Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

Steven Rostedt
2018-11-29T19:31:38Z

On Thu, 29 Nov 2018 11:24:43 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Thu, Nov 29, 2018 at 11:16 AM Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > But then we need to implement all numbers of parameters.
>
> Oh, I agree, it's nasty.
>
> But it's actually a nastiness that we've solved before. In particular,
> with the system call mappings, which have pretty much the exact same
> issue of "map unknown number of arguments to registers".
>
> Yes, it's different - there you map the unknown number of arguments to
> a structure access instead. And yes, the macros are unbelievably ugly.
> See
>
> arch/x86/include/asm/syscall_wrapper.h

Those are not doing inline assembly.

>
> and the __MAP() macro from
>
> include/linux/syscalls.h
>
> so it's not pretty. But it would solve all the problems.
>

Again, not inline assembly, and those only handle up to 6 parameters.

My POC started down this route, until I notice that there's tracepoints
that have 13 parameters! And I need to handle all tracepoints.

Yes, we can argue that we need to change those (if that doesn't break
the API of something using it).

-- Steve