linux-kernel - Re: Strange output on the console

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Message-ID: <20220225132541.GD18720@1wt.eu>
Date:   Fri, 25 Feb 2022 14:25:41 +0100
From:   Willy Tarreau <w@....eu>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     David Laight <David.Laight@...lab.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        John Ogness <john.ogness@...utronix.de>
Subject: Re: Strange output on the console

On Fri, Feb 25, 2022 at 08:17:19AM -0500, Steven Rostedt wrote:
> On Fri, 25 Feb 2022 13:25:46 +0100
> Willy Tarreau <w@....eu> wrote:
> 
> > > TnsTesOT s T sKTesOT sKTvsOTtsTtsKTtsT sKTesTesKT sKTesOT siT stTnsaTvsaTesKTnsOT s
> > > TesKTnsT s TvsKTeslT sOTesT sKTtseTnseTvs_Tts_T sOTes TnsOT s T spTespTesdTesdTeseTtseTeseTt_rTe_rTv_oTes:T s:Tes:TnfwOTvfrKT fwT frTefpuTefpKTefpTvf:TnsOTvsOTnsoTvs Tvs TvsTtssTnsT sKTesTnsTvsTtsoTesmTnsgTesiTeslTtsTvsKTnsTvsOTtsT s_Tnsu
> > > 
> > > which really doesn't have enough different characters in it to be a fifo problem.
> > > That looks like a UART struggling to find valid start and stop bits
> > > on a continuous data stream that doesn't match the baud rate.
> > > 
> > > It may also be that whatever 'terminal' is being used is masking off the 0x80 bit.  
> > 
> > That could be one option I thought about but still, that sounds quite
> > suspicious. You don't even get any #!:$/ etc. Or maybe the UART is
> > configured in 6-bit mode (most 16550 support 5-8 bits), and maybe even
> > the stop bit and/or parity participates.
> 
> One thing that's not easy to demonstrate here (I could try to video it), is
> that this output is the final result. It shows a bunch of other characters
> as it is displayed but then the cursor goes backwards and writes over it.
> 
> But the characters that are deleted still do not make sense. When watching
> it, it reminds me of the Matrix characters, but running horizontal and not
> vertical.

Ah, so 6-bit might definitely make sense.

> > ... and Steven having fun reading our proposals after having made this
> > up entirely in preparation of the next April's fool :-)
> 
> 
> I was thinking the same thing, but this output being the joke. Someone
> planning on slipping in Matrix characters for printk?

;-)

Willy