I'm using Emacs 26.3 with Spacemacs 0.300 and the registers don't cross from buffer to buffer (global registers). From what I read on the EmacsWiki this is supposed to be global by default. Mine apparently is not, I can't find anywhere it's being set to local but it's behaving as such. However, while this:
(make-variable-buffer-local 'register-alist)
makes a variable local to the buffer, I can't find what to do to make it back global, there's no make-variable-global function.
Hope someone has a suggestion, it's frustrating to insert a register I just saved and have it tell me there's nothing there!
You can't make a variable global that's been declared to always be buffer-local.
This is why this hammer is used relatively infrequently - when you know that the variable should always be buffer local.
Instead, you typically just use setq-local or set with make-local-variable, which assign a buffer-local value only for the given buffer. Nothing then prevents some other buffer from not having any buffer-local value.
You can of course use makunbound to, in effect, start over with your variable unbound. But that's hardly a great solution for a situation where a variable has already been declared to always be buffer-local and you want it to not have a buffer-local value in some buffer.