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    The Word: C++ Std::Condition_Variable Null Pointer Derreference

    http://upliftingpresence.blogspot.com


    This story is about a bug generated by g++ and clang compilers (at least)
    The condition_variables is a feature on the standard library of c++ (libstdc++), when its compiled statically a weird asm code is generated.


    Any example on the link below will crash if its compiled statically:
     https://en.cppreference.com/w/cpp/thread/condition_variable



    In this case the condition_variable.wait() crashed, but this happens with other methods, a simple way to trigger it:




    If this program is compiled dynamically the crash doesn't occur:

    Looking the dissasembly there is a surprise created by the compiler:


    Compilers:
        g++  9.2.1+20200130-2
        clang++ v9

    Both compilers are generating the "call 0x00"

    If we check this call in a dynamic compiled:




    The implementation of condition_variable in github:
    https://github.com/gcc-mirror/gcc/blob/b7c9bd36eaacac42631b882dc67a6f0db94de21c/libstdc%2B%2B-v3/include/std/condition_variable


    The compilers can't copile well this code in static,  and same happens on  other condition_variable methods.
    I would say the _lock is being assembled improperly in static, is not exacly a null pointer derreference but the effects are the same, executing code at address 0x00 which on linux is a crash on most of cases.

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    Posted by BLoG cHiC  

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