Hi Tony,

On Nov 29, 2021, at 7:51 AM, Tony Garnock-Jones ***@***.***> wrote:

 I'm running Cog on aarch64, and because I have an old linux kernel (v3.18.140) which I cannot upgrade (it's a repurposed PostmarketOS Android device), Cog yields illegal instruction trying to execute mrs x0, id_aa64isar0_el1. This instruction is privileged, but later linux kernels trap and emulate it for userspace.

Given that it's currently only being used to detect presence of atomic instructions (self setHasAtomicInstructions: (idISAR0 >> 20 bitAnd: 2r1111) = 2r10), and there's a kernel API for retrieving that specific bit of information (https://www.kernel.org/doc/html/latest/arm64/elf_hwcaps.html suggests HWCAP_ATOMICS), perhaps instead of using the instruction directly Cog could call the relevant getauxval variant?

Good suggestion. I’ll try and get this folded in I the next couple of days.

For now, I have the Stack VM running well on aarch64, so I can make progress, even if it is a little slower than it could be :-)

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Should be fixed by 6f2914e4484fa2d6f0e0107391b674daea85b60c Author: Eliot Miranda eliot.miranda@gmail.com Date: Thu Dec 2 14:03:25 2021 -0800

CogVm source as per VMMaker.oscog-eem.3117

Cog ARMv8: Since id_aa64isar0_el1 is a priviledged instruction use getauxval on linux to derive the value(s) derived there-from, currenty whether atomic instructions are available or not. This addresses opensmalltalk-vm Issue #608.

Just reporting back: running the latest Cog VM on aarch64 on PostmarketOS (i.e. Alpine) on Pinephone 1.2 works very well. No problems with illegal instructions. (I did have to `mount -o remount,exec /dev/shm` to allow the `mprotect` with `PROT_EXEC` to work, but other than that, no hitches.)