[Rcpp-devel] Passing pointers to objects between libs results in weird UBSAN warning

[Iñaki Ucar]

El lun., 20 ago. 2018 a las 16:18, Jan van der Laan
(<rhelp at eoos.dds.nl>) escribió:
>
> > pkg2 compiles a shared library using pkg1's headers, but it does not
> > link against libpkg1.so (in general, this is not possible in R). So
> > both libpkg2.so and libpkg1.so define two copies of the same types,
> > Foo and FooBar. pkg2 allocates FooBar from libpkg1.so and then
> > dynamically casts it as FooBar from libpkg2.so. This is why clang
> > complains. It has to do with how RTTI comparisons are done across
> > dynamic objects (see, e.g.,
> > https://whatofhow.wordpress.com/2015/03/17/odr-rtti-dso/).
>
> This is roughly what I suspected. However, if I understand that article
> correctly problems should only occur with clang (which I am using;
> didn't mention that) and not with g++. However, the problems also occur
> with g++
> (https://www.stats.ox.ac.uk/pub/bdr/memtests/gcc-UBSAN/ldat/ldat-Ex.Rout).

I don't know, maybe things have changed in recent versions of gcc.

> > I'd say that these errors can be safely ignored, because types are
> > exactly the same. Anyway, shouldn't it be easier to export get_foobar
> > in pkg1?
>
> Don't know how easy it is to convince the CRAN members to ignore the
> warnings. Of course, in this simple case, it is easier to define
> get_foobar in pkg1, but in the general case, for performance reasons, I
> would like to be able to access FooBar from other packages from c++ code.

I've just submitted a PR to your repo that fixes the issue:
https://github.com/djvanderlaan/lvec_ubsan/pull/1

Copy&paste of the explanation there, for the interest of this list:

Instead of using useDynLib in the NAMESPACE, this patch loads the
library using library.dynam in .onLoad. In this way, we can take
advantage of library.dynam's dots, which are mapped into the
subsequent dyn.load call. This call has local=TRUE by default, i.e.,
dlopen is called with the RTLD_LOCALattribute. Instead, local=FALSE
sets RTLD_GLOBAL, which makes type_info from pkg1 available globally,
and thus the RTTI error goes away.

Iñaki

>
>
> Thanks for the response.
>
> Jan
>
>
>
>
>
>
>
> >
> > Iñaki
> >
> >>
> >> So, help!?
> >>
> >> Jan
> >>
> >>
> >>
> >>
> >>
> >> _______________________________________________
> >> Rcpp-devel mailing list
> >> Rcpp-devel at lists.r-forge.r-project.org
> >> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
> >
> >
> >



-- 
Iñaki Ucar