Message-ID: <1403905024.9064.16.camel@joe-AO725>
Subject: Re: [PATCH 1/1] scripts/checkpatch.pl: update kmalloc_array/kcalloc
 conversion warning
From: Joe Perches <joe@perches.com>
To: Fabian Frederick <fabf@skynet.be>
Cc: linux-kernel@vger.kernel.org, "Theodore Ts'o" <tytso@mit.edu>,
        Andrew Morton <akpm@linux-foundation.org>
Date: Fri, 27 Jun 2014 14:37:04 -0700
In-Reply-To: <1403899823-4461-1-git-send-email-fabf@skynet.be>
References: <1403899823-4461-1-git-send-email-fabf@skynet.be>
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Sender: linux-kernel-owner@vger.kernel.org

On Fri, 2014-06-27 at 22:10 +0200, Fabian Frederick wrote:
> Avoid automatic k[mz]alloc with multiplies conversions
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -4427,7 +4427,7 @@ sub process {
>  			$newfunc = "kcalloc" if ($oldfunc eq "kzalloc");
>  			if ($a1 =~ /^sizeof\s*\S/ || $a2 =~ /^sizeof\s*\S/) {
>  				if (WARN("ALLOC_WITH_MULTIPLY",
> -					 "Prefer $newfunc over $oldfunc with multiply\n" . $herecurr) &&
> +					 "Prefer $newfunc over $oldfunc with multiply when arguments are not fixed or come from unvalidated source\n" . $herecurr) &&
>  				    $fix) {
>  					my $r1 = $a1;
>  					my $r2 = $a2;

I'm not sure of the value of this as I think at some point
if not already today, the compiler will optimize the multiply
away.

But it's probably better to look at the non-sizeof variable
and emit the warning only when it's not $Constant or some
upper-case only macro #define like "\b[A-Z_]+\b" is used.

Maybe something like this:

 scripts/checkpatch.pl | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 6c7cbaf..e0d0ead 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4486,22 +4486,23 @@ sub process {
 
 # check for k[mz]alloc with multiplies that could be kmalloc_array/kcalloc
 		if ($^V && $^V ge 5.10.0 &&
-		    $line =~ /\b($Lval)\s*\=\s*(?:$balanced_parens)?\s*(k[mz]alloc)\s*\(\s*($FuncArg)\s*\*\s*($FuncArg)/) {
+		    $line =~ /\b($Lval)\s*\=\s*(?:$balanced_parens)?\s*(k[mz]alloc)\s*\(\s*($FuncArg)\s*\*\s*($FuncArg)\s*,/) {
 			my $oldfunc = $3;
 			my $a1 = $4;
 			my $a2 = $10;
 			my $newfunc = "kmalloc_array";
 			$newfunc = "kcalloc" if ($oldfunc eq "kzalloc");
-			if ($a1 =~ /^sizeof\s*\S/ || $a2 =~ /^sizeof\s*\S/) {
+			my $r1 = $a1;
+			my $r2 = $a2;
+			if ($a1 =~ /^sizeof\s*\S/) {
+				$r1 = $a2;
+				$r2 = $a1;
+			}
+			if ($r1 !~ /^sizeof\b/ && $r2 =~ /^sizeof\s*\S/ &&
+			    !($r1 =~ /^$Constant$/ || $r1 =~ /^[A-Z_]+$/)) {
 				if (WARN("ALLOC_WITH_MULTIPLY",
 					 "Prefer $newfunc over $oldfunc with multiply\n" . $herecurr) &&
 				    $fix) {
-					my $r1 = $a1;
-					my $r2 = $a2;
-					if ($a1 =~ /^sizeof\s*\S/) {
-						$r1 = $a2;
-						$r2 = $a1;
-					}
 					$fixed[$linenr - 1] =~ s/\b($Lval)\s*\=\s*(?:$balanced_parens)?\s*(k[mz]alloc)\s*\(\s*($FuncArg)\s*\*\s*($FuncArg)/$1 . ' = ' . "$newfunc(" . trim($r1) . ', ' . trim($r2)/e;
 
 				}


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