DOS ain't dead - User exception handler in C

User exception handler in C (Developers)

posted by tkchia , 31.07.2020, 19:36

Hello RayeR,

> Thanks, it led me to this example:
> http://www.delorie.com/djgpp/doc/libc/libc_641.html
> It seems DJGPP have good tools for exception handling.
> CPU context is probably saved automatically in __djgpp_exception_state
> structure from where I can check the opcode caused exception, read an
> manipulate registers and also skip "bad" opcode and resume program
> execution by longjmp(__djgpp_exception_state, 0);

Hmm... this is interesting. One worry I have with using
longjmp(__djgpp_exception_state, 0);
is that a longjmp(, ) will always alter eax, because that is how longjmp(, ) works. This may be problematic if your code doing the RDMSR (or whatever) happens to rely on eax not changing at that particular point.

I guess I will need to learn more about the finer details of how __djgpp_exception_state works. But for now, I suspect that it might be safer for you to set up your own jmp_buf (using sigsetjmp) and then jump to it.

Thank you!

---
https://gitlab.com/tkchia · https://codeberg.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

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Complete thread:

User exception handler in C - RayeR, 24.07.2020, 13:15 (Developers)
- User exception handler in C - Japheth, 24.07.2020, 18:07
- User exception handler in C - Rugxulo, 24.07.2020, 18:39
- User exception handler in C - tkchia, 24.07.2020, 20:47
  - User exception handler in C - RayeR, 30.07.2020, 13:18
    - User exception handler in C - tom, 30.07.2020, 23:54
      - User exception handler in C - RayeR, 01.08.2020, 02:13
        User exception handler in C - Laaca, 16.08.2020, 21:27
        User exception handler in C - Laaca, 16.08.2020, 22:38
        User exception handler in C - Rugxulo, 17.08.2020, 22:35
        User exception handler in C - marcov, 18.08.2020, 12:23
        User exception handler in C - Laaca, 18.08.2020, 20:15
        User exception handler in C - Rugxulo, 19.08.2020, 19:44
        User exception handler in C - Laaca, 19.08.2020, 21:50
        User exception handler in C - Rugxulo, 23.08.2020, 17:32
        User exception handler in C - Japheth, 23.08.2020, 20:36
        User exception handler in C - Rugxulo, 17.08.2020, 22:26
        User exception handler in C - tkchia, 19.08.2020, 18:52
        User exception handler in C - marcov, 20.08.2020, 00:00
        User exception handler in C - Laaca, 20.08.2020, 15:31
    - User exception handler in C - tkchia, 31.07.2020, 19:36
      - User exception handler in C - RayeR, 01.08.2020, 02:16
- User exception handler in C - Guti, 27.07.2020, 08:22