From: Junio C Hamano <gitster@pobox.com>
To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Cc: Daniel Gurney <dgurney99@gmail.com>,
"brian m. carlson" <sandals@crustytoothpaste.net>,
Jeff King <peff@peff.net>,
git@vger.kernel.org
Subject: Re: [PATCH v2] compat/bswap.h: simplify MSVC endianness detection
Date: Tue, 10 Nov 2020 09:30:43 -0800 [thread overview]
Message-ID: <xmqqtutx6rwc.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <xmqqy2j96sd4.fsf@gitster.c.googlers.com> (Junio C. Hamano's message of "Tue, 10 Nov 2020 09:20:39 -0800")
Junio C Hamano <gitster@pobox.com> writes:
> Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
>
>> As a maintainer, I am less concerned about the "result today" than I am
>> about keeping things easy and effortless to maintain. One of your patches
>> accomplishes that. The other one made it into `next`:
>> https://github.com/git/git/commit/91a67b86f77
>
> I do not think reverting it and requeuing
>
> https://lore.kernel.org/git/20201107221916.1428757-1-dgurney99@gmail.com/
>
> would help future folks why we ignore _MSC_VER as any sign usable to
> detect endianness, so I'd prefer to see a patch *on top* of 1af265f0
> (compat/bswap.h: simplify MSVC endianness detection, 2020-11-08),
> which is 91a67b86f77^2, that explains why we prefer to list archs
> explicitly in its log message, which would be the primary value of
> that commit.
>
> Something along this line, perhaps?
>
> -- >8 --
>
> Subject: compat/bswap.h: do not assume MSVC is little-endian only
>
> Earlier, with 1af265f0 (compat/bswap.h: simplify MSVC endianness
> detection, 2020-11-08), we tried to simplify endianness detection
> used in compat/bswap.h by assuming that any version Git compiled by
> MSVC (detected by _MSC_VER preprocessor macro) is meant to run on
> little endian boxes, as the versions of old MSVC that support m68k
> and MIPS do not support some C99 features used in the codebase
> anyway.
>
> While it might hold true that modern versions of Windows are all
> little-endian, MSVC is and/or can be ported to build for big-endian
> boxes, so tying _MSC_VER with endianness is a bit too restrictive.
>
> Let's go back to the old way to use _MSC_VER to learn what
> preprocessor macros compiler uses to tell us which arch we are
> building for, and list these arches that are little-endian
> explicitly.
>
> ... signed-off-by from you and helped-by from others ...
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
> diffstat
> patch
Daniel's patch adds _M_ARM64 to the list, but do we need to do
anything further to tell the endian on such a bi-endian arch, or
does MSVC only support little-endian for that architecture?
Just double-checking as the "confusion" that started this thread
came from an assumption that MSVC == Windows == big-endian, and you
told us MSVC != Windows. Now the patch assumes ARM64-on-MSVC is
little-endian only and we want to make sure that assumption is true.
And perhaps it is worth documenting in the log, perhaps
... that are little-endian explicitly. Note that ARM64 is
bi-endian in nature but we treat it little-endian as MSVC
does not treat the arch as bi-endian.
or something like that at the end (I do not know what MSVC actually
does---just illustrating the level of details I expect in the
explanation).
Thanks.
next prev parent reply other threads:[~2020-11-10 17:30 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-07 23:47 [PATCH] compat/bswap.h: Simplify MSVC endianness detection Daniel Gurney
2020-11-08 0:12 ` brian m. carlson
2020-11-08 9:57 ` [PATCH v2] compat/bswap.h: simplify " Daniel Gurney
2020-11-10 0:31 ` Jeff King
2020-11-10 2:36 ` brian m. carlson
2020-11-10 6:00 ` Junio C Hamano
2020-11-10 14:04 ` Johannes Schindelin
2020-11-10 15:35 ` Daniel Gurney
2020-11-10 15:47 ` Johannes Schindelin
2020-11-10 17:20 ` Junio C Hamano
2020-11-10 17:30 ` Junio C Hamano [this message]
2020-11-10 22:37 ` Johannes Schindelin
2020-11-10 14:21 ` Jeff King
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