panic: vm_fault: fault on stack guard, addr: 0xfffff80090204000
vm_fault() at vm_fault+0x12eb 0xffffffff8099ef9b 
vm_fault() at vm_fault+0x12eb 0xffffffff8099ef9b 
trap_pfault() at trap_pfault+0x9a 0xffffffff80bd52ca 
calltrap() at calltrap+0x9 0xffffffff80b991fa 
--- trap 000000000000000c, rip = ffffffff80bcaeaa, rsp = fffff80117ee16f0, rbp = fffff80117ee1758 ---
std_copyout() at std_copyout+0x15a 0xffffffff80bcaeaa 
ufs_readlink() at ufs_readlink+0x42 0xffffffff80917d72 
Stopped at      Debugger+0x7c:  movb    $0,0xbdaf09(%rip)
db>