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Displaying QR codes for kernel crashes

Displaying QR codes for kernel crashes

Posted Jul 2, 2012 15:03 UTC (Mon) by bokr (subscriber, #58369)
In reply to: Displaying QR codes for kernel crashes by mjg59
Parent article: Displaying QR codes for kernel crashes

kdump means sacrificing ~128MB of RAM at all times in order to have somewhere to put the kdump kernel, and reliability on consumer hardware is less than stellar. It's a hard problem.

How about keeping a static piece of code in the kernel that can be executed in real mode to use BIOS to reset display to 25x80 (or whatever it was) and just loop circularly over pages of dump info, outputting it in the most primitive way, with just hit-any-key as page advance? IWT this shouldn't take up more than a few KB, never mind MB.

Last gasp would be to transfer to this code.

Maybe you could use box characters to generate QR codes, 3 per screen, at 25x25 or 21x21, but that would be more code.


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Displaying QR codes for kernel crashes

Posted Jul 2, 2012 15:10 UTC (Mon) by mjg59 (subscriber, #23239) [Link]

"Hit any key" won't work via BIOS if you've got a USB keyboard, and as we head to UEFI you don't have BIOS either.

Displaying QR codes for kernel crashes

Posted Jul 2, 2012 15:20 UTC (Mon) by apoelstra (subscriber, #75205) [Link]

Drop into real mode and use INT 10. ;)

Displaying QR codes for kernel crashes

Posted Jul 2, 2012 15:27 UTC (Mon) by mjg59 (subscriber, #23239) [Link]

The thing about not having BIOS is that you don't have any video BIOS either :)

Displaying QR codes for kernel crashes

Posted Jul 2, 2012 21:03 UTC (Mon) by rvfh (subscriber, #31018) [Link]

I know you're the expert here, but my USB keyboard works in my BIOS... What am I missing here?

Displaying QR codes for kernel crashes

Posted Jul 2, 2012 21:19 UTC (Mon) by mjg59 (subscriber, #23239) [Link]

Not once the OS has taken over. It's a one-way transition.

Displaying QR codes for kernel crashes

Posted Jul 2, 2012 21:48 UTC (Mon) by apoelstra (subscriber, #75205) [Link]

Once you step out of "real mode" (i.e., 16-bit DOS mode) into "protected mode" (32-bit or 64-bit, multiple memory permission rings, all that jazz), you no longer have access to the BIOS or its interrupts, so you can't ask it for help with peripherals anymore.

Before then, the BIOS will give you keyboard access, tell you what drives are installed and what size they are, let you write to the screen, all sorts of wonderful stuff. For example, you can write "Hello world!" in assembler for an x86 PC, using only a couple dozen opcodes, which is very exciting when you're first learning about such a low level.

If UEFI really means the loss of all that, it makes me kinda sad.


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