Re: lost serial characters on boot

[Frediano Ziglio <freddy77@xxxxxxxxx>]

On Fri, Oct 17, 2025 at 6:16 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> Hi,
>
> I think we've got a bug with the serial console.  I'm reliably loosing a
> small part of the boot message. e.g.:
>
> (XEN) Latest ChangeSet: Fri Oct 17 17:24:59 2025 git:5e79cfcd2100
> (XEN) build-id: d1536ff6698b3e3ba307d551abf
>  Family 25 (0x19 Stepping 1 (raw 00a00f11)
> (XEN) BSP microcode revision: 0x0a001137
>
> whereas from xl dmesg after the system boots, we see things correctly:
>
> (XEN) Latest ChangeSet: Fri Oct 17 17:24:59 2025 git:5e79cfcd2100
> (XEN) build-id: d1536ff6698b3b8968e883fc39e3ba307d551abf
> (XEN) CPU Vendor: AMD, Family 25 (0x19), Model 1 (0x1), Stepping 1 (raw
> 00a00f11)
> (XEN) BSP microcode revision: 0x0a001137
>
>
> The lost bit of text differs even when rebooting the same Xen binary,
> but it's always around this area, very early on boot.
>
> I've been seeing this for a little while, but one of my common dev
> machines is showing it fairly reliably at the moment.
>
> Checking a transcript of the terminal, we're missing characters, rather
> than having additional control characters causing the corruption.
>
> I suppose I need to stare at console_init_preirq() some more, but if
> anyone has ideas, I'm all ears.
>
> ~Andrew
>

Which kind of serial do you have ? Standard ns16550 ?

Frediano