erlang cross compilation

[Brian Zhou]

I'd like to share what I did to cross compile erlang for NSLU2 
(http://www.nslu2-linux.org).

The compilation build host machine:
$ uname -a
Linux hostname 2.6.10-co-0.6.2 #5 Sat Feb 5 10:19:16 IST 2005 i686 GNU/Linux

The target machine:
$ uname -a
Linux slug 2.4.22-xfs #1 Sun Jun 12 21:17:17 PDT 2005 armv5b unknown unknown 
GNU/Linux

The general steps should work for other cross compilation settings as well, 
it has been used to package R10B-5 and R10B-6. The Makefile and patches are 
checked in

    http://cvs.sourceforge.net/viewcvs.py/nslu/unslung/make/erlang.mk?view=markup
    http://cvs.sourceforge.net/viewcvs.py/nslu/unslung/sources/erlang/

The steps are fully automated in the Makefile, basically

1. Make sure there's an erlang version on the build host with matching 
version. To be absolutely sure and minimize build dependencies, a host 
version is built first in erlang-host/ subdirectory.

2. Patch erts/emulator/Makefile.in to use host gcc for the mkliteral tool. 
See sources/erlang/erts-emulator-Makefile.in.patch for detail.

3. Configure. It's always a good idea to run configure natively so we have a 
reference. The goal is for the cross configure to generate the exact same 
erts/$arch/config.h as a native configure does.

Lots of the configuration settings can be overriden using ac_cv_ environment 
variables. Examples here are
        ac_cv_c_bigendian=yes
        ac_cv_func_mmap_fixed_mapped=yes

In some other cases you have to patch erts/configure.in and run "autoconf 
configure.in > configure" in erts/, see 
sources/erlang/erts-configure.in.patch for example.

4. Build the target erlang, this can take a little while (much better than 
the 10+ hours native build anyway). Start the build by
    PATH="fullpath_of_erlang-host/bin:$PATH" make -C erlang noboot

5. Building SAE will involve some more patches. The basic idea is to build 
host version of SAE first, then use the host version of ecc and elink to 
build the native SAE, see erts-boot-src-Makefile.patch.

6. Packaging. The only tricky part is start_sasl.boot. This can be 
accomplished by patching erts/etc/unix/Install.src to use the erlang-host/ 
executables. For NSLU2, we also need to use /opt as prefix for everything.

Some simple tests I did:

    # ipkg install erlang

    $ erl
    Erlang (BEAM) emulator version 5.4.6 [source]

    Eshell V5.4.6  (abort with ^G)
    1>
    User switch command
     --> q

    $ cat fib2
    #!/usr/bin/env escript

    -export([main/1]).

    -mode(compile).

    main([X]) ->
        J = list_to_integer(X),
        N = fib(J),
        io:format("fib ~w = ~w~n",[J, N]).

    fib(0) -> 0;
    fib(1) -> 1;
    fib(N) ->
        fib(N-1) + fib(N-2).

    $ ./fib2 20
    fib 20 = 6765

Thanks  Matthias Lang for the wonderful web page about his previous erlang 
cross compilation experience 
http://www.corelatus.com/~matthias/erlang_on_860.html

Cheers,

-Brian Zhou