gistfile1.txt

struct block_literal {
    void *isa;
    int flags;
    int reserved; 
    void (*invoke)(void *);
    void *descriptor;
    void *byref_obj;
};

void foo(void)
{
    id block = ^(void) {
        NSLog(@"test");
    };
    void (*invoke)(void *) = ((__bridge struct block_literal *)block)->invoke;
    invoke(NULL);
}