[CMake] Passthrough additional flags to custom libcxx CMake build

[phosek]

Summary

This is needed when we're cross-compiling compiler-rt.

[morehouse]

compiler-rt/cmake/Modules/AddCompilerRT.cmake

522 ↗

(On Diff #150159)

What is this code block doing?

[morehouse]

compiler-rt/cmake/Modules/AddCompilerRT.cmake

513 ↗

(On Diff #150176)

Why is this replacement necessary?

[phosek]

compiler-rt/cmake/Modules/AddCompilerRT.cmake

513 ↗

(On Diff #150176)

This is an equivalent of the foreach originally on line 477 but done as a one-liner. The reason is that flags passed via an argument will be a ; separated CMake list, so we need to convert it to a string where individual flags are separated by spaces.

522 ↗

(On Diff #150159)

I was planning on using variables like CLANG_DEFAULT_RTLIB to infer whether to use compiler-rt builtins by default in libc++ like we do in compiler-rt now hence passing these variables through, but that functionality isn't implemented yet so it's probably easier to just punt on it for now and do it later in a separate patch.

[morehouse]

compiler-rt/cmake/Modules/AddCompilerRT.cmake

516 ↗

(On Diff #150176)

Does it make sense to move this whole section closer to the ExternalProject_Add below?

[morehouse]

Reverted in https://reviews.llvm.org/rCRT334528 due to bot breakage: http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/12522.

[phosek]

Thanks for the heads up and sorry about the breakage, I'll see if I can reproduce this locally and come up with a fix.

[phosek]

Turned out that passing all CFLAGS, CXXFLAGS and LDFLAGS throught to libc++ isn't really going to work because some of those such as -Werror -Wall might break some CMake checks. Instead we should pass flags to libc++ more selectively.

[phosek]

@morehouse is it still LGTM? Can I try to reland this?

[morehouse]

LGTM

compiler-rt/trunk/cmake/Modules/AddCompilerRT.cmake

 #                   CFLAGS <list of compile flags>
 #                   USE_TOOLCHAIN)
 macro(add_custom_libcxx name prefix)
   if(NOT COMPILER_RT_LIBCXX_PATH)
     message(FATAL_ERROR "libcxx not found!")
   endif()
 
   cmake_parse_arguments(LIBCXX "USE_TOOLCHAIN" "" "DEPS;CFLAGS;CMAKE_ARGS" ${ARGN})
-  foreach(flag ${LIBCXX_CFLAGS})
-    set(flagstr "${flagstr} ${flag}")
-  endforeach()
-  set(LIBCXX_C_FLAGS ${flagstr})
-  set(LIBCXX_CXX_FLAGS ${flagstr})
 
   if(LIBCXX_USE_TOOLCHAIN)
     set(compiler_args -DCMAKE_C_COMPILER=${COMPILER_RT_TEST_COMPILER}
                       -DCMAKE_CXX_COMPILER=${COMPILER_RT_TEST_CXX_COMPILER})
     if(NOT COMPILER_RT_STANDALONE_BUILD)
       set(toolchain_deps $<TARGET_FILE:clang>)
       set(force_deps DEPENDS $<TARGET_FILE:clang>)
     endif()
add_custom_command(
     COMMAND ${CMAKE_COMMAND} -E touch ${STAMP_DIR}/${name}-mkdir
     COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_CURRENT_BINARY_DIR}/${name}-clobber-stamp
     COMMENT "Clobbering bootstrap build and stamp directories"
     )
 
   add_custom_target(${name}-clobber
     DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${name}-clobber-stamp)
 
-  if(CMAKE_SYSROOT)
-    set(sysroot_arg -DCMAKE_SYSROOT=${CMAKE_SYSROOT})
+  set(PASSTHROUGH_VARIABLES
+    CMAKE_C_COMPILER_TARGET
+    CMAKE_CXX_COMPILER_TARGET
+    CMAKE_SHARED_LINKER_FLAGS
+    CMAKE_MODULE_LINKER_FLAGS
+    CMAKE_EXE_LINKER_FLAGS
+    CMAKE_INSTALL_PREFIX
+    CMAKE_MAKE_PROGRAM
+    CMAKE_LINKER
+    CMAKE_AR
+    CMAKE_RANLIB
+    CMAKE_NM
+    CMAKE_OBJCOPY
+    CMAKE_OBJDUMP
+    CMAKE_STRIP
+    CMAKE_SYSROOT
+    CMAKE_SYSTEM_NAME)
+  foreach(variable ${PASSTHROUGH_VARIABLES})
+    if(${variable})
+      list(APPEND CMAKE_PASSTHROUGH_VARIABLES -D${variable}=${${variable}})
     endif()
+  endforeach()
+
+  string(REPLACE ";" " " FLAGS_STRING "${LIBCXX_CFLAGS}")
+  set(LIBCXX_C_FLAGS "${CMAKE_C_FLAGS} ${FLAGS_STRING}")
+  set(LIBCXX_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${FLAGS_STRING}")
 
   ExternalProject_Add(${name}
     DEPENDS ${name}-clobber ${LIBCXX_DEPS}
     PREFIX ${prefix}
     SOURCE_DIR ${COMPILER_RT_LIBCXX_PATH}
     STAMP_DIR ${STAMP_DIR}
     BINARY_DIR ${BINARY_DIR}
-    CMAKE_ARGS -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
+    CMAKE_ARGS ${CMAKE_PASSTHROUGH_VARIABLES}
                ${compiler_args}
-               ${sysroot_arg}
                -DCMAKE_C_FLAGS=${LIBCXX_C_FLAGS}
                -DCMAKE_CXX_FLAGS=${LIBCXX_CXX_FLAGS}
                -DCMAKE_BUILD_TYPE=Release
-               -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
                -DLLVM_PATH=${LLVM_MAIN_SRC_DIR}
                -DLLVM_BINARY_DIR=${prefix}
                -DLLVM_LIBRARY_OUTPUT_INTDIR=${prefix}/lib
                -DLIBCXX_STANDALONE_BUILD=ON
                ${LIBCXX_CMAKE_ARGS}
     INSTALL_COMMAND ""
     STEP_TARGETS configure build
     BUILD_ALWAYS 1

compiler-rt/trunk/lib/fuzzer/CMakeLists.txt

foreach(arch ${FUZZER_SUPPORTED_ARCH})
     set(LIBCXX_${arch}_PREFIX ${CMAKE_CURRENT_BINARY_DIR}/libcxx_fuzzer_${arch})
     add_custom_libcxx(libcxx_fuzzer_${arch} ${LIBCXX_${arch}_PREFIX}
       CFLAGS ${TARGET_CFLAGS}
              -D_LIBCPP_ABI_VERSION=Fuzzer
              -D_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS=1
              -fvisibility=hidden
       CMAKE_ARGS -DCMAKE_CXX_COMPILER_WORKS=ON
                  -DLIBCXX_ENABLE_EXCEPTIONS=OFF
+                 -DLIBCXX_ENABLE_SHARED=OFF
                  -DLIBCXX_CXX_ABI=none)
     target_compile_options(RTfuzzer.${arch} PRIVATE -isystem ${LIBCXX_${arch}_PREFIX}/include/c++/v1)
     add_dependencies(RTfuzzer.${arch} libcxx_fuzzer_${arch}-build)
     target_compile_options(RTfuzzer_main.${arch} PRIVATE -isystem ${LIBCXX_${arch}_PREFIX}/include/c++/v1)
     add_dependencies(RTfuzzer_main.${arch} libcxx_fuzzer_${arch}-build)
     partially_link_libcxx(fuzzer_no_main ${LIBCXX_${arch}_PREFIX} ${arch})
     partially_link_libcxx(fuzzer ${LIBCXX_${arch}_PREFIX} ${arch})
   endforeach()