From: Florian Weimer <fw@deneb.enyo.de>
To: Jason Merrill <jason@redhat.com>
Cc: Joseph Myers <joseph@codesourcery.com>,
Eli Zaretskii <eliz@gnu.org>, Jakub Jelinek <jakub@redhat.com>,
gabravier@gmail.com, jwakely.gcc@gmail.com, fweimer@redhat.com,
gcc@gcc.gnu.org, arsen@aarsen.me
Subject: Re: More C type errors by default for GCC 14
Date: Fri, 12 May 2023 22:57:46 +0200 [thread overview]
Message-ID: <87v8gxe08l.fsf@mid.deneb.enyo.de> (raw)
In-Reply-To: <CADzB+2=CzGh0Oru1HxhcBYyKdmo+x4dFrS7u2JzKjc1OuF5sXA@mail.gmail.com> (Jason Merrill's message of "Fri, 12 May 2023 16:18:18 -0400")
* Jason Merrill:
> On Fri, May 12, 2023 at 11:03 AM Florian Weimer <fw@deneb.enyo.de> wrote:
>>
>> * Joseph Myers:
>>
>> > On Wed, 10 May 2023, Eli Zaretskii via Gcc wrote:
>> >
>> >> That is not the case we are discussing, AFAIU. Or at least no one has
>> >> yet explained why accepting those old K&R programs will adversely
>> >> affect the ability of GCC to compile C2x programs.
>> >
>> > At block scope,
>> >
>> > auto x = 1.5;
>> >
>> > declares x to have type double in C2x (C++-style auto), but type int in
>> > C89 (and is invalid for versions in between). In this case, there is an
>> > incompatible semantic change between implicit int and C++-style auto.
>> > Giving an error before we make -std=gnu2x the default seems like a
>> > particularly good idea, to further alert anyone who has been ignoring the
>> > warnings about implicit int that semantics will change incompatibly.
>>
>> Obviously makes sense to me.
>
> Agreed. But we could safely continue to accept
>
> static x = 42;
>
> or even
>
> auto x = 42; // meaning of 'auto' changes, meaning of the declaration does not
>
> We might make -Wimplicit-int an error by default only if the
> initializer has a type other than 'int'.
Based on what I saw fixing Fedora, these cases are not very common.
Sure, sometimes common program such as valgrind have an instance
<https://bugs.kde.org/show_bug.cgi?id=462007>, but that's really an
exception.
Implicit int is common as the return type of main (especially in
autoconf tests), and due to a missing declaration list entry of an
old-style function definition. The main case could be treated as an
exception. The old-style function definition case is a common source
of bugs and therefore worth fixing. The addition of unnamed function
parameters as an extension actually created a new class of bugs here
(a typo in the type name of a single unnamed parameter results in an
old-style function definition by accident).
>> > In cases where the standard requires a diagnostic, some are errors, some
>> > are pedwarns-by-default or unconditional pedwarns, some are
>> > pedwarns-if-pedantic - the choice depending on how suspicious the
>> > construct in question is and whether it corresponds to a meaningful
>> > extension (this is not making an automatic choice for every such situation
>> > in the standard, it's a case-by-case judgement by maintainers). By now,
>> > the cases discussed in this thread are sufficiently suspicious -
>> > sufficiently likely to result in unintended execution at runtime (not, of
>> > course, reliably detected because programs with such dodgy code are very
>> > unlikely to have thorough automated tests covering all their code) - that
>> > is it in the interests of users for them to be errors by default (for C99
>> > and later modes, in the cases that were valid in C89).
>>
>> Just to recap, those are controlled by
>> -Wimplicit-function-declaration, -Wimplicit-int, -Wint-conversion, and
>> -Wincompatible-pointer-types, roughly in increasing order of
>> compatibility impact with old sources.
>
> What would the impact be of making -Wint-conversion an error by
> default only if the types are different sizes?
From a distribution perspective, it does not change anything because
we build everything on 64-bit anyway. Unlike e.g. Fedora, Debian
doesn't require all builds to succeed before the new package can be
installed, but given that the primary targets are 64 bit, I don't
think a restricted -Wint-conversion error would be much of a
simplification. The target-dependent nature of the warning is
probably more confusing.
next prev parent reply other threads:[~2023-05-12 20:57 UTC|newest]
Thread overview: 246+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-09 12:15 Florian Weimer
2023-05-09 14:16 ` Dave Blanchard
2023-05-09 15:03 ` David Edelsohn
2023-05-09 15:07 ` Sam James
2023-05-09 15:35 ` Dave Blanchard
2023-05-09 15:58 ` Jonathan Wakely
2023-05-09 16:26 ` Arsen Arsenović
2023-05-09 15:14 ` Jonathan Wakely
2023-05-09 15:22 ` Dave Blanchard
2023-05-09 16:38 ` Arsen Arsenović
2023-05-09 16:57 ` Eli Zaretskii
2023-05-09 17:05 ` Sam James
2023-05-09 18:55 ` Eli Zaretskii
2023-05-09 17:15 ` Jonathan Wakely
2023-05-09 19:04 ` Eli Zaretskii
2023-05-09 19:07 ` Jakub Jelinek
2023-05-09 19:22 ` Eli Zaretskii
2023-05-09 20:13 ` David Edelsohn
2023-05-09 20:21 ` Arsen Arsenović
2023-05-10 2:38 ` Eli Zaretskii
2023-05-10 8:36 ` Arsen Arsenović
2023-05-10 11:52 ` Eli Zaretskii
2023-05-10 11:56 ` Jonathan Wakely
2023-05-10 12:25 ` Eli Zaretskii
2023-05-10 12:30 ` Jonathan Wakely
2023-05-10 12:44 ` Eli Zaretskii
2023-05-15 12:28 ` Richard Earnshaw (lists)
2023-05-15 20:17 ` Eric Gallager
2023-05-16 7:05 ` Florian Weimer
2023-05-16 15:56 ` Jason Merrill
2023-05-09 20:40 ` Jonathan Wakely
2023-05-09 22:27 ` David Edelsohn
2023-05-09 22:37 ` Joel Sherrill
2023-05-09 22:45 ` Jonathan Wakely
2023-05-10 10:40 ` Eric Gallager
2023-05-10 10:45 ` Sam James
2023-05-10 10:56 ` Neal Gompa
2023-05-10 12:06 ` Eli Zaretskii
2023-05-10 12:10 ` Neal Gompa
2023-05-10 12:41 ` Eli Zaretskii
2023-05-10 10:48 ` Jonathan Wakely
2023-05-10 10:51 ` Jonathan Wakely
2023-05-10 12:00 ` Eli Zaretskii
2023-05-10 12:42 ` Sam James
2023-05-10 15:10 ` Joel Sherrill
2023-05-10 15:14 ` Jakub Jelinek
2023-05-10 16:36 ` Joel Sherrill
2023-05-10 16:44 ` Jakub Jelinek
2023-05-10 17:05 ` Jonathan Wakely
2023-05-10 18:37 ` James K. Lowden
2023-05-10 23:26 ` Jonathan Wakely
2023-05-11 18:47 ` Jason Merrill
2023-05-10 23:33 ` Sam James
2023-05-11 5:48 ` Eli Zaretskii
2023-05-11 2:28 ` Po Lu
2023-05-11 2:09 ` Po Lu
2023-05-11 2:14 ` Sam James
2023-05-11 2:23 ` Po Lu
2023-05-11 3:14 ` Eli Schwartz
2023-05-11 3:56 ` Po Lu
2023-05-11 4:46 ` Eli Schwartz
2023-05-11 4:49 ` Eli Schwartz
2023-05-11 6:23 ` Po Lu
2023-05-11 6:18 ` Po Lu
2023-05-11 22:41 ` Eli Schwartz
2023-05-12 2:08 ` Po Lu
2023-05-12 3:07 ` Eli Schwartz
2023-05-12 5:57 ` Po Lu
2023-05-12 11:05 ` Gabriel Ravier
2023-05-12 13:53 ` Po Lu
2023-05-12 14:03 ` Jonathan Wakely
2023-05-14 12:35 ` Mark Wielaard
2023-05-12 11:48 ` Is the GNUC dialect anything that GCC does when given source code containing UB? (Was: More C type errors by default for GCC 14) Eli Schwartz
2023-05-12 13:07 ` Is the GNUC dialect anything that GCC does when given source code containing UB? Po Lu
2023-05-12 6:56 ` More C type errors by default for GCC 14 Eli Zaretskii
2023-05-12 7:28 ` Jonathan Wakely
2023-05-12 10:36 ` Eli Zaretskii
2023-05-12 13:19 ` Po Lu
2023-05-12 13:25 ` Gabriel Ravier
2023-05-13 0:45 ` Po Lu
2023-05-13 5:30 ` Thomas Koenig
2023-05-13 5:53 ` Po Lu
2023-05-14 5:10 ` Eli Schwartz
2023-05-14 5:38 ` Po Lu
2023-05-14 9:46 ` David Brown
2023-05-14 10:21 ` Jonathan Wakely
2023-05-14 10:23 ` Jonathan Wakely
2023-05-14 5:08 ` Eli Schwartz
2023-05-14 5:28 ` Po Lu
2023-05-14 5:56 ` Eli Schwartz
2023-05-14 11:55 ` Po Lu
2023-05-14 12:22 ` Arsen Arsenović
2023-05-15 1:05 ` Po Lu
2023-05-14 6:03 ` Eli Schwartz
2023-05-14 8:47 ` Jonathan Wakely
2023-05-14 12:05 ` Po Lu
2023-05-14 12:48 ` Nicholas Vinson
2023-05-14 10:29 ` David Brown
2023-05-12 15:51 ` Jason Merrill
2023-05-17 10:06 ` Florian Weimer
2023-05-12 11:26 ` David Brown
2023-05-11 6:24 ` Eli Zaretskii
2023-05-11 22:43 ` Eli Schwartz
2023-05-12 2:38 ` Po Lu
2023-05-12 2:55 ` Jason Merrill
2023-05-12 6:01 ` Po Lu
2023-05-12 6:40 ` Jonathan Wakely
2023-05-12 13:23 ` Po Lu
2023-05-12 10:49 ` Pedro Alves
2023-05-12 13:26 ` Po Lu
2023-05-12 11:55 ` Eli Schwartz
2023-05-12 13:54 ` Po Lu
2023-05-12 6:49 ` Eli Zaretskii
2023-05-12 2:56 ` Sam James
2023-05-12 6:03 ` Po Lu
2023-05-12 3:06 ` Sam James
2023-05-12 6:25 ` Eli Zaretskii
2023-05-12 11:23 ` Gabriel Ravier
2023-05-11 6:12 ` Eli Zaretskii
2023-05-11 7:04 ` Jonathan Wakely
2023-05-11 22:30 ` Eli Schwartz
2023-05-11 22:35 ` Sam James
2023-05-12 2:40 ` Po Lu
2023-05-12 2:52 ` Sam James
2023-05-12 5:32 ` Po Lu
2023-05-12 2:39 ` Po Lu
2023-05-12 3:18 ` Eli Schwartz
2023-05-12 6:17 ` Eli Zaretskii
2023-05-11 7:59 ` David Brown
2023-05-09 21:00 ` Thomas Koenig
2023-05-09 21:17 ` Arsen Arsenović
2023-05-10 13:57 ` Florian Weimer
2023-05-10 11:00 ` David Brown
2023-05-11 10:49 ` James K. Lowden
2023-05-11 1:38 ` Po Lu
2023-05-11 1:43 ` Sam James
2023-05-11 2:20 ` Po Lu
2023-05-09 20:57 ` Florian Weimer
2023-05-10 2:33 ` Eli Zaretskii
2023-05-10 8:04 ` Jonathan Wakely
2023-05-10 8:46 ` Richard Biener
2023-05-10 12:26 ` Florian Weimer
2023-05-10 11:30 ` Eli Zaretskii
2023-05-10 12:03 ` Jakub Jelinek
2023-05-10 12:36 ` Eli Zaretskii
2023-05-10 12:41 ` Gabriel Ravier
2023-05-10 14:14 ` Eli Zaretskii
2023-05-10 14:22 ` Jakub Jelinek
2023-05-10 15:30 ` Eli Zaretskii
2023-05-10 16:02 ` Jakub Jelinek
2023-05-10 16:31 ` Eli Zaretskii
2023-05-10 16:33 ` Richard Biener
2023-05-10 16:57 ` Eli Zaretskii
2023-05-10 17:08 ` Joseph Myers
2023-05-10 18:18 ` Eli Zaretskii
2023-05-12 15:02 ` Florian Weimer
2023-05-12 17:52 ` Florian Weimer
2023-05-12 17:55 ` Gabriel Ravier
2023-05-12 18:00 ` Florian Weimer
2023-05-12 18:08 ` Alexander Monakov
2023-05-12 18:14 ` Florian Weimer
2023-05-15 12:51 ` Michael Matz
2023-05-16 8:55 ` Florian Weimer
2023-05-16 10:39 ` Alexander Monakov
2023-05-16 11:01 ` Jakub Jelinek
2023-05-16 11:09 ` Jonathan Wakely
2023-05-16 11:15 ` Florian Weimer
2023-05-12 19:44 ` Joseph Myers
2023-05-12 20:43 ` Florian Weimer
2023-05-12 20:18 ` Jason Merrill
2023-05-12 20:57 ` Florian Weimer [this message]
2023-05-12 21:20 ` Sam James
2023-05-12 21:21 ` Sam James
2023-05-12 21:37 ` Florian Weimer
2023-05-12 21:47 ` Sam James
2023-05-12 21:59 ` Florian Weimer
2023-05-10 15:58 ` David Brown
2023-05-10 16:28 ` Eli Zaretskii
2023-05-11 6:52 ` David Brown
2023-05-11 7:39 ` Eli Zaretskii
2023-05-10 14:31 ` Thomas Koenig
2023-05-10 15:37 ` Eli Zaretskii
2023-05-11 2:38 ` Po Lu
2023-05-11 7:38 ` Arsen Arsenović
2023-05-11 8:31 ` Po Lu
2023-05-11 8:44 ` Arsen Arsenović
2023-05-11 9:28 ` Po Lu
2023-05-11 21:10 ` Arsen Arsenović
2023-05-12 1:41 ` Po Lu
2023-05-11 10:35 ` Eli Zaretskii
2023-05-11 19:25 ` Arsen Arsenović
2023-05-12 2:36 ` Po Lu
2023-05-12 12:30 ` Gabriel Ravier
2023-05-12 13:56 ` Po Lu
2023-05-12 7:53 ` Eli Zaretskii
2023-05-12 8:15 ` Jakub Jelinek
2023-05-12 10:40 ` Eli Zaretskii
2023-05-12 8:45 ` Christian Groessler
2023-05-12 10:14 ` Jonathan Wakely
2023-05-12 9:11 ` Thomas Koenig
2023-05-11 8:53 ` Jonathan Wakely
2023-05-11 9:29 ` Po Lu
2023-05-10 8:49 ` David Brown
2023-05-10 11:37 ` Eli Zaretskii
2023-05-10 11:49 ` Jonathan Wakely
2023-05-10 12:22 ` Eli Zaretskii
2023-05-10 13:30 ` David Brown
2023-05-10 14:39 ` Eli Zaretskii
2023-05-10 15:21 ` Paul Koning
2023-05-10 16:20 ` David Brown
2023-05-10 16:48 ` Eli Zaretskii
2023-05-10 12:32 ` Sam James
2023-05-10 12:47 ` Eli Zaretskii
2023-05-09 19:33 ` Arsen Arsenović
2023-05-09 15:25 ` David Edelsohn
2023-05-11 1:25 ` Po Lu
2023-05-11 1:30 ` Sam James
2023-05-11 1:33 ` Sam James
2023-05-11 2:18 ` Po Lu
2023-05-11 6:44 ` Jonathan Wakely
2023-05-11 8:32 ` Po Lu
2023-05-11 8:52 ` Jonathan Wakely
2023-05-11 7:36 ` Arsen Arsenović
2023-05-11 8:23 ` Po Lu
2023-05-09 18:22 ` Florian Weimer
2023-05-11 21:32 ` Segher Boessenkool
2023-05-09 15:16 ` Richard Biener
2023-05-09 16:05 ` Jakub Jelinek
2023-05-09 16:11 ` Sam James
2023-05-09 16:13 ` David Edelsohn
[not found] ` <BBE9950C-28AA-4A1C-A4C5-7F486538004E@gmail.com>
2023-05-09 16:44 ` Florian Weimer
2023-05-09 16:58 ` Ian Lance Taylor
2023-05-09 17:08 ` Jason Merrill
2023-05-09 17:16 ` Sam James
2023-05-09 16:59 ` Florian Weimer
2023-05-09 17:07 ` Sam James
2023-05-09 17:35 ` Florian Weimer
2023-05-11 15:21 ` Peter0x44
2023-05-12 9:33 ` Martin Jambor
2023-05-12 12:30 ` Jakub Jelinek
2023-05-15 12:46 ` Michael Matz
2023-05-15 13:14 ` Richard Earnshaw (lists)
2023-05-10 12:41 Marcin Jaczewski
2023-05-10 14:19 ` Eli Zaretskii
2023-05-10 13:10 Basile Starynkevitch
2023-05-10 14:20 ` David Brown
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