We've had a report from Marko Schuetz <marko@ki.informatik.uni-frankfurt.de>
that on FreeBSD you need to pass the `--disable-extern-debug' to configure:

	> From: Marko Schuetz <marko@ki.informatik.uni-frankfurt.de>
	> Date: 13 Oct 1999
	...
	> I grabbed mercury-compiler-1999-10-12. It compiles and
	> installs when configured with --disable-extern-debug.
	> Without --disable-extern-debug the compile fails in
	> trace/mercury_trace_external.c in the include files
	> <arpa/inet.h> and <netdb.h> (??!?!?)

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'.

The rest of this file 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"