all: add support for GOARM

This environment variable can be set to 5, 6, or 7 and controls which
ARM version (ARMv5, ARMv6, ARMv7) is used when compiling for GOARCH=arm.

I have picked the default value ARMv6, which I believe is supported on
most common single board computers including all Raspberry Pis. The
difference in code size is pretty big.

We could even go further and support ARMv4 if anybody is interested. It
should be pretty simple to add this if needed.

builder/builder_test.go

@@ -52,7 +52,9 @@ func TestClangAttributes(t *testing.T) {
 	for _, options := range []*compileopts.Options{
 		{GOOS: "linux", GOARCH: "386"},
 		{GOOS: "linux", GOARCH: "amd64"},
-		{GOOS: "linux", GOARCH: "arm"},
+		{GOOS: "linux", GOARCH: "arm", GOARM: "5"},
+		{GOOS: "linux", GOARCH: "arm", GOARM: "6"},
+		{GOOS: "linux", GOARCH: "arm", GOARM: "7"},
 		{GOOS: "linux", GOARCH: "arm64"},
 		{GOOS: "darwin", GOARCH: "amd64"},
 		{GOOS: "darwin", GOARCH: "arm64"},

compileopts/config.go

@@ -60,6 +60,12 @@ func (c *Config) GOARCH() string {
 	return c.Target.GOARCH
 }
 
+// GOARM will return the GOARM environment variable given to the compiler when
+// building a program.
+func (c *Config) GOARM() string {
+	return c.Options.GOARM
+}
+
 // BuildTags returns the complete list of build tags used during this build.
 func (c *Config) BuildTags() []string {
 	tags := append(c.Target.BuildTags, []string{"tinygo", "math_big_pure_go", "gc." + c.GC(), "scheduler." + c.Scheduler(), "serial." + c.Serial()}...)

compileopts/options.go

@@ -21,6 +21,7 @@ var (
 type Options struct {
 	GOOS            string // environment variable
 	GOARCH          string // environment variable
+	GOARM           string // environment variable (only used with GOARCH=arm)
 	Target          string
 	Opt             string
 	GC              string

compileopts/target.go

@@ -5,6 +5,7 @@ package compileopts
 import (
 	"encoding/json"
 	"errors"
+	"fmt"
 	"io"
 	"os"
 	"os/exec"
@@ -165,13 +166,26 @@ func LoadTarget(options *Options) (*TargetSpec, error) {
 	if options.Target == "" {
 		// Configure based on GOOS/GOARCH environment variables (falling back to
 		// runtime.GOOS/runtime.GOARCH), and generate a LLVM target based on it.
-		llvmarch := map[string]string{
-			"386":   "i386",
-			"amd64": "x86_64",
-			"arm64": "aarch64",
-			"arm":   "armv7",
-		}[options.GOARCH]
-		if llvmarch == "" {
+		var llvmarch string
+		switch options.GOARCH {
+		case "386":
+			llvmarch = "i386"
+		case "amd64":
+			llvmarch = "x86_64"
+		case "arm64":
+			llvmarch = "aarch64"
+		case "arm":
+			switch options.GOARM {
+			case "5":
+				llvmarch = "armv5"
+			case "6":
+				llvmarch = "armv6"
+			case "7":
+				llvmarch = "armv7"
+			default:
+				return nil, fmt.Errorf("invalid GOARM=%s, must be 5, 6, or 7", options.GOARM)
+			}
+		default:
 			llvmarch = options.GOARCH
 		}
 		llvmos := options.GOOS
@@ -245,7 +259,14 @@ func defaultTarget(goos, goarch, triple string) (*TargetSpec, error) {
 		spec.Features = "+cx8,+fxsr,+mmx,+sse,+sse2,+x87"
 	case "arm":
 		spec.CPU = "generic"
-		spec.Features = "+armv7-a,+dsp,+fp64,+vfp2,+vfp2sp,+vfp3d16,+vfp3d16sp,-thumb-mode"
+		switch strings.Split(triple, "-")[0] {
+		case "armv5":
+			spec.Features = "+armv5t,+strict-align,-thumb-mode"
+		case "armv6":
+			spec.Features = "+armv6,+dsp,+fp64,+strict-align,+vfp2,+vfp2sp,-thumb-mode"
+		case "armv7":
+			spec.Features = "+armv7-a,+dsp,+fp64,+vfp2,+vfp2sp,+vfp3d16,+vfp3d16sp,-thumb-mode"
+		}
 	case "arm64":
 		spec.CPU = "generic"
 		spec.Features = "+neon"

goenv/goenv.go

@@ -25,6 +25,12 @@ var Keys = []string{
 	"TINYGOROOT",
 }
 
+func init() {
+	if Get("GOARCH") == "arm" {
+		Keys = append(Keys, "GOARM")
+	}
+}
+
 // TINYGOROOT is the path to the final location for checking tinygo files. If
 // unset (by a -X ldflag), then sourceDir() will fallback to the original build
 // directory.
@@ -44,6 +50,20 @@ func Get(name string) string {
 			return dir
 		}
 		return runtime.GOARCH
+	case "GOARM":
+		if goarm := os.Getenv("GOARM"); goarm != "" {
+			return goarm
+		}
+		if goos := Get("GOOS"); goos == "windows" || goos == "android" {
+			// Assume Windows and Android are running on modern CPU cores.
+			// This matches upstream Go.
+			return "7"
+		}
+		// Default to ARMv6 on other devices.
+		// The difference between ARMv5 and ARMv6 is big, much bigger than the
+		// difference between ARMv6 and ARMv7. ARMv6 binaries are much smaller,
+		// especially when floating point instructions are involved.
+		return "6"
 	case "GOROOT":
 		return getGoroot()
 	case "GOPATH":

main.go

@@ -1192,6 +1192,7 @@ func main() {
 	options := &compileopts.Options{
 		GOOS:            goenv.Get("GOOS"),
 		GOARCH:          goenv.Get("GOARCH"),
+		GOARM:           goenv.Get("GOARM"),
 		Target:          *target,
 		Opt:             *opt,
 		GC:              *gc,
@@ -1401,6 +1402,7 @@ func main() {
 		fmt.Printf("LLVM triple:       %s\n", config.Triple())
 		fmt.Printf("GOOS:              %s\n", config.GOOS())
 		fmt.Printf("GOARCH:            %s\n", config.GOARCH())
+		fmt.Printf("GOARM:             %s\n", config.GOARM())
 		fmt.Printf("build tags:        %s\n", strings.Join(config.BuildTags(), " "))
 		fmt.Printf("garbage collector: %s\n", config.GC())
 		fmt.Printf("scheduler:         %s\n", config.Scheduler())

main_test.go

@@ -95,13 +95,13 @@ func TestCompiler(t *testing.T) {
 
 	if runtime.GOOS == "linux" {
 		t.Run("X86Linux", func(t *testing.T) {
-			runPlatTests(optionsFromOSARCH("linux", "386"), tests, t)
+			runPlatTests(optionsFromOSARCH("linux/386"), tests, t)
 		})
 		t.Run("ARMLinux", func(t *testing.T) {
-			runPlatTests(optionsFromOSARCH("linux", "arm"), tests, t)
+			runPlatTests(optionsFromOSARCH("linux/arm/6"), tests, t)
 		})
 		t.Run("ARM64Linux", func(t *testing.T) {
-			runPlatTests(optionsFromOSARCH("linux", "arm64"), tests, t)
+			runPlatTests(optionsFromOSARCH("linux/arm64"), tests, t)
 		})
 		t.Run("WebAssembly", func(t *testing.T) {
 			runPlatTests(optionsFromTarget("wasm"), tests, t)
@@ -125,6 +125,7 @@ func TestCompiler(t *testing.T) {
 			runTestWithConfig("stdlib.go", t, compileopts.Options{
 				GOOS:   goenv.Get("GOOS"),
 				GOARCH: goenv.Get("GOARCH"),
+				GOARM:  goenv.Get("GOARM"),
 				Opt:    "1",
 			}, nil, nil)
 		})
@@ -136,6 +137,7 @@ func TestCompiler(t *testing.T) {
 			runTestWithConfig("print.go", t, compileopts.Options{
 				GOOS:   goenv.Get("GOOS"),
 				GOARCH: goenv.Get("GOARCH"),
+				GOARM:  goenv.Get("GOARM"),
 				Opt:    "0",
 			}, nil, nil)
 		})
@@ -145,6 +147,7 @@ func TestCompiler(t *testing.T) {
 			runTestWithConfig("ldflags.go", t, compileopts.Options{
 				GOOS:   goenv.Get("GOOS"),
 				GOARCH: goenv.Get("GOARCH"),
+				GOARM:  goenv.Get("GOARM"),
 				GlobalValues: map[string]map[string]string{
 					"main": {
 						"someGlobal": "foobar",
@@ -200,15 +203,24 @@ func optionsFromTarget(target string) compileopts.Options {
 		// GOOS/GOARCH are only used if target == ""
 		GOOS:   goenv.Get("GOOS"),
 		GOARCH: goenv.Get("GOARCH"),
+		GOARM:  goenv.Get("GOARM"),
 		Target: target,
 	}
 }
 
-func optionsFromOSARCH(goos, goarch string) compileopts.Options {
-	return compileopts.Options{
-		GOOS:   goos,
-		GOARCH: goarch,
+// optionsFromOSARCH returns a set of options based on the "osarch" string. This
+// string is in the form of "os/arch/subarch", with the subarch only sometimes
+// being necessary. Examples are "darwin/amd64" or "linux/arm/7".
+func optionsFromOSARCH(osarch string) compileopts.Options {
+	parts := strings.Split(osarch, "/")
+	options := compileopts.Options{
+		GOOS:   parts[0],
+		GOARCH: parts[1],
 	}
+	if options.GOARCH == "arm" {
+		options.GOARM = parts[2]
+	}
+	return options
 }
 
 func runTest(name string, options compileopts.Options, t *testing.T, cmdArgs, environmentVars []string) {