* Andrey Ryabinin <aryabi...@virtuozzo.com> wrote:
> +#define __READ_ONCE_SIZE \
> +({ \
> + switch (size) { \
> + case 1: *(__u8 *)res = *(volatile __u8 *)p; break; \
> + case 2: *(__u16 *)res = *(volatile __u16 *)p; break; \
> + case 4: *(__u32 *)res = *(volatile __u32 *)p; break; \
> + case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \
> + default: \
> + barrier(); \
> + __builtin_memcpy((void *)res, (const void *)p, size); \
> + barrier(); \
> + } \
> +})
> +
> +static __always_inline
> +void __read_once_size_check(const volatile void *p, void *res, int size)
> {
> + __READ_ONCE_SIZE;
> }
> +#ifdef CONFIG_KASAN
> +static __no_sanitize_address __maybe_unused
> +void __read_once_size_nocheck(const volatile void *p, void *res, int size)
> +{
> + __READ_ONCE_SIZE;
> +}
> +#else
> +static __always_inline __alias(__read_once_size_check)
> +void __read_once_size_nocheck(const volatile void *p, void *res, int size);
> +#endif
> +#define __READ_ONCE(x, check) \
> +({ \
> + union { typeof(x) __val; char __c[1]; } __u; \
> + __read_once_size##check(&(x), __u.__c, sizeof(x)); \
> + __u.__val; \
> +})
> +#define READ_ONCE(x) __READ_ONCE(x, _check)
> +#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, _nocheck)
So all this code is quite convoluted, and as the changelog explains it's done
to
work around a GCC inlining + no-kasan bug.
But please explain this in the code as well, in a comment, so future
generations
are not kept wondering why these relatively simple wrappers are coded in such
an
ugly and roundabout fashion.
Thanks,
Ingo
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