Re: [PATCH 1/2] DONTAPPLY: -Og fallout workaround

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 10, 2024, 20:05 UTC
Message-ID: <xmqqsexk1s43.fsf@gitster.g>
In-Reply-To: <xmqqjziw3arr.fsf@gitster.g>

Junio C Hamano <gitster@pobox.com> writes:

Show 34 quoted lines

> These "workarounds" are to mark variables that are used after
> initialized, but some compilers with lower optimization levels
> cannot see and report "used uninitialized".
>
> This set targets "gcc-12 -Og".  For the reason why this is a wrong
> thing to do for longer-term code health, see
>
>   https://lore.kernel.org/git/xmqqed946auc.fsf@gitster.g/
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>
>  * Even though I said I won't do the actual patch, since I had to
>    gauge the extent of damage, I ended up doing so anyways.
>
>    As I explained already, the size of this patch, i.e. number of
>    places that need the workaround, does not really matter.  What
>    is horrible is how each of these workaround will hide real bugs
>    we may introduce in the future from the compilers.
>
>  builtin/branch.c          | 2 +-
>  builtin/fast-import.c     | 4 ++--
>  builtin/repack.c          | 2 +-
>  fetch-pack.c              | 2 +-
>  http-backend.c            | 2 +-
>  http.c                    | 2 +-
>  pack-mtimes.c             | 2 +-
>  pack-revindex.c           | 2 +-
>  refs/packed-backend.c     | 2 +-
>  reftable/stack.c          | 2 +-
>  remote-curl.c             | 4 ++--
>  t/helper/test-ref-store.c | 2 +-
>  trailer.c                 | 4 ++--
>  13 files changed, 16 insertions(+), 16 deletions(-)

And depending on the version of compilers, apparently even this is not enough. I do not offhand know what GitHub CI is running for linux-gcc-default (ubuntu-latest), but this gets flagged for using (try to guess which one without looking at the answer below) ...

        static int parse_count(const char *arg)
        {
                int count;

                if (strtol_i(arg, 10, &count) < 0)
                        die("'%s': not an integer", arg);
                return count;
        }

... count uninitilaized, since the compiler does not realize that strtol_i() always touches "count" unless the function returns negative, and die() never returns. Exactly the same pattern continues.

So, unless we disable -Werror, let's not continue this experiment with -Og or -Os as the damage seems to be far greater than the benefit (which I haven't seen any, but that is largely due to timezone differences---I asked "what's the real bug you found with this" a few hours ago that is past EOB in Europe).