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This question was a challenge because I have never done kernel debugging, or used QEMU before. But a few doses of Google later, and using simple deduction based on other experiences, I'm getting through.
> Get this KVM qcow2 image
KVM = Kernel Virtual Machine based on (hypervisor) compatible with [[wp:QEMU]] (https://QEMU.org)-- a machine emulator and virtualizer. File is an [[wp:Xz]]-compressed (like 7-zip; only GPL) "debug-crash.qcow"
So, I installed QEMU + dependencieson my Bionic workstation.
> Please show the commands you use to start via libvirt with this XML.
The xml had <code>/usr/bin/kvm-spice</code> in it as the emulator; so I searched <code>dpkg -S /usr/bin/kvm-spice</code> which turns out to be '''qemu-kvm''' (that I already have installed). So I assume that I'll need to run qemu-kvm. So then I researched how to start a qemu-kvm session/machine, using libvirt, and given an XML manifest / configuration file. I didn't find anything like that, so I went with basic commands for starting QEMU. (Failing fast and early reveals the path to perfection.) Listing the user and system emulators in <code>/usr/bin/qemu-*</code>, there is <code>qemu-system-x86_64-spice</code>. I started the system with:
<source lang="bash">/usr/bin/qemu-system-x86_64-spice -hda /home/greg/Downloads/debug-crash.qcow
</source>
But, from the Arch wiki<ref>https://wiki.archlinux.org/index.php/QEMU</ref> I found that
<blockquote>
To start QEMU in KVMmode, append -enable-kvm to the additional start options. To check if KVM is enabled for a running VM, enter the QEMU Monitor using <kbd>Ctrl</kbd>+<kbd>Alt</kbd>+<kbd>Shift</kbd>+<kbd>2</kbd> , and type <code>info kvm</code>.
</blockquote>
That informed me that I was not running in KVM mode (disabled). So I halted the machine. I then launched the GUI '''virt-manager''' <code>sudo virt-manager</code>, created a new machine using the qcow image, and started it. Looking at the <code>ps axjfww</code> output on the host, I could see that the command "I" used to start the VM was
<blockquote>
qemu-system-x86_64 -enable-kvm -name guest=generic,debug-threads=o
n -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-1-generic/master-key.aes -machine pc-i440fx-
bionic,accel=kvm,usb=off,vmport=off,dump-guest-core=off -cpu Broadwell-noTSX-IBRS -m 1024 -realtime mlock=off -smp 1,socket
s=1,cores=1,threads=1 -uuid 4cbd5a21-bff7-4e66-8632-2e936507c658 -no-user-config -nodefaults -chardev socket,id=charmonitor
,path=/var/lib/libvirt/qemu/domain-1-generic/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -r
tc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-hpet -no-shutdown -global PIIX4_PM.disable_s3=1 -globa
l PIIX4_PM.disable_s4=1 -boot strict=on -device ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x5.0x7 -device ich9-usb-uhci1,masterb
us=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x5 -device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=
0x5.0x1 -device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x5.0x2 -device virtio-serial-pci,id=virtio-seria
l0,bus=pci.0,addr=0x6 -drive file=/home/greg/Downloads/debug-crash.qcow,format=qcow2,if=none,id=drive-ide0-0-0 -device ide-
hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 -netdev tap,fd=26,id=hostnet0 -device rtl8139,netdev=hostn
et0,id=net0,mac=52:54:00:4e:3e:15,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=
serial0 -chardev spicevmc,id=charchannel0,name=vdagent -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel
0,id=channel0,name=com.redhat.spice.0 -spice port=5900,addr=127.0.0.1,disable-ticketing,image-compression=off,seamless-migr
ation=on -device qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci
.0,addr=0x2 -device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -chardev
spicevmc,id=charredir0,name=usbredir -device usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=1 -chardev spicevmc,id=c
harredir1,name=usbredir -device usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=2 -device virtio-balloon-pci,id=ballo
on0,bus=pci.0,addr=0x7 -msg timestamp=on
</blockquote>
== Apache ==
> Apache is not starting, why?
There's a syntax error on line 153 of /etc/apache2/apache2.conf. More accurately, it can not open the file that it's trying to open at /etc/apache2/extra.conf. And actually, looking at that file, someone with a sense of humor symlinked it to <code>/dev/urandom</code> -- which is why Apache has a problem with the syntax :-D
== LDFLAGS ==
> It turns out this change actually made LDFLAGS empty. Why?
I thought this was a trick question, because it looked like the syntax for $CFLAGS and $CPPFLAGS are incorrect. But, that syntax actually does look correct. Since the sed expression also looks correct, I have to surmise that somehow CFLAGS and/or LDFLAGS weren't configured correctly. But that's only a guess. '''R'''eading '''T'''he '''F'''ine '''M'''anual on <code>dpkg-buildflags</code>, it tells me that <code>LDFLAGS</code> defaults to empty. So sed is a no-op, and LDFLAGS would still be empty.
== Instructions ==
<pre>
To login use
actually made LDFLAGS empty. Why?
</pre>
{{References}}