lld/macho application_extension support

[carlokok]

Summary

This adds the application_extension which basically sets a header flag.

[mstorsjo]

Can you add a testcase for this? Also it's appreciated if the uploaded diffs are made with a larger context (diff -U999 or similar) to allow expanding the context here in phabricator.

include/lld/ReaderWriter/MachOLinkingContext.h

 
   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;
   }

   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;

lib/Driver/DarwinLdDriver.cpp

     }
   }
 
+  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)) {

lib/Driver/DarwinLdOptions.td

      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">;

lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp

       flags |= MH_PIE;
     if (_hasTLVDescriptors)
       flags |= (MH_PIE | MH_HAS_TLV_DESCRIPTORS);
+    if (_ctx.applicationExtension())
+      flags |= MH_APP_EXTENSION_SAFE;
     return flags;
   }
 }