Index: include/lld/ReaderWriter/MachOLinkingContext.h
===================================================================
--- include/lld/ReaderWriter/MachOLinkingContext.h
+++ include/lld/ReaderWriter/MachOLinkingContext.h
@@ -321,6 +321,8 @@
 
   void setBundleLoader(StringRef loader) { _bundleLoader = loader; }
   void setPrintAtoms(bool value=true) { _printAtoms = value; }
+  void setApplicationExtension(bool value = true) { _applicationExtension = value; }
+  bool applicationExtension() const { return _applicationExtension; }
   void setTestingFileUsage(bool value = true) {
     _testingFileUsage = value;
   }
@@ -487,6 +489,7 @@
   bool _generateVersionLoadCommand = false;
   bool _generateFunctionStartsLoadCommand = false;
   bool _generateDataInCodeLoadCommand = false;
+  bool _applicationExtension = false;
   StringRef _bundleLoader;
   mutable std::unique_ptr<mach_o::ArchHandler> _archHandler;
   mutable std::unique_ptr<Writer> _writer;
Index: lib/Driver/DarwinLdDriver.cpp
===================================================================
--- lib/Driver/DarwinLdDriver.cpp
+++ lib/Driver/DarwinLdDriver.cpp
@@ -366,6 +366,10 @@
     }
   }
 
+  if (llvm::opt::Arg *kind = parsedArgs.getLastArg(OPT_applicationextension)) {
+    ctx.setApplicationExtension(true);
+  }
+
   // Handle -arch xxx
   MachOLinkingContext::Arch arch = MachOLinkingContext::arch_unknown;
   if (llvm::opt::Arg *archStr = parsedArgs.getLastArg(OPT_arch)) {
Index: lib/Driver/DarwinLdOptions.td
===================================================================
--- lib/Driver/DarwinLdOptions.td
+++ lib/Driver/DarwinLdOptions.td
@@ -17,6 +17,8 @@
      HelpText<"Create main executable (default)">, Group<grp_kind>;
 def preload : Flag<["-"], "preload">,
      HelpText<"Create binary for use with embedded systems">, Group<grp_kind>;
+def applicationextension : Flag<["-"], "application_extension">,
+     HelpText<"Mark a library as an application extension">, Group<grp_kind>;
 
 // optimizations
 def grp_opts : OptionGroup<"opts">, HelpText<"OPTIMIZATIONS">;
Index: lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
===================================================================
--- lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
+++ lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
@@ -1571,6 +1573,8 @@
       flags |= MH_PIE;
     if (_hasTLVDescriptors)
       flags |= (MH_PIE | MH_HAS_TLV_DESCRIPTORS);
+    if (_ctx.applicationExtension())
+      flags |= MH_APP_EXTENSION_SAFE;
     return flags;
   }
 }