[lldb] [Process/FreeBSDRemote] Fix handling user-generated SIGTRAP

[mgorny]

Summary

Update the SIGTRAP handler to account for the possibility of SIGTRAP
being generated by the user, i.e. not having any specific debugging
event associated with it, as well as receiving unknown SIGTRAPs. These
instances of SIGTRAP are passed to the regular signal handler.

[krytarowski]

I propose to filter all user induced signals at once and check & 0x10000 and SI_USER.

http://src.illumos.org/source/xref/freebsd-head/sys/sys/signal.h#406

This way we will avoid all future fallout and crashing the debugger on unknown signal.

[mgorny]

Updated to treat generic SIGTRAP as a fallback as requested by @krytarowski. This happens either if si_code >= SI_USER, or there is no siginfo and no other flag is set.

[labath]

lldb/source/Plugins/Process/FreeBSDRemote/NativeProcessFreeBSD.cpp

287

What will happen in case this returns? Will the process auto-resume or just hang stopped? It sounds like it would still be useful to report this as "SIGTRAP" even if we are unable to give any details about it...

[mgorny]

lldb/source/Plugins/Process/FreeBSDRemote/NativeProcessFreeBSD.cpp

287

Good catch. Should it be reported as an arbitrary SIGTRAP then or maybe as a trace trap?

[labath]

lldb/source/Plugins/Process/FreeBSDRemote/NativeProcessFreeBSD.cpp

287

I don't have a strong opinion there. I'd probably just go with a regular SIGTRAP.

[mgorny]

Pass unknown SIGTRAPs to the user too.

[mgorny]

clang-format

lldb/source/Plugins/Process/FreeBSDRemote/NativeProcessFreeBSD.cpp

void NativeProcessFreeBSD::MonitorSIGTRAP(lldb::pid_t pid) {
 
   const auto siginfo_err = PtraceWrapper(PT_LWPINFO, pid, &info, sizeof(info));
   if (siginfo_err.Fail()) {
     LLDB_LOG(log, "PT_LWPINFO failed {0}", siginfo_err);
     return;
   }
   assert(info.pl_event == PL_EVENT_SIGNAL);
 
-  LLDB_LOG(log, "got SIGTRAP, pid = {0}, lwpid = {1}", pid, info.pl_lwpid);
+  LLDB_LOG(log, "got SIGTRAP, pid = {0}, lwpid = {1}, flags = {2:x}", pid,
+           info.pl_lwpid, info.pl_flags);
   NativeThreadFreeBSD *thread = nullptr;
 
   if (info.pl_flags & (PL_FLAG_BORN | PL_FLAG_EXITED)) {
     if (info.pl_flags & PL_FLAG_BORN) {
       LLDB_LOG(log, "monitoring new thread, tid = {0}", info.pl_lwpid);
       AddThread(info.pl_lwpid);
     } else /*if (info.pl_flags & PL_FLAG_EXITED)*/ {
       LLDB_LOG(log, "thread exited, tid = {0}", info.pl_lwpid);
if (info.pl_lwpid > 0) {
     }
     if (!thread)
       LLDB_LOG(log, "thread not found in m_threads, pid = {0}, LWP = {1}", pid,
                info.pl_lwpid);
   }
 
   if (info.pl_flags & PL_FLAG_SI) {
     assert(info.pl_siginfo.si_signo == SIGTRAP);
+    LLDB_LOG(log, "SIGTRAP siginfo: si_code = {0}, pid = {1}",
+             info.pl_siginfo.si_code, info.pl_siginfo.si_pid);
 
     switch (info.pl_siginfo.si_code) {
     case TRAP_BRKPT:
       if (thread) {
         thread->SetStoppedByBreakpoint();
         FixupBreakpointPCAsNeeded(*thread);
       }
       SetState(StateType::eStateStopped, true);
-      break;
+      return;
     case TRAP_TRACE:
       if (thread) {
         auto &regctx = static_cast<NativeRegisterContextFreeBSD &>(
             thread->GetRegisterContext());
         uint32_t wp_index = LLDB_INVALID_INDEX32;
         Status error =
             regctx.GetWatchpointHitIndex(wp_index, LLDB_INVALID_ADDRESS);
         if (error.Fail())
           LLDB_LOG(log,
                    "received error while checking for watchpoint hits, pid = "
                    "{0}, LWP = {1}, error = {2}",
                    pid, info.pl_lwpid, error);
         if (wp_index != LLDB_INVALID_INDEX32) {
           regctx.ClearWatchpointHit(wp_index);
           thread->SetStoppedByWatchpoint(wp_index);
           SetState(StateType::eStateStopped, true);
           break;
         }
 
         thread->SetStoppedByTrace();
       }
 
       SetState(StateType::eStateStopped, true);
-      break;
+      return;
     }
   }
+
+  // Either user-generated SIGTRAP or an unknown event that would
+  // otherwise leave the debugger hanging.
+  LLDB_LOG(log, "unknown SIGTRAP, passing to generic handler");
+  MonitorSignal(pid, SIGTRAP);
 }
 
 void NativeProcessFreeBSD::MonitorSignal(lldb::pid_t pid, int signal) {
   Log *log(ProcessPOSIXLog::GetLogIfAllCategoriesSet(POSIX_LOG_PROCESS));
   struct ptrace_lwpinfo info;
 
   const auto siginfo_err = PtraceWrapper(PT_LWPINFO, pid, &info, sizeof(info));
   if (siginfo_err.Fail()) {
     LLDB_LOG(log, "PT_LWPINFO failed {0}", siginfo_err);
     return;

lldb/test/API/functionalities/signal/raise/TestRaise.py

class RaiseTestCase(TestBase):
 
     @skipIfDarwin  # darwin does not support real time signals
     @skipIfTargetAndroid()
     def test_sigsigrtmin(self):
         self.build()
         self.signal_test('SIGRTMIN', True)
 
     @skipIfNetBSD  # Hangs on NetBSD
-    @skipIfFreeBSD  # hangs
     def test_sigtrap(self):
         self.build()
         self.signal_test('SIGTRAP', True)
 
     def launch(self, target, signal):
         # launch the process, do not stop at entry point.
         process = target.LaunchSimple(
             [signal], None, self.get_process_working_directory())