Support building x86-64 wheel on arm64 macOS machine

[messense]

This makes arch -x86_64 python3.9 setup.py build_ext works on Apple Silicon Macs.

cc #108 @ronaldoussoren

[davidhewitt]

Thanks for looking into this. Gotta admit I'm not a macOS user / expert so have been reading up as best I can to give this a review...

Also please add a CHANGELOG entry 😃

[davidhewitt]

Perhaps we can allow target to be either way around? e.g. depending on the output of platform.processor() we could allow either x86_64-apple-darwin or aarch64-apple-darwin

... also should it be x86_64 instead of i386 ?

[messense]

Perhaps we can allow target to be either way around?

I don't think so. Only arch -x86_64 ... works on arm64 macOS, arch -arm64 ... doesn't work on x86_64 macOS.

also should it be x86_64 instead of i386 ?

I've checked on arm64 macOS with arch -x86_64 python3.9 setup.py build_ext it says i386, but I'm not sure whether i386 is the only possible value or not.

[messense]

I've also tried using sysctl.proc_translated, but it doesn't seem to work for us.

x86_64 emulation, ret should be 1 but got 0

❯ arch -x86_64 python -m IPython
Python 3.9.1 (default, Jan 14 2021, 04:46:20)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.20.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import platform

In [2]: platform.machine()
Out[2]: 'arm64'

In [3]: platform.processor()
Out[3]: 'i386'

In [4]: import ctypes

In [5]:
   ...: from ctypes import cdll, c_char_p, c_void_p, c_size_t, c_int, POINTER, byref
   ...:
   ...: libc = cdll.LoadLibrary("libc.dylib")
   ...: libc.sysctlbyname.argtypes = [c_char_p, c_void_p, POINTER(c_size_t), c_void_p, c_size_t]
   ...: libc.sysctlbyname.restype = c_int

In [6]: ret = c_size_t(0)

In [7]: size = c_size_t(ctypes.sizeof(ret))

In [8]: libc.sysctlbyname(b"sysctl.proc_translated", byref(ret), byref(size), None, 0)
Out[8]: 0

In [9]: ret
Out[9]: c_ulong(0)

native arm64, ret is 0

❯ python -m IPython
Python 3.9.1 (default, Jan 14 2021, 04:46:20)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.20.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import ctypes

In [2]: import platform

In [3]: platform.machine()
Out[3]: 'arm64'

In [4]: platform.processor()
Out[4]: 'arm'

In [5]:
   ...: from ctypes import cdll, c_char_p, c_void_p, c_size_t, c_int, POINTER, byref
   ...:
   ...: libc = cdll.LoadLibrary("libc.dylib")
   ...: libc.sysctlbyname.argtypes = [c_char_p, c_void_p, POINTER(c_size_t), c_void_p, c_size_t]
   ...: libc.sysctlbyname.restype = c_int

In [6]: ret = c_size_t(0)

In [7]: size = c_size_t(ctypes.sizeof(ret))

In [8]: libc.sysctlbyname(b"sysctl.proc_translated", byref(ret), byref(size), None, 0)
Out[8]: 0

In [9]: ret
Out[9]: c_ulong(0)

[messense]

My bad, sysctlbyname should works with universal2 Python interpreter, I was testing with a arm64 only Python.

Interesting though, the arm64 only Python 3.9.1 was installed with pyenv, while arch -x86_64 python runs fine and results in the weird platform.machine() == 'arm64' and platform.processor() == 'i386', arch -x86_64 /absolute/path/to/python errored with arch: posix_spawnp: /Users/messense/.pyenv/versions/test/bin/python: Bad CPU type in executable

With a universal2 Python interpreter, I get platform.machine() == 'x86_64' and platform.processor() == 'i386' when running it with arch -x86_64 python.

[davidhewitt]

Thanks, I've fixed CHANGELOG merge conflict and will merge once CI has finished.