From 4230509978f2921182da4e9197964dccdbe463c3 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 18 Sep 2018 09:39:55 +0100 Subject: [PATCH] arm64: cmpxchg: Use "K" instead of "L" for ll/sc immediate constraint 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 Signed-off-by: Will Deacon --- arch/arm64/include/asm/atomic_ll_sc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/atomic_ll_sc.h b/arch/arm64/include/asm/atomic_ll_sc.h index b53f70dd6e10e..af7b990054536 100644 --- a/arch/arm64/include/asm/atomic_ll_sc.h +++ b/arch/arm64/include/asm/atomic_ll_sc.h @@ -276,7 +276,7 @@ __LL_SC_PREFIX(__cmpxchg_case_##name##sz(volatile void *ptr, \ "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; \ -- 2.30.2