memory scrubbing

Kevin Day thekevinday at
Tue Jan 29 16:20:10 PST 2008

On Jan 29, 2008 3:47 AM, For All My Junk Mail
<junk_mail at> wrote:
> Robert Connolly wrote:
> > Hello.
> >
> > I've noticed that when I start Xorg I see a screenshot of my previous Xorg
> > session. This survives a reboot. It looks like the memory just becomes free
> > when Xorg is shut down, and the image stays there until it's overwritten.
> >
> > Are any of you familiar with ways to scrub this memory, and any other memory,
> > during a shutdown?
> >
> Change your memory, motherboard, or power supply for normal stuff or
> make sure the box is actually being powered down. The box switching
> itself "off" ( halt -p) actually leaves at least one live voltage rail
> powered internally. Remember all those stupid "Wake up on ..." options
> in your bios? Something has to be live.
> If you're running HLFS, your kernel is not moving X around. I thought
> all these programs were to be hidden where nobody would expect them to
> be; -pie or -pic and all that agony one goes through to build HLFS. Back
> to the drawing board :-P.
> I never have that problem, because I remove mains power. I did have a
> memory problem on startup with a microcontroller once and I wrote about
> six lines of assembler into a routine to simply write zeroes to the
> offending address space. Despite my slothful clock speed (32khz) there
> was no noticable delay.
> The routine would be quickest if it wrote to memory in  the largest
> width available. For 32 bit processors, that would be a 64 bit number.
> For _true_ 64 bit cpus, you should write a 128 bit number, which would
> still of course be a register pair.
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I suspect it is a problem with your Video Memory not being cleared.
You'll need to directly write to the your video's memory...
I suspect the best approach would be to look at what video card driver
is being used, and make a patch for it to clear the video memory with
something, maybe the default X (static-like grey) background. (maybe
even an Xorg-server patch itself to always clear on exit when safe to
do so.)

Of course, if you are using "integrated memory", then you do not have
any real video-memory. In which case, your main-memory scrubbing
should work.

Kevin Day

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