Re: [Boost-build] Passing <cxxflags>-fPIC with use-project /boost

Subject: Re: [Boost-build] Passing <cxxflags>-fPIC with use-project /boost
From: Michael Weber (michael.weber_at_[hidden])
Date: 2009-05-07 11:26:11

On Thu, May 7, 2009 at 8:08 AM, Vladimir Prus <ghost_at_[hidden]> wrote:
>
> On Thursday 07 May 2009 14:07:30 Martin Dyring-Andersen wrote:
> > Hello everybody,
> >
> > I have a Jamroot that looks like this:
> >
> > project       :       requirements
> >                       <threading>multi
> >                       <toolkit>gcc,<address-model>64:<cxxflags>-fPIC
> >       :       build-dir stage
> >       :       default-build release
> > ;
> >
> > use-project /boost    : dependencies/boost_1_39_0 ;
> > use-project /test     : test ;
> >
> > and a Jamfile located in test subdirectory that looks like this:
> >
> > lib test      :       [ glob-tree *.cpp ]
> >               /boost//thread/<link>static
> >               /boost//date_time/<link>static
> > ;
> >
> > Now, to get the static linking to /boost//thread and date_time working I need to pass -fPIC when building with GCC on 64 bit platforms.
> >
> > I can see that my own targets in lib sfcg gets compiled with -fPIC, but for some reason the /boost//thread and date_time libraries does not seem to "notice" it.
> >
> > Everything will work perfectly if I pass cxxflags=-fPIC as a parameter to bjam on the command line. But I would prefer to cram as many details as possible into the Jamfiles, so I don't have to remember them later on ;-).
>
> cxxflags is so called "free" feature -- which is feature which value is not
> interpreted. Such features are not propagated to dependencies, for various
> reasons. So, you have to use something like:
>
>                /boost//thread/<link>static/<cxxflags>-fPIC
>
> - Volodya

Is this really a case of propagating across dependencies? The flags
are specified in a Jamroot file, and not on the lib target itself.

I have a similar setup as Martin, with a Jamroot in a high level
directory setting cxxflags for my entire project, and projects in
subdirectories depending upon each other. e.g., subproject B depends
upon A, and when I build B, the cxxflags specified in Jamroot for the
whole project are passed to both subprojects A and B during the build.

It is possible that the Jamroot file in the boost project folder is
hiding Martin's cxxflags. When analyzing the boost project jamfiles,
jam will stop at the first Jamroot file it finds when traversing up
the folder hierarchy, and boost has its own. In fact, I use that
behaviour to occasionally override the cxxflags as specified in my own
Jamroot for subprojects that require exceptions to otherwise globally
applicable settings.

Michael Weber