RE: optimization/8537: Optimizer Removes Code Necessary for Security

["Joseph D. Wagner" <wagnerjd@prodigy.net>]

The following reply was made to PR optimization/8537; it has been noted by GNATS.

From: "Joseph D. Wagner" <wagnerjd@prodigy.net>
To: <fw@gcc.gnu.org>,
	<gcc-bugs@gcc.gnu.org>,
	<gcc-prs@gcc.gnu.org>,
	<nobody@gcc.gnu.org>,
	<wagnerjd@prodigy.net>,
	<gcc-gnats@gcc.gnu.org>
Cc:  
Subject: RE: optimization/8537: Optimizer Removes Code Necessary for Security
Date: Sun, 17 Nov 2002 08:59:53 -0600

 Direct quote from:
 http://gcc.gnu.org/onlinedocs/gcc-3.2/gcc/Bug-Criteria.html
 
 "If the compiler produces valid assembly code that does not correctly
 execute the input source code, that is a compiler bug."
 
 So to all you naysayers out there who claim this is a programming error
 or poor coding, YES, IT IS A BUG!
 
 From:
 http://gcc.gnu.org/ml/gcc/2002-01/msg00518.html
 
 > The problem is the standard gives wide latitude in what the optimizer
 can optimize
 
 Isn't this also the solution?  Can't the optimizer check to see if the
 function is memset(), and if so check to see if the value is 0 or NULL,
 and if so leave it in?
 
 The optimizer could check if memset() is zeroing out memory by checking
 if the fill value is 0 or NULL.  If the fill value is 0 or NULL, the
 optimizer can reasonably presume that this instance of memset() is for
 security and not optimize it out.
 
 Joseph Wagner
 
 -----Original Message-----
 From: fw@gcc.gnu.org [mailto:fw@gcc.gnu.org] 
 Sent: Sunday, November 17, 2002 8:28 AM
 To: gcc-bugs@gcc.gnu.org; gcc-prs@gcc.gnu.org; nobody@gcc.gnu.org;
 wagnerjd@prodigy.net
 Subject: Re: optimization/8537: Optimizer Removes Code Necessary for
 Security
 
 Synopsis: Optimizer Removes Code Necessary for Security
 
 State-Changed-From-To: open->closed
 State-Changed-By: fw
 State-Changed-When: Sun Nov 17 06:28:05 2002
 State-Changed-Why:
     This is not a bug in GCC.  The call to memset() clear hasn't any
 externally visible effect according to the C language specification, so
 it can be removed by the optimizer.
     
     See the discussion around
 http://gcc.gnu.org/ml/gcc/2002-01/msg00518.html for additional
 information on a very similar topic.
     
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=g
 cc&pr=8537