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

[Andy Lutomirski]

On Thu, Nov 29, 2018 at 11:25 AM 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
>
> and the __MAP() macro from
>
>     include/linux/syscalls.h
>
> so it's not pretty. But it would solve all the problems.
>

Until someone does:

struct foo foo;
static_call(thingy, foo);

For syscalls, we know better than to do that.  For static calls, I'm
less confident.