RFR(S)[13]: AArch64: float point register corruption in ZBarrierSetAssembler::load_at

[Stuart Monteith]

The first thing you'll hit is a call from the interpreter.
TemplateInterpreterGenerator::generate_fixed_frame

On Thu, 20 Jun 2019 at 18:48, Andrew Haley <aph at redhat.com> wrote:
>
> On 6/20/19 5:27 PM, Stuart Monteith wrote:
> >    I see that we get a tmp1 register, however I've found that is not
> > something we can reliably use - whether it is set to noreg or matches
> > the src/dst registers. I've found rscratch2 to be reliably untouched.
> > The use of scratch registers is something that needs to get fixed up
> > on AArch64.
>
> The worst abuse of AArch64 scratch registers is definitely in the
> GC barriers. The rule is simple: scratch registers are always
> clobbered in assembler macros. If any code calls, say, load_at() but
> expects scratch registers to be preserved, that code is broken. We
> need to fix it.
>
> So, please tell me: where is the code which is broken by load_at()
> using rscratch1?
>
> --
> Andrew Haley
> Java Platform Lead Engineer
> Red Hat UK Ltd. <https://www.redhat.com>
> https://keybase.io/andrewhaley
> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671