Towards a patch for boost build under gcc 4.0, link=shared

From: Mat Marcus (mat-lists_at_[hidden])
Date: 2005-08-24 14:31:41

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I am working towards a patch for boost build (both versions) to allow
executables produced by boost-build to work when linked against shared
library versions of boost, under gcc 4.0. See for example:

<http://article.gmane.org/gmane.comp.lib.boost.build/10072>

I am more familiar with bbv2 so I will begin with there. The idea is to
add a new feature <symbol-visibility>, which defaults to
- -fvisibility=hidden:

### add to builtins.jam

feature symbol-visibility : exported hidden : propagated ;

### add to gcc.jam

flags gcc.compile OPTIONS <symbol-visibility>exported :
- -fvisibility=default ;
flags gcc.compile OPTIONS <symbol-visibility>hidden :
- -fvisibility=hidden ;

### end

That won't quite work, since gcc versions prior to 4.0 don't understand
this flag (except for some patched versions IIUC). I tried to make it
conditional, following some code I found in darwin.jam, by wrapping it
as follows:

local gccversion = [ SHELL "$(command) -dumpversion" ] ;
if $(version) >= "4.0.0"
{
flags gcc.compile OPTIONS <symbol-visibility>exported :
- -fvisibility=default ;
flags gcc.compile OPTIONS <symbol-visibility>hidden :
- -fvisibility=hidden ; 
} 

This doesn't work well when under cygwin for me though.

Questions: 
1) What is the right way to make some flags dependent on compiler
version?
2) Does anyone dislike the idea of making <symbol-visibility> a feature?

Same questions for BBv1.

Thanks,
Mat

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