From: Florian Weimer <fweimer@redhat.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: David Edelsohn <dje.gcc@gmail.com>,
Jakub Jelinek <jakub@redhat.com>,
gcc@gcc.gnu.org, c-std-porting@lists.linux.dev
Subject: Re: More C type errors by default for GCC 14
Date: Tue, 09 May 2023 18:44:48 +0200 [thread overview]
Message-ID: <87y1lx4fpb.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <BBE9950C-28AA-4A1C-A4C5-7F486538004E@gmail.com> (Richard Biener's message of "Tue, 9 May 2023 18:18:02 +0200")
* Richard Biener:
> > Am 09.05.2023 um 18:13 schrieb David Edelsohn <dje.gcc@gmail.com>:
> >
> > On Tue, May 9, 2023 at 12:07 PM Jakub Jelinek via Gcc <gcc@gcc.gnu.org> wrote:
> >
> > On Tue, May 09, 2023 at 05:16:19PM +0200, Richard Biener via Gcc wrote:
> > >
> > >
> > > > 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-?
> >
> > Can't people just compile C89/K&R code with -std=c89/-std=gnu89 and not get
> > these errors that way?
> >
> > As Florian mentioned:
> >
> > "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). "
>
> But surely it would reduce the number of packages to fix? So I
> support both having only C99 and up reject no longer valid code _and_
> having -fpermissive be forgiving (demoting errors to warnings).
It makes sense to disable the new erros in C89 mode. It's what I did in
the instrumented compiler. It also gives you yet another way to disable
the errors, using CC=c89, which works for some packages that do not
honor CFLAGS and do not support whitespace in CC.
The part David quoted above is about this:
$ gcc -fno-gnu89-inline -std=gnu89 t.c
cc1: error: ‘-fno-gnu89-inline’ is only supported in GNU99 or C99 mode
And some packages need -fno-gnu89-inline, but also rely on implicit ints
and implicit function declarations heavily. With a purely C89-based
opt-out and the -fno-gnu89-inline limitation, we wouldn't have a way to
compile these self-contradictory programs. Hence the idea of
-fpermissive, in addition to the -std=gnu89 escape hatch.
But perhaps the -fno-gnu89-inline limitation is easy to eliminate. The
remaining reason for -fpermissive would be a flag that is accepted by
both gcc and g++, in case a package build system passes CFLAGS to g++ as
well, which sometimes happens. And -fno-gnu89-inline is currently not
accepted by g++. But in the Fedora package set, this (some C++ and a
C89 requirement) must be exceedingly rare because it's a subset of the
already tiny set of -fno-gnu89-inline -std=gnu89 packages.
Thanks,
Florian
next parent reply other threads:[~2023-05-09 16:44 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAGWvnynMpa83AduLhRhf1PxkVujngDmmwE7Z4vk1z6+UqqAuKA@mail.gmail.com>
[not found] ` <BBE9950C-28AA-4A1C-A4C5-7F486538004E@gmail.com>
2023-05-09 16:44 ` Florian Weimer [this message]
2023-05-09 16:58 ` More C type errors by default for GCC 14 Ian Lance Taylor
2023-05-09 17:08 ` Jason Merrill
2023-05-09 17:16 ` Sam James
2023-05-09 12:15 Florian Weimer
2023-05-09 15:16 ` Richard Biener
2023-05-09 16:05 ` Jakub Jelinek
2023-05-09 16:11 ` Sam James
2023-05-09 16:59 ` Florian Weimer
2023-05-09 17:07 ` Sam James
2023-05-09 17:35 ` Florian Weimer
[not found] ` <CAGWvnykoEtT0BQtuN70DN6tWohtf=Mm7SW55psZvVmj3OvKUEg@mail.gmail.com>
2023-05-09 15:07 ` Sam James
2023-05-09 15:14 ` Jonathan Wakely
[not found] ` <20230509102201.6aa2a7d14fdb2f1e7abff449@killthe.net>
[not found] ` <87r0rp5uf8.fsf@aarsen.me>
[not found] ` <83ttwla1ep.fsf@gnu.org>
[not found] ` <CAH6eHdS-7USHzX3rPJaR66sEdjG+-nHp7mDb0gD7ceBnp+Fmpg@mail.gmail.com>
[not found] ` <83lehx9vix.fsf@gnu.org>
[not found] ` <ZFqZ25xKm4w4IkqF@tucnak>
[not found] ` <83fs859unu.fsf@gnu.org>
[not found] ` <CAGWvny=xi++Ghyo2Ez5MJdYy5h3yH16gVpviKC99Ufu_bUmdYQ@mail.gmail.com>
[not found] ` <CAH6eHdRAVwBcCmBgiuPyQNWGx3x33diAgQU8UG3s_NrJxK3ucQ@mail.gmail.com>
[not found] ` <CAGWvnyk_MkQOrNNh1C=ubPj8qzg5x-p8CBfgWNqqtDVJ1mbhMg@mail.gmail.com>
[not found] ` <CAF9ehCWsq-N9+U1+mTQahKT7cXEqLTptLb=b3Yq58gsWFEnxgA@mail.gmail.com>
[not found] ` <CAH6eHdS_sQ37VTpJHL7cqtgSdCSL3i4=tqMoY65wep9G56cf5g@mail.gmail.com>
[not found] ` <CAMfHzOsR=gY6QTss2R029Q-uMOTpC-RDV09bEF2FO7x5jpy5gg@mail.gmail.com>
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
2023-05-09 18:22 ` Florian Weimer
2023-05-11 21:32 ` Segher Boessenkool
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)
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