tracing: Add build bug if we have more trace_flags than bits

Add a enum that denotes the last bit of the trace_flags and have a
BUILD_BUG_ON(last_bit > 32).

If we add more bits than we have in trace_flags, the kernel wont build.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -7046,6 +7046,12 @@ __init static int tracer_alloc_buffers(void)
 	int ring_buf_size;
 	int ret = -ENOMEM;
 
+	/*
+	 * Make sure we don't accidently add more trace options
+	 * than we have bits for.
+	 */
+	BUILD_BUG_ON(TRACE_ITER_LAST_BIT > 32);
+
 	if (!alloc_cpumask_var(&tracing_buffer_mask, GFP_KERNEL))
 		goto out;
 

kernel/trace/trace.h

@@ -966,7 +966,11 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
 #undef C
 #define C(a, b) TRACE_ITER_##a##_BIT
 
-enum trace_iterator_bits { TRACE_FLAGS };
+enum trace_iterator_bits {
+	TRACE_FLAGS
+	/* Make sure we don't go more than we have bits for */
+	TRACE_ITER_LAST_BIT
+};
 
 /*
  * By redefining C, we can make TRACE_FLAGS a list of masks that