linux-kernel - Re: [tip:x86/boot] x86/boot/compressed/64: Prepare trampoline memory

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Message-ID: <20180226084955.GB5308@uranus.lan>
Date:   Mon, 26 Feb 2018 11:49:55 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        tglx@...utronix.de, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, willy@...radead.org, hpa@...or.com,
        kirill.shutemov@...ux.intel.com, peterz@...radead.org,
        luto@...capital.net, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/boot] x86/boot/compressed/64: Prepare trampoline memory

On Mon, Feb 26, 2018 at 11:37:09AM +0300, Kirill A. Shutemov wrote:
> On Mon, Feb 26, 2018 at 11:15:34AM +0300, Cyrill Gorcunov wrote:
> > On Mon, Feb 26, 2018 at 11:02:56AM +0300, Kirill A. Shutemov wrote:
> > ...
> > > > Also, could do a puts() hexdump of the affected memory area _before_ we overwrite 
> > > > it? Is it empty? Could we add some debug warning that checks that it's all zeroes?
> > > 
> > > The problem is that we don't really have a way get a message out of there.
> > > 
> > > http://lkml.kernel.org/r/793b9c55-e85b-97b5-c857-dd8edcda4081@zytor.com
> > > 
> > 
> > I'm sorry for stepping in (since I didn't follow the series in details)
> > but can't we use vga memory here and print this early data tere?
> 
> I have no idea how to do this :/

https://wiki.osdev.org/Printing_To_Screen

Kirill, note that it might not do the trick at all, just give
the link a shot and check if it would worth the efforts.

> 
> And what about systems without monitor at all?

Such early boot things *require* additional equipment
anyway jtag/monitors/etc for debug stage at least.