RE: [PATCH] kbuild: treat char as always signed

From: David Laight <David.Laight@ACULAB.COM>
To: 'Linus Torvalds' <torvalds@linux-foundation.org>,
	Segher Boessenkool <segher@kernel.crashing.org>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-kbuild@vger.kernel.org" <linux-kbuild@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-toolchains@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>
Subject: RE: [PATCH] kbuild: treat char as always signed
Date: Wed, 19 Oct 2022 21:07:01 +0000	[thread overview]
Message-ID: <e0f6a641c7464d71abbddb4befd35e59@AcuMS.aculab.com> (raw)
In-Reply-To: <CAHk-=wiNNKLFfa0d+Hk=Wm5caiKjLY4V9wwu9DhcSSwPuMbxrg@mail.gmail.com>

From: Linus Torvalds
> Sent: 19 October 2022 19:11
...
> Explicit casts are bad (unless, of course, you are explicitly trying
> to violate the type system, when they are both required, and a great
> way to say "look, I'm doing something dangerous").

The worst ones in the kernel are the __force ones for sparse.
They really ought to be a function (#define) so that they
are not seen by the compiler at all.
Otherwise they can hide a multitude of sins.

There are also the casts to convert integer values to/from unsigned.
and to different sized integers.
They all happen far too often and can hide things.
A '+ 0u' will convert into to unsigned int without a cast.
Casts really ought to be rare.
Even the casts to from (void *) (for 'buffers') can usually be
made implicit in a function call argument.

	David

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