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".
-Kevin
> +
> /* Check if the QEMU debug output port is active */
> if (CONFIG_DEBUG_IO &&
> inb(GET_GLOBAL(DebugOutputPort)) != QEMU_DEBUGCON_READBACK)
> --
> 2.25.1
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