On Sun, 6 Jun 2021, Linus Torvalds wrote:

On Sun, Jun 6, 2021 at 11:59 AM Jakub Jelinek [off-list ref] wrote:

quoted

I think just
#define barrier() __asm__ __volatile__("" : : "i" (__COUNTER__) : "memory")
should be enough

Oh, I like that. Much better.

It avoids all the issues with comments etc, and because it's not using
__COUNTER__ as a string, it doesn't need the preprocessor games with
double expansion either.

So yeah, that seems like a nice solution to the issue, and should make
the barriers all unique to the compiler.

It also plants a nice LTO time-bomb (__COUNTER__ values will be unique
only within each LTO input unit, not across all of them).

Alexander