linux-kernel - Re: [PATCH] checkpatch: Improve TYPECAST_INT

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Date:   Mon, 18 Jan 2021 15:16:42 -0500
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] checkpatch: Improve TYPECAST_INT_CONSTANT test message

On 2021-01-18 12:19 p.m., Joe Perches wrote:
> Improve the TYPECAST_INT_CONSTANT test by showing the suggested
> conversion for various type of uses like (unsigned int)1 to 1U.

The questionable code snippet was:
         unsigned int nent, nalloc;

         ....
         if (check_add_overflow(nent, (unsigned int)1, &nalloc))

where the check_add_overflow() macro [include/linux/overflow.h]
uses typeid to check its first and second arguments have the
same type. So it is likely others could meet this issue.

Doug Gilbert


> Signed-off-by: Joe Perches <joe@...ches.com>
> ---
> 
> Douglas Gilbert sent me a private email (and in that email said he
> 'loves to hate checkpatch' ;) complaining that checkpatch warned on the
> use of the cast of '(unsigned int)1' so make it more obvious why the
> message is emitted by always showing the suggested conversion.
> 
>   scripts/checkpatch.pl | 20 ++++++++++----------
>   1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 016115a62a9f..4f8494527139 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -6527,18 +6527,18 @@ sub process {
>   		if ($line =~ /(\(\s*$C90_int_types\s*\)\s*)($Constant)\b/) {
>   			my $cast = $1;
>   			my $const = $2;
> +			my $suffix = "";
> +			my $newconst = $const;
> +			$newconst =~ s/${Int_type}$//;
> +			$suffix .= 'U' if ($cast =~ /\bunsigned\b/);
> +			if ($cast =~ /\blong\s+long\b/) {
> +			    $suffix .= 'LL';
> +			} elsif ($cast =~ /\blong\b/) {
> +			    $suffix .= 'L';
> +			}
>   			if (WARN("TYPECAST_INT_CONSTANT",
> -				 "Unnecessary typecast of c90 int constant\n" . $herecurr) &&
> +				 "Unnecessary typecast of c90 int constant - '$cast$const' could be '$const$suffix'\n" . $herecurr) &&
>   			    $fix) {
> -				my $suffix = "";
> -				my $newconst = $const;
> -				$newconst =~ s/${Int_type}$//;
> -				$suffix .= 'U' if ($cast =~ /\bunsigned\b/);
> -				if ($cast =~ /\blong\s+long\b/) {
> -					$suffix .= 'LL';
> -				} elsif ($cast =~ /\blong\b/) {
> -					$suffix .= 'L';
> -				}
>   				$fixed[$fixlinenr] =~ s/\Q$cast\E$const\b/$newconst$suffix/;
>   			}
>   		}
> 
>