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

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Message-ID: <Y1CP/uJb1SQjyS0n@zx2c4.com>
Date:   Thu, 20 Oct 2022 02:02:06 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     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>
Subject: Re: [PATCH v2] kbuild: treat char as always unsigned

On Wed, Oct 19, 2022 at 04:56:03PM -0700, Linus Torvalds wrote:
> On Wed, Oct 19, 2022 at 1:30 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
> >
> > So let's just eliminate this particular variety of heisensign bugs
> > entirely. Set `-funsigned-char` globally, so that gcc makes the type
> > unsigned on all architectures.
> >
> > This will break things in some places and fix things in others, so this
> > will likely cause a bit of churn while reconciling the type misuse.
> 
> Yeah, if we were still in the merge window, I'd probably apply this,
> but as things stand, I think it should go into linux-next and cook
> there for the next merge window.
> 
> Anybody willing to put this in their -next trees?

Sure, happy to take it.


> 
> Any breakage it causes is likely going to be fairly subtle, and in
> some random driver that isn't used on architectures that already have
> an unsigned 'char' type.
> 
> I think the architectures with an unsigned 'char' are arm, powerpc and
> s390, in all their variations (ie both 32- and 64-bit).
> 
> So all *core* code should be fine with this, but that still leaves a
> lot of drivers that have likely never been tested on anything but x86,
> and could just stop working.
> 
> I don't think breakage is very *likely*, but I suspect it exists.

Given I've started with cleaning up one driver already, I'll keep my eye
on further breakage.

Jason

> 
>                        Linus