[compiler-rt] Support for passing through linker flags to libc++ build

[phosek]

Summary

This may be needed when cross-compiling to certain platforms.

[MaskRay]

Feel free to ignore me.. but would be glad if you happen to know the cause. ninja -C ~/llvm/Release TFuzzer-x86_64-Test appears to be broken to me due to some cmake change landed yesterday

ld.lld: error: undefined symbol: fuzzer::ParseOneDictionaryEntry(std::__Fuzzer::basic_string<char, std::__Fuzzer::char_traits<char>, std::__Fuzzer::allocator<char> > const&, std::__Fuzzer::vector<unsigned char, fuzzer::fuzzer_allocator<unsigned char> >*)
>>> referenced by FuzzerUnittest.cpp
>>>               FuzzerTestObjects.FuzzerUnittest.cpp.x86_64.o:(FuzzerDictionary_ParseOneDictionaryEntry_Test::TestBody())

The issue is that projects/compiler-rt/lib/fuzzer/CMakeFiles/RTfuzzer.x86_64.dir/FuzzerUtil.cpp.o has (incorrect) hidden symbols.

64: 0000000000000000  2175 FUNC    GLOBAL HIDDEN    19 fuzzer::ParseOneDictionaryEntry(std::Fuzzer::basic_string<char, std::Fuzzer::char_traits<char>, std::Fuzzer::allocator<char> > const&, std::Fuzzer::vector<unsigned char, fuzzer::fuzzer_allocator<unsigned char> >*)

A quick (and improper) fix is to delete -fvisibility=hidden on compiler-rt/lib/fuzzer/CMakeLists.txt#L128.

[eugenis]

The same failure as MaskRay describes has kept sanitizer-linux bot red for several days now:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux/builds/17090

[phosek]

I'm looking into that issue now, although that's independent from this change.

[phosek]

D54058 is a fix for the broken bot build. I've decided to keep that change separate since it's independent from this change.

[phosek]

Is it OK to land this now that D54058 has landed?

[vitalybuka]

LGTM

[eugenis]

Yes, thanks you! LGTM

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

macro(add_custom_libcxx name prefix)
 
   add_custom_target(${name}-clobber
     DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${name}-clobber-stamp)
   set_target_properties(${name}-clobber PROPERTIES FOLDER "Compiler-RT Misc")
 
   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}})
+    get_property(is_value_set CACHE ${variable} PROPERTY VALUE SET)
+    if(${is_value_set})
+      get_property(value CACHE ${variable} PROPERTY VALUE)
+      list(APPEND CMAKE_PASSTHROUGH_VARIABLES -D${variable}=${value})
     endif()
   endforeach()
 
   string(REPLACE ";" " " LIBCXX_C_FLAGS "${LIBCXX_CFLAGS}")
   get_property(C_FLAGS CACHE CMAKE_C_FLAGS PROPERTY VALUE)
   set(LIBCXX_C_FLAGS "${LIBCXX_C_FLAGS} ${C_FLAGS}")
 
   string(REPLACE ";" " " LIBCXX_CXX_FLAGS "${LIBCXX_CFLAGS}")