From: Will Deacon will.deacon@arm.com
commit 4230509978f2921182da4e9197964dccdbe463c3 upstream.
The "L" AArch64 machine constraint, which we use for the "old" value in an LL/SC cmpxchg(), generates an immediate that is suitable for a 64-bit logical instruction. However, for cmpxchg() operations on types smaller than 64 bits, this constraint can result in an invalid instruction which is correctly rejected by GAS, such as EOR W1, W1, #0xffffffff.
Whilst we could special-case the constraint based on the cmpxchg size, it's far easier to change the constraint to "K" and put up with using a register for large 64-bit immediates. For out-of-line LL/SC atomics, this is all moot anyway.
Reported-by: Robin Murphy robin.murphy@arm.com Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/atomic_ll_sc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm64/include/asm/atomic_ll_sc.h +++ b/arch/arm64/include/asm/atomic_ll_sc.h @@ -268,7 +268,7 @@ __LL_SC_PREFIX(__cmpxchg_case_##name##sz "2:" \ : [tmp] "=&r" (tmp), [oldval] "=&r" (oldval), \ [v] "+Q" (*(u##sz *)ptr) \ - : [old] "Lr" (old), [new] "r" (new) \ + : [old] "Kr" (old), [new] "r" (new) \ : cl); \ \ return oldval; \