Index: docs/CommandGuide/clang.rst
===================================================================
--- docs/CommandGuide/clang.rst
+++ docs/CommandGuide/clang.rst
@@ -313,6 +313,13 @@
   model can be overridden with the tls_model attribute. The compiler will try
   to choose a more efficient model if possible.
 
+.. option:: -fruntime-init
+
+  Emit code for functions that permits them to be used both during and after
+  initialization of the runtime environment. This is only meaningful when
+  combined with the SafeStack pass. See the documentation associated with that
+  pass for more details.
+
 .. option:: -flto, -emit-llvm
 
   Generate output files in LLVM formats, suitable for link time optimization.
Index: include/clang/Basic/LangOptions.def
===================================================================
--- include/clang/Basic/LangOptions.def
+++ include/clang/Basic/LangOptions.def
@@ -132,6 +132,7 @@
 LANGOPT(Freestanding, 1, 0, "freestanding implementation")
 LANGOPT(NoBuiltin         , 1, 0, "disable builtin functions")
 LANGOPT(NoMathBuiltin     , 1, 0, "disable math builtin functions")
+LANGOPT(RuntimeInit       , 1, 0, "used during runtime initialization")
 LANGOPT(GNUAsm            , 1, 1, "GNU-style inline assembly")
 LANGOPT(Coroutines        , 1, 0, "C++ coroutines")
 
Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1031,6 +1031,7 @@
 def freg_struct_return : Flag<["-"], "freg-struct-return">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Override the default ABI to return small structs in registers">;
 def frtti : Flag<["-"], "frtti">, Group<f_Group>;
+def fruntime_init : Flag<["-"], "fruntime-init">, Group<f_Group>, Flags<[CC1Option]>;
 def : Flag<["-"], "fsched-interblock">, Group<clang_ignored_f_Group>;
 def fshort_enums : Flag<["-"], "fshort-enums">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Allocate to an enum type only as many bytes as it needs for the declared range of possible values">;
Index: lib/CodeGen/CGDeclCXX.cpp
===================================================================
--- lib/CodeGen/CGDeclCXX.cpp
+++ lib/CodeGen/CGDeclCXX.cpp
@@ -279,6 +279,9 @@
       Fn->addFnAttr(llvm::Attribute::SafeStack);
   }
 
+  if (getLangOpts().RuntimeInit)
+    Fn->addFnAttr(llvm::Attribute::RuntimeInit);
+
   return Fn;
 }
 
Index: lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- lib/CodeGen/CodeGenFunction.cpp
+++ lib/CodeGen/CodeGenFunction.cpp
@@ -698,6 +698,9 @@
   if (SanOpts.has(SanitizerKind::SafeStack))
     Fn->addFnAttr(llvm::Attribute::SafeStack);
 
+  if (getLangOpts().RuntimeInit)
+    Fn->addFnAttr(llvm::Attribute::RuntimeInit);
+
   // Pass inline keyword to optimizer if it appears explicitly on any
   // declaration. Also, in the case of -fno-inline attach NoInline
   // attribute to all function that are not marked AlwaysInline.
Index: lib/Driver/Tools.cpp
===================================================================
--- lib/Driver/Tools.cpp
+++ lib/Driver/Tools.cpp
@@ -4777,6 +4777,9 @@
       KernelOrKext)
     CmdArgs.push_back("-ffreestanding");
 
+  if (Args.hasArg(options::OPT_fruntime_init))
+    CmdArgs.push_back("-fruntime-init");
+
   // Forward -f (flag) options which we can pass directly.
   Args.AddLastArg(CmdArgs, options::OPT_femit_all_decls);
   Args.AddLastArg(CmdArgs, options::OPT_fheinous_gnu_extensions);
Index: lib/Frontend/CompilerInvocation.cpp
===================================================================
--- lib/Frontend/CompilerInvocation.cpp
+++ lib/Frontend/CompilerInvocation.cpp
@@ -1730,6 +1730,7 @@
   if (!Opts.NoBuiltin)
     getAllNoBuiltinFuncValues(Args, Opts.NoBuiltinFuncs);
   Opts.NoMathBuiltin = Args.hasArg(OPT_fno_math_builtin);
+  Opts.RuntimeInit = Args.hasArg(OPT_fruntime_init);
   Opts.SizedDeallocation = Args.hasArg(OPT_fsized_deallocation);
   Opts.ConceptsTS = Args.hasArg(OPT_fconcepts_ts);
   Opts.HeinousExtensions = Args.hasArg(OPT_fheinous_gnu_extensions);
Index: test/CodeGen/runtime-init-attr.c
===================================================================
--- /dev/null
+++ test/CodeGen/runtime-init-attr.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple i386-unknown-unknown -emit-llvm -o - %s -fruntime-init | FileCheck -check-prefix=DEF -check-prefix=CHECK %s
+// RUN: %clang_cc1 -triple i386-unknown-unknown -emit-llvm -o - %s -fruntime-init -fsanitize=safe-stack | FileCheck -check-prefix=DEF -check-prefix=SAFESTACK %s
+
+// DEF: define {{.*}}void @test1() #[[A:.*]] {
+void test1() {
+}
+
+// CHECK: attributes #[[A]] = {{.*}} runtime_init
+// SAFESTACK: attributes #[[A]] = {{.*}} runtime_init safestack