Rebar: Cross Compilation Options - erlang

Question

I'm trying use rebar to generate a 32-bit arch release on 64-bit arch system. It's unclear to me how I need to modify an application's rebar.config to be able to do this.
I have taken a look at the rebar source to see how they are detecting my environment: rebar_utils.erl gets the architecture as "x86_64-unknown-linux-gnu" and this is set in rebar_port_compiler as the "default_env". I'm wondering how I can get rebar to compile for another target architecture.
I have tried the following port_env options
{port_env, [{"CFLAGS", "$CFLAGS -fPIC -m32"},{"LDFLAGS", "-arch i386"}]}.
With those options (and a 32-bit Erlang installation in my path), when I run rebar get-deps compile my dependencies are still being built as 64-bit and thus ld skips over my 32-bit libraries (and ultimately fails because it cant find a 64-bit implementation)
/usr/bin/ld: skipping incompatible <PATH TO 32-bit erlang install>/lib/erlang/lib/erl_interface-3.7.14/lib/liberl_interface.a when searching for -lerl_interface
/usr/bin/ld: cannot find -lerl_interface
collect2: ld returned 1 exit status
ERROR: sh(cc c_src/epam.o $LDFLAGS -shared -L"<PATH TO 32-bit erlang install>/lib/erlang/lib/erl_interface-3.7.14/lib" -lerl_interface -lei -o priv/lib/epam.so)
What do I need to do to force my dependencies to compile as 32 bit? My attempt here isn't working.

Answer 1

The port_env settings in rebar.config can make use of the ERLANG_ARCH environment variable to determine whether the Erlang runtime was built for a 32- or 64-bit system. For example, the following port_env definition sets either -m32 or -m64 as appropriate for the C compiler for the x86_64, i686, and i386 chip architectures:
{port_env, [{"x86_64", "CFLAGS", "$CFLAGS -m$ERLANG_ARCH"},
{"i[36]86", "CFLAGS", "$CFLAGS -m$ERLANG_ARCH"}]}.
The first string in each tuple is a regular expression matched against the system architecture string of the Erlang runtime as returned by the erlang:system_info(system_architecture) function. In this example, the additional -m$ERLANG_ARCH option is added only when the regular expression matches, and all other architectures get the default CFLAGS setting.