[libcxx-dev] Building a program with -D_LIBCPP_DEBUG=1 against a libc++ that is not itself built with that define

[Arthur O'Dwyer via libcxx-dev]

On Fri, Oct 29, 2021 at 9:09 AM Stephan Bergmann via libcxx-dev <
libcxx-dev at lists.llvm.org> wrote:

> At least with recent LLVM 14 trunk,
> [...]
> > Segmentation fault
> [...]
> because the std::string instance returned from std::to_string
> (implemented in libc++, not itself built with -D_LIBCPP_DEBUG=1) never
> called __libcpp_db::__insert_c(this), so __libcpp_db::swap doesn't find
> it in the __cbeg_/__cend_ table and then dereferences a null pointer.
>
> I wonder how usable and mature -D_LIBCPP_DEBUG=1 is considered in
> practice.  Is this a well-known shortcoming (in which case it might be
> good to mention it explicitly in libcxx/docs/DesignDocs/DebugMode.rst,
> beyond just "Users should compile their whole program at the same
> debugging level."), or would it be worth filing a bug?
>

Just to link up the two threads: I ran into this earlier this year.
https://lists.llvm.org/pipermail/libcxx-dev/2021-May/001119.html
It is the reason at least one test in libcxx/test/ is marked
"LIBCXX-DEBUG-FIXME". I don't have any ideas how to fix it, though.

–Arthur
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