[lldb] Send QPassSignals packet on attach, and at start for remote platforms

[kpdev42]

Summary

Before this patch, lldb did not send signal filtering information (QPassSignals packet) to lldb-server on remote platforms until signal settings were explicitly changed. Patch changes last sent signals version to be initialized with an invalid value instead of 0, so that the signal filtering information is sent to the server when the version is actually 0, which happens on remote platforms when the signal structure is copied and the version is reset. Also changes Process so that the information is sent not only right after launch, but right after attach too to be more consistent.

[DavidSpickett]

What is the practical impact of the bug you are fixing?

I guess it is something like if you set signal handling info, then attach to something, that info is not used. Until you set it again, then it'll be sent and used.

[kpdev42]

In D144390#4138869, @DavidSpickett wrote:

What is the practical impact of the bug you are fixing?

I guess it is something like if you set signal handling info, then attach to something, that info is not used. Until you set it again, then it'll be sent and used.

The signal filtering settings can only be changed for an already created process, so the bug is that lldb does not send the default settings for remote platforms (for example, ignoring of real-time signals inside lldb-server is not applied)

[kpdev42]

ping

[DavidSpickett]

This is probably an obvious change, but I have no experience with this area so I don't feel comfortable approving.

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

protected:
 
   Status DoGetMemoryRegionInfo(lldb::addr_t load_addr,
                                MemoryRegionInfo &region_info) override;
 
 private:
   // For ProcessGDBRemote only
   std::string m_partial_profile_data;
   std::map<uint64_t, uint32_t> m_thread_id_to_used_usec_map;
-  uint64_t m_last_signals_version = 0;
+  uint64_t m_last_signals_version = UINT64_MAX;
 
   static bool NewThreadNotifyBreakpointHit(void *baton,
                                            StoppointCallbackContext *context,
                                            lldb::user_id_t break_id,
                                            lldb::user_id_t break_loc_id);
 
   // ContinueDelegate interface
   void HandleAsyncStdout(llvm::StringRef out) override;

lldb/source/Target/Process.cpp

if (state == eStateStopped || state == eStateCrashed) {
 
     SystemRuntime *system_runtime = GetSystemRuntime();
     if (system_runtime)
       system_runtime->DidLaunch();
 
     if (!m_os_up)
       LoadOperatingSystemPlugin(false);
 
-    // We successfully launched the process and stopped, now it the
+    // We successfully launched the process and stopped, now it is the
     // right time to set up signal filters before resuming.
     UpdateAutomaticSignalFiltering();
     return Status();
   }
 
   return Status("Unexpected process state after the launch: %s, expected %s, "
                 "%s, %s or %s",
                 StateAsCString(state), StateAsCString(eStateInvalid),
if (log) {
       LLDB_LOGF(
           log,
           "Process::%s after looping through modules, target executable is %s",
           __FUNCTION__,
           exe_module_sp ? exe_module_sp->GetFileSpec().GetPath().c_str()
                         : "<none>");
     }
   }
+
+  // We successfully attached to the process and stopped, now it is the
+  // right time to set up signal filters before resuming.
+  UpdateAutomaticSignalFiltering();
 }
 
 Status Process::ConnectRemote(llvm::StringRef remote_url) {
   m_abi_sp.reset();
   m_process_input_reader.reset();
 
   // Find the process and its architecture.  Make sure it matches the
   // architecture of the current Target, and if not adjust it.

lldb/test/API/functionalities/gdb_remote_client/TestGDBRemoteSignalFiltering.py

+"""Test that GDBRemoteProcess sends default signal filtering info when necessary"""
+
+import lldb
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test.decorators import *
+from lldbsuite.test.gdbclientutils import *
+from lldbsuite.test.lldbgdbclient import GDBRemoteTestBase
+
+
+class TestGDBRemoteSignalFiltering(GDBRemoteTestBase):
+
+    def test_signals_sent_on_connect(self):
+        """Test that signal filtering info is sent on connect"""
+        class Responder(MockGDBServerResponder):
+            def qSupported(self, client_supported):
+                return "PacketSize=3fff;QStartNoAckMode+;QPassSignals+"
+
+            def respond(self, packet):
+                if packet == "QPassSignals":
+                    return self.QPassSignals()
+                return MockGDBServerResponder.respond(self, packet)
+
+            def QPassSignals(self):
+                return "OK"
+
+        self.server.responder = Responder()
+        target = self.createTarget("a.yaml")
+        process = self.connect(target)
+        self.assertGreater(
+                len([p for p in self.server.responder.packetLog if p.startswith("QPassSignals:")]),
+                0)