[PATCH v4] checkpatch: do not apply "initialise globals to 0" check to BPF progs

[Song Liu]

BPF programs explicitly initialise global variables to 0 to make sure
clang (v10 or older) do not put the variables in the common section.
Skip "initialise globals to 0" check for BPF programs to elimiate error
messages like:

    ERROR: do not initialise globals to 0
    #19: FILE: samples/bpf/tracex1_kern.c:21:

Cc: Andy Whitcroft <a...@canonical.com>
Cc: Joe Perches <j...@perches.com>
Signed-off-by: Song Liu <songliubrav...@fb.com>

---
Changes v3 => v4:
  1. Yet more fixes to regexes.
Changes v2 => v3:
  1. Fix regex.
Changes v1 => v2:
  1. Add function exclude_global_initialisers() to keep the code clean.
---
 scripts/checkpatch.pl | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 1afe3af1cc097..f5b7ec9170999 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2428,6 +2428,15 @@ sub get_raw_comment {
        return $comment;
 }
 
+sub exclude_global_initialisers {
+       my ($realfile) = @_;
+
+       # Do not check for BPF programs (tools/testing/selftests/bpf/progs/*.c, 
samples/bpf/*_kern.c, *.bpf.c).
+       return $realfile =~ m@^tools/testing/selftests/bpf/progs/.*\.c$@ ||
+               $realfile =~ m@^samples/bpf/.*_kern\.c$@ ||
+               $realfile =~ m@/bpf/.*\.bpf\.c$@;
+}
+
 sub process {
        my $filename = shift;
 
@@ -4323,7 +4332,8 @@ sub process {
                }
 
 # check for global initialisers.
-               if ($line =~ 
/^\+$Type\s*$Ident(?:\s+$Modifier)*\s*=\s*($zero_initializer)\s*;/) {
+               if ($line =~ 
/^\+$Type\s*$Ident(?:\s+$Modifier)*\s*=\s*($zero_initializer)\s*;/ &&
+                   !exclude_global_initialisers($realfile)) {
                        if (ERROR("GLOBAL_INITIALISERS",
                                  "do not initialise globals to $1\n" . 
$herecurr) &&
                            $fix) {
-- 
2.24.1