diff --git a/src/cmd/link/internal/ld/outbuf.go b/src/cmd/link/internal/ld/outbuf.go
index f043168f1a2..b58dee368b2 100644
--- a/src/cmd/link/internal/ld/outbuf.go
+++ b/src/cmd/link/internal/ld/outbuf.go
@@ -13,6 +13,13 @@ import (
 	"os"
 )
 
+// If fallocate is not supported on this platform, return this error.
+// Note this is the same error returned by filesystems that don't support
+// fallocate, and that is intentional. The error is ignored where needed, and
+// OutBuf writes to heap memory.
+const fallocateNotSupportedErr = "operation not supported"
+const outbufMode = 0775
+
 // OutBuf is a buffered file writer.
 //
 // It is simlar to the Writer in cmd/internal/bio with a few small differences.
@@ -70,7 +77,7 @@ func (out *OutBuf) Open(name string) error {
 	if out.f != nil {
 		return errors.New("cannot open more than one file")
 	}
-	f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0775)
+	f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_TRUNC, outbufMode)
 	if err != nil {
 		return err
 	}
diff --git a/src/cmd/link/internal/ld/outbuf_darwin.go b/src/cmd/link/internal/ld/outbuf_darwin.go
new file mode 100644
index 00000000000..299902ec626
--- /dev/null
+++ b/src/cmd/link/internal/ld/outbuf_darwin.go
@@ -0,0 +1,26 @@
+// 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 ld
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func (out *OutBuf) fallocate(size uint64) error {
+	store := &syscall.Fstore_t{
+		Flags:   syscall.F_ALLOCATEALL,
+		Posmode: syscall.F_PEOFPOSMODE,
+		Offset:  0,
+		Length:  int64(size),
+	}
+
+	_, _, err := syscall.Syscall(syscall.SYS_FCNTL, uintptr(out.f.Fd()), syscall.F_PREALLOCATE, uintptr(unsafe.Pointer(store)))
+	if err != 0 {
+		return err
+	}
+
+	return nil
+}
diff --git a/src/cmd/link/internal/ld/outbuf_linux.go b/src/cmd/link/internal/ld/outbuf_linux.go
new file mode 100644
index 00000000000..93e621a70f9
--- /dev/null
+++ b/src/cmd/link/internal/ld/outbuf_linux.go
@@ -0,0 +1,11 @@
+// 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 ld
+
+import "syscall"
+
+func (out *OutBuf) fallocate(size uint64) error {
+	return syscall.Fallocate(int(out.f.Fd()), outbufMode, 0, int64(size))
+}
diff --git a/src/cmd/link/internal/ld/outbuf_mmap.go b/src/cmd/link/internal/ld/outbuf_mmap.go
index a2493d7d16e..e6ee041abbc 100644
--- a/src/cmd/link/internal/ld/outbuf_mmap.go
+++ b/src/cmd/link/internal/ld/outbuf_mmap.go
@@ -8,11 +8,19 @@ package ld
 
 import (
 	"syscall"
-	"unsafe"
 )
 
 func (out *OutBuf) Mmap(filesize uint64) error {
-	err := out.f.Truncate(int64(filesize))
+	err := out.fallocate(filesize)
+	if err != nil {
+		// Some file systems do not support fallocate. We ignore that error as linking
+		// can still take place, but you might SIGBUS when you write to the mmapped
+		// area.
+		if err.Error() != fallocateNotSupportedErr {
+			return err
+		}
+	}
+	err = out.f.Truncate(int64(filesize))
 	if err != nil {
 		Exitf("resize output file failed: %v", err)
 	}
@@ -24,27 +32,10 @@ func (out *OutBuf) munmap() {
 	if out.buf == nil {
 		return
 	}
-	err := out.Msync()
-	if err != nil {
-		Exitf("msync output file failed: %v", err)
-	}
 	syscall.Munmap(out.buf)
 	out.buf = nil
-	_, err = out.f.Seek(out.off, 0)
+	_, err := out.f.Seek(out.off, 0)
 	if err != nil {
 		Exitf("seek output file failed: %v", err)
 	}
 }
-
-func (out *OutBuf) Msync() error {
-	if out.buf == nil {
-		return nil
-	}
-	// TODO: netbsd supports mmap and msync, but the syscall package doesn't define MSYNC.
-	// It is excluded from the build tag for now.
-	_, _, errno := syscall.Syscall(syscall.SYS_MSYNC, uintptr(unsafe.Pointer(&out.buf[0])), uintptr(len(out.buf)), syscall.MS_SYNC)
-	if errno != 0 {
-		return errno
-	}
-	return nil
-}
diff --git a/src/cmd/link/internal/ld/outbuf_nofallocate.go b/src/cmd/link/internal/ld/outbuf_nofallocate.go
new file mode 100644
index 00000000000..51b4fe7affe
--- /dev/null
+++ b/src/cmd/link/internal/ld/outbuf_nofallocate.go
@@ -0,0 +1,13 @@
+// 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 !darwin,!linux
+
+package ld
+
+import "errors"
+
+func (out *OutBuf) fallocate(size uint64) error {
+	return errors.New(fallocateNotSupportedErr)
+}
diff --git a/src/cmd/link/internal/ld/outbuf_nommap.go b/src/cmd/link/internal/ld/outbuf_nommap.go
index 472fca22d74..51218d8ae7b 100644
--- a/src/cmd/link/internal/ld/outbuf_nommap.go
+++ b/src/cmd/link/internal/ld/outbuf_nommap.go
@@ -12,5 +12,4 @@ func (out *OutBuf) Mmap(filesize uint64) error {
 	return nil
 }
 
-func (out *OutBuf) munmap()      { panic("unreachable") }
-func (out *OutBuf) Msync() error { panic("unreachable") }
+func (out *OutBuf) munmap() { panic("unreachable") }
diff --git a/src/cmd/link/internal/ld/outbuf_test.go b/src/cmd/link/internal/ld/outbuf_test.go
index 58f9b10cfa4..d8c21426b35 100644
--- a/src/cmd/link/internal/ld/outbuf_test.go
+++ b/src/cmd/link/internal/ld/outbuf_test.go
@@ -33,6 +33,9 @@ func TestMMap(t *testing.T) {
 	if err := ob.Mmap(1 << 20); err != nil {
 		t.Errorf("error mmapping file %v", err)
 	}
+	if !ob.isMmapped() {
+		t.Errorf("should be mmapped")
+	}
 }
 
 // TestWriteLoc ensures that the math surrounding writeLoc is correct.
diff --git a/src/cmd/link/internal/ld/outbuf_windows.go b/src/cmd/link/internal/ld/outbuf_windows.go
index fc4fc5fb3bc..a7140cce388 100644
--- a/src/cmd/link/internal/ld/outbuf_windows.go
+++ b/src/cmd/link/internal/ld/outbuf_windows.go
@@ -41,10 +41,3 @@ func (out *OutBuf) munmap() {
 		Exitf("UnmapViewOfFile failed: %v", err)
 	}
 }
-
-func (out *OutBuf) Msync() error {
-	if out.buf == nil {
-		return nil
-	}
-	return syscall.FlushViewOfFile(uintptr(unsafe.Pointer(&out.buf[0])), 0)
-}