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

[Steven Rostedt]

On Thu, 29 Nov 2018 11:24:43 -0800
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Thu, Nov 29, 2018 at 11:16 AM Steven Rostedt <rostedt@xxxxxxxxxxx> 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