Re: Xen MP panics in cpu_switchto()

[Andrew Doran <ad%netbsd.org@localhost>]

On Mon, Jan 13, 2020 at 05:43:51PM +0100, Manuel Bouyer wrote:

> On Mon, Jan 13, 2020 at 04:59:50PM +0100, Manuel Bouyer wrote:
> > It also sets rsp and rbp. I think rbp is not set by anything else, at last
> > in the Xen case.
> > The different rbp value would explain why in one case we hit a KASSERT()
> > in lwp_startup later.
> > But I don't know what pcb_rbp contains; I couldn't find where the pcb for
> > idlelwp is initialized.
> 
> I tried the attached patch, which should set rsp/rbp as cpu_switchto()
> does. It doens't cause the lwp_startup() KASSERT as calling cpu_switchto()
> does; it also doesn't change the scheduler behavior.

Wait - do you mean that everything works now?  Or that everything still runs
on CPU0?

The very first thing that idle_loop() does on amd64/i386 is set up the frame
pointer - ebp/rbp.

0000000000000000 <idle_loop>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   41 56                   push   %r14
   6:   41 55                   push   %r13

Andrew