Index: lib/Transforms/Instrumentation/SafeStack.cpp
===================================================================
--- lib/Transforms/Instrumentation/SafeStack.cpp
+++ lib/Transforms/Instrumentation/SafeStack.cpp
@@ -47,6 +47,10 @@
 
 #define DEBUG_TYPE "safestack"
 
+static cl::opt<bool> UseTLS("safe-stack-tls",
+    cl::Hidden, cl::init(true),
+    cl::desc("Use thread-local storage for the unsafe stack pointer"));
+
 namespace llvm {
 
 STATISTIC(NumFunctions, "Total number of functions");
@@ -345,18 +349,22 @@
       dyn_cast_or_null<GlobalVariable>(M.getNamedValue(UnsafeStackPtrVar));
 
   if (!UnsafeStackPtr) {
+    auto TLSModel = UseTLS ?
+        GlobalValue::InitialExecTLSModel :
+        GlobalValue::NotThreadLocal;
     // The global variable is not defined yet, define it ourselves.
     // We use the initial-exec TLS model because we do not support the
     // variable living anywhere other than in the main executable.
     UnsafeStackPtr = new GlobalVariable(
         M, StackPtrTy, false, GlobalValue::ExternalLinkage, nullptr,
-        UnsafeStackPtrVar, nullptr, GlobalValue::InitialExecTLSModel);
+        UnsafeStackPtrVar, nullptr, TLSModel);
   } else {
     // The variable exists, check its type and attributes.
     if (UnsafeStackPtr->getValueType() != StackPtrTy)
       report_fatal_error(Twine(UnsafeStackPtrVar) + " must have void* type");
-    if (!UnsafeStackPtr->isThreadLocal())
-      report_fatal_error(Twine(UnsafeStackPtrVar) + " must be thread-local");
+    if (UseTLS != UnsafeStackPtr->isThreadLocal())
+      report_fatal_error(Twine(UnsafeStackPtrVar) + " must " +
+                         (UseTLS ? "" : "not ") + "be thread-local");
   }
   return UnsafeStackPtr;
 }