From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Jeff King <peff@peff.net>
Cc: "René Scharfe" <l.s.r@web.de>,
git@vger.kernel.org, "Junio C Hamano" <gitster@pobox.com>,
"Taylor Blau" <me@ttaylorr.com>,
"Đoàn Trần Công Danh" <congdanhqx@gmail.com>,
"SZEDER Gábor" <szeder.dev@gmail.com>,
"Lukáš Doktor" <ldoktor@redhat.com>,
"Johannes Schindelin" <Johannes.Schindelin@gmx.de>
Subject: Re: [PATCH 09/13] parse-options API: don't restrict OPT_SUBCOMMAND() to one *_fn type
Date: Sat, 12 Nov 2022 17:55:52 +0100 [thread overview]
Message-ID: <221112.8635aom6p5.gmgdl@evledraar.gmail.com> (raw)
In-Reply-To: <Y2/LF/qiZI99YuxM@coredump.intra.peff.net>
On Sat, Nov 12 2022, Jeff King wrote:
> On Sat, Nov 12, 2022 at 11:42:09AM +0100, René Scharfe wrote:
>
>> > E.g. we have plenty of code that assumes ASCII, instead of catering to
>> > EBCDIC, and assuming NULL is (void *)0, not (void *)123456 or whatever.
>>
>> NULL is defined as "0" or "(void *)0" by C99 6.3.2.3 Pointers paragraph
>> 3 and 7.17 Common definitions <stddef.h> paragraph 3.
>
> I think he is alluding to the fact that while the standard requires that
> a "0" constant refers to a NULL pointer, the representation does not
> have to be all-bits-zero. So:
>
> char *foo = 0;
>
> is fine, but:
>
> char *foo;
> memset(foo, 0, sizeof(&foo));
Yes, to elaborate: the "null pointer constant" referred to in 6.3.2.3
deliberately leaves room for the representation being unequal to the
"all zero bits". And as you point out the former example is portable,
but not the latter.
> is not. And we absolutely do the latter in our code base anyway, because
> it's convenient and unlikely to be a problem on practical platforms. And
> I think it has always been our attitude in this community to let
> engineering practicality trump strict adherence to the standard. But
> "practicality" there should be measuring the tradeoff of how useful
> something is versus how likely it is to bite us.
All I've been trying to get across in this sub-thread is that there's an
interesting empirical question here: Are we in fact targeting an
architecture where J.5.7 isn't implemented, or likely to have one sneak
up on us?
I don't think so, and timing-wise deciding to be paranoid about this
particular thing would leave that question unanswered, when all we have
to do is wait a bit (some of the slower platforms tend to be a few
releases behind).
The argument for the change[1] (further articulated upthread) hasn't
answered the "do we target such an arch?", but seems to just fall back
to general standards paranoia.
Which isn't an invalid argument in itself. But doesn't really address
why we'd be worried about *this* particular thing, but not e.g. those
sort of memsets, assuming ASCII ordering for 'A'..'z' etc.
> In the case under discussion, my gut feeling agrees with you, though.
> I'm skeptical that equivalence of object and function pointers is all
> that useful in practice. And your mention of CHERI seems like a
> plausible way it could bite us.
I think the post-image of [1] looks nicer when reviewed stand-alone, so
I'm not against the change per-se, I actually like it.
And I don't have a use-case for using that feature further, in a way
that isn't easy to do differently.
But e.g. now we're having a parallel discussion about using some 3rd
party bitmap library. We might e.g. want to incorporate some 3rd party
JIT or whatever in the future. If we run into this question again it
would be nice to have it answered already.
And if we didn't have this J.5.7 reliance in that code already I don't
think it would be worth the effort to introduce one as a test
balloon. I'm only saying this in the context that we already have one.
1. https://lore.kernel.org/git/c64e4fa5-62c2-2a93-a4ef-bd84407ea570@web.de/
next prev parent reply other threads:[~2022-11-12 17:19 UTC|newest]
Thread overview: 106+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-04 6:31 "git bisect run" strips "--log" from the list of arguments Lukáš Doktor
2022-11-04 9:45 ` Jeff King
2022-11-04 11:10 ` Đoàn Trần Công Danh
2022-11-04 12:51 ` Jeff King
2022-11-04 11:36 ` Ævar Arnfjörð Bjarmason
2022-11-04 12:45 ` Jeff King
2022-11-04 13:07 ` Ævar Arnfjörð Bjarmason
2022-11-04 12:37 ` SZEDER Gábor
2022-11-04 12:44 ` Jeff King
2022-11-04 11:40 ` [PATCH 0/3] Convert git-bisect--helper to OPT_SUBCOMMAND Đoàn Trần Công Danh
2022-11-04 11:40 ` [PATCH 1/3] bisect--helper: remove unused options Đoàn Trần Công Danh
2022-11-04 12:53 ` Jeff King
2022-11-04 11:40 ` [PATCH 2/3] bisect--helper: move all subcommands into their own functions Đoàn Trần Công Danh
2022-11-04 12:55 ` Jeff King
2022-11-04 13:32 ` Ævar Arnfjörð Bjarmason
2022-11-04 14:03 ` Đoàn Trần Công Danh
2022-11-04 11:40 ` [PATCH 3/3] bisect--helper: parse subcommand with OPT_SUBCOMMAND Đoàn Trần Công Danh
2022-11-04 13:00 ` Jeff King
2022-11-04 13:46 ` Ævar Arnfjörð Bjarmason
2022-11-04 14:07 ` Đoàn Trần Công Danh
2022-11-04 13:55 ` [PATCH 0/3] Convert git-bisect--helper to OPT_SUBCOMMAND Ævar Arnfjörð Bjarmason
2022-11-05 17:03 ` [PATCH v2 " Đoàn Trần Công Danh
2022-11-05 17:03 ` [PATCH v2 1/3] bisect--helper: remove unused options Đoàn Trần Công Danh
2022-11-05 17:03 ` [PATCH v2 2/3] bisect--helper: move all subcommands into their own functions Đoàn Trần Công Danh
2022-11-05 17:13 ` Đoàn Trần Công Danh
2022-11-05 17:03 ` [PATCH v2 3/3] bisect--helper: parse subcommand with OPT_SUBCOMMAND Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 00/13] Turn git-bisect to be builtin Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 01/13] bisect tests: test for v2.30.0 "bisect run" regressions Đoàn Trần Công Danh
2022-11-07 21:31 ` Ævar Arnfjörð Bjarmason
2022-11-08 1:17 ` Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 02/13] bisect: refactor bisect_run() to match CodingGuidelines Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 03/13] bisect--helper: pass arg[cv] down to do_bisect_run Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 04/13] bisect: fix output regressions in v2.30.0 Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 05/13] bisect run: keep some of the post-v2.30.0 output Đoàn Trần Công Danh
2022-11-07 21:40 ` Ævar Arnfjörð Bjarmason
2022-11-08 1:26 ` Đoàn Trần Công Danh
2022-11-08 3:11 ` Ævar Arnfjörð Bjarmason
2022-11-05 17:07 ` [PATCH 06/13] bisect--helper: remove unused arguments from do_bisect_run Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 07/13] bisect--helper: pretend we're real bisect when report error Đoàn Trần Công Danh
2022-11-07 21:29 ` Ævar Arnfjörð Bjarmason
2022-11-05 17:07 ` [PATCH 08/13] bisect test: test exit codes on bad usage Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 09/13] bisect--helper: emit usage for "git bisect" Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 10/13] bisect--helper: make `state` optional Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 11/13] bisect--helper: remove subcommand state Đoàn Trần Công Danh
2022-11-07 21:45 ` Ævar Arnfjörð Bjarmason
2022-11-08 1:27 ` Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 12/13] bisect--helper: log: allow arbitrary number of arguments Đoàn Trần Công Danh
2022-11-05 17:07 ` [PATCH 13/13] Turn `git bisect` into a full built-in Đoàn Trần Công Danh
2022-11-05 23:18 ` [PATCH v2 0/3] Convert git-bisect--helper to OPT_SUBCOMMAND Taylor Blau
2022-11-10 16:36 ` [PATCH v3 " Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v3 1/3] bisect--helper: remove unused options Đoàn Trần Công Danh
2022-11-11 12:42 ` Ævar Arnfjörð Bjarmason
2022-11-10 16:36 ` [PATCH v3 2/3] bisect--helper: move all subcommands into their own functions Đoàn Trần Công Danh
2022-11-11 13:51 ` Ævar Arnfjörð Bjarmason
2022-11-10 16:36 ` [PATCH v3 3/3] bisect--helper: parse subcommand with OPT_SUBCOMMAND Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 00/11] Turn git-bisect to be builtin Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 01/11] bisect tests: test for v2.30.0 "bisect run" regressions Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 02/11] bisect: refactor bisect_run() to match CodingGuidelines Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 03/11] bisect: fix output regressions in v2.30.0 Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 04/11] bisect run: keep some of the post-v2.30.0 output Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 05/11] bisect-run: verify_good: account for non-negative exit status Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 06/11] bisect--helper: identify as bisect when report error Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 07/11] bisect test: test exit codes on bad usage Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 08/11] bisect--helper: emit usage for "git bisect" Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 09/11] bisect--helper: handle states directly Đoàn Trần Công Danh
2022-11-10 16:36 ` [PATCH v2 10/11] bisect--helper: log: allow arbitrary number of arguments Đoàn Trần Công Danh
2022-11-11 14:01 ` Ævar Arnfjörð Bjarmason
2022-11-10 16:36 ` [PATCH v2 11/11] Turn `git bisect` into a full built-in Đoàn Trần Công Danh
2022-11-11 13:53 ` Ævar Arnfjörð Bjarmason
2022-11-11 15:37 ` Jeff King
2022-11-11 21:09 ` Ævar Arnfjörð Bjarmason
2022-11-11 22:07 ` [PATCH v2 00/11] Turn git-bisect to be builtin Taylor Blau
2022-11-15 19:18 ` Taylor Blau
2022-11-15 19:36 ` Jeff King
2022-11-15 19:40 ` Taylor Blau
2022-11-11 12:32 ` [PATCH v3 0/3] Convert git-bisect--helper to OPT_SUBCOMMAND Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 00/13] bisect: v2.30.0 "run" regressions + make it built-in Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 01/13] bisect tests: test for v2.30.0 "bisect run" regressions Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 02/13] bisect: refactor bisect_run() to match CodingGuidelines Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 03/13] bisect: fix output regressions in v2.30.0 Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 04/13] bisect run: fix "--log" eating regression " Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 05/13] bisect run: keep some of the post-v2.30.0 output Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 06/13] bisect test: test exit codes on bad usage Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 07/13] bisect--helper: emit usage for "git bisect" Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 08/13] bisect--helper: have all functions take state, argc, argv, prefix Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 09/13] parse-options API: don't restrict OPT_SUBCOMMAND() to one *_fn type Ævar Arnfjörð Bjarmason
2022-11-05 8:32 ` René Scharfe
2022-11-05 11:34 ` Đoàn Trần Công Danh
2022-11-05 21:32 ` Phillip Wood
2022-11-05 13:52 ` Ævar Arnfjörð Bjarmason
2022-11-05 16:36 ` Phillip Wood
2022-11-05 21:59 ` Ævar Arnfjörð Bjarmason
2022-11-05 17:26 ` René Scharfe
2022-11-05 22:33 ` Ævar Arnfjörð Bjarmason
2022-11-06 8:25 ` René Scharfe
2022-11-06 13:28 ` Ævar Arnfjörð Bjarmason
2022-11-12 10:42 ` René Scharfe
2022-11-12 16:34 ` Jeff King
2022-11-12 16:55 ` Ævar Arnfjörð Bjarmason [this message]
2022-11-13 17:31 ` René Scharfe
2022-11-04 13:22 ` [PATCH 10/13] bisect--helper: remove dead --bisect-{next-check,autostart} code Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 11/13] bisect--helper: convert to OPT_SUBCOMMAND_CB() Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 12/13] bisect--helper: make `state` optional Ævar Arnfjörð Bjarmason
2022-11-04 13:22 ` [PATCH 13/13] Turn `git bisect` into a full built-in Ævar Arnfjörð Bjarmason
2022-11-05 0:13 ` [PATCH 00/13] bisect: v2.30.0 "run" regressions + make it built-in Taylor Blau
2022-11-10 12:50 ` Johannes Schindelin
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