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utils: ensure that byte-order conversion functions evaluate the argument only once

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Signed-off-by: Felix Fietkau <nbd@nbd.name>
This commit is contained in:
Felix Fietkau 2018-04-07 10:43:48 +02:00
parent 42a8ecd858
commit 92009b7f98
1 changed files with 24 additions and 16 deletions
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40
utils.h
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@ -117,21 +117,29 @@ int clock_gettime(int type, struct timespec *tv);
(((uint64_t)(x) & (uint64_t)0x00ff000000000000ULL) >> 40) | \
(((uint64_t)(x) & (uint64_t)0xff00000000000000ULL) >> 56)))
/*
* This returns a constant expression while determining if an argument is
* a constant expression, most importantly without evaluating the argument.
*/
#define __is_constant(x) \
(sizeof(int) == sizeof(*(1 ? ((void*)((long)(x) * 0l)) : (int*)1)))
static inline uint16_t __u_bswap16(uint16_t val)
{
return ((val >> 8) & 0xffu) | ((val & 0xffu) << 8);
}
#define __eval_once(func, x) \
({ typeof(x) __x = x; func(__x); })
#define __eval_safe(func, x) \
__builtin_choose_expr(__is_constant(x), \
func(x), __eval_once(func, x))
#if __BYTE_ORDER == __LITTLE_ENDIAN
#define cpu_to_be64(x) __constant_swap64(x)
#define cpu_to_be32(x) __constant_swap32(x)
#define cpu_to_be16(x) __constant_swap16(x)
#define cpu_to_be64(x) __eval_safe(__constant_swap64, x)
#define cpu_to_be32(x) __eval_safe(__constant_swap32, x)
#define cpu_to_be16(x) __eval_safe(__constant_swap16, x)
#define be64_to_cpu(x) __constant_swap64(x)
#define be32_to_cpu(x) __constant_swap32(x)
#define be16_to_cpu(x) __constant_swap16(x)
#define be64_to_cpu(x) __eval_safe(__constant_swap64, x)
#define be32_to_cpu(x) __eval_safe(__constant_swap32, x)
#define be16_to_cpu(x) __eval_safe(__constant_swap16, x)
#define cpu_to_le64(x) (x)
#define cpu_to_le32(x) (x)
@ -143,13 +151,13 @@ static inline uint16_t __u_bswap16(uint16_t val)
#else /* __BYTE_ORDER == __LITTLE_ENDIAN */
#define cpu_to_le64(x) __constant_swap64(x)
#define cpu_to_le32(x) __constant_swap32(x)
#define cpu_to_le16(x) __constant_swap16(x)
#define cpu_to_le64(x) __eval_safe(__constant_swap64, x)
#define cpu_to_le32(x) __eval_safe(__constant_swap32, x)
#define cpu_to_le16(x) __eval_safe(__constant_swap16, x)
#define le64_to_cpu(x) __constant_swap64(x)
#define le32_to_cpu(x) __constant_swap32(x)
#define le16_to_cpu(x) __constant_swap16(x)
#define le64_to_cpu(x) __eval_safe(__constant_swap64, x)
#define le32_to_cpu(x) __eval_safe(__constant_swap32, x)
#define le16_to_cpu(x) __eval_safe(__constant_swap16, x)
#define cpu_to_be64(x) (x)
#define cpu_to_be32(x) (x)