diff --git a/fuzzer/fuzzer.go b/fuzzer/fuzzer.go
index 5cca527a..e0ee11ab 100644
--- a/fuzzer/fuzzer.go
+++ b/fuzzer/fuzzer.go
@@ -342,17 +342,7 @@ func execute1(env *ipc.Env, p *prog.Prog, workerId int) []cover.Cover {
 
 	try := 0
 retry:
-	exec := p.SerializeForExec()
-	if len(exec) > len(env.In) {
-		panic("program is too long")
-	}
-	copy(env.In, exec)
-	// Zero out the first word (ncmd), so that we don't have garbage there
-	// if executor crashes before writing non-garbage there.
-	for i := 0; i < 4; i++ {
-		env.Out[i] = 0
-	}
-	output, strace, failed, hanged, err := env.Exec()
+	output, strace, failed, hanged, err := env.Exec(p)
 	if err != nil {
 		if try > 10 {
 			panic(err)
diff --git a/ipc/ipc.go b/ipc/ipc.go
index 81aee497..678e7963 100644
--- a/ipc/ipc.go
+++ b/ipc/ipc.go
@@ -12,6 +12,8 @@ import (
 	"strings"
 	"syscall"
 	"time"
+
+	"github.com/google/syzkaller/prog"
 )
 
 type Env struct {
@@ -74,7 +76,19 @@ func (env *Env) Close() error {
 	}
 }
 
-func (env *Env) Exec() (output, strace []byte, failed, hanged bool, err0 error) {
+func (env *Env) Exec(p *prog.Prog) (output, strace []byte, failed, hanged bool, err0 error) {
+	if p != nil {
+		progData := p.SerializeForExec()
+		if len(progData) > len(env.In) {
+			panic("program is too long")
+		}
+		copy(env.In, progData)
+	}
+	// Zero out the first word (ncmd), so that we don't have garbage there
+	// if executor crashes before writing non-garbage there.
+	for i := 0; i < 4; i++ {
+		env.Out[i] = 0
+	}
 	dir, err := ioutil.TempDir("./", "syzkaller-testdir")
 	if err != nil {
 		err0 = fmt.Errorf("failed to create temp dir: %v", err)
@@ -184,8 +198,7 @@ func createMapping(size int) (f *os.File, mem []byte, err error) {
 	if err != nil {
 		return
 	}
-	if _, err = f.Write(make([]byte, size)); err != nil {
-		// if err = f.Truncate(int64(size)); err != nil {
+	if err = f.Truncate(int64(size)); err != nil {
 		f.Close()
 		os.Remove(f.Name())
 		return
diff --git a/ipc/ipc_test.go b/ipc/ipc_test.go
index d017b703..87a57d23 100644
--- a/ipc/ipc_test.go
+++ b/ipc/ipc_test.go
@@ -73,10 +73,7 @@ func TestEmptyProg(t *testing.T) {
 	defer env.Close()
 
 	p := new(prog.Prog)
-	data := p.SerializeForExec()
-	copy(env.In, data)
-
-	output, strace, failed, hanged, err := env.Exec()
+	output, strace, failed, hanged, err := env.Exec(p)
 	if err != nil {
 		t.Fatalf("failed to run executor: %v", err)
 	}
@@ -102,10 +99,7 @@ func TestStrace(t *testing.T) {
 	defer env.Close()
 
 	p := new(prog.Prog)
-	data := p.SerializeForExec()
-	copy(env.In, data)
-
-	_, strace, failed, hanged, err := env.Exec()
+	_, strace, failed, hanged, err := env.Exec(p)
 	if err != nil {
 		t.Fatalf("failed to run executor: %v", err)
 	}
@@ -132,10 +126,7 @@ func TestExecute(t *testing.T) {
 
 		for i := 0; i < iters/len(flags); i++ {
 			p := prog.Generate(rs, 10, nil)
-			data := p.SerializeForExec()
-			copy(env.In, data)
-
-			_, _, _, _, err := env.Exec()
+			_, _, _, _, err := env.Exec(p)
 			if err != nil {
 				t.Fatalf("failed to run executor: %v", err)
 			}
@@ -169,10 +160,7 @@ func TestCompare(t *testing.T) {
 	rs, iters := initTest(t)
 	for i := 0; i < iters; i++ {
 		p := prog.Generate(rs, 10, nil)
-		data := p.SerializeForExec()
-		copy(env1.In, data)
-
-		_, strace1, _, _, err := env1.Exec()
+		_, strace1, _, _, err := env1.Exec(p)
 		if err != nil {
 			t.Fatalf("failed to run executor: %v", err)
 		}
@@ -187,7 +175,7 @@ func TestCompare(t *testing.T) {
 		}
 		defer env2.Close() // yes, that's defer in a loop
 
-		_, strace2, _, _, err := env2.Exec()
+		_, strace2, _, _, err := env2.Exec(nil)
 		if err != nil {
 			t.Fatalf("failed to run c binary: %v", err)
 		}
diff --git a/tools/execlog/execlog.go b/tools/execlog/execlog.go
index 5d39bb95..a9081761 100644
--- a/tools/execlog/execlog.go
+++ b/tools/execlog/execlog.go
@@ -24,7 +24,7 @@ var (
 
 func main() {
 	flag.Parse()
-	var progs [][]byte
+	var progs []*prog.Prog
 	for _, fn := range strings.Split(*flagLog, ",") {
 		logf, err := os.Open(fn)
 		if err != nil {
@@ -45,13 +45,13 @@ func main() {
 				continue
 			}
 			if last != nil {
-				progs = append(progs, last.SerializeForExec())
+				progs = append(progs, last)
 				last = nil
 				cur = cur[:0]
 			}
 		}
 		if last != nil {
-			progs = append(progs, last.SerializeForExec())
+			progs = append(progs, last)
 		}
 	}
 	log.Printf("parsed %v programs", len(progs))
@@ -71,8 +71,7 @@ func main() {
 				if idx%1000 == 0 {
 					log.Printf("executing %v\n", idx)
 				}
-				copy(env.In, progs[idx%len(progs)])
-				_, _, _, _, err := env.Exec()
+				_, _, _, _, err := env.Exec(progs[idx%len(progs)])
 				if err != nil {
 					log.Printf("failed to execute program: %v", err)
 				}
diff --git a/tools/execprog/execprog.go b/tools/execprog/execprog.go
index 9ffe3911..d82ea514 100644
--- a/tools/execprog/execprog.go
+++ b/tools/execprog/execprog.go
@@ -53,8 +53,7 @@ func main() {
 		fmt.Fprintf(os.Stderr, "failed to create execution environment: %v\n", err)
 		os.Exit(1)
 	}
-	copy(env.In, p.SerializeForExec())
-	output, strace, failed, hanged, err := env.Exec()
+	output, strace, failed, hanged, err := env.Exec(p)
 	fmt.Printf("result: failed=%v hanged=%v err=%v\n\n%s", failed, hanged, err, output)
 	if *flagStrace {
 		fmt.Printf("strace output:\n%s", strace)
diff --git a/tools/stress/stress.go b/tools/stress/stress.go
index 5b84e81b..05bd5153 100644
--- a/tools/stress/stress.go
+++ b/tools/stress/stress.go
@@ -59,8 +59,7 @@ func execute(env *ipc.Env, p *prog.Prog) {
 	if *flagExecutor == "" {
 		return
 	}
-	copy(env.In, p.SerializeForExec())
-	output, _, _, _, err := env.Exec()
+	output, _, _, _, err := env.Exec(p)
 	if err != nil {
 		fmt.Printf("failed to execute executor: %v\n", err)
 	}