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

[Jan Kiszka <jan.kiszka@siemens.com>]

Jun Koi wrote:
> 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.
> 

So what does "i b" report about your watchpoint? Hard or soft?

> 
>> 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.

You could also try "set debug remote 1" to see what gdb does when it
stops and resumes the guest continuously.

Jan

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