On Mon, Feb 28, 2022 at 12:37:15PM -0800, Linus Torvalds wrote:
On Mon, Feb 28, 2022 at 12:16 PM Matthew Wilcox willy@infradead.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.
#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)