diff -ruN tools/clang/include/clang/Basic/LangOptions.def tools/clang/include/clang/Basic/LangOptions.def
--- tools/clang/include/clang/Basic/LangOptions.def	2014-07-16 07:13:50.000000000 +0400
+++ tools/clang/include/clang/Basic/LangOptions.def	2014-10-24 21:38:38.000000000 +0400
@@ -87,6 +87,7 @@
 LANGOPT(RTTIData          , 1, 1, "emit run-time type information data")
 LANGOPT(MSBitfields       , 1, 0, "Microsoft-compatible structure layout")
 LANGOPT(Freestanding, 1, 0, "freestanding implementation")
+LANGOPT(FormatExtensions  , 1, 0, "FreeBSD format extensions")
 LANGOPT(NoBuiltin         , 1, 0, "disable builtin functions")
 LANGOPT(NoMathBuiltin     , 1, 0, "disable math builtin functions")
 
diff -ruN tools/clang/include/clang/Driver/Options.td tools/clang/include/clang/Driver/Options.td
--- tools/clang/include/clang/Driver/Options.td	2014-08-07 08:51:51.000000000 +0400
+++ tools/clang/include/clang/Driver/Options.td	2014-10-24 21:39:23.000000000 +0400
@@ -563,6 +563,8 @@
 
 def ffreestanding : Flag<["-"], "ffreestanding">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Assert that the compilation takes place in a freestanding environment">;
+def fformat_extensions: Flag<["-"], "fformat-extensions">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Enable FreeBSD kernel specific format string extensions">;
 def fgnu_keywords : Flag<["-"], "fgnu-keywords">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Allow GNU-extension keywords regardless of language standard">;
 def fgnu89_inline : Flag<["-"], "fgnu89-inline">, Group<f_Group>, Flags<[CC1Option]>,
diff -ruN tools/clang/lib/Driver/Tools.cpp tools/clang/lib/Driver/Tools.cpp
--- tools/clang/lib/Driver/Tools.cpp	2014-08-07 08:51:51.000000000 +0400
+++ tools/clang/lib/Driver/Tools.cpp	2014-10-24 21:39:54.000000000 +0400
@@ -3517,6 +3517,7 @@
 
   // Forward -f (flag) options which we can pass directly.
   Args.AddLastArg(CmdArgs, options::OPT_femit_all_decls);
+  Args.AddLastArg(CmdArgs, options::OPT_fformat_extensions);
   Args.AddLastArg(CmdArgs, options::OPT_fheinous_gnu_extensions);
   Args.AddLastArg(CmdArgs, options::OPT_fstandalone_debug);
   Args.AddLastArg(CmdArgs, options::OPT_fno_standalone_debug);
diff -ruN tools/clang/lib/Frontend/CompilerInvocation.cpp tools/clang/lib/Frontend/CompilerInvocation.cpp
--- tools/clang/lib/Frontend/CompilerInvocation.cpp	2014-08-07 08:51:51.000000000 +0400
+++ tools/clang/lib/Frontend/CompilerInvocation.cpp	2014-10-24 21:40:32.000000000 +0400
@@ -1443,6 +1443,7 @@
   Opts.ShortWChar = Args.hasFlag(OPT_fshort_wchar, OPT_fno_short_wchar, false);
   Opts.ShortEnums = Args.hasArg(OPT_fshort_enums);
   Opts.Freestanding = Args.hasArg(OPT_ffreestanding);
+  Opts.FormatExtensions = Args.hasArg(OPT_fformat_extensions);
   Opts.NoBuiltin = Args.hasArg(OPT_fno_builtin) || Opts.Freestanding;
   Opts.NoMathBuiltin = Args.hasArg(OPT_fno_math_builtin);
   Opts.AssumeSaneOperatorNew = !Args.hasArg(OPT_fno_assume_sane_operator_new);