main: add -debug flag that controls debuginfo stripping

Debug information is useful in many case, but in the case of WebAssembly
it increases the binary size by a large amount. It also inhibits
compression of relocations. Therefore I've made debug information
optional and disabled by default.

(Debug information is still generated, but stripped from the binary at
the link step).

builder/build.go

@@ -100,7 +100,7 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 		AutomaticStackSize: config.AutomaticStackSize(),
 		DefaultStackSize:   config.Target.DefaultStackSize,
 		NeedsStackObjects:  config.NeedsStackObjects(),
-		Debug:              config.Debug(),
+		Debug:              config.EmitDWARF(),
 		LLVMFeatures:       config.LLVMFeatures(),
 	}
 
@@ -537,6 +537,41 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 		ldflags = append(ldflags, lprogram.LDFlags...)
 	}
 
+	// Strip debug information if -debug is true. This is sometimes the default,
+	// such as with WebAssembly targets.
+	if !config.Debug() {
+		for _, tag := range config.BuildTags() {
+			if tag == "baremetal" {
+				// Don't use -debug=false on baremetal targets. It makes no
+				// sense: the debug information isn't flashed to the device
+				// anyway.
+				return fmt.Errorf("stripping debug information is unnecessary for baremetal targets")
+			}
+		}
+		if config.Target.Linker == "wasm-ld" {
+			// Don't just strip debug information, also compress relocations
+			// while we're at it. Relocations can only be compressed when debug
+			// information is stripped.
+			ldflags = append(ldflags, "--strip-debug", "--compress-relocations")
+		} else {
+			switch config.GOOS() {
+			case "linux":
+				// Either real linux or an embedded system (like AVR) that
+				// pretends to be Linux. It's a ELF linker wrapped by GCC in any
+				// case.
+				ldflags = append(ldflags, "-Wl,--strip-debug")
+			case "darwin":
+				// MacOS (darwin) doesn't have a linker flag to strip debug
+				// information. Apple expects you to use the strip command
+				// instead.
+				return errors.New("cannot remove debug information: MacOS doesn't suppor this linker flag")
+			default:
+				// Other OSes may have different flags.
+				return errors.New("cannot remove debug information: unknown OS: " + config.GOOS())
+			}
+		}
+	}
+
 	// Create a linker job, which links all object files together and does some
 	// extra stuff that can only be done after linking.
 	jobs = append(jobs, &compileJob{

compileopts/config.go

@@ -209,7 +209,7 @@ func (c *Config) CFlags() []string {
 		cflags = append(cflags, "-nostdlibinc", "-Xclang", "-internal-isystem", "-Xclang", filepath.Join(root, "lib", "picolibc", "newlib", "libc", "include"))
 		cflags = append(cflags, "-I"+filepath.Join(root, "lib/picolibc-include"))
 	}
-	if c.Debug() {
+	if c.EmitDWARF() {
 		cflags = append(cflags, "-g")
 	}
 	return cflags
@@ -250,10 +250,33 @@ func (c *Config) VerifyIR() bool {
 	return c.Options.VerifyIR
 }
 
-// Debug returns whether to add debug symbols to the IR, for debugging with GDB
-// and similar.
+// EmitDWARF returns whether to add debug symbols to the IR, for debugging with
+// GDB and similar.
+func (c *Config) EmitDWARF() bool {
+	return c.Options.EmitDWARF
+}
+
+// Debug returns whether debug (DWARF) information should be retained by the
+// linker. The default varies by target but can be controlled with the -debug
+// command line flag.
 func (c *Config) Debug() bool {
-	return c.Options.Debug
+	switch c.Options.Debug {
+	case "true":
+		return true
+	case "false":
+		return false
+	case "auto":
+		// Emit debug information everywhere by default except on WebAssembly.
+		for _, tag := range c.BuildTags() {
+			if tag == "tinygo.wasm" {
+				return false
+			}
+		}
+		return true
+	default:
+		// This is already checked so shouldn't happen.
+		panic("unknown -debug flag")
+	}
 }
 
 // BinaryFormat returns an appropriate binary format, based on the file

compileopts/options.go

@@ -9,6 +9,7 @@ import (
 var (
 	validGCOptions            = []string{"none", "leaking", "extalloc", "conservative"}
 	validSchedulerOptions     = []string{"none", "tasks", "coroutines"}
+	validDebugOptions         = []string{"auto", "true", "false"}
 	validSerialOptions        = []string{"none", "uart", "usb"}
 	validPrintSizeOptions     = []string{"none", "short", "full"}
 	validPanicStrategyOptions = []string{"print", "trap"}
@@ -28,7 +29,8 @@ type Options struct {
 	DumpSSA         bool
 	VerifyIR        bool
 	PrintCommands   func(cmd string, args ...string)
-	Debug           bool
+	EmitDWARF       bool
+	Debug           string
 	PrintSizes      string
 	PrintAllocs     *regexp.Regexp // regexp string
 	PrintStacks     bool
@@ -70,6 +72,12 @@ func (o *Options) Verify() error {
 		}
 	}
 
+	if !isInArray(validDebugOptions, o.Debug) {
+		return fmt.Errorf(`invalid debug option '%s': valid values are %s`,
+			o.Debug,
+			strings.Join(validDebugOptions, ", "))
+	}
+
 	if o.PrintSizes != "" {
 		valid := isInArray(validPrintSizeOptions, o.PrintSizes)
 		if !valid {

main.go

@@ -1019,6 +1019,7 @@ func main() {
 	printStacks := flag.Bool("print-stacks", false, "print stack sizes of goroutines")
 	printAllocsString := flag.String("print-allocs", "", "regular expression of functions for which heap allocations should be printed")
 	printCommands := flag.Bool("x", false, "Print commands")
+	debug := flag.String("debug", "auto", "remove debug information (auto, true, false)")
 	nodebug := flag.Bool("no-debug", false, "disable DWARF debug symbol generation")
 	ocdCommandsString := flag.String("ocd-commands", "", "OpenOCD commands, overriding target spec (can specify multiple separated by commas)")
 	ocdOutput := flag.Bool("ocd-output", false, "print OCD daemon output during debug")
@@ -1086,7 +1087,8 @@ func main() {
 		PrintIR:         *printIR,
 		DumpSSA:         *dumpSSA,
 		VerifyIR:        *verifyIR,
-		Debug:           !*nodebug,
+		EmitDWARF:       !*nodebug,
+		Debug:           *debug,
 		PrintSizes:      *printSize,
 		PrintStacks:     *printStacks,
 		PrintAllocs:     printAllocs,
@@ -1173,7 +1175,7 @@ func main() {
 			err := Flash(pkgName, *port, options)
 			handleCompilerError(err)
 		} else {
-			if !options.Debug {
+			if !options.EmitDWARF {
 				fmt.Fprintln(os.Stderr, "Debug disabled while running gdb?")
 				usage()
 				os.Exit(1)

main_test.go

@@ -194,7 +194,7 @@ func runTest(name, target string, t *testing.T, cmdArgs, environmentVars []strin
 		PrintIR:    false,
 		DumpSSA:    false,
 		VerifyIR:   true,
-		Debug:      true,
+		EmitDWARF:  true,
 		PrintSizes: "",
 		WasmAbi:    "",
 	}