trace: disable traces at compilation

Some applications want to omit the trace feature.
Either to reduce the memory footprint, to reduce the exposed attack
surface, or for other reasons.

This patch adds an option in rte_config.h to include or omit trace in the
build.
Trace is included by default.

Omitting trace works by omitting all trace points.
For API and ABI compatibility, the trace feature itself remains.

Furthermore, a public function to determine if trace is build time enabled
is added; mainly for the benefit of the unit tests.

Signed-off-by: Morten Brørup <[email protected]>
Acked-by: Stephen Hemminger <[email protected]>
Acked-by: Jerin Jacob <[email protected]>

Author: MortenBroerup

app/test/test_trace.c

@@ -245,6 +245,10 @@ static struct unit_test_suite trace_tests = {
 static int
 test_trace(void)
 {
+	if (!rte_trace_feature_is_enabled()) {
+		printf("Trace omitted at build-time, skipping test\n");
+		return TEST_SKIPPED;
+	}
 	return unit_test_suite_runner(&trace_tests);
 }
 

config/rte_config.h

@@ -49,6 +49,7 @@
 #define RTE_MAX_TAILQ 32
 #define RTE_LOG_DP_LEVEL RTE_LOG_INFO
 #define RTE_MAX_VFIO_CONTAINERS 64
+#define RTE_TRACE 1
 
 /* bsd module defines */
 #define RTE_CONTIGMEM_MAX_NUM_BUFS 64

lib/eal/include/rte_trace.h

@@ -35,6 +35,26 @@ extern "C" {
 __rte_experimental
 bool rte_trace_is_enabled(void);
 
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change, or be removed, without prior notice
+ *
+ * Test if trace feature is enabled at compile time.
+ *
+ * @return
+ *   true if trace feature is enabled, false otherwise.
+ */
+__rte_experimental
+static __rte_always_inline bool
+rte_trace_feature_is_enabled(void)
+{
+#ifdef RTE_TRACE
+	return true;
+#else
+	return false;
+#endif
+}
+
 /**
  * Enumerate trace mode operation.
  */

lib/eal/include/rte_trace_point.h

@@ -30,6 +30,7 @@ extern "C" {
 #include <rte_per_lcore.h>
 #include <rte_stdatomic.h>
 #include <rte_string_fns.h>
+#include <rte_trace.h>
 #include <rte_uuid.h>
 
 /** The tracepoint object. */
@@ -359,6 +360,8 @@ __rte_trace_point_emit_ev_header(void *mem, uint64_t in)
 #define __rte_trace_point_emit_header_generic(t) \
 void *mem; \
 do { \
+	if (!rte_trace_feature_is_enabled()) \
+		return; \
 	const uint64_t val = rte_atomic_load_explicit(t, rte_memory_order_acquire); \
 	if (likely(!(val & __RTE_TRACE_FIELD_ENABLE_MASK))) \
 		return; \

lib/eal/include/rte_trace_point_register.h

@@ -23,6 +23,8 @@ rte_trace_point_t __rte_section("__rte_trace_point") __##trace; \
 static const char __##trace##_name[] = RTE_STR(name); \
 RTE_INIT(trace##_init) \
 { \
+	if (!rte_trace_feature_is_enabled()) \
+		return; \
 	__rte_trace_point_register(&__##trace, __##trace##_name, \
 		(void (*)(void)) trace); \
 }