Somes lines in PDP-11 assembly from 2.11BSD:

  mov r1,-(sp)
  mov $1024.,-(sp)
  mov $outbuf,-(sp)
  mov fout,-(sp)
  jsr pc,_write
  add $6,sp
  mov (sp)+,r1
  tst r0
  bpl 2f
  jmp wrterr