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DBVM and Windows 8.1

 
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vonbraun
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PostPosted: Sat Jun 07, 2014 1:42 pm    Post subject: DBVM and Windows 8.1 Reply with quote

I've compiled DBVM from the latest source code, copied vmdisk.img to a USB stick and I get into the start menu of DBVM.

Once I press 0 to boot up the VM, I only get an orange text saying "BOOT" and nothing after that. If I press b to boot without VM, Windows boots up normally.

Any ideas what might be going wrong?
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master3395
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PostPosted: Mon Jun 09, 2014 7:00 pm    Post subject: Reply with quote

I got the same problem, it starts up normal.
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Dark Byte
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PostPosted: Tue Jun 10, 2014 3:07 am    Post subject: Reply with quote

You may have to set the correct boot disk.
E.g. 80 might be in use by the usb now, so try 81

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vonbraun
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PostPosted: Thu Jun 12, 2014 4:02 pm    Post subject: Reply with quote

Thanks for the reply Dark Byte.

I tried some different boot disk values. DBVM selected 81 by default so I tried a bunch of numbers around that, but I always got that red "raah" message when pressing 0 to boot. Is there a way to determine what the value should be? Also, I should clarify that I put Windows 8.1 in the title because I thought maybe the problem might be something specific to it... My custom DBVM loads completely fine in Windows 8.1 though, when I compile it and dbk64.sys and testsign the driver. It would be much cooler to boot up with DBVM from a usb stick though. Cool

I'm trying to learn how all this virtualization stuff works with DBVM, and I think it's a really cool project you have made! It's maybe a bit offtopic for this thread, but if you know any good resources for learning more about the subject, I'd love to hear about them.
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Dark Byte
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PostPosted: Thu Jun 12, 2014 4:22 pm    Post subject: Reply with quote

The bios sometimes supports emulating the USB as a floppy disk, so it turns into disk 0, leaving disk 80 intact

Also, if you really wish to find out what goes on, get a serial port, a nulmodem cable and another system with serial port and build the debug build of dbvm.
Then you can use the debug interface to inspect the state and step through every vmexit.
(note that AMD systems do NOT properly support booting of USB, they don't implement wake-on-sipi emulation so only one cpu will be running virtualized)

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vonbraun
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PostPosted: Thu Jun 12, 2014 4:39 pm    Post subject: Reply with quote

I think the BIOS on my testing laptop doesn't support that. In the boot device menu there is something called USB floppy but nothing related to floppy emulation anywhere.

I'll go buy a serial cable and see if I can manage to debug the boot process. Just to make sure, I just need to add -DDEBUG to compile with all debug info right? Also, I've never done this type of debugging so can I use windbg for it or is there some better debugger for this purpose?

I have Intel i5 cpu so I guess that should support this at least. Smile
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Dark Byte
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PostPosted: Thu Jun 12, 2014 4:45 pm    Post subject: Reply with quote

actually, common.h in the vmm foler has two defines commented out. Just put them back, and adjust the makefile to set the correct port of your serial port (if pci extension port you may have to find that in windows or some other way. I recommend sweex serial ports as dbvm has a pci detection for those)

and no, windbg doesn't work, it's a lot worse than you might imagine
basically you need to get a terminal program (like putty) and then give commands through that.
run, view state, experimental code routines, ...

and often when you find that stepping is too slow, add several new cs/ip combinations to skip and recompile dbvm and start again (it's a pain)

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vonbraun
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PostPosted: Thu Jun 12, 2014 5:10 pm    Post subject: Reply with quote

Ahh ok, I see that the debugging won't be quite as simple as I thought then... Was hoping I could just load up a debugger. Smile I'll try experimenting with this stuff and will let you know if I'm able to figure out the problem.

On a slightly different subject, have you ever tried PXE booting DBVM from the network? I tried to set that up with the ISO image as it gets annoying to move the USB stick around constantly, but it always just rebooted after showing some kind of dialog for a short time.
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Dark Byte
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PostPosted: Thu Jun 12, 2014 5:35 pm    Post subject: Reply with quote

No, i haven't tried that. I just use two usb cables, one to one system, the other to the one i work on, and just switch between the left cable and the right cable right next to me

also, most likely part that goes wrong when booting is the realmode emulation part
haswell, or the one after that, may have hardware realmode support so that emulation layer can go then

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vonbraun
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PostPosted: Thu Jun 12, 2014 5:56 pm    Post subject: Reply with quote

Okay, I suspect that fixing it might be beyond my capabilities, but I'll give it a try and look at Intel docs and report back if I figure it out.

Thanks for the help! Smile
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