[Qemu-devel] [Question]WinDbg runs too slowly or exits unexpectly when debug windows guest driver under QEMU 0.15.50

[Mars.Cao]

WinDbg runs too slowly or exits unexpectedly when debug windows guest 
driver under QEMU 0.15.


I installed 2 windows (WinXP SP3)VMs on my host (RHEL6.1).
The basic debug method is :


1.Setup the Windows driver Kit in host


/usr/local/bin/qemu-system-x86_64 -drive 
file=winxpsp3.img,if=virtio,format=qcow2,cache=none,aio=threads -smp 2 
-net tap,ifname=tap0,script=no,downscript=no -net 
nic,model=virtio,macaddr=52:54:00:d6:be:bb -m 1024 --enable-kvm -serial 
tcp:127.0.0.1:4445,server,nowait -cdrom WDK.iso



power off.


2.Run the guest and edit the boot.ini of the guest windows


/usr/local/bin/qemu-system-x86_64 -drive 
file=winxp-guest.img,if=virtio,format=qcow2,cache=none,aio=threads -smp 
2 -net tap,ifname=tap1,script=no,downscript=no -net 
nic,model=virtio,macaddr=52:54:00:d6:be:ee -m 1024 --enable-kvm

edit boot.ini and duplicate the default boot option add the line "/debug 
/debugport=COM1 /baudrate=115200"


3.Run host and WinDbg


/usr/local/bin/qemu-system-x86_64 -drive 
file=winxpsp3.img,if=virtio,format=qcow2,cache=none,aio=threads -smp 2 
-net tap,ifname=tap0,script=no,downscript=no -net 
nic,model=virtio,macaddr=52:54:00:d6:be:bb -m 1024 --enable-kvm -serial 
tcp:127.0.0.1:4445,server,nowait

Run the host VM,and then run WinDbg then "Ctrl+k" kernel debug to 
connect the guest for debugging through COM1.


4.Run the guest to debug

Restart the guest,select the windows debug option in the boot menu.

/usr/local/bin/qemu-system-x86_64 -drive 
file=winxp-guest.img,if=virtio,format=qcow2,cache=none,aio=threads -smp 
2 -net tap,ifname=tap1,script=no,downscript=no -net 
nic,model=virtio,macaddr=52:54:00:d6:be:ee -m 1024 --enable-kvm -serial 
tcp:127.0.0.1:4445


There are several problems when debugging:

1).The Windows VM boot slow (more than 20 seconds)and does not run smoothly.
I use the qemu-kvm (version 0.12.1) which pre-installed in the RedHat 
RHEL6.1 with same option and same image file, the VM boots and runs much 
more better than using QEMU-0.15.0.

address@hidden images]# /usr/local/bin/qemu-system-x86_64 --version
QEMU emulator version 0.15.50, Copyright (c) 2003-2008 Fabrice Bellard

address@hidden images]# /usr/libexec/qemu-kvm --version
QEMU PC emulator version 0.12.1 (qemu-kvm-0.12.1.2), Copyright (c) 
2003-2008 Fabrice Bellard




2).The process of WinDbg on the host VM connecting to the guest occupy 
so much time.

It spend at least 10 minutes to connect the guest VM when debugging the 
windows kernel by WinDbg.

3).When WinDbg connecting to the guest VM(not connected yet),WinDbg exit 
unexpected sometimes, and sometimes can not connect to the guest. And 
the probability of the problem is high.



I have no idea what is wrong?
The COM rate is too slow,the QEMU is not used correctly or some bugs in 
QEMU?
Can anyone give me some tips?