Re: [Xenomai-help] Calling native API in user-space signal handler

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Andreas Glatz wrote:
> Hi,
> 
> I wrote my on SIGSEGV signal handler which gathers information about
> the fault and passes that info to a separate process for
> post-processing.
> 
> I'm wondering if it's always save to call native API functions in a
> signal handler?
> 
> (As according to man 7 signal', it's just save to call a subset of
> Glibc functions from within a signal handler.)

It is definitely not safe to assume that you may call any function in a
signal handler.

Calling pthread_mutex_lock in a signal handler can cause a multithreaded
application to deadlock for instance (if the preempted code was also in
the middle of a pthread_mutex_lock), so that calling the apparently
inocuous printf might deadlock.

Now, for the Xenomai services. You can in fact call any function whose
implementation is in fact a simple syscall. If a function does more than
simply emitting a syscall, then all bets are off. And of course, we can
not guarantee you that a function which is emitting a syscall now will
not get more complicated in later releases.

Another safe solution is to use the "ptrace" syscall, the one used by
gdb, instead of installing a handler for SIGSEGV. Granted, this will
become a bit more completely, but should be more safe.

Or enable generation of core files.

-- 
					    Gilles.