From: Richard Biener <richard.guenther@gmail.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: gcc@gcc.gnu.org, c-std-porting@lists.linux.dev
Subject: Re: More C type errors by default for GCC 14
Date: Tue, 9 May 2023 17:16:19 +0200 [thread overview]
Message-ID: <97CCB305-9ECD-4B3C-B13E-4F2790FE0543@gmail.com> (raw)
In-Reply-To: <877cth66qb.fsf@oldenburg.str.redhat.com>
> Am 09.05.2023 um 14:16 schrieb Florian Weimer via Gcc <gcc@gcc.gnu.org>:
>
> TL;DR: This message is about turning implicit-int,
> implicit-function-declaration, and possibly int-conversion into errors
> for GCC 14.
I suppose the goal is to not need to rely on altering CFLAGS but change the default behavior with still being able to undo this using -Wno-error= or -Wno-?
I think instead of hard-coding a set of changes would it be possible to alter the default setting of diagnostic options during GCC configuration? And maybe even note that when diagnosing?
Thanks,
Richard
> A few of you might remember that I've been looking into turning some
> type errors from warnings into errors by default. Mainly I've been
> looking at implicit function declarations because in too many cases, the
> synthesized declaration does not match the prototype used at function
> definition and can cause subtle ABI issues.
>
> To recap, the main challenge is that GCC has to serve disparate groups
> of users: some use GCC for writing programs themselves, but others just
> need GCC to build sources that they have obtained from somewhere. The
> first group benefits from more type errors because they catch errors
> earlier during development (experience shows that compiler warnings are
> easy to miss in a long build log). The second group might find these
> errors challenging because the sources they have no longer build.
>
> To see how large the impact is on that second group, we've mostly
> removed implicit function declarations and implicit ints from Fedora:
>
> <https://fedoraproject.org/wiki/Changes/PortingToModernC>
> <https://fedoraproject.org/wiki/Toolchain/PortingToModernC>
>
> Roughly 870 packages out of ~14,500 that have GCC present during the
> build needed fixing (or flagging that they can't be built with the
> additional errors), so 6%. Most of the changes are mechanical in
> nature, like adding additional headers to configure checks. For about
> ~150 packages, automated patching could be used to rewrite problematic
> built-in checks generated by long-obsolete autoconf versions.
>
> Some of these changes prevent the compiler behavior for altering the
> build results silently because the new errors changed the outcome of
> autoconf checks. (We had one of those in libstdc++, changing the ABI on
> GNU/Linux because futex support oculd no longer be detected.)
> Unfortunately, I did not record numbers about them, but think those were
> quite rare; most autoconf problems were also accompanied with other
> problems, or the incorrect results from autoconf led to build failures
> later. So it seems to me that the risk that the second group mentioned
> above would silently get unexpected build results is fairly low.
>
> Where possible, we tried to upstream patches, to simplify sharing across
> distributions and to help those who compile upstream sources directly.
> We also benefited from other distributions upstreaming changes along
> similar lines (notably Gentoo for their Clang 16 project, but also from
> Homebrew to a lesser extent).
>
> An area we started exploring only recently for Fedora is implicit
> conversions between integers and pointers (covered by -Wint-conversion).
> These add another ~170 packages, but some of those are false positives
> (due to our instrumented compiler approach) that do not change the build
> outcome at all. I'm still negotiating whether we have the capacity to
> develop fixes for these packages proactively.
>
> I brought up the matter with distributions, and the feedback was neutral
> (not overly negative, as in “this would be the end of the world for
> us”).
>
> <https://discourse.nixos.org/t/rfc-more-c-errors-by-default-in-gcc-14/27390>
> <https://lists.debian.org/debian-gcc/2023/04/msg00015.html>
> <https://lists.opensuse.org/archives/list/factory@lists.opensuse.org/thread/5OL76NH5AX75WOTZ43O3ZF2JOS3ABBXL/#QZLCA5YPN5CWSS7BCC6TNBC6N7RFTW7J>
>
> (I tried to contact Arch, but my message didn't make it past the
> moderators, it seems.)
>
> All in all, the whole situation is not great, but it still seems
> manageable to me.
>
> Anyway, thanks for reading this far.
>
> I would like to suggest to turn implicit-int,
> implicit-function-declaration, and possibly int-conversion from warnings
> into errors for GCC 14. This would give upstream projects roughly
> another year to make new releases with compatibility fixes that have
> been contributed so far. I do not think waiting longer, until GCC 15,
> would make a meaningful difference because any upstream project that
> does not release within the next 12 months is not likely to release in
> the next 24 months, either.
>
> Regarding mechanics of the necessary opt out facility, Clang used
> -Werror=… by default, but that seems a bit hackish to me. Presently, we
> cannot use -std=gnu89 etc. to opt out because there are packages which
> require both C89-only language features and C99-style inlining, which is
> currently not a combination supported by GCC (but maybe that could be
> changed). Some build systems do not treat CFLAGS and CXXFLAGS as fully
> separate, and a flag approach that works for C and C++ without
> introducing any new warnings would be most convenient. So maybe we
> could use -fpermissive for C as well.
>
> One fairly big GCC-internal task is to clear up the C test suite so that
> it passes with the new compiler defaults. I already have an offer of
> help for that, so I think we can complete this work in a reasonable time
> frame.
>
> I have no data how big the compatibility impact of turning
> incompatible-pointer-types into errors will be. For now, int-conversion
> has higher priority. However, it looks like another change that could
> benefit developers (the first group).
>
> I do not plan to work specifically on C2X compatibility fixes for now
> (to support bool-as-keyword, for example), but I could imagine a similar
> project a few years from now, fewer than 25 hopefully, that would enable
> GCC to make the switch to C2X by default.
>
> Thanks,
> Florian
>
next prev parent reply other threads:[~2023-05-09 15:16 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
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 [this message]
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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