L4/Fiasco kernel debugger (jdb) and step over command

Valery V. Sedletski _valerius at mail.ru
Thu Dec 28 03:59:05 CET 2017


On 28.12.2017 03:22, Adam Lackorzynski wrote:
> On Thu Dec 28, 2017 at 02:54:20 +0300, Valery V. Sedletski wrote:
>> On 28.12.2017 02:29, Adam Lackorzynski wrote:
>>> On Wed Dec 27, 2017 at 18:33:16 +0300, Valery V. Sedletski wrote:
>>>> On 27.12.2017 13:05, Matthias Lange wrote:
>>>>> Hi Valery,
>>>>>
>>>>>> On 26. Dec 2017, at 17:54, Valery V. Sedletski <_valerius at mail.ru> wrote:
>>>>>>
>>>>>> Hi. I'm trying to debug my program with jdb. (I'm using the old L4/Fiasco / L4Env, not the current Fiasco.OC / L4Re). I enabled the permanent single step mode (with the S+ command) and a permanent show the Thread Control Block (with the t+ command) option. So, I was able to single-step with "g" command. Also, I found "jr" (go until return (ret or iret) is encountered) and "jb" (go until the next branch instruction, like jmp/call/int) commands, but they don't seem to work. When I enter them, I see only a single step to the next instruction. Are these two commands broken? How do I step over a "call"/"int" instruction?
>>>>> Fiasco/L4Env has been outdated for almost 10 years now and hasn’t been maintained since then. Sorry, but here we are unable to help you with your problem.
>>>> Yes, I know that  it's outdated now.
>>>>> Are there any reasons you chose Fiasco/L4Env over Fiasco.OC/L4Re?
>>>> My program is based on L4Env. I'm porting it to L4Re now. But first I need
>>>> to fix some bug and then continue porting it to L4Re. I think, someone could
>>>> remember some problems existed with L4/Fiasco kernel debugger. Also,
>>>> Fiasco.OC debugger may be very similar, so I expected someone could help me.
>>>> The problem is that I cannot find any commands similar to "step over"
>>>> command. There are "jb" (continue to the next branch instruction) and "jr"
>>>> (continue until next return instruction), but they don't seem to work. They
>>>> just do a single stepping. Does still anybody remember how could I step over
>>>> a "call" instruction? Maybe, in Fiasco.OC it's similar? Or, in Fiasco, it
>>>> was completely broken in the end?
>>> Indeed, jdb's functionality is still pretty similar here, including
>>> non-functionalities. Would you have a chance to run your code within
>>> QEMU and attach gdb to QEMU so that you could do your debugging?
>>>
>> So, it still does not work in jdb until now? Good, so debugging in GDB
>> inside QEMU still should work?
>> Is there any examples how to do GDB debugging (or, it is not specific to
>> L4/Fiasco or Fiasco.OC?)? I suspect that I need to link a GDB stub with my
>> program and connect to it with GDB via network somehow? Are there any
>> manuals somewhere?
> What I mean is rather attaching GDB to QEMU and using that to debug the
> whole L4 system. What maybe tricky here is to stop the system at the
> right point but breakpoints should do it here. QEMU options are
> -s and -S.
>
>
> Adam

So, I need to add the GDB stub to a microkernel somehow? Is this an 
option somewhere in Fiasco configuration menu?




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