[libFuzzer] Run libFuzzer unit tests only on host architecture.

[george.karpenkov]

Summary

LIT tests are used to test other cross-compiled architectures,

unit tests are only run on the host.
NFC now as currently only a single architecture is supported.

[morehouse]

What happens without this change? Do we get failing tests on other architectures, or does the build fail?

[george.karpenkov]

What happens without this change?

IIRC that's how it is for all sanitizers.
I'm not sure about the "hard" reason, but I can see a few soft ones:

• There's no supporting machinery for running those on devices
• Unit tests are allowed to have dependencies which do not necessarily compile on the device
• Integration tests are more suitable for testing multi-arch support

[george.karpenkov]

IIRC that's how it is for all sanitizers.

I've meant that unit tests run only on the host for all sanitizers.

lib/fuzzer/tests/CMakeLists.txt

 else()
   list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS -lstdc++ -lpthread)
 endif()
 
 if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND COMPILER_RT_LIBCXX_PATH)
   list(APPEND LIBFUZZER_UNITTEST_CFLAGS -nostdinc++ -D_LIBCPP_ABI_VERSION=Fuzzer)
 endif()
 
-foreach(arch ${FUZZER_SUPPORTED_ARCH})
-  set(LIBFUZZER_TEST_RUNTIME RTFuzzerTest.${arch})
-  if(APPLE)
-    set(LIBFUZZER_TEST_RUNTIME_OBJECTS
-      $<TARGET_OBJECTS:RTfuzzer.osx>)
-  else()
-    set(LIBFUZZER_TEST_RUNTIME_OBJECTS
-      $<TARGET_OBJECTS:RTfuzzer.${arch}>)
-  endif()
-  add_library(${LIBFUZZER_TEST_RUNTIME} STATIC
-    ${LIBFUZZER_TEST_RUNTIME_OBJECTS})
-  set_target_properties(${LIBFUZZER_TEST_RUNTIME} PROPERTIES
-    ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
-    FOLDER "Compiler-RT Runtime tests")
+# libFuzzer unit tests are only run on the host machine.
+set(arch "x86_64")
+
 
-  if("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux" AND COMPILER_RT_LIBCXX_PATH)
-    set(LIBFUZZER_TEST_RUNTIME_DEPS libcxx_fuzzer_${arch}-build)
-    set(LIBFUZZER_TEST_RUNTIME_CFLAGS -isystem ${COMPILER_RT_LIBCXX_PATH}/include)
-    set(LIBFUZZER_TEST_RUNTIME_LINK_FLAGS ${LIBCXX_${arch}_PREFIX}/lib/libc++.a)
-  endif()
 
-  set(FuzzerTestObjects)
-  generate_compiler_rt_tests(FuzzerTestObjects
-    FuzzerUnitTests "Fuzzer-${arch}-Test" ${arch}
-    SOURCES FuzzerUnittest.cpp ${COMPILER_RT_GTEST_SOURCE}
-    RUNTIME ${LIBFUZZER_TEST_RUNTIME}
-    DEPS gtest ${LIBFUZZER_TEST_RUNTIME_DEPS}
-    CFLAGS ${LIBFUZZER_UNITTEST_CFLAGS} ${LIBFUZZER_TEST_RUNTIME_CFLAGS}
-    LINK_FLAGS ${LIBFUZZER_UNITTEST_LINK_FLAGS} ${LIBFUZZER_TEST_RUNTIME_LINK_FLAGS})
-  set_target_properties(FuzzerUnitTests PROPERTIES
-    RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
-endforeach()