Date: Sun, 16 Mar 2008 07:50:02 GMT From: linimon@lonesome.com (Mark Linimon) To: freebsd-bugs@FreeBSD.org Subject: Re: bin/71613: [PATCH] traceroute(8): cleanup of the usr.sbin/traceroute6 code Message-ID: <200803160750.m2G7o21t025830@freefall.freebsd.org>
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The following reply was made to PR bin/71613; it has been noted by GNATS. From: linimon@lonesome.com (Mark Linimon) To: bug-followup@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@optusnet.com.au> ----- From: Bruce Evans <brde@optusnet.com.au> To: Dan Lukes <dan@obluda.cz> Cc: freebsd-bugs@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 -----
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