memory scrubbing

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Tue Jan 29 01:47:34 PST 2008

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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