checkpatch: Check for 0-length and 1-element arrays

Fake flexible arrays have been deprecated since last millennium. Proper
C99 flexible arrays must be used throughout the kernel so
CONFIG_FORTIFY_SOURCE and CONFIG_UBSAN_BOUNDS can provide proper array
bounds checking.

Cc: Andy Whitcroft <[e-mail]>
Cc: Dwaipayan Ray <[e-mail]>
Cc: Lukas Bulwahn <[e-mail]>
Fixed-by: Joe Perches <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>
Acked-by: Gustavo A. R. Silva <[e-mail]>
Acked-by: Joe Perches <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

scripts/checkpatch.pl

···
 			}
 		}
 
+# check for array definition/declarations that should use flexible arrays instead
+		if ($sline =~ /^[\+ ]\s*\}(?:\s*__packed)?\s*;\s*$/ &&
+		    $prevline =~ /^\+\s*(?:\}(?:\s*__packed\s*)?|$Type)\s*$Ident\s*\[\s*(0|1)\s*\]\s*;\s*$/) {
+			if (ERROR("FLEXIBLE_ARRAY",
+				  "Use C99 flexible arrays - see https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays\n" . $hereprev) &&
+			    $1 == '0' && $fix) {
+				$fixed[$fixlinenr - 1] =~ s/\[\s*0\s*\]/[]/;
+			}
+		}
+
 # nested likely/unlikely calls
 		if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
 			WARN("LIKELY_MISUSE",