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 		} else if pesym.SectionNumber > 0 && int(pesym.SectionNumber) <= len(f.Sections) {
 			sect = f.Sections[pesym.SectionNumber-1]
 			if _, found := sectsyms[sect]; !found {
-				return nil, 0, fmt.Errorf("%s: %v: missing sect.sym", pn, s)
+				return nil, nil, fmt.Errorf("%s: %v: missing sect.sym", pn, s)
 			}
 		} else {
-			return nil, 0, fmt.Errorf("%s: %v: sectnum < 0!", pn, s)
+			return nil, nil, fmt.Errorf("%s: %v: sectnum < 0!", pn, s)
 		}
 
 		if sect == nil {
-			return nil, 0, nil
+			return nil, nil, nil
 		}
 
 		if l.OuterSym(s) != 0 {
@@ -418,7 +421,7 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 			}
 			outerName := l.SymName(l.OuterSym(s))
 			sectName := l.SymName(sectsyms[sect])
-			return nil, 0, fmt.Errorf("%s: duplicate symbol reference: %s in both %s and %s", pn, l.SymName(s), outerName, sectName)
+			return nil, nil, fmt.Errorf("%s: duplicate symbol reference: %s in both %s and %s", pn, l.SymName(s), outerName, sectName)
 		}
 
 		bld = makeUpdater(l, bld, s)
@@ -429,7 +432,7 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 		bld.SetSize(4)
 		if l.SymType(sectsym) == sym.STEXT {
 			if bld.External() && !bld.DuplicateOK() {
-				return nil, 0, fmt.Errorf("%s: duplicate symbol definition", l.SymName(s))
+				return nil, nil, fmt.Errorf("%s: duplicate symbol definition", l.SymName(s))
 			}
 			bld.SetExternal(true)
 		}
@@ -446,7 +449,7 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, input *bio.Read
 		if l.SymType(s) == sym.STEXT {
 			for ; s != 0; s = l.SubSym(s) {
 				if l.AttrOnList(s) {
-					return nil, 0, fmt.Errorf("symbol %s listed multiple times", l.SymName(s))
+					return nil, nil, fmt.Errorf("symbol %s listed multiple times", l.SymName(s))
 				}
 				l.SetAttrOnList(s, true)
 				textp = append(textp, s)
diff --git a/src/cmd/link/link_test.go b/src/cmd/link/link_test.go
index 4eb02c9e8a..7eeb7ef568 100644
--- a/src/cmd/link/link_test.go
+++ b/src/cmd/link/link_test.go
@@ -786,6 +786,25 @@ func TestPErsrc(t *testing.T) {
 	if !bytes.Contains(b, []byte("Hello Gophers!")) {
 		t.Fatalf("binary does not contain expected content")
 	}
+
+	pkgdir = filepath.Join("testdata", "testPErsrc-complex")
+	exe = filepath.Join(tmpdir, "a.exe")
+	cmd = exec.Command(testenv.GoToolPath(t), "build", "-o", exe)
+	cmd.Dir = pkgdir
+	// cmd.Env = append(os.Environ(), "GOOS=windows", "GOARCH=amd64") // uncomment if debugging in a cross-compiling environment
+	out, err = cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("building failed: %v, output:\n%s", err, out)
+	}
+
+	// Check that the binary contains the rsrc data
+	b, err = ioutil.ReadFile(exe)
+	if err != nil {
+		t.Fatalf("reading output failed: %v", err)
+	}
+	if !bytes.Contains(b, []byte("resname RCDATA a.rc")) {
+		t.Fatalf("binary does not contain expected content")
+	}
 }
 
 func TestContentAddressableSymbols(t *testing.T) {
diff --git a/src/cmd/link/testdata/testPErsrc-complex/main.go b/src/cmd/link/testdata/testPErsrc-complex/main.go
new file mode 100644
index 0000000000..affd6eada2
--- /dev/null
+++ b/src/cmd/link/testdata/testPErsrc-complex/main.go
@@ -0,0 +1,43 @@
+// Copyright 2020 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.
+
+// Test that a PE rsrc section is handled correctly, when the object files
+// have been created by llvm-rc or msvc's rc.exe, which means there's the
+// @feat.00 symbol as well as split .rsrc$00 and .rsrc$01 section to deal with.
+//
+// rsrc.syso is created with:
+//    windres -i a.rc -o rsrc.syso -O coff
+// where this windres calls into llvm-rc and llvm-cvtres. The source file,
+// a.rc, simply contains a reference to its own bytes:
+//
+//    resname RCDATA a.rc
+//
+// Object dumping the resultant rsrc.syso, we can see the split sections and
+// the @feat.00 SEH symbol:
+//
+//     rsrc.syso:      file format coff-x86-64
+//
+//     architecture: x86_64
+//     start address: 0x0000000000000000
+//
+//     Export Table:
+//     Sections:
+//     Idx Name          Size     VMA              Type
+//       0 .rsrc$01      00000068 0000000000000000 DATA
+//       1 .rsrc$02      00000018 0000000000000000 DATA
+//
+//     SYMBOL TABLE:
+//     [ 0](sec -1)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000011 @feat.00
+//     [ 1](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .rsrc$01
+//     AUX scnlen 0x68 nreloc 1 nlnno 0 checksum 0x0 assoc 0 comdat 0
+//     [ 3](sec  2)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .rsrc$02
+//     AUX scnlen 0x18 nreloc 0 nlnno 0 checksum 0x0 assoc 0 comdat 0
+//     [ 5](sec  2)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x00000000 $R000000
+//     RELOCATION RECORDS FOR [.rsrc$01]:
+//     OFFSET           TYPE                     VALUE
+//     0000000000000048 IMAGE_REL_AMD64_ADDR32NB $R000000
+
+package main
+
+func main() {}
diff --git a/src/cmd/link/testdata/testPErsrc-complex/rsrc.syso b/src/cmd/link/testdata/testPErsrc-complex/rsrc.syso
new file mode 100644
index 0000000000..eff630b8a2
Binary files /dev/null and b/src/cmd/link/testdata/testPErsrc-complex/rsrc.syso differ
diff --git a/src/cmd/pack/pack.go b/src/cmd/pack/pack.go
index 82546ea7dc..412ea36d60 100644
--- a/src/cmd/pack/pack.go
+++ b/src/cmd/pack/pack.go
@@ -43,7 +43,7 @@ func main() {
 		ar = openArchive(os.Args[2], os.O_RDONLY, os.Args[3:])
 		ar.scan(ar.printContents)
 	case 'r':
-		ar = openArchive(os.Args[2], os.O_RDWR, os.Args[3:])
+		ar = openArchive(os.Args[2], os.O_RDWR|os.O_CREATE, os.Args[3:])
 		ar.addFiles()
 	case 'c':
 		ar = openArchive(os.Args[2], os.O_RDWR|os.O_TRUNC|os.O_CREATE, os.Args[3:])
@@ -124,10 +124,13 @@ func openArchive(name string, mode int, files []string) *Archive {
 		log.Fatal(err)
 	}
 	var a *archive.Archive
-	if mode&os.O_CREATE != 0 { // the c command
+	if mode&os.O_TRUNC != 0 { // the c command
 		a, err = archive.New(f)
 	} else {
 		a, err = archive.Parse(f, verbose)
+		if err != nil && mode&os.O_CREATE != 0 { // the r command
+			a, err = archive.New(f)
+		}
 	}
 	if err != nil {
 		log.Fatal(err)
@@ -315,20 +318,25 @@ func (ar *Archive) extractContents1(e *archive.Entry, out io.Writer) {
 }
 
 // isGoCompilerObjFile reports whether file is an object file created
-// by the Go compiler, which is an archive file with exactly two entries:
-// __.PKGDEF and _go_.o.
+// by the Go compiler, which is an archive file with exactly one entry
+// of __.PKGDEF, or _go_.o, or both entries.
 func isGoCompilerObjFile(a *archive.Archive) bool {
-	if len(a.Entries) != 2 {
+	switch len(a.Entries) {
+	case 1:
+		return (a.Entries[0].Type == archive.EntryGoObj && a.Entries[0].Name == "_go_.o") ||
+			(a.Entries[0].Type == archive.EntryPkgDef && a.Entries[0].Name == "__.PKGDEF")
+	case 2:
+		var foundPkgDef, foundGo bool
+		for _, e := range a.Entries {
+			if e.Type == archive.EntryPkgDef && e.Name == "__.PKGDEF" {
+				foundPkgDef = true
+			}
+			if e.Type == archive.EntryGoObj && e.Name == "_go_.o" {
+				foundGo = true
+			}
+		}
+		return foundPkgDef && foundGo
+	default:
 		return false
 	}
-	var foundPkgDef, foundGo bool
-	for _, e := range a.Entries {
-		if e.Type == archive.EntryPkgDef && e.Name == "__.PKGDEF" {
-			foundPkgDef = true
-		}
-		if e.Type == archive.EntryGoObj && e.Name == "_go_.o" {
-			foundGo = true
-		}
-	}
-	return foundPkgDef && foundGo
 }
diff --git a/src/cmd/pack/pack_test.go b/src/cmd/pack/pack_test.go
index 218c7acda6..118376f9df 100644
--- a/src/cmd/pack/pack_test.go
+++ b/src/cmd/pack/pack_test.go
@@ -302,6 +302,95 @@ func TestIssue21703(t *testing.T) {
 	run(goBin, "tool", "compile", "-I", ".", "b.go")
 }
 
+// Test the "c" command can "see through" the archive generated by the compiler.
+// This is peculiar. (See issue #43271)
+func TestCreateWithCompilerObj(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	dir := tmpDir(t)
+	defer os.RemoveAll(dir)
+	src := filepath.Join(dir, "p.go")
+	prog := "package p; var X = 42\n"
+	err := os.WriteFile(src, []byte(prog), 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	run := func(args ...string) string {
+		return doRun(t, dir, args...)
+	}
+
+	goBin := testenv.GoToolPath(t)
+	run(goBin, "build", "cmd/pack") // writes pack binary to dir
+	run(goBin, "tool", "compile", "-pack", "-o", "p.a", "p.go")
+	run("./pack", "c", "packed.a", "p.a")
+	fi, err := os.Stat(filepath.Join(dir, "p.a"))
+	if err != nil {
+		t.Fatalf("stat p.a failed: %v", err)
+	}
+	fi2, err := os.Stat(filepath.Join(dir, "packed.a"))
+	if err != nil {
+		t.Fatalf("stat packed.a failed: %v", err)
+	}
+	// For compiler-generated object file, the "c" command is
+	// expected to get (essentially) the same file back, instead
+	// of packing it into a new archive with a single entry.
+	if want, got := fi.Size(), fi2.Size(); want != got {
+		t.Errorf("packed file with different size: want %d, got %d", want, got)
+	}
+
+	// Test -linkobj flag as well.
+	run(goBin, "tool", "compile", "-linkobj", "p2.a", "-o", "p.x", "p.go")
+	run("./pack", "c", "packed2.a", "p2.a")
+	fi, err = os.Stat(filepath.Join(dir, "p2.a"))
+	if err != nil {
+		t.Fatalf("stat p2.a failed: %v", err)
+	}
+	fi2, err = os.Stat(filepath.Join(dir, "packed2.a"))
+	if err != nil {
+		t.Fatalf("stat packed2.a failed: %v", err)
+	}
+	if want, got := fi.Size(), fi2.Size(); want != got {
+		t.Errorf("packed file with different size: want %d, got %d", want, got)
+	}
+
+	run("./pack", "c", "packed3.a", "p.x")
+	fi, err = os.Stat(filepath.Join(dir, "p.x"))
+	if err != nil {
+		t.Fatalf("stat p.x failed: %v", err)
+	}
+	fi2, err = os.Stat(filepath.Join(dir, "packed3.a"))
+	if err != nil {
+		t.Fatalf("stat packed3.a failed: %v", err)
+	}
+	if want, got := fi.Size(), fi2.Size(); want != got {
+		t.Errorf("packed file with different size: want %d, got %d", want, got)
+	}
+}
+
+// Test the "r" command creates the output file if it does not exist.
+func TestRWithNonexistentFile(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	dir := tmpDir(t)
+	defer os.RemoveAll(dir)
+	src := filepath.Join(dir, "p.go")
+	prog := "package p; var X = 42\n"
+	err := os.WriteFile(src, []byte(prog), 0666)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	run := func(args ...string) string {
+		return doRun(t, dir, args...)
+	}
+
+	goBin := testenv.GoToolPath(t)
+	run(goBin, "build", "cmd/pack") // writes pack binary to dir
+	run(goBin, "tool", "compile", "-o", "p.o", "p.go")
+	run("./pack", "r", "p.a", "p.o") // should succeed
+}
+
 // doRun runs a program in a directory and returns the output.
 func doRun(t *testing.T, dir string, args ...string) string {
 	cmd := exec.Command(args[0], args[1:]...)
diff --git a/src/runtime/defs_freebsd_386.go b/src/runtime/defs_freebsd_386.go
index 767755425c..f822934d58 100644
--- a/src/runtime/defs_freebsd_386.go
+++ b/src/runtime/defs_freebsd_386.go
@@ -13,10 +13,11 @@ const (
 )
 
 const (
-	_EINTR  = 0x4
-	_EFAULT = 0xe
-	_EAGAIN = 0x23
-	_ENOSYS = 0x4e
+	_EINTR     = 0x4
+	_EFAULT    = 0xe
+	_EAGAIN    = 0x23
+	_ENOSYS    = 0x4e
+	_ETIMEDOUT = 0x3c
 
 	_O_NONBLOCK = 0x4
 	_O_CLOEXEC  = 0x100000
diff --git a/src/runtime/defs_freebsd_amd64.go b/src/runtime/defs_freebsd_amd64.go
index 5a833426fd..0b696cf227 100644
--- a/src/runtime/defs_freebsd_amd64.go
+++ b/src/runtime/defs_freebsd_amd64.go
@@ -13,10 +13,11 @@ const (
 )
 
 const (
-	_EINTR  = 0x4
-	_EFAULT = 0xe
-	_EAGAIN = 0x23
-	_ENOSYS = 0x4e
+	_EINTR     = 0x4
+	_EFAULT    = 0xe
+	_EAGAIN    = 0x23
+	_ENOSYS    = 0x4e
+	_ETIMEDOUT = 0x3c
 
 	_O_NONBLOCK = 0x4
 	_O_CLOEXEC  = 0x100000
diff --git a/src/runtime/defs_freebsd_arm.go b/src/runtime/defs_freebsd_arm.go
index b55dfd88cf..b6f3e790cf 100644
--- a/src/runtime/defs_freebsd_arm.go
+++ b/src/runtime/defs_freebsd_arm.go
@@ -13,10 +13,11 @@ const (
 )
 
 const (
-	_EINTR  = 0x4
-	_EFAULT = 0xe
-	_EAGAIN = 0x23
-	_ENOSYS = 0x4e
+	_EINTR     = 0x4
+	_EFAULT    = 0xe
+	_EAGAIN    = 0x23
+	_ENOSYS    = 0x4e
+	_ETIMEDOUT = 0x3c
 
 	_O_NONBLOCK = 0x4
 	_O_CLOEXEC  = 0x100000
diff --git a/src/runtime/defs_freebsd_arm64.go b/src/runtime/defs_freebsd_arm64.go
index 5b9d504ba6..0759a1238f 100644
--- a/src/runtime/defs_freebsd_arm64.go
+++ b/src/runtime/defs_freebsd_arm64.go
@@ -13,10 +13,11 @@ const (
 )
 
 const (
-	_EINTR  = 0x4
-	_EFAULT = 0xe
-	_EAGAIN = 0x23
-	_ENOSYS = 0x4e
+	_EINTR     = 0x4
+	_EFAULT    = 0xe
+	_EAGAIN    = 0x23
+	_ENOSYS    = 0x4e
+	_ETIMEDOUT = 0x3c
 
 	_O_NONBLOCK = 0x4
 	_O_CLOEXEC  = 0x100000
diff --git a/src/runtime/metrics/example_test.go b/src/runtime/metrics/example_test.go
new file mode 100644
index 0000000000..cade0c38bf
--- /dev/null
+++ b/src/runtime/metrics/example_test.go
@@ -0,0 +1,96 @@
+// Copyright 2020 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 metrics_test
+
+import (
+	"fmt"
+	"runtime/metrics"
+)
+
+func ExampleRead_readingOneMetric() {
+	// Name of the metric we want to read.
+	const myMetric = "/memory/classes/heap/free:bytes"
+
+	// Create a sample for the metric.
+	sample := make([]metrics.Sample, 1)
+	sample[0].Name = myMetric
+
+	// Sample the metric.
+	metrics.Read(sample)
+
+	// Check if the metric is actually supported.
+	// If it's not, the resulting value will always have
+	// kind KindBad.
+	if sample[0].Value.Kind() == metrics.KindBad {
+		panic(fmt.Sprintf("metric %q no longer supported", myMetric))
+	}
+
+	// Handle the result.
+	//
+	// It's OK to assume a particular Kind for a metric;
+	// they're guaranteed not to change.
+	freeBytes := sample[0].Value.Uint64()
+
+	fmt.Printf("free but not released memory: %d\n", freeBytes)
+}
+
+func ExampleRead_readingAllMetrics() {
+	// Get descriptions for all supported metrics.
+	descs := metrics.All()
+
+	// Create a sample for each metric.
+	samples := make([]metrics.Sample, len(descs))
+	for i := range samples {
+		samples[i].Name = descs[i].Name
+	}
+
+	// Sample the metrics. Re-use the samples slice if you can!
+	metrics.Read(samples)
+
+	// Iterate over all results.
+	for _, sample := range samples {
+		// Pull out the name and value.
+		name, value := sample.Name, sample.Value
+
+		// Handle each sample.
+		switch value.Kind() {
+		case metrics.KindUint64:
+			fmt.Printf("%s: %d\n", name, value.Uint64())
+		case metrics.KindFloat64:
+			fmt.Printf("%s: %f\n", name, value.Float64())
+		case metrics.KindFloat64Histogram:
+			// The histogram may be quite large, so let's just pull out
+			// a crude estimate for the median for the sake of this example.
+			fmt.Printf("%s: %f\n", name, medianBucket(value.Float64Histogram()))
+		case metrics.KindBad:
+			// This should never happen because all metrics are supported
+			// by construction.
+			panic("bug in runtime/metrics package!")
+		default:
+			// This may happen as new metrics get added.
+			//
+			// The safest thing to do here is to simply log it somewhere
+			// as something to look into, but ignore it for now.
+			// In the worst case, you might temporarily miss out on a new metric.
+			fmt.Printf("%s: unexpected metric Kind: %v\n", name, value.Kind())
+		}
+	}
+}
+
+func medianBucket(h *metrics.Float64Histogram) float64 {
+	total := uint64(0)
+	for _, count := range h.Counts {
+		total += count
+	}
+	thresh := total / 2
+	total = 0
+	for i, count := range h.Counts {
+		total += count
+		if total > thresh {
+			return h.Buckets[i]
+		}
+	}
+	panic("should not happen")
+}
diff --git a/src/runtime/os_freebsd.go b/src/runtime/os_freebsd.go
index 730973a202..1c60ee2a57 100644
--- a/src/runtime/os_freebsd.go
+++ b/src/runtime/os_freebsd.go
@@ -166,7 +166,7 @@ func futexsleep1(addr *uint32, val uint32, ns int64) {
 		utp = &ut
 	}
 	ret := sys_umtx_op(addr, _UMTX_OP_WAIT_UINT_PRIVATE, val, unsafe.Sizeof(*utp), utp)
-	if ret >= 0 || ret == -_EINTR {
+	if ret >= 0 || ret == -_EINTR || ret == -_ETIMEDOUT {
 		return
 	}
 	print("umtx_wait addr=", addr, " val=", val, " ret=", ret, "\n")
@@ -208,7 +208,6 @@ func newosproc(mp *m) {
 
 	var oset sigset
 	sigprocmask(_SIG_SETMASK, &sigset_all, &oset)
-	// TODO: Check for error.
 	ret := thr_new(&param, int32(unsafe.Sizeof(param)))
 	sigprocmask(_SIG_SETMASK, &oset, nil)
 	if ret < 0 {
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 64e102fb0a..5adcbf07dc 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -2882,7 +2882,9 @@ func wakeNetPoller(when int64) {
 	} else {
 		// There are no threads in the network poller, try to get
 		// one there so it can handle new timers.
-		wakep()
+		if GOOS != "plan9" { // Temporary workaround - see issue #42303.
+			wakep()
+		}
 	}
 }
 
@@ -5128,6 +5130,26 @@ func sysmon() {
 			}
 		}
 		mDoFixup()
+		if GOOS == "netbsd" {
+			// netpoll is responsible for waiting for timer
+			// expiration, so we typically don't have to worry
+			// about starting an M to service timers. (Note that
+			// sleep for timeSleepUntil above simply ensures sysmon
+			// starts running again when that timer expiration may
+			// cause Go code to run again).
+			//
+			// However, netbsd has a kernel bug that sometimes
+			// misses netpollBreak wake-ups, which can lead to
+			// unbounded delays servicing timers. If we detect this
+			// overrun, then startm to get something to handle the
+			// timer.
+			//
+			// See issue 42515 and
+			// https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=50094.
+			if next, _ := timeSleepUntil(); next < now {
+				startm(nil, false)
+			}
+		}
 		if atomic.Load(&scavenge.sysmonWake) != 0 {
 			// Kick the scavenger awake if someone requested it.
 			wakeScavenger()
diff --git a/src/runtime/sys_darwin.go b/src/runtime/sys_darwin.go
index c89ce78012..55845bf2e5 100644
--- a/src/runtime/sys_darwin.go
+++ b/src/runtime/sys_darwin.go
@@ -467,7 +467,7 @@ func setNonblock(fd int32) {
 //go:cgo_import_dynamic libc_pthread_create pthread_create "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_pthread_self pthread_self "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_pthread_kill pthread_kill "/usr/lib/libSystem.B.dylib"
-//go:cgo_import_dynamic libc_exit exit "/usr/lib/libSystem.B.dylib"
+//go:cgo_import_dynamic libc_exit _exit "/usr/lib/libSystem.B.dylib"
 //go:cgo_import_dynamic libc_raise raise "/usr/lib/libSystem.B.dylib"
 
 //go:cgo_import_dynamic libc_open open "/usr/lib/libSystem.B.dylib"
diff --git a/src/runtime/sys_freebsd_386.s b/src/runtime/sys_freebsd_386.s
index c346e719e1..97e6d9ab36 100644
--- a/src/runtime/sys_freebsd_386.s
+++ b/src/runtime/sys_freebsd_386.s
@@ -13,12 +13,16 @@
 TEXT runtime·sys_umtx_op(SB),NOSPLIT,$-4
 	MOVL	$454, AX
 	INT	$0x80
+	JAE	2(PC)
+	NEGL	AX
 	MOVL	AX, ret+20(FP)
 	RET
 
 TEXT runtime·thr_new(SB),NOSPLIT,$-4
 	MOVL	$455, AX
 	INT	$0x80
+	JAE	2(PC)
+	NEGL	AX
 	MOVL	AX, ret+8(FP)
 	RET
 
@@ -120,6 +124,8 @@ TEXT runtime·pipe2(SB),NOSPLIT,$12-16
 	MOVL	flags+0(FP), BX
 	MOVL	BX, 8(SP)
 	INT	$0x80
+	JAE	2(PC)
+	NEGL	AX
 	MOVL	AX, errno+12(FP)
 	RET
 
diff --git a/src/runtime/sys_freebsd_amd64.s b/src/runtime/sys_freebsd_amd64.s
index 010b2ec4d4..07734b0d7d 100644
--- a/src/runtime/sys_freebsd_amd64.s
+++ b/src/runtime/sys_freebsd_amd64.s
@@ -18,6 +18,8 @@ TEXT runtime·sys_umtx_op(SB),NOSPLIT,$0
 	MOVQ ut+24(FP), R8
 	MOVL $454, AX
 	SYSCALL
+	JCC	2(PC)
+	NEGQ	AX
 	MOVL	AX, ret+32(FP)
 	RET
 
@@ -26,6 +28,8 @@ TEXT runtime·thr_new(SB),NOSPLIT,$0
 	MOVL size+8(FP), SI
 	MOVL $455, AX
 	SYSCALL
+	JCC	2(PC)
+	NEGQ	AX
 	MOVL	AX, ret+16(FP)
 	RET
 
@@ -118,6 +122,8 @@ TEXT runtime·pipe2(SB),NOSPLIT,$0-20
 	MOVL	flags+0(FP), SI
 	MOVL	$542, AX
 	SYSCALL
+	JCC	2(PC)
+	NEGQ	AX
 	MOVL	AX, errno+16(FP)
 	RET
 
diff --git a/src/runtime/sys_freebsd_arm.s b/src/runtime/sys_freebsd_arm.s
index 1e12f9cfcb..b12e47c576 100644
--- a/src/runtime/sys_freebsd_arm.s
+++ b/src/runtime/sys_freebsd_arm.s
@@ -51,6 +51,7 @@ TEXT runtime·sys_umtx_op(SB),NOSPLIT,$0
 	ADD $20, R13 // arg 5 is passed on stack
 	MOVW $SYS__umtx_op, R7
 	SWI $0
+	RSB.CS $0, R0
 	SUB $20, R13
 	// BCS error
 	MOVW	R0, ret+20(FP)
@@ -61,6 +62,7 @@ TEXT runtime·thr_new(SB),NOSPLIT,$0
 	MOVW size+4(FP), R1
 	MOVW $SYS_thr_new, R7
 	SWI $0
+	RSB.CS $0, R0
 	MOVW	R0, ret+8(FP)
 	RET
 
@@ -144,6 +146,7 @@ TEXT runtime·pipe2(SB),NOSPLIT,$0-16
 	MOVW	flags+0(FP), R1
 	MOVW	$SYS_pipe2, R7
 	SWI	$0
+	RSB.CS $0, R0
 	MOVW	R0, errno+12(FP)
 	RET
 
diff --git a/src/runtime/sys_freebsd_arm64.s b/src/runtime/sys_freebsd_arm64.s
index 8a4f9b7fa1..1aa09e87ca 100644
--- a/src/runtime/sys_freebsd_arm64.s
+++ b/src/runtime/sys_freebsd_arm64.s
@@ -60,6 +60,9 @@ TEXT runtime·sys_umtx_op(SB),NOSPLIT,$0
 	MOVD	ut+24(FP), R4
 	MOVD	$SYS__umtx_op, R8
 	SVC
+	BCC	ok
+	NEG	R0, R0
+ok:
 	MOVW	R0, ret+32(FP)
 	RET
 
@@ -69,6 +72,9 @@ TEXT runtime·thr_new(SB),NOSPLIT,$0
 	MOVW	size+8(FP), R1
 	MOVD	$SYS_thr_new, R8
 	SVC
+	BCC	ok
+	NEG	R0, R0
+ok:
 	MOVW	R0, ret+16(FP)
 	RET
 
diff --git a/src/syscall/mksyscall.pl b/src/syscall/mksyscall.pl
index 790df3825b..26c93ffe5b 100755
--- a/src/syscall/mksyscall.pl
+++ b/src/syscall/mksyscall.pl
@@ -125,7 +125,7 @@ while(<>) {
 	# without reading the header.
 	$text .= "// THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT\n\n";
 
-	if ($darwin && $func eq "ptrace") {
+	if ($darwin && $func eq "ptrace1") {
 		# The ptrace function is called from forkAndExecInChild where stack
 		# growth is forbidden.
 		$text .= "//go:nosplit\n"
diff --git a/src/syscall/ptrace_darwin.go b/src/syscall/ptrace_darwin.go
new file mode 100644
index 0000000000..a873d826b8
--- /dev/null
+++ b/src/syscall/ptrace_darwin.go
@@ -0,0 +1,14 @@
+// Copyright 2020 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 !ios
+
+package syscall
+
+// Nosplit because it is called from forkAndExecInChild.
+//
+//go:nosplit
+func ptrace(request int, pid int, addr uintptr, data uintptr) error {
+	return ptrace1(request, pid, addr, data)
+}
diff --git a/src/syscall/ptrace_ios.go b/src/syscall/ptrace_ios.go
new file mode 100644
index 0000000000..2f61a88a08
--- /dev/null
+++ b/src/syscall/ptrace_ios.go
@@ -0,0 +1,12 @@
+// Copyright 2020 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 syscall
+
+// Nosplit because it is called from forkAndExecInChild.
+//
+//go:nosplit
+func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
+	panic("unimplemented")
+}
diff --git a/src/syscall/syscall_darwin_amd64.go b/src/syscall/syscall_darwin_amd64.go
index 96fadf7837..687efff770 100644
--- a/src/syscall/syscall_darwin_amd64.go
+++ b/src/syscall/syscall_darwin_amd64.go
@@ -21,7 +21,7 @@ func setTimeval(sec, usec int64) Timeval {
 //sys	Stat(path string, stat *Stat_t) (err error) = SYS_stat64
 //sys	Statfs(path string, stat *Statfs_t) (err error) = SYS_statfs64
 //sys   fstatat(fd int, path string, stat *Stat_t, flags int) (err error) = SYS_fstatat64
-//sys   ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
+//sys   ptrace1(request int, pid int, addr uintptr, data uintptr) (err error) = SYS_ptrace
 
 func SetKevent(k *Kevent_t, fd, mode, flags int) {
 	k.Ident = uint64(fd)
diff --git a/src/syscall/syscall_darwin_arm64.go b/src/syscall/syscall_darwin_arm64.go
index d267a4ae6e..ab57117475 100644
--- a/src/syscall/syscall_darwin_arm64.go
+++ b/src/syscall/syscall_darwin_arm64.go
@@ -21,7 +21,7 @@ func setTimeval(sec, usec int64) Timeval {
 //sys	Stat(path string, stat *Stat_t) (err error)
 //sys	Statfs(path string, stat *Statfs_t) (err error)
 //sys	fstatat(fd int, path string, stat *Stat_t, flags int) (err error)
-//sys	ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
+//sys	ptrace1(request int, pid int, addr uintptr, data uintptr) (err error) = SYS_ptrace
 
 func SetKevent(k *Kevent_t, fd, mode, flags int) {
 	k.Ident = uint64(fd)
diff --git a/src/syscall/zsyscall_darwin_amd64.go b/src/syscall/zsyscall_darwin_amd64.go
index ee726fb24d..4f2cdf861e 100644
--- a/src/syscall/zsyscall_darwin_amd64.go
+++ b/src/syscall/zsyscall_darwin_amd64.go
@@ -1971,7 +1971,7 @@ func libc_fstatat64_trampoline()
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
 //go:nosplit
-func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
+func ptrace1(request int, pid int, addr uintptr, data uintptr) (err error) {
 	_, _, e1 := syscall6(funcPC(libc_ptrace_trampoline), uintptr(request), uintptr(pid), uintptr(addr), uintptr(data), 0, 0)
 	if e1 != 0 {
 		err = errnoErr(e1)
diff --git a/src/syscall/zsyscall_darwin_arm64.go b/src/syscall/zsyscall_darwin_arm64.go
index ac530f3108..0d8598d816 100644
--- a/src/syscall/zsyscall_darwin_arm64.go
+++ b/src/syscall/zsyscall_darwin_arm64.go
@@ -1971,7 +1971,7 @@ func libc_fstatat_trampoline()
 // THIS FILE IS GENERATED BY THE COMMAND AT THE TOP; DO NOT EDIT
 
 //go:nosplit
-func ptrace(request int, pid int, addr uintptr, data uintptr) (err error) {
+func ptrace1(request int, pid int, addr uintptr, data uintptr) (err error) {
 	_, _, e1 := syscall6(funcPC(libc_ptrace_trampoline), uintptr(request), uintptr(pid), uintptr(addr), uintptr(data), 0, 0)
 	if e1 != 0 {
 		err = errnoErr(e1)
diff --git a/test/fixedbugs/issue11656.go b/test/fixedbugs/issue11656.go
index 62b36cf790..acd3f4f3e5 100644
--- a/test/fixedbugs/issue11656.go
+++ b/test/fixedbugs/issue11656.go
@@ -54,27 +54,30 @@ func f(n int) {
 		x uintptr
 	}
 
-	// We want to force an illegal instruction, to get a crash
-	// at a PC value != 0.
+	// We want to force a seg fault, to get a crash at a PC value != 0.
 	// Not all systems make the data section non-executable.
 	ill := make([]byte, 64)
 	switch runtime.GOARCH {
 	case "386", "amd64":
-		binary.LittleEndian.PutUint16(ill, 0x0b0f) // ud2
+		ill = append(ill, 0x89, 0x04, 0x25, 0x00, 0x00, 0x00, 0x00) // MOVL AX, 0
 	case "arm":
-		binary.LittleEndian.PutUint32(ill, 0xe7f000f0) // no name, but permanently undefined
+		binary.LittleEndian.PutUint32(ill, 0xe3a00000) // MOVW $0, R0
+		binary.LittleEndian.PutUint32(ill, 0xe5800000) // MOVW R0, (R0)
 	case "arm64":
-		binary.LittleEndian.PutUint32(ill, 0xd4207d00) // brk #1000
+		binary.LittleEndian.PutUint32(ill, 0xf90003ff) // MOVD ZR, (ZR)
 	case "ppc64":
-		binary.BigEndian.PutUint32(ill, 0x7fe00008) // trap
+		binary.BigEndian.PutUint32(ill, 0xf8000000) // MOVD R0, (R0)
 	case "ppc64le":
-		binary.LittleEndian.PutUint32(ill, 0x7fe00008) // trap
+		binary.LittleEndian.PutUint32(ill, 0xf8000000) // MOVD R0, (R0)
 	case "mips", "mips64":
-		binary.BigEndian.PutUint32(ill, 0x00000034) // trap
+		binary.BigEndian.PutUint32(ill, 0xfc000000) // MOVV R0, (R0)
 	case "mipsle", "mips64le":
-		binary.LittleEndian.PutUint32(ill, 0x00000034) // trap
+		binary.LittleEndian.PutUint32(ill, 0xfc000000) // MOVV R0, (R0)
 	case "s390x":
-		binary.BigEndian.PutUint32(ill, 0) // undefined instruction
+		ill = append(ill, 0xa7, 0x09, 0x00, 0x00)             // MOVD $0, R0
+		ill = append(ill, 0xe3, 0x00, 0x00, 0x00, 0x00, 0x24) // MOVD R0, (R0)
+	case "riscv64":
+		binary.LittleEndian.PutUint32(ill, 0x00003023) // MOV X0, (X0)
 	default:
 		// Just leave it as 0 and hope for the best.
 	}