proc: Continue does not work with breakpoints set on NOP (OSX)

Fixes #262

_fixtures/bpcountstest.go

@@ -11,7 +11,7 @@ func demo(id int, wait *sync.WaitGroup) {
 	for i := 0; i < 100; i++ {
 		sleep := rand.Intn(10) + 1
 		fmt.Printf("id: %d step: %d sleeping %d\n", id, i, sleep)
-		time.Sleep(time.Duration(sleep) *  time.Millisecond)
+		time.Sleep(time.Duration(sleep) * time.Millisecond)
 	}
 
 	wait.Done()

_fixtures/issue262.go

+package main
+
+import "fmt"
+
+func typicalFunction() (res int) {
+	defer func() {
+		res = 2
+		return
+	}()
+	res = 10
+	return // setup breakpoint here
+}
+
+func main() {
+	fmt.Println(typicalFunction())
+}

proc/proc_darwin.go

@@ -329,5 +329,13 @@ func (dbp *Process) wait(pid, options int) (int, *sys.WaitStatus, error) {
 }
 
 func (dbp *Process) exitGuard(err error) error {
+	if err != ErrContinueThread {
+		return err
+	}
+	_, status, werr := dbp.wait(dbp.Pid, sys.WNOHANG)
+	if werr == nil && status.Exited() {
+		dbp.postExit()
+		return ProcessExitedError{Pid: dbp.Pid, Status: status.ExitStatus()}
+	}
 	return err
 }

proc/proc_test.go

@@ -953,7 +953,7 @@ func TestFrameEvaluation(t *testing.T) {
 		assertNoError(err, t, "setFunctionBreakpoint")
 		assertNoError(p.Continue(), t, "Continue()")
 
-		/**** Testing evaluation on goroutines ****/
+		// Testing evaluation on goroutines
 		gs, err := p.GoroutinesInfo()
 		assertNoError(err, t, "GoroutinesInfo")
 		found := make([]bool, 10)
@@ -992,7 +992,7 @@ func TestFrameEvaluation(t *testing.T) {
 			}
 		}
 
-		/**** Testing evaluation on frames ****/
+		// Testing evaluation on frames
 		assertNoError(p.Continue(), t, "Continue() 2")
 		g, err := p.CurrentThread.GetG()
 		assertNoError(err, t, "GetG()")
@@ -1129,3 +1129,23 @@ func TestBreakpointCounts(t *testing.T) {
 		}
 	})
 }
+
+func TestIssue262(t *testing.T) {
+	// Continue does not work when the current breakpoint is set on a NOP instruction
+	withTestProcess("issue262", t, func(p *Process, fixture protest.Fixture) {
+		addr, _, err := p.goSymTable.LineToPC(fixture.Source, 11)
+		assertNoError(err, t, "LineToPC")
+		_, err = p.SetBreakpoint(addr)
+		assertNoError(err, t, "SetBreakpoint()")
+
+		assertNoError(p.Continue(), t, "Continue()")
+		err = p.Continue()
+		if err == nil {
+			t.Fatalf("No error on second continue")
+		}
+		_, exited := err.(ProcessExitedError)
+		if !exited {
+			t.Fatalf("Process did not exit after second continue: %v", err)
+		}
+	})
+}

proc/threads_darwin.go

 package proc
 
 // #include "threads_darwin.h"
+// #include "proc_darwin.h"
 import "C"
 import (
 	"fmt"
@@ -12,6 +13,8 @@ type OSSpecificDetails struct {
 	registers  C.x86_thread_state64_t
 }
 
+var ErrContinueThread = fmt.Errorf("could not continue thread")
+
 func (t *Thread) halt() (err error) {
 	kret := C.thread_suspend(t.os.thread_act)
 	if kret != C.KERN_SUCCESS {
@@ -27,7 +30,13 @@ func (t *Thread) singleStep() error {
 	if kret != C.KERN_SUCCESS {
 		return fmt.Errorf("could not single step")
 	}
-	t.dbp.trapWait(0)
+	for {
+		port := C.mach_port_wait(t.dbp.os.portSet)
+		if port == C.mach_port_t(t.Id) {
+			break
+		}
+	}
+
 	kret = C.clear_trap_flag(t.os.thread_act)
 	if kret != C.KERN_SUCCESS {
 		return fmt.Errorf("could not clear CPU trap flag")
@@ -45,7 +54,7 @@ func (t *Thread) resume() error {
 	}
 	kret := C.resume_thread(t.os.thread_act)
 	if kret != C.KERN_SUCCESS {
-		return fmt.Errorf("could not continue thread")
+		return ErrContinueThread
 	}
 	return nil
 }