From: Tejun Heo <tj@kernel.org> To: Jiri Slaby <jirislaby@kernel.org> Cc: Christoph Hellwig <hch@infradead.org>, linux-kernel@vger.kernel.org, Martin Liska <mliska@suse.cz>, Josef Bacik <josef@toxicpanda.com>, Jens Axboe <axboe@kernel.dk>, cgroups@vger.kernel.org, linux-block@vger.kernel.org Subject: Re: [PATCH] block/blk-iocost (gcc13): cast enum members to int in prints Date: Tue, 1 Nov 2022 06:46:35 -1000 [thread overview] Message-ID: <Y2FNa4bGhJoevRKT@slm.duckdns.org> (raw) In-Reply-To: <d833ad15-f458-d43d-cab7-de62ff54a939@kernel.org> Hello, On Tue, Nov 01, 2022 at 06:46:56AM +0100, Jiri Slaby wrote: > Yes. The real problem is that using anything else then an INT_MIN <= x <= > INT_MAX _constant_ in an enum is undefined in ANSI C < 2x (in particular, 1 > << x is undefined too). gcc manual defines unsigned int on the top of that > as defined too (so this holds for our -std=g*). > > > I suppose the most reasonable thing to do here is just splitting them into > > separate enum definitions. Does anyone know how this behavior change came to > > be? > > C2x which introduces un/signed long enums. See the bug I linked in the > commit log: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36113 I see. So, it was an extension but the new standard is defined differently and we're gonna end up with that behavior. > The change is also turned on in < C2x on purpose. AIUI, unless there is too > much breakage. So we'd need to sort it out in (rather distant) future anyway > (when we come up to -std=g2x). The part that the new behavior applying to <C2x feels like an odd decision. I'm having a hard time seeing the upsides in doing so but maybe that's just me not knowing the area well enough. > > Do we know whether clang is gonna be changed the same way? > > In C2x, Likely. In < C2x, dunno what'd be the default. It looks like we can do one of the following two: * If gcc actually changes the behavior for <c2x, split the enums according to their sizes. This feels rather silly but I can't think of a better way to cater to divergent compiler behaviors. * If gcc doesn't change the behavior for <c2x, there's nothing to do for the time being. Later when we switch to -std=g2x, we can just change the format strings to use the now larger types. Does the above make sense? Thanks. -- tejun
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From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> To: Jiri Slaby <jirislaby-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Cc: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Martin Liska <mliska-AlSwsSmVLrQ@public.gmane.org>, Josef Bacik <josef-DigfWCa+lFGyeJad7bwFQA@public.gmane.org>, Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Subject: Re: [PATCH] block/blk-iocost (gcc13): cast enum members to int in prints Date: Tue, 1 Nov 2022 06:46:35 -1000 [thread overview] Message-ID: <Y2FNa4bGhJoevRKT@slm.duckdns.org> (raw) In-Reply-To: <d833ad15-f458-d43d-cab7-de62ff54a939-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Hello, On Tue, Nov 01, 2022 at 06:46:56AM +0100, Jiri Slaby wrote: > Yes. The real problem is that using anything else then an INT_MIN <= x <= > INT_MAX _constant_ in an enum is undefined in ANSI C < 2x (in particular, 1 > << x is undefined too). gcc manual defines unsigned int on the top of that > as defined too (so this holds for our -std=g*). > > > I suppose the most reasonable thing to do here is just splitting them into > > separate enum definitions. Does anyone know how this behavior change came to > > be? > > C2x which introduces un/signed long enums. See the bug I linked in the > commit log: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36113 I see. So, it was an extension but the new standard is defined differently and we're gonna end up with that behavior. > The change is also turned on in < C2x on purpose. AIUI, unless there is too > much breakage. So we'd need to sort it out in (rather distant) future anyway > (when we come up to -std=g2x). The part that the new behavior applying to <C2x feels like an odd decision. I'm having a hard time seeing the upsides in doing so but maybe that's just me not knowing the area well enough. > > Do we know whether clang is gonna be changed the same way? > > In C2x, Likely. In < C2x, dunno what'd be the default. It looks like we can do one of the following two: * If gcc actually changes the behavior for <c2x, split the enums according to their sizes. This feels rather silly but I can't think of a better way to cater to divergent compiler behaviors. * If gcc doesn't change the behavior for <c2x, there's nothing to do for the time being. Later when we switch to -std=g2x, we can just change the format strings to use the now larger types. Does the above make sense? Thanks. -- tejun
next prev parent reply other threads:[~2022-11-01 16:46 UTC|newest] Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-10-31 11:45 [PATCH] block/blk-iocost (gcc13): cast enum members to int in prints Jiri Slaby (SUSE) 2022-10-31 11:45 ` Jiri Slaby (SUSE) 2022-10-31 12:24 ` Christoph Hellwig 2022-10-31 12:24 ` Christoph Hellwig 2022-10-31 17:57 ` Tejun Heo 2022-11-01 5:46 ` Jiri Slaby 2022-11-01 5:46 ` Jiri Slaby 2022-11-01 16:46 ` Tejun Heo [this message] 2022-11-01 16:46 ` Tejun Heo 2022-11-02 8:35 ` David Laight 2022-11-02 16:27 ` 'Tejun Heo' 2022-11-02 16:43 ` 'Tejun Heo' 2022-11-02 16:43 ` 'Tejun Heo' 2022-12-12 12:14 ` Jiri Slaby 2022-12-12 12:14 ` Jiri Slaby 2022-12-12 21:46 ` 'Tejun Heo' 2022-12-13 8:30 ` David Laight 2022-12-13 11:15 ` Jiri Slaby 2022-12-13 11:15 ` Jiri Slaby 2022-12-13 11:50 ` David Laight 2022-12-13 11:50 ` David Laight 2022-12-13 12:05 ` Jiri Slaby 2022-12-13 12:05 ` Jiri Slaby 2022-12-13 12:58 ` David Laight 2022-12-13 12:58 ` David Laight
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