[Bug 201784] [libcxxrt] C++ dynamic_cast does not recognize same types across dynamically loaded modules when downcasting

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=201784

David Chisnall <theraven at FreeBSD.org> changed:

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                 CC|                            |theraven at FreeBSD.org

--- Comment #3 from David Chisnall <theraven at FreeBSD.org> ---
This is a known issue (I can't find the closed bug report for it at the
moment).  If you don't link with -Wl,-export-dynamic, then the RTTI symbols
will not be merged.  This then means that the pointer comparison in libcxxrt
will fail.  The work-around that libsupc++ implements replaces the pointer
comparison with string comparison.  This adds a noticeable performance hit in
all dynamic_casts.  We decided not to impose a performance hit on all C++
programs just to benefit people who can pass different linker flags to avoid a
bug.

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