[PATCH v2] libtraceeval: Have TRACEEVAL_SET_*() functions fail on wrong type

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

I've hit a few bugs using libtraceeval because of a common cut and paste
error. To assign keys, the following is common to do:

  TRACEEVAL_SET_STRING(keys[0], "string");
  TRACEEVAL_SET_NUMBER(keys[0], 123);

But the above has a bug! The second entry was supposed to be keys[1], and
not keys[0]. This bug had me scratching my head a few times until I found
it. The failure is that passing keys to traceeval_insert() or something
similar, the traceeval_insert() will fail because it's expecting keys[0]
to be a string, but the above converted it to a number.

Help prevent this by passing a string into one of the NUMBER() macros or a
number in the STRING() macro fail to build. It doesn't prevent all
combinations as it is common to pass various size to NUMBER() for example:

  unsigned long long val;
  TRACEEVAL_SET_NUMBER_16(keys[0], val);

The above is allowed, but a string should never go into a number and vice
versa. Catching that should find some bugs at build.

Nothing is done with TRACEEVAL_SET_POINTER() as pointers are totally the
responsibility of the developer.

This also requires that you can not just pass a void pointer to one of the
STRING() macros and it requires a typecast now (as the samples had to be
updated).

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v1: https://lore.kernel.org/linux-trace-devel/20231006131647.0bae5a20@gandalf.local.home

 - Rebased to updated wake-lat.c example.

 include/traceeval.h | 28 +++++++++++++++++++++-------
 samples/wake-lat.c  |  4 +++-
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/include/traceeval.h b/include/traceeval.h
index d8095ba5c1a1..5464a5a55fe4 100644
--- a/include/traceeval.h
+++ b/include/traceeval.h
@@ -97,13 +97,27 @@ struct traceeval_data {
 		(data).member = (val);				\
 	} while (0)
 
-#define TRACEEVAL_SET_NUMBER(data, val)	     __TRACEEVAL_SET(data, NUMBER, number, val)
-#define TRACEEVAL_SET_NUMBER_8(data, val)    __TRACEEVAL_SET(data, NUMBER_8, number_8, val)
-#define TRACEEVAL_SET_NUMBER_16(data, val)   __TRACEEVAL_SET(data, NUMBER_16, number_16, val)
-#define TRACEEVAL_SET_NUMBER_32(data, val)   __TRACEEVAL_SET(data, NUMBER_32, number_32, val)
-#define TRACEEVAL_SET_NUMBER_64(data, val)   __TRACEEVAL_SET(data, NUMBER_64, number_64, val)
-#define TRACEEVAL_SET_STRING(data, val)	     __TRACEEVAL_SET(data, STRING, string, val)
-#define TRACEEVAL_SET_CSTRING(data, val)     __TRACEEVAL_SET(data, STRING, cstring, val)
+/* Have strings and pointers fail to be set to numbers */
+#define __TRACEEVAL_SET_NUM(data, data_type, member, val)	\
+	do {							\
+		char *__test__[val] __attribute__((unused));	\
+		__TRACEEVAL_SET(data, data_type, member, val);	\
+	} while (0)
+
+/* Have numbers fail to be assigned as strings */
+#define __TRACEEVAL_SET_STR(data, data_type, member, val)		\
+	do {								\
+		char __test__  __attribute__((unused)) = (val)[0];	\
+		__TRACEEVAL_SET(data, data_type, member, val);		\
+	} while (0)
+
+#define TRACEEVAL_SET_NUMBER(data, val)	     __TRACEEVAL_SET_NUM(data, NUMBER, number, val)
+#define TRACEEVAL_SET_NUMBER_8(data, val)    __TRACEEVAL_SET_NUM(data, NUMBER_8, number_8, val)
+#define TRACEEVAL_SET_NUMBER_16(data, val)   __TRACEEVAL_SET_NUM(data, NUMBER_16, number_16, val)
+#define TRACEEVAL_SET_NUMBER_32(data, val)   __TRACEEVAL_SET_NUM(data, NUMBER_32, number_32, val)
+#define TRACEEVAL_SET_NUMBER_64(data, val)   __TRACEEVAL_SET_NUM(data, NUMBER_64, number_64, val)
+#define TRACEEVAL_SET_STRING(data, val)	     __TRACEEVAL_SET_STR(data, STRING, string, val)
+#define TRACEEVAL_SET_CSTRING(data, val)     __TRACEEVAL_SET_STR(data, STRING, cstring, val)
 #define TRACEEVAL_SET_POINTER(data, val)     __TRACEEVAL_SET(data, POINTER, pointer, val)
 
 struct traceeval_type;
diff --git a/samples/wake-lat.c b/samples/wake-lat.c
index 086f67d8fe49..163815997793 100644
--- a/samples/wake-lat.c
+++ b/samples/wake-lat.c
@@ -84,6 +84,7 @@ static int sched_callback(struct tracecmd_input *handle, struct tep_event *event
 	struct traceeval_data keys[2];
 	struct traceeval_data vals[2];
 	const struct traceeval_data *results;
+	const char *comm;
 
 	if (!next_pid_field) {
 		next_pid_field = tep_find_field(event, "next_pid");
@@ -101,7 +102,8 @@ static int sched_callback(struct tracecmd_input *handle, struct tep_event *event
 	delta = record->ts - results[0].number_64;
 	traceeval_results_release(data->teval_wakeup, results);
 
-	TRACEEVAL_SET_CSTRING(keys[0], record->data + next_comm_field->offset);
+	comm = (char *)record->data + next_comm_field->offset;
+	TRACEEVAL_SET_CSTRING(keys[0],comm);
 	TRACEEVAL_SET_NUMBER(keys[1], pid);
 
 	TRACEEVAL_SET_NUMBER_64(vals[0], record->ts);
-- 
2.40.1