From: sjoerd DOT s DOT bakker AT tip DOT nl (sjoerd DOT s DOT bakker AT tip DOT nl)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: My INT 1 handler crashes under Windows 95
Date: Thu, 17 Dec 1998 16:48:36 GMT
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To: djgpp AT delorie DOT com
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On Wed, 16 Dec 1998 10:18:20 +0200, Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
wrote:

>
>On Wed, 9 Dec 1998 sjoerd DOT s DOT bakker AT tip DOT nl wrote:
>
>> The following test-code installs a protected mode  INT 1 (single-step)
>> handler that runs well with CWSDPMI but crashes under Windows 95 with
>> a registerdump caused by SIGTRAP.
>
>INT 1 is not a hardware interrupt in the normal sense.  Try installing a 
>signal handler for SIGTRAP instead.  You will probably need to make the 
>handler do a longjmp (instead of returning to the caller), to prevent the 
>program from crashing.

If I do a longjmp, then I will lose track of the executing program and
I want to trace each instruction. Longjmp restores the stack-segment
and -pointer, so there would be no way to get back to the instruction
following the one that caused SIGTRAP.

I had tried a normal return from the signal handler, but I got a
SIGTRAP registerdump with an error message about the handler not being
able to return... as to be expected since the cause of the exception
(TRAP-flag set) still exists after returning.