Travis CI shows linking errors on Linux and OS X when __cxa_uncaught_exceptions
is used to implement uncaught_exceptions. There's probably some library missing,
which should be linked in implicitly by the compiler, or the library indeed
does not export the symbol. In any case, __cxa_get_globals-based implementation
should provide the same effect.
This is in attempt to debug/work around strange issues in CI with cxxabi.h
provided by libc++abi-dev. The header declares __cxa_uncaught_exceptions
function, but on linking stage the function is missing. The current theory
is that the header and the libc++abi library do not match on CI machines for
some reason, and this commit tries to mitigate or verify that.
Apparently, gcc < 4.7 on Linux also don't have __cxa_get_globals
declaration in cxxabi.h. Declare the function ourselves.
Also, on OpenBSD it seems there is no declaration either, and
on that platform the function implementation has no exception
specification, like on FreeBSD. Add a declaration of that platform.
Lastly, changed __cxa_get_globals and _getptd-based implementations
to avoid violating strict aliasing rules. This is still formally UB
to access structure fields like we do, but this is one less reason to
cause miscompilation or compiler warnings.
This should resolve gcc errors caused by mismatch of the return types of
aur declaration of __cxa_get_globals and the original in cxxabi.h.
Fixes https://github.com/boostorg/core/issues/45.
The uncaught_exceptions function is functionally equivalent to
unhandled_exceptions_count in Boost.Log and implements functionality
similar to the same named C++17 standard function. Tests and docs are
also included.
One notable difference from std::uncaught_exceptions is that the return
type is unsigned rather than signed. This is deliberate as uncaught_exceptions
must never return a negative value and unsigned int better documents that.
Theoretically, as a counter, it may also overflow.
