PING [Patch][Middle-end]Add -fzero-call-used-regs=[skip|used-gpr|all-gpr|used|all]

[Segher Boessenkool]

[ Please quote correctly.  I fixed this up a bit. ]

On Mon, Aug 24, 2020 at 02:47:22PM +0000, Rodriguez Bahena, Victor wrote:
> > The call-clobbered regs are the only ones you *can* touch.  That does
> > not mean you should clear them all (it doesn't help much at all in some
> > cases).  Only the backend knows.
> 
> I think that for ROP mitigation purpose, we only need to clear the call-used (i.e, call-clobbered) registers that are used in the current routine and
> can pass parameters.

Which is more than you *can* do as well (consider return value registers
for example; there are more cases, in general; only the backend code can
know what is safe to do).


Segher