[CMake][libcxxabi] Use -nodefaultlibs for CMake checks

[phosek]

Summary

Since libc++abi is built with -nodefaultlibs, we should be using this option even for CMake checks to avoid any inconsistency and also to avoid dependency on a working C++ standard library just for the setting up the build itself because check_cxx_compile_flags adds the flag to COMPILE_DEFINITIONS when calling try_compile and this variable is only considered for compilation but not for linking where -nodefaultlibs actually makes a difference.. The implementation is largely similar to the one used by libc++.

[phosek]

Ping, can someone please look at this one as well?

[beanz]

This looks reasonable to me.

[kaz7]

Hi, I have a question about this patch. I appreciate any answers. Thanks!

libcxxabi/trunk/cmake/config-ix.cmake

26 ↗

(On Diff #94563)

Hi!

Is it possible to ask about this implementation?

I'm trying to build libcxxabi.so and libclang_rt.builtins-ve.a for VE architecture. However, generated libcxxabi.so requires libclang_rt.builtins-ve.a for __multi3 function. Then, ld causes following errors, when I compile any c++ test programs using generated clang++, libc++.so, libcxxabi.so, and libclang_rt.builtins-ve.a. I think that this is an error trying to refer __multi3 function in libclang_rt.builtins-ve.a from libcxxabi.so.

/opt/nec/ve/bin/nld: cmTC_f428b: hidden symbol `__veabi_multi3' in /home/jam/llvm-upstream/install/lib/clang/12.0.0/lib/linux/libclang_rt.builtins-ve.a(multi3.c.o) is referenced by DSO
    /opt/nec/ve/bin/nld: final link failed: Bad value

In order to solve this problem, I can add following CMakefile code to link libcxxabi.so with libclang_rt.builtins-ve.a at build-time. It works fine for VE. But, I'm not sure whther this modification works for all other architectures or not. Or, I guess, there is better answer for this problem.

     list(APPEND CMAKE_REQUIRED_FLAGS -rtlib=compiler-rt)
     find_compiler_rt_library(builtins LIBCXXABI_BUILTINS_LIBRARY)
     list(APPEND CMAKE_REQUIRED_LIBRARIES "${LIBCXXABI_BUILTINS_LIBRARY}")
+    # CMAKE_REQUIRED_LIBRARIES is not used to link libc++abi.so, so
+    # append builtins to LIBCXXABI_SHARED_LIBRARIES too
+    list(APPEND LIBCXXABI_SHARED_LIBRARIES "${LIBCXXABI_BUILTINS_LIBRARY}")

I appreciate if you have any suggestions for me here. Thanks!

[phosek]

libcxxabi/trunk/cmake/config-ix.cmake

26 ↗

(On Diff #94563)

I think this is because no other target requires builtins, looks like VE architecture is the first one that does. Rather than using the LIBCXXABI_SHARED_LIBRARIES global variable, we prefer to set dependencies directly for each target which is a more modern CMake approach. See how this is implemented in libcxx: https://github.com/llvm/llvm-project/blob/cfc60730179042a93cb9cb338982e71d20707a24/libcxx/CMakeLists.txt#L750. I'd prefer to use a similar implementation for libcxxabi.

[kaz7]

libcxxabi/trunk/cmake/config-ix.cmake

26 ↗

(On Diff #94563)

Thank you for your answer. That makes sense. I appreciate if you have time to modify it in described way. Or, I can try to modify config-ix.cmake following your suggestions. Please let me know which way is good for you. Thanks!

[kaz7]

libcxxabi/trunk/cmake/config-ix.cmake

26 ↗

(On Diff #94563)

I was working on CMakeLists, but I've understood modifying libcxxabi/CMakeLists.txt similar to libcxx/CMakeLists.txt is not easy...

So, I'll submit a patch to modify only this config-ix.cmake. Thank you for your previous answer.

CMakeLists.txt

 #===============================================================================
 # Setup Project
 #===============================================================================
 
 cmake_minimum_required(VERSION 3.4.3)
 
 if(POLICY CMP0042)
   cmake_policy(SET CMP0042 NEW) # Set MACOSX_RPATH=YES by default
 endif()
 
+# Add path for custom modules
+set(CMAKE_MODULE_PATH
+  "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Modules"
+  ${CMAKE_MODULE_PATH}
+  )
+
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(libcxxabi)
 
   # Rely on llvm-config.
   set(CONFIG_OUTPUT)
   if (NOT LLVM_CONFIG_PATH)
     find_program(LLVM_CONFIG_PATH "llvm-config")
   endif()
else()
   set(LLVM_MAIN_SRC_DIR "${CMAKE_SOURCE_DIR}" CACHE PATH "Path to LLVM source tree")
   set(LLVM_LIT "${CMAKE_SOURCE_DIR}/utils/lit/lit.py")
   set(LIBCXXABI_LIBDIR_SUFFIX ${LLVM_LIBDIR_SUFFIX})
 endif()
 
 #===============================================================================
 # Setup CMake Options
 #===============================================================================
+include(HandleCompilerRT)
 
 # Define options.
 option(LIBCXXABI_ENABLE_EXCEPTIONS "Use exceptions." ON)
 option(LIBCXXABI_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
 option(LIBCXXABI_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
 option(LIBCXXABI_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 option(LIBCXXABI_USE_LLVM_UNWINDER "Build and use the LLVM unwinder." OFF)
 option(LIBCXXABI_ENABLE_STATIC_UNWINDER "Statically link the LLVM unwinder." OFF)

cmake/Modules/HandleCompilerRT.cmake

+function(find_compiler_rt_library name dest)
+  if (NOT DEFINED LIBCXXABI_COMPILE_FLAGS)
+    message(FATAL_ERROR "LIBCXXABI_COMPILE_FLAGS must be defined when using this function")
+  endif()
+  set(dest "" PARENT_SCOPE)
+  set(CLANG_COMMAND ${CMAKE_CXX_COMPILER} ${TARGET_TRIPLE} ${LIBCXXABI_COMPILE_FLAGS}
+      "--rtlib=compiler-rt" "--print-libgcc-file-name")
+  if (CMAKE_CXX_COMPILER_ID MATCHES Clang AND CMAKE_CXX_COMPILER_TARGET)
+    list(APPEND CLANG_COMMAND "--target=${CMAKE_CXX_COMPILER_TARGET}")
+  endif()
+  execute_process(
+      COMMAND ${CLANG_COMMAND}
+      RESULT_VARIABLE HAD_ERROR
+      OUTPUT_VARIABLE LIBRARY_FILE
+  )
+  string(STRIP "${LIBRARY_FILE}" LIBRARY_FILE)
+  string(REPLACE "builtins" "${name}" LIBRARY_FILE "${LIBRARY_FILE}")
+  if (NOT HAD_ERROR AND EXISTS "${LIBRARY_FILE}")
+    message(STATUS "Found compiler-rt library: ${LIBRARY_FILE}")
+    set(${dest} "${LIBRARY_FILE}" PARENT_SCOPE)
+  else()
+    message(STATUS "Failed to find compiler-rt library")
+  endif()
+endfunction()
+
+function(find_compiler_rt_dir dest)
+  if (NOT DEFINED LIBCXXABI_COMPILE_FLAGS)
+    message(FATAL_ERROR "LIBCXXABI_COMPILE_FLAGS must be defined when using this function")
+  endif()
+  set(dest "" PARENT_SCOPE)
+  if (APPLE)
+    set(CLANG_COMMAND ${CMAKE_CXX_COMPILER} ${LIBCXXABI_COMPILE_FLAGS}
+        "-print-file-name=lib")
+    execute_process(
+        COMMAND ${CLANG_COMMAND}
+        RESULT_VARIABLE HAD_ERROR
+        OUTPUT_VARIABLE LIBRARY_DIR
+    )
+    string(STRIP "${LIBRARY_DIR}" LIBRARY_DIR)
+    set(LIBRARY_DIR "${LIBRARY_DIR}/darwin")
+  else()
+    set(CLANG_COMMAND ${CMAKE_CXX_COMPILER} ${LIBCXXABI_COMPILE_FLAGS}
+        "--rtlib=compiler-rt" "--print-libgcc-file-name")
+    execute_process(
+        COMMAND ${CLANG_COMMAND}
+        RESULT_VARIABLE HAD_ERROR
+        OUTPUT_VARIABLE LIBRARY_FILE
+    )
+    string(STRIP "${LIBRARY_FILE}" LIBRARY_FILE)
+    get_filename_component(LIBRARY_DIR "${LIBRARY_FILE}" DIRECTORY)
+  endif()
+  if (NOT HAD_ERROR AND EXISTS "${LIBRARY_DIR}")
+    message(STATUS "Found compiler-rt directory: ${LIBRARY_DIR}")
+    set(${dest} "${LIBRARY_DIR}" PARENT_SCOPE)
+  else()
+    message(STATUS "Failed to find compiler-rt directory")
+  endif()
+endfunction()

cmake/config-ix.cmake

 include(CheckLibraryExists)
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 
+check_library_exists(c fopen "" LIBCXXABI_HAS_C_LIB)
+if (NOT LIBCXXABI_USE_COMPILER_RT)
+  check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXXABI_HAS_GCC_S_LIB)
+endif ()
+
+# libc++abi is built with -nodefaultlibs, so we want all our checks to also
+# use this option, otherwise we may end up with an inconsistency between
+# the flags we think we require during configuration (if the checks are
+# performed without -nodefaultlibs) and the flags that are actually
+# required during compilation (which has the -nodefaultlibs). libc is
+# required for the link to go through. We remove sanitizers from the
+# configuration checks to avoid spurious link errors.
+check_c_compiler_flag(-nodefaultlibs LIBCXXABI_HAS_NODEFAULTLIBS_FLAG)
+if (LIBCXXABI_HAS_NODEFAULTLIBS_FLAG)
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nodefaultlibs")
+  if (LIBCXXABI_HAS_C_LIB)
+    list(APPEND CMAKE_REQUIRED_LIBRARIES c)
+  endif ()
+  if (LIBCXXABI_USE_COMPILER_RT)
+    list(APPEND CMAKE_REQUIRED_FLAGS -rtlib=compiler-rt)
+    find_compiler_rt_library(builtins LIBCXXABI_BUILTINS_LIBRARY)
+    list(APPEND CMAKE_REQUIRED_LIBRARIES "${LIBCXXABI_BUILTINS_LIBRARY}")
+  elseif (LIBCXXABI_HAS_GCC_S_LIB)
+    list(APPEND CMAKE_REQUIRED_LIBRARIES gcc_s)
+  endif ()
+  if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
+    set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")
+  endif ()
+  if (CMAKE_C_FLAGS MATCHES -fsanitize-coverage OR CMAKE_CXX_FLAGS MATCHES -fsanitize-coverage)
+    set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize-coverage=edge,trace-cmp,indirect-calls,8bit-counters")
+  endif ()
+endif ()
+
 # Check compiler flags
 check_c_compiler_flag(-funwind-tables         LIBCXXABI_HAS_FUNWIND_TABLES)
 check_cxx_compiler_flag(-fPIC                 LIBCXXABI_HAS_FPIC_FLAG)
 check_cxx_compiler_flag(-fno-exceptions       LIBCXXABI_HAS_NO_EXCEPTIONS_FLAG)
 check_cxx_compiler_flag(-fno-rtti             LIBCXXABI_HAS_NO_RTTI_FLAG)
 check_cxx_compiler_flag(-fstrict-aliasing     LIBCXXABI_HAS_FSTRICT_ALIASING_FLAG)
-check_cxx_compiler_flag(-nodefaultlibs        LIBCXXABI_HAS_NODEFAULTLIBS_FLAG)
 check_cxx_compiler_flag(-nostdinc++           LIBCXXABI_HAS_NOSTDINCXX_FLAG)
 check_cxx_compiler_flag(-Wall                 LIBCXXABI_HAS_WALL_FLAG)
 check_cxx_compiler_flag(-W                    LIBCXXABI_HAS_W_FLAG)
 check_cxx_compiler_flag(-Wunused-function     LIBCXXABI_HAS_WUNUSED_FUNCTION_FLAG)
 check_cxx_compiler_flag(-Wunused-variable     LIBCXXABI_HAS_WUNUSED_VARIABLE_FLAG)
 check_cxx_compiler_flag(-Wunused-parameter    LIBCXXABI_HAS_WUNUSED_PARAMETER_FLAG)
 check_cxx_compiler_flag(-Wstrict-aliasing     LIBCXXABI_HAS_WSTRICT_ALIASING_FLAG)
 check_cxx_compiler_flag(-Wstrict-overflow     LIBCXXABI_HAS_WSTRICT_OVERFLOW_FLAG)

 check_cxx_compiler_flag(/GR-                  LIBCXXABI_HAS_NO_GR_FLAG)
 check_cxx_compiler_flag(-std=c++11            LIBCXXABI_HAS_STD_CXX11)
 
 if(LIBCXXABI_HAS_STD_CXX11)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 endif()
 
 # Check libraries
-check_library_exists(c fopen "" LIBCXXABI_HAS_C_LIB)
 check_library_exists(dl dladdr "" LIBCXXABI_HAS_DL_LIB)
 check_library_exists(pthread pthread_once "" LIBCXXABI_HAS_PTHREAD_LIB)
-if (NOT LIBCXXABI_USE_COMPILER_RT)
-  check_library_exists(gcc_s __gcc_personality_v0 "" LIBCXXABI_HAS_GCC_S_LIB)
-endif ()
 check_library_exists(c __cxa_thread_atexit_impl ""
   LIBCXXABI_HAS_CXA_THREAD_ATEXIT_IMPL)