linux-kernel - Re: [PATCH] Don't compare unsigned variable for <0 in sys

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Date:	Wed, 29 Nov 2006 02:10:43 +0100
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Linus Torvalds" <torvalds@...l.org>
Cc:	linux-kernel@...r.kernel.org, "Andrew Morton" <akpm@...l.org>,
	trivial@...nel.org
Subject: Re: [PATCH] Don't compare unsigned variable for <0 in sys_prctl()

On 29/11/06, Linus Torvalds <torvalds@...l.org> wrote:
>
>
> On Wed, 29 Nov 2006, Jesper Juhl wrote:
> >
> > I would venture that "-Wshadow" is another one of those.
>
> I'd agree, except for the fact that gcc does a horribly _bad_ job of
> -Wshadow, making it (again) totally unusable.
>
> For example, it's often entirely interesting to hear about local variables
> that shadow each other. No question about it.
>
> HOWEVER. It's _not_ really interesting to hear about a local variable that
> happens to have a common name that is also shared by a extern function.
>
> There just isn't any room for confusion, and it's actually not even that
> unusual - I tried using -Wshadow on real programs, and it was just
> horribly irritating.
>
> In the kernel, we had obvious things like local use of "jiffies" that just
> make _total_ sense in a small inline function, and the fact that there
> happens to be an extern declaration for "jiffies" just isn't very
> interesting.
>
> Similarly, with nested macro expansion, even the "local variable shadows
> another local variable" case - that looks like it should have an obvious
> warning on the face of it - really isn't always necessarily that
> interesting after all. Maybe it is a bug, maybe it isn't, but it's no
> longer _obviously_ bogus any more.
>
> So I'm not convinced about the usefulness of "-Wshadow". ESPECIALLY the
> way that gcc implements it, it's almost totally useless in real life.
>
> For example, I tried it on "git" one time, and this is a perfect example
> of why "-Wshadow" is totally broken:
>
>         diff-delta.c: In function 'create_delta_index':
>         diff-delta.c:142: warning: declaration of 'index' shadows a global declaration
>
> (and there's a _lot_ of those). If I'm not allowed to use "index" as a
> local variable and include <string.h> at the same time, something is
> simply SERIOUSLY WRONG with the warning.
>
> So the fact is, the C language has scoping rules for a reason. Can you
> screw yourself by usign them badly? Sure. But that does NOT mean that the
> same name in different scopes is a bad thing that should be warned about.
>
> If I wanted a language that didn't allow me to do anything wrong, I'd be
> using Pascal. As it is, it turns out that things that "look" wrong on a
> local level are often not wrong after all.
>

I can't really say anything else at this point but, point conceded...

-- 
Jesper Juhl <jesper.juhl@...il.com>
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