RFC: Should x86-64 support arbitrary calling conventions?

[Florian Weimer]

* H. J. Lu:

> I compared time for "make check" in glibc.  On Nehalem and Skylake,
> the time differences are within noises.  On Knights Landing, xsave
> is about 1% slower.

Thanks for doing this benchmarking.

What's the increase in stack usage?

> I don't expect xsave will make any differences for long running
> benchmarks.  Its impact may only show up on short programs which
> call external functions a few times with lazy binding.
>
> Should we consider it at all?

I think the main benefit is that we don't have to adjust the dynamic
linker trampoline for each new microarchitecture, and applications can
safely start using new CPU features once the kernel indicates support.