[lldb] Improve isolation between Process plugins and OS plugins

lldb/source/Breakpoint/BreakpointSite.cpp

@@ -12,6 +12,7 @@
 
 #include "lldb/Breakpoint/Breakpoint.h"
 #include "lldb/Breakpoint/BreakpointLocation.h"
+#include "lldb/Target/Thread.h"
 #include "lldb/Utility/Stream.h"
 
 using namespace lldb;
@@ -161,6 +162,8 @@ BreakpointLocationSP BreakpointSite::GetConstituentAtIndex(size_t index) {
 
 bool BreakpointSite::ValidForThisThread(Thread &thread) {
   std::lock_guard<std::recursive_mutex> guard(m_constituents_mutex);
+  if (ThreadSP backed_thread = thread.GetBackedThread())
+    return m_constituents.ValidForThisThread(*backed_thread);
   return m_constituents.ValidForThisThread(thread);
 }
 

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

@@ -1726,10 +1726,6 @@ ThreadSP ProcessGDBRemote::SetThreadStopInfo(
 
   if (!thread_sp->StopInfoIsUpToDate()) {
     thread_sp->SetStopInfo(StopInfoSP());
-    // If there's a memory thread backed by this thread, we need to use it to
-    // calculate StopInfo.
-    if (ThreadSP memory_thread_sp = thread_sp->GetBackedThread())
-      thread_sp = memory_thread_sp;
 
     if (exc_type != 0) {
       // For thread plan async interrupt, creating stop info on the

lldb/unittests/OperatingSystem/CMakeLists.txt

@@ -0,0 +1,21 @@
+add_lldb_unittest(ProcessGdbRemoteTests
+  GDBRemoteClientBaseTest.cpp
+  GDBRemoteCommunicationClientTest.cpp
+  GDBRemoteCommunicationServerLLGSTest.cpp
+  GDBRemoteCommunicationServerTest.cpp
+  GDBRemoteCommunicationTest.cpp
+  GDBRemoteTestUtils.cpp
+
+  LINK_LIBS
+    LLVMTestingSupport
+    lldbCore
+    lldbHost
+    lldbInterpreter
+    lldbPluginProcessUtility
+    lldbSymbol
+    lldbTarget
+    lldbValueObject
+
+  LINK_COMPONENTS
+    Support
+  )

lldb/unittests/OperatingSystem/OperatingSystemPlugin.h

@@ -0,0 +1,59 @@
+//===-- OperatingSystemPlugin.h ---------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/Core/PluginManager.h"
+#include "lldb/Target/OperatingSystem.h"
+#include "lldb/Target/Thread.h"
+#include "lldb/Target/ThreadList.h"
+
+/// An operating system plugin that does nothing: simply keeps the thread lists
+/// as they are.
+class OperatingSystemIdentityMap : public lldb_private::OperatingSystem {
+public:
+  OperatingSystemIdentityMap(lldb_private::Process *process)
+      : OperatingSystem(process) {}
+
+  static OperatingSystem *CreateInstance(lldb_private::Process *process,
+                                         bool force) {
+    return new OperatingSystemIdentityMap(process);
+  }
+  static llvm::StringRef GetPluginNameStatic() { return "identity map"; }
+  static llvm::StringRef GetPluginDescriptionStatic() { return ""; }
+
+  static void Initialize() {
+    lldb_private::PluginManager::RegisterPlugin(GetPluginNameStatic(),
+                                                GetPluginDescriptionStatic(),
+                                                CreateInstance, nullptr);
+  }
+  static void Terminate() {
+    lldb_private::PluginManager::UnregisterPlugin(CreateInstance);
+  }
+  llvm::StringRef GetPluginName() override { return GetPluginNameStatic(); }
+
+  // Simply adds the threads from real_thread_list into new_thread_list.
+  bool UpdateThreadList(lldb_private::ThreadList &old_thread_list,
+                        lldb_private::ThreadList &real_thread_list,
+                        lldb_private::ThreadList &new_thread_list) override {
+    for (const auto &real_thread : real_thread_list.Threads())
+      new_thread_list.AddThread(real_thread);
+    return true;
+  }
+
+  void ThreadWasSelected(lldb_private::Thread *thread) override {}
+
+  lldb::RegisterContextSP
+  CreateRegisterContextForThread(lldb_private::Thread *thread,
+                                 lldb::addr_t reg_data_addr) override {
+    return thread->GetRegisterContext();
+  }
+
+  lldb::StopInfoSP
+  CreateThreadStopReason(lldb_private::Thread *thread) override {
+    return thread->GetStopInfo();
+  }
+};

lldb/unittests/OperatingSystem/TestThreadSpecificBreakpoints.cpp

@@ -0,0 +1,10 @@
+//===-- OperatingSystemPlugin.h ---------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "OperatingSystemPlugin.h"
+LLDB_PLUGIN_DEFINE(OperatingSystemIdentityMap)