[lldb] Add ability to inspect backing threads with thread info

lldb/source/Commands/CommandObjectThread.cpp

@@ -1270,6 +1270,7 @@ class CommandObjectThreadInfo : public CommandObjectIterateOverThreads {
     void OptionParsingStarting(ExecutionContext *execution_context) override {
       m_json_thread = false;
       m_json_stopinfo = false;
+      m_backing_thread = false;
     }
 
     Status SetOptionValue(uint32_t option_idx, llvm::StringRef option_arg,
@@ -1286,6 +1287,10 @@ class CommandObjectThreadInfo : public CommandObjectIterateOverThreads {
         m_json_stopinfo = true;
         break;
 
+      case 'b':
+        m_backing_thread = true;
+        break;
+
       default:
         llvm_unreachable("Unimplemented option");
       }
@@ -1298,6 +1303,7 @@ class CommandObjectThreadInfo : public CommandObjectIterateOverThreads {
 
     bool m_json_thread;
     bool m_json_stopinfo;
+    bool m_backing_thread;
   };
 
   CommandObjectThreadInfo(CommandInterpreter &interpreter)
@@ -1334,6 +1340,8 @@ class CommandObjectThreadInfo : public CommandObjectIterateOverThreads {
     }
 
     Thread *thread = thread_sp.get();
+    if (m_options.m_backing_thread && thread->GetBackingThread())
+      thread = thread->GetBackingThread().get();
 
     Stream &strm = result.GetOutputStream();
     if (!thread->GetDescription(strm, eDescriptionLevelFull,

lldb/source/Commands/Options.td

@@ -1108,6 +1108,9 @@ let Command = "thread info" in {
     " JSON format.">;
   def thread_info_stop_info : Option<"stop-info", "s">, Desc<"Display the "
     "extended stop info in JSON format.">;
+  def thread_info_backing_thread : Option<"backing-thread", "b">,
+    Desc<"If this is an OS plugin thread, query the backing thread instead; has"
+    " no effect otherwise.">;
 }
 
 let Command = "thread return" in {

lldb/test/API/functionalities/plugins/python_os_plugin/TestPythonOSPlugin.py

@@ -131,6 +131,26 @@ def run_python_os_funcionality(self):
             "Make sure there is no thread 0x333333333 after we unload the python OS plug-in",
         )
 
+    tid_regex = re.compile(r"tid = ((0x)?[0-9a-fA-F]+)")
+
+    def get_tid_from_thread_info_command(self, thread, use_backing_thread):
+        interp = self.dbg.GetCommandInterpreter()
+        result = lldb.SBCommandReturnObject()
+
+        backing_thread_arg = ""
+        if use_backing_thread:
+            backing_thread_arg = "--backing-thread"
+
+        interp.HandleCommand(
+            "thread info {0} {1}".format(thread.GetIndexID(), backing_thread_arg),
+            result,
+            True,
+        )
+        self.assertTrue(result.Succeeded(), "failed to run thread info")
+        match = self.tid_regex.search(result.GetOutput())
+        self.assertNotEqual(match, None)
+        return int(match.group(1), 0)
+
     def run_python_os_step(self):
         """Test that the Python operating system plugin works correctly and allows single stepping of a virtual thread that is backed by a real thread"""
 
@@ -209,6 +229,11 @@ def run_python_os_step(self):
         # it to
         thread.StepOver()
 
+        tid_os = self.get_tid_from_thread_info_command(thread, False)
+        self.assertEqual(tid_os, 0x111111111)
+        tid_real = self.get_tid_from_thread_info_command(thread, True)
+        self.assertNotEqual(tid_os, tid_real)
+
         frame = thread.GetFrameAtIndex(0)
         self.assertTrue(
             frame.IsValid(), "Make sure we get a frame from thread 0x111111111"