Mail Archives: djgpp/1997/02/17/04:41:13
On Sun, 16 Feb 1997, Alberto Vignani wrote:
> Can someone (Eli?) enlighten me on what's going on when you press ^C?
> When a djgpp program terminates normally, I see all the shutdown sequence
> up to the int0x21-AX=4Cxx which signals dosemu to quit the DPMI server.
> This doesn't happen with ^C; on the dosemu side, I have currently to rely
> on the stack fault to understand what went on.
I'm not the best person to ask about these issues, so I cc: this to
Charles Sandmann who might have better insight. Please take the info
below with a grain of salt, in case I confuse things.
I think this is a bug in DOSEmu. It probably handles ^C specially and
kills the DJGPP program before ^C ever gets to it. Because if ^C
would get to your program, it will cause (almost) the same chain of
events as with Ctrl-Break (which works, right?):
1) the ^C key is detected by the keyboard interrupt handler
installed by the DJGPP startup code;
2) the keyboard handler invalidates the DJGPP DS selector;
3) when your program accesses any of its data, the invalid DS
causes an exception;
4) the exception gets caught by the DJGPP exception processor;
5) the exception processor prints the message about SIGINT and
aborts your program by calling `_exit' (or calls your SIGINT handler
if you installed one);
6) `_exit' shuts down the program and eventually calls the DOS
Int 21h/AH=4Ch function.
[What's different about Ctrl-Break is that it generates interrupt 1Bh
which is hooked by the DJGPP startup code, instead of being detected
by the keyboard handler.]
One thing that I would suggest testing is to install a handler for
SIGINT and see if it gets called at all when you press ^C or
Ctr-Break.
Charles?
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