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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 19 Oct 2022 16:56:03 -0700
Message-ID: <CAHk-=wit-67VU=kt-8Ojtx04m6wxfqypKLzW7CuSeEH_9MYZvw@mail.gmail.com>
Subject: Re: [PATCH v2] kbuild: treat char as always unsigned
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     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>
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On Wed, Oct 19, 2022 at 1:30 PM Jason A. Donenfeld <Jason@zx2c4.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?

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.

                       Linus