[lldb] [llgs] Include process ID in stop responses

[mgorny]

Summary

Include the process identifier in the T stop responses when
multiprocess extension is enabled (i.e. prepend it to the thread
identifier). Use the exposed identifier to simplify the fork-and-follow
tests.

The LLDB client accounts for the possible PID since the multiprocess
extension support was added in b601c6719226fb83c43dae62a581e5ee08bfb169.

Sponsored by: The FreeBSD Foundation

[mgorny]

Fix formatting.

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

LLDB_LOG(
       log,
       "pid {0}, tid {1}, got signal signo = {2}, reason = {3}, exc_type = {4}",
       m_current_process->GetID(), tid, signum, int(tid_stop_info.reason),
       tid_stop_info.details.exception.type);
 
   // Print the signal number.
   response.PutHex8(signum & 0xff);
 
-  // Include the tid.
-  response.Printf("thread:%" PRIx64 ";", tid);
+  // Include the (pid and) tid.
+  response.PutCString("thread:");
+  if (bool(m_extensions_supported &
+           NativeProcessProtocol::Extension::multiprocess))
+    response.Format("p{0:x-}.", m_current_process->GetID());
+  response.Format("{0:x-};", tid);
 
   // Include the thread name if there is one.
   const std::string thread_name = thread->GetName();
   if (!thread_name.empty()) {
     size_t thread_name_len = thread_name.length();
 
     if (::strcspn(thread_name.c_str(), "$#+-;:") == thread_name_len) {
       response.PutCString("name:");

lldb/test/API/tools/lldb-server/TestGdbRemoteFork.py

def fork_and_follow_test(self, variant):
         self.prep_debug_monitor_and_inferior(inferior_args=[variant])
         self.add_qSupported_packets(["multiprocess+",
                                      "{}-events+".format(variant)])
         ret = self.expect_gdbremote_sequence()
         self.assertIn("{}-events+".format(variant), ret["qSupported_response"])
         self.reset_test_sequence()
 
         # continue and expect fork
-        procinfo_regex = "[$]pid:([0-9a-f]+);.*"
-        fork_regex = "[$]T.*;{}:p([0-9a-f]+)[.]([0-9a-f]+).*".format(variant)
+        fork_regex = ("[$]T[0-9a-f]{{2}}thread:p([0-9a-f]+)[.][0-9a-f]+;.*"
+                      "{}:p([0-9a-f]+)[.]([0-9a-f]+).*".format(variant))
         self.test_sequence.add_log_lines([
-            "read packet: $qProcessInfo#00",
-            {"direction": "send", "regex": procinfo_regex,
-             "capture": {1: "parent_pid"}},
             "read packet: $c#00",
             {"direction": "send", "regex": fork_regex,
-             "capture": {1: "pid", 2: "tid"}},
+             "capture": {1: "parent_pid", 2: "pid", 3: "tid"}},
         ], True)
         ret = self.expect_gdbremote_sequence()
         parent_pid, pid, tid = (int(ret[x], 16) for x
                                 in ("parent_pid", "pid", "tid"))
         self.reset_test_sequence()
 
         # switch to the forked child
         self.test_sequence.add_log_lines([