On 03/04/17 05:05, Russell King - ARM Linux wrote:
>>
>> +static int futex_atomic_op_inuser(int encoded_op, u32 __user *uaddr)
>> +{
>> + int op = (encoded_op >> 28) & 7;
>> + int cmp = (encoded_op >> 24) & 15;
>> + int oparg = (encoded_op << 8) >> 20;
>> + int cmparg = (encoded_op << 20) >> 20;
>
> Hmm. oparg and cmparg look like they're doing these shifts to get sign
> extension of the 12-bit values by assuming that "int" is 32-bit -
> probably worth a comment, or for safety, they should be "s32" so it's
> not dependent on the bit-width of "int".
>
For readability, perhaps we should make sign- and zero-extension an
explicit facility?
/*
* Truncate an integer x to n bits, using sign- or
* zero-extension, respectively.
*/
static inline __const_func__ s32 sex32(s32 x, int n)
{
return (x << (32-n)) >> (32-n);
}
static inline __const_func__ s64 sex64(s64 x, int n)
{
return (x << (64-n)) >> (64-n);
}
#define sex(x,y) \
((__typeof__(x)) \
(((__builtin_constant_p(y) && ((y) <= 32)) || \
(sizeof(x) <= sizeof(s32))) \
? sex32((x),(y)) : sex64((x),(y))))
static inline __const_func__ u32 zex32(u32 x, int n)
{
return (x << (32-n)) >> (32-n);
}
static inline __const_func__ u64 zex64(u64 x, int n)
{
return (x << (64-n)) >> (64-n);
}
#define zex(x,y) \
((__typeof__(x)) \
(((__builtin_constant_p(y) && ((y) <= 32)) || \
(sizeof(x) <= sizeof(u32))) \
? zex32((x),(y)) : zex64((x),(y))))
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