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From: Tejun Heo <>
To: Jiri Slaby <>
Cc: Christoph Hellwig <>,, Martin Liska <>,
	Josef Bacik <>, Jens Axboe <>,,
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: <> (raw)
In-Reply-To: <>


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:

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?



  reply	other threads:[~2022-11-01 16:46 UTC|newest]

Thread overview: 15+ 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 12:24 ` Christoph Hellwig
2022-10-31 17:57   ` Tejun Heo
2022-11-01  5:46     ` Jiri Slaby
2022-11-01 16:46       ` Tejun Heo [this message]
2022-11-02  8:35         ` David Laight
2022-11-02 16:27           ` 'Tejun Heo'
2022-11-02 16:43             ` 'Tejun Heo'
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 11:50                       ` David Laight
2022-12-13 12:05                         ` Jiri Slaby
2022-12-13 12:58                           ` David Laight

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