Use the Privileged Only Thread ID Register aka TPIDRPRW to store the current thread pointer. The Privileged Only Thread ID Register is only accessible in privileged modes, and is read/write. see: ARMv7 Architecture Reference Manual, section B3.12.46 CP15 c13 Software Thread ID registers Change-Id: I5273bee8a80b78cdc547b2f6c96632d120eb3d55 Reviewed-on: https://review.haiku-os.org/c/haiku/+/5608 Tested-by: Commit checker robot <[email protected]> Reviewed-by: waddlesplash <[email protected]>