linuxkpi compiler.h: replace dummy expressions with dummy statements

[rlibby]

Summary

It looks like the __acquire and __release macros are for the consumption of static analysis tools and have no semantic effect. Transform the definitions from constant expressions to empty statements in order to avoid -Wunused-value from gcc.

I glanced through linux kernel code and didn't see any places where __acquire or __release were actually being used as expressions.

Test Plan

buildkernel with gcc

[markj]

sys/compat/linuxkpi/common/include/linux/compiler.h

42–43

It looks like these require the same treatment. They're unused at the moment, but it wouldn't hurt to fix them while here.

[rlibby]

sys/compat/linuxkpi/common/include/linux/compiler.h

42–43

So I actually did look at __chk_user_ptr & __chk_io_ptr and it looked like they were being used in an expression context in some linux kernel code (uselessly, in non-ultimate position of comma expressions. Define a value, cast off its type, then comma off its value ... ). So I thought to punt for now. Since, as you say, they're unused by us for now, it won't matter. Alternate could be (void)0 (for just those two or all four). What's your preference here?

[markj]

sys/compat/linuxkpi/common/include/linux/compiler.h

42–43

Ah, I see. I think it'd make sense to use (void)0 in this case and keep the dummy statements below, but I don't feel strongly about it.

[rlibby]

markj feedback: also quiet future warnings for __chk_{user,io}_ptr

[markj]

Thanks for fixing this, approved.

[• hselasky]

Looks good!