Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -90,6 +90,10 @@
 option(SANITIZER_CAN_USE_CXXABI "Sanitizers can use cxxabi" ${use_cxxabi_default})
 pythonize_bool(SANITIZER_CAN_USE_CXXABI)
 
+option(SANITIZER_USE_SOFTWARE_MEMORY_MANAGER
+  "Experimental: Do not rely on availability of mmap() in sanitizers." OFF)
+mark_as_advanced(SANITIZER_USE_SOFTWARE_MEMORY_MANAGER)
+
 #================================
 # Setup Compiler Flags
 #================================
Index: lib/asan/tests/CMakeLists.txt
===================================================================
--- lib/asan/tests/CMakeLists.txt
+++ lib/asan/tests/CMakeLists.txt
@@ -34,6 +34,13 @@
   -Wno-non-virtual-dtor)
 append_list_if(COMPILER_RT_HAS_WVARIADIC_MACROS_FLAG -Wno-variadic-macros ASAN_UNITTEST_COMMON_CFLAGS)
 
+# With the software memory manager enabled we need the RTL to handle all
+# shadow memory accesses.
+if(SANITIZER_USE_SOFTWARE_MEMORY_MANAGER)
+  list(APPEND ASAN_UNITTEST_COMMON_CFLAGS
+    -mllvm -asan-instrumentation-with-call-threshold=0)
+endif()
+
 # This will ensure the target linker is used
 # during cross compilation
 set(ASAN_UNITTEST_COMMON_LINK_FLAGS
@@ -328,9 +335,14 @@
     darwin_filter_host_archs(ASAN_SUPPORTED_ARCH ASAN_TEST_ARCH)
   endif()
   foreach(arch ${ASAN_TEST_ARCH})
-    add_asan_tests_for_arch_and_kind(${arch} "-inline")
-    add_asan_tests_for_arch_and_kind(${arch} "-with-calls"
-      -mllvm -asan-instrumentation-with-call-threshold=0)
+    # The software memory manager requires out-of-line instrumentation.
+    if(SANITIZER_USE_SOFTWARE_MEMORY_MANAGER)
+      add_asan_tests_for_arch_and_kind(${arch} "-with-calls")
+    else()
+      add_asan_tests_for_arch_and_kind(${arch} "-inline")
+      add_asan_tests_for_arch_and_kind(${arch} "-with-calls"
+        -mllvm -asan-instrumentation-with-call-threshold=0)
+    endif()
   endforeach()
 endif()
 
Index: test/asan/lit.cfg
===================================================================
--- test/asan/lit.cfg
+++ test/asan/lit.cfg
@@ -81,6 +81,9 @@
                             config.debug_info_flags + target_cflags)
 if config.target_arch == 's390x':
   clang_asan_static_cflags.append("-mbackchain")
+if config.use_software_memory_manager == 'ON':
+  clang_asan_static_cflags.extend(
+    ["-mllvm", "-asan-instrumentation-with-call-threshold=0"])
 clang_asan_static_cxxflags = config.cxx_mode_flags + clang_asan_static_cflags
 
 asan_dynamic_flags = []
Index: test/lit.common.configured.in
===================================================================
--- test/lit.common.configured.in
+++ test/lit.common.configured.in
@@ -28,6 +28,8 @@
 set_default("sanitizer_can_use_cxxabi", @SANITIZER_CAN_USE_CXXABI_PYBOOL@)
 set_default("has_lld", @COMPILER_RT_HAS_LLD_PYBOOL@)
 set_default("can_symbolize", @CAN_SYMBOLIZE@)
+set_default("use_software_memory_manager",
+            "@SANITIZER_USE_SOFTWARE_MEMORY_MANAGER@")
 config.available_features.add('target-is-%s' % config.target_arch)
 
 # LLVM tools dir can be passed in lit parameters, so try to