linux-kernel - Re: [PATCH v3] checkpatch: add warning for unnecessary use of %h[xudi] and %hh[xudi]

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Message-ID: <55d38c770a3316a3c67f5380ffb8ed37540900da.camel@perches.com>
Date:   Sat, 28 Nov 2020 10:46:50 -0800
From:   Joe Perches <joe@...ches.com>
To:     Dwaipayan Ray <dwaipayanray1@...il.com>
Cc:     linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-kernel@...r.kernel.org, lukas.bulwahn@...il.com
Subject: Re: [PATCH v3] checkpatch: add warning for unnecessary use of
 %h[xudi] and %hh[xudi]

On Sat, 2020-11-28 at 23:08 +0530, Dwaipayan Ray wrote:
> Modifiers %h and %hh should never be used.
> 
> Commit cbacb5ab0aa0 ("docs: printk-formats: Stop encouraging use
> of unnecessary %h[xudi] and %hh[xudi]") specifies that:
> 
> "Standard integer promotion is already done and %hx and %hhx is useless
> so do not encourage the use of %hh[xudi] or %h[xudi]."
> 
> "The "h" and "hh" things should never be used. The only reason for them
> being used if you have an "int", but you want to print it out as a
> "char" (and honestly, that is a really bad reason, you'd be better off
> just using a proper cast to make the code more obvious)."
> 
> Add a new check to emit a warning on finding an unneeded use of %h or
> %hh modifier.
> 
> Also add a fix option to the check.
> 
> Link: https://lore.kernel.org/lkml/4910042649a4f3ab22fac93191b8c1fa0a2e17c3.camel@perches.com/
> 
> Suggested-by: Joe Perches <joe@...ches.com>
> Suggested-by: Lukas Bulwahn <lukas.bulwahn@...il.com>
> Signed-off-by: Dwaipayan Ray <dwaipayanray1@...il.com>
> ---
> Changes in v3:
> - Change warning message
> - Fix regex match to include capture group
> - Warn on every unnecesary use of %h on a line
> - Add fix option when the format line matches current line
> 
> Changes in v2:
> - Use $logFunctions instead of the manual list.
> - Relocate the check to after logging continuations check.
> - Remove perl_version_ok check
> 
>  scripts/checkpatch.pl | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 7dc094445d83..dc25d32f0c5f 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -6027,6 +6027,22 @@ sub process {
>  			     "Avoid logging continuation uses where feasible\n" . $herecurr);
>  		}
>  
> 
> +# check for unnecessary use of %h[xudi] and %hh[xudi] in logging functions
> +		if (defined $stat &&
> +		    $line =~ /\b$logFunctions\s*\(/) {
> +			my $lc = $stat =~ tr@\n@@;
> +			for (my $cur_ln = $linenr; $cur_ln <= $linenr + $lc; $cur_ln++) {
> +				my $cur_rawline = raw_line($cur_ln, 0);
> +				while ($cur_rawline =~ /^\+.*\"[^\"]*(%[\d\.\*\-]*h+[idux])/g) {
> +					if (WARN("INTEGER_PROMOTION",
> +						 "Using 'h' in $1 is unnecessary\n" . "$cur_rawline\n") &&
> +					    $fix && ($cur_ln == $linenr)) {
> +						$fixed[$fixlinenr] =~ s/(\"[^\"]*%[\d\.\*\-]*)h+([idux])/$1$2/;
> +					}
> +				}
> +			}
> +		}
> +

Here was what I tried:

There are uses like %#06hh", so # was addedto the format block
and multiple line uses were also inspected.


 scripts/checkpatch.pl | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7dc094445d83..b985b6b37ba8 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6027,6 +6027,29 @@ sub process {
 			     "Avoid logging continuation uses where feasible\n" . $herecurr);
 		}
 
+# check for unnecessary use of %h[xudi] and %hh[xudi] in logging functions
+		if (defined $stat &&
+		    $line =~ /\b$logFunctions\s*\(/ &&
+		    index($stat, '"') >= 0) {
+			my $lc = $stat =~ tr@\n@@;
+			$lc = $lc + $linenr;
+			my $stat_real = get_stat_real($linenr, $lc);
+			pos($stat_real) = index($stat_real, '"');
+			my $lineoff = substr($stat_real, 0, pos($stat_real)) =~ tr/\n//;
+			while ($stat_real =~ /[^"%]*(%[#\d\.\*\-]*(h+)[idux])/g) {
+				my $pspec = $1;
+				my $h = $2;
+				if (WARN("UNNECESSARY_MODIFIER",
+					 "Integer promotion: '$h' use in '$pspec' is unnecessary\n" . "$here\n$stat_real\n") &&
+				    $fix &&
+				    $fixed[$fixlinenr + $lineoff] =~ /^\+/) {
+					my $nspec = $pspec;
+					$nspec =~ s/h//g;
+					$fixed[$fixlinenr + $lineoff] =~ s/\Q$pspec\E/$nspec/;
+				}
+			}
+		}
+
 # check for mask then right shift without a parentheses
 		if ($perl_version_ok &&
 		    $line =~ /$LvalOrFunc\s*\&\s*($LvalOrFunc)\s*>>/ &&