1.global vfork
 2.type vfork,@function
 3vfork:
 4	/* riscv does not have SYS_vfork, so we must use clone instead */
 5	/* note: riscv's clone = clone(flags, sp, ptidptr, tls, ctidptr) */
 6	li a7, 220
 7	li a0, 0x100 | 0x4000 | 17 /* flags = CLONE_VM | CLONE_VFORK | SIGCHLD */
 8	mv a1, sp
 9	/* the other arguments are ignoreable */
10	ecall
11	.hidden __syscall_ret
12	j __syscall_ret