Add a flag to choose a compiler for libFuzzer tests

[george.karpenkov]

Summary

This is needed if the user does not have a compiler in LLVM tree, but still wishes to run libFuzzer tests.
Removes a dependency on Clang and Asan, and removes a guard variable for including libFuzzer tests (but excludes them from check-all).

[kcc]

Will we need this once the code is moved to compiler-rt?

docs/LibFuzzer.rst

 
 
 Developing libFuzzer
 ====================
 
 LibFuzzer is built as a part of LLVM project by default on macos and Linux.
 Users of other operating systems can explicitly request compilation using
 ``-DLIBFUZZER_ENABLE=YES`` flag.
-Tests are run using ``check-fuzzer`` target from the build directory
-which was configured with ``-DLIBFUZZER_ENABLE_TESTS=ON`` flag.
+Tests are run using ``check-fuzzer`` target from the build directory,
+provided Clang is checked out in your source tree:
 
 .. code-block:: console
 
     ninja check-fuzzer
 
+If you wish to use a different Clang, you can specify it using
+``LIBFUZZER_TEST_COMPILER`` environment variable.
+
 
 Fuzzing components of LLVM
 ==========================
 .. contents::
    :local:
    :depth: 1
 
 To build any of the LLVM fuzz targets use the build instructions above.

lib/Fuzzer/CMakeLists.txt

if (CMAKE_SYSTEM_NAME MATCHES "Darwin|Linux")
   set(LIBFUZZER_ENABLED_CHECK ON)
 else()
   set(LIBFUZZER_ENABLED_CHECK OFF)
 endif()
 
 # Compile libFuzzer if the compilation is specifically requested, OR
 # if the platform is known to be working.
 set(LIBFUZZER_ENABLE ${LIBFUZZER_ENABLED_CHECK} CACHE BOOL "Build libFuzzer and its tests")
-set(LIBFUZZER_ENABLE_TESTS OFF CACHE BOOL "Build libFuzzer and its tests")
 
 if (LLVM_USE_SANITIZE_COVERAGE)
   set(CMAKE_CXX_FLAGS
     "${CMAKE_CXX_FLAGS} -fno-sanitize-coverage=trace-pc-guard,edge,trace-cmp,indirect-calls,8bit-counters -Werror")
 endif()
 
 if (LIBFUZZER_ENABLE)
   add_library(LLVMFuzzerNoMainObjects OBJECT

 
 if (MSVC)
 
   # Until bots are reconfigured, check-fuzzer on Windows is a no-OP.
   add_custom_target(check-fuzzer)
   add_custom_command(TARGET check-fuzzer
     COMMAND cmake -E echo "check-fuzzer is disalbed on Windows")
 else()
-  if (LLVM_INCLUDE_TESTS AND LIBFUZZER_ENABLE_TESTS)
+  if (LLVM_INCLUDE_TESTS)
     add_subdirectory(test)
   endif()
 endif()

lib/Fuzzer/test/CMakeLists.txt

 
 if(APPLE)
   # LeakSanitizer is not supported on OSX and Windows right now
   set(HAS_LSAN 0)
   message(WARNING "LeakSanitizer is not supported."
     " Building and running LibFuzzer LeakSanitizer tests is disabled."
     )
 else()
   set(HAS_LSAN 1)
 endif()
 
 ###############################################################################
 # Unit tests
 ###############################################################################
 
+# Do not register fuzzer tests under check-all.
+set(EXCLUDE_FROM_ALL On)
+
 add_custom_target(FuzzerUnitTests)
 set_target_properties(FuzzerUnitTests PROPERTIES FOLDER "libFuzzer tests")
 
 add_executable(LLVMFuzzer-Unittest FuzzerUnittest.cpp)
 
 target_link_libraries(LLVMFuzzer-Unittest
   gtest
   gtest_main

 # Configure lit to run the tests
 #
 # Note this is done after declaring all tests so we can inform lit if any tests
 # need to be disabled.
 ###############################################################################
 
 # Use just-built Clang to compile/link tests on all platforms, except for
 # Windows where we need to use clang-cl instead.
-set(LIBFUZZER_TEST_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang)
-set(LIBFUZZER_TEST_CXX_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang++)
+set(LIBFUZZER_TEST_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang CACHE PATH "Path to Clang compiler")
 
 # LIT-based libFuzzer tests.
 configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.in
   ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg
   )
 
 # libFuzzer unit tests.
 configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/unit/lit.site.cfg.in
   ${CMAKE_CURRENT_BINARY_DIR}/unit/lit.site.cfg
   )
 
 add_lit_testsuite(check-fuzzer "Running Fuzzer tests"
   ${CMAKE_CURRENT_BINARY_DIR}
   DEPENDS LLVMFuzzer-Unittest)
 
-add_dependencies(check-fuzzer LLVMFuzzer asan clang llvm-symbolizer FileCheck sancov not)
+add_dependencies(check-fuzzer LLVMFuzzer llvm-symbolizer FileCheck sancov not)

lib/Fuzzer/test/lit.cfg

if sys.platform.startswith('linux'):
   lit_config.note('linux feature available')
   config.available_features.add('linux')
 else:
   lit_config.note('linux feature unavailable')
 
 config.substitutions.append(('%build_dir', config.cmake_binary_dir))
 
 def generate_compiler_cmd(is_cpp=True, fuzzer_enabled=True):
-  compiler_cmd = config.cpp_compiler if is_cpp else config.c_compiler
+  compiler_cmd = config.c_compiler
+  driver_mode_cmd = '--driver-mode=g++' if is_cpp else ''
   std_cmd = '-std=c++11' if is_cpp else ''
   sanitizers = ['address']
   if fuzzer_enabled:
     sanitizers.append('fuzzer')
   sanitizers_cmd = ('-fsanitize=%s' % ','.join(sanitizers))
   isysroot_cmd = ('-isysroot %s' % config.osx_sysroot
       ) if 'darwin' in config.target_triple else ''
   include_cmd = '-I%s/../.' % config.test_source_root
-  return '%s %s -gline-tables-only %s %s %s' % (
-      compiler_cmd, std_cmd, isysroot_cmd, sanitizers_cmd, include_cmd)
+  return '%s %s %s -gline-tables-only %s %s %s' % (
+      compiler_cmd, driver_mode_cmd, std_cmd,
+      isysroot_cmd, sanitizers_cmd, include_cmd)
 
 config.substitutions.append(('%cpp_compiler',
       generate_compiler_cmd(is_cpp=True, fuzzer_enabled=True)
       ))
 
 config.substitutions.append(('%c_compiler',
       generate_compiler_cmd(is_cpp=False, fuzzer_enabled=True)
       ))
 
 config.substitutions.append(('%no_fuzzer_cpp_compiler',
       generate_compiler_cmd(is_cpp=True, fuzzer_enabled=False)
       ))
 
 config.substitutions.append(('%no_fuzzer_c_compiler',
       generate_compiler_cmd(is_cpp=False, fuzzer_enabled=False)
       ))

lib/Fuzzer/test/lit.site.cfg.in

 config.test_exec_root = "@CMAKE_CURRENT_BINARY_DIR@"
 config.llvm_tools_dir = "@LLVM_TOOLS_DIR@"
 config.has_lsan = True if @HAS_LSAN@ == 1 else False
-config.cpp_compiler = "@LIBFUZZER_TEST_CXX_COMPILER@"
 config.c_compiler = "@LIBFUZZER_TEST_COMPILER@"
 config.osx_sysroot = "@CMAKE_OSX_SYSROOT@"
 config.cmake_binary_dir = "@CMAKE_BINARY_DIR@"
 config.target_triple = "@TARGET_TRIPLE@"
 lit_config.load_config(config, "@CMAKE_CURRENT_SOURCE_DIR@/lit.cfg")