[Xenomai-help] Debugging RT threads with GDB on ARM/PowerPC

[Xenomai-help] Debugging RT threads with GDB on ARM/PowerPC

[Wolfgang Grandegger]

Hello,

I understood that GDB can be used to debug Xenomai real-time
applications but it seems not to work with my application on PowerPC or
ARM. The applications looses determinism quickly, mainly because RT
threads switch to secondary mode somehow. Have I missed something? Are
there any known issues with GDB on ARM or PowerPC?

Wolfgang.

Re: [Xenomai-help] Debugging RT threads with GDB on ARM/PowerPC

[Philippe Gerum]

Wolfgang Grandegger wrote:
> Hello,
> 
> I understood that GDB can be used to debug Xenomai real-time
> applications but it seems not to work with my application on PowerPC or
> ARM. The applications looses determinism quickly, mainly because RT
> threads switch to secondary mode somehow. Have I missed something? Are
> there any known issues with GDB on ARM or PowerPC?
>

Using GDB means that you lose determinism, by essence. Debugging time can't be
for free anyway. Additionally, GDB is based on ptrace(), ptrace() makes heavy
use of Linux signals to control the debuggee, so as a matter of fact, the
application under debug has to switch to secondary mode each time GDB takes
control over it, which means, most of the time as soon as you are actually
debugging it. The same goes for breakpointing, since this triggers faults, hence
needs a switch to Linux mode as well, because ptrace() would not be happy to
process the breakpoint in the middle of a primary context.

This is not a ppc or arm issue. This is common to all archs.

> Wolfgang.
> 
> _______________________________________________
> Xenomai-help mailing list
> Xenomai-help@domain.hid
> https://mail.gna.org/listinfo/xenomai-help
> 


-- 
Philippe.

Re: [Xenomai-help] Debugging RT threads with GDB on ARM/PowerPC

[Wolfgang Grandegger]

Philippe Gerum wrote:
> Wolfgang Grandegger wrote:
>> Hello,
>>
>> I understood that GDB can be used to debug Xenomai real-time
>> applications but it seems not to work with my application on PowerPC or
>> ARM. The applications looses determinism quickly, mainly because RT
>> threads switch to secondary mode somehow. Have I missed something? Are
>> there any known issues with GDB on ARM or PowerPC?
>>
> 
> Using GDB means that you lose determinism, by essence. Debugging time can't be
> for free anyway. Additionally, GDB is based on ptrace(), ptrace() makes heavy
> use of Linux signals to control the debuggee, so as a matter of fact, the
> application under debug has to switch to secondary mode each time GDB takes
> control over it, which means, most of the time as soon as you are actually
> debugging it. The same goes for breakpointing, since this triggers faults, hence
> needs a switch to Linux mode as well, because ptrace() would not be happy to
> process the breakpoint in the middle of a primary context.
> 
> This is not a ppc or arm issue. This is common to all archs.

OK, that's what I suspected. After the first GDB intervention, real-time
is lost. Thanks for clarification.

Wolfgang.