linux-kernel - Re: [PATCH] checkpatch: add --strict "pointer comparison to NULL" test

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Date:	Thu, 27 Aug 2015 09:09:07 +0200 (CEST)
From:	Nicolas Morey Chaisemartin <nmorey@...ray.eu>
To:	Joe Perches <joe@...ches.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mike Holmes <mike.holmes@...aro.org>
Subject: Re: [PATCH] checkpatch: add --strict "pointer comparison to NULL"
 test

----- Original Message -----
> From: "Joe Perches" <joe@...ches.com>
> To: "Viresh Kumar" <viresh.kumar@...aro.org>
> Cc: "Andrew Morton" <akpm@...ux-foundation.org>, "Dan Carpenter" <dan.carpenter@...cle.com>, "Greg KH"
> <gregkh@...uxfoundation.org>, "LKML" <linux-kernel@...r.kernel.org>, "Mike Holmes" <mike.holmes@...aro.org>,
> nmorey@...ray.eu
> Sent: Thursday, 27 August, 2015 5:05:37 AM
> Subject: Re: [PATCH] checkpatch: add --strict "pointer comparison to NULL" test
> 
> On Thu, 2015-08-27 at 07:49 +0530, Viresh Kumar wrote:
> > Few colleagues asked me why isn't checkpatch warning for (NULL == ptr)
> > or (NULL != ptr) checks, as it warns for (ptr == NULL) and (ptr != NULL).
> > 
> > Did you miss it? or was it intentional ?
> 
> I didn't miss it.
> 
> NULL == foo is relatively unusual and not really worth the
> bother.
> 
> And because most likely, "CONST test variable" checks like
> 	NULL != foo
> and
> 	0 < bar
> 
> should probably be a separate test.
> 
> Something like:
> ---
>  scripts/checkpatch.pl | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index e14dcdb..457ddef 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -4231,6 +4231,29 @@ sub process {
>  			}
>  		}
>  
> +# comparisons with a constant on the left
> +		if ($^V && $^V ge 5.10.0 &&
> +		    $line =~ /\b($Constant|[A-Z_]+)\s*($Compare)\s*($LvalOrFunc)/) {
> +			my $const = $1;
> +			my $comp = $2;
> +			my $to = $3;
> +			my $newcomp = $comp;
> +			if (WARN("CONSTANT_COMPARISON",
> +				 "Comparisons should place the constant on the right side of the test\n"
> . $herecurr) &&
> +			    $fix) {
> +				if ($comp eq "<") {
> +					$newcomp = ">=";
> +				} elsif ($comp eq "<=") {
> +					$newcomp = ">";
> +				} elsif ($comp eq ">") {
> +					$newcomp = "<=";
> +				} elsif ($comp eq ">=") {
> +					$newcomp = "<";
> +				}

I like the concept but are you sure about this? I think the "=" should be added or removed. If a < b, b > a, not b >= a.

Nicolas
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