Re: [PATCH 2/2] x86/irqflags: Use ASM_OUTPUT_RM in native_save_fl()

[Linus Torvalds]

On Sun, 21 Dec 2025 at 13:47, Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> Unfortunately I was told it was not better, some clang versions had
> bugs with it.

The whole "builtin is worse than inline asm" is actually a thing even
when not actively buggy. We've had things like that a few times
before.

It's why we have out own variable_ffs() implementation, for example,
and do things like

   #define ffs(x) (__builtin_constant_p(x) ? __builtin_ffs(x) : variable_ffs(x))

because __builtin_ffs() generates pointlessly silly code on at least
some compiler versions:

    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106471

So then just using inline asm gets us at least reliable results, and
we can - and do - tweak it for specific known configs.

             Linus