checkpatch: do not apply "initialise globals to 0" check to BPF progs

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 <[email protected]>
Cc: Joe Perches <[email protected]>
Signed-off-by: Song Liu <[email protected]>

Author: liu-song-6

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;
 
@@ -4330,7 +4339,8 @@ 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) {