Re: [Xenomai] Mayday issues again

[Jan Kiszka <jan.kiszka@web.de>]

On 2015-06-20 16:46, Gilles Chanteperdrix wrote:
> 
> Jan Kiszka wrote:
>> Hi Philippe,
>>
>> the mayday mechanism is causing troubles to me again.
>>
>> First of all, there is a bug /wrt restarting the mayday syscall. We
>> current don't restart on pending signals, thus destroy the register of
>> the interrupted thread that contains the syscall return code. See my
>> for-forge branch for a fix proposal.
>>
>> But actually I would like to get rid of the syscall trampoline
>> completely if somehow possible, at least for certain archs. The reason
>> is that it ruins debuggability. If a RT thread is stopped by gdb with
>> the help of the mayday mechanism, it ends up waiting for resumption on
>> the mayday page. Even worse, backtracing is broken, at least on x86.
> 
> The problem here seems to be mixing mayday with gdb. As its name
> indicates, the mayday mechanism is something exceptional, that should not
> happen during a casual debugging session with gdb.

Yes, mayday is a misnomer today. It is also used to synchronously inject
Linux signals into the RT threads (handle_sigwake_event ->
__xnthread_kick -> ipipe_raise_mayday), like SIGSTOP.

Jan


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