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

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

Differential revision: https://reviews.llvm.org/D117623

(cherry picked from commit d230848)

Author: JDevlieghere

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

@@ -672,7 +672,7 @@ AppleObjCRuntimeV2::AppleObjCRuntimeV2(Process *process,
   static const ConstString g_objc_copyRealizedClassList(
       "_ZL33objc_copyRealizedClassList_nolockPj");
   m_has_objc_copyRealizedClassList = HasSymbol(g_objc_copyRealizedClassList);
-
+  WarnIfNoExpandedSharedCache();
   RegisterObjCExceptionRecognizer(process);
 }
 
@@ -2372,6 +2372,32 @@ void AppleObjCRuntimeV2::WarnIfNoClassesCached(
   }
 }
 
+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);

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

@@ -401,6 +401,7 @@ class AppleObjCRuntimeV2 : public AppleObjCRuntime {
   };
 
   void WarnIfNoClassesCached(SharedCacheWarningReason reason);
+  void WarnIfNoExpandedSharedCache();
 
   lldb::addr_t GetSharedCacheReadOnlyAddress();
   lldb::addr_t GetSharedCacheBaseAddress();