Xref: news2.mv.net comp.os.msdos.djgpp:5516
From: snarfy AT goodguy DOT goodnet DOT com (Snarfy AT GoodNet DOT Com)
Newsgroups: comp.os.msdos.djgpp
Subject: __djgpp_exception_state is protected? (raise problems)
Date: 29 Jun 1996 06:38:41 GMT
Organization: Telesoft Corporation.
Lines: 83
Message-ID: <4r2j1h$lhe@news1.goodnet.com>
NNTP-Posting-Host: goodnet.com
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

This program explodes with a SIGSEGV when ran:
----------------Cut here---------------
#include <stdio.h>
#include <signal.h>
#include <setjmp.h>
#include <sys/exceptn.h>
void my_sig_handler(int signum)
{
   unsigned long foo;
   foo = __djgpp_exception_state->__eax;
   printf("foo = %d\n", foo);
}

main()
{
   signal(SIGINT, my_sig_handler);
   raise(SIGINT);
   return(0);
}
---------------Cut here-----------------

This program, very similar, does not:

---------------Cut here-----------------
#include <stdio.h>
#include <signal.h>
#include <setjmp.h>
#include <sys/exceptn.h>
void my_sig_handler(int signum)
{
   unsigned long foo;
   foo = __djgpp_exception_state->__eax;
   printf("foo = %d\n", foo);
}

main()
{
   signal(SIGINT, my_sig_handler);
   printf("Press control-C dude.\n");
   while(!kbhit()) {};
   return(0);
}
---------------Cut Here-----------------

I have no idea why, but for some reason, __djgpp_exception_state is 
either undefined or protected in the first program.  It works fine
in the second program.  Is this due to the hw_interrupt reflection?

On a side note, is there a reason why __djgpp_exception_state->__flags
is different than what 'should' be there?  For example:

-------------cut here----------------------
#include <stdio.h>
#include <signal.h>
#include <setjmp.h>
#include <sys/exceptn.h>
jmp_buf my_buf;

void my_sig_handler(int signum)
{
    unsigned int foo, bar;
    foo = __djgpp_exception_state->__flags;
    bar = my_buf->__flags;
    printf("foo = %d, bar = %d\n", foo, bar);
}

main()
{
   signal(SIGINT, my_sig_handler);
   printf("Press Control-C dude\n");
   while(!kbhit()) {setjmp(my_buf);}
}  
------------cut here-------------------------

A sample output would be that my_bufs flags = 3216 while the other flags
are 13216 or 13214.  The only thing I can think of is that control-C is
getting pressed inside of the kbhit() function or before setjmp finishes,
or that the interrupt flag is set.   


Thanks
Josh
snarfy AT goodnet DOT com