Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -54,6 +54,7 @@
 option(LIBCXX_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 option(LIBCXX_ENABLE_CXX1Y "Enable -std=c++1y and use of c++1y language features if the compiler supports it." OFF)
 option(LIBCXX_ENABLE_SHARED "Build libc++ as a shared library." ON)
+option(LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE "Build libc++ with support for the global filesystem namespace." ON)
 option(LIBCXX_ENABLE_THREADS "Build libc++ with support for threads." ON)
 option(LIBCXX_BUILD_32_BITS "Build 32 bit libc++" OFF)
 option(LIBCXX_ENABLE_MONOTONIC_CLOCK
@@ -232,6 +233,11 @@
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)
 endif()
 
+# LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE configuration
+if (NOT LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE)
+  add_definitions(-D_LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE)
+endif()
+
 # LIBCXX_ENABLE_THREADS configuration
 if (NOT LIBCXX_ENABLE_THREADS)
   add_definitions(-D_LIBCPP_HAS_NO_THREADS)
Index: include/__config
===================================================================
--- include/__config
+++ include/__config
@@ -719,4 +719,12 @@
          _LIBCPP_HAS_NO_THREADS is defined.
 #endif
 
+// Systems that use capability-based security (FreeBSD with Capsicum,
+// Nuxi CloudABI) may only provide local filesystem access (using *at()).
+// Functions like open(), rename(), unlink() and stat() should not be
+// used, as they attempt to access the global filesystem namespace.
+#ifdef __CloudABI__
+#define _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
+#endif
+
 #endif  // _LIBCPP_CONFIG
Index: include/cstdio
===================================================================
--- include/cstdio
+++ include/cstdio
@@ -144,14 +144,18 @@
 using ::fpos_t;
 using ::size_t;
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 using ::remove;
 using ::rename;
 using ::tmpfile;
 using ::tmpnam;
+#endif
 using ::fclose;
 using ::fflush;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 using ::fopen;
 using ::freopen;
+#endif
 using ::setbuf;
 using ::setvbuf;
 using ::fprintf;
Index: include/fstream
===================================================================
--- include/fstream
+++ include/fstream
@@ -206,8 +206,10 @@
 
     // 27.9.1.4 Members:
     bool is_open() const;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     basic_filebuf* open(const char* __s, ios_base::openmode __mode);
     basic_filebuf* open(const string& __s, ios_base::openmode __mode);
+#endif
     basic_filebuf* close();
 
 protected:
@@ -463,6 +465,7 @@
     return __file_ != 0;
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 basic_filebuf<_CharT, _Traits>*
 basic_filebuf<_CharT, _Traits>::open(const char* __s, ios_base::openmode __mode)
@@ -550,6 +553,7 @@
 {
     return open(__s.c_str(), __mode);
 }
+#endif
 
 template <class _CharT, class _Traits>
 basic_filebuf<_CharT, _Traits>*
@@ -1005,8 +1009,10 @@
     typedef typename traits_type::off_type off_type;
 
     basic_ifstream();
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     explicit basic_ifstream(const char* __s, ios_base::openmode __mode = ios_base::in);
     explicit basic_ifstream(const string& __s, ios_base::openmode __mode = ios_base::in);
+#endif
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
     basic_ifstream(basic_ifstream&& __rhs);
 #endif
@@ -1018,8 +1024,10 @@
 
     basic_filebuf<char_type, traits_type>* rdbuf() const;
     bool is_open() const;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     void open(const char* __s, ios_base::openmode __mode = ios_base::in);
     void open(const string& __s, ios_base::openmode __mode = ios_base::in);
+#endif
     void close();
 
 private:
@@ -1033,6 +1041,7 @@
 {
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
 basic_ifstream<_CharT, _Traits>::basic_ifstream(const char* __s, ios_base::openmode __mode)
@@ -1050,6 +1059,7 @@
     if (__sb_.open(__s, __mode | ios_base::in) == 0)
         this->setstate(ios_base::failbit);
 }
+#endif
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
@@ -1107,6 +1117,7 @@
     return __sb_.is_open();
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 void
 basic_ifstream<_CharT, _Traits>::open(const char* __s, ios_base::openmode __mode)
@@ -1126,6 +1137,7 @@
     else
         this->setstate(ios_base::failbit);
 }
+#endif
 
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
@@ -1163,8 +1175,10 @@
 
     basic_filebuf<char_type, traits_type>* rdbuf() const;
     bool is_open() const;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     void open(const char* __s, ios_base::openmode __mode = ios_base::out);
     void open(const string& __s, ios_base::openmode __mode = ios_base::out);
+#endif
     void close();
 
 private:
@@ -1178,6 +1192,7 @@
 {
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
 basic_ofstream<_CharT, _Traits>::basic_ofstream(const char* __s, ios_base::openmode __mode)
@@ -1195,6 +1210,7 @@
     if (__sb_.open(__s, __mode | ios_base::out) == 0)
         this->setstate(ios_base::failbit);
 }
+#endif
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
@@ -1252,6 +1268,7 @@
     return __sb_.is_open();
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 void
 basic_ofstream<_CharT, _Traits>::open(const char* __s, ios_base::openmode __mode)
@@ -1271,6 +1288,7 @@
     else
         this->setstate(ios_base::failbit);
 }
+#endif
 
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
@@ -1295,8 +1313,10 @@
     typedef typename traits_type::off_type off_type;
 
     basic_fstream();
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     explicit basic_fstream(const char* __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
     explicit basic_fstream(const string& __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
+#endif
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
     basic_fstream(basic_fstream&& __rhs);
 #endif
@@ -1308,8 +1328,10 @@
 
     basic_filebuf<char_type, traits_type>* rdbuf() const;
     bool is_open() const;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     void open(const char* __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
     void open(const string& __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
+#endif
     void close();
 
 private:
@@ -1323,6 +1345,7 @@
 {
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
 basic_fstream<_CharT, _Traits>::basic_fstream(const char* __s, ios_base::openmode __mode)
@@ -1340,6 +1363,7 @@
     if (__sb_.open(__s, __mode) == 0)
         this->setstate(ios_base::failbit);
 }
+#endif
 
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
@@ -1397,6 +1421,7 @@
     return __sb_.is_open();
 }
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 template <class _CharT, class _Traits>
 void
 basic_fstream<_CharT, _Traits>::open(const char* __s, ios_base::openmode __mode)
@@ -1416,6 +1441,7 @@
     else
         this->setstate(ios_base::failbit);
 }
+#endif
 
 template <class _CharT, class _Traits>
 inline _LIBCPP_INLINE_VISIBILITY
Index: test/CMakeLists.txt
===================================================================
--- test/CMakeLists.txt
+++ test/CMakeLists.txt
@@ -42,6 +42,7 @@
   pythonize_bool(LIBCXX_ENABLE_RTTI)
   pythonize_bool(LIBCXX_ENABLE_SHARED)
   pythonize_bool(LIBCXX_BUILD_32_BITS)
+  pythonize_bool(LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE)
   pythonize_bool(LIBCXX_ENABLE_THREADS)
   pythonize_bool(LIBCXX_ENABLE_MONOTONIC_CLOCK)
   # The tests shouldn't link to any ABI library when it has been linked into
Index: test/libcxx/test/config.py
===================================================================
--- test/libcxx/test/config.py
+++ test/libcxx/test/config.py
@@ -347,6 +347,7 @@
         # Configure feature flags.
         self.configure_compile_flags_exceptions()
         self.configure_compile_flags_rtti()
+        self.configure_compile_flags_no_global_filesystem_namespace()
         enable_32bit = self.get_lit_bool('enable_32bit', False)
         if enable_32bit:
             self.cxx.flags += ['-m32']
@@ -395,6 +396,15 @@
             self.config.available_features.add('libcpp-no-rtti')
             self.cxx.compile_flags += ['-fno-rtti', '-D_LIBCPP_NO_RTTI']
 
+    def configure_compile_flags_no_global_filesystem_namespace(self):
+        enable_global_filesystem_namespace = self.get_lit_bool(
+            'enable_global_filesystem_namespace', True)
+        if not enable_global_filesystem_namespace:
+            self.config.available_features.add(
+                'libcpp-has-no-global-filesystem-namespace')
+            self.cxx.compile_flags += [
+                '-D_LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE']
+
     def configure_compile_flags_no_threads(self):
         self.cxx.compile_flags += ['-D_LIBCPP_HAS_NO_THREADS']
         self.config.available_features.add('libcpp-has-no-threads')
Index: test/lit.site.cfg.in
===================================================================
--- test/lit.site.cfg.in
+++ test/lit.site.cfg.in
@@ -8,6 +8,7 @@
 config.enable_rtti              = "@LIBCXX_ENABLE_RTTI@"
 config.enable_shared            = "@LIBCXX_ENABLE_SHARED@"
 config.enable_32bit             = "@LIBCXX_BUILD_32_BITS@"
+config.enable_global_filesystem_namespace = "@LIBCXX_ENABLE_GLOBAL_FILESYSTEM_NAMESPACE@"
 config.enable_threads           = "@LIBCXX_ENABLE_THREADS@"
 config.enable_monotonic_clock   = "@LIBCXX_ENABLE_MONOTONIC_CLOCK@"
 config.cxx_abi                  = "@LIBCXX_CXX_ABI_LIBNAME@"
Index: test/std/input.output/file.streams/c.files/cstdio.pass.cpp
===================================================================
--- test/std/input.output/file.streams/c.files/cstdio.pass.cpp
+++ test/std/input.output/file.streams/c.files/cstdio.pass.cpp
@@ -88,14 +88,18 @@
     std::size_t s = 0;
     char* cp = 0;
     std::va_list va;
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     static_assert((std::is_same<decltype(std::remove("")), int>::value), "");
     static_assert((std::is_same<decltype(std::rename("","")), int>::value), "");
     static_assert((std::is_same<decltype(std::tmpfile()), std::FILE*>::value), "");
     static_assert((std::is_same<decltype(std::tmpnam(cp)), char*>::value), "");
+#endif
     static_assert((std::is_same<decltype(std::fclose(fp)), int>::value), "");
     static_assert((std::is_same<decltype(std::fflush(fp)), int>::value), "");
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     static_assert((std::is_same<decltype(std::fopen("", "")), std::FILE*>::value), "");
     static_assert((std::is_same<decltype(std::freopen("", "", fp)), std::FILE*>::value), "");
+#endif
     static_assert((std::is_same<decltype(std::setbuf(fp,cp)), void>::value), "");
     static_assert((std::is_same<decltype(std::vfprintf(fp,"",va)), int>::value), "");
     static_assert((std::is_same<decltype(std::fprintf(fp," ")), int>::value), "");
Index: test/std/input.output/file.streams/c.files/no.global.filesystem.namespace/fopen.fail.cpp
===================================================================
--- test/std/input.output/file.streams/c.files/no.global.filesystem.namespace/fopen.fail.cpp
+++ test/std/input.output/file.streams/c.files/no.global.filesystem.namespace/fopen.fail.cpp
@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstdio>
+
+int main() {
+    // fopen is not available on systems without a global filesystem namespace.
+    std::fopen("", "");
+}
Index: test/std/input.output/file.streams/c.files/no.global.filesystem.namespace/lit.local.cfg
===================================================================
--- test/std/input.output/file.streams/c.files/no.global.filesystem.namespace/lit.local.cfg
+++ test/std/input.output/file.streams/c.files/no.global.filesystem.namespace/lit.local.cfg
@@ -0,0 +1,2 @@
+if 'libcpp-has-no-global-filesystem-namespace' not in config.available_features:
+    config.unsupported = True
Index: test/std/input.output/file.streams/fstreams/lit.local.cfg
===================================================================
--- test/std/input.output/file.streams/fstreams/lit.local.cfg
+++ test/std/input.output/file.streams/fstreams/lit.local.cfg
@@ -0,0 +1,2 @@
+if 'libcpp-has-no-global-filesystem-namespace' in config.available_features:
+    config.unsupported = True
Index: test/std/localization/locales/locale.convenience/conversions/conversions.buffer/lit.local.cfg
===================================================================
--- test/std/localization/locales/locale.convenience/conversions/conversions.buffer/lit.local.cfg
+++ test/std/localization/locales/locale.convenience/conversions/conversions.buffer/lit.local.cfg
@@ -0,0 +1,2 @@
+if 'libcpp-has-no-global-filesystem-namespace' in config.available_features:
+    config.unsupported = True
Index: test/support/platform_support.h
===================================================================
--- test/support/platform_support.h
+++ test/support/platform_support.h
@@ -15,6 +15,8 @@
 #ifndef PLATFORM_SUPPORT_H
 #define PLATFORM_SUPPORT_H
 
+#include <__config>
+
 // locale names
 #ifdef _WIN32
 // WARNING: Windows does not support UTF-8 codepages.
@@ -65,6 +67,7 @@
 }
 #endif
 
+#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 inline
 std::string
 get_temp_file_name()
@@ -90,5 +93,6 @@
     return Name;
 #endif
 }
+#endif // _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
 
 #endif // PLATFORM_SUPPORT_H