[PATCH v2] checkpatch: Detect '%#' or '%0#' in printf-style format strings

[Dov Murik]

According to the coding style document, we should use literal '0x' prefix
instead of printf's '#' flag (which appears as '%#' or '%0#' in the format
string).  Add a checkpatch rule to enforce that.

Note that checkpatch already had a similar rule for trace-events files.

Example usage:

  $ scripts/checkpatch.pl --file chardev/baum.c
  ...
  ERROR: Don't use '#' flag of printf format ('%#') in format strings, use '0x' 
prefix instead
  #366: FILE: chardev/baum.c:366:
  +            DPRINTF("Broken packet %#2x, tossing\n", req); \
  ...
  ERROR: Don't use '#' flag of printf format ('%#') in format strings, use '0x' 
prefix instead
  #472: FILE: chardev/baum.c:472:
  +        DPRINTF("unrecognized request %0#2x\n", req);
  ...

Signed-off-by: Dov Murik <dovmurik@linux.vnet.ibm.com>
---

Since v1:
- consolidate format string checks to avoid code duplication

---
 scripts/checkpatch.pl | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index bd3faa154c..f8dac953b2 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2880,14 +2880,20 @@ sub process {
                                $herecurr);
                }
 
-# check for %L{u,d,i} in strings
+# format strings checks
                my $string;
                while ($line =~ /(?:^|")([X\t]*)(?:"|$)/g) {
                        $string = substr($rawline, $-[1], $+[1] - $-[1]);
                        $string =~ s/%%/__/g;
+                       # check for %L{u,d,i} in strings
                        if ($string =~ /(?<!%)%L[udi]/) {
                                ERROR("\%Ld/%Lu are not-standard C, use 
%lld/%llu\n" . $herecurr);
-                               last;
+                       }
+                       # check for %# or %0# in printf-style format strings
+                       if ($string =~ /(?<!%)%0?#/) {
+                               ERROR("Don't use '#' flag of printf format " .
+                                     "('%#') in format strings, use '0x' " .
+                                     "prefix instead\n" . $herecurr);
                        }
                }
 
-- 
2.20.1