Runtime error when using UBSan with clang-10

[maximaximal]

The enum manipulation code of shared_library_load_mode produces an invalid-enum-load error with clang-10's UBSan in line 226 of shared_library_load_mode.hpp. This seems like a true positive, as the enumeration really becomes an invalid value at this stage.

This is the produced error output:

/usr/include/boost/dll/shared_library_load_mode.hpp:226:19: runtime error: load of value 4278190079, which is not a valid value for type 'boost::dll::load_mode::type'
SUMMARY: UndefinedBehaviorSanitizer: invalid-enum-load /usr/include/boost/dll/shared_library_load_mode.hpp:226:19 in 

A quick fix would be adding the invalid enum value that this manipulation code produces (4278190079) to the enum. enum above:

#else
    rtld_deepbind                         = RTLD_DEEPBIND,
#endif

    append_decorations                    = 0x00800000,
    search_system_folders                 = (append_decorations << 1),

    _ubsan_fix = 4278190079 // this line fixes the issue for the time being
#endif
};

Completely fixing this undefined behavior seems to require some changes in how the manipulation code is used... But with this fix, I can use UBSan again. I hope this report helps!

[apolukhin]

Could you please provide a testcase, to reproduce the issue?

[maximaximal]

Yes, the issue occurred with the standard quickstart example:

#include <boost/dll.hpp>

int main() {
    boost::dll::shared_library lib("/lib64/libc.so.6");
}

Compiled using clang 11.0.0 (downloaded from its releases page, I used the SuSE Linux Enterprise Server 12SP4 x86_64 variant) using the following command:

/opt/llvm11/bin/clang++ boost-dll-bug.cpp -ldl -lboost_filesystem -lboost_system -fsanitize=undefined -o boost-dll-bug

The produced binary prints the following runtime error on OpenSUSE Leap 15.2, using boost version 1.66:

/usr/include/boost/dll/shared_library_load_mode.hpp:226:19: runtime error: load of value 4278190079, which is not a valid value for type 'boost::dll::load_mode::type'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /usr/include/boost/dll/shared_library_load_mode.hpp:226:19 in 
/usr/include/boost/dll/shared_library_load_mode.hpp:222:69: runtime error: load of value 4278190079, which is not a valid value for type 'boost::dll::load_mode::type'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /usr/include/boost/dll/shared_library_load_mode.hpp:222:69 in 

When I initially reported this bug, it also occurred on Arch Linux with the then-newest boost version, which is why I suspected this to be new compared to #30. But after testing again with the updated boost version 1.75, the issue is gone. I couldn't find the change that fixed this bug, but I suspect something in boost 1.74 fixed it, as nothing else really happened in the meantime.

It would be interesting to find out what caused this undefined behavior on Arch Linux, but as it is fixed, I can close this issue. Thank you for looking into this!