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From: David Laight <David.Laight@ACULAB.COM>
To: 'Jiri Slaby' <jirislaby@kernel.org>, 'Tejun Heo' <tj@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
	"linux-kernel@vger.kernel.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" <cgroups@vger.kernel.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: RE: [PATCH] block/blk-iocost (gcc13): cast enum members to int in prints
Date: Tue, 13 Dec 2022 12:58:10 +0000	[thread overview]
Message-ID: <d26f03e828c94df5b4653ac6980def59@AcuMS.aculab.com> (raw)
In-Reply-To: <c7539121-c8fc-b4b7-b722-ead833420b2b@kernel.org>

From: Jiri Slaby <jirislaby@kernel.org>
> Sent: 13 December 2022 12:05
> 
> On 13. 12. 22, 12:50, David Laight wrote:
> > From: Jiri Slaby
> >> Sent: 13 December 2022 11:15
> >>
...
> >>>> Oh man, it's kinda crazy that the compiler is changing in a way that the
> >>>> same piece of code can't be compiled the same way across two adjoining
> >>>> versions of the same compiler. But, yeah, if that's what gcc is gonna do and
> >>>> splitting enums is the only way to be okay across the compiler versions,
> >>>> there isn't any other choice we can make.
> >>>
> >>> It is also a silent code-breaker.
> >>> Compile this for 32bit x86:
> >>>
> >>> enum { a = 1, b = ~0ull};
> >>
> >> But having ull in an enum is undefined anyway. C99 allows only int
> >> constants. gnuC supports ulong expressions (IIRC).
> >
> > gcc supports 'long long' as well - 64bit on 32bit systems.
> 
> Can you elaborate what's source of this? ...

Experimentation, for example:

https://godbolt.org/z/n4rnc7cKG


	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

WARNING: multiple messages have this Message-ID (diff)
From: David Laight <David.Laight-ZS65k/vG3HxXrIkS9f7CXA@public.gmane.org>
To: 'Jiri Slaby' <jirislaby-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	'Tejun Heo' <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	"linux-kernel-u79uwXL29TY76Z2rM5mHXA@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"
	<cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"linux-block-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, 13 Dec 2022 12:58:10 +0000	[thread overview]
Message-ID: <d26f03e828c94df5b4653ac6980def59@AcuMS.aculab.com> (raw)
In-Reply-To: <c7539121-c8fc-b4b7-b722-ead833420b2b-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>

From: Jiri Slaby <jirislaby@kernel.org>
> Sent: 13 December 2022 12:05
> 
> On 13. 12. 22, 12:50, David Laight wrote:
> > From: Jiri Slaby
> >> Sent: 13 December 2022 11:15
> >>
...
> >>>> Oh man, it's kinda crazy that the compiler is changing in a way that the
> >>>> same piece of code can't be compiled the same way across two adjoining
> >>>> versions of the same compiler. But, yeah, if that's what gcc is gonna do and
> >>>> splitting enums is the only way to be okay across the compiler versions,
> >>>> there isn't any other choice we can make.
> >>>
> >>> It is also a silent code-breaker.
> >>> Compile this for 32bit x86:
> >>>
> >>> enum { a = 1, b = ~0ull};
> >>
> >> But having ull in an enum is undefined anyway. C99 allows only int
> >> constants. gnuC supports ulong expressions (IIRC).
> >
> > gcc supports 'long long' as well - 64bit on 32bit systems.
> 
> Can you elaborate what's source of this? ...

Experimentation, for example:

https://godbolt.org/z/n4rnc7cKG


	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

  reply	other threads:[~2022-12-13 12:58 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
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 [this message]
2022-12-13 12:58                             ` David Laight

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