More aarch64 stuff

This value saved in x18 is overwritten immediately

It was like that before me and i decided not to touch it for now. I just reused x18 register because it is overwritten anyway for temp storage to align stack pointer

It's just a hack to debug SP misalign issues in kernel, ideally we should have separate stack so kernel would be able to output nice stack trace even if stack is messed up

https://developer.arm.com/documentation/den0024/a/The-ABI-for-ARM-64-bit-Architecture/Register-use-in-the-AArch64-Procedure-Call-Standard/Parameters-in-general-purpose-registers

X18 is the platform register and is reserved for the use of platform ABIs. This is an additional temporary register on platforms that don't assign a special meaning to it.

So for now i decided to not remove this

merged

mentioned in commit 78a8173f