checkpatch: add --strict "pointer comparison to NULL" test

It seems there are more and more uses of "if (!ptr)" in preference to "if
(ptr == NULL)" so add a --strict test to emit a message when using the
latter form.

This also finds (ptr != NULL).

Fix it too if desired.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 5e63dce2e428..6d85c7b1b27e 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4522,6 +4522,20 @@ sub process {
                              "Possible precedence defect with mask then right shift - may need parentheses\n" . $herecurr);
                 }
 
+# check for pointer comparisons to NULL
+                if ($^V && $^V ge 5.10.0) {
+                        while ($line =~ /\b$LvalOrFunc\s*(==|\!=)\s*NULL\b/g) {
+                                my $val = $1;
+                                my $equal = "!";
+                                $equal = "" if ($4 eq "!=");
+                                if (CHK("COMPARISON_TO_NULL",
+                                        "Comparison to NULL could be written \"${equal}${val}\"\n" . $herecurr) &&
+                                            $fix) {
+                                        $fixed[$fixlinenr] =~ s/\b\Q$val\E\s*(?:==|\!=)\s*NULL\b/$equal$val/;
+                                }
+                        }
+                }
+
 # check for bad placement of section $InitAttribute (e.g.: __initdata)
                 if ($line =~ /(\b$InitAttribute\b)/) {
                         my $attr = $1;