[Xenomai] xenomai 2 LDFLAGS wrappers, posix only

Henning Schild henning.schild at siemens.com
Thu Jan 12 18:32:31 CET 2017

Am Wed, 11 Jan 2017 15:47:59 +0100
schrieb Henning Schild <henning.schild at siemens.com>:

> Am Wed, 11 Jan 2017 12:03:23 +0100
> schrieb Philippe Gerum <rpm at xenomai.org>:
> > On 01/10/2017 04:07 PM, Henning Schild wrote:  
> > > Hi,
> > > 
> > > i am about to include three more wrappers into xenomai2 to
> > > assert_nrt, later i plan to create a xenomai3 patch as well. The
> > > functions to wrap are __cxa_guard_(acquire|release|abort). They
> > > contain mutexes protecting the initialization state of static
> > > objects in c++ code, often found when people implement the
> > > singleton pattern.
> > > 
> > > I have got the wrapping code but found that xeno-config will
> > > create the wrapping LDFLAGS only for the posix skin. Is that
> > > intentional or an inconsistency?
> > > Even the wrappers in the "common" skin get applied for posix only.
> > > 
> > > I tried calling malloc/free in a "--skin=native" example and did
> > > not get the SIGXCPU.
> > > 
> > > Now i am guessing that the way wrappers are applied in xenomai2 is
> > > somehow inconsistent. Is that something that should be fixed by
> > > having common and per skin wrappers, or would it be ok to simply
> > > always append the posix LDFLAGS as well?    
> > 
> > --posix is supposed to be passed only when a wrapping is expected.
> > Omitting it allows to build apps over non-POSIX Xenomai APIs, while
> > assuming that any POSIX call also present in the code can only be
> > obtained from the glibc.  
> Ok i see. Just adding the --posix all the time would change the
> implementation of all the pthread_* stuff where the developer might
> just want to use non-rt pthreads.
> There seem to be two classes of wrappers. Those that just assert_nrt()
> and do not change the implementation of the function to be called. And
> the other class actually replaces the original implementation.
> The ones that just insert the assert_nrt() are relevant for all skins
> and should be applied there, while at the moment they are only used
> for posix/rtdm.
> For xenomai3 that is malloc and free (./lib/cobalt/assert_context.c),
> for xenomai2 it is those two plus gettimeofday
> (src/skins/common/assert_context.c). These should be wrapped in any
> skin, not just posix.
> The three __cxa_guard wrappers would also be of the "insert assertion"
> type and should therefore go into all skins.

Do you agree with the observation? Should the assert_nrt guys be
applied on all skins? Should we add the stdc++ __cxa_guard functions as
such wrappers?

I am working on patches to extract the assert_nrt wrappers out of
posix.wrappers and put them into common.wrappers. The last patch of the
series would add the stdc++ guys to the common wrappers.

The file posix.wrappers is mentioned in configure.in and
skins/posix/Makefile.(in|am). And a new file will probably have to go
there as well. So this seemingly little change might produce a rather
big changeset including autotool changes.

Maybe i should start with the xenomai3 version of it to have a better
basis for a discussion?


> Henning

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