On Tue, Oct 10, 2023 at 8:26 PM Jeff Law <jeffreya...@gmail.com> wrote: > > > > On 10/10/23 18:24, Andrew Waterman wrote: > > I remembered another concern since we discussed this patch privately. > > Using ra for long calls results in a sequence that will corrupt the > > return-address stack. > Yup. We've actually got data on that internally, it's not showing up in > a significant way in practice. > > > I know nothing > > about the complexity of register scavenging, but it would be nice to > > opportunistically use a scratch register (other than t0), falling back > > to ra only when necessary. > The nice thing about making $ra fixed is some can add a register > scavenging approach, then fall back to $ra if they're unable to find a > register to reuse. > > > > > Tangentially, I noticed the patch uses `jump label, ra' for far > > branches but uses `call label' for far jumps. These corrupt the RAS > > in opposite ways (the former pops the RAS and the latter pushes it. > > Any reason for using a different sequence in one than the other? > I'd noticed it as well -- that's the way it was in the patch that was > already in Ventana's tree ;-) My plan was to address that separately > after dropping in enough infrastructure to allow me to force everything > to be far branches for testing purposes.
Sounds like we're thinking many of the same thoughts... thanks for dragging this patch towards the finish line! > > jeff
