On Mon, Feb 28, 2022 at 12:37:15PM -0800, Linus Torvalds wrote:

On Mon, Feb 28, 2022 at 12:16 PM Matthew Wilcox [off-list ref] wrote:

quoted

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.

#define ___PASTE(a, b)	a##b
#define __PASTE(a, b) ___PASTE(a, b)
#define _min(a, b, u) ({         \
        typeof(a) __PASTE(__a,u) = (a);            \
        typeof(b) __PASTE(__b,u) = (b);            \
        __PASTE(__a,u) < __PASTE(__b,u) ? __PASTE(__a,u) : __PASTE(__b,u); })

#define min(a, b) _min(a, b, __COUNTER__)

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

(probably there's a more elegant way to do this)