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. Cheers, Alejandro
