[lldb] [Process/FreeBSDRemote] Fix attaching via lldb-server

[mgorny]

Summary

Fix two bugs that caused attaching to a process in a pre-connected
lldb-server to fail. These are:

1. Prematurely reporting status in NativeProcessFreeBSD::Attach(). The SetState() call defaulted to notify the process, and LLGS tried to send the stopped packet before the process instance was assigned to it. While at it, add an assert for that in LLGS.

2. Duplicate call to ReinitializeThreads() (via SetupTrace()) that overwrote the stopped status in threads. Now SetupTrace() is called directly by NativeProcessFreeBSD::Attach() (not the Factory) in place of ReinitializeThreads().

This fixes at least commands/process/attach/TestProcessAttach.py
and python_api/hello_world/TestHelloWorld.py.

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

Status NativeProcessFreeBSD::Attach() {
 
   int wstatus;
   // Need to use WALLSIG otherwise we receive an error with errno=ECHLD At this
   // point we should have a thread stopped if waitpid succeeds.
   if ((wstatus = llvm::sys::RetryAfterSignal(-1, waitpid, m_pid, nullptr, 0)) <
       0)
     return Status(errno, eErrorTypePOSIX);
 
-  /* Initialize threads */
-  status = ReinitializeThreads();
+  // Initialize threads and tracing status
+  // NB: this needs to be called before we set thread state
+  status = SetupTrace();
   if (status.Fail())
     return status;
 
   for (const auto &thread : m_threads)
     static_cast<NativeThreadFreeBSD &>(*thread).SetStoppedBySignal(SIGSTOP);
 
   // Let our process instance know the thread has stopped.
-  SetState(StateType::eStateStopped);
+  SetCurrentThreadID(m_threads.front()->GetID());
+  SetState(StateType::eStateStopped, false);
   return Status();
 }
 
 Status NativeProcessFreeBSD::ReadMemory(lldb::addr_t addr, void *buf,
                                         size_t size, size_t &bytes_read) {
   unsigned char *dst = static_cast<unsigned char *>(buf);
   struct ptrace_io_desc io;
 

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp

GDBRemoteCommunicationServerLLGS::SendStopReasonForState(
   case eStateDetached:
     // NOTE: gdb protocol doc looks like it should return $OK
     // when everything is running (i.e. no stopped result).
     return PacketResult::Success; // Ignore
 
   case eStateSuspended:
   case eStateStopped:
   case eStateCrashed: {
+    assert(m_debugged_process_up != nullptr);
     lldb::tid_t tid = m_debugged_process_up->GetCurrentThreadID();
     // Make sure we set the current thread so g and p packets return the data
     // the gdb will expect.
     SetCurrentThreadID(tid);
     return SendStopReplyPacketForThread(tid);
   }
 
   case eStateInvalid: