[lldb] [gdb-remote] Refactor killing process and move it to client

[mgorny]

Summary

Refactor the code responsible for sending the "k" packet and move it
into GDBRemoteCommunicationClient::KillProcess() method. This is part
of refactoring to enable multiprocess support in the client,
and to support using the vKill packet instead.

As part of the refactoring, the following functional changes apply:

• Some redundant logging has been removed, as any failures are returned via exit_string anyway.

• SetLastStopPacket() is no longer called. It is used only to populate the thread list, and since the process has just exited and we're terminating the process instance, there's really no reason to set it.

• On successful kill, exit_string is set to "killed", to clearly indicate that the process has terminated on our request rather than on its own.

Sponsored by: The FreeBSD Foundation

lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationClient.h

SendTraceGetState(llvm::StringRef type,
                     std::chrono::seconds interrupt_timeout);
 
   llvm::Expected<std::vector<uint8_t>>
   SendTraceGetBinaryData(const TraceGetBinaryDataRequest &request,
                          std::chrono::seconds interrupt_timeout);
 
   bool GetSaveCoreSupported() const;
 
+  llvm::Expected<int> KillProcess(lldb::pid_t pid);
+
 protected:
   LazyBool m_supports_not_sending_acks = eLazyBoolCalculate;
   LazyBool m_supports_thread_suffix = eLazyBoolCalculate;
   LazyBool m_supports_threads_in_stop_reply = eLazyBoolCalculate;
   LazyBool m_supports_vCont_all = eLazyBoolCalculate;
   LazyBool m_supports_vCont_any = eLazyBoolCalculate;
   LazyBool m_supports_vCont_c = eLazyBoolCalculate;
   LazyBool m_supports_vCont_C = eLazyBoolCalculate;

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

if (m_uses_native_signals == eLazyBoolCalculate)
     GetRemoteQSupported();
   if (m_uses_native_signals == eLazyBoolYes)
     return true;
 
   // If the remote didn't indicate native-signal support explicitly,
   // check whether it is an old version of lldb-server.
   return GetThreadSuffixSupported();
 }
+
+llvm::Expected<int> GDBRemoteCommunicationClient::KillProcess(lldb::pid_t pid) {
+  StringExtractorGDBRemote response;
+  GDBRemoteCommunication::ScopedTimeout(*this, seconds(3));
+
+  if (SendPacketAndWaitForResponse("k", response, GetPacketTimeout()) !=
+      PacketResult::Success)
+    return llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                   "failed to send k packet");
+
+  char packet_cmd = response.GetChar(0);
+  if (packet_cmd == 'W' || packet_cmd == 'X')
+    return response.GetHexU8();
+
+  return llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                 "unexpected response to k packet: %s",
+                                 response.GetStringRef().str().c_str());
+}

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

Status ProcessGDBRemote::DoDetach(bool keep_stopped) {
   SetPrivateState(eStateDetached);
   ResumePrivateStateThread();
 
   // KillDebugserverProcess ();
   return error;
 }
 
 Status ProcessGDBRemote::DoDestroy() {
-  Status error;
   Log *log = GetLog(GDBRLog::Process);
   LLDB_LOGF(log, "ProcessGDBRemote::DoDestroy()");
 
   // Interrupt if our inferior is running...
   int exit_status = SIGABRT;
   std::string exit_string;
 
   if (m_gdb_comm.IsConnected()) {
     if (m_public_state.GetValue() != eStateAttaching) {
-      StringExtractorGDBRemote response;
-      GDBRemoteCommunication::ScopedTimeout(m_gdb_comm,
-                                            std::chrono::seconds(3));
+      llvm::Expected<int> kill_res = m_gdb_comm.KillProcess(GetID());
 
-      if (m_gdb_comm.SendPacketAndWaitForResponse("k", response,
-                                                  GetInterruptTimeout()) ==
-          GDBRemoteCommunication::PacketResult::Success) {
-        char packet_cmd = response.GetChar(0);
-
-        if (packet_cmd == 'W' || packet_cmd == 'X') {
+      if (kill_res) {
+        exit_status = kill_res.get();
 #if defined(__APPLE__)
-          // For Native processes on Mac OS X, we launch through the Host
-          // Platform, then hand the process off to debugserver, which becomes
-          // the parent process through "PT_ATTACH".  Then when we go to kill
-          // the process on Mac OS X we call ptrace(PT_KILL) to kill it, then
-          // we call waitpid which returns with no error and the correct
-          // status.  But amusingly enough that doesn't seem to actually reap
-          // the process, but instead it is left around as a Zombie.  Probably
-          // the kernel is in the process of switching ownership back to lldb
-          // which was the original parent, and gets confused in the handoff.
-          // Anyway, so call waitpid here to finally reap it.
-          PlatformSP platform_sp(GetTarget().GetPlatform());
-          if (platform_sp && platform_sp->IsHost()) {
-            int status;
-            ::pid_t reap_pid;
-            reap_pid = waitpid(GetID(), &status, WNOHANG);
-            LLDB_LOGF(log, "Reaped pid: %d, status: %d.\n", reap_pid, status);
-          }
 #endif
-          SetLastStopPacket(response);
-          ClearThreadIDList();
-          exit_status = response.GetHexU8();
-        } else {
-          LLDB_LOGF(log,
-                    "ProcessGDBRemote::DoDestroy - got unexpected response "
-                    "to k packet: %s",
-                    response.GetStringRef().data());
-          exit_string.assign("got unexpected response to k packet: ");
-          exit_string.append(std::string(response.GetStringRef()));
-        }
-      } else {
-        LLDB_LOGF(log, "ProcessGDBRemote::DoDestroy - failed to send k packet");
-        exit_string.assign("failed to send the k packet");
+        exit_string.assign("killed");
+        exit_string.assign(llvm::toString(kill_res.takeError()));
       }
     } else {
-      LLDB_LOGF(log,
-                "ProcessGDBRemote::DoDestroy - killed or interrupted while "
-                "attaching");
       exit_string.assign("killed or interrupted while attaching.");
     }
   } else {
     // If we missed setting the exit status on the way out, do it here.
     // NB set exit status can be called multiple times, the first one sets the
     // status.
     exit_string.assign("destroying when not connected to debugserver");
   }
 
   SetExitStatus(exit_status, exit_string.c_str());
 
   StopAsyncThread();
   KillDebugserverProcess();
-  return error;
+  return Status();
 }
 
 void ProcessGDBRemote::SetLastStopPacket(
     const StringExtractorGDBRemote &response) {
   const bool did_exec =
       response.GetStringRef().find(";reason:exec;") != std::string::npos;
   if (did_exec) {
     Log *log = GetLog(GDBRLog::Process);