[libc++] Add support for cross compiling.

[danalbert]

CMakeLists.txt

87

We can't use CMAKE_CROSSCOMPILING for this because AFAICT cmake (prior to 3.x) will only set that if you are compiling to a different system (i.e. Linux to Windows), but not to a different architecture. Since the variable can't be overridden, we just introduce our own.

libc++abi will need a similar one, so perhaps it should just be LLVM_CROSSCOMPILING? Do we already have such a thing? I need to take another look through how LLVM handles this.

Another option would just be removing it entirely. I suppose setting a sysroot/toolchain is probably helpful for non-cross compiles as well, and the only other thing this guards is the passing of LIBCXX_TARGET_TRIPLE to lit.site.cfg and its subsequent use in lit.cfg.

[jroelofs]

libc++abi will need a similar one, so perhaps it should just be LLVM_CROSSCOMPILING? Do we already have such a thing? I need to take another look through how LLVM handles this.

LLVM_CROSSCOMPILING and LIBCXX{ABI}_CROSSCOMPILING should be fundamentally different things. The former would only apply when host!=build, whereas the latter, because libcxx{abi} is a runtime component, applies when host!=target.

Another option would just be removing it entirely. I suppose setting a sysroot/toolchain is probably helpful for non-cross compiles as well

Yeah, there are valid use cases for this outside of cross compiles. I'd get rid of the guard.

It's awesome how terribly simple this is.

test/CMakeLists.txt

26 ↗

(On Diff #18206)

I think this might belong in a separate patch.

[danalbert]

Remove LIBCXX_CROSSCOMPILING. The options it was guarding are useful outside a
cross compiling situation.

[danalbert]

In D6990#109177, @jroelofs wrote:

It's awesome how terribly simple this is.

If we could use cmake 3 the cmake part of this patch wouldn't even exist :(

[jroelofs]

LGTM

[danalbert]

Use set() instead of option() for string options.

CMakeLists.txt

 option(LIBCXX_ENABLE_SHARED "Build libc++ as a shared library." 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
   "Build libc++ with support for a monotonic clock.
    This option may only be used when LIBCXX_ENABLE_THREADS=OFF." ON)
 option(LIBCXX_INSTALL_HEADERS "Install the libc++ headers." ON)
 option(LIBCXX_INSTALL_SUPPORT_HEADERS "Install libc++ support headers." ON)
+set(LIBCXX_SYSROOT "" CACHE STRING "Use alternate sysroot.")
+set(LIBCXX_GCC_TOOLCHAIN "" CACHE STRING "Use alternate GCC toolchain.")
 if (LIBCXX_BUILT_STANDALONE)
   set(LLVM_USE_SANITIZER "" CACHE STRING
       "Define the sanitizer used to build the library and tests")
 endif()
 
 set(CXXABIS none libcxxabi libcxxrt libstdc++ libsupc++)
 if (NOT LIBCXX_CXX_ABI)
   if (NOT DEFINED LIBCXX_BUILT_STANDALONE AND

 endif ()
 set(LIBCXX_CXX_ABI "${LIBCXX_CXX_ABI}" CACHE STRING
     "Specify C++ ABI library to use." FORCE)
 set_property(CACHE LIBCXX_CXX_ABI PROPERTY STRINGS ;${CXXABIS})
 
 #===============================================================================
 # Configure System
 #===============================================================================
 
 # Get triples.
 include(GetTriple)
 get_host_triple(LIBCXX_HOST_TRIPLE
   LIBCXX_HOST_ARCH
   LIBCXX_HOST_VENDOR
   LIBCXX_HOST_OS
   )
 set(LIBCXX_HOST_TRIPLE ${LIBCXX_HOST_TRIPLE} CACHE STRING "Host triple.")
if (LLVM_USE_SANITIZER AND NOT MSVC)
     else()
       message(WARNING "Unsupported value of LLVM_USE_SANITIZER: ${LLVM_USE_SANITIZER}")
     endif()
   elseif(MSVC)
     message(WARNING "LLVM_USE_SANITIZER is not supported with MSVC")
   endif()
 endif()
 
+list(APPEND LIBCXX_CXX_FLAGS "-target ${LIBCXX_TARGET_TRIPLE}")
+append_if(LIBCXX_CXX_FLAGS LIBCXX_SYSROOT "--sysroot ${LIBCXX_SYSROOT}")
+append_if(LIBCXX_CXX_FLAGS LIBCXX_GCC_TOOLCHAIN
+          "-gcc-toolchain ${LIBCXX_GCC_TOOLCHAIN}")
+
 string(REPLACE ";" " " LIBCXX_CXX_FLAGS "${LIBCXX_CXX_FLAGS}")
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${LIBCXX_CXX_FLAGS}")
 
 #===============================================================================
 # Setup Source Code
 #===============================================================================
 
 include_directories(include)

test/libcxx/test/config.py

def configure_features(self):
                     'locale.{0}'.format(feature))
             except locale.Error:
                 self.lit_config.warning('The locale {0} is not supported by '
                                         'your platform. Some tests will be '
                                         'unsupported.'.format(loc))
         locale.setlocale(locale.LC_ALL, default_locale)
 
         # Write an "available feature" that combines the triple when
-        # use_system_cxx_lib is enabled. This is so that we can easily write XFAIL
-        # markers for tests that are known to fail with versions of libc++ as
-        # were shipped with a particular triple.
+        # use_system_cxx_lib is enabled. This is so that we can easily write
+        # XFAIL markers for tests that are known to fail with versions of
+        # libc++ as were shipped with a particular triple.
         if self.use_system_cxx_lib:
             self.config.available_features.add(
                 'with_system_cxx_lib=%s' % self.config.target_triple)
 
         # Some linux distributions have different locale data than others.
         # Insert the distributions name and name-version into the available
         # features to allow tests to XFAIL on them.
         if sys.platform.startswith('linux'):
def configure_compile_flags(self):
             self.compile_flags += ['-m32']
         # Configure threading features.
         enable_threads = self.get_lit_bool('enable_threads', True)
         enable_monotonic_clock = self.get_lit_bool('enable_monotonic_clock',
                                                    True)
         if not enable_threads:
             self.configure_compile_flags_no_threads()
             if not enable_monotonic_clock:
-                self.configure_compile_flags_no_monotonic_clock() 
+                self.configure_compile_flags_no_monotonic_clock()
         elif not enable_monotonic_clock:
             self.lit_config.fatal('enable_monotonic_clock cannot be false when'
                                   ' enable_threads is true.')
         # Use verbose output for better errors
         self.compile_flags += ['-v']
         # Configure extra compile flags.
         compile_flags_str = self.get_lit_conf('compile_flags', '')
         self.compile_flags += shlex.split(compile_flags_str)
 
+        sysroot = self.get_lit_conf('sysroot')
+        if sysroot:
+            self.compile_flags += ['--sysroot', sysroot]
+        gcc_toolchain = self.get_lit_conf('gcc_toolchain')
+        if gcc_toolchain:
+            self.compile_flags += ['-gcc-toolchain', gcc_toolchain]
+
+        self.compile_flags += ['-target', self.config.target_triple]
+
     def configure_compile_flags_header_includes(self):
         self.compile_flags += ['-I' + self.libcxx_src_root + '/test/support']
         libcxx_headers = self.get_lit_conf('libcxx_headers',
                                            self.libcxx_src_root + '/include')
         if not os.path.isdir(libcxx_headers):
             self.lit_config.fatal("libcxx_headers='%s' is not a directory."
                                   % libcxx_headers)
         self.compile_flags += ['-I' + libcxx_headers]

test/lit.site.cfg.in

 @AUTO_GEN_COMMENT@
 config.cxx_under_test           = "@LIBCXX_COMPILER@"
 config.std                      = "@LIBCXX_STD_VERSION@"
 config.libcxx_src_root          = "@LIBCXX_SOURCE_DIR@"
 config.libcxx_obj_root          = "@LIBCXX_BINARY_DIR@"
 config.cxx_library_root         = "@LIBCXX_LIBRARY_DIR@"
 config.enable_exceptions        = "@LIBCXX_ENABLE_EXCEPTIONS@"
 config.enable_rtti              = "@LIBCXX_ENABLE_RTTI@"
 config.enable_shared            = "@LIBCXX_ENABLE_SHARED@"
 config.enable_32bit             = "@LIBCXX_BUILD_32_BITS@"
 config.enable_threads           = "@LIBCXX_ENABLE_THREADS@"
 config.enable_monotonic_clock   = "@LIBCXX_ENABLE_MONOTONIC_CLOCK@"
 config.cxx_abi                  = "@LIBCXX_CXX_ABI_LIBNAME@"
 config.use_sanitizer            = "@LLVM_USE_SANITIZER@"
 config.abi_library_path         = "@LIBCXX_CXX_ABI_LIBRARY_PATH@"
 config.configuration_variant    = "@LIBCXX_LIT_VARIANT@"
+config.target_triple            = "@LIBCXX_TARGET_TRIPLE@"
+config.sysroot                  = "@LIBCXX_SYSROOT@"
+config.gcc_toolchain            = "@LIBCXX_GCC_TOOLCHAIN@"
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@LIBCXX_SOURCE_DIR@/test/lit.cfg")