On Thu, Oct 02, 2025 at 04:56:48PM +0200, Alejandro Vallejo wrote: > On Thu Oct 2, 2025 at 4:17 PM CEST, Roger Pau Monné wrote: > > On Thu, Oct 02, 2025 at 04:02:00PM +0200, Alejandro Vallejo wrote: > >> On Thu Oct 2, 2025 at 3:38 PM CEST, Roger Pau Monné wrote: > >> > On Thu, Oct 02, 2025 at 11:37:36AM +0100, Andrew Cooper wrote: > >> >> On 02/10/2025 11:22 am, Roger Pau Monne wrote: > >> >> > Reading from the E9 port if the emergency console is active should > >> >> > return > >> >> > 0xe9 according to the documentation from Bochs: > >> >> > > >> >> > https://bochs.sourceforge.io/doc/docbook/user/bochsrc.html > >> >> > > >> >> > See `port_e9_hack` section description. > >> >> > > >> >> > Fix Xen so it also returns the port address. OSes can use it to > >> >> > detect > >> >> > whether the emergency console is available or not. > >> >> > > >> >> > Fixes: d1bd157fbc9b ("Big merge the HVM full-virtualisation > >> >> > abstractions.") > >> >> > Signed-off-by: Roger Pau Monné <[email protected]> > >> >> > >> >> Reviewed-by: Andrew Cooper <[email protected]> > >> >> > >> >> That's been wrong for rather a long time. How did you find it? > >> > > >> > I came across the documentation above and I didn't remember Xen > >> > returning any value for reads, which sadly was indeed true. > >> > > >> > This was because I had the intention to suggest Alejandro to (also?) use > >> > the port 0xe9 hack for printing from XTF, which should work for both > >> > Xen and QEMU. > >> > >> QEMU doesn't support 0xE9 though? > > > > AFAICT it does: > > > > https://wiki.osdev.org/QEMU#The_debug_console > > > > However when running QEMU on Xen as a device model writes to 0xe9 are > > handled in the hypervisor, and never forwarded to any device model. > > > > Regards, Roger. > > The more you know. I searched for it once upon a time and couldn't find it. > Thanks for the pointer. > > Regardless, "-debugcon stdio" is functionally equivalent to "-serial stdio" > and the latter can be adapted to work on real hardware too.
The emulated serial is possibly equivalent to the 0xe9 hack in QEMU, as I expect the serial is mostly setup to "just work". On native you likely need to configure the baud rate &c, plus implement flow control? Is there any testing XTF should do to ensure the serial is there, before blindly writing at 0x3f8? Thanks, Roger.
