[Bug libstdc++/85813] make_exception_ptr should support __cxa_init_primary_exception path even with -fno-exceptions

cvs-commit at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Thu Dec 9 23:29:40 GMT 2021


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85813

--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:a8e02a00a0fcac42657c8ef7921566e42db8ef49

commit r12-5880-ga8e02a00a0fcac42657c8ef7921566e42db8ef49
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Dec 9 18:37:38 2021 +0000

    libstdc++: Make std::make_exception_ptr work with -fno-exceptions [PR85813]

    This allows std::make_exception_ptr to be used in a translation unit
    compiled with -fno-exceptions. This works because the new implementation
    added for PR 68297 doesn't need to throw or catch anything. The catch is
    there to handle exceptions from the constructor of the exception object,
    which we can assume won't happen in a -fno-exceptions TU and so use the
    __catch macro instead. If the constructor does throw (because it's
    defined in a different TU which was compiled with exceptions enabled)
    then that exception will propagate to the make_exception_ptr caller.
    That seems acceptable for a program that is trying to mix & match TUs
    compiled with and without exceptions, and using types that throw when
    constructed. That should be rare, and can't reasonably be expected to
    have sensible behaviour.

    This also enables the new implementation for targets that use a
    non-standard calling convention for the exceptionDestructor callback
    (specifically, mingw, which uses __thiscall). All we need to do is mark
    the __dest_thunk function template with the right calling convention.

    Finally, the useless no-op definition of make_exception_ptr (which is
    only used if both RTTI and exceptions are disabled) is marked
    always_inline, to ensure that the linker won't keep that definition and
    discard the functional ones when both definitions of the function are
    present in the link. An alternative would be to add the abi_tag
    attribute to the useless definition, but making it always_inline should
    work, and it's small enough to always be inlined reliably.

    libstdc++-v3/ChangeLog:

            PR libstdc++/85813
            * libsupc++/exception_ptr.h (__dest_thunk): Add macro for
            destructor calling convention.
            (make_exception_ptr): Enable non-throwing implementation for
            -fno-exceptions and for non-standard calling conventions. Use
            always_inline attribute on the useless no-rtti no-exceptions
            definition.
            * testsuite/18_support/exception_ptr/64241.cc: Add -fno-rtti so
            the no-op implementation is still used.


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