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std::lognormal_distribution can overwrite const memory #52906

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Quuxplusone opened this issue Dec 28, 2021 · 2 comments
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std::lognormal_distribution can overwrite const memory #52906

Quuxplusone opened this issue Dec 28, 2021 · 2 comments
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@Quuxplusone
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libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi.

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@Quuxplusone
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#include <cassert>
#include <random>

int main() {
    typedef std::lognormal_distribution<> D;
    typedef D::param_type P;
    typedef std::mt19937 G;
    G g;
    D d;

    const P p1 = d.param();
    const P p2 = d.param();
    assert(p1 == p2);
    double r1 = d(g, p1); // This line must not modify p1.
    assert(p1 == p2);
}

libc++ fails the final assert, because D::param_type secretly contains a whole normal_distribution object(!) and then d(g, p1) secretly contains a const_cast so it can call that normal_distribution's operator().
@Quuxplusone Quuxplusone added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Dec 28, 2021
@Quuxplusone Quuxplusone self-assigned this Dec 28, 2021
@Quuxplusone
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This is now https://reviews.llvm.org/D116344

@cebowler
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cebowler commented May 5, 2022

We haven't shipped this change on IBM's Open XL C++ compiler yet so I haven't been able to assess whether or not any customers will need to define _LIBCPP_ABI_OLD_LOGNORMAL_DISTRIBUTION.

As a courtesy I would appreciate it if we can add a deprecation warning (when _LIBCPP_ABI_OLD_LOGNORMAL_DISTRIBUTION is defined) in LLVM 15 with intention to remove it in LLVM 16.

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