Generated Makefile for NIFs on Apple M1 processor is incorrect

[NAR]

Pre-Check

Environment

Rebar3 report
version 3.17.0+build.5120.ref26d929b0
generated at 2021-11-29T21:05:24+00:00

Current behaviour

I followed the description at http://rebar3.org/docs/tutorials/building_c_cpp/ to create a NIF library. I executed the

rebar3 new lib test_nif
cd test_nif
rebar3 new cmake

commands which generated a c_src/Makefile. This Makefile has an OS X-specific section:

ifeq ($(UNAME_SYS), Darwin)
	CC ?= cc
	CFLAGS ?= -O3 -std=c99 -arch x86_64 -finline-functions -Wall -Wmissing-prototypes
	CXXFLAGS ?= -O3 -arch x86_64 -finline-functions -Wall
	LDFLAGS ?= -arch x86_64 -flat_namespace -undefined suppress

The problem is that the M1 processor in newer Macs is not an x86_64, so the generated shared library can't be loaded by the native Erlang VM. According to the file command the shared library is a Mach-O 64-bit dynamically linked shared library x86_64, but the Erlang VM says:

1> erlang:system_info(system_architecture).
"arm-apple-darwin20.6.0"

Expected behaviour

I expected the generated Makefile to be correct :-) I'm not quite sure what should be the correct solution, my workaround was to remove the -arch x86_64 options (see for example at maxlapshin/fix#14). However, if that option was there for a reason, we might need to branch on machine type too, not only on OS.

[NAR]

I created a PR: #2656

[ferd]

Thanks! Already merged. I don't imagine this option was essential (the architecture isn't specified for other OSes either) and the build worked, so I suppose it to be fine.