arm64: uaccess: permit __smp_store_release() to use zero register

Browse source

Currently the asm constraints for __smp_store_release() 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:

    __smp_store_release(ptr, 0)

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

    mov     xN, #0
    stlr    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:

    stlr    xzr, [<addr>]

Modify the asm constaints for __smp_store_release() 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/20230314153700.787701-3-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

...

This commit is contained in:

Mark Rutland 2023-03-14 15:36:58 +00:00 • committed by Will Deacon

parent e5cacb540f

commit 39c8275de8

1 changed files with 5 additions and 5 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

10

arch/arm64/include/asm/barrier.h

View file