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

Linus Torvalds
2022-10-19T17:14:53Z

On Wed, Oct 19, 2022 at 9:57 AM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> This is an ABI change. It is also hugely detrimental to generated
> code quality on architectures that make the saner choice (that is, have
> most instructions zero-extend byte quantities).

Yeah, I agree. We should just accept the standard wording, and be
aware that 'char' has indeterminate signedness.

But:

> Instead, don't actively disable the compiler warnings that catch such
> cases? So start with removing footguns like
>
> # disable pointer signed / unsigned warnings in gcc 4.0
> KBUILD_CFLAGS += -Wno-pointer-sign

Nope, that won't fly.

The pointer-sign thing doesn't actually help (ie it won't find places
where you actually compare a char), and it causes untold damage in
doing completely insane things.

For example, it suddenly starts warning if you *are* being careful,
and explicitly use 'unsigned char array[]' things to avoid any sign
issues, and then want to do simple and straightforward things with
said array (like doing a 'strcmp()' on it).

Seriously, -Wpointer-sign is not just useless, it's actively _evil_.
The fact that you suggest that clearly means that you've never used
it.

Linus