Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!nss1!mrm
From: mrm@nss1.com (Michael R. Miller)
Newsgroups: comp.windows.x
Subject: Re: tvtwm patch 5 dumps core
Summary: patch may not work as written
Message-ID: <1991May15.094059.8696@nss1.com>
Date: 15 May 91 09:40:59 GMT
References: <jsparkes.673896965@bwdls49> <1991May11.004433.14527@agate.berkeley.edu>
Sender: uunet!nss1!mrm (Michael R. Miller)
Organization: XZaphod of Rockville, MD
Lines: 54
Send-Reply-To: uunet!xzaphod!michael

In article <1991May11.004433.14527@agate.berkeley.edu> stolcke@ICSI.Berkeley.EDU (Andreas Stolcke) writes:
>In article <jsparkes.673896965@bwdls49>, jsparkes@bwdls49.bnr.ca (Jeff Sparkes) writes:
>|> 
>|> 	It's dereferencing a null menu pointer.  If you have menus on more
>|> than one button:  hold one down, and then press a button that brings up 
>|> another menu.  Boom!
>
>That's gross! How about the following fix.
>
>-- 
>Andreas Stolcke					stolcke@icsi.berkeley.edu
>International Computer Science Institute	stolcke@ucbicsi.bitnet
>1957 Center St., Suite 600, Berkeley, CA 94704	(415) 642-4274 ext. 126
>
>*** menus.c.dist	Tue Apr 23 07:17:14 1991
>--- menus.c	Fri May 10 17:32:06 1991
>***************
>*** 569,576 ****
>  
>  	}
>  
>! 	/* if we haven't recieved the enter notify yet, wait */
>! 	if (ActiveMenu && !ActiveMenu->entered)
>  	    continue;
>  
>  	done = FALSE;
>--- 569,576 ----
>  
>  	}
>  
>! 	/* if we haven't received the enter notify yet, wait */
>! 	if (!ActiveMenu || !ActiveMenu->entered)
>  	    continue;
>  
>  	done = FALSE;

This is not a correct solution.  C compilers are NOT constrained to
resolve the '||' test in any particular order resulting in the test
"!ActiveMenu->entered" possibly being accomplished prior to the
checking of the validity (non-NULLness) of ActiveMenu.  This can
still core dump if compiled under some C compilers.

Presuming the intent of the test is correct, _A_ correct way to
implement this test is:

 	if (!(ActiveMenu && ActiveMenu->entered))
  	    continue;

There isn't enough context here to determine if the intent of the
test is correct or not.  A guess would be that the intent is valid
but that's only a guess.

Michael R. Miller
XZaphod: uunet!xzaphod!michael