use buildinfo to detect ARM version instead of taping the runtime.goa…

…rm internal variable

arm.go

@@ -1,9 +1,28 @@
 package selfupdate
 
 import (
-	// unsafe is used to get a private variable from the runtime package
-	_ "unsafe"
+	"debug/buildinfo"
+	"os"
 )
 
-//go:linkname goarm runtime.goarm
 var goarm uint8
+
+//nolint:gochecknoinits
+func init() {
+	// avoid using runtime.goarm directly
+	goarm = getGOARM(os.Args[0])
+}
+
+func getGOARM(goBinary string) uint8 {
+	build, err := buildinfo.ReadFile(goBinary)
+	if err != nil {
+		return 0
+	}
+	for _, setting := range build.Settings {
+		if setting.Key == "GOARM" {
+			// the value is coming from the linker, so it should be safe to convert
+			return uint8(setting.Value[0] - '0')
+		}
+	}
+	return 0
+}

arm_test.go

@@ -0,0 +1,45 @@
+package selfupdate
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetGOARM(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		goOS          string
+		goArch        string
+		goArm         string
+		expectedGoArm uint8
+	}{
+		{"linux", "arm", "7", 7},
+		{"linux", "arm", "6", 6},
+		{"linux", "arm", "5", 5},
+		{"linux", "arm", "", 7}, // armv7 is the default
+		{"linux", "arm64", "", 0},
+		{"linux", "amd64", "", 0},
+		{"darwin", "arm64", "", 0},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.goOS+" "+tc.goArch+" "+tc.goArm, func(t *testing.T) {
+			tempBinary := t.TempDir() + "/tempBinary-" + tc.goOS + tc.goArch + "v" + tc.goArm
+			buildCmd := fmt.Sprintf("GOOS=%s GOARCH=%s GOARM=%s go build -o %s ./testdata/hello", tc.goOS, tc.goArch, tc.goArm, tempBinary)
+			cmd := exec.Command("sh", "-c", buildCmd)
+			cmd.Stdout = os.Stdout
+			cmd.Stderr = os.Stderr
+			err := cmd.Run()
+			require.NoError(t, err)
+
+			goArm := getGOARM(tempBinary)
+			assert.Equal(t, tc.expectedGoArm, goArm)
+		})
+	}
+}

cmd/macho/.gitignore

@@ -0,0 +1 @@
+/macho_*

cmd/macho/Makefile

@@ -0,0 +1,5 @@
+.PHONY: build
+build:
+	GOOS=darwin GOARCH=amd64 go build -o macho_amd64 .
+	GOOS=darwin GOARCH=arm64 go build -o macho_arm64 .
+	lipo -create -output macho_universal macho_amd64 macho_arm64

cmd/macho/main.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"debug/macho"
+	"fmt"
+	"os"
+)
+
+func main() {
+	fatFile, err := macho.OpenFat(os.Args[0])
+	if err != nil {
+		fmt.Printf("not a universal binary: %s\n", err)
+	} else {
+		fmt.Printf("this is a universal binary\n")
+		fatFile.Close()
+	}
+}

testdata/hello/main.go

@@ -0,0 +1,5 @@
+package main
+
+func main() {
+	// This is a dummy main function
+}