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Subject[RFC PATCH 8/8] arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release macros
Date
Passing volatile-qualified pointers to the arm64 implementations of the
load-acquire/store-release macros results in a re-load from the stack
and a bunch of associated stack-protector churn due to the temporary
result variable inheriting the volatile semantics thanks to the use of
'typeof()'.

Define these temporary variables using 'unqual_scalar_typeof' to drop
the volatile qualifier in the case that they are scalar types.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/barrier.h | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index 7d9cc5ec4971..fb4c27506ef4 100644
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -76,8 +76,8 @@ static inline unsigned long array_index_mask_nospec(unsigned long idx,
#define __smp_store_release(p, v) \
do { \
typeof(p) __p = (p); \
- union { typeof(*p) __val; char __c[1]; } __u = \
- { .__val = (__force typeof(*p)) (v) }; \
+ union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u = \
+ { .__val = (__force __unqual_scalar_typeof(*p)) (v) }; \
compiletime_assert_atomic_type(*p); \
kasan_check_write(__p, sizeof(*p)); \
switch (sizeof(*p)) { \
@@ -110,7 +110,7 @@ do { \

#define __smp_load_acquire(p) \
({ \
- union { typeof(*p) __val; char __c[1]; } __u; \
+ union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u; \
typeof(p) __p = (p); \
compiletime_assert_atomic_type(*p); \
kasan_check_read(__p, sizeof(*p)); \
@@ -136,33 +136,33 @@ do { \
: "Q" (*__p) : "memory"); \
break; \
} \
- __u.__val; \
+ (typeof(*p))__u.__val; \
})

#define smp_cond_load_relaxed(ptr, cond_expr) \
({ \
typeof(ptr) __PTR = (ptr); \
- typeof(*ptr) VAL; \
+ __unqual_scalar_typeof(*ptr) VAL; \
for (;;) { \
VAL = READ_ONCE(*__PTR); \
if (cond_expr) \
break; \
__cmpwait_relaxed(__PTR, VAL); \
} \
- VAL; \
+ (typeof(*ptr))VAL; \
})

#define smp_cond_load_acquire(ptr, cond_expr) \
({ \
typeof(ptr) __PTR = (ptr); \
- typeof(*ptr) VAL; \
+ __unqual_scalar_typeof(*ptr) VAL; \
for (;;) { \
VAL = smp_load_acquire(__PTR); \
if (cond_expr) \
break; \
__cmpwait_relaxed(__PTR, VAL); \
} \
- VAL; \
+ (typeof(*ptr))VAL; \
})

#include <asm-generic/barrier.h>
--
2.25.0.rc1.283.g88dfdc4193-goog
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