[PATCH] 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 <dovmu...@linux.vnet.ibm.com>
---
 scripts/checkpatch.pl | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index bd3faa154c..6ec2a9f6a1 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2891,6 +2891,18 @@ sub process {
                        }
                }
 
+# check for %# or %0# in printf-style format strings
+               while ($line =~ /(?:^|")([X\t]*)(?:"|$)/g) {
+                       my $string = substr($rawline, $-[1], $+[1] - $-[1]);
+                       $string =~ s/%%/__/g;
+                       if ($string =~ /(?<!%)%0?#/) {
+                               ERROR("Don't use '#' flag of printf format " .
+                                     "('%#') in format strings, use '0x' " .
+                                     "prefix instead\n" . $herecurr);
+                               last;
+                       }
+               }
+
 # QEMU specific tests
                if ($rawline =~ /\b(?:Qemu|QEmu)\b/) {
                        ERROR("use QEMU instead of Qemu or QEmu\n" . $herecurr);
-- 
2.20.1