"typedef name omitted" warning

[sergey-senozhatsky]

#include <linux/types.h>

#define barrier __sync_synchronize

typedef __u8  __attribute__((__may_alias__))  __u8_alias_t;
typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;
typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;
typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;

static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
{
        switch (size) {
        case 1: *(__u8_alias_t  *) res = *(volatile __u8_alias_t  *) p; break;
        case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break;
        case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break;
        case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break;
        default:
                barrier();
                __builtin_memcpy((void *)res, (const void *)p, size);
                barrier();
        }
}

static __always_inline void __write_once_size(volatile void *p, void *res, int size)
{
        switch (size) {
        case 1: *(volatile  __u8_alias_t *) p = *(__u8_alias_t  *) res; break;
        case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break;
        case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break;
        case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;
        default:
                barrier();
                __builtin_memcpy((void *)p, (const void *)res, size);
                barrier();
        }
}

#define READ_ONCE(x)                                    \
({                                                      \
        union { typeof(x) __val; char __c[1]; } __u =   \
                { .__c = { 0 } };                       \
        __read_once_size(&(x), __u.__c, sizeof(x));     \
        __u.__val;                                      \
})

#define WRITE_ONCE(x, val)                              \
({                                                      \
        union { typeof(x) __val; char __c[1]; } __u =   \
                { .__val = (val) };                     \
        __write_once_size(&(x), __u.__c, sizeof(x));    \
        __u.__val;                                      \
})

int main()
{
        int test_wr = 1;

        int val = READ_ONCE(test_wr);
        val++;
        WRITE_ONCE(test_wr, 1);
        return 0;
}

Gives

test.c:5: typedef __u8  __attribute__((__may_alias__))  __u8_alias_t;
                         ^ typedef name omitted