linux-kernel - [PATCH] checkpatch: Warn on self-assignments

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Message-ID: <afc2cffdd315d3e4394af149278df9e8af7f49f4.camel@perches.com>
Date:   Sat, 05 Sep 2020 10:58:29 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     cocci@...teme.lip6.fr, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Denis Efremov <efremov@...ux.com>, julia.lawall@...ia.fr
Subject: [PATCH] checkpatch: Warn on self-assignments

The uninitialized_var() macro was removed recently via
commit 63a0895d960a ("compiler: Remove uninitialized_var() macro")
as it's not a particularly useful warning and its use can
"paper over real bugs".

Add a checkpatch test to warn on self-assignments as a means
to avoid compiler warnings and as a back-door mechanism to
reproduce the old uninitialized_var macro behavior.

Signed-off-by: Joe Perches <joe@...ches.com>
---
 scripts/checkpatch.pl | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 149518d2a6a7..300b2659aab3 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3901,6 +3901,17 @@ sub process {
 #ignore lines not being added
 		next if ($line =~ /^[^\+]/);
 
+# check for self assigments used to avoid compiler warnings
+# e.g.:	int foo = foo, *bar = NULL;
+#	struct foo bar = *(&(bar));
+		if ($line =~ /^\+\s*(?:$Declare)?([A-Za-z_][A-Za-z\d_]*)\s*=/) {
+			my $var = $1;
+			if ($line =~ /^\+\s*(?:$Declare)?$var\s*=\s*(?:$var|\*\s*\(?\s*&\s*\(?\s*$var\s*\)?\s*\)?)\s*[;,]/) {
+				WARN("SELF_ASSIGNMENT",
+				     "Do not use self-assignments to avoid compiler warnings\n" . $herecurr);
+			}
+		}
+
 # check for dereferences that span multiple lines
 		if ($prevline =~ /^\+.*$Lval\s*(?:\.|->)\s*$/ &&
 		    $line =~ /^\+\s*(?!\#\s*(?!define\s+|if))\s*$Lval/) {