[lldb] Print an error message when we're reading libobjc.A.dylib from memory

[JDevlieghere]

Summary

Use libobjc.A.dylib as a sentinel to detect situations where we're reading libraries from memory instead of the shared cache.

[JDevlieghere]

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

2361–2362

Let's bikeshed about the wording!

[JDevlieghere]

Unbotch the patch

[aprantl]

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

2377

Here's my take:

libobjc.A.dylib is being read from process memory. This indicates that LLDB could not find the the on-disk %s shared cache for this device. This will likely reduce debugging performance.

[JDevlieghere]

Update warning message

[aprantl]

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

2379

I would replace we with LLDB. Users might see this in their IDE's console and not even know who we is.

[jingham]

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

2359

Why is this code #ifdef APPLE?

If you were debugging from a Linux machine to a macOS system, wouldn't you also want to at least see the warning so you would know why their session was slow?

[JDevlieghere]

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

2379

Good point!

[JDevlieghere]

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

2359

My reasoning was that the error wouldn't be actionable so I'd rather not show it all. I don't feel strongly about it though.

[jingham]

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

2359

It would save people wasting time to try to figure out why this seemed slow, which is worth something on its own. And the Linux user could expand the cache on the Mac, copy it over and lldb should be able to use it - with "target modules add" by hand if nothing more automatic works.

[JDevlieghere]

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

2359

Fair enough!

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.h

uint32_t ParseClassInfoArray(const lldb_private::DataExtractor &data,
                                uint32_t num_class_infos);
 
   enum class SharedCacheWarningReason {
     eExpressionExecutionFailure,
     eNotEnoughClassesRead
   };
 
   void WarnIfNoClassesCached(SharedCacheWarningReason reason);
+  void WarnIfNoExpandedSharedCache();
 
   lldb::addr_t GetSharedCacheReadOnlyAddress();
   lldb::addr_t GetSharedCacheBaseAddress();
 
   bool GetCFBooleanValuesIfNeeded();
 
   bool HasSymbol(ConstString Name);
 

lldb/source/Plugins/LanguageRuntime/ObjC/AppleObjCRuntime/AppleObjCRuntimeV2.cpp

: AppleObjCRuntime(process), m_objc_module_sp(objc_module_sp),
           TaggedPointerVendorV2::CreateInstance(*this, objc_module_sp)),
       m_encoding_to_type_sp(), m_noclasses_warning_emitted(false),
       m_CFBoolean_values(), m_realized_class_generation_count(0) {
   static const ConstString g_gdb_object_getClass("gdb_object_getClass");
   m_has_object_getClass = HasSymbol(g_gdb_object_getClass);
   static const ConstString g_objc_copyRealizedClassList(
       "_ZL33objc_copyRealizedClassList_nolockPj");
   m_has_objc_copyRealizedClassList = HasSymbol(g_objc_copyRealizedClassList);
-
+  WarnIfNoExpandedSharedCache();
   RegisterObjCExceptionRecognizer(process);
 }
 
 bool AppleObjCRuntimeV2::GetDynamicTypeAndAddress(
     ValueObject &in_value, lldb::DynamicValueType use_dynamic,
     TypeAndOrName &class_type_or_name, Address &address,
     Value::ValueType &value_type) {
   // We should never get here with a null process...
case SharedCacheWarningReason::eExpressionExecutionFailure:
                          "Objective-C class data in the process. This may "
                          "reduce the quality of type information available.\n");
       m_noclasses_warning_emitted = true;
       break;
     }
   }
 }
 
+void AppleObjCRuntimeV2::WarnIfNoExpandedSharedCache() {
+  if (!m_objc_module_sp)
+    return;
+
+  ObjectFile *object_file = m_objc_module_sp->GetObjectFile();
+  if (!object_file)
+    return;
+
+  if (!object_file->IsInMemory())
+    return;
+
+  Target &target = GetProcess()->GetTarget();
+  Debugger &debugger = target.GetDebugger();
+  if (auto stream = debugger.GetAsyncOutputStream()) {
+    const char *msg = "read from the shared cache";
+    if (PlatformSP platform_sp = target.GetPlatform())
+      msg = platform_sp->IsHost()
+                ? "read from the host's in-memory shared cache"
+                : "find the on-disk shared cache for this device";
+    stream->Printf("warning: libobjc.A.dylib is being read from process "
+                   "memory. This indicates that LLDB could not %s. This will "
+                   "likely reduce debugging performance.\n",
+                   msg);
+  }
+}
+
 DeclVendor *AppleObjCRuntimeV2::GetDeclVendor() {
   if (!m_decl_vendor_up)
     m_decl_vendor_up = std::make_unique<AppleObjCDeclVendor>(*this);
 
   return m_decl_vendor_up.get();
 }
 
 lldb::addr_t AppleObjCRuntimeV2::LookupRuntimeSymbol(ConstString name) {