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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	"Jason A. Donenfeld" <Jason@zx2c4.com>,
	linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-toolchains@vger.kernel.org,
	Masahiro Yamada <masahiroy@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-m68k@lists.linux-m68k.org
Subject: Re: [PATCH v2] kbuild: treat char as always unsigned
Date: Wed, 21 Dec 2022 11:08:05 -0800	[thread overview]
Message-ID: <CAHk-=wiL2njz3b-_jY7iSJ15eu-9Drb4TOyPdd0cJ=kk_RQEvg@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wjOcqWxpUUrWKLKznRg-HXxRn1AXLW9B6SPq-ioLObdjw@mail.gmail.com>

On Wed, Dec 21, 2022 at 10:46 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> But it looked very obvious indeed, and I hate having buggy code that
> is architecture-specific when we have generic code that isn't buggy.

Side note: we have an x86-64 implementation that looks fine (but not
really noticeably better than the generic one) that is based on the
'return subtraction' model. But it seems to get it right.

And we have a 32-bit x86 assembly thing that is based on 'rep scasb',
that then uses the carry bit to also get things right.

That 32-bit asm goes back to Linux 0.01 (with some changes since to
use "sbbl+or" instead of a conditional neg). I was playing around a
lot with the 'rep' instructions back when, since it was all part of
"learn the instruction set" for me.

Both of them should probably be removed as pointless too, but they
don't seem actively buggy.

               Linus

  reply	other threads:[~2022-12-21 19:08 UTC|newest]

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-19 16:26 [PATCH] kbuild: treat char as always signed Jason A. Donenfeld
2022-10-19 16:54 ` Segher Boessenkool
2022-10-19 17:14   ` Linus Torvalds
2022-10-19 17:26     ` Linus Torvalds
2022-10-19 18:10       ` Nick Desaulniers
2022-10-19 18:35         ` Linus Torvalds
2022-10-19 19:23           ` Andy Shevchenko
2022-10-19 19:36             ` Linus Torvalds
2022-10-19 17:43     ` Segher Boessenkool
2022-10-19 18:11       ` Linus Torvalds
2022-10-19 18:20         ` Nick Desaulniers
2022-10-19 18:56           ` Linus Torvalds
2022-10-19 19:11             ` Kees Cook
2022-10-19 19:30               ` Linus Torvalds
2022-10-19 20:35                 ` Jason A. Donenfeld
2022-10-20  0:10                   ` Linus Torvalds
2022-10-20  3:11                     ` Jason A. Donenfeld
2022-10-19 20:15             ` Segher Boessenkool
2022-10-19 21:07         ` David Laight
2022-10-19 21:26           ` Segher Boessenkool
2022-10-20 10:41         ` Gabriel Paubert
2022-10-21 22:46           ` Linus Torvalds
2022-10-22  6:06             ` Gabriel Paubert
2022-10-22 18:16               ` Linus Torvalds
2022-10-23 20:23                 ` Gabriel Paubert
2022-10-25 23:00                   ` Kees Cook
2022-10-26  0:04                     ` Jason A. Donenfeld
2022-10-26 15:41                       ` Kees Cook
2022-10-19 19:54 ` Linus Torvalds
2022-10-19 20:23   ` Jason A. Donenfeld
2022-10-19 20:30     ` [PATCH v2] kbuild: treat char as always unsigned Jason A. Donenfeld
2022-10-19 23:56       ` Linus Torvalds
2022-10-20  0:02         ` Jason A. Donenfeld
2022-10-20  0:38           ` Linus Torvalds
2022-10-20  2:59             ` Jason A. Donenfeld
2022-10-20 18:41             ` Kees Cook
2022-10-21  1:01               ` Jason A. Donenfeld
2022-10-20 20:24         ` Segher Boessenkool
2022-10-24  9:24       ` Dan Carpenter
2022-10-24  9:30         ` Dan Carpenter
2022-10-24 16:33           ` Jason A. Donenfeld
2022-10-24 17:10             ` Linus Torvalds
2022-10-24 17:17               ` Jason A. Donenfeld
2022-10-25 19:22                 ` Kalle Valo
2022-10-25 10:16               ` David Laight
2022-10-24 15:17         ` Jason A. Donenfeld
2022-12-21 14:53       ` Guenter Roeck
2022-12-21 15:05         ` Geert Uytterhoeven
2022-12-21 15:23           ` Guenter Roeck
2022-12-21 15:29           ` Rasmus Villemoes
2022-12-21 15:56             ` Guenter Roeck
2022-12-21 17:06               ` Linus Torvalds
2022-12-21 17:19                 ` Guenter Roeck
2022-12-21 18:46                   ` Linus Torvalds
2022-12-21 19:08                     ` Linus Torvalds [this message]
2022-12-21 21:01                     ` Guenter Roeck
2022-12-22 13:05                     ` Geert Uytterhoeven
2022-12-22 10:41                 ` David Laight
     [not found]                   ` <f02e0ac7f2d805020a7ba66803aaff3e31b5eeff.camel@t-online.de>
2022-12-24  9:47                     ` Geert Uytterhoeven
2022-12-30 11:39                     ` David Laight
2022-12-30 13:13                       ` David Laight
2023-01-02  8:29                       ` Geert Uytterhoeven
2022-12-21 17:49               ` Andreas Schwab
2022-12-21 16:57             ` Geert Uytterhoeven
2022-10-19 20:58   ` [PATCH] kbuild: treat char as always signed David Laight
2022-10-26  0:10   ` make ctype ascii only? (was [PATCH] kbuild: treat char as always signed) Rasmus Villemoes
2022-10-26 18:10     ` Linus Torvalds
2022-10-27  7:59       ` Rasmus Villemoes
2022-10-27 18:28         ` Linus Torvalds
2022-10-20  8:39 ` [PATCH] kbuild: treat char as always signed kernel test robot
2022-10-20 16:33   ` Jason A. Donenfeld

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