asm_setjmp:
  pop WORD [env]
  push WORD [env] ; get and put back the return address
  push cx
  push dx
  push bx
  push bp
  push si
  push di ; push all registers except ax
  push WORD [env] ; return address stacked for asm_longjmp
  mov [env], sp ; save sp for asm_longjmp to restore
  add WORD [env], 2 ; adjust sp to point to di on the stack
                    ; which also clears the carry flag for
  ret               ; the initial return to asm_setjmp

asm_longjmp:
  push WORD [env]
  pop sp ; retore sp
  pop di
  pop si
  pop bp
  pop bx
  pop dx
  pop cx ; pop all registers except ax
  stc
  ret ; return to asm_setjmp with the carry flag set

env dw 0
    

  call asm_setjmp
  jnc .1
; handle errors here, any error code in ax
; even use 0 for a no error exit for example
.1:

; ...

; handle errors here
  mov ax, -1 ; any error code in ax
  jmp asm_longjmp ; no need to "call ahead" since "you ain't comin' back"