Re: Debuggin XNU build

Subject: Re: Debuggin XNU build
From: Prokash Sinha <email@hidden>
Date: Wed, 08 Apr 2015 19:43:43 -0700

Thanks much Brian.

I will try some of these alternatives, and I need to understand a bit more about the vmware bundle and file system layout for the VMS.

I want to make sure that I conveyed my problem precisely. So here it is again -

I build the XNU kernel ( w/o any ancillary open source or whatever), following Shantonu’s great blog. Now I just take the kernel (either from the Release or Debug build) and replace the Off-the-shelf kernel and boot. In either case I don’t get the boot to finish and get to a command prompt. ( This is what I thought I would get, and probably it would boot to single user, run level 0 or 1 ).

So I get back to the Off-The_shelf based snapshot, and make changes to make sure I have Host/Target over ip debugging works. Then when the debugging set up is done. I replace the kernel as before,and boot up. The configuration takes effect,so instead of panic, it gets to the Waiting for debugger connection …

Now since the ip and mac are bogus, I can not connect the debugger to the target.

one more question (though different ) is that - Is there any kernel variable that we can toggle on the target using sysctl to trigger a break into the debugger. Or if there is any key-combination that would do that. This is when kernel debugger connection is fine, and I let the target to boot completely, then I want to break in. Assume I don’t have any component running where I can set BP before letting the target go on running.

Thanks,

Prokash

On Apr 7, 2015, at 9:22 AM, Brian Bechtel <email@hidden> wrote:

VMware maintains the nvram variables in the virtual machine bundle, in the *nvram file inside the bundle. Running in the vm, you can set the boot-args in a working partition and then boot to your test partition, or boot single user and set the nvram values there. The typical value would be
sudo nvram boot-args="debug=0x146"
as described in technote 2063 <https://developer.apple.com/library/mac/technotes/tn2063/_index.html> (which is heavily out of date, but still contains useful information.)

You can also use the "gdb-server" command; see https://twitter.com/comex/status/477650961448439808 where Shantonu Sen comments
you have to use the target definitions file at http://llvm.org/svn/llvm-project/lldb/trunk/examples/python/ …

Also, I found this little shell script somewhere on the Intarweb which sends an NMI to your VM. Keep a copy inside the vmwarevm bundle.

#!/bin/bash

DIR=$(dirname $0)

/Applications/VMware\ Fusion.app/Contents/Library/vmrun suspend $DIR/*.vmx
perl -i -pe 's/(?<=pendingNMI\x00{4})\x00/\x01/' *.vmss
/Applications/VMware\ Fusion.app/Contents/Library/vmrun start $DIR/*.vmx

On Wed, Apr 1, 2015 at 8:41 PM, Prokash Sinha <email@hidden> wrote:
Folks,

Here is another problem I'm stuck with.

On 10.10 I have the corresponding xnu source that I can now build ( both DEBUG and RELEASE). I uses Fusion, so taking snapshot of the running VM instance is not a problem, and I wanted to drop the kernel.debug to /Systems/Library/Kernel directory, named it as kernel, and boot from there.

Since the KDP based LLDB is working when I try to connect from the host while I'm running the original OS version ( with or without the corresponding Kernel Debug Kit), I was hoping that in case of a continuous panic while trying to boot, I should be able to connect from the host.

But the problem is that while the boot messages comes to the screen, it tells that both ip and mac addresses are 0s. Like 0.0.0.0 and 00:00:00:00:00:00. And I can not connect. I looked the debug.c and kdp.c code, there seem to be some variables related to ip etc., that are being set to 0s as default. Not sure if I could hard code them based on what have from the original setup, and that would work or not.

If not, then how could I setup KDB/DDB using either nvram or using the com.apple.Boot.plist. I know this should give me just the single VM debugging !!

Would love to see if I could do Host/Target with KDP based debugging !

Any suggestion, please ?

Prokash
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References:
	>Debuggin XNU build (From: Prokash Sinha <email@hidden>)
	>Re: Debuggin XNU build (From: Brian Bechtel <email@hidden>)

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