netdev - Re: [PATCH 1/3] wimax: fix '#ifdef CONFIG

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Message-Id: <200901071257.27225.inaky@linux.intel.com>
Date:	Wed, 7 Jan 2009 12:57:25 -0800
From:	Inaky Perez-Gonzalez <inaky@...ux.intel.com>
To:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Cc:	Netdev <netdev@...r.kernel.org>, wimax@...uxwimax.org,
	greg@...ah.com
Subject: Re: [PATCH 1/3] wimax: fix '#ifdef CONFIG_BUG' layout to avoid warning

On Wednesday 07 January 2009, Ilpo Järvinen wrote:
> On Wed, 7 Jan 2009, Inaky Perez-Gonzalez wrote:
> > On Wednesday 07 January 2009, Ilpo Järvinen wrote:
> > > On Tue, 6 Jan 2009, Inaky Perez-Gonzalez wrote:
> > > > Reported by Randy Dunlap:
> > > > > Also, this warning needs to be fixed:
> > > > >
> > > > > linux-next-20090106/net/wimax/id-table.c:133: warning: ISO C90
> > > > > forbids mixed declarations and code
> > > >
> > > > Move the return on #defined(CONFIG_BUG) below the variable
> > > > declarations so it doesn't violate ISO C90.
> > > >
> > > > On wimax_id_table_release() we want to do a debug check if CONFIG_BUG
> > > > is enabled. However, we also want the debug code to be always
> > > > compiled to ensure there is no bitrot.
> > >
> > > I hope this kind of solution won't add some warnings? Besides, this
> > > seems rather strange reasoning as CONFIG_BUG is mostly enabled anyway?
> >
> > Well, it is legal code -- short of 'if (1) return'. It doesn't warn (and
> > it should not).
>
> Obviously, but I was concerned on the other lines than that
> particular one, e.g., gcc might think that wimax_dev is unused
> variable and emit a warning or along those lines...?

Ah, I see -- no, it won't. [disclaimer: not know much about compiler 
optimization] In theory, as we were saying, it works just as in a case 
where you have

int somevar;

if (1)
   return;

somevar = call_some_func();

with 1 being the result of a compile time evaluation. The compiler sees
that somevar is being used, but the code path is never executed, so everything
gets dumped.

If it ever did, it'd be a matter of changing that return to an if (1) return.
It'd look uglier though.

-- 
Inaky
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