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

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Message-ID: <20221221171922.GA2470607@roeck-us.net>
Date:   Wed, 21 Dec 2022 09:19:22 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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-kbuild@...r.kernel.org,
        linux-arch@...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
Subject: Re: [PATCH v2] kbuild: treat char as always unsigned

On Wed, Dec 21, 2022 at 09:06:41AM -0800, Linus Torvalds wrote:
> On Wed, Dec 21, 2022 at 7:56 AM Guenter Roeck <linux@...ck-us.net> wrote:
> >
> > The above assumes an unsigned char as input to strcmp(). I consider that
> > a hypothetical problem because "comparing" strings with upper bits
> > set doesn't really make sense in practice (How does one compare Günter
> > against Gunter ? And how about Gǖnter ?). On the other side, the problem
> > observed here is real and immediate.
> 
> POSIX does actually specify "Günter" vs "Gunter".
> 
> The way strcmp is supposed to work is to return the sign of the
> difference between the byte values ("unsigned char").
> 
> But that sign has to be computed in 'int', not in 'signed char'.
> 
> So yes, the m68k implementation is broken regardless, but with a
> signed char it just happened to work for the US-ASCII case that the
> crypto case tested.
> 

I understand. I just prefer a known limited breakage to completely
broken code.

> I think the real fix is to just remove that broken implementation
> entirely, and rely on the generic one.

Perfectly fine with me.

Thanks,
Guenter