linux-kernel - Re: [PATCH 1/1] minmax.h: Slightly relax the type checking done by min() and max().

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Message-ID: <CAHk-=wjgqs7Uev9=X8qP0mR0C+KoRze6d+1SoMib5x6o3yZSQg@mail.gmail.com>
Date:   Sun, 27 Nov 2022 13:54:12 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH 1/1] minmax.h: Slightly relax the type checking done by
 min() and max().

On Sun, Nov 27, 2022 at 1:42 PM David Laight <David.Laight@...lab.com> wrote:
>
> Why should it be a problem?
> min(-4, sizeof(X)) becomes min(-4, (int)sizeof(X)) and thus -4.
> Without the cast the -4 is converted to a very large unsigned
> value so the result is sizeof(X) - not at all expected.

That is EXACTLY the problem.

You even enumerate it, and work through exactly what happens, and then
you STILL say "this is not a problem".

It damn well is a HUGE problem. When people say "I need my offset to
be smaller than the size of the object", then a value like -4 IS NOT
ACCEPTABLE. It should cause a huge type warning about how the test was
broken.

David, this is literally *EXACTLY* why we have those strict type issues.

The fact that you don't even seem to realize why this would be a
problem makes me NAK this patch so hard that it isn't even funny.

Andrew, please remove this from your queue. It's not even remotely
acceptable. I was hoping I was misreading the patch, but it turns out
that this "relax the rules way too much" was apparently intentional.

            Linus