[msan][test] Unset LD_LIBRARY_PATH to avoid un-sanitized libc++

[Hahnfeld]

Summary

This is another attempt to solve the issues mentioned in D42390: If there is
a libc++.so in LD_LIBRARY_PATH, it will be preferred over rpath set by lld
which uses DT_RUNPATH instead of DT_RPATH (called "new-dtags"). That causes
problems because the libc++ from LD_LIBRARY_PATH is not instrumented for use
with msan which breaks the unit tests.

There are two solutions:

1. Pass --disable-new-dtags but that's not really great, especially going forward.
2. Unset LD_LIBRARY_PATH when executing the tests. This needs to be done with some care to make sure that the compiled unit tests can indeed run without the need for any external library.

[phosek]

Wouldn't it be easiest to link the instrumented libc++ statically and avoid the rpath issues altogether?

[Hahnfeld]

In D58014#1392222, @phosek wrote:

Wouldn't it be easiest to link the instrumented libc++ statically and avoid the rpath issues altogether?

Yep, closing this in favor of D58013 that I'll update in a second ;-)

compiler-rt/lib/msan/tests/CMakeLists.txt

macro(add_msan_tests_for_arch arch kind cflags)
   set(MSAN_TEST_OBJECTS ${MSAN_INST_TEST_OBJECTS} ${MSAN_INST_GTEST})
   set(MSAN_TEST_DEPS ${MSAN_TEST_OBJECTS} libcxx_msan_${arch}-build
                      ${MSAN_LOADABLE_SO})
   if(NOT COMPILER_RT_STANDALONE_BUILD)
     list(APPEND MSAN_TEST_DEPS msan)
   endif()
   get_target_flags_for_arch(${arch} TARGET_LINK_FLAGS)
   add_compiler_rt_test(MsanUnitTests "Msan-${arch}${kind}-Test" ${arch}
-    OBJECTS ${MSAN_TEST_OBJECTS} ${MSAN_LIBCXX_SO}
+    OBJECTS ${MSAN_TEST_OBJECTS} "${MSAN_LIBCXX_SO_DIR}/libc++.so"
     DEPS ${MSAN_TEST_DEPS}
     LINK_FLAGS ${MSAN_UNITTEST_LINK_FLAGS}
                ${TARGET_LINK_FLAGS}
+               "-L${MSAN_LIBCXX_SO_DIR}"
                "-Wl,-rpath=${CMAKE_CURRENT_BINARY_DIR}"
-               "-Wl,-rpath=${LIBCXX_PREFIX}/lib")
+               "-Wl,-rpath=${MSAN_LIBCXX_SO_DIR}"
+               "-Wl,-rpath=${LLVM_LIBRARY_OUTPUT_INTDIR}")
 endmacro()
 
 # We should only build MSan unit tests if we can build instrumented libcxx.
 if(COMPILER_RT_CAN_EXECUTE_TESTS AND COMPILER_RT_LIBCXX_PATH)
   foreach(arch ${MSAN_SUPPORTED_ARCH})
     get_target_flags_for_arch(${arch} TARGET_CFLAGS)
     set(LIBCXX_PREFIX ${CMAKE_CURRENT_BINARY_DIR}/../libcxx_msan_${arch})
     add_custom_libcxx(libcxx_msan_${arch} ${LIBCXX_PREFIX}
       DEPS ${MSAN_RUNTIME_LIBRARIES}
       CFLAGS ${MSAN_LIBCXX_CFLAGS} ${TARGET_CFLAGS}
       USE_TOOLCHAIN)
-    set(MSAN_LIBCXX_SO ${LIBCXX_PREFIX}/lib/libc++.so)
+    set(MSAN_LIBCXX_SO_DIR ${LIBCXX_PREFIX}/lib/)
 
     add_msan_tests_for_arch(${arch} "" "")
     add_msan_tests_for_arch(${arch} "-with-call"
                             "-mllvm;-msan-instrumentation-with-call-threshold=0")
   endforeach()
 endif()

compiler-rt/test/msan/Unit/lit.site.cfg.in

 @LIT_SITE_CFG_IN_HEADER@
 
 # Load common config for all compiler-rt unit tests.
 lit_config.load_config(config, "@COMPILER_RT_BINARY_DIR@/unittests/lit.common.unit.configured")
 
 # Setup config name.
 config.name = 'MemorySanitizer-Unit'
 
 # Setup test source and exec root. For unit tests, we define
 # it as build directory with MSan unit tests.
 # FIXME: Don't use hardcoded path to MSan unit tests.
 config.test_exec_root = "@COMPILER_RT_BINARY_DIR@/lib/msan/tests"
 config.test_source_root = config.test_exec_root
+
+# Clean LD_LIBRARY_PATH to avoid using un-sanitized libc++ versions.
+config.environment['LD_LIBRARY_PATH'] = ''