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Date: Wed, 19 Oct 2022 10:14:20 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Segher Boessenkool <segher@...nel.crashing.org> Cc: "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> Subject: Re: [PATCH] kbuild: treat char as always signed On Wed, Oct 19, 2022 at 9:57 AM Segher Boessenkool <segher@...nel.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
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