[lldb] [Process/FreeBSD] Set current thread ID on events

[mgorny]

Summary

Set the current thread ID to the thread where an event happened.
As a result, e.g. when a signal is delivered to a thread other than
the first one, the respective T packet refers to the signaled thread
rather than the first thread (with no stop reason). While this doesn't
strictly make a difference to the LLDB client, some of the lldb-server
tests rely on that for convenience.

[labath]

LG, though I wouldn't say this is just "convenience". I'd say this is the expected behaviour, and it just happens that the lldb client does not mind if we do not do that.

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

if (error.Fail()) {
       return;
     }
 
     // Let our delegate know we have just exec'd.
     NotifyDidExec();
 
     for (const auto &thread : m_threads)
       static_cast<NativeThreadFreeBSD &>(*thread).SetStoppedByExec();
+    SetCurrentThreadID(m_threads.front()->GetID());
     SetState(StateType::eStateStopped, true);
     return;
   }
 
   if (info.pl_lwpid > 0) {
     for (const auto &t : m_threads) {
       if (t->GetID() == static_cast<lldb::tid_t>(info.pl_lwpid))
         thread = static_cast<NativeThreadFreeBSD *>(t.get());
case TRAP_BRKPT:
           Status brkpt_error = RemoveBreakpoint(thread_info->second);
           if (brkpt_error.Fail())
             LLDB_LOG(log, "pid = {0} remove stepping breakpoint: {1}",
                      thread_info->first, brkpt_error);
           m_threads_stepping_with_breakpoint.erase(thread_info);
         } else
           thread->SetStoppedByBreakpoint();
         FixupBreakpointPCAsNeeded(*thread);
+        SetCurrentThreadID(thread->GetID());
       }
       SetState(StateType::eStateStopped, true);
       return;
     case TRAP_TRACE:
       LLDB_LOG(log, "SIGTRAP/TRAP_TRACE: si_addr: {0}",
                info.pl_siginfo.si_addr);
 
       if (thread) {
         auto &regctx = static_cast<NativeRegisterContextFreeBSD &>(
             thread->GetRegisterContext());
         uint32_t wp_index = LLDB_INVALID_INDEX32;
         Status error = regctx.GetWatchpointHitIndex(
             wp_index, reinterpret_cast<uintptr_t>(info.pl_siginfo.si_addr));
         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);
+          SetCurrentThreadID(thread->GetID());
           SetState(StateType::eStateStopped, true);
           break;
         }
 
         thread->SetStoppedByTrace();
+        SetCurrentThreadID(thread->GetID());
       }
 
       SetState(StateType::eStateStopped, true);
       return;
     }
   }
 
   // Either user-generated SIGTRAP or an unknown event that would
void NativeProcessFreeBSD::MonitorSignal(lldb::pid_t pid, int signal) {
   assert(info.pl_flags & PL_FLAG_SI);
   assert(info.pl_siginfo.si_signo == signal);
 
   for (const auto &abs_thread : m_threads) {
     NativeThreadFreeBSD &thread =
         static_cast<NativeThreadFreeBSD &>(*abs_thread);
     assert(info.pl_lwpid >= 0);
     if (info.pl_lwpid == 0 ||
-        static_cast<lldb::tid_t>(info.pl_lwpid) == thread.GetID())
+        static_cast<lldb::tid_t>(info.pl_lwpid) == thread.GetID()) {
       thread.SetStoppedBySignal(info.pl_siginfo.si_signo, &info.pl_siginfo);
-    else
+      SetCurrentThreadID(thread.GetID());
+    } else
       thread.SetStoppedWithNoReason();
   }
   SetState(StateType::eStateStopped, true);
 }
 
 Status NativeProcessFreeBSD::PtraceWrapper(int req, lldb::pid_t pid, void *addr,
                                            int data, int *result) {
   Log *log(ProcessPOSIXLog::GetLogIfAllCategoriesSet(POSIX_LOG_PTRACE));
assert(HasThreadNoLock(thread_id) &&
          "attempted to remove a thread that does not exist");
 
   for (auto it = m_threads.begin(); it != m_threads.end(); ++it) {
     if ((*it)->GetID() == thread_id) {
       m_threads.erase(it);
       break;
     }
   }
+
+  if (GetCurrentThreadID() == thread_id)
+    SetCurrentThreadID(m_threads.front()->GetID());
 }
 
 Status NativeProcessFreeBSD::Attach() {
   // Attach to the requested process.
   // An attach will cause the thread to stop with a SIGSTOP.
   Status status = PtraceWrapper(PT_ATTACH, m_pid);
   if (status.Fail())
     return status;