x86, cpufeature: Catch duplicate CPU feature strings

We had a case of duplicate CPU feature strings, a user space ABI
violation, for almost two years.  Make it a build error so that
doesn't happen again.

Link: http://lkml.kernel.org/r/4FE34BCB.5050305@linux.intel.com
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Jean Delvare <khali@linux-fr.org>

arch/x86/kernel/cpu/mkcapflags.pl

@@ -11,22 +11,35 @@
 print OUT "#include <asm/cpufeature.h>\n\n";
 print OUT "const char * const x86_cap_flags[NCAPINTS*32] = {\n";
 
+%features = ();
+$err = 0;
+
 while (defined($line = <IN>)) {
 	if ($line =~ /^\s*\#\s*define\s+(X86_FEATURE_(\S+))\s+(.*)$/) {
 		$macro = $1;
-		$feature = $2;
+		$feature = "\L$2";
 		$tail = $3;
 		if ($tail =~ /\/\*\s*\"([^"]*)\".*\*\//) {
-			$feature = $1;
+			$feature = "\L$1";
 		}
 
-		if ($feature ne '') {
-			printf OUT "\t%-32s = \"%s\",\n",
-				"[$macro]", "\L$feature";
+		next if ($feature eq '');
+
+		if ($features{$feature}++) {
+			print STDERR "$in: duplicate feature name: $feature\n";
+			$err++;
 		}
+		printf OUT "\t%-32s = \"%s\",%s\n", "[$macro]", $feature;
 	}
 }
 print OUT "};\n";
 
 close(IN);
 close(OUT);
+
+if ($err) {
+	unlink($out);
+	exit(1);
+}
+
+exit(0);