Get real architecture of M1 Mac regardless of Rosetta

Question

I need to retrieve the real architecture of a Mac regardless of if the process is running through Rosetta or not.

Right now in Node.js, process.arch returns x64 and in shell, uname -m returns x86_64.

Answer 1

Thanks to @Ouroborus, this note describes how to figure out if your app is translated.

If it's translated:

$ sysctl sysctl.proc_translated
sysctl.proc_translated: 1

If not:

$ sysctl sysctl.proc_translated
sysctl.proc_translated: 0

On non-ARM Macs:

$ sysctl sysctl.proc_translated
sysctl: unknown oid 'sysctl.proc_translated'

Answer 2

As @Elmo's answer indicates, the command line sysctl -n sysctl.proc_translated or the native equivalent sysctlbyname() call will indicate whether you are running under Rosetta.

Two other sysctl values are relevant. On M1 hardware without Rosetta, these values are returned:

hw.cputype: 16777228
hw.cpufamily: 458787763

hw.cputype is 0x0100000C (CPU_TYPE_ARM64) and hw.cpufamily is 0x1b588bb3 (CPUFAMILY_ARM_FIRESTORM_ICESTORM).

However, when executed under Rosetta, the low-level machine code which collects CPUID takes precendence and following two values are returned, both via sysctlbyname() and the command line:

hw.cputype: 7
hw.cpufamily: 1463508716

These correspond to 0x7 (CPU_TYPE_X86) and 0x573b5eec (INTEL_WESTMERE).

It appears Rosetta reports an x86-compatible Westmere chip under Rosetta, but this choice seems consistent everywhere I've seen. This "virtual architecture" may be useful information for some programs.

Another possibility presents itself in the IO Registry. While the default IOService plane collects data in real-time, the IODeviceTree plane is stored at boot, and includes these entries in the tree (command line ioreg -p IODeviceTree or ioreg -c IOPlatformDevice):

cpu0@0  <class IOPlatformDevice, id 0x10000010f, registered, matched, active, busy 0 (180 ms), retain 8>
    | | | {
...
    | | |   "compatible" = <"apple,icestorm","ARM,v8">

(for CPUs 0-3) and

cpu4@100  <class IOPlatformDevice, id 0x100000113, registered, matched, active, busy 0 (186 ms), retain 8>
    | | | {
...
    | | |   "compatible" = <"apple,firestorm","ARM,v8">

(for CPUs 4-7)

This clearly indicates the ARMv8 Firestorm + Icestorm M1 chip.

The same approach should work for the M1 Pro and M1 Max.