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 <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230314153700.787701-4-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
"2:\n" \
_ASM_EXTABLE_##type##ACCESS_ERR(1b, 2b, %w0) \
: "+r" (err) \
- : "r" (x), "r" (addr))
+ : "rZ" (x), "r" (addr))
#define __raw_put_mem(str, x, ptr, err, type) \
do { \