linux-kernel - Re: [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr

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Message-ID: <CAHk-=wgBfJ1-cPA2LTvFyyy8owpfmtCuyiZi4+um8DhFNe+CyA@mail.gmail.com>
Date:   Mon, 28 Feb 2022 12:37:15 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christian König <christian.koenig@....com>,
        Jakob Koschel <jakobkoschel@...il.com>,
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Subject: Re: [PATCH 2/6] treewide: remove using list iterator after loop body
 as a ptr

On Mon, Feb 28, 2022 at 12:16 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> Then we can never use -Wshadow ;-(  I'd love to be able to turn it on;
> it catches real bugs.

Oh, we already can never use -Wshadow regardless of things like this.
That bridge hasn't just been burned, it never existed in the first
place.

The whole '-Wshadow' thing simply cannot work with local variables in
macros - something that we've used since day 1.

Try this (as a "p.c" file):

        #define min(a,b) ({                     \
                typeof(a) __a = (a);            \
                typeof(b) __b = (b);            \
                __a < __b ? __a : __b; })

        int min3(int a, int b, int c)
        {
                return min(a,min(b,c));
        }

and now do "gcc -O2 -S t.c".

Then try it with -Wshadow.

In other words, -Wshadow is simply not acceptable. Never has been,
never will be, and that has nothing to do with the

        typeof(pos) pos

kind of thing.

Your argument just isn't an argument.

              Linus