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

Adam Lackorzynski adam at os.inf.tu-dresden.de
Thu Dec 28 23:27:06 CET 2017


On Thu Dec 28, 2017 at 05:59:05 +0300, Valery V. Sedletski wrote:
> 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 Fiasco/L4Env has been outdated for almost 10 years now and hasn’t been maintained since then.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 Yes, I know that  it's outdated now.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?

No. The GDB stub is already there in QEMU, allowing to debug what is
running inside QEMU. Just try it out :)


Adam



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