Re: [Boost-build] Improving --layout=system

From: Chris Fairles (chris.fairles_at_[hidden])
Date: 2007-08-03 10:55:15

Thanks for providing this. I've been using a hacked patch for a long
while now to do this when building rpms.

Just for kicks I attached another patch I use that modifies the
optimization levels a little:
off = -O0, basic=-O1, speed=-O2, space=-Os, insane=-O3

This makes release variants default to -O2 since in some cases the
aggressive loop unrolling and inlining in -O3 hinders instead of
helps.

Chris

On 8/2/07, Caleb Epstein <caleb.epstein_at_[hidden]> wrote:
> On systems that support shared library version numbers, I believe that these
> should be used even when building with --layout=system.
>
> At present, when you build Boost with --layout=system, you end up with
> libraries called libboost_xyz-mt.so that have this same value set at their
> ELF SONAME (this is the shared library version number embedded into the
> library itself).
>
> The problem with these libraries is that you can never have multiple
> versions of them installed side-by-side in the same place. Go too far down
> this road and you end up with Windows-style 'DLL hell'.
>
> If instead the BOOST_VERSION is appended to the target name as it is with
> --layout=versioned, you end up with SONAME'd libraries that can live
> side-by-side with earlier/later versions of Boost.
>
> For example, by adding the version number to the libraries, you end up with
> a lib directory that looks like:
>
> lrwxrwxrwx 1 cepstein   33 Aug  2 13:44 libboost_date_time-mt-d.so ->
> libboost_date_time-mt-d.so.1.35.0
> -rwxrwxr-x 1 cepstein 388K Aug  2 13:44 libboost_date_time-mt-d.so.1.35.0
>  lrwxrwxrwx 1 cepstein   31 Aug  2 13:44 libboost_date_time-mt.so ->
> libboost_date_time-mt.so.1.35.0
>  -rwxrwxr-x 1 cepstein  52K Aug  2 13:44 libboost_date_time-mt.so.1.35.0
> ...
>
> Now when you link applications using -lboost_date_time-mt, the linker
> records the dependency on the library's SONAME, which is
> libboost_date_time_mt.so.1.35.0.  No other name will satisfy this runtime
> dependency.  As a result, you can install the (hypothetical) Boost 1.36.0
> libs into the same directory and old applications will continue to pick up
> the *.so.1.35.0 libs correctly, while new applications built when the
> symlink points to the new library versions will pick up *.so.1.36.0.
>
> This is how Boost.Build v1 handled --layout=system and I believe this is the
> most correct and desirable behavior for platforms that support versioned
> shared libraries.  Attached is my simple patch against the latest SVN trunk
> to make this work.
>
> --
> Caleb Epstein
>
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