Implement backend breakpoint functionality

fixtures/continuetestprog.go

+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func sleepytime() {
+	time.Sleep(time.Millisecond)
+}
+
+func sayhi() {
+	fmt.Println("Hello, World!")
+}
+
+func main() {
+	sleepytime()
+	sayhi()
+}

fixtures/testprog.go

@@ -5,7 +5,17 @@ import (
 	"time"
 )
 
-func main() {
+func sleepytime() {
 	time.Sleep(time.Millisecond)
+}
+
+func sayhi() {
 	fmt.Println("Hello, World!")
 }
+
+func main() {
+	for {
+		sleepytime()
+		sayhi()
+	}
+}

proctl/proctl_linux_amd64.go

@@ -78,6 +78,22 @@ func (dbp *DebuggedProcess) Registers() (*syscall.PtraceRegs, error) {
 	return dbp.Regs, nil
 }
 
+// Sets a breakpoint in the running process.
+func (dbp *DebuggedProcess) Break(fname string) error {
+	var (
+		breakpoint = []byte{'0', 'x', 'C', 'C'}
+		fn         = dbp.GoSymTable.LookupFunc(fname)
+		addr       = uintptr(fn.LineTable.PC)
+	)
+
+	_, err := syscall.PtracePokeData(dbp.Pid, addr, breakpoint)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
 // Steps through process.
 func (dbp *DebuggedProcess) Step() error {
 	err := dbp.handleResult(syscall.PtraceSingleStep(dbp.Pid))

proctl/proctl_test.go

@@ -6,8 +6,8 @@ import (
 	"testing"
 )
 
-func StartTestProcess() (*exec.Cmd, error) {
-	cmd := exec.Command("../fixtures/testprog")
+func StartTestProcess(name string) (*exec.Cmd, error) {
+	cmd := exec.Command("../fixtures/" + name)
 
 	err := cmd.Start()
 	if err != nil {
@@ -18,7 +18,7 @@ func StartTestProcess() (*exec.Cmd, error) {
 }
 
 func TestAttachProcess(t *testing.T) {
-	cmd, err := StartTestProcess()
+	cmd, err := StartTestProcess("testprog")
 	if err != nil {
 		t.Fatal("Starting test process:", err)
 	}
@@ -32,10 +32,12 @@ func TestAttachProcess(t *testing.T) {
 	if !p.ProcessState.Sys().(syscall.WaitStatus).Stopped() {
 		t.Errorf("Process was not stopped correctly")
 	}
+
+	cmd.Process.Kill()
 }
 
 func TestStep(t *testing.T) {
-	cmd, err := StartTestProcess()
+	cmd, err := StartTestProcess("testprog")
 	if err != nil {
 		t.Fatal("Starting test process:", err)
 	}
@@ -71,7 +73,7 @@ func TestStep(t *testing.T) {
 }
 
 func TestContinue(t *testing.T) {
-	cmd, err := StartTestProcess()
+	cmd, err := StartTestProcess("continuetestprog")
 	if err != nil {
 		t.Fatal("Starting test process:", err)
 	}
@@ -95,3 +97,41 @@ func TestContinue(t *testing.T) {
 		t.Fatal("Process did not exit successfully")
 	}
 }
+
+func TestBreakPoint(t *testing.T) {
+	cmd, err := StartTestProcess("testprog")
+	if err != nil {
+		t.Fatal("Starting test process:", err)
+	}
+
+	pid := cmd.Process.Pid
+	p, err := NewDebugProcess(pid)
+	if err != nil {
+		t.Fatal("NewDebugProcess():", err)
+	}
+
+	err = p.Break("main.sleepytime")
+	if err != nil {
+		t.Fatal("Break():", err)
+	}
+
+	sleepytimefunc := p.GoSymTable.LookupFunc("main.sleepytime")
+	sleepyaddr := sleepytimefunc.LineTable.PC
+
+	err = p.Continue()
+	if err != nil {
+		t.Fatal("Continue():", err)
+	}
+
+	regs, err := p.Registers()
+	if err != nil {
+		t.Fatal("Registers():", err)
+	}
+
+	pc := regs.PC()
+	if pc != sleepyaddr {
+		t.Fatal("Break not respected:\nPC:%d\nFN:%d\n", pc, sleepyaddr)
+	}
+
+	cmd.Process.Kill()
+}