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Commit 0bc671d3 authored by Will Deacon's avatar Will Deacon
Browse files

arm64: cmpxchg: avoid "cc" clobber in ll/sc routines 



We can perform the cmpxchg comparison using eor and cbnz which avoids
the "cc" clobber for the ll/sc case and consequently for the LSE case
where we may have to fall-back on the ll/sc code at runtime.

Reviewed-by: default avatarSteve Capper <steve.capper@arm.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent e9a4b795

arch/arm64/include/asm/atomic_ll_sc.h

+6 −8
Original line number Diff line number Diff line
@@ -101,14 +101,13 @@ __LL_SC_PREFIX(atomic_cmpxchg(atomic_t *ptr, int old, int new)) 


	asm volatile("// atomic_cmpxchg\n"

"1:	ldxr	%w1, %2\n"

"	cmp	%w1, %w3\n"

"	b.ne	2f\n"

"	eor	%w0, %w1, %w3\n"

"	cbnz	%w0, 2f\n"

"	stxr	%w0, %w4, %2\n"

"	cbnz	%w0, 1b\n"

"2:"

	: "=&r" (tmp), "=&r" (oldval), "+Q" (ptr->counter)

	: "Ir" (old), "r" (new)

	: "cc");

	: "Lr" (old), "r" (new));



	smp_mb();

	return oldval;
@@ -179,14 +178,13 @@ __LL_SC_PREFIX(atomic64_cmpxchg(atomic64_t *ptr, long old, long new)) 


	asm volatile("// atomic64_cmpxchg\n"

"1:	ldxr	%1, %2\n"

"	cmp	%1, %3\n"

"	b.ne	2f\n"

"	eor	%0, %1, %3\n"

"	cbnz	%w0, 2f\n"

"	stxr	%w0, %4, %2\n"

"	cbnz	%w0, 1b\n"

"2:"

	: "=&r" (res), "=&r" (oldval), "+Q" (ptr->counter)

	: "Ir" (old), "r" (new)

	: "cc");

	: "Lr" (old), "r" (new));



	smp_mb();

	return oldval;

arch/arm64/include/asm/atomic_lse.h

+2 −2
Original line number Diff line number Diff line
@@ -166,7 +166,7 @@ static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new) 
	"	mov	%w[ret], w30")

	: [ret] "+r" (x0), [v] "+Q" (ptr->counter)

	: [old] "r" (w1), [new] "r" (w2)

	: "x30", "cc", "memory");

	: "x30", "memory");



	return x0;

}
@@ -313,7 +313,7 @@ static inline long atomic64_cmpxchg(atomic64_t *ptr, long old, long new) 
	"	mov	%[ret], x30")

	: [ret] "+r" (x0), [v] "+Q" (ptr->counter)

	: [old] "r" (x1), [new] "r" (x2)

	: "x30", "cc", "memory");

	: "x30", "memory");



	return x0;

}