Re: [RFC PATCH 14/21] treewide: static_call: Pass call arguments to the macro

Peter Zijlstra
2022-05-02T07:46:57Z

On Fri, Apr 29, 2022 at 05:49:21PM -0700, Sami Tolvanen wrote:
> On Fri, Apr 29, 2022 at 4:21 PM Peter Zijlstra <peterz@infradead.org> wrote:
> > Can you explain why this is needed? I don't think there are any indirect
> > calls to get confused about. That is, if you have STATIC_CALL_INLINE
> > then the compiler should be emitting direct calls to the trampoline.
>
> Clang emits an indirect call for ({ &f; })(), which is optimized into
> a direct call when possible. Come to think of it, the recent
> InstCombine change to the compiler patch should solve this issue. Let
> me double check, I'd be more than happy to drop these two patches.

Oooh, but this must not require any magic. That is, we have a *ton* of
code that relies on constant propagation of function pointers to not
emit indirect calls.

Please make sure that 'just-works'.

Look at all the __always_inline functions in rbtree*.h for instance,
some like latch and augment rely on quite complicated const propagation
for the actual function pointer is in a const struct.

I've verified all that actually generates direct calls when we did that
code (on GCC, clang wasn't really a thing back then).