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Re: C11 compiler and runtime support?
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: Carlos O'Donell <carlos at redhat dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>, Andreas Jaeger <aj at suse dot com>
- Date: Mon, 9 Dec 2013 00:40:59 +0000
- Subject: Re: C11 compiler and runtime support?
- Authentication-results: sourceware.org; auth=none
- References: <52A20182 dot 5060007 at redhat dot com>
On Fri, 6 Dec 2013, Carlos O'Donell wrote:
> Are we considering that gcc and glibc are C11 ready?
Yes, as of GCC 4.9 and glibc 2.16.
> I know you've made comments that you feel that the
> C11 support equivalent to the C99 support.
> Does that mean that glibc can declare the C11 support
> ready for pre-production uses (modulo bugs)?
Yes. Obviously bugs may be found as people start using the features more
widely, though I think that's most likely with the atomics support in GCC
rather than the library features.
> Should we have a wiki page to track this feature and
> missing functionality such that interested parties can
> sign up to do more work?
Describing exactly what's meant by supporting a standard is rather
complicated and liable to have lots of caveats about e.g. particular
configurations or optional features.
We already have
mentions various possible additions, including the optional C11 threads
library (which as far as I know no-one has expressed any interest in
implementing for glibc). That's not a small project, of course. Then
there's the matter of the optional Annex K bounds-checking interfaces.
Ulrich Bayer posted some initial patch versions and the assignment
paperwork was completed and there was some review, but there haven't been
updated versions posted since June; it needs patches posting / pinging
until we get consensus on a version to include (and then there will be
various extra functions from that Annex to add bit by bit). For the
__STDC_WANT_LIB_EXT1__ handling it may make sense not to include
consistency checks for now, given the WG14 mood for simpler __STDC_WANT_*
Strictly there's the matter of using _Noreturn in glibc headers for C11
compilers not claiming to be GCC - see analysis at
<https://sourceware.org/ml/libc-alpha/2012-01/msg00084.html> - but that's
not much of an issue in practice.
It would be useful for people to add such features to the todo list if not
already there. Conformance bugs (C or POSIX) should be filed in Bugzilla
if not already there. It would be useful for someone to go through past
discussions of such issues
(and followups with some analysis) and ensure that all identified issues
from those discussions are in Bugzilla or the todo list as appropriate.
In general the main issues with optional floating-point features (Annexes
F and G, in both C99 and C11) are on the GCC side rather than the glibc
side, and while there may be some its admitting more or less local
incremental fixes, proper GCC support for exceptions and rounding modes
would probably take several person-months.
Joseph S. Myers