GNU bug report logs - #78903
[PATCH] ISO C99 does not support _Noreturn

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Helmut Eller <eller.helmut <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: [PATCH] ISO C99 does not support _Noreturn
Date: Thu, 26 Jun 2025 09:20:51 +0200

[Message part 1 (text/plain, inline)]

Tags: patch

When I use gcc 14 with -std=gnu99 -Wpedantic I get lots of warnings of
the form

 warning: ISO C99 does not support ‘_Noreturn’ [-Wpedantic].

To avoid those warnings, I propose to use __attribute__ ((__noreturn__))
instead.

[0001-Don-t-use-_Noreturn-with-GCC-unless-__STDC_VERSION__.patch (text/patch, attachment)]

Message #8 received at 78903 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Helmut Eller <eller.helmut <at> gmail.com>,
 Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 78903 <at> debbugs.gnu.org
Subject: Re: bug#78903: [PATCH] ISO C99 does not support _Noreturn
Date: Thu, 26 Jun 2025 10:51:39 +0300

> From: Helmut Eller <eller.helmut <at> gmail.com>
> Date: Thu, 26 Jun 2025 09:20:51 +0200
> 
> When I use gcc 14 with -std=gnu99 -Wpedantic I get lots of warnings of
> the form
> 
>  warning: ISO C99 does not support ‘_Noreturn’ [-Wpedantic].

Why did you use -Wpedantic?  The Emacs build doesn't use that, and for
a good reason.

> To avoid those warnings, I propose to use __attribute__ ((__noreturn__))
> instead.

We have already a portable solution for _Noreturn, see src/config.in.
We could modify it if needed, but I'm not sure we should try straying
too far from what we have (which works), definitely not for the
benefit of "-Wpedantic".

Paul, WDYT?

Message #11 received at 78903 <at> debbugs.gnu.org (full text, mbox):

From: Helmut Eller <eller.helmut <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 78903 <at> debbugs.gnu.org, Paul Eggert <eggert <at> cs.ucla.edu>
Subject: Re: bug#78903: [PATCH] ISO C99 does not support _Noreturn
Date: Thu, 26 Jun 2025 10:08:54 +0200

On Thu, Jun 26 2025, Eli Zaretskii wrote:

>> From: Helmut Eller <eller.helmut <at> gmail.com>
>> Date: Thu, 26 Jun 2025 09:20:51 +0200
>> 
>> When I use gcc 14 with -std=gnu99 -Wpedantic I get lots of warnings of
>> the form
>> 
>>  warning: ISO C99 does not support ‘_Noreturn’ [-Wpedantic].
>
> Why did you use -Wpedantic?

To get warnings when I use a non-C99 feature.  Emacs' C code should be
written in C99.  It would be easier to follow that rule it were checked
automatically.

Message #14 received at 78903 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: 78903 <at> debbugs.gnu.org, eggert <at> cs.ucla.edu
Subject: Re: bug#78903: [PATCH] ISO C99 does not support _Noreturn
Date: Thu, 26 Jun 2025 11:23:10 +0300

> From: Helmut Eller <eller.helmut <at> gmail.com>
> Cc: Paul Eggert <eggert <at> cs.ucla.edu>,  78903 <at> debbugs.gnu.org
> Date: Thu, 26 Jun 2025 10:08:54 +0200
> 
> On Thu, Jun 26 2025, Eli Zaretskii wrote:
> 
> >> From: Helmut Eller <eller.helmut <at> gmail.com>
> >> Date: Thu, 26 Jun 2025 09:20:51 +0200
> >> 
> >> When I use gcc 14 with -std=gnu99 -Wpedantic I get lots of warnings of
> >> the form
> >> 
> >>  warning: ISO C99 does not support ‘_Noreturn’ [-Wpedantic].
> >
> > Why did you use -Wpedantic?
> 
> To get warnings when I use a non-C99 feature.  Emacs' C code should be
> written in C99.  It would be easier to follow that rule it were checked
> automatically.

AFAIK, Emacs is written in C99 with extensions.

Can you tell why the definition of _Noreturn in src/config.in doesn't
work for you?  AFAIU, it exactly defines _Noreturn to use
__attribute__ ((__noreturn__)), but I'm probably missing something.
is the problem that you use clang, and config.in currently doesn't
cater to that?  If so, the change should be in config.in, I think.

Message #17 received at 78903 <at> debbugs.gnu.org (full text, mbox):

From: Helmut Eller <eller.helmut <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 78903 <at> debbugs.gnu.org, eggert <at> cs.ucla.edu
Subject: Re: bug#78903: [PATCH] ISO C99 does not support _Noreturn
Date: Thu, 26 Jun 2025 10:40:47 +0200

On Thu, Jun 26 2025, Eli Zaretskii wrote:

>> From: Helmut Eller <eller.helmut <at> gmail.com>
>> Cc: Paul Eggert <eggert <at> cs.ucla.edu>,  78903 <at> debbugs.gnu.org
>> Date: Thu, 26 Jun 2025 10:08:54 +0200
>> 
>> On Thu, Jun 26 2025, Eli Zaretskii wrote:
>> 
>> >> From: Helmut Eller <eller.helmut <at> gmail.com>
>> >> Date: Thu, 26 Jun 2025 09:20:51 +0200
>> >> 
>> >> When I use gcc 14 with -std=gnu99 -Wpedantic I get lots of warnings of
>> >> the form
>> >> 
>> >>  warning: ISO C99 does not support ‘_Noreturn’ [-Wpedantic].
>> >
>> > Why did you use -Wpedantic?
>> 
>> To get warnings when I use a non-C99 feature.  Emacs' C code should be
>> written in C99.  It would be easier to follow that rule it were checked
>> automatically.
>
> AFAIK, Emacs is written in C99 with extensions.

It would still be easier if the somewhat arbitrary set of extensions
would be checked automatically.

> Can you tell why the definition of _Noreturn in src/config.in doesn't
> work for you?  AFAIU, it exactly defines _Noreturn to use
> __attribute__ ((__noreturn__)), but I'm probably missing something.

Without the patch, the case with the comment /* _Noreturn works as-is.
*/ is used.  That causes the warnings.

> is the problem that you use clang, and config.in currently doesn't
> cater to that?

No. I don't use clang.

> If so, the change should be in config.in, I think.

I don't think so, because config.in is generated by autogen.sh.

Helmut

Message #20 received at 78903 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: 78903 <at> debbugs.gnu.org, eggert <at> cs.ucla.edu
Subject: Re: bug#78903: [PATCH] ISO C99 does not support _Noreturn
Date: Thu, 26 Jun 2025 12:13:39 +0300

> From: Helmut Eller <eller.helmut <at> gmail.com>
> Cc: eggert <at> cs.ucla.edu,  78903 <at> debbugs.gnu.org
> Date: Thu, 26 Jun 2025 10:40:47 +0200
> 
> On Thu, Jun 26 2025, Eli Zaretskii wrote:
> 
> >> From: Helmut Eller <eller.helmut <at> gmail.com>
> >> Cc: Paul Eggert <eggert <at> cs.ucla.edu>,  78903 <at> debbugs.gnu.org
> >> Date: Thu, 26 Jun 2025 10:08:54 +0200
> >> 
> >> On Thu, Jun 26 2025, Eli Zaretskii wrote:
> >> 
> >> >> From: Helmut Eller <eller.helmut <at> gmail.com>
> >> >> Date: Thu, 26 Jun 2025 09:20:51 +0200
> >> >> 
> >> >> When I use gcc 14 with -std=gnu99 -Wpedantic I get lots of warnings of
> >> >> the form
> >> >> 
> >> >>  warning: ISO C99 does not support ‘_Noreturn’ [-Wpedantic].
> >> >
> >> > Why did you use -Wpedantic?
> >> 
> >> To get warnings when I use a non-C99 feature.  Emacs' C code should be
> >> written in C99.  It would be easier to follow that rule it were checked
> >> automatically.
> >
> > AFAIK, Emacs is written in C99 with extensions.
> 
> It would still be easier if the somewhat arbitrary set of extensions
> would be checked automatically.
> 
> > Can you tell why the definition of _Noreturn in src/config.in doesn't
> > work for you?  AFAIU, it exactly defines _Noreturn to use
> > __attribute__ ((__noreturn__)), but I'm probably missing something.
> 
> Without the patch, the case with the comment /* _Noreturn works as-is.
> */ is used.  That causes the warnings.
> 
> > is the problem that you use clang, and config.in currently doesn't
> > cater to that?
> 
> No. I don't use clang.
> 
> > If so, the change should be in config.in, I think.
> 
> I don't think so, because config.in is generated by autogen.sh.

OK, let's see what Paul thinks about this.

Message #23 received at 78903 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Helmut Eller <eller.helmut <at> gmail.com>, Eli Zaretskii <eliz <at> gnu.org>
Cc: 78903 <at> debbugs.gnu.org
Subject: Re: bug#78903: [PATCH] ISO C99 does not support _Noreturn
Date: Thu, 26 Jun 2025 11:43:24 -0700

On 2025-06-26 01:08, Helmut Eller wrote:
> On Thu, Jun 26 2025, Eli Zaretskii wrote:
> 
>>> From: Helmut Eller<eller.helmut <at> gmail.com>
>>> Date: Thu, 26 Jun 2025 09:20:51 +0200
>>>
>>> When I use gcc 14 with -std=gnu99 -Wpedantic I get lots of warnings of
>>> the form
>>>
>>>   warning: ISO C99 does not support ‘_Noreturn’ [-Wpedantic].
>> Why did you use -Wpedantic?
> To get warnings when I use a non-C99 feature.

To do that, you can run something like this:

  ./configure CFLAGS='-std=c99 -Wpedantic'
  make

You'll still see many warnings, though none about _Noreturn.

'-std=gnu99' says "it's OK to use GNU extensions" and so is not the best 
choice to test for C99 conformance. '-std=c99' is better (though still 
not perfect of course). Running 'configure' as shown above should avoid 
the _Noreturn warnings you mentioned.

Alternatively, you can compile with -D_Noreturn='__attribute__ 
((__noreturn__))'.

Not sure it's worth changing Gnulib to support what appears to be a GCC 
option clash. I suppose I could ask on bug-gnulib.

Message #26 received at 78903 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: 78903 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>
Subject: Re: bug#78903: [PATCH] ISO C99 does not support _Noreturn
Date: Thu, 26 Jun 2025 14:06:33 -0700

[Message part 1 (text/plain, inline)]

After looking at the definition of _Noreturn, perhaps you're right and 
it would be a win to simplify m4/gnulib-common.m4, which should pacify 
the unusual GCC configuration you mentioned. Does the attached patch 
work for you?

[noreturn.diff (text/x-patch, attachment)]

Message #29 received at 78903 <at> debbugs.gnu.org (full text, mbox):

From: Helmut Eller <eller.helmut <at> gmail.com>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 78903 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>
Subject: Re: bug#78903: [PATCH] ISO C99 does not support _Noreturn
Date: Fri, 27 Jun 2025 16:05:35 +0200

On Thu, Jun 26 2025, Paul Eggert wrote:

> After looking at the definition of _Noreturn, perhaps you're right and
> it would be a win to simplify m4/gnulib-common.m4, which should pacify
> the unusual GCC configuration you mentioned. Does the attached patch
> work for you?

Yes, after a fashion.  The combination -Og -std=gnu99 -Wpedantic is
usable; -Og -std=cc99 -Wpedantic produces fewer warnings though.  With
-O0, both -std=gnu99 and -std=c99 produce too many warnings about
statement expressions to be of any use.

I would place the 201112 <= STDC_VERSION test first and only if it fails
fall back to __attribute__((__return__)).

Helmut

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