Re: [RFC] kasan stack overflow warnings again: READ_ONCE(), typecheck()

[Christian Borntraeger]

On 02/15/2017 12:03 AM, Arnd Bergmann wrote:
> 
> -#define WRITE_ONCE(x, val) \
> -({							\
> -	union { typeof(x) __val; char __c[1]; } __u =	\
> -		{ .__val = (__force typeof(x)) (val) }; \
> -	__write_once_size(&(x), __u.__c, sizeof(x));	\
> -	__u.__val;					\
> -})
> +#define WRITE_ONCE(x, val)								\
> +(											\
> +	__builtin_choose_expr(sizeof(x) == 1, *(volatile typeof(&(x)))&(x) = (val),	\
> +	__builtin_choose_expr(sizeof(x) == 2, *(volatile typeof(&(x)))&(x) = (val),	\
> +	__builtin_choose_expr(sizeof(x) == 4, *(volatile typeof(&(x)))&(x) = (val),	\
> +	__builtin_choose_expr(sizeof(x) == sizeof(long), *(volatile typeof(&(x)))&(x) = (val),	\

Have you run sparse on those changes?
IIRC we had to add the __force to get rid of address space annotations
in that macro above. Cannot tell if we need something like that here.