Make stop-hooks fire when lldb first gains control of a process. (llvm#137410)

stop-hooks are supposed to trigger every time the process stops, but as
initially implemented they would only fire when control was returned to
the user. So for instance when a process was launched the stop hook
would only trigger when the process hit a breakpoint or crashed.

However, it would be really useful to be able to trigger a stop hook
when lldb first gains control over the process. One way to do that would
be to implement general "target lifecycle events" and then send process
created events that users could bind actions to.

OTOH, extending the stop hooks to fire when lldb first gains control
over the process is a pretty natural extension to the notion of a stop
hook. So this patch takes the shorter route to that ability by making
stop-hooks fire when lldb first gains control over the process.

I also added the ability to specify whether to trigger the stop hook "on
gaining control". I'm on the fence about whether to set the default to
be "trigger on gaining control" or "don't trigger on gaining control".
Since I think it's a generally useful feature, I've set the default to
"trigger on gaining control".

Author: jimingham

lldb/include/lldb/Target/Target.h

@@ -1370,6 +1370,12 @@ class Target : public std::enable_shared_from_this<Target>,
 
     bool GetAutoContinue() const { return m_auto_continue; }
 
+    void SetRunAtInitialStop(bool at_initial_stop) {
+      m_at_initial_stop = at_initial_stop;
+    }
+
+    bool GetRunAtInitialStop() const { return m_at_initial_stop; }
+
     void GetDescription(Stream &s, lldb::DescriptionLevel level) const;
     virtual void GetSubclassDescription(Stream &s,
                                         lldb::DescriptionLevel level) const = 0;
@@ -1380,6 +1386,7 @@ class Target : public std::enable_shared_from_this<Target>,
     std::unique_ptr<ThreadSpec> m_thread_spec_up;
     bool m_active = true;
     bool m_auto_continue = false;
+    bool m_at_initial_stop = true;
 
     StopHook(lldb::TargetSP target_sp, lldb::user_id_t uid);
   };
@@ -1446,7 +1453,9 @@ class Target : public std::enable_shared_from_this<Target>,
 
   // Runs the stop hooks that have been registered for this target.
   // Returns true if the stop hooks cause the target to resume.
-  bool RunStopHooks();
+  // Pass at_initial_stop if this is the stop where lldb gains
+  // control over the process for the first time.
+  bool RunStopHooks(bool at_initial_stop = false);
 
   size_t GetStopHookSize();
 

lldb/source/Commands/CommandObjectTarget.cpp

@@ -4794,6 +4794,17 @@ class CommandObjectTargetStopHookAdd : public CommandObjectParsed,
         m_one_liner.push_back(std::string(option_arg));
         break;
 
+      case 'I': {
+        bool value, success;
+        value = OptionArgParser::ToBoolean(option_arg, false, &success);
+        if (success)
+          m_at_initial_stop = value;
+        else
+          error = Status::FromErrorStringWithFormat(
+              "invalid boolean value '%s' passed for -F option",
+              option_arg.str().c_str());
+      } break;
+
       default:
         llvm_unreachable("Unimplemented option");
       }
@@ -4820,6 +4831,7 @@ class CommandObjectTargetStopHookAdd : public CommandObjectParsed,
       m_use_one_liner = false;
       m_one_liner.clear();
       m_auto_continue = false;
+      m_at_initial_stop = true;
     }
 
     std::string m_class_name;
@@ -4840,6 +4852,7 @@ class CommandObjectTargetStopHookAdd : public CommandObjectParsed,
     // Instance variables to hold the values for one_liner options.
     bool m_use_one_liner = false;
     std::vector<std::string> m_one_liner;
+    bool m_at_initial_stop;
 
     bool m_auto_continue = false;
   };
@@ -5005,6 +5018,9 @@ Filter Options:
     if (specifier_up)
       new_hook_sp->SetSpecifier(specifier_up.release());
 
+    // Should we run at the initial stop:
+    new_hook_sp->SetRunAtInitialStop(m_options.m_at_initial_stop);
+
     // Next see if any of the thread options have been entered:
 
     if (m_options.m_thread_specified) {

lldb/source/Commands/Options.td

@@ -1052,8 +1052,14 @@ let Command = "target stop hook add" in {
     Arg<"FunctionName">, Desc<"Set the function name within which the stop hook"
     " will be run.">, Completion<"Symbol">;
   def target_stop_hook_add_auto_continue : Option<"auto-continue", "G">,
-    Arg<"Boolean">, Desc<"The breakpoint will auto-continue after running its"
+    Arg<"Boolean">, Desc<"The stop-hook will auto-continue after running its"
     " commands.">;
+  def target_stop_hook_add_at_initial_stop : Option<"at-initial-stop", "I">,
+    Arg<"Boolean">, Desc<"Whether the stop-hook will trigger when lldb  "
+    "initially gains control of the process.  For a process launch, this "
+    "initial stop may happen very early on - before the loader has run.  You "
+    "can use this option if you do not want some stop-hooks to run then.  "
+    "Defaults to true.">;
 }
 
 let Command = "thread backtrace" in {

lldb/source/Target/Process.cpp

@@ -2841,6 +2841,9 @@ Status Process::LoadCore() {
           "Did not get stopped event after loading the core file.");
     }
     RestoreProcessEvents();
+    // Since we hijacked the event stream, we will have we won't have run the
+    // stop hooks.  Make sure we do that here:
+    GetTarget().RunStopHooks(/* at_initial_stop= */ true);
   }
   return error;
 }
@@ -3211,6 +3214,9 @@ void Process::CompleteAttach() {
                         : "<none>");
     }
   }
+  // Since we hijacked the event stream, we will have we won't have run the
+  // stop hooks.  Make sure we do that here:
+  GetTarget().RunStopHooks(/* at_initial_stop= */ true);
 }
 
 Status Process::ConnectRemote(llvm::StringRef remote_url) {

lldb/source/Target/Target.cpp

@@ -3038,7 +3038,7 @@ void Target::SetAllStopHooksActiveState(bool active_state) {
   }
 }
 
-bool Target::RunStopHooks() {
+bool Target::RunStopHooks(bool at_initial_stop) {
   if (m_suppress_stop_hooks)
     return false;
 
@@ -3047,14 +3047,19 @@ bool Target::RunStopHooks() {
 
   // Somebody might have restarted the process:
   // Still return false, the return value is about US restarting the target.
-  if (m_process_sp->GetState() != eStateStopped)
+  lldb::StateType state = m_process_sp->GetState();
+  if (!(state == eStateStopped || state == eStateAttaching))
     return false;
 
   if (m_stop_hooks.empty())
     return false;
 
   bool no_active_hooks =
-      llvm::none_of(m_stop_hooks, [](auto &p) { return p.second->IsActive(); });
+      llvm::none_of(m_stop_hooks, [at_initial_stop](auto &p) {
+        bool should_run_now =
+            !at_initial_stop || p.second->GetRunAtInitialStop();
+        return p.second->IsActive() && should_run_now;
+      });
   if (no_active_hooks)
     return false;
 
@@ -3084,9 +3089,22 @@ bool Target::RunStopHooks() {
   }
 
   // If no threads stopped for a reason, don't run the stop-hooks.
+  // However, if this is the FIRST stop for this process, then we are in the
+  // state where an attach or a core file load was completed without designating
+  // a particular thread as responsible for the stop.  In that case, we do
+  // want to run the stop hooks, but do so just on one thread.
   size_t num_exe_ctx = exc_ctx_with_reasons.size();
-  if (num_exe_ctx == 0)
-    return false;
+  if (num_exe_ctx == 0) {
+    if (at_initial_stop && num_threads > 0) {
+      lldb::ThreadSP thread_to_use_sp = cur_threadlist.GetThreadAtIndex(0);
+      exc_ctx_with_reasons.emplace_back(
+          m_process_sp.get(), thread_to_use_sp.get(),
+          thread_to_use_sp->GetStackFrameAtIndex(0).get());
+      num_exe_ctx = 1;
+    } else {
+      return false;
+    }
+  }
 
   StreamSP output_sp = m_debugger.GetAsyncOutputStream();
   auto on_exit = llvm::make_scope_exit([output_sp] { output_sp->Flush(); });
@@ -3100,6 +3118,8 @@ bool Target::RunStopHooks() {
     StopHookSP cur_hook_sp = stop_entry.second;
     if (!cur_hook_sp->IsActive())
       continue;
+    if (at_initial_stop && !cur_hook_sp->GetRunAtInitialStop())
+      continue;
 
     bool any_thread_matched = false;
     for (auto exc_ctx : exc_ctx_with_reasons) {
@@ -3426,10 +3446,14 @@ Status Target::Launch(ProcessLaunchInfo &launch_info, Stream *stream) {
   m_process_sp->RestoreProcessEvents();
 
   if (rebroadcast_first_stop) {
+    // We don't need to run the stop hooks by hand here, they will get
+    // triggered when this rebroadcast event gets fetched.
     assert(first_stop_event_sp);
     m_process_sp->BroadcastEvent(first_stop_event_sp);
     return error;
   }
+  // Run the stop hooks that want to run at entry.
+  RunStopHooks(true /* at entry point */);
 
   switch (state) {
   case eStateStopped: {
@@ -3582,6 +3606,10 @@ Status Target::Attach(ProcessAttachInfo &attach_info, Stream *stream) {
           true, SelectMostRelevantFrame);
       process_sp->RestoreProcessEvents();
 
+      // Run the stop hooks here.  Since we were hijacking the events, they
+      // wouldn't have gotten run as part of event delivery.
+      RunStopHooks(/* at_initial_stop= */ true);
+
       if (state != eStateStopped) {
         const char *exit_desc = process_sp->GetExitDescription();
         if (exit_desc)

lldb/test/API/commands/target/stop-hooks/TestStopHookScripted.py

@@ -50,7 +50,11 @@ def test_bad_handler(self):
 
     def test_stop_hooks_scripted(self):
         """Test that a scripted stop hook works with no specifiers"""
-        self.stop_hooks_scripted(5)
+        self.stop_hooks_scripted(5, "-I false")
+
+    def test_stop_hooks_scripted_no_entry(self):
+        """Test that a scripted stop hook works with no specifiers"""
+        self.stop_hooks_scripted(10)
 
     def test_stop_hooks_scripted_right_func(self):
         """Test that a scripted stop hook fires when there is a function match"""

lldb/test/API/commands/target/stop-hooks/TestStopHooks.py

@@ -55,7 +55,7 @@ def step_out_test(self):
     def after_expr_test(self):
         interp = self.dbg.GetCommandInterpreter()
         result = lldb.SBCommandReturnObject()
-        interp.HandleCommand("target stop-hook add -o 'expr g_var++'", result)
+        interp.HandleCommand("target stop-hook add -o 'expr g_var++' -I false", result)
         self.assertTrue(result.Succeeded(), "Set the target stop hook")
 
         (target, process, thread, first_bkpt) = lldbutil.run_to_source_breakpoint(

lldb/test/API/commands/target/stop-hooks/on-core-load/TestStopHookOnCoreLoad.py

@@ -0,0 +1,55 @@
+"""
+Test that stop hooks fire on core load (first stop)
+"""
+
+
+import lldb
+import os
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestStopOnCoreLoad(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    # This was originally marked as expected failure on Windows, but it has
+    # started timing out instead, so the expectedFailure attribute no longer
+    # correctly tracks it: llvm.org/pr37371
+    @skipIfWindows
+    def test_hook_runs_no_threads(self):
+        # Create core form YAML.
+        core_path = self.getBuildArtifact("test.core")
+        self.yaml2obj("test.core.yaml", core_path)
+
+        # Since mach core files don't have stop reasons, we should choose
+        # the first thread:
+        self.do_test(core_path, 1)
+
+    def test_hook_one_thread(self):
+        core_path = os.path.join(self.getSourceDir(), "linux-x86_64.core")
+        self.do_test(core_path, 3)
+
+    def do_test(self, core_path, stop_thread):
+        # Set debugger into synchronous mode
+        self.dbg.SetAsync(False)
+
+        # Create a target by the debugger.
+        target = self.dbg.CreateTarget("")
+
+        # load the stop hook module and add the stop hook:
+        stop_hook_path = os.path.join(self.getSourceDir(), "stop_hook.py")
+        self.runCmd(f"command script import {stop_hook_path}")
+        self.runCmd("target stop-hook add -P stop_hook.stop_handler")
+
+        # Load core.
+        process = target.LoadCore(core_path)
+        self.assertTrue(process, PROCESS_IS_VALID)
+        # Now run our report command and make sure we get the right answer.
+
+        result = lldb.SBCommandReturnObject()
+        self.dbg.GetCommandInterpreter().HandleCommand("report_command", result)
+        print(f"Command Output: '{result.GetOutput}'")
+        self.assertIn(
+            f"Stop Threads: {stop_thread}", result.GetOutput(), "Ran the stop hook"
+        )

lldb/test/API/commands/target/stop-hooks/on-core-load/linux-x86_64.core

@@ -0,0 +1,30 @@
+import lldb
+
+
+def report_command(debugger, command, exe_ctx, result, internal_dict):
+    global stop_thread
+    print(f"About to report out stop_thread: {stop_thread}")
+    mssg = f"Stop Threads: {stop_thread}"
+    result.AppendMessage(mssg)
+
+    result.SetStatus(lldb.eReturnStatusSuccessFinishResult)
+
+
+class stop_handler:
+    def __init__(self, target, extra_args, dict):
+        global stop_thread
+        stop_thead = 0
+        self.target = target
+
+    def handle_stop(self, exe_ctx, stream):
+        global stop_thread
+        thread = exe_ctx.thread
+        stop_thread = thread.idx
+
+
+def __lldb_init_module(debugger, internal_dict):
+    global stop_thread
+    stop_thread = 0
+    debugger.HandleCommand(
+        f"command script add -o -f '{__name__}.report_command' report_command"
+    )