linux-kernel - [for-linus][PATCH 01/10] tracing: Suppress sparse warnings triggered by is_signed

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Date:   Sat, 20 Aug 2022 20:07:38 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Bart Van Assche <bvanassche@....org>
Subject: [for-linus][PATCH 01/10] tracing: Suppress sparse warnings triggered by is_signed_type()

From: Bart Van Assche <bvanassche@....org>

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.

Note: work is in progress to improve sparse but has not yet landed. See
also "[PATCH 0/5] allow -1 and compares in bitwise types"
(https://lore.kernel.org/all/20220627190540.13358-1-luc.vanoostenryck@gmail.com/ ).

Link: https://lore.kernel.org/linux-trace-devel/20220717151047.19220-1-bvanassche@acm.org

Suggested-by: Christoph Hellwig <hch@....de>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Bart Van Assche <bvanassche@....org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 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 b18759a673c6..b60347a0ccde 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__.
+ *
+ * Since there is another definition of is_signed_type() in <linux/overflow.h>,
+ * 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);
-- 
2.35.1