Add option to disable linking of libcxx into fuzzer

[pirama]

Summary

The ability to partially link libcxx into fuzzer does not work for cross
compilations. CMAKE_EXE_LINKER_FLAGS, etc are not passed to the custom CMake
invocation and cross-compiling libcxx without a libcxxabi, as is done here, has
further issues as well.

Add an option to disable linking of libcxx into fuzzer. The default for this
option is to link libcxx.

[phosek]

Can you elaborate on the further issues with cross-compiling libcxx without a libcxxabi you mentioned in your commit message? I'd like to improve the build to handle all cases.

CMakeLists.txt

41

This should be probably called COMPILER_RT_FUZZER_LINK_LIBCXX for consistency with other options.

[pirama]

Change name of option to COMPILER_RT_FUZZER_LINK_LIBCXX.

[pirama]

In D44532#1039666, @phosek wrote:

Can you elaborate on the further issues with cross-compiling libcxx without a libcxxabi you mentioned in your commit message? I'd like to improve the build to handle all cases.

The built libcxx had references to some symbols from libcxxabi (__cxa_guard_acquire, I think). I'll reproduce the error tomorrow and report back.

[pirama]

Ping...

In D44532#1039682, @pirama wrote:

In D44532#1039666, @phosek wrote:

Can you elaborate on the further issues with cross-compiling libcxx without a libcxxabi you mentioned in your commit message? I'd like to improve the build to handle all cases.

The built libcxx had references to some symbols from libcxxabi (__cxa_guard_acquire, I think). I'll reproduce the error tomorrow and report back.

I haven't reproduced the error yet (because had a bunch of local changes/fixes before I hit the brickwall). Nonetheless, I think this option can help in the intermediate time when we haven't been able to cross-compile libcxx using CMake (for Android).

CMakeLists.txt

 option(COMPILER_RT_BUILD_XRAY "Build xray" ON)
 mark_as_advanced(COMPILER_RT_BUILD_XRAY)
 option(COMPILER_RT_BUILD_LIBFUZZER "Build libFuzzer" ON)
 mark_as_advanced(COMPILER_RT_BUILD_LIBFUZZER)
 option(COMPILER_RT_BUILD_PROFILE "Build profile runtime" ON)
 mark_as_advanced(COMPILER_RT_BUILD_PROFILE)
 option(COMPILER_RT_BUILD_XRAY_NO_PREINIT "Build xray with no preinit patching" OFF)
 mark_as_advanced(COMPILER_RT_BUILD_XRAY_NO_PREINIT)
+option(COMPILER_RT_FUZZER_LINK_LIBCXX "Link a copy of libcxx into libfuzzer" ON)
+mark_as_advanced(COMPILER_RT_FUZZER_LINK_LIBCXX)
 
 set(COMPILER_RT_ASAN_SHADOW_SCALE ""
     CACHE STRING "Override the shadow scale to be used in ASan runtime")
 
 if (NOT COMPILER_RT_ASAN_SHADOW_SCALE STREQUAL "")
   # Check that the shadow scale value is valid.
   if (NOT (COMPILER_RT_ASAN_SHADOW_SCALE GREATER -1 AND
            COMPILER_RT_ASAN_SHADOW_SCALE LESS 8))

lib/fuzzer/CMakeLists.txt

CHECK_CXX_SOURCE_COMPILES("
   static thread_local int blah;
   int main() {
   return 0;
   }
   " HAS_THREAD_LOCAL)
 
 set(LIBFUZZER_CFLAGS ${SANITIZER_COMMON_CFLAGS})
 
-if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND COMPILER_RT_LIBCXX_PATH)
+if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND COMPILER_RT_LIBCXX_PATH AND COMPILER_RT_FUZZER_LINK_LIBCXX)
   list(APPEND LIBFUZZER_CFLAGS -nostdinc++ -D_LIBCPP_ABI_VERSION=Fuzzer)
   # Remove -stdlib= which is unused when passing -nostdinc++.
   string(REGEX REPLACE "-stdlib=[a-zA-Z+]*" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
 endif()
 
 append_list_if(COMPILER_RT_HAS_OMIT_FRAME_POINTER_FLAG -fno-omit-frame-pointer LIBFUZZER_CFLAGS)
 
 if (CMAKE_CXX_FLAGS MATCHES "fsanitize-coverage")

 add_compiler_rt_runtime(clang_rt.fuzzer_no_main
   STATIC
   OS ${FUZZER_SUPPORTED_OS}
   ARCHS ${FUZZER_SUPPORTED_ARCH}
   OBJECT_LIBS RTfuzzer
   CFLAGS ${LIBFUZZER_CFLAGS}
   PARENT_TARGET fuzzer)
 
-if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND COMPILER_RT_LIBCXX_PATH)
+if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND COMPILER_RT_LIBCXX_PATH AND COMPILER_RT_FUZZER_LINK_LIBCXX)
   macro(partially_link_libcxx name dir arch)
     set(cxx_${arch}_merge_dir "${CMAKE_CURRENT_BINARY_DIR}/cxx_${arch}_merge.dir")
     file(MAKE_DIRECTORY ${cxx_${arch}_merge_dir})
     add_custom_command(TARGET clang_rt.${name}-${arch} POST_BUILD
       COMMAND ${CMAKE_LINKER} --whole-archive "$<TARGET_LINKER_FILE:clang_rt.${name}-${arch}>" --no-whole-archive ${dir}/lib/libc++.a -r -o ${name}.o
       COMMAND ${CMAKE_OBJCOPY} --localize-hidden ${name}.o
       COMMAND ${CMAKE_COMMAND} -E remove "$<TARGET_LINKER_FILE:clang_rt.${name}-${arch}>"
       COMMAND ${CMAKE_AR} qcs "$<TARGET_LINKER_FILE:clang_rt.${name}-${arch}>" ${name}.o