bugfix: proc: propagate debug events we don't cause back to the targe…

…t process

Fixes: #594

_fixtures/issue594.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+	"runtime"
+)
+
+func dontsegfault() {
+	var p *int
+	func() int {
+		defer func() {
+			recover()
+		}()
+		return *p
+	}()
+}
+
+func main() {
+	dontsegfault()
+	runtime.Breakpoint()
+	fmt.Println("should stop here")
+}

proc/proc_test.go

@@ -1909,3 +1909,17 @@ func TestTestvariables2Prologue(t *testing.T) {
 		}
 	})
 }
+
+func TestIssue594(t *testing.T) {
+	// Exceptions that aren't caused by breakpoints should be propagated
+	// back to the target.
+	// In particular the target should be able to cause a nil pointer
+	// dereference panic and recover from it.
+	withTestProcess("issue594", t, func(p *Process, fixture protest.Fixture) {
+		assertNoError(p.Continue(), t, "Continue()")
+		f, ln := currentLineNumber(p, t)
+		if ln != 21 {
+			t.Fatalf("Program stopped at %s:%d, expected :21", f, ln)
+		}
+	})
+}

proc/proc_windows.go

@@ -438,6 +438,7 @@ func (dbp *Process) waitForDebugEvent(flags waitForDebugEventFlags) (threadID, e
 	var debugEvent _DEBUG_EVENT
 	shouldExit := false
 	for {
+		continueStatus := uint32(_DBG_CONTINUE)
 		var milliseconds uint32 = 0
 		if flags&waitBlocking != 0 {
 			milliseconds = syscall.INFINITE
@@ -494,9 +495,14 @@ func (dbp *Process) waitForDebugEvent(flags waitForDebugEventFlags) (threadID, e
 		case _RIP_EVENT:
 			break
 		case _EXCEPTION_DEBUG_EVENT:
-			tid := int(debugEvent.ThreadId)
-			dbp.os.breakThread = tid
-			return tid, 0, nil
+			exception := (*_EXCEPTION_DEBUG_INFO)(unionPtr)
+			if code := exception.ExceptionRecord.ExceptionCode; code == _EXCEPTION_BREAKPOINT || code == _EXCEPTION_SINGLE_STEP {
+				tid := int(debugEvent.ThreadId)
+				dbp.os.breakThread = tid
+				return tid, 0, nil
+			} else {
+				continueStatus = _DBG_EXCEPTION_NOT_HANDLED
+			}
 		case _EXIT_PROCESS_DEBUG_EVENT:
 			debugInfo := (*_EXIT_PROCESS_DEBUG_INFO)(unionPtr)
 			exitCode = int(debugInfo.ExitCode)
@@ -506,7 +512,7 @@ func (dbp *Process) waitForDebugEvent(flags waitForDebugEventFlags) (threadID, e
 		}
 
 		// .. and then continue unless we received an event that indicated we should break into debugger.
-		err = _ContinueDebugEvent(debugEvent.ProcessId, debugEvent.ThreadId, _DBG_CONTINUE)
+		err = _ContinueDebugEvent(debugEvent.ProcessId, debugEvent.ThreadId, continueStatus)
 		if err != nil {
 			return 0, 0, err
 		}

proc/syscall_windows.go

@@ -54,6 +54,20 @@ type _LOAD_DLL_DEBUG_INFO struct {
 	Unicode             uint16
 }
 
+type _EXCEPTION_DEBUG_INFO struct {
+	ExceptionRecord _EXCEPTION_RECORD
+	FirstChance     uint32
+}
+
+type _EXCEPTION_RECORD struct {
+	ExceptionCode        uint32
+	ExceptionFlags       uint32
+	ExceptionRecord      *_EXCEPTION_RECORD
+	ExceptionAddress     uintptr
+	NumberParameters     uint32
+	ExceptionInformation [_EXCEPTION_MAXIMUM_PARAMETERS]uintptr
+}
+
 const (
 	_ThreadBasicInformation = 0
 
@@ -72,6 +86,11 @@ const (
 
 	// DEBUG_ONLY_THIS_PROCESS tracks https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863(v=vs.85).aspx
 	_DEBUG_ONLY_THIS_PROCESS = 0x00000002
+
+	_EXCEPTION_BREAKPOINT  = 0x80000003
+	_EXCEPTION_SINGLE_STEP = 0x80000004
+
+	_EXCEPTION_MAXIMUM_PARAMETERS = 15
 )
 
 func _NT_SUCCESS(x _NTSTATUS) bool {