Bug report

Bug description:

If we build cpython 3.13 for Linux/ARMv5 using -march=armv5te and then run inside a qemu with the versatilepb machine (which uses a ARM926EJ-S processor) then python crashes with "Illegal Instruction". Specifically, mrc is used in a few places to get the thread ID, but this not possible in cores lower than ARMv6K.

Users of mrc:

• https://github.com/python/cpython/blob/main/Include/object.h#L195
• https://github.com/python/cpython/blob/main/Include/internal/mimalloc/mimalloc/prim.h#L172
• https://github.com/python/cpython/blob/main/Include/internal/mimalloc/mimalloc/prim.h#L199

I suspect the best way of implemented the required check would be:

#if defined(__arm__) && __ARM_ARCH >= 6 && !defined(__ARM_ARCH_6__)

That is, if Arm and if the architecture level is 6 or great and if this is not bare v6 (so v6K/v6Z are included).

Or a blunter but simpler hammer on the grounds that v5/v6 is pretty niche these days could be:

#if defined(__arm__) && __ARM_ARCH >= 7

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-125444: Fix illegal instruction for older Arm architectures #125574
• [3.13] gh-125444: Fix illegal instruction for older Arm architectures (GH-125574) #125595