Messages in this thread | | | Date | Sun, 3 May 2020 14:58:13 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 14/18] static_call: Add static_cond_call() |
| |
On Sat, May 02, 2020 at 03:08:00PM +0200, Rasmus Villemoes wrote: > On 01/05/2020 22.29, Peter Zijlstra wrote: > > Extend the static_call infrastructure to optimize the following common > > pattern: > > > > if (func_ptr) > > func_ptr(args...) > > > > + > > #define static_call(name) __static_call(name) > > +#define static_cond_call(name) (void)__static_call(name) > > > > + > > #define static_call(name) __static_call(name) > > +#define static_cond_call(name) (void)__static_call(name) > > > > > +#define static_cond_call(name) \ > > + if (STATIC_CALL_KEY(name).func) \ > > + ((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func)) > > + > > This addresses neither the READ_ONCE issue nor the fact that,
> AFAICT, > the semantics of > > static_cond_call(foo)(i++) > > will depend on CONFIG_HAVE_STATIC_CALL.
True.
So there is something utterly terrible we can do to address both:
void __static_call_nop(void) { }
#define __static_cond_call(name) \ ({ \ void *func = READ_ONCE(STATIC_CALL_KEY(name).func); \ if (!func) \ func = &__static_call_nop; \ (typeof(STATIC_CALL_TRAMP(name))*)func; \ })
#define static_cond_call(name) (void)__static_cond_call(name)
This gets us into Undefined Behaviour territory, but it ought to work.
It adds the READ_ONCE(), and it cures the argument evaluation issue.
> Also, I'd have appreciated being > cc'ed on new revisions instead of stumbling on it by chance.
Sorry, my bad, I forgot about that :-/. I rushed to repost, and simply forgot a few things.
| |