DOS ain't dead

CTRL-break handling in the Freepascal programs (Developers)

posted by Laaca , Czech republic, 15.10.2022, 00:52

As you maybe know, FPC uses the DJGPP compatible memory and interrupt architecture (but not the LibC library).

One of the consequencies is that the FPC programs can be anytime interrupted by CTRL-C, CTRL-Break and CTRL-\

It is not always the desidered behaviour.
Unfortunately, the FreePascal documentation says nothing about it.

However for a quite long time I know that the CTRL-C and CTRL-\ signaling can be turned off by calling <Set_CTRL_C(false)> from unit DPMIExcp.

But this does not help for CTRL-Break.

I had to investigate the DJGPP sources and there I found that there is a variable __djgpp_hwint_flags.

It has even an alias in the DPMIExcp to <djgpp_hwint_flags>

So, the magic code for turning off the CTRL-C, CTRL-Break and CTRL-\ is:

var djgpp_hwint_flags : word;external name '___djgpp_hwint_flags';
begin
djgpp_hwint_flags:=3;
writeln('Do not shy to press CTRL-C or CTRL-Break and then Enter);
readln;
writeln('We survived the CTRL-C and CTRL-Break');
end.


Note, that in the code I set the <djgpp_hwint_flags> to WORD and not to LONGINT like is done in the DPMIEXCP.
I am pretty sure that that is a bug in DPMIEXCP code (it should really be WORD)

---
DOS-u-akbar!

Complete thread:

• CTRL-break handling in the Freepascal programs - Laaca, 15.10.2022, 00:52
  • CTRL-break handling in the Freepascal programs - glennmcc, 15.10.2022, 02:09
    • CTRL-break handling in the Freepascal programs - Laaca, 15.10.2022, 08:31