main: remove -no-debug flag

The -no-debug flag controls whether to emit DWARF debug information.
However, instead of limiting debug information altogether, I think it's
better to strip it off at the end if it isn't needed. For several
reasons:

  * Some parts of the compiler now rely on the presence of debug
    information for proper diagnostics.
  * It works better with the cache: there is no distinction between
    debug and no-debug builds.
  * It makes it easier (or possible at all) to enable debug information
    in the wasi-libc library without big downsides.

I'm doing this in a separate commit so this can be reverted if needed.

builder/build.go

@@ -100,7 +100,6 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 		AutomaticStackSize: config.AutomaticStackSize(),
 		DefaultStackSize:   config.Target.DefaultStackSize,
 		NeedsStackObjects:  config.NeedsStackObjects(),
-		Debug:              config.Debug(),
 		LLVMFeatures:       config.LLVMFeatures(),
 	}
 
@@ -537,6 +536,41 @@ 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

@@ -209,9 +209,8 @@ 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() {
-		cflags = append(cflags, "-g")
-	}
+	// Always emit debug information. It is optionally stripped at link time.
+	cflags = append(cflags, "-g")
 	return cflags
 }
 
@@ -250,10 +249,27 @@ 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.
+// 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 +29,7 @@ type Options struct {
 	DumpSSA         bool
 	VerifyIR        bool
 	PrintCommands   func(cmd string, args ...string)
-	Debug           bool
+	Debug           string
 	PrintSizes      string
 	PrintAllocs     *regexp.Regexp // regexp string
 	PrintStacks     bool
@@ -70,6 +71,12 @@ 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 {

compiler/compiler.go

@@ -58,7 +58,6 @@ type Config struct {
 	AutomaticStackSize bool
 	DefaultStackSize   uint64
 	NeedsStackObjects  bool
-	Debug              bool // Whether to emit debug information in the LLVM module.
 	LLVMFeatures       string
 }
 
@@ -103,9 +102,7 @@ func newCompilerContext(moduleName string, machine llvm.TargetMachine, config *C
 	c.mod = c.ctx.NewModule(moduleName)
 	c.mod.SetTarget(config.Triple)
 	c.mod.SetDataLayout(c.targetData.String())
-	if c.Debug {
-		c.dibuilder = llvm.NewDIBuilder(c.mod)
-	}
+	c.dibuilder = llvm.NewDIBuilder(c.mod)
 
 	c.uintptrType = c.ctx.IntType(c.targetData.PointerSize() * 8)
 	if c.targetData.PointerSize() <= 4 {
@@ -263,15 +260,13 @@ func CompilePackage(moduleName string, pkg *loader.Package, ssaPkg *ssa.Package,
 	ssaPkg.Build()
 
 	// Initialize debug information.
-	if c.Debug {
-		c.cu = c.dibuilder.CreateCompileUnit(llvm.DICompileUnit{
-			Language:  0xb, // DW_LANG_C99 (0xc, off-by-one?)
-			File:      "<unknown>",
-			Dir:       "",
-			Producer:  "TinyGo",
-			Optimized: true,
-		})
-	}
+	c.cu = c.dibuilder.CreateCompileUnit(llvm.DICompileUnit{
+		Language:  0xb, // DW_LANG_C99 (0xc, off-by-one?)
+		File:      "<unknown>",
+		Dir:       "",
+		Producer:  "TinyGo",
+		Optimized: true,
+	})
 
 	// Load comments such as //go:extern on globals.
 	c.loadASTComments(pkg)
@@ -286,23 +281,21 @@ func CompilePackage(moduleName string, pkg *loader.Package, ssaPkg *ssa.Package,
 	c.createPackage(irbuilder, ssaPkg)
 
 	// see: https://reviews.llvm.org/D18355
-	if c.Debug {
-		c.mod.AddNamedMetadataOperand("llvm.module.flags",
-			c.ctx.MDNode([]llvm.Metadata{
-				llvm.ConstInt(c.ctx.Int32Type(), 1, false).ConstantAsMetadata(), // Error on mismatch
-				c.ctx.MDString("Debug Info Version"),
-				llvm.ConstInt(c.ctx.Int32Type(), 3, false).ConstantAsMetadata(), // DWARF version
-			}),
-		)
-		c.mod.AddNamedMetadataOperand("llvm.module.flags",
-			c.ctx.MDNode([]llvm.Metadata{
-				llvm.ConstInt(c.ctx.Int32Type(), 1, false).ConstantAsMetadata(),
-				c.ctx.MDString("Dwarf Version"),
-				llvm.ConstInt(c.ctx.Int32Type(), 4, false).ConstantAsMetadata(),
-			}),
-		)
-		c.dibuilder.Finalize()
-	}
+	c.mod.AddNamedMetadataOperand("llvm.module.flags",
+		c.ctx.MDNode([]llvm.Metadata{
+			llvm.ConstInt(c.ctx.Int32Type(), 1, false).ConstantAsMetadata(), // Error on mismatch
+			c.ctx.MDString("Debug Info Version"),
+			llvm.ConstInt(c.ctx.Int32Type(), 3, false).ConstantAsMetadata(), // DWARF version
+		}),
+	)
+	c.mod.AddNamedMetadataOperand("llvm.module.flags",
+		c.ctx.MDNode([]llvm.Metadata{
+			llvm.ConstInt(c.ctx.Int32Type(), 1, false).ConstantAsMetadata(),
+			c.ctx.MDString("Dwarf Version"),
+			llvm.ConstInt(c.ctx.Int32Type(), 4, false).ConstantAsMetadata(),
+		}),
+	)
+	c.dibuilder.Finalize()
 
 	return c.mod, c.diagnostics
 }
@@ -812,20 +805,18 @@ func (b *builder) createFunction() {
 		b.llvmFn.AddFunctionAttr(noinline)
 	}
 
-	// Add debug info, if needed.
-	if b.Debug {
-		if b.fn.Synthetic == "package initializer" {
-			// Package initializers have no debug info. Create some fake debug
-			// info to at least have *something*.
-			filename := b.fn.Package().Pkg.Path() + "/<init>"
-			b.difunc = b.attachDebugInfoRaw(b.fn, b.llvmFn, "", filename, 0)
-		} else if b.fn.Syntax() != nil {
-			// Create debug info file if needed.
-			b.difunc = b.attachDebugInfo(b.fn)
-		}
-		pos := b.program.Fset.Position(b.fn.Pos())
-		b.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), b.difunc, llvm.Metadata{})
+	// Add debug info.
+	if b.fn.Synthetic == "package initializer" {
+		// Package initializers have no debug info. Create some fake debug
+		// info to at least have *something*.
+		filename := b.fn.Package().Pkg.Path() + "/<init>"
+		b.difunc = b.attachDebugInfoRaw(b.fn, b.llvmFn, "", filename, 0)
+	} else if b.fn.Syntax() != nil {
+		// Create debug info file if needed.
+		b.difunc = b.attachDebugInfo(b.fn)
 	}
+	pos := b.program.Fset.Position(b.fn.Pos())
+	b.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), b.difunc, llvm.Metadata{})
 
 	// Pre-create all basic blocks in the function.
 	for _, block := range b.fn.DomPreorder() {
@@ -850,7 +841,7 @@ func (b *builder) createFunction() {
 		b.locals[param] = b.collapseFormalParam(llvmType, fields)
 
 		// Add debug information to this parameter (if available)
-		if b.Debug && b.fn.Syntax() != nil {
+		if b.fn.Syntax() != nil {
 			dbgParam := b.getLocalVariable(param.Object().(*types.Var))
 			loc := b.GetCurrentDebugLocation()
 			if len(fields) == 1 {
@@ -910,9 +901,6 @@ func (b *builder) createFunction() {
 		b.currentBlock = block
 		for _, instr := range block.Instrs {
 			if instr, ok := instr.(*ssa.DebugRef); ok {
-				if !b.Debug {
-					continue
-				}
 				object := instr.Object()
 				variable, ok := object.(*types.Var)
 				if !ok {
@@ -1029,10 +1017,8 @@ func getPos(val posser) token.Pos {
 // createInstruction builds the LLVM IR equivalent instructions for the
 // particular Go SSA instruction.
 func (b *builder) createInstruction(instr ssa.Instruction) {
-	if b.Debug {
-		pos := b.program.Fset.Position(getPos(instr))
-		b.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), b.difunc, llvm.Metadata{})
-	}
+	pos := b.program.Fset.Position(getPos(instr))
+	b.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), b.difunc, llvm.Metadata{})
 
 	switch instr := instr.(type) {
 	case ssa.Value:

compiler/goroutine.go

@@ -182,27 +182,26 @@ func (c *compilerContext) createGoroutineStartWrapper(fn llvm.Value, prefix stri
 		entry := c.ctx.AddBasicBlock(wrapper, "entry")
 		builder.SetInsertPointAtEnd(entry)
 
-		if c.Debug {
-			pos := c.program.Fset.Position(pos)
-			diFuncType := c.dibuilder.CreateSubroutineType(llvm.DISubroutineType{
-				File:       c.getDIFile(pos.Filename),
-				Parameters: nil, // do not show parameters in debugger
-				Flags:      0,   // ?
-			})
-			difunc := c.dibuilder.CreateFunction(c.getDIFile(pos.Filename), llvm.DIFunction{
-				Name:         "<goroutine wrapper>",
-				File:         c.getDIFile(pos.Filename),
-				Line:         pos.Line,
-				Type:         diFuncType,
-				LocalToUnit:  true,
-				IsDefinition: true,
-				ScopeLine:    0,
-				Flags:        llvm.FlagPrototyped,
-				Optimized:    true,
-			})
-			wrapper.SetSubprogram(difunc)
-			builder.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
-		}
+		// Add debug information.
+		pos := c.program.Fset.Position(pos)
+		diFuncType := c.dibuilder.CreateSubroutineType(llvm.DISubroutineType{
+			File:       c.getDIFile(pos.Filename),
+			Parameters: nil, // do not show parameters in debugger
+			Flags:      0,   // ?
+		})
+		difunc := c.dibuilder.CreateFunction(c.getDIFile(pos.Filename), llvm.DIFunction{
+			Name:         "<goroutine wrapper>",
+			File:         c.getDIFile(pos.Filename),
+			Line:         pos.Line,
+			Type:         diFuncType,
+			LocalToUnit:  true,
+			IsDefinition: true,
+			ScopeLine:    0,
+			Flags:        llvm.FlagPrototyped,
+			Optimized:    true,
+		})
+		wrapper.SetSubprogram(difunc)
+		builder.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
 
 		// Create the list of params for the call.
 		paramTypes := fn.Type().ElementType().ParamTypes()
@@ -246,27 +245,26 @@ func (c *compilerContext) createGoroutineStartWrapper(fn llvm.Value, prefix stri
 		entry := c.ctx.AddBasicBlock(wrapper, "entry")
 		builder.SetInsertPointAtEnd(entry)
 
-		if c.Debug {
-			pos := c.program.Fset.Position(pos)
-			diFuncType := c.dibuilder.CreateSubroutineType(llvm.DISubroutineType{
-				File:       c.getDIFile(pos.Filename),
-				Parameters: nil, // do not show parameters in debugger
-				Flags:      0,   // ?
-			})
-			difunc := c.dibuilder.CreateFunction(c.getDIFile(pos.Filename), llvm.DIFunction{
-				Name:         "<goroutine wrapper>",
-				File:         c.getDIFile(pos.Filename),
-				Line:         pos.Line,
-				Type:         diFuncType,
-				LocalToUnit:  true,
-				IsDefinition: true,
-				ScopeLine:    0,
-				Flags:        llvm.FlagPrototyped,
-				Optimized:    true,
-			})
-			wrapper.SetSubprogram(difunc)
-			builder.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
-		}
+		// Add debug information.
+		pos := c.program.Fset.Position(pos)
+		diFuncType := c.dibuilder.CreateSubroutineType(llvm.DISubroutineType{
+			File:       c.getDIFile(pos.Filename),
+			Parameters: nil, // do not show parameters in debugger
+			Flags:      0,   // ?
+		})
+		difunc := c.dibuilder.CreateFunction(c.getDIFile(pos.Filename), llvm.DIFunction{
+			Name:         "<goroutine wrapper>",
+			File:         c.getDIFile(pos.Filename),
+			Line:         pos.Line,
+			Type:         diFuncType,
+			LocalToUnit:  true,
+			IsDefinition: true,
+			ScopeLine:    0,
+			Flags:        llvm.FlagPrototyped,
+			Optimized:    true,
+		})
+		wrapper.SetSubprogram(difunc)
+		builder.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
 
 		// Get the list of parameters, with the extra parameters at the end.
 		paramTypes := fn.Type().ElementType().ParamTypes()

compiler/interface.go

@@ -501,12 +501,10 @@ func (c *compilerContext) getInterfaceInvokeWrapper(fn *ssa.Function, llvmFn llv
 	}
 	defer b.Builder.Dispose()
 
-	// add debug info if needed
-	if c.Debug {
-		pos := c.program.Fset.Position(fn.Pos())
-		difunc := c.attachDebugInfoRaw(fn, wrapper, "$invoke", pos.Filename, pos.Line)
-		b.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
-	}
+	// add debug info
+	pos := c.program.Fset.Position(fn.Pos())
+	difunc := c.attachDebugInfoRaw(fn, wrapper, "$invoke", pos.Filename, pos.Line)
+	b.SetCurrentDebugLocation(uint(pos.Line), uint(pos.Column), difunc, llvm.Metadata{})
 
 	// set up IR builder
 	block := b.ctx.AddBasicBlock(wrapper, "entry")

compiler/interrupt.go

@@ -52,19 +52,17 @@ func (b *builder) createInterruptGlobal(instr *ssa.CallCommon) (llvm.Value, erro
 	global.SetInitializer(initializer)
 
 	// Add debug info to the interrupt global.
-	if b.Debug {
-		pos := b.program.Fset.Position(instr.Pos())
-		diglobal := b.dibuilder.CreateGlobalVariableExpression(b.getDIFile(pos.Filename), llvm.DIGlobalVariableExpression{
-			Name:        "interrupt" + strconv.FormatInt(id.Int64(), 10),
-			LinkageName: globalName,
-			File:        b.getDIFile(pos.Filename),
-			Line:        pos.Line,
-			Type:        b.getDIType(globalType),
-			Expr:        b.dibuilder.CreateExpression(nil),
-			LocalToUnit: false,
-		})
-		global.AddMetadata(0, diglobal)
-	}
+	pos := b.program.Fset.Position(instr.Pos())
+	diglobal := b.dibuilder.CreateGlobalVariableExpression(b.getDIFile(pos.Filename), llvm.DIGlobalVariableExpression{
+		Name:        "interrupt" + strconv.FormatInt(id.Int64(), 10),
+		LinkageName: globalName,
+		File:        b.getDIFile(pos.Filename),
+		Line:        pos.Line,
+		Type:        b.getDIType(globalType),
+		Expr:        b.dibuilder.CreateExpression(nil),
+		LocalToUnit: false,
+	})
+	global.AddMetadata(0, diglobal)
 
 	// Create the runtime/interrupt.Interrupt type. It is a struct with a single
 	// member of type int.

compiler/symbol.go

@@ -386,7 +386,7 @@ func (c *compilerContext) getGlobal(g *ssa.Global) llvm.Value {
 			llvmGlobal.SetAlignment(alignment)
 		}
 
-		if c.Debug && !info.extern {
+		if !info.extern {
 			// Add debug info.
 			pos := c.program.Fset.Position(g.Pos())
 			diglobal := c.dibuilder.CreateGlobalVariableExpression(c.difiles[pos.Filename], llvm.DIGlobalVariableExpression{

main.go

@@ -1019,7 +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")
-	nodebug := flag.Bool("no-debug", false, "disable DWARF debug symbol generation")
+	debug := flag.String("debug", "auto", "remove debug information (auto, true, false)")
 	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")
 	port := flag.String("port", "", "flash port (can specify multiple candidates separated by commas)")
@@ -1086,7 +1086,7 @@ func main() {
 		PrintIR:         *printIR,
 		DumpSSA:         *dumpSSA,
 		VerifyIR:        *verifyIR,
-		Debug:           !*nodebug,
+		Debug:           *debug,
 		PrintSizes:      *printSize,
 		PrintStacks:     *printStacks,
 		PrintAllocs:     printAllocs,
@@ -1173,11 +1173,6 @@ func main() {
 			err := Flash(pkgName, *port, options)
 			handleCompilerError(err)
 		} else {
-			if !options.Debug {
-				fmt.Fprintln(os.Stderr, "Debug disabled while running gdb?")
-				usage()
-				os.Exit(1)
-			}
 			err := FlashGDB(pkgName, *ocdOutput, options)
 			handleCompilerError(err)
 		}

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:    "",
 	}