What does this i386 os code mean? The code is for resetting the system

Question

/* jump to reset vector. esp := 0 */
int main(int argc, char **argv) {
    PRINT("reset\n");
    _eflags = 0; // interrupt disabled
    __asm__ __volatile__ ("\
        mov $0x0, %%esp;\
        jmp *%0"
        :: "r"(_vector[0]));
    /* never return here */
    return 0;
}

This is i386 os code, and I have difficulty understanding it. What does the code below mean? Especially I want to know what is "r"(_vector[0]).

__asm__ __volatile__ ("\
        mov $0x0, %%esp;\
        jmp *%0"
        :: "r"(_vector[0]));