On 6/25/22 02:23, Christoph Hellwig wrote:
On Fri, Jun 24, 2022 at 12:57:56PM -0700, Bart Van Assche wrote:
BTW, I discovered the code in the tracing infrastructure
that makes sparse unhappy:
#define is_signed_type(type) (((type)(-1)) < (type)1)
Sparse reports four warnings for that expression if 'type' is a bitwise
type. Two of these warnings can be suppressed by changing 'type' into
'__force type'. I have not yet found a way to suppress all the sparse
warnings triggered by the is_signed_type() macro for bitwise types.
Yeah, that is a bit of a mess. Rasmus, Steven - any good idea how
we can make the trace even macros fit for sparse? Maybe just drop the
is_signed_type check for __CHECKER__ ?
How about the patch below?
Subject: [PATCH] tracing: Suppress sparse warnings triggered by
is_signed_type()
Using a __bitwise type in a tracing __field() definition triggers four
sparse warnings in stage 4 of expanding the TRACE_EVENT() macro. These
warnings are triggered by the is_signed_type() macro implementation.
Since there is no known way of checking signedness of a bitwise type
without triggering sparse warnings, disable signedness checking when
verifying code with sparse.
Suggested-by: Christoph Hellwig <hch@xxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
include/linux/trace_events.h | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index e6e95a9f07a5..f7b2a5467361 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -814,7 +814,19 @@ extern int trace_add_event_call(struct trace_event_call *call);
extern int trace_remove_event_call(struct trace_event_call *call);
extern int trace_event_get_offsets(struct trace_event_call *call);
+/*
+ * There is no known way to check signedness of __bitwise types without
+ * triggering a sparse warning. Hence the #ifdef __CHECKER__.
+ *
+ * There is another definition of is_signed_type() in <linux/overflow.h>.
+ * Hence undefine is_signed_type() before redefining it.
+ */
+#undef is_signed_type
+#ifdef __CHECKER__
+#define is_signed_type(type) 0
+#else
#define is_signed_type(type) (((type)(-1)) < (type)1)
+#endif
int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set);
int trace_set_clr_event(const char *system, const char *event, int set);
