From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4B73D202.5050004@domain.hid> Date: Thu, 11 Feb 2010 10:46:42 +0100 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <4B72A7E2.5020001@domain.hid> <4B72A9DA.1090104@domain.hid> <4B730A04.9040908@domain.hid> <4B731608.6010803@domain.hid> <4B73180C.6070301@domain.hid> <4B73207C.6020400@domain.hid> <4B73218A.9080306@domain.hid> <4B7323D5.1040804@domain.hid> <4B732487.50103@domain.hid> <4B732679.4030306@domain.hid> <4B73278F.9050603@domain.hid> <4B73C214.3010107@domain.hid> <4B73C421.1020200@domain.hid> <4B73CFD9.6010904@domain.hid> In-Reply-To: <4B73CFD9.6010904@domain.hid> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] [Xenomai-git] Jan Kiszka : Make xnarch_init_timeconv an uninlined weak function List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: Xenomai core Jan Kiszka wrote: > Gilles Chanteperdrix wrote: >> Jan Kiszka wrote: >>> Gilles Chanteperdrix wrote: >>>> Jan Kiszka wrote: >>>>> Gilles Chanteperdrix wrote: >>>>>> Jan Kiszka wrote: >>>>>>> Gilles Chanteperdrix wrote: >>>>>>>> Jan Kiszka wrote: >>>>>>>>> Gilles Chanteperdrix wrote: >>>>>>>>>> Jan Kiszka wrote: >>>>>>>>>>> Gilles Chanteperdrix wrote: >>>>>>>>>>>> Jan Kiszka wrote: >>>>>>>>>>>>> Gilles Chanteperdrix wrote: >>>>>>>>>>>>>> GIT version control wrote: >>>>>>>>>>>>>>> Module: xenomai-jki >>>>>>>>>>>>>>> Branch: for-upstream >>>>>>>>>>>>>>> Commit: 6b40653e9c3c4a2433bb4e91344fc378eb860f75 >>>>>>>>>>>>>>> URL: http://git.xenomai.org/?p=xenomai-jki.git;a=commit;h=6b40653e9c3c4a2433bb4e91344fc378eb860f75 >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Author: Jan Kiszka >>>>>>>>>>>>>>> Date: Wed Feb 10 13:24:29 2010 +0100 >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Make xnarch_init_timeconv an uninlined weak function >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Otherwise the wrong set of time conversion variables might get >>>>>>>>>>>>>>> initialized when using > 1 skin libraries. >>>>>>>>>>>>>> If that would be possible, then it is the conversion variables which >>>>>>>>>>>>>> should made be weak, not the function. >>>>>>>>>>>>>> >>>>>>>>>>>>>> The way I see it, the posix and native skins currently get a different >>>>>>>>>>>>>> set of variables and functions, which works, but with your change, since >>>>>>>>>>>>>> there is only one function, only one set of variable gets initialized by >>>>>>>>>>>>>> the two function calls. And one skin just broke. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Or am I missing something? Does the patch fix a problem you really had? >>>>>>>>>>>>> Frankly, I wasn't able to test in the field yet as replacing the libs >>>>>>>>>>>>> there is non-trivial. But I was able to observe that only one set of >>>>>>>>>>>>> functions is used - which is logical considering the weak marks. And >>>>>>>>>>>>> this breaks due to the static inline initialization. >>>>>>>>>>>>> >>>>>>>>>>>>> However, let's mark both functions and variables weak to fix the issue >>>>>>>>>>>>> and avoid leaving unused variables around. Will update my patch in a minute. >>>>>>>>>>>> Ok. I am reverting this patch until you provide me with another >>>>>>>>>>>> solution. It causes latency to segfault purely and simply at startup on >>>>>>>>>>>> my dual PIII. >>>>>>>>>>>> >>>>>>>>>>> Cannot reproduce yet. Do you have a backtrace? >>>>>>>>>> No. But the problem is probably the same as the one signaled by Henri, >>>>>>>>>> a misplaced weak directive ending up in a symbol with no address at all. >>>>>>>>>> Since the current situation works, I am going to wait for the "clean" >>>>>>>>>> fix which puts some code/data in the src/skins/common directory. >>>>>>>>>> >>>>>>>>> Find it in my tree. But it's not yet well tested. >>>>>>>> I do not like it either. Functions which are in src/skins/common should >>>>>>>> still be weak, since this lib is included in all the skins libraries. >>>>>>> Those functions are now in libxeno_common only, so I see no point in >>>>>>> allowing them to be overloaded. >>>>>> Yes, but libxeno_common is included in libpthread_rt.so and >>>>>> libnative.so. So, if you link with both libraries, you get >>>>>> libxeno_common twice. >>>>>> >>>>> Do we link libxeno_common statically? Otherwise, this conflict is not >>>>> logical to me. Also, there are other symbols in bind.c that are non-weak. >>>> libxeno_common is a "convenience library", which means that when >>>> libpthread_rt.so is assembled, the object files from libxeno_common are >>>> included. >>> BTW, what speaks against making it a dynamic library? >> Complications. Currently the way of linking a native application is to do: >> >> `xeno-config --ldflags` -lnative >> >> Since when linking, the order matter, we can not hide this new library >> in xeno-config --ldflags, so we would have to turn this into: >> >> `xeno-config --ldflags` -lnative -lxeno-common >> >> i.e. breaking user way of building applications. I do not think the gain >> is worth the trouble: linking against only one xenomai library looks to >> me like the most common case. > > What would break when swapping -lnative and -xeno-common arbitrarily? If you are linking with static libraries (which is the case that matters), the linker would skip all objects from xeno-common completely since none of their symbols are required, then fail after libnative because of missing symbols (defined in libxeno_common). > > There is a _lot_ of cleanup potential. E.g. all that redundant __real > wrappers are good candidates for libxeno-common. Thanks to the wrap-link.sh script, the __real wrappers are no longer required. Besides, they are only needed for the posix skin, so there is no need to put them in libxeno-common. This is something which needs to be fixed too. > >> >>>> I guess the loader eliminates the duplicates. >>>> >>> It has to. For the same reason, we should be able to clean up >>> skins/common/current.c now. >> I am not that confident about that change. By using the weak directive, >> we make sure that the same __thread variable is used for instance. If we >> do not do that, what prevents the code from using the local symbols in >> each library ? IOW, removing the duplicate could work for libxeno_common >> symbols when invoked externally (which probably almost never happens), >> but not inside the skin libraries. I do not know about that, which is >> why I kept the weak declarations. > > Mixing weak functions with non-weak variables can cause troubles as > well. Sticking our head into the sand is no good approach, understanding > the requirements for weak or not is better - and eliminating weak would > be best. Yes, all non static variables must be made weak. But this should already be the case in libxeno_common. Using the weak attribute is the best approach. Having symbols multiply defined is a bad idea and not "standard compliant". The problem is not to understand what happens with one instance of a toolchain, the problem is to know whether the behaviour is the same on all the toolchains of all the seven architectures supported by Xenomai. The --wrap directive proved that not all versions of all toolchains on all platforms are equal. The only alternative I would accept is a guaranteed portable ld directive that would make all the symbols of the library automagically weak. -- Gilles.