proc,service/dap,proc/gdbserial: fixes for debugserver --unmask-signals (#3541)

- fix TestRefreshCurThreadSelGAfterContinueOnceError and TestBadAccess
  to work when debugserver has --unmask-signals
- when a fatal signal is received while singlestepping delay its
  delivery until the subsequent continue, otherwise debugserver will get
  stuck completely (fixes TestNilPtrDerefInBreakInstr)

pkg/proc/gdbserial/gdbserver_conn.go

@@ -650,8 +650,20 @@ func (conn *gdbConn) step(th *gdbThread, tu *threadUpdater, ignoreFaultSignal bo
 			if ignoreFaultSignal { // we attempting to read the TLS, a fault here should be ignored
 				return nil
 			}
+			if conn.isDebugserver {
+				// For some reason trying to deliver a signal in vCont step makes
+				// debugserver lockup (no errors, it just gets stuck), store the signal
+				// to deliver it later with the vCont;c
+				th.sig = sig
+				return nil
+			}
 		case _SIGILL, _SIGBUS, _SIGFPE:
-			// propagate these signals to inferior immediately
+			if conn.isDebugserver {
+				// See comment above
+				th.sig = sig
+				return nil
+			}
+			// otherwise propagate these signals to inferior immediately
 		case interruptSignal, breakpointSignal, stopSignal:
 			return nil
 		case childSignal: // stop on debugserver but SIGCHLD on lldb-server/linux

pkg/proc/proc_test.go

@@ -5044,7 +5044,13 @@ func TestRefreshCurThreadSelGAfterContinueOnceError(t *testing.T) {
 		setFileBreakpoint(p, t, fixture.Source, 4)
 		assertNoError(grp.Continue(), t, "Continue() (first)")
 		if grp.Continue() == nil {
-			t.Fatalf("Second continue did not return an error")
+			pc := currentPC(p, t)
+			f, l, fn := p.BinInfo().PCToLine(pc)
+			t.Logf("Second continue did not return an error %s:%d %#v", f, l, fn)
+			if fn != nil && fn.Name == "runtime.fatalpanic" {
+				// this is also ok, it just means this debugserver supports --unmask-signals and it's working as intented.
+				return
+			}
 		}
 		g := p.SelectedGoroutine()
 		if g.CurrentLoc.Line != 9 {

service/dap/server_test.go

@@ -4874,12 +4874,12 @@ func TestBadAccess(t *testing.T) {
 					expectStoppedOnError := func(errorPrefix string) {
 						t.Helper()
 						se := client.ExpectStoppedEvent(t)
-						if se.Body.ThreadId != 1 || se.Body.Reason != "exception" || se.Body.Description != "runtime error" || !strings.HasPrefix(se.Body.Text, errorPrefix) {
+						if se.Body.ThreadId != 1 || se.Body.Reason != "exception" || (se.Body.Description != "runtime error" && se.Body.Description != "panic") || !strings.Contains(se.Body.Text, errorPrefix) {
 							t.Errorf("\ngot  %#v\nwant ThreadId=1 Reason=\"exception\" Description=\"runtime error\" Text=\"%s\"", se, errorPrefix)
 						}
 						client.ExceptionInfoRequest(1)
 						eInfo := client.ExpectExceptionInfoResponse(t)
-						if eInfo.Body.ExceptionId != "runtime error" || !strings.HasPrefix(eInfo.Body.Description, errorPrefix) {
+						if (eInfo.Body.ExceptionId != "runtime error" && eInfo.Body.ExceptionId != "panic") || !strings.Contains(eInfo.Body.Description, errorPrefix) {
 							t.Errorf("\ngot  %#v\nwant ExceptionId=\"runtime error\" Text=\"%s\"", eInfo, errorPrefix)
 						}
 					}
@@ -4888,6 +4888,13 @@ func TestBadAccess(t *testing.T) {
 					client.ExpectContinueResponse(t)
 					expectStoppedOnError("invalid memory address or nil pointer dereference")
 
+					client.StackTraceRequest(1, 0, 2)
+					st := client.ExpectStackTraceResponse(t)
+					if len(st.Body.StackFrames) > 0 && st.Body.StackFrames[0].Name == "runtime.fatalpanic" {
+						// this debugserver has --unmask-signals and it works correctly
+						return
+					}
+
 					client.NextRequest(1)
 					client.ExpectNextResponse(t)
 					expectStoppedOnError("invalid memory address or nil pointer dereference")