Remote Non-Stop Support

[EwanCrawford]

Summary

This patch is the beginnings of support for Non-stop mode in the remote protocol. Letting a user examine stopped threads, while other threads execute freely.

Non-stop mode is enabled using the setting target.non-stop-mode, which sends a QNonStop packet when establishing the remote connection.
Changes are also made to treat the '?' stop reply packet differently in non-stop mode, according to spec https://sourceware.org/gdb/current/onlinedocs/gdb/Remote-Non_002dStop.html#Remote-Non_002dStop.
A setting for querying the remote for default thread on setup is also included.

Handling of '%' async notification packets will be added next.

[clayborg]

Everything looks good. Just one quests on why we need the "default-thread" setting. Can you explain why we need a user settable setting here? Shouldn't we just do this if non stop mode is enabled?

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

111

Why do we need a setting for this? Why would anyone want to set this manually? It would be great to not require this and just "do the right thing". Please explain why this is needed.

[EwanCrawford]

Thanks for having a look Greg. I removed the setting so that we only query for a default thread when non stop mode is enabled.

[clayborg]

As long as default mode still works, this looks good.

[jingham]

This patch seems okay for what it does, but there are a bunch of places where the stepping machinery assumes that it can stop all the threads to do things like stepping over breakpoints, etc. You are going to get lots of subtle funny behavior - like missing breakpoint hits on live threads when stepping over the breakpoint hit on another thread, or getting confused if a live thread hits a breakpoint when we think we are only running one thread for some other purpose. That part is going to take a bit more thought to get it to work correctly. This needs to be designed...

include/lldb/Target/Target.h

 
     void
     SetUserSpecifiedTrapHandlerNames (const Args &args);
+
+    bool
+    GetNonStopModeEnabled () const;
     
     bool
     GetDisplayRuntimeSupportValues () const;

source/Commands/CommandObjectThread.cpp

             m_step_in_avoid_no_debug = eLazyBoolCalculate;
             m_step_out_avoid_no_debug = eLazyBoolCalculate;
             m_run_mode = eOnlyDuringStepping;
+
+            // Check if we are in Non-Stop mode
+            lldb::TargetSP target_sp = m_interpreter.GetDebugger().GetSelectedTarget();
+            if (target_sp.get() != nullptr && target_sp->GetNonStopModeEnabled())
+                m_run_mode = eOnlyThisThread;
+
             m_avoid_regexp.clear();
             m_step_in_target.clear();
             m_class_name.clear();

source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp

                 content_length = total_length = 1;  // The command is one byte long...
                 break;
 
+            case '%': // Async notify packet
             case '$':
                 // Look for a standard gdb packet?
                 {

                         case '+':
                         case '-':
                         case '\x03':
+                        case '%':
                         case '$':
                             done = true;
                             break;

                 }
             }
 
-            if (m_bytes[0] == '$')
+            if (m_bytes[0] == '$' || m_bytes[0] == '%')
             {
                 assert (checksum_idx < m_bytes.size());
                 if (::isxdigit (m_bytes[checksum_idx+0]) || 

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

 
     bool
     GetHostInfo (bool force = false);
+
+    bool
+    GetDefaultThreadId (lldb::tid_t &tid);
     
     bool
     GetOSVersion (uint32_t &major, 

                                 lldb::addr_t addr,        // Address of breakpoint or watchpoint
                                 uint32_t length);         // Byte Size of breakpoint or watchpoint
 
+    bool
+    SetNonStopMode (const bool enable);
+
     void
     TestPacketSpeed (const uint32_t num_packets);
 

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

 }
 
 bool
+GDBRemoteCommunicationClient::GetDefaultThreadId (lldb::tid_t &tid)
+{
+    StringExtractorGDBRemote response;
+    if (SendPacketAndWaitForResponse("qC",response,false) !=  PacketResult::Success)
+        return false;
+
+    if (!response.IsNormalResponse())
+        return false;
+
+    if (response.GetChar() == 'Q' && response.GetChar() == 'C')
+        tid = response.GetHexMaxU32(true, -1);
+
+    return true;
+}
+
+bool
 GDBRemoteCommunicationClient::GetHostInfo (bool force)
 {
     Log *log (ProcessGDBRemoteLog::GetLogIfAnyCategoryIsSet (GDBR_LOG_PROCESS));

     return false;
 }
 
+bool
+GDBRemoteCommunicationClient::SetNonStopMode (const bool enable)
+{
+    // Form non-stop packet request
+    char packet[32];
+    const int packet_len = ::snprintf(packet, sizeof(packet), "QNonStop:%1d", (int)enable);
+    assert(packet_len < (int)sizeof(packet));
+
+    StringExtractorGDBRemote response;
+    // Send to target
+    if (SendPacketAndWaitForResponse(packet, packet_len, response, false) == PacketResult::Success)
+        if (response.IsOKResponse())
+            return true;
+
+    // Failed or not supported
+    return false;
+
+}
+
 void
 GDBRemoteCommunicationClient::TestPacketSpeed (const uint32_t num_packets)
 {

source/Plugins/Process/gdb-remote/ProcessGDBRemote.h

     bool m_destroy_tried_resuming;
     lldb::CommandObjectSP m_command_sp;
     int64_t m_breakpoint_pc_offset;
+    lldb::tid_t m_initial_tid; // The inital thread ID, given by stub on attach
 
     bool
     StartAsyncThread ();

     SetThreadStopInfo (StringExtractor& stop_packet);
 
     void
+    HandleStopReplySequence ();
+
+    void
     ClearThreadIDList ();
 
     bool

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

     m_waiting_for_attach (false),
     m_destroy_tried_resuming (false),
     m_command_sp (),
-    m_breakpoint_pc_offset (0)
+    m_breakpoint_pc_offset (0),
+    m_initial_tid (LLDB_INVALID_THREAD_ID)
 {
     m_async_broadcaster.SetEventName (eBroadcastBitAsyncThreadShouldExit,   "async thread should exit");
     m_async_broadcaster.SetEventName (eBroadcastBitAsyncContinue,           "async thread continue");

         // We have a valid process
         SetID (pid);
         GetThreadList();
-        if (m_gdb_comm.SendPacketAndWaitForResponse("?", 1, m_last_stop_packet, false) == GDBRemoteCommunication::PacketResult::Success)
+        if (m_gdb_comm.GetStopReply(m_last_stop_packet))
         {
+
+            // '?' Packets must be handled differently in non-stop mode
+            if (GetTarget().GetNonStopModeEnabled())
+                HandleStopReplySequence();
+
             if (!m_target.GetArchitecture().IsValid()) 
             {
                 if (m_gdb_comm.GetProcessArchitecture().IsValid())

                 return error;
             }
 
-            if (m_gdb_comm.SendPacketAndWaitForResponse("?", 1, m_last_stop_packet, false) == GDBRemoteCommunication::PacketResult::Success)
+            if (m_gdb_comm.GetStopReply(m_last_stop_packet))
             {
+
+                // '?' Packets must be handled differently in non-stop mode
+                if (GetTarget().GetNonStopModeEnabled())
+                    HandleStopReplySequence();
+
                 const ArchSpec &process_arch = m_gdb_comm.GetProcessArchitecture();
 
                 if (process_arch.IsValid())

             error.SetErrorString("not connected to remote gdb server");
         return error;
     }
+
+    // Send $QNonStop:1 packet on startup if required
+    if (GetTarget().GetNonStopModeEnabled())
+        m_gdb_comm.SetNonStopMode(true);
+
     m_gdb_comm.GetThreadSuffixSupported ();
     m_gdb_comm.GetListThreadsInStopReplySupported ();
     m_gdb_comm.GetHostInfo ();
     m_gdb_comm.GetVContSupported ('c');
     m_gdb_comm.GetVAttachOrWaitSupported();
-    
+    // Ask the remote server for the default thread id
+    if (GetTarget().GetNonStopModeEnabled())
+        m_gdb_comm.GetDefaultThreadId(m_initial_tid);
+
+
     size_t num_cmds = GetExtraStartupCommands().GetArgumentCount();
     for (size_t idx = 0; idx < num_cmds; idx++)
     {

         bool continue_packet_error = false;
         if (m_gdb_comm.HasAnyVContSupport ())
         {
-            if (m_continue_c_tids.size() == num_threads ||
+            if (!GetTarget().GetNonStopModeEnabled() &&
+                (m_continue_c_tids.size() == num_threads ||
                 (m_continue_c_tids.empty() &&
                  m_continue_C_tids.empty() &&
                  m_continue_s_tids.empty() &&
-                 m_continue_S_tids.empty()))
+                 m_continue_S_tids.empty())))
             {
                 // All threads are continuing, just send a "c" packet
                 continue_packet.PutCString ("c");

 }
 
 void
+ProcessGDBRemote::HandleStopReplySequence ()
+{
+    while(true)
+    {
+        // Send vStopped
+        StringExtractorGDBRemote response;
+        m_gdb_comm.SendPacketAndWaitForResponse("vStopped", response, false);
+
+        // OK represents end of signal list
+        if (response.IsOKResponse())
+            break;
+
+        // If not OK or a normal packet we have a problem
+        if (!response.IsNormalResponse())
+            break;
+
+        SetLastStopPacket(response);
+    }
+}
+
+void
 ProcessGDBRemote::ClearThreadIDList ()
 {
     Mutex::Locker locker(m_thread_list_real.GetMutex());

         UpdateThreadIDList();
     }
 
+    // If we have queried for a default thread id
+    if (m_initial_tid != LLDB_INVALID_THREAD_ID)
+    {
+        m_thread_list.SetSelectedThreadByID(m_initial_tid);
+        m_initial_tid = LLDB_INVALID_THREAD_ID;
+    }
+
     // Let all threads recover from stopping and do any clean up based
     // on the previous thread state (if any).
     m_thread_list_real.RefreshStateAfterStop();

source/Target/Target.cpp

     { "display-expression-in-crashlogs"    , OptionValue::eTypeBoolean   , false, false,                      NULL, NULL, "Expressions that crash will show up in crash logs if the host system supports executable specific crash log strings and this setting is set to true." },
     { "trap-handler-names"                 , OptionValue::eTypeArray     , true,  OptionValue::eTypeString,   NULL, NULL, "A list of trap handler function names, e.g. a common Unix user process one is _sigtramp." },
     { "display-runtime-support-values"     , OptionValue::eTypeBoolean   , false, false,                      NULL, NULL, "If true, LLDB will show variables that are meant to support the operation of a language's runtime support." },
+    { "non-stop-mode"                      , OptionValue::eTypeBoolean   , false, 0,                          NULL, NULL, "Disable lock-step debugging, instead control threads independently." },
     { NULL                                 , OptionValue::eTypeInvalid   , false, 0                         , NULL, NULL, NULL }
 };
 

     ePropertyMemoryModuleLoadLevel,
     ePropertyDisplayExpressionsInCrashlogs,
     ePropertyTrapHandlerNames,
-    ePropertyDisplayRuntimeSupportValues
+    ePropertyDisplayRuntimeSupportValues,
+    ePropertyNonStopModeEnabled
 };
 
 

     m_collection_sp->SetPropertyAtIndexAsBoolean (NULL, idx, b);
 }
 
+bool
+TargetProperties::GetNonStopModeEnabled () const
+{
+    const uint32_t idx = ePropertyNonStopModeEnabled;
+    return m_collection_sp->GetPropertyAtIndexAsBoolean (NULL, idx, false);
+}
+
 const ProcessLaunchInfo &
 TargetProperties::GetProcessLaunchInfo ()
 {

source/Utility/StringExtractorGDBRemote.h

 
         eServerPacketType__M,
         eServerPacketType__m,
+        eServerPacketType_notify, // '%' notification
     };
     
     ServerPacketType

source/Utility/StringExtractorGDBRemote.cpp

     const char *packet_cstr = m_packet.c_str();
     switch (m_packet[0])
     {
+
+    case '%':
+        return eServerPacketType_notify;
+
     case '\x03':
         if (packet_size == 1) return eServerPacketType_interrupt;
         break;