DOS ain't dead

indirect far jmp (Developers)

posted by ecm  , Düsseldorf, Germany, 10.05.2012, 13:26

this isn't NASM-specific. you have to load a segment register to access data there. you can use the stack to preserve it though; in that case, use a far return instead of the far jump instruction. example:

__seg equ 1234h
__ofs equ 5678h

        push ds
        push ax
        mov ax, __seg
        mov ds, ax
        push bp
        mov bp, sp
        mov ax, [__ofs+2]
        xchg ax, [bp+4]
        push ax
        mov ax, [__ofs]
        xchg ax, [bp+2]
        pop ds
        pop bp
        retf

freeing up one of the segment registers (usually es or ds) for direct access is usually simpler of course

---
l

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