all: implement gdb sub-command for easy debugging

colorwriter.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"io"
+)
+
+// ANSI escape codes for terminal colors.
+const (
+	TermColorReset  = "\x1b[0m"
+	TermColorYellow = "\x1b[93m"
+)
+
+// ColorWriter wraps an io.Writer but adds a prefix and a terminal color.
+type ColorWriter struct {
+	Out    io.Writer
+	Color  string
+	Prefix string
+	line   []byte
+}
+
+// Write implements io.Writer, but with an added prefix and terminal color.
+func (w *ColorWriter) Write(p []byte) (n int, err error) {
+	for _, c := range p {
+		if c == '\n' {
+			w.line = append(w.line, []byte(TermColorReset)...)
+			w.line = append(w.line, '\n')
+			// Write this line.
+			_, err := w.Out.Write(w.line)
+			w.line = w.line[:0]
+			w.line = append(w.line, []byte(w.Color+w.Prefix)...)
+			if err != nil {
+				return 0, err
+			}
+		} else {
+			w.line = append(w.line, c)
+		}
+	}
+	return len(p), nil
+}

main.go

@@ -8,8 +8,10 @@ import (
 	"io/ioutil"
 	"os"
 	"os/exec"
+	"os/signal"
 	"path/filepath"
 	"strings"
+	"syscall"
 
 	"github.com/aykevl/go-llvm"
 	"github.com/aykevl/tinygo/compiler"
@@ -199,6 +201,70 @@ func Flash(pkgName, target, port string, printIR, dumpSSA, debug bool, printSize
 	})
 }
 
+// Flash a program on a microcontroller and drop into a GDB shell.
+//
+// Note: this command is expected to execute just before exiting, as it
+// modifies global state.
+func FlashGDB(pkgName, target, port string, printIR, dumpSSA bool, printSizes string) error {
+	spec, err := LoadTarget(target)
+	if err != nil {
+		return err
+	}
+
+	if spec.GDB == "" {
+		return errors.New("gdb not configured in the target specification")
+	}
+
+	debug := true // always enable debug symbols
+	return Compile(pkgName, "", spec, printIR, dumpSSA, debug, printSizes, func(tmppath string) error {
+		if len(spec.OCDDaemon) != 0 {
+			// We need a separate debugging daemon for on-chip debugging.
+			daemon := exec.Command(spec.OCDDaemon[0], spec.OCDDaemon[1:]...)
+			// Make it clear which output is from the daemon.
+			daemon.Stderr = &ColorWriter{
+				Out:    os.Stderr,
+				Prefix: spec.OCDDaemon[0] + ": ",
+				Color:  TermColorYellow,
+			}
+			// Make sure the daemon doesn't receive Ctrl-C that is intended for
+			// GDB (to break the currently executing program).
+			// https://stackoverflow.com/a/35435038/559350
+			daemon.SysProcAttr = &syscall.SysProcAttr{
+				Setpgid: true,
+				Pgid:    0,
+			}
+			// Start now, and kill it on exit.
+			daemon.Start()
+			defer func() {
+				daemon.Process.Signal(os.Interrupt)
+				// Maybe we should send a .Kill() after x seconds?
+				daemon.Wait()
+			}()
+		}
+
+		// Ignore Ctrl-C, it must be passed on to GDB.
+		c := make(chan os.Signal, 1)
+		signal.Notify(c, os.Interrupt)
+		go func() {
+			for range c {
+			}
+		}()
+
+		// Construct and execute a gdb command.
+		// By default: gdb -ex run <binary>
+		// Exit GDB with Ctrl-D.
+		params := []string{tmppath}
+		for _, cmd := range spec.GDBCmds {
+			params = append(params, "-ex", cmd)
+		}
+		cmd := exec.Command(spec.GDB, params...)
+		cmd.Stdin = os.Stdin
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		return cmd.Run()
+	})
+}
+
 // Run the specified package directly (using JIT or interpretation).
 func Run(pkgName string) error {
 	config := compiler.Config{
@@ -284,13 +350,18 @@ func main() {
 			fmt.Fprintln(os.Stderr, "error:", err)
 			os.Exit(1)
 		}
-	case "flash":
+	case "flash", "gdb":
 		if *outpath != "" {
 			fmt.Fprintln(os.Stderr, "Output cannot be specified with the flash command.")
 			usage()
 			os.Exit(1)
 		}
-		err := Flash(flag.Arg(0), *target, *port, *printIR, *dumpSSA, !*nodebug, *printSize)
+		var err error
+		if command == "flash" {
+			err = Flash(flag.Arg(0), *target, *port, *printIR, *dumpSSA, !*nodebug, *printSize)
+		} else {
+			err = FlashGDB(flag.Arg(0), *target, *port, *printIR, *dumpSSA, *printSize)
+		}
 		if err != nil {
 			fmt.Fprintln(os.Stderr, "error:", err)
 			os.Exit(1)

target.go

@@ -20,6 +20,9 @@ type TargetSpec struct {
 	PreLinkArgs []string `json:"pre-link-args"`
 	Objcopy     string   `json:"objcopy"`
 	Flasher     string   `json:"flash"`
+	OCDDaemon   []string `json:"ocd-daemon"`
+	GDB         string   `json:"gdb"`
+	GDBCmds     []string `json:"gdb-initial-cmds"`
 }
 
 // Load a target specification
@@ -30,6 +33,8 @@ func LoadTarget(target string) (*TargetSpec, error) {
 		Linker:      "cc",
 		PreLinkArgs: []string{"-no-pie"}, // WARNING: clang < 5.0 requires -nopie
 		Objcopy:     "objcopy",
+		GDB:         "gdb",
+		GDBCmds:     []string{"run"},
 	}
 
 	// See whether there is a target specification for this target (e.g.
@@ -37,6 +42,7 @@ func LoadTarget(target string) (*TargetSpec, error) {
 	path := filepath.Join(sourceDir(), "targets", strings.ToLower(target)+".json")
 	if fp, err := os.Open(path); err == nil {
 		defer fp.Close()
+		*spec = TargetSpec{} // reset all fields
 		err := json.NewDecoder(fp).Decode(spec)
 		if err != nil {
 			return nil, err

targets/pca10040.json

@@ -4,5 +4,8 @@
 	"linker": "arm-none-eabi-gcc",
 	"pre-link-args": ["-nostdlib", "-nostartfiles", "-mcpu=cortex-m4", "-mthumb", "-T", "targets/nrf52.ld", "-Wl,--gc-sections", "-fno-exceptions", "-fno-unwind-tables", "-ffunction-sections", "-fdata-sections", "-Os", "-DNRF52832_XXAA", "-Ilib/CMSIS/CMSIS/Include", "lib/nrfx/mdk/system_nrf52.c", "src/device/nrf/nrf52.s"],
 	"objcopy": "arm-none-eabi-objcopy",
-	"flash": "nrfjprog -f nrf52 --sectorerase --program {hex} --reset"
+	"flash": "nrfjprog -f nrf52 --sectorerase --program {hex} --reset",
+	"ocd-daemon": ["openocd", "-f", "interface/jlink.cfg", "-c", "transport select swd", "-f", "target/nrf51.cfg"],
+	"gdb": "arm-none-eabi-gdb",
+	"gdb-initial-cmds": ["target remote :3333", "monitor halt", "load", "monitor reset", "c"]
 }