fuzzers: Fix CFLAGS

nelhage · nelhage · commit 4cd34f1d941b · 2025-03-03T22:51:52.000Z
I'm seeing the current fuzzer build fail (during `cmake`) like so: ``` -- Performing Test IS_FSANITIZE_FUZZER_NO_LINK_SUPPORTED -- Performing Test IS_FSANITIZE_FUZZER_NO_LINK_SUPPORTED - Failed CMake Error at cmake/AddCFlagIfSupported.cmake:17 (message): Required flag -fsanitize=fuzzer-no-link is not supported Call Stack (most recent call first): fuzzers/CMakeLists.txt:6 (add_c_flag) ``` The cmake log output contains something like so: ``` /src/aflplusplus/libAFLDriver.a(aflpp_driver.o): in function `main': aflpp_driver.c:(.text+0x11b): undefined reference to `LLVMFuzzerTestOneInput' clang: error: linker command failed with exit code 1 (use -v to see invocation) ``` I haven't figured out exactly what's happening, but I believe that once line 5 has added `-fsanitize=fuzzer` to `CFLAGS`, future compile- tests **also** use it during linking. This in turn pulls in the fuzzer `main`, which expects an `LLVMFuzzerTestOneInput` symbol, and thus fails. Instead, just add `-fsanitize=fuzzer-no-link` to CFLAGS (as suggested [by the documentation][libfuzzer]), and then use `-fsanitize=fuzzer` only for linking the fuzzer targets. At least in my environment, this results in a working fuzzer build. [libfuzzer]: https://llvm.org/docs/LibFuzzer.html#fuzzer-usage
diff --git a/fuzzers/CMakeLists.txt b/fuzzers/CMakeLists.txt
@@ -2,7 +2,6 @@
 
 if(BUILD_FUZZERS AND NOT USE_STANDALONE_FUZZERS)
 	set(CMAKE_REQUIRED_FLAGS "-fsanitize=fuzzer-no-link")
-	add_c_flag(-fsanitize=fuzzer)
 	add_c_flag(-fsanitize=fuzzer-no-link)
 	unset(CMAKE_REQUIRED_FLAGS)
 endif()
@@ -24,6 +23,7 @@ foreach(fuzz_target_src ${SRC_FUZZERS})
 	target_include_directories(${fuzz_target_name} SYSTEM PRIVATE ${LIBGIT2_SYSTEM_INCLUDES})
 
 	target_link_libraries(${fuzz_target_name} ${LIBGIT2_SYSTEM_LIBS})
+	target_link_options(${fuzz_target_name} PRIVATE "-fsanitize=fuzzer")
 
 	add_test(${fuzz_target_name} "${CMAKE_CURRENT_BINARY_DIR}/${fuzz_target_name}" "${CMAKE_CURRENT_SOURCE_DIR}/corpora/${fuzz_name}")
 endforeach()
