diff --git a/unix/mkasm_darwin.go b/unix/mkasm_darwin.go
index 4e33c7a6..cfb565fc 100644
--- a/unix/mkasm_darwin.go
+++ b/unix/mkasm_darwin.go
@@ -21,11 +21,29 @@ import (
 
 const ptrsize = 8 // Pointer size. All supported platforms are 64-bit.
 
-func writeASMFile(in string, fileName string, buildTags string) map[string]bool {
+func generateASMFile(inFileNames []string, outFileName string, buildTags string) map[string]bool {
 	trampolines := map[string]bool{}
+	var orderedTrampolines []string
+	for _, inFileName := range inFileNames {
+		in, err := ioutil.ReadFile(inFileName)
+		if err != nil {
+			log.Fatalf("Failed to read file: %v", err)
+		}
+		for _, line := range strings.Split(string(in), "\n") {
+			const prefix = "var "
+			const suffix = "_trampoline_addr uintptr"
+			if !strings.HasPrefix(line, prefix) || !strings.HasSuffix(line, suffix) {
+				continue
+			}
+			fn := strings.TrimSuffix(strings.TrimPrefix(line, prefix), suffix)
+			if !trampolines[fn] {
+				orderedTrampolines = append(orderedTrampolines, fn)
+				trampolines[fn] = true
+			}
+		}
+	}
 
 	var out bytes.Buffer
-
 	fmt.Fprintf(&out, "// go run mkasm_darwin.go %s\n", strings.Join(os.Args[1:], " "))
 	fmt.Fprintf(&out, "// Code generated by the command above; DO NOT EDIT.\n")
 	fmt.Fprintf(&out, "\n")
@@ -33,24 +51,15 @@ func writeASMFile(in string, fileName string, buildTags string) map[string]bool
 	fmt.Fprintf(&out, "// +build %s\n", buildTags)
 	fmt.Fprintf(&out, "\n")
 	fmt.Fprintf(&out, "#include \"textflag.h\"\n")
-	for _, line := range strings.Split(in, "\n") {
-		const prefix = "var "
-		const suffix = "_trampoline_addr uintptr"
-		if !strings.HasPrefix(line, prefix) || !strings.HasSuffix(line, suffix) {
-			continue
-		}
-		fn := strings.TrimSuffix(strings.TrimPrefix(line, prefix), suffix)
-		if !trampolines[fn] {
-			trampolines[fn] = true
-			fmt.Fprintf(&out, "\nTEXT %s_trampoline<>(SB),NOSPLIT,$0-0\n", fn)
-			fmt.Fprintf(&out, "\tJMP\t%s(SB)\n\n", fn)
-			fmt.Fprintf(&out, "GLOBL\t·%s_trampoline_addr(SB), RODATA, $%d\n", fn, ptrsize)
-			fmt.Fprintf(&out, "DATA\t·%s_trampoline_addr(SB)/%d, $%s_trampoline<>(SB)\n", fn, ptrsize, fn)
-		}
+	for _, fn := range orderedTrampolines {
+		fmt.Fprintf(&out, "\nTEXT %s_trampoline<>(SB),NOSPLIT,$0-0\n", fn)
+		fmt.Fprintf(&out, "\tJMP\t%s(SB)\n\n", fn)
+		fmt.Fprintf(&out, "GLOBL\t·%s_trampoline_addr(SB), RODATA, $%d\n", fn, ptrsize)
+		fmt.Fprintf(&out, "DATA\t·%s_trampoline_addr(SB)/%d, $%s_trampoline<>(SB)\n", fn, ptrsize, fn)
 	}
-	err := ioutil.WriteFile(fileName, out.Bytes(), 0644)
-	if err != nil {
-		log.Fatalf("can't write %s: %s", fileName, err)
+
+	if err := ioutil.WriteFile(outFileName, out.Bytes(), 0644); err != nil {
+		log.Fatalf("Failed to write assembly file %q: %v", outFileName, err)
 	}
 
 	return trampolines
@@ -70,62 +79,46 @@ var darwinTests = [...]darwinTest{
 `
 
 func writeDarwinTest(trampolines map[string]bool, fileName, arch string) {
-	// sort trampolines
-	sorted := make([]string, len(trampolines))
-	i := 0
-	for trampoline := range trampolines {
-		sorted[i] = trampoline
-		i++
+	var sortedTrampolines []string
+	for fn := range trampolines {
+		sortedTrampolines = append(sortedTrampolines, fn)
 	}
-	sort.Slice(sorted, func(i, j int) bool { return sorted[i] < sorted[j] })
+	sort.Strings(sortedTrampolines)
 
 	var out bytes.Buffer
 
 	const prefix = "libc_"
-	for _, trampoline := range sorted {
-		fmt.Fprintf(&out, fmt.Sprintf("\t{%q, %s_trampoline_addr},\n", strings.TrimPrefix(trampoline, prefix), trampoline))
+	for _, fn := range sortedTrampolines {
+		fmt.Fprintf(&out, fmt.Sprintf("\t{%q, %s_trampoline_addr},\n", strings.TrimPrefix(fn, prefix), fn))
 	}
 	lines := out.String()
 
 	out.Reset()
 	fmt.Fprintf(&out, darwinTestTemplate, strings.Join(os.Args[1:], " "), arch, lines)
 
-	err := ioutil.WriteFile(fileName, out.Bytes(), 0644)
-	if err != nil {
-		log.Fatalf("can't write %s: %s", fileName, err)
+	if err := ioutil.WriteFile(fileName, out.Bytes(), 0644); err != nil {
+		log.Fatalf("Failed to write test file %q: %v", fileName, err)
 	}
 }
 
 func main() {
-	in1, err := ioutil.ReadFile("syscall_darwin.go")
-	if err != nil {
-		log.Fatalf("can't open syscall_darwin.go: %s", err)
+	if len(os.Args) != 2 {
+		log.Fatalf("Usage: %s <arch>", os.Args[0])
 	}
 	arch := os.Args[1]
-	in2, err := ioutil.ReadFile(fmt.Sprintf("syscall_darwin_%s.go", arch))
-	if err != nil {
-		log.Fatalf("can't open syscall_darwin_%s.go: %s", arch, err)
-	}
-	in3, err := ioutil.ReadFile(fmt.Sprintf("zsyscall_darwin_%s.go", arch))
-	if err != nil {
-		log.Fatalf("can't open zsyscall_darwin_%s.go: %s", arch, err)
-	}
-	in := string(in1) + string(in2) + string(in3)
 
-	trampolines := writeASMFile(in, fmt.Sprintf("zsyscall_darwin_%s.s", arch), "go1.12")
-
-	in1, err = ioutil.ReadFile("syscall_darwin.1_13.go")
-	if err != nil {
-		log.Fatalf("can't open syscall_darwin.1_13.go: %s", err)
+	inFileNames := []string{
+		"syscall_darwin.go",
+		fmt.Sprintf("syscall_darwin_%s.go", arch),
+		fmt.Sprintf("zsyscall_darwin_%s.go", arch),
 	}
-	in2, err = ioutil.ReadFile(fmt.Sprintf("zsyscall_darwin_%s.1_13.go", arch))
-	if err != nil {
-		log.Fatalf("can't open zsyscall_darwin_%s.1_13.go: %s", arch, err)
+	trampolines := generateASMFile(inFileNames, fmt.Sprintf("zsyscall_darwin_%s.s", arch), "go1.12")
+
+	inFileNames = []string{
+		"syscall_darwin.1_13.go",
+		fmt.Sprintf("zsyscall_darwin_%s.1_13.go", arch),
 	}
-
-	in = string(in1) + string(in2)
-
-	trampolines2 := writeASMFile(in, fmt.Sprintf("zsyscall_darwin_%s.1_13.s", arch), "go1.13")
+	trampolines2 := generateASMFile(inFileNames, fmt.Sprintf("zsyscall_darwin_%s.1_13.s", arch), "go1.13")
 
 	// merge trampolines
 	for trampoline := range trampolines2 {