[Qemu-devel] Re: Problem with watchpoint in gdbstub

[Jun Koi <junkoi2004@gmail.com>]

On Tue, Apr 27, 2010 at 5:10 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
> Jun Koi wrote:
>> Hi,
>>
>> I am trying to debug a VM using gdb. I connected gdb to Qemu (latest
>> code from git repo), and issued below command:
>>
>> ...
>> (gdb) watch *0x77f44cd8
>> (gdb) c
>>
>> The idea is to catch the write access to address 0x77f44cd8.
>>
>> But after the "c" command, I saw that the window title of my VM
>> continuously flip between "QEMU [Stopped]" and "QEMU", non-stop.
>> This makes the VM unusable.
>>
>> Is it a bug? Anybody sees the same problem?
>
> I would bet your watchpoint was established by gdb as a software
> watchpoint. In that case gdb will step through the target, checking
> after each instruction if the memory changed.

But that is certainly not the reason of the symptom I saw.


>
> Is that address valid at the time gdb wants to install it? I saw gdb
> choosing a software watchpoint before when it wasn't.

Yes, that address is valid.

thanks,
J