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Laurent Stacul authored
Summary: Hello, Adding data in those variables can have an impact upon feature detections. For instance, using 'check_cxx_source_compiles' to detect libatomic can fail because the link command uses -rdynamic and the list of shared objects. But as libcrypto needs zlib which is not added in CMAKE_REQUIRED_LIBRARIES, the test will fail, as we can see here (from CMakeError.log, modified for readability): ``` $ g++ -DNDEBUG -O3 -flto -ffat-lto-objects -fuse-linker-plugin -std=gnu++20 -fno-working-directory -ggdb3 -Wno-error=maybe-uninitialized -Wno-error=shadow=compatible-local -Wno-error=array-bounds -Wno-error=stringop-overflow -DFOLLY_CPP_ATOMIC_BUILTIN -std=gnu++20 -DNDEBUG -O3 -Wl,-flto -ffat-lto-objects -fuse-linker-plugin -fno-working-directory -ggdb3 -L /path/to/mylibs -pthread -lgflags -lglog -levent -levent_core -ldouble-conversion -rdynamic CMakeFiles/cmTC_4a1a2.dir/src.cxx.o -o cmTC_4a1a2 /path/to/mylibs/libgflags.so /path/to/mylibs/libssl.so /path/to/mylibs/libcrypto.so -ldl ld: warning: libz.so.1, needed by /path/to/mylibs/libssl.so, not found (try using -rpath or -rpath-link) ld: /path/to/mylibs/libcrypto.so: undefined reference to `deflateInit_' ld: /path/to/mylibs/libcrypto.so: undefined reference to `deflate' ld: /path/to/mylibs/libcrypto.so: undefined reference to `deflateEnd' ld: /path/to/mylibs/libcrypto.so: undefined reference to `inflate' ld: /path/to/mylibs/libcrypto.so: undefined reference to `inflateInit_' ld: /path/to/mylibs/libcrypto.so: undefined reference to `inflateEnd' ld: /path/to/mylibs/libcrypto.so: undefined reference to `zError' ``` I only give the example of the detection of libatomic but this error prevents the probing mechanism from detecting other features like the presence of ASN1_TIME_diff function or elf.h. I propose to avoid setting things in those variables or, if it needs to be modified, clean it up after it was useful. Pull Request resolved: https://github.com/facebook/folly/pull/1463 Reviewed By: yfeldblum Differential Revision: D24000700 Pulled By: Orvid fbshipit-source-id: ace1b5b5dee6362c4a30ab0a986984005e7dc569
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