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From: john@uw-nsr.UUCP (John Sambrook)
Newsgroups: net.bugs
Subject: Bug in "pathalias"
Message-ID: <344@uw-nsr.UUCP>
Date: Mon, 11-Aug-86 23:53:51 EDT
Article-I.D.: uw-nsr.344
Posted: Mon Aug 11 23:53:51 1986
Date-Received: Wed, 13-Aug-86 01:20:57 EDT
Reply-To: john@uw-nsr.UUCP (John Sambrook 5-2018)
Organization: UW-Bioengineering, Seattle, WA
Lines: 43
Keywords: static, parse.y, yylex()

The version of "pathalias" posted to mod.sources seems to contain a bug.
From the "CHANGES" file it seems that we have the version distributed
on or about 1/86.  

The bug concerns the function yylex() as contained in file "parse.y".
Within the body of yylex() there is a declaration of the variable
"buf" as follows:

	char	buf[BUFSIZ], errbuf[128];

Unfortunately, the value contained in buf is used after the function
has returned.  For example, when a HOST token has been scanned the 
following code is executed: 

			.
		    	.
			.

		yylval.y_name = buf;
		return(HOST);
	}

Of course, as soon as the return statement is executed the value of
buf is no longer guaranteed.  On many implementations this "happens"
to work, but it is not correct.

While this was tedious to find, it is easy to fix.  Simply change the
old declaration to the following:

	#if 0	/* bug fix */
		char	buf[BUFSIZ], errbuf[128];
	#else
		static	char	buf[BUFSIZ];
			char	errbuf[128];
	#endif

After fixing this one minor problem "pathalias" works like a champ.  I 
should point out that very few programs have been as easy to port to our
system.  We have a DG MV/10000 and we find all the "dereference through 
NULL" bugs and then some :-)
-- 
John Sambrook				Work: (206) 545-2018
University of Washington WD-12		Home: (206) 487-0180
Seattle, Washington  98195		UUCP: uw-beaver!uw-nsr!john