linux-kernel - RE: [PATCH v2] kbuild: treat char as always unsigned

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Message-ID: <a296bd41278d4bd4a4e9f0d31a540613@AcuMS.aculab.com>
Date:   Fri, 30 Dec 2022 13:13:55 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     David Laight <David.Laight@...LAB.COM>,
        'Holger Lubitz' <holger.lubitz@...nline.de>,
        'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>
CC:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-toolchains@...r.kernel.org" <linux-toolchains@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-m68k@...ts.linux-m68k.org" <linux-m68k@...ts.linux-m68k.org>
Subject: RE: [PATCH v2] kbuild: treat char as always unsigned

....
> > int strcmp1(const char *cs, const char *ct)
> > {
> >         int res;
> >
> >         asm ("\n"
> >                 "1: move.b  (%0)+,%2\n"  /* get *cs */
> >                 "   jeq     2f\n"        /* end of first string? */
> >                 "   cmp.b   (%1)+,%2\n"  /* compare *ct */
> >                 "   jeq     1b\n"        /* if equal, continue */
> >                 "   jra     3f\n"        /* else skip to tail */
> >                 "2: cmp.b   (%1)+,%2\n"  /* compare one last byte */
> >                 "3: subx.l  %2, %2\n"    /* -1 if borrow, 0 if not */
> >                 "   jls     4f\n"        /* if set, z is from sub.b */
> 
> The subx will set Z unless C was set.
> So that doesn't seem right.

Clearly my brain was asleep earlier.
subx will clear Z not set it.

	David

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