Re: [Boost-build] linking a library from static libraries

Subject: Re: [Boost-build] linking a library from static libraries
From: Vladimir Prus (ghost_at_[hidden])
Date: 2009-06-04 02:17:05

On Thursday 04 June 2009 09:21:02 Paul Fox wrote:
> I am working on the build system for a fairly large project, which will
> produce a static and a shared-object version of a library. In order to keep
> the project manageable, it has been divided into several modules.
> Each module is currently building as a static library, and the Jamroot for
> the project lists all of the applicable sub-projects as dependencies.
> However, I found that it was in fact building an empty library, both in
> static and dynamic mode!
> 
> Doing some poking around, I discovered that for the static build, it was not
> passing ar the static libraries at all, instead only giving it one system
> shared library to link against. I also discovered that in dynamic mode, it
> was giving ld the appropriate list of libraries, but ld was ignoring them.
> 
> Upon further investigation, I discovered that neither ar nor ld will accept
> static (.a) libraries as arguments to build a library by default. ar expects
> object files, which would require the relevant .a files to be unpacked, and
> ld will only include .a files in a dynamic library if you use the
> --whole-archive flag preceding the list, and the --no-whole-archive flag
> following it.
> 
> I therefore currently have to execute the last linking step manually after
> boost-build executes, which is far from ideal. What would be the best way to
> handle this in boost-build? Is there another way I can type the modules so
> that they will return a bunch of object files instead of a library? Is there
> a way to make boost-build aware of how to create a library from a library?

Given that the underlying tools don't really allow this, I don't think
much can be done on Boost.Build side.

> What is the cleanest solution?

The simplest solution might be this:

submodule/Jamfile:

        alias the_submodule : a.cpp b.cpp ;

Jamroot:

   lib all : submodule//the_submodule ;

However, this approach does not make it possible to use different
compiler options for different submodules. If that is desired,
do this:

1. Put the attached convert.jam to 'tools' dir of boost.build.
2. In your Jamroot, add:

   import convert ;

3. In your submodule/Jamfile, use:

  convert submodule obj : a.cpp b.cpp ;

4. In you Jamroot, just use the 'submodule' target as you would
use a library.

You can also grab SVN HEAD version of Boost.Build -- in which cases
steps (1) and (2) are not necessary.

Let me know if this helps.

- Volodya