DOS ain't dead

indirect far jmp - calling old INT problem (Developers)

posted by RayeR , CZ, 13.05.2012, 15:33
(edited by RayeR on 13.05.2012, 16:37)

> This way, you're not passing the returned CF (Carry Flag) back to the
> caller, leaving theirs in their saved FL word unmodified instead. Here's

Aha, it was too late yesterday :)

> some code that would return it correctly, it goes right before your iret
> instruction and needs to be entered with the CF that you want to return:
>
>         push bp
> mov bp, sp
> rcr byte [bp+6], 1      ; flip
> rol byte [bp+6], 1      ; flop
> pop bp
>
> Understanding what this does is left as an exercise to the reader ;)

Hm some magic with rotating saved flags on stack through carry... It works fine now. Anyway with this code it's still 3 bytes longer than my old method with placing FAR JMP byte opcode before saved vector and jumping on that...

EDIT:
I got some idea how to pass original int 13 flags:

        INT     OLD_INT13H      ;call old INT 13h handler / zavolej puvodni preruseni INT 13h
pushf
pop dx

add sp,6
push dx
sub sp,4
        IRET                    ;and return to caller program / a predej rizeni zpet volajicimu programu


but there's issue that ADD instruction also affect flags. so I temporarly use DX to save them and it works. But I must preserve DX too. To be continued...

---
DOS gives me freedom to unlimited HW access.

Complete thread:

• indirect far jmp in NASM - RayeR, 10.05.2012, 10:46 (Developers)
  • indirect far jmp in NASM - RayeR, 10.05.2012, 13:16
    • indirect far jmp - ecm, 10.05.2012, 13:26
    • indirect far jmp in NASM - Rugxulo, 10.05.2012, 13:26
      • indirect far jmp in NASM - RayeR, 10.05.2012, 14:07
        • indirect far jmp - ecm, 10.05.2012, 15:17
          • indirect far jmp - RayeR, 11.05.2012, 00:47
            • indirect far jmp - ecm, 11.05.2012, 12:46
            • indirect far jmp - bretjohn, 11.05.2012, 18:53
              • indirect far jmp - RayeR, 11.05.2012, 19:31
                • indirect far jmp - bretjohn, 11.05.2012, 22:31
                  • indirect far jmp - ecm, 11.05.2012, 22:33
                    • indirect far jmp - RayeR, 12.05.2012, 00:33
                      • indirect far jmp - Arjay, 12.05.2012, 01:07
                        • indirect far jmp - ecm, 12.05.2012, 01:27
                          • indirect far jmp - Arjay, 12.05.2012, 11:09
                            • indirect far jmp - ecm, 12.05.2012, 21:18
                        • indirect far jmp - RayeR, 12.05.2012, 21:17
                          • indirect far jmp/call - Chaining Interrupt Service Routines - Arjay, 13.05.2012, 13:16
                      • indirect far jmp - calling old INT problem - RayeR, 13.05.2012, 04:01
                        • indirect far jmp - calling old INT problem - ecm, 13.05.2012, 04:27
                          • indirect far jmp - calling old INT problem - RayeR, 13.05.2012, 15:33
                            • indirect far jmp - calling old INT problem - bretjohn, 13.05.2012, 17:05
                              • indirect far jmp - calling old INT problem - RayeR, 13.05.2012, 17:15
                                • indirect far jmp - calling old INT problem - RayeR, 13.05.2012, 19:19
                                  • indirect far jmp - calling old INT problem - Rugxulo, 13.05.2012, 20:02
                                    • indirect far jmp - calling old INT problem - RayeR, 13.05.2012, 20:49
                                    • indirect far jmp - calling old INT problem - ecm, 13.05.2012, 23:49
                                  • indirect far jmp - calling old INT problem - ecm, 13.05.2012, 23:40
                                    • indirect far jmp - calling old INT problem - ecm, 14.05.2012, 00:07
                                      • indirect far jmp - calling old INT problem - RayeR, 14.05.2012, 01:19
                            • indirect far jmp - calling old INT problem - ecm, 13.05.2012, 23:44
                              • indirect far jmp - calling old INT problem - bretjohn, 14.05.2012, 18:30
                                • redundant override in "ss:bp" for clarity - ecm, 14.05.2012, 18:47
                                • indirect far jmp - calling old INT problem - RayeR, 14.05.2012, 18:50
                                  • indirect far jmp - calling old INT problem - bretjohn, 14.05.2012, 20:16
                                    • indirect far jmp - calling old INT problem - ecm, 14.05.2012, 20:21
                                      • indirect far jmp - calling old INT problem - bretjohn, 14.05.2012, 21:42
                                        • indirect far jmp - calling old INT problem - bretjohn, 15.05.2012, 18:45
                                          • indirect far jmp - calling old INT problem - ecm, 15.05.2012, 18:53
                                            • indirect far jmp - calling old INT problem - bretjohn, 15.05.2012, 20:13
                                              • indirect far jmp - calling old INT problem - RayeR, 17.05.2012, 01:25