arm64: uaccess: permit put_{user,kernel} to use zero register

Currently the asm constraints for __put_mem_asm() require that the value
is placed in a "real" GPR (i.e. one other than [XW]ZR or SP). This means
that for cases such as:

	__put_user(0, addr)

... the compiler has to move '0' into "real" GPR, e.g.

	mov	xN, #0
	sttr	xN, [<addr>]

This is unfortunate, as using the zero register would require fewer
instructions and save a "real" GPR for other usage, allowing the
compiler to generate:

	sttr	xzr, [<addr>]

Modify the asm constaints for __put_mem_asm() to permit the use of the
zero register for the value.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Robin Murphy <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

0 files changed, 0 insertions, 0 deletions