[cfe-dev] Overlap/clash between libc++ and libsupc++

[Michael Spencer]

On Tue, Nov 6, 2012 at 12:44 AM, M.E. O'Neill <oneill at cs.hmc.edu> wrote:
> [This message got lost in the shuffle during the mail outage back in August, so I'm resending it.]
>
> In trying to use libc++ on Linux, I attempted to go the simple route of using libsupc++ to provide the ABI support, but in addition to a crash in std::uncaught_exception() (see http://llvm.org/bugs/show_bug.cgi?id=13669), I've noticed that the following functions are defined in *both* libsupc++ and libc++.  Note that these are in std::, *not* std::__1:: so these are genuine duplicate definitions.
>
>         operator delete(void*, std::nothrow_t const&)
>         operator delete[](void*, std::nothrow_t const&)
>         operator new(unsigned long, std::nothrow_t const&)
>         operator new[](unsigned long, std::nothrow_t const&)
>         std::bad_alloc::what() const
>         std::bad_alloc::~bad_alloc()
>         std::bad_cast::what() const
>         std::bad_cast::~bad_cast()
>         std::bad_exception::what() const
>         std::bad_exception::~bad_exception()
>         std::bad_typeid::what() const
>         std::bad_typeid::~bad_typeid()
>         std::current_exception()
>         std::exception::what() const
>         std::exception::~exception()
>         std::nested_exception::~nested_exception()
>         std::set_new_handler(void (*)())
>         std::set_terminate(void (*)())
>         std::set_unexpected(void (*)())
>         std::terminate()
>         std::uncaught_exception()
>         std::unexpected()
>
> In addition to the duplication (which may be problematic by itself?), libc++ doesn't currently provide good implementations for some of these functions (for example, on Linux, libc++'s version of std::uncaught_exception() actually just calls abort, causing the crash I mentioned earlier), it would seem like the best thing to do on Linux would be to not provide them at all.
>
> Thoughts?
>
> One thought I had was to just #ifdef out the code in src/new.cpp and src/exception.cpp but that fails because libc++ relies on (at least)
>
>         std::exception_ptr::~exception_ptr()
>         std::bad_alloc::bad_alloc()
>         std::exception_ptr::exception_ptr(std::exception_ptr const&)
>         std::exception_ptr::operator=(std::exception_ptr const&)
>         std::rethrow_exception(std::exception_ptr)
>
> which are defined by libc++, but not defined by libsupc++.
>
> In general, as others have said multiple times on this mailing list, it would be really nice if there was a simple way for people to use clang with libc++ on Linux and have it "just work".   I don't really mind *how* that is accomplished.  I don't even care about compatibility with code compiled by GCC. It still amazes me that there isn't an *easy* recipe to follow for this.
>
>    M.E.O.
>
> P.S.  Also of interest, libc++ (only) provides the following functions.
>
>         std::__throw_bad_alloc()
>         std::bad_alloc::bad_alloc()
>         std::bad_array_new_length::bad_array_new_length()
>         std::bad_array_new_length::what() const
>         std::bad_array_new_length::~bad_array_new_length()
>         std::bad_cast::bad_cast()
>         std::bad_typeid::bad_typeid()
>         std::domain_error::~domain_error()
>         std::exception_ptr::exception_ptr(std::exception_ptr const&)
>         std::exception_ptr::operator=(std::exception_ptr const&)
>         std::exception_ptr::~exception_ptr()
>         std::get_new_handler()
>         std::get_terminate()
>         std::get_unexpected()
>         std::invalid_argument::~invalid_argument()
>         std::length_error::~length_error()
>         std::logic_error::logic_error(char const*)
>         std::logic_error::logic_error(std::logic_error const&)
>         std::logic_error::operator=(std::logic_error const&)
>         std::logic_error::what() const
>         std::logic_error::~logic_error()
>         std::nested_exception::nested_exception()
>         std::nested_exception::rethrow_nested() const
>         std::out_of_range::~out_of_range()
>         std::overflow_error::~overflow_error()
>         std::range_error::~range_error()
>         std::rethrow_exception(std::exception_ptr)
>         std::runtime_error::operator=(std::runtime_error const&)
>         std::runtime_error::runtime_error(char const*)
>         std::runtime_error::runtime_error(std::runtime_error const&)
>         std::runtime_error::what() const
>         std::runtime_error::~runtime_error()
>         std::underflow_error::~underflow_error()
>
>
> P.P.S. on Jul 10, 2012, at 6:28 AM, Joerg Sonnenberger <joerg at britannica.bec.de> wrote:
>> Not only them. Last time I checked, libc++abi and libc++ still don't have working iostream on Linux, i.e. abort() as soon as you try to use cout or cerr.
>
> I believe that may have been due to std::uncaught_exception() as mentioned above and documented in bug 13669.  Certainly that's why I/O was crashing for me.
>
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There now is a simplish way. The CMake build now has support for
properly handling libc++ on Linux with libsupc++ ABI. The interface
could be much nicer, but it does work.

1) Configure libc++ with CMAKE_INSTALL_PREFIX=/usr (clang only looks
for libc++ here on Linux)
2) Set LIBCXX_CXX_ABI to libsupc++ and reconfigure.
3) Set LIBCXX_LIBSUPCXX_INCLUDE_PATHS to a ; separated list of paths
to the libsupc++ headers. On my linux machine this is
"usr/include/c++/4.6;/usr/include/c++/4.6/x86_64-linux-gnu"
4) Reconfigure
5) Generate, build, install

- Michael Spencer