This file documents the port of Mercury to Mac OS X,
i.e. the "*-apple-darwin*" configuration. 

=========================================================
IMPORTANT NOTE FOR FOR USERS OF MAC OS X 10.7 AND XCODE 4
=========================================================

The default C compiler provided in XCode 4 is llvm-gcc.
Mercury does NOT work with llvm-gcc.  In order to build Mercury you will either
need to use one of the other C compilers available on the system, either GCC
4.2 or clang.  With XCode 4 "gcc" is actually a symbolic link for llvm-gcc; the
GCC 4.2 executable is named "gcc-4.2".

Alternatively, the MacPorts project, <http://www.macports.org/>, provides more
recent versions of GCC for Mac OS X.

As llvm-gcc is no longer supported as of version 3.0 of LLVM, we have no
intention of ever supporting Mercury with it.

----------------------------------
Mercury on Mac OS X 10.5 and 10.6
----------------------------------

Mercury should build and install "out-of-the-box" on Mac OS X 10.5 or 10.6
using Apple's gcc version 4.2.  This version of gcc is included with the
Developer Tools.  On Mac OS X 10.6 you may also use clang.

The 'asm_fast*' and 'reg*' grades are not currently available on Mac OS X 10.5
or 10.6.  The only low-level C grades available are the 'none*' grades.  The
high-level C, Java, Erlang and C# grades all work.  The 'erlang' grade requires
an Erlang installation to be available and the C# grades require the Mono .NET
implementation.  (See README.Erlang and README.CSharp for further details.)

When installing from the source distribution the configure script will
automatically select the 'none.gc' grade for building the Mercury system.
Unless otherwise directed, the 'hlc.gc' grade will be used as the default grade
for compiling applications.

By default, 64-bit versions of the executables and libraries in the Mercury
system will be installed on x86-64 machines running Mac OS X 10.6.  To build a
32-bit installation on such a machine, you need to arrange to have the option
"-m32" passed to gcc or clang.  This can be done by invoking Mercury's
configure script with the option:

    --with-cc="gcc -m32"

By default, 32-bit versions of the executables and libraries are installed on
x86-64 machines running Mac OS X 10.5.  To build and install 64-bit Mercury on
such a system you must pass the "-m64" option to gcc. 

Note that if you are building Mercury from scratch using an existing installed
Mercury compiler, i.e. you are not installing using the pre-generated C files in
the source distribution, and you are using a 32-bit Mercury compiler to
bootstrap a 64-bit installation (or vice versa) then you must compile with
--cross-compiling enabled.  Not enabling it will result in library installation
aborting with an error message like the following:

    Uncaught Mercury exception:
    Software Error: pred_table.m: Unexpected: can't locate compare/3

You can enable cross-compilation by putting the following line in a file named
Mmake.params at the top-level of the source tree:

    MCFLAGS = --cross-compiling

Mercury cannot currently be compiled with llvm-gcc on Mac OS X.

If, after installing Mercury, you encounter errors about missing .mih files,
and you have fink installed, then try removing the fink components from your
PATH (these usually start with /sw) and reinstalling.

---------------------------------
Mercury on Mac OS X 10.3 and 10.4
---------------------------------

Mercury should work on Mac OS X 10.3 and 10.4 (both PowerPC and Intel),
although it has not been tested with either of these for some time.

Apple gcc 2.95 does not work with Mercury because it cannot handle the length
of some of the identifier names that the Mercury compiler generates.

Apple gcc 3.3 works with Mercury and there are no known issues (other than the
problem with gcc's powerpc backend described below).  We recommend that users
of Mac OS X 10.3 and 10.4 use this version.

Apple gcc 4.0 does not work with Mercury.  Users of Mac OS X 10.4 should note
that this version of gcc is the default one on their systems.

On 10.3 and 10.4, if you are using an Apple build of gcc then you must use the
gcc_select command to set the system's default gcc to that version of gcc.  It
is not sufficient to just point Mercury to a version of gcc using the configure
script's `--with-cc' option.  This restriction applies only to the builds of
gcc supplied by Apple.

Mainline gcc 3.3.X and 3.4.X are known to work with Mercury on 10.3.
Mainline gcc 4.0.X does not.


-------------------------------------
Mercury on older versions of Mac OS X
-------------------------------------

There may be problems with building Mercury on versions of Mac OS X less than
10.3.  In particular, building shared libraries with Mercury on these systems
is not supported.

The version of tar in /usr/bin/tar on some older versions of Mac OS X (e.g.
10.1) doesn't work properly -- it truncates long path names.  Make sure you
use GNU tar, which is available in /sw/bin/gtar, when unpacking the Mercury
source or binary distributions.  (Also, make sure to use GNU tar if/when
*building* such distributions!) The version of tar that comes with Mac OS X
10.3.3 does not have this problem.

Also, Apple's version of gcc includes support for precompiled headers.
Unfortunately this support seems to be somewhat buggy, causing it to sometimes
crash with mysterious errors when building Mercury.  Furthermore, for the
kinds of C code that the Mercury compiler generates, it results in a very big
slow-down, rather than any speedup.  Fortunately this can be disabled by using
the `--traditional-cpp' option.  The Mercury configure script should enable
this option automatically if it is needed.


------------------------
PowerPC Linking Problems
------------------------

On PowerPC machines, the linker may have problems linking large executables
(particularly in debug grades; technically when the program requires a branch
larger than +/- 32 MB). It complains about relocation displacements being too
large. The only known workaround for this problem is to replace the
system-provided versions of crt1.o (Darwin module 'Csu') and crt2.o (part of
gcc) with versions that are compiled with the gcc options `-mlongcall' and (if
using gcc < ~ 3.4) `-mlong-branch'. C code generated by the Mercury compiler
will also need to be compiled with the above options. This can be achieved by
adding:

    EXTRA_CFLAGS=-mlongcall -mlong-branch

to your Mercury.options or Mmakefile.


-----------------------------------
Known bugs and unsupported features
-----------------------------------

The following feature is not supported on Mac OS X:
	- interactive queries in mdb

The 'asm_fast' grades will not work on *-apple-darwin machines, primarily
because of a (long-standing) bug in gcc (GCC bug #10901).  By default, 
the configure script will choose either 'reg' or 'none' as the default base
grade.  If you do not intend to use debugging (e.g. with production code), then
you will probably get better performance by using the hlc.gc grade.

Executables created by the Mercury compiler cannot be statically linked against
the system libraries, on Mac OS X.  Setting `MLFLAGS=-static' or invoking mmc
with the `--linkage static' option will result in an error message like the
following from the linker:
	
	ld: can't locate file for: -lcrt0.o
 
The reason that this does not work is that static version of the system
libraries are not installed on OS X systems by default.  (See Technical Q&A
QA118 <http://developer.apple.com/qa/qa2001/qa1118.html> for further details.)

This restriction only applies to system libraries.  Statically linking against
Mercury libraries is fine.


--------------------------
Deep profiling on Mac OS X
--------------------------

The following discussion assumes a standard installation of Mac OS X.  By
default Apache should have been installed as the default webserver.

In order to use the deep profiler you need to ensure that the deep profiling
CGI "script" is installed and that the webserver is running.

The deep profiling CGI script, mdprof_cgi, should be installed in the
directory /Library/WebServer/CGI-Executables.  Mercury's normal installation
process should take care of this if deep profiling is enabled.

To ensure the webserver is running:

- Open the Apple Menu and open the System Preferences window.
- In the `System Preferences' window, click on the icon labelled `Sharing'.
- Make sure that `Personal Web Sharing' is enabled.  If it is then
  the webserver should be running.

The remaining instructions for using the deep profiler are the same as those
found in the ``Mercury User's Guide''.  We recommend against using Safari 1.5
as it has been found to be somewhat unstable with the deep profiler.  Later
versions of Safari are fine. 
