
Mercury on FreeBSD
==================

GCC 4.2.1 Compatibility
-----------------------

FreeBSD 9.1's default version of GCC (version 4.2.1) sometimes locks up when
compiling the C code generated by the Mercury compiler.  Installing GCC
4.4.7 from ports and directing Mercury to use gcc44 as follows can fix this
problem:

    CC=gcc44 ./configure <your normal configure arguments>


Shared library support
----------------------

For FreeBSD, the Boehm conservative garbage collector does not yet support
shared libraries.  So Mercury does not yet support shared libraries on FreeBSD,
except in the (not very useful) case where you compile with GC disabled,
e.g. using the option `--gc none'.

This has not been retested recently.

The rest of this section contains some hints for eager FreeBSD hackers
about what would need to be done to make the Boehm collector support
shared libraries on FreeBSD.

    The basic problem is that on FreeBSD the conservative collector does not
    scan the memory regions that contain global variables from dynamically
    linked shared object files.

    First, check the `recent_changes' file at
    <http://reality.sgi.com/boehm/gc_source/> to see if someone else has
    already solved the problem.

    In order to support dynamic linking, I think you need to implement the
    GC_register_dynamic_libraries() function in boehm_gc/dyn_load.c.  This
    function needs to call GC_add_root(low_address, high_plus_one_address,
    TRUE) for every memory region in dynamically loaded code that needs to
    be scanned by the collector, so that the collector can scan global
    variables defined in shared libraries.

    If FreeBSD uses ELF and supports ELF in exactly the same way that Linux
    does, then you could try the following patch, which just enables the
    Linux code in the FreeBSD case.  But most likely there are some
    differences between FreeBSD and Linux in this respect, so this will
    probably not work as is -- you should consider this just a starting
    point.

    Read the comments at the top of dyn_load.c for more details.

    --- dyn_load.c	Mon Aug 31 15:05:05 1998
    +++ dyn_load.c.new	Wed Jun 16 22:58:48 1999
    @@ -260,7 +260,7 @@
     # endif /* !USE_PROC ... */
     # endif /* SUNOS */
     
    -#if defined(LINUX) && defined(__ELF__) || defined(SCO_ELF)
    +#if defined(LINUX) && defined(__ELF__) || defined(SCO_ELF) || defined(FREEBSD)
     
     /* Dynamic loading code for Linux running ELF. Somewhat tested on
      * Linux/x86, untested but hopefully should work on Linux/Alpha. 
    --- config.h	Wed Oct 28 10:16:49 1998
    +++ config.h.new	Wed Jun 16 23:08:56 1999
    @@ -699,6 +699,7 @@
     #   ifdef FREEBSD
     #	define OS_TYPE "FREEBSD"
     #	define MPROTECT_VDB
    +#	define DYNAMIC_LOADING
     #   endif
     #   ifdef NETBSD
     #	define OS_TYPE "NETBSD"

