unix: make mkasm_darwin.go usable with other operating systems

Rename mkasm_darwin.go to mkasm.go and pass the operating system as an
argument. This will allow mkasm to be used to generate assembly for
OpenBSD.

Updates golang/go#36435

Change-Id: I42f54f5c6edc3a18a156e0e8e3c38d07ecf26d0b
Reviewed-on: https://go-review.googlesource.com/c/sys/+/421795
Run-TryBot: Joel Sing <joel@sing.id.au>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

unix/darwin_amd64_test.go

@@ -1,4 +1,4 @@
-// go run mkasm_darwin.go amd64
+// go run mkasm.go darwin amd64
 // Code generated by the command above; DO NOT EDIT.
 
 //go:build darwin && go1.12

unix/darwin_arm64_test.go

@@ -1,4 +1,4 @@
-// go run mkasm_darwin.go arm64
+// go run mkasm.go darwin arm64
 // Code generated by the command above; DO NOT EDIT.
 
 //go:build darwin && go1.12

unix/mkall.sh

@@ -73,12 +73,12 @@ aix_ppc64)
 darwin_amd64)
 	mkerrors="$mkerrors -m64"
 	mktypes="GOARCH=$GOARCH go tool cgo -godefs"
-	mkasm="go run mkasm_darwin.go"
+	mkasm="go run mkasm.go"
 	;;
 darwin_arm64)
 	mkerrors="$mkerrors -m64"
 	mktypes="GOARCH=$GOARCH go tool cgo -godefs"
-	mkasm="go run mkasm_darwin.go"
+	mkasm="go run mkasm.go"
 	;;
 dragonfly_amd64)
 	mkerrors="$mkerrors -m64"
@@ -232,5 +232,5 @@ esac
 	if [ -n "$mksysctl" ]; then echo "$mksysctl |gofmt >$zsysctl"; fi
 	if [ -n "$mksysnum" ]; then echo "$mksysnum |gofmt >zsysnum_$GOOSARCH.go"; fi
 	if [ -n "$mktypes" ]; then echo "$mktypes types_$GOOS.go | go run mkpost.go > ztypes_$GOOSARCH.go"; fi
-	if [ -n "$mkasm" ]; then echo "$mkasm $GOARCH"; fi
+	if [ -n "$mkasm" ]; then echo "$mkasm $GOOS $GOARCH"; fi
 ) | $run

unix/mkasm.go

@@ -5,7 +5,7 @@
 //go:build ignore
 // +build ignore
 
-// mkasm_darwin.go generates assembly trampolines to call libSystem routines from Go.
+// mkasm.go generates assembly trampolines to call library routines from Go.
 // This program must be run after mksyscall.go.
 package main
 
@@ -19,9 +19,19 @@ import (
 	"strings"
 )
 
-const ptrsize = 8 // Pointer size. All supported platforms are 64-bit.
+func archPtrSize(arch string) int {
+	switch arch {
+	case "386", "arm":
+		return 4
+	case "amd64", "arm64", "mips64":
+		return 8
+	default:
+		log.Fatalf("Unknown arch %q", arch)
+		return 0
+	}
+}
 
-func generateASMFile(inFileNames []string, outFileName string, buildTags string) map[string]bool {
+func generateASMFile(arch string, inFileNames []string, outFileName, buildTags string) map[string]bool {
 	trampolines := map[string]bool{}
 	var orderedTrampolines []string
 	for _, inFileName := range inFileNames {
@@ -43,19 +53,23 @@ func generateASMFile(inFileNames []string, outFileName string, buildTags string)
 		}
 	}
 
+	ptrSize := archPtrSize(arch)
+
 	var out bytes.Buffer
-	fmt.Fprintf(&out, "// go run mkasm_darwin.go %s\n", strings.Join(os.Args[1:], " "))
+	fmt.Fprintf(&out, "// go run mkasm.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")
-	fmt.Fprintf(&out, "//go:build %s\n", buildTags)
+	if buildTags != "" {
-	fmt.Fprintf(&out, "// +build %s\n", buildTags)
+		fmt.Fprintf(&out, "//go:build %s\n", buildTags)
-	fmt.Fprintf(&out, "\n")
+		fmt.Fprintf(&out, "// +build %s\n", buildTags)
+		fmt.Fprintf(&out, "\n")
+	}
 	fmt.Fprintf(&out, "#include \"textflag.h\"\n")
 	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, "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)
+		fmt.Fprintf(&out, "DATA\t·%s_trampoline_addr(SB)/%d, $%s_trampoline<>(SB)\n", fn, ptrSize, fn)
 	}
 
 	if err := ioutil.WriteFile(outFileName, out.Bytes(), 0644); err != nil {
@@ -65,7 +79,7 @@ func generateASMFile(inFileNames []string, outFileName string, buildTags string)
 	return trampolines
 }
 
-const darwinTestTemplate = `// go run mkasm_darwin.go %s
+const darwinTestTemplate = `// go run mkasm.go %s
 // Code generated by the command above; DO NOT EDIT.
 
 //go:build darwin && go1.12
@@ -102,23 +116,37 @@ func writeDarwinTest(trampolines map[string]bool, fileName, arch string) {
 }
 
 func main() {
-	if len(os.Args) != 2 {
+	if len(os.Args) != 3 {
-		log.Fatalf("Usage: %s <arch>", os.Args[0])
+		log.Fatalf("Usage: %s <goos> <arch>", os.Args[0])
 	}
-	arch := os.Args[1]
+	goos, arch := os.Args[1], os.Args[2]
+
+	buildTags := ""
+	syscallFilename := fmt.Sprintf("syscall_%s.go", goos)
+	syscallArchFilename := fmt.Sprintf("syscall_%s_%s.go", goos, arch)
+	zsyscallArchFilename := fmt.Sprintf("zsyscall_%s_%s.go", goos, arch)
+	zsyscallASMFileName := fmt.Sprintf("zsyscall_%s_%s.s", goos, arch)
 
 	inFileNames := []string{
-		"syscall_darwin.go",
+		syscallFilename,
-		fmt.Sprintf("syscall_darwin_%s.go", arch),
+		syscallArchFilename,
-		fmt.Sprintf("zsyscall_darwin_%s.go", arch),
+		zsyscallArchFilename,
+	}
+
+	if goos == "darwin" {
+		buildTags = "go1.12"
+	}
+	trampolines := generateASMFile(arch, inFileNames, zsyscallASMFileName, buildTags)
+
+	if goos != "darwin" {
+		return
 	}
-	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),
 	}
-	trampolines2 := generateASMFile(inFileNames, fmt.Sprintf("zsyscall_darwin_%s.1_13.s", arch), "go1.13")
+	trampolines2 := generateASMFile(arch, inFileNames, fmt.Sprintf("zsyscall_darwin_%s.1_13.s", arch), "go1.13")
 
 	// merge trampolines
 	for trampoline := range trampolines2 {

unix/zsyscall_darwin_amd64.1_13.s

@@ -1,4 +1,4 @@
-// go run mkasm_darwin.go amd64
+// go run mkasm.go darwin amd64
 // Code generated by the command above; DO NOT EDIT.
 
 //go:build go1.13

unix/zsyscall_darwin_amd64.s

@@ -1,4 +1,4 @@
-// go run mkasm_darwin.go amd64
+// go run mkasm.go darwin amd64
 // Code generated by the command above; DO NOT EDIT.
 
 //go:build go1.12

unix/zsyscall_darwin_arm64.1_13.s

@@ -1,4 +1,4 @@
-// go run mkasm_darwin.go arm64
+// go run mkasm.go darwin arm64
 // Code generated by the command above; DO NOT EDIT.
 
 //go:build go1.13

unix/zsyscall_darwin_arm64.s

@@ -1,4 +1,4 @@
-// go run mkasm_darwin.go arm64
+// go run mkasm.go darwin arm64
 // Code generated by the command above; DO NOT EDIT.
 
 //go:build go1.12