Re: [PATCH 1/2] config.mak.dev: workaround gcc 12 bug affecting "pedantic" CI job

From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: "Carlo Marcelo Arenas Belón" <carenas@gmail.com>
Cc: git@vger.kernel.org, gitster@pobox.com, phillip.wood@talktalk.net
Subject: Re: [PATCH 1/2] config.mak.dev: workaround gcc 12 bug affecting "pedantic" CI job
Date: Sat, 16 Apr 2022 01:41:27 +0200	[thread overview]
Message-ID: <220416.8635idc3mk.gmgdl@evledraar.gmail.com> (raw)
In-Reply-To: <20220415231342.35980-2-carenas@gmail.com>

On Fri, Apr 15 2022, Carlo Marcelo Arenas Belón wrote:

> Originally noticed by Peff[1], but yet to be corrected[2] and planned to
> be released with Fedora 36 (scheduled for Apr 19).
>
>   dir.c: In function ‘git_url_basename’:
>   dir.c:3085:13: error: ‘memchr’ specified bound [9223372036854775808, 0] exceeds maximum object size 9223372036854775807 [-Werror=stringop-overread]
>    3085 |         if (memchr(start, '/', end - start) == NULL
>         |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Fedora is used as part of the CI, and therefore that release will trigger
> failures, unless the version of the image used is locked to an older
> release, as an alternative.
>
> Restricting the flag to the affected source file, as well as implementing
> an independent facility to track these workarounds was specifically punted
> to minimize the risk of introducing problems so close to a release.
>
> This change should be reverted once the underlying gcc bug is solved and
> which should be visible by NOT triggering a warning, otherwise.
>
> [1] https://lore.kernel.org/git/YZQhLh2BU5Hquhpo@coredump.intra.peff.net/
> [2] https://bugzilla.redhat.com/show_bug.cgi?id=2075786
>
> Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
> ---
>  config.mak.dev | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/config.mak.dev b/config.mak.dev
> index 3deb076d5e3..335efd46203 100644
> --- a/config.mak.dev
> +++ b/config.mak.dev
> @@ -65,4 +65,9 @@ DEVELOPER_CFLAGS += -Wno-uninitialized
>  endif
>  endif
>  
> +# https://bugzilla.redhat.com/show_bug.cgi?id=2075786
> +ifneq ($(filter gcc12,$(COMPILER_FEATURES)),)
> +DEVELOPER_CFLAGS += -Wno-error=stringop-overread
> +endif

What I meant with "just set -Wno-error=stringop-overread on gcc12 for
dir.(o|s|sp)?" was that you can set this per-file:

	dir.sp dir.s dir.o: EXTRA_CPPFLAGS += -Wno-error=stringop-overread

Ditto for the warning suppression in 2/2, we don't currently have any
other warnings like this, but we can suppress them more narrowly.