bin/71613: [PATCH] traceroute(8): cleanup of the usr.sbin/traceroute6 code

[Mark Linimon]

The following reply was made to PR bin/71613; it has been noted by GNATS.

From: linimon at lonesome.com (Mark Linimon)
To: bug-followup at FreeBSD.org
Cc:  
Subject: Re: bin/71613: [PATCH] traceroute(8): cleanup of the usr.sbin/traceroute6 code
Date: Sun, 16 Mar 2008 02:42:13 -0500

 ----- Forwarded message from Bruce Evans <brde at optusnet.com.au> -----
 
 From: Bruce Evans <brde at optusnet.com.au>
 To: Dan Lukes <dan at obluda.cz>
 Cc: freebsd-bugs at freebsd.org
 
 __COPYRIGHT() in <sys/cdefs.h> reduces this problem by concatenating
 __LINE__.  It could also concatenate a file name (but not __FILE__, since
 that is probably not an identifier).
 
 >	It seems we need 'static'. Unfortunately, static unused variable can 
 >be optimized out.
 >
 >	Adding 'const' and/or __used clear the warning, but doesn't prevent 
 >"optimized-out" problem. The 'const' shall be used because the string is 
 >constant. We can use __used, but it has limited portability.
 >
 >	We still have the problem the variable may be optimized out.
 
 __used prevents this.
 
 >	The 'volatile' is way to tell an ANSI C compiler "this variable may 
 >be modified via mechanism you don't know about it" - it mean "count it as 
 >used" and "don't optimize it". Note, the 'const' and 'static' are ANSI C 
 >keywords also, so compiler knowing 'static' shall handle 'volatile' as well.
 
 volatile doesn't prevent the variable being optimized out for gcc-4.2.
 This makes some sense -- volatile sort of means "use it carefully", but
 when it is not used no care with it is needed.
 
 >	Conclusion (for the case we can't guarantee the unique name of 
 >variable):
 >static   MUST
 >const    SHALL
 >__used   SHALL
 >volatile MUST
 >
 >So my recomentation is:
 >0: static volatile const char __used copyright[]=...
 >
 >because of __unused the sys/cdefs.h must be included first.
 
 I prefer 'static char const __used copyright[]'.  Not sure where __used
 belongs.
 
 >The other way to fix it is
 >1: the sys/copyright.h way - e.g. plain char variable - but the variable 
 >must be unique across the sources which sound not so easy for me
 
 Not too bad -- there is supposed to be only one copyright[] per executable.
 
 >2. the __COPYRIGHT way, but
 >2a: IDSTRING must be corrected first
 >2b: the '\n' must be removed from the source.
 >
 >sys/cdefs.h must be included first.
 >
 >	In my opinion the preference shall be 2a then 0 then 1 or 2b but 
 >	it's not strict. The commiter shall select the best way.
 
 2b is no good.
 
 __COPYRIGHT() of course allows putting all the unportabilities in one
 place and changing the easily.  It's just too ugly for me.  Everything in
 <sys/cdefs.h> should have gone away with __P(()).
 
 Bruce
 
 ----- End forwarded message -----