RFC: Should x86-64 support arbitrary calling conventions?

[Zack Weinberg]

On Thu, Mar 16, 2017 at 6:07 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> According to x86-64 psABI, xmm0-xmm7 can be used to pass function
> parameters.  But ICC also uses xmm8-xmm15 to pass function parameters.
> This doesn't work with newer glibc since _dl_runtime_resolve only preserves
> the first 8 vector registers:

I don't understand why it's necessary for _dl_runtime_resolve to touch
the vector registers _at all_.  It's called from a PLT stub, so it has
to be careful to preserve all the integer registers including the
usually-call-clobbered ones, but shouldn't it be able to do all of its
work without disturbing the floating point and vector registers?

zw