diff --git a/src/cmd/link/internal/amd64/asm.go b/src/cmd/link/internal/amd64/asm.go
index 5c4ffe19c256591adeb43b820a4a6eaadf999df3..d26a9a234cc3fd081b45c93376b0baa1c47d3ab3 100644
--- a/src/cmd/link/internal/amd64/asm.go
+++ b/src/cmd/link/internal/amd64/asm.go
@@ -756,7 +756,6 @@ func asmb2(ctxt *ld.Link) {
 			if ctxt.IsELF {
 				ctxt.Out.SeekSet(symo)
 				ld.Asmelfsym(ctxt)
-				ctxt.Out.Flush()
 				ctxt.Out.Write(ld.Elfstrdat)
 
 				if ctxt.LinkMode == ld.LinkExternal {
@@ -766,13 +765,11 @@ func asmb2(ctxt *ld.Link) {
 
 		case objabi.Hplan9:
 			ld.Asmplan9sym(ctxt)
-			ctxt.Out.Flush()
 
 			sym := ctxt.Syms.Lookup("pclntab", 0)
 			if sym != nil {
 				ld.Lcsize = int32(len(sym.P))
 				ctxt.Out.Write(sym.P)
-				ctxt.Out.Flush()
 			}
 
 		case objabi.Hwindows:
@@ -817,8 +814,6 @@ func asmb2(ctxt *ld.Link) {
 	case objabi.Hwindows:
 		ld.Asmbpe(ctxt)
 	}
-
-	ctxt.Out.Flush()
 }
 
 func tlsIEtoLE(s *sym.Symbol, off, size int) {
diff --git a/src/cmd/link/internal/arm/asm.go b/src/cmd/link/internal/arm/asm.go
index f3d1262879a6edc876190254e7de6934a231b9f9..e9eea5ce2c9ec1c8819092e1e2b30a62c4f68b41 100644
--- a/src/cmd/link/internal/arm/asm.go
+++ b/src/cmd/link/internal/arm/asm.go
@@ -816,7 +816,6 @@ func asmb2(ctxt *ld.Link) {
 		default:
 			if ctxt.IsELF {
 				ld.Asmelfsym(ctxt)
-				ctxt.Out.Flush()
 				ctxt.Out.Write(ld.Elfstrdat)
 
 				if ctxt.LinkMode == ld.LinkExternal {
@@ -826,13 +825,11 @@ func asmb2(ctxt *ld.Link) {
 
 		case objabi.Hplan9:
 			ld.Asmplan9sym(ctxt)
-			ctxt.Out.Flush()
 
 			sym := ctxt.Syms.Lookup("pclntab", 0)
 			if sym != nil {
 				ld.Lcsize = int32(len(sym.P))
 				ctxt.Out.Write(sym.P)
-				ctxt.Out.Flush()
 			}
 
 		case objabi.Hwindows:
@@ -863,7 +860,6 @@ func asmb2(ctxt *ld.Link) {
 		ld.Asmbpe(ctxt)
 	}
 
-	ctxt.Out.Flush()
 	if *ld.FlagC {
 		fmt.Printf("textsize=%d\n", ld.Segtext.Filelen)
 		fmt.Printf("datsize=%d\n", ld.Segdata.Filelen)
diff --git a/src/cmd/link/internal/arm64/asm.go b/src/cmd/link/internal/arm64/asm.go
index 053b8d119d99b6ace1692a688b7a2a27374530fa..46bda74c4c5118b3d4c8c36c6e07871a6015257c 100644
--- a/src/cmd/link/internal/arm64/asm.go
+++ b/src/cmd/link/internal/arm64/asm.go
@@ -866,7 +866,6 @@ func asmb2(ctxt *ld.Link) {
 		default:
 			if ctxt.IsELF {
 				ld.Asmelfsym(ctxt)
-				ctxt.Out.Flush()
 				ctxt.Out.Write(ld.Elfstrdat)
 
 				if ctxt.LinkMode == ld.LinkExternal {
@@ -876,13 +875,11 @@ func asmb2(ctxt *ld.Link) {
 
 		case objabi.Hplan9:
 			ld.Asmplan9sym(ctxt)
-			ctxt.Out.Flush()
 
 			sym := ctxt.Syms.Lookup("pclntab", 0)
 			if sym != nil {
 				ld.Lcsize = int32(len(sym.P))
 				ctxt.Out.Write(sym.P)
-				ctxt.Out.Flush()
 			}
 
 		case objabi.Hdarwin:
@@ -915,7 +912,6 @@ func asmb2(ctxt *ld.Link) {
 		ld.Asmbmacho(ctxt)
 	}
 
-	ctxt.Out.Flush()
 	if *ld.FlagC {
 		fmt.Printf("textsize=%d\n", ld.Segtext.Filelen)
 		fmt.Printf("datsize=%d\n", ld.Segdata.Filelen)
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 3979880cf4d7a7ad3e6ad69e75f3df3edc3e455c..36708ee5d1ebb16689f2185d8af085b38e042d6b 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -32,7 +32,6 @@
 package ld
 
 import (
-	"bufio"
 	"bytes"
 	"cmd/internal/gcprog"
 	"cmd/internal/objabi"
@@ -958,11 +957,10 @@ func Datblk(ctxt *Link, out *OutBuf, addr, size int64) {
 
 // Used only on Wasm for now.
 func DatblkBytes(ctxt *Link, addr int64, size int64) []byte {
-	buf := bytes.NewBuffer(make([]byte, 0, size))
-	out := &OutBuf{w: bufio.NewWriter(buf)}
+	buf := make([]byte, size)
+	out := &OutBuf{heap: buf}
 	writeDatblkToOutBuf(ctxt, out, addr, size)
-	out.Flush()
-	return buf.Bytes()
+	return buf
 }
 
 func writeDatblkToOutBuf(ctxt *Link, out *OutBuf, addr int64, size int64) {
diff --git a/src/cmd/link/internal/ld/main.go b/src/cmd/link/internal/ld/main.go
index dd089e6efa5ae19344f23b409f374d694923968b..ff9d1b51a3cf08d21893801eb48dbbf396238c17 100644
--- a/src/cmd/link/internal/ld/main.go
+++ b/src/cmd/link/internal/ld/main.go
@@ -319,35 +319,25 @@ func Main(arch *sys.Arch, theArch Arch) {
 	// for which we have computed the size and offset, in a
 	// mmap'd region. The second part writes more content, for
 	// which we don't know the size.
-	var outputMmapped bool
 	if ctxt.Arch.Family != sys.Wasm {
 		// Don't mmap if we're building for Wasm. Wasm file
 		// layout is very different so filesize is meaningless.
-		err := ctxt.Out.Mmap(filesize)
-		outputMmapped = err == nil
-	}
-	if outputMmapped {
-		// Asmb will redirect symbols to the output file mmap, and relocations
-		// will be applied directly there.
-		bench.Start("Asmb")
-		thearch.Asmb(ctxt)
-		bench.Start("reloc")
-		ctxt.reloc()
-	} else {
-		// If we don't mmap, we need to apply relocations before
-		// writing out.
-		bench.Start("reloc")
-		ctxt.reloc()
-		bench.Start("Asmb")
-		thearch.Asmb(ctxt)
+		if err := ctxt.Out.Mmap(filesize); err != nil {
+			ctxt.Errorf(0, "error mapping file: %v", err)
+		}
 	}
+
+	// Asmb will redirect symbols to the output file mmap, and relocations
+	// will be applied directly there.
+	bench.Start("Asmb")
+	thearch.Asmb(ctxt)
+	bench.Start("reloc")
+	ctxt.reloc()
 	bench.Start("Asmb2")
 	thearch.Asmb2(ctxt)
 
-	if outputMmapped {
-		bench.Start("Munmap")
-		ctxt.Out.Munmap()
-	}
+	bench.Start("Munmap")
+	ctxt.Out.Close() // Close handles Munmapping if necessary.
 
 	bench.Start("undef")
 	ctxt.undef()
diff --git a/src/cmd/link/internal/ld/outbuf.go b/src/cmd/link/internal/ld/outbuf.go
index c36fc74a445dab6d811a8dbb889a5c8add57c5e3..490d9b5b7a96c54705a1323129303b5ecf644a7f 100644
--- a/src/cmd/link/internal/ld/outbuf.go
+++ b/src/cmd/link/internal/ld/outbuf.go
@@ -5,7 +5,6 @@
 package ld
 
 import (
-	"bufio"
 	"cmd/internal/sys"
 	"cmd/link/internal/sym"
 	"encoding/binary"
@@ -61,7 +60,6 @@ type OutBuf struct {
 	buf  []byte // backing store of mmap'd output file
 	heap []byte // backing store for non-mmapped data
 
-	w      *bufio.Writer
 	name   string
 	f      *os.File
 	encbuf [8]byte // temp buffer used by WriteN methods
@@ -78,7 +76,6 @@ func (out *OutBuf) Open(name string) error {
 	}
 	out.off = 0
 	out.name = name
-	out.w = bufio.NewWriter(f)
 	out.f = f
 	return nil
 }
@@ -110,10 +107,17 @@ func (out *OutBuf) Close() error {
 	if out.isView {
 		return viewCloseError
 	}
-	out.Flush()
+	if out.isMmapped() {
+		return out.Munmap()
+	}
 	if out.f == nil {
 		return nil
 	}
+	if len(out.heap) != 0 {
+		if _, err := out.f.Write(out.heap); err != nil {
+			return err
+		}
+	}
 	if err := out.f.Close(); err != nil {
 		return err
 	}
@@ -151,10 +155,6 @@ func (out *OutBuf) Munmap() error {
 // writing. When the mmapped section is full, we switch over the heap memory
 // for writing.
 func (out *OutBuf) writeLoc(lenToWrite int64) (int64, []byte) {
-	if !out.isMmapped() {
-		panic("shouldn't happen")
-	}
-
 	// See if we have enough space in the mmaped area.
 	bufLen := int64(len(out.buf))
 	if out.off+lenToWrite <= bufLen {
@@ -178,15 +178,6 @@ func (out *OutBuf) writeLoc(lenToWrite int64) (int64, []byte) {
 }
 
 func (out *OutBuf) SeekSet(p int64) {
-	if p == out.off {
-		return
-	}
-	if !out.isMmapped() {
-		out.Flush()
-		if _, err := out.f.Seek(p, 0); err != nil {
-			Exitf("seeking to %d in %s: %v", p, out.name, err)
-		}
-	}
 	out.off = p
 }
 
@@ -195,33 +186,18 @@ func (out *OutBuf) Offset() int64 {
 }
 
 // Write writes the contents of v to the buffer.
-//
-// As Write is backed by a bufio.Writer, callers do not have
-// to explicitly handle the returned error as long as Flush is
-// eventually called.
 func (out *OutBuf) Write(v []byte) (int, error) {
-	if out.isMmapped() {
-		n := len(v)
-		pos, buf := out.writeLoc(int64(n))
-		copy(buf[pos:], v)
-		out.off += int64(n)
-		return n, nil
-	}
-	n, err := out.w.Write(v)
+	n := len(v)
+	pos, buf := out.writeLoc(int64(n))
+	copy(buf[pos:], v)
 	out.off += int64(n)
-	return n, err
+	return n, nil
 }
 
 func (out *OutBuf) Write8(v uint8) {
-	if out.isMmapped() {
-		pos, buf := out.writeLoc(1)
-		buf[pos] = v
-		out.off++
-		return
-	}
-	if err := out.w.WriteByte(v); err == nil {
-		out.off++
-	}
+	pos, buf := out.writeLoc(1)
+	buf[pos] = v
+	out.off++
 }
 
 // WriteByte is an alias for Write8 to fulfill the io.ByteWriter interface.
@@ -256,16 +232,11 @@ func (out *OutBuf) Write64b(v uint64) {
 }
 
 func (out *OutBuf) WriteString(s string) {
-	if out.isMmapped() {
-		pos, buf := out.writeLoc(int64(len(s)))
-		n := copy(buf[pos:], s)
-		if n != len(s) {
-			log.Fatalf("WriteString truncated. buffer size: %d, offset: %d, len(s)=%d", len(out.buf), out.off, len(s))
-		}
-		out.off += int64(n)
-		return
+	pos, buf := out.writeLoc(int64(len(s)))
+	n := copy(buf[pos:], s)
+	if n != len(s) {
+		log.Fatalf("WriteString truncated. buffer size: %d, offset: %d, len(s)=%d", len(out.buf), out.off, len(s))
 	}
-	n, _ := out.w.WriteString(s)
 	out.off += int64(n)
 }
 
@@ -297,26 +268,10 @@ func (out *OutBuf) WriteStringPad(s string, n int, pad []byte) {
 // edit to the symbol content.
 // If the output file is not Mmap'd, just writes the content.
 func (out *OutBuf) WriteSym(s *sym.Symbol) {
-	// NB: We inline the Write call for speediness.
-	if out.isMmapped() {
-		n := int64(len(s.P))
-		pos, buf := out.writeLoc(n)
-		copy(buf[pos:], s.P)
-		out.off += n
-		s.P = buf[pos : pos+n]
-		s.Attr.Set(sym.AttrReadOnly, false)
-	} else {
-		n, _ := out.w.Write(s.P)
-		out.off += int64(n)
-	}
-}
-
-func (out *OutBuf) Flush() {
-	var err error
-	if out.w != nil {
-		err = out.w.Flush()
-	}
-	if err != nil {
-		Exitf("flushing %s: %v", out.name, err)
-	}
+	n := int64(len(s.P))
+	pos, buf := out.writeLoc(n)
+	copy(buf[pos:], s.P)
+	out.off += n
+	s.P = buf[pos : pos+n]
+	s.Attr.Set(sym.AttrReadOnly, false)
 }
diff --git a/src/cmd/link/internal/ld/outbuf_test.go b/src/cmd/link/internal/ld/outbuf_test.go
index aae206f511a824d7bde953a7caf98c7e14d830bf..58f9b10cfa46485ba6305c12f9d30ad44fe7ba71 100644
--- a/src/cmd/link/internal/ld/outbuf_test.go
+++ b/src/cmd/link/internal/ld/outbuf_test.go
@@ -50,6 +50,7 @@ func TestWriteLoc(t *testing.T) {
 		{100, 100, 0, 100, 100, 0, true},
 		{10, 10, 0, 100, 100, 0, true},
 		{10, 20, 10, 100, 110, 10, true},
+		{0, 0, 0, 100, 100, 0, true},
 	}
 
 	for i, test := range tests {
diff --git a/src/cmd/link/internal/ld/xcoff.go b/src/cmd/link/internal/ld/xcoff.go
index 4ff123e8cd6c591bb0afc825676e5374fc8e044d..9fe3669eee2f32d997b3ddfd251011bc8818c9bc 100644
--- a/src/cmd/link/internal/ld/xcoff.go
+++ b/src/cmd/link/internal/ld/xcoff.go
@@ -1389,7 +1389,6 @@ func (f *xcoffFile) writeLdrScn(ctxt *Link, globalOff uint64) {
 	}
 
 	f.loaderSize = off + uint64(stlen)
-	ctxt.Out.Flush()
 
 	/* again for printing */
 	if !*flagA {
@@ -1559,8 +1558,6 @@ func Asmbxcoff(ctxt *Link, fileoff int64) {
 	// write string table
 	xfile.stringTable.write(ctxt.Out)
 
-	ctxt.Out.Flush()
-
 	// write headers
 	xcoffwrite(ctxt)
 }
diff --git a/src/cmd/link/internal/mips/asm.go b/src/cmd/link/internal/mips/asm.go
index b50112ad750ffa83567d421af2ba2df86c054077..21a57ccbb0d182345685c87985c74272813bc123 100644
--- a/src/cmd/link/internal/mips/asm.go
+++ b/src/cmd/link/internal/mips/asm.go
@@ -204,7 +204,6 @@ func asmb2(ctxt *ld.Link) {
 
 		ctxt.Out.SeekSet(int64(symo))
 		ld.Asmelfsym(ctxt)
-		ctxt.Out.Flush()
 		ctxt.Out.Write(ld.Elfstrdat)
 
 		if ctxt.LinkMode == ld.LinkExternal {
@@ -220,7 +219,6 @@ func asmb2(ctxt *ld.Link) {
 		ld.Asmbelf(ctxt, int64(symo))
 	}
 
-	ctxt.Out.Flush()
 	if *ld.FlagC {
 		fmt.Printf("textsize=%d\n", ld.Segtext.Filelen)
 		fmt.Printf("datsize=%d\n", ld.Segdata.Filelen)
diff --git a/src/cmd/link/internal/mips64/asm.go b/src/cmd/link/internal/mips64/asm.go
index 1b2914eea398f5af4516360f062f6eb299201149..0a2a3c11f3eff41195fac9ef1b7c339957964853 100644
--- a/src/cmd/link/internal/mips64/asm.go
+++ b/src/cmd/link/internal/mips64/asm.go
@@ -223,7 +223,6 @@ func asmb2(ctxt *ld.Link) {
 		default:
 			if ctxt.IsELF {
 				ld.Asmelfsym(ctxt)
-				ctxt.Out.Flush()
 				ctxt.Out.Write(ld.Elfstrdat)
 
 				if ctxt.LinkMode == ld.LinkExternal {
@@ -233,13 +232,11 @@ func asmb2(ctxt *ld.Link) {
 
 		case objabi.Hplan9:
 			ld.Asmplan9sym(ctxt)
-			ctxt.Out.Flush()
 
 			sym := ctxt.Syms.Lookup("pclntab", 0)
 			if sym != nil {
 				ld.Lcsize = int32(len(sym.P))
 				ctxt.Out.Write(sym.P)
-				ctxt.Out.Flush()
 			}
 		}
 	}
@@ -268,7 +265,6 @@ func asmb2(ctxt *ld.Link) {
 		ld.Asmbelf(ctxt, int64(symo))
 	}
 
-	ctxt.Out.Flush()
 	if *ld.FlagC {
 		fmt.Printf("textsize=%d\n", ld.Segtext.Filelen)
 		fmt.Printf("datsize=%d\n", ld.Segdata.Filelen)
diff --git a/src/cmd/link/internal/ppc64/asm.go b/src/cmd/link/internal/ppc64/asm.go
index d86738538d9cdca71e03656a6d1093995d729094..0e3a69143225754eff3ffa24d9c6aac762ae26ae 100644
--- a/src/cmd/link/internal/ppc64/asm.go
+++ b/src/cmd/link/internal/ppc64/asm.go
@@ -1130,7 +1130,6 @@ func asmb2(ctxt *ld.Link) {
 		default:
 			if ctxt.IsELF {
 				ld.Asmelfsym(ctxt)
-				ctxt.Out.Flush()
 				ctxt.Out.Write(ld.Elfstrdat)
 
 				if ctxt.LinkMode == ld.LinkExternal {
@@ -1140,18 +1139,15 @@ func asmb2(ctxt *ld.Link) {
 
 		case objabi.Hplan9:
 			ld.Asmplan9sym(ctxt)
-			ctxt.Out.Flush()
 
 			sym := ctxt.Syms.Lookup("pclntab", 0)
 			if sym != nil {
 				ld.Lcsize = int32(len(sym.P))
 				ctxt.Out.Write(sym.P)
-				ctxt.Out.Flush()
 			}
 
 		case objabi.Haix:
 			// symtab must be added once sections have been created in ld.Asmbxcoff
-			ctxt.Out.Flush()
 		}
 	}
 
@@ -1180,7 +1176,6 @@ func asmb2(ctxt *ld.Link) {
 		ld.Asmbxcoff(ctxt, int64(fileoff))
 	}
 
-	ctxt.Out.Flush()
 	if *ld.FlagC {
 		fmt.Printf("textsize=%d\n", ld.Segtext.Filelen)
 		fmt.Printf("datsize=%d\n", ld.Segdata.Filelen)
diff --git a/src/cmd/link/internal/riscv64/asm.go b/src/cmd/link/internal/riscv64/asm.go
index db3b602b848af45aae392a07b7014435e1a363e9..51cc5980c89a75a76a93fb4aab1251a2252fa685 100644
--- a/src/cmd/link/internal/riscv64/asm.go
+++ b/src/cmd/link/internal/riscv64/asm.go
@@ -142,7 +142,6 @@ func asmb2(ctxt *ld.Link) {
 		ctxt.Out.SeekSet(int64(symo))
 
 		ld.Asmelfsym(ctxt)
-		ctxt.Out.Flush()
 		ctxt.Out.Write(ld.Elfstrdat)
 
 		if ctxt.LinkMode == ld.LinkExternal {
@@ -157,7 +156,6 @@ func asmb2(ctxt *ld.Link) {
 	default:
 		ld.Errorf(nil, "unsupported operating system")
 	}
-	ctxt.Out.Flush()
 
 	if *ld.FlagC {
 		fmt.Printf("textsize=%d\n", ld.Segtext.Filelen)
diff --git a/src/cmd/link/internal/s390x/asm.go b/src/cmd/link/internal/s390x/asm.go
index 5d55a190726615e7489dcb78cd15bf47284a6145..9b6be28421f144d554e53a48d2bf4daa49b90250 100644
--- a/src/cmd/link/internal/s390x/asm.go
+++ b/src/cmd/link/internal/s390x/asm.go
@@ -515,7 +515,6 @@ func asmb2(ctxt *ld.Link) {
 
 		ctxt.Out.SeekSet(int64(symo))
 		ld.Asmelfsym(ctxt)
-		ctxt.Out.Flush()
 		ctxt.Out.Write(ld.Elfstrdat)
 
 		if ctxt.LinkMode == ld.LinkExternal {
@@ -531,7 +530,6 @@ func asmb2(ctxt *ld.Link) {
 		ld.Asmbelf(ctxt, int64(symo))
 	}
 
-	ctxt.Out.Flush()
 	if *ld.FlagC {
 		fmt.Printf("textsize=%d\n", ld.Segtext.Filelen)
 		fmt.Printf("datsize=%d\n", ld.Segdata.Filelen)
diff --git a/src/cmd/link/internal/wasm/asm.go b/src/cmd/link/internal/wasm/asm.go
index 550ed5bc3c43276bd94380ad61e969e9dfcc5028..7f8742d00823648701324e5eb06bb437db53c099 100644
--- a/src/cmd/link/internal/wasm/asm.go
+++ b/src/cmd/link/internal/wasm/asm.go
@@ -187,8 +187,6 @@ func asmb2(ctxt *ld.Link) {
 	if !*ld.FlagS {
 		writeNameSec(ctxt, len(hostImports), fns)
 	}
-
-	ctxt.Out.Flush()
 }
 
 func lookupType(sig *wasmFuncType, types *[]*wasmFuncType) uint32 {
diff --git a/src/cmd/link/internal/x86/asm.go b/src/cmd/link/internal/x86/asm.go
index cbc79c987b9323654d180eb7c2f17c24c76ec868..7dcdda0fa80d4539a605acf60ba7b8d67bb63a58 100644
--- a/src/cmd/link/internal/x86/asm.go
+++ b/src/cmd/link/internal/x86/asm.go
@@ -646,7 +646,6 @@ func asmb2(ctxt *ld.Link) {
 		default:
 			if ctxt.IsELF {
 				ld.Asmelfsym(ctxt)
-				ctxt.Out.Flush()
 				ctxt.Out.Write(ld.Elfstrdat)
 
 				if ctxt.LinkMode == ld.LinkExternal {
@@ -656,13 +655,11 @@ func asmb2(ctxt *ld.Link) {
 
 		case objabi.Hplan9:
 			ld.Asmplan9sym(ctxt)
-			ctxt.Out.Flush()
 
 			sym := ctxt.Syms.Lookup("pclntab", 0)
 			if sym != nil {
 				ld.Lcsize = int32(len(sym.P))
 				ctxt.Out.Write(sym.P)
-				ctxt.Out.Flush()
 			}
 
 		case objabi.Hwindows:
@@ -702,6 +699,4 @@ func asmb2(ctxt *ld.Link) {
 	case objabi.Hwindows:
 		ld.Asmbpe(ctxt)
 	}
-
-	ctxt.Out.Flush()
 }