5 files changed, 25 insertions, 0 deletions
diff --git a/clang/lib/CodeGen/CGDeclCXX.cpp b/clang/lib/CodeGen/CGDeclCXX.cpp
index 6635af88939..ed25b6db38e 100644
--- a/clang/lib/CodeGen/CGDeclCXX.cpp
+++ b/clang/lib/CodeGen/CGDeclCXX.cpp
@@ -149,6 +149,14 @@ CodeGenFunction::EmitCXXGlobalDtorRegistration(llvm::Constant *DtorFn,
 
 void CodeGenFunction::EmitCXXGuardedInit(const VarDecl &D,
                                          llvm::GlobalVariable *DeclPtr) {
+  // If we've been asked to forbid guard variables, emit an error now.
+  // This diagnostic is hard-coded for Darwin's use case;  we can find
+  // better phrasing if someone else needs it.
+  if (CGM.getCodeGenOpts().ForbidGuardVariables)
+    CGM.Error(D.getLocation(),
+              "this initialization requires a guard variable, which "
+              "the kernel does not support");
+
   CGM.getCXXABI().EmitGuardedInit(*this, D, DeclPtr);
 }
 
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 61814702bdd..11e85870d14 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -154,6 +154,11 @@ bool CodeGenModule::isTargetDarwin() const {
   return getContext().Target.getTriple().getOS() == llvm::Triple::Darwin;
 }
 
+void CodeGenModule::Error(SourceLocation loc, llvm::StringRef error) {
+  unsigned diagID = getDiags().getCustomDiagID(Diagnostic::Error, error);
+  getDiags().Report(Context.getFullLoc(loc), diagID);
+}
+
 /// ErrorUnsupported - Print out an error that codegen doesn't support the
 /// specified stmt yet.
 void CodeGenModule::ErrorUnsupported(const Stmt *S, const char *Type,
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 02057970b64..5b8164f6be3 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -527,6 +527,9 @@ public:
   llvm::Constant *EmitAnnotateAttr(llvm::GlobalValue *GV,
                                    const AnnotateAttr *AA, unsigned LineNo);
 
+  /// Error - Emit a general error that something can't be done.
+  void Error(SourceLocation loc, llvm::StringRef error);
+
   /// ErrorUnsupported - Print out an error that codegen doesn't support the
   /// specified stmt yet.
   /// \param OmitOnError - If true, then this error should only be emitted if no
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 45fdd8be2e6..ee4976ee72b 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -1138,6 +1138,12 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (getToolChain().getTriple().getOS() != llvm::Triple::Darwin)
     CmdArgs.push_back("-mconstructor-aliases");
 
+  // Darwin's kernel doesn't support guard variables; just die if we
+  // try to use them.
+  if (KernelOrKext &&
+      getToolChain().getTriple().getOS() == llvm::Triple::Darwin)
+    CmdArgs.push_back("-fforbid-guard-variables");
+
   if (Args.hasArg(options::OPT_mms_bitfields)) {
     CmdArgs.push_back("-mms-bitfields");
   }
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 859eb74a8a0..31fcee2de88 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -127,6 +127,8 @@ static void CodeGenOptsToArgs(const CodeGenOptions &Opts,
     Res.push_back("-fno-merge-all-constants");
   if (Opts.NoCommon)
     Res.push_back("-fno-common");
+  if (Opts.ForbidGuardVariables)
+    Res.push_back("-fforbid-guard-variables");
   if (Opts.NoImplicitFloat)
     Res.push_back("-no-implicit-float");
   if (Opts.OmitLeafFramePointer)
@@ -896,6 +898,7 @@ static void ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.LimitDebugInfo = Args.hasArg(OPT_flimit_debug_info);
   Opts.DisableLLVMOpts = Args.hasArg(OPT_disable_llvm_optzns);
   Opts.DisableRedZone = Args.hasArg(OPT_disable_red_zone);
+  Opts.ForbidGuardVariables = Args.hasArg(OPT_fforbid_guard_variables);
   Opts.RelaxedAliasing = Args.hasArg(OPT_relaxed_aliasing);
   Opts.DwarfDebugFlags = Args.getLastArgValue(OPT_dwarf_debug_flags);
   Opts.MergeAllConstants = !Args.hasArg(OPT_fno_merge_all_constants);