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Subject: Re: [Boost-build] vacpp.jam
From: Jim Hague (jim.hague_at_[hidden])
Date: 2009-03-16 06:36:48

Vladimir Prus <ghost <at>> writes:
> > diff -r 5b628f6ec088 boost-build/tools/vacpp.jam
> > --- a/boost-build/tools/vacpp.jam Fri Mar 13 16:42:46 2009 +0000
> > +++ b/boost-build/tools/vacpp.jam Fri Mar 13 17:30:22 2009 +0000
> > @@ -16,7 +16,8 @@
> >
> > feature.extend toolset : vacpp ;
> > toolset.inherit vacpp : unix ;
> > -generators.override vacpp.prebuilt : builtin.lib-generator ;
> > +generators.override vacpp.prebuilt : builtin.prebuilt ;
> > generators.override vacpp.searched-lib-generator : searched-lib-generator
> > ;
> This is the right fix. I've checked it in in SVN.

So, I made a good guess. Thanks.

> > The offender is the '-qtwolink' link option. The docs at
> >
> > describe this option [...]
> >
> > I suggest that this should only be applied by vacpp.jam as an option; I
> > think it too aggressive for a universal link option.
> I must admit I don't understand neither the problem your had, nor the
> linker option. But if you say this option breaks builds, then so it does
> I've removed it, in SVN HEAD. Can you update and see if things are better?

Sorry, I edited the included text very badly. -qtwolink attempts to minimize the
number of C++ static constructors included in the final executable by omitting
them if the object is question does not appear to be referenced. The linked page
above has a simple example. The page notes explicitly
'Before using -qtwolink, make sure that any .o files placed in an archive do not
change the behavior of the program.' In other words, putting a .o into an
archive and using this option CAN change the behaviour of the program. As I see
it, having '-qtwolink' cannot be a universally applied option for this reason.

In my case, the (third-party, binary only) library contains components that (I
guess) use the static constructor to link themselves into a pool of available
components. -qtwolink causes the program to fail, as some components are suddely
not available. Note as well that on AIX shared libraries are more akin to
Windows DLLs than Unix shared objects, so the option may (I am not clear) be
doing stuff when creating a shared library.

I checked your change. It removed the first -qtwolink, but a second -qtwolink
remains in the EXE-LINKFLAGS; it needs to go too for my program to work.


Jim Hague - jim.hague_at_[hidden]          Never trust a computer you can't lift.

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