了解rdtscp中的运算符（即“ = a”，“ = d”，“ = c”）吗？

Question

https://stackoverflow.com/a/14783909/391104

static inline uint64_t rdtscp( uint32_t & aux )
{
    uint64_t rax,rdx;
    asm volatile ( "rdtscp\n" : "=a" (rax), "=d" (rdx), "=c" (aux) : : );
    return (rdx << 32) + rax;
}

问题>“ = a”，“ = d”和“ = c”是什么意思？

谢谢