On Mon, Jun 22, 2020 at 8:40 PM Kevin O'Connor <ke...@koconnor.net> wrote:
>
> On Tue, Jun 16, 2020 at 10:31:17PM -0400, Jason Andryuk wrote:
> > xen_preinit() runs early and changes DebugOutputPort. qemu_preinit() runs
> > soon after. inb on DebugOutputPort doesn't work on Xen, so the check
> > will always fail and DebugOutputPort will be cleared to 0 disabling
> > output.
> >
> > Quick exit the function when running on Xen to preserve the modified
> > DebugOutputPort.
> >
> > Signed-off-by: Jason Andryuk <jandr...@gmail.com>
> > ---
> > src/hw/serialio.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/src/hw/serialio.c b/src/hw/serialio.c
> > index 3163344..c6297bc 100644
> > --- a/src/hw/serialio.c
> > +++ b/src/hw/serialio.c
> > @@ -106,6 +106,10 @@ u16 DebugOutputPort VARFSEG = 0x402;
> > void
> > qemu_debug_preinit(void)
> > {
> > + /* Xen already overrode DebugOutputPort in xen_preinit(). */
> > + if (runningOnXen())
> > + return;
>
> Thanks. The code looks fine to me. However, I find the comment
> confusing as this function only checks if output is enabled - it
> doesn't check the validity of the port itself. Perhaps a comment like
> "Xen doesn't support checking if debug output is active".
Sure, I can change it. The other part I was trying to convey is that
even though Xen uses QEMU, and this function is prefixed with qemu_,
DebugOutputPort is different and cannot be checked. Since
DebugOutputPort is set right above this function, a reader may not
expect it to have changed. Having said that, your wording clearly
explains why Xen is leaving this function early.
Thanks,
Jason
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