[Lldb-commits] [lldb] [lldb][Target] Clear selected frame index after a StopInfo::PerformAction (PR #133078)

[Michael Buch via lldb-commits]

https://github.com/Michael137 updated https://github.com/llvm/llvm-project/pull/133078

>From 4a0d13ef2751071505ab797c63c2ee20d14a6c61 Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12 at gmail.com>
Date: Wed, 26 Mar 2025 13:20:24 +0000
Subject: [PATCH 1/3] [lldb][Target] Clear selected frame index after a
 StopInfo::PerformAction

---
 lldb/include/lldb/Target/StackFrameList.h | 3 +++
 lldb/include/lldb/Target/Thread.h         | 5 +++++
 lldb/source/Target/Process.cpp            | 2 ++
 lldb/source/Target/StackFrameList.cpp     | 4 ++++
 4 files changed, 14 insertions(+)

diff --git a/lldb/include/lldb/Target/StackFrameList.h b/lldb/include/lldb/Target/StackFrameList.h
index 8a66296346f2d..d805b644b0b31 100644
--- a/lldb/include/lldb/Target/StackFrameList.h
+++ b/lldb/include/lldb/Target/StackFrameList.h
@@ -46,6 +46,9 @@ class StackFrameList {
   /// Mark a stack frame as the currently selected frame and return its index.
   uint32_t SetSelectedFrame(lldb_private::StackFrame *frame);
 
+  /// Resets the selected frame index of this object.
+  void ClearSelectedFrameIndex();
+
   /// Get the currently selected frame index.
   /// We should only call SelectMostRelevantFrame if (a) the user hasn't already
   /// selected a frame, and (b) if this really is a user facing
diff --git a/lldb/include/lldb/Target/Thread.h b/lldb/include/lldb/Target/Thread.h
index 6ede7fa301a82..688c056da2633 100644
--- a/lldb/include/lldb/Target/Thread.h
+++ b/lldb/include/lldb/Target/Thread.h
@@ -479,6 +479,11 @@ class Thread : public std::enable_shared_from_this<Thread>,
   bool SetSelectedFrameByIndexNoisily(uint32_t frame_idx,
                                       Stream &output_stream);
 
+  /// Resets the selected frame index of this object.
+  void ClearSelectedFrameIndex() {
+    return GetStackFrameList()->ClearSelectedFrameIndex();
+  }
+
   void SetDefaultFileAndLineToSelectedFrame() {
     GetStackFrameList()->SetDefaultFileAndLineToSelectedFrame();
   }
diff --git a/lldb/source/Target/Process.cpp b/lldb/source/Target/Process.cpp
index 369933234ccca..c51bab20f56ee 100644
--- a/lldb/source/Target/Process.cpp
+++ b/lldb/source/Target/Process.cpp
@@ -4295,6 +4295,8 @@ bool Process::ProcessEventData::ShouldStop(Event *event_ptr,
         // appropriately. We also need to stop processing actions, since they
         // aren't expecting the target to be running.
 
+        thread_sp->ClearSelectedFrameIndex();
+
         // FIXME: we might have run.
         if (stop_info_sp->HasTargetRunSinceMe()) {
           SetRestarted(true);
diff --git a/lldb/source/Target/StackFrameList.cpp b/lldb/source/Target/StackFrameList.cpp
index 9c6208e9e0a65..3592c3c03db74 100644
--- a/lldb/source/Target/StackFrameList.cpp
+++ b/lldb/source/Target/StackFrameList.cpp
@@ -936,3 +936,7 @@ size_t StackFrameList::GetStatus(Stream &strm, uint32_t first_frame,
   strm.IndentLess();
   return num_frames_displayed;
 }
+
+void StackFrameList::ClearSelectedFrameIndex() {
+  m_selected_frame_idx.reset();
+}

>From 1a1a55786de369b1c9771623c21de459848c7e20 Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12 at gmail.com>
Date: Wed, 26 Mar 2025 13:35:23 +0000
Subject: [PATCH 2/3] fixup! clang-format

---
 lldb/source/Target/Process.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lldb/source/Target/Process.cpp b/lldb/source/Target/Process.cpp
index c51bab20f56ee..46e8028160d04 100644
--- a/lldb/source/Target/Process.cpp
+++ b/lldb/source/Target/Process.cpp
@@ -4295,6 +4295,12 @@ bool Process::ProcessEventData::ShouldStop(Event *event_ptr,
         // appropriately. We also need to stop processing actions, since they
         // aren't expecting the target to be running.
 
+        // Clear the selected frame which may have been set as part of utility
+        // expressions that have been run as part of this stop. If we didn't
+        // clear this, then StopInfo::GetSuggestedStackFrameIndex would not
+        // take affect when we next called SelectMostRelevantFrame. PerformAction
+        // should not be the one setting a selected frame, instead this should be
+        // done via GetSuggestedStackFrameIndex.
         thread_sp->ClearSelectedFrameIndex();
 
         // FIXME: we might have run.

>From 158f0b2cd664ba1864e510bf8293d16790c6a65a Mon Sep 17 00:00:00 2001
From: Michael Buch <michaelbuch12 at gmail.com>
Date: Fri, 28 Mar 2025 15:40:47 +0000
Subject: [PATCH 3/3] fixup! add thread-safety comment

---
 lldb/include/lldb/Target/StackFrameList.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lldb/include/lldb/Target/StackFrameList.h b/lldb/include/lldb/Target/StackFrameList.h
index d805b644b0b31..8d455dc831df3 100644
--- a/lldb/include/lldb/Target/StackFrameList.h
+++ b/lldb/include/lldb/Target/StackFrameList.h
@@ -175,6 +175,15 @@ class StackFrameList {
   /// The currently selected frame. An optional is used to record whether anyone
   /// has set the selected frame on this stack yet. We only let recognizers
   /// change the frame if this is the first time GetSelectedFrame is called.
+  ///
+  /// Thread-safety:
+  /// This member is not protected by a mutex.
+  /// LLDB really only should have an opinion about the selected frame index
+  /// when a process stops, before control gets handed back to the user.
+  /// After that, it's up to them to change it whenever they feel like it.
+  /// If two parts of lldb decided they wanted to be in control of the selected
+  /// frame index on stop the right way to fix it would need to be some explicit
+  /// negotiation for who gets to control this.
   std::optional<uint32_t> m_selected_frame_idx;
 
   /// The number of concrete frames fetched while filling the frame list. This