linux-kernel - Re: [PATCH 12/15] kconfig: sort found symbols by relevance

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Message-ID: <20130713130651.GB3280@free.fr>
Date:	Sat, 13 Jul 2013 15:06:51 +0200
From:	"Yann E. MORIN" <yann.morin.1998@...e.fr>
To:	Jean Delvare <jdelvare@...e.de>
Cc:	Michal Marek <mmarek@...e.cz>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Roland Eggner <edvx1@...temanalysen.net>,
	Wang YanQing <udknight@...il.com>
Subject: Re: [PATCH 12/15] kconfig: sort found symbols by relevance

Jean, All,

On 2013-07-12 11:07 +0200, Jean Delvare spake thusly:
[--SNIP--]
> > > > > +static int sym_rel_comp( const void *sym1, const void *sym2 )
> > > > > +{
> > > > > +	struct sym_match *s1 = *(struct sym_match **)sym1;
> > > > > +	struct sym_match *s2 = *(struct sym_match **)sym2;
> > > > 
> > > > You shouldn't need these casts.
> > > 
> > > Probably not, indeed, but I like to write (and read) what I expect to
> > > happen, and pointer arithmetics is always something I dread to foobar.
> > 
> > In fact, we need the cast, otherwise gcc whines about const/non-const.
> 
> And quite rightly so, as you are taking const pointers (i.e. the caller
> told you you are _not_ allowed to change the contents) and making them
> non-const pointers (i.e. you give yourself the right to still change the
> contents.) It happens that your function doesn't actually change the
> contents, so no harm done, but this is still conceptually wrong.
> Preserving the const nature of pointers down the call chain lets the
> compiler warn you if a function changes data it was not supposed to.
> 
> So what you want to do is:
> 
> static int sym_rel_comp(const void *sym1, const void *sym2)
> {
> 	const struct sym_match *s1 = sym1;
> 	const struct sym_match *s2 = sym2; 
> 
> This is both concise and correct, and it makes gcc happy.

Yes, that's what I thought to, and what I was about to do. Thanks for
confirming this! :-)

Regards,
Yann E. MORIN.

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