Re: [PATCH] compiler.h: simplify data_race() macro

From: Marco Elver
Date: Mon Jun 24 2024 - 08:28:39 EST


On Mon, 24 Jun 2024 at 13:49, Alexey Dobriyan <adobriyan@xxxxxxxxx> wrote:
>
> Use auto type deduction and comma expression to decrease macro expansion
> size.
>
> __unqual_scalar_typeof() is quite wordy macro by itself.
>
> "expr" can be arbitrary complex so not expanding it twice is good.
> Should be faster too because type is deduced only once
> from the initializer.
>
> Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>

Thanks for cleaning up. That code certainly predates the availability
of __auto_type. Although if I recall correctly, __unqual_scalar_typeof
became the first user of _Generic (the first C11 keyword we used in
the kernel?), but we used some ifdef to still support ancient
compilers initially (that definitely also didn't have __auto_type).

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

Which tree is this for?

> ---
>
> include/linux/compiler.h | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -200,10 +200,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> */
> #define data_race(expr) \
> ({ \
> - __unqual_scalar_typeof(({ expr; })) __v = ({ \
> - __kcsan_disable_current(); \
> - expr; \
> - }); \
> + __auto_type __v = (__kcsan_disable_current(), expr); \
> __kcsan_enable_current(); \
> __v; \
> })