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/*
* User helpers.
*
* These are segment of kernel provided user code reachable from user space
* at a fixed address in kernel memory.  This is used to provide user space
* with some operations which require kernel help because of unimplemented
* native feature and/or instructions in many ARM CPUs. The idea is for
* this code to be executed directly in user mode for best efficiency but
* which is too intimate with the kernel counter part to be left to user
* libraries.  In fact this code might even differ from one CPU to another
* depending on the available  instruction set and restrictions like on
* SMP systems.  In other words, the kernel reserves the right to change
* this code as needed without warning. Only the entry points and their
* results are guaranteed to be stable.
*
* Each segment is 32-byte aligned and will be moved to the top of the high
* vector page.  New segments (if ever needed) must be added in front of
* existing ones.  This mechanism should be used only for things that are
* really small and justified, and not be abused freely.
*
* User space is expected to implement those things inline when optimizing
* for a processor that has the necessary native supp