trace: Better structure lib/trace and configure options

In the next commits, we'll add more tracing options for instrumentation and
specific tracer.

This rename follows a more meaningful naming standard. It also adds a catch
all "HAVE_TRACING" define that indicate in the code that we have tracing
enabled.

Part of #32910

Signed-off-by: David Goulet <dgoulet@torproject.org>

configure.ac

@@ -256,15 +256,22 @@ AC_ARG_ENABLE(seccomp,
 AC_ARG_ENABLE(libscrypt,
      AS_HELP_STRING(--disable-libscrypt, [do not attempt to use libscrypt]))
 
-dnl Enable event tracing which are transformed to debug log statement.
-AC_ARG_ENABLE(event-tracing-debug,
-     AS_HELP_STRING(--enable-event-tracing-debug, [build with event tracing to debug log]))
-AM_CONDITIONAL([USE_EVENT_TRACING_DEBUG], [test "x$enable_event_tracing_debug" = "xyes"])
+dnl --- Tracing Options. ---
 
-if test x$enable_event_tracing_debug = xyes; then
-  AC_DEFINE([USE_EVENT_TRACING_DEBUG], [1], [Tracing framework to log debug])
-  AC_DEFINE([TOR_EVENT_TRACING_ENABLED], [1], [Compile the event tracing instrumentation])
-fi
+dnl Tracepoints event to debug logs.
+AC_ARG_ENABLE(tracing-instrumentation-log-debug,
+     AS_HELP_STRING([--enable-tracing-instrumentation-log-debug],
+                    [build with tracing event to debug log]),
+     AC_DEFINE([USE_TRACING_INSTRUMENTATION_LOG_DEBUG], [1],
+               [Tracepoints to log debug]), [])
+AM_CONDITIONAL([USE_TRACING_INSTRUMENTATION_LOG_DEBUG],
+               [test "x$enable_tracing_instrumentation_log_debug" = "xyes"])
+
+dnl Define that tracing is supported.
+AM_COND_IF([USE_TRACING_INSTRUMENTATION_LOG_DEBUG],
+           AC_DEFINE([HAVE_TRACING], [1], [Compiled with tracing support]))
+
+dnl -- End Tracing Options. --
 
 dnl Enable Android only features.
 AC_ARG_ENABLE(android,
@@ -2718,6 +2725,12 @@ PPRINT_PROP_BOOL([libFuzzer support (--enable-libfuzzer)], $value)
 test "x$enable_oss_fuzz" = "xyes" && value=1 || value=0
 PPRINT_PROP_BOOL([OSS-Fuzz support (--enable-oss-fuzz)], $value)
 
+AS_ECHO
+PPRINT_SUBTITLE([Tracing])
+
+test "x$enable_tracing_instrumentation_log_debug" = "xyes" && value=1 || value=0
+PPRINT_PROP_BOOL([Tracepoints to log_debug() (--enable-tracing-instrumentation-log-debug)], $value)
+
 AS_ECHO
 PPRINT_SUBTITLE([Install Directories])
 

src/lib/trace/debug.h

@@ -6,8 +6,10 @@
  * \brief Macros for debugging our event-trace support.
  **/
 
-#ifndef TOR_TRACE_LOG_DEBUG_H
-#define TOR_TRACE_LOG_DEBUG_H
+#ifndef TOR_TRACE_DEBUG_H
+#define TOR_TRACE_DEBUG_H
+
+#ifdef USE_TRACING_INSTRUMENTATION_LOG_DEBUG
 
 #include "lib/log/log.h"
 
@@ -17,14 +19,20 @@
 
 /* Send every event to a debug log level. This is useful to debug new trace
  * events without implementing them for a specific event tracing framework.
- * Note that the arguments are ignored since at this step we do not know the
- * types and amount there is. */
+ *
+ * NOTE: arguments can't be used becaue there is no easy generic ways to learn
+ * their type and amount. It is probably doable with massive C pre-processor
+ * trickery but this is meant to be simple. */
 
-/* Example on how to map a tracepoint to log_debug(). */
-#undef tor_trace
-#define tor_trace(subsystem, name, args...) \
-  log_debug(LD_GENERAL, "Trace event \"" XSTR(name) "\" from " \
-                        "\"" XSTR(subsystem) "\" hit. " \
-                        "(line "XSTR(__LINE__) ")")
+#define TOR_TRACE_LOG_DEBUG(subsystem, event_name, ...)             \
+  log_debug(LD_GENERAL, "Tracepoint \"" XSTR(event_name) "\" from " \
+                        "subsystem \"" XSTR(subsystem) "\" hit.")
 
-#endif /* !defined(TOR_TRACE_LOG_DEBUG_H) */
+#else /* defined(USE_TRACING_INSTRUMENTATION_LOG_DEBUG) */
+
+/* NOP the debug event. */
+#define TOR_TRACE_LOG_DEBUG(subsystem, name, ...)
+
+#endif /* defined(USE_TRACING_INSTRUMENTATION_LOG_DEBUG) */
+
+#endif /* !defined(TOR_TRACE_DEBUG_H) */

src/lib/trace/events.h

@@ -6,40 +6,28 @@
  * \brief Header file for Tor event tracing.
  **/
 
-#ifndef TOR_TRACE_EVENTS_H
-#define TOR_TRACE_EVENTS_H
+#ifndef TOR_LIB_TRACE_EVENTS_H
+#define TOR_LIB_TRACE_EVENTS_H
 
-/*
- * The following defines a generic event tracing function name that has to be
- * used to trace events in the code base.
- *
- * That generic function is then defined by a event tracing framework. For
- * instance, the "log debug" framework sends all trace events to log_debug()
- * which is defined in src/trace/debug.h which can only be enabled at compile
- * time (--enable-event-tracing-debug).
- *
- * By default, every trace events in the code base are replaced by a NOP. See
- * doc/HACKING/Tracing.md for more information on how to use event tracing or
- * add events.
- */
+/* XXX: DOCDOC once framework is stable. */
 
-#ifdef TOR_EVENT_TRACING_ENABLED
-/* Map every trace event to a per subsystem macro. */
-#define tor_trace(subsystem, name, ...) \
-  tor_trace_##subsystem(name, __VA_ARGS__)
+#ifdef HAVE_TRACING
 
-/* Enable event tracing for the debug framework where all trace events are
- * mapped to a log_debug(). */
-#ifdef USE_EVENT_TRACING_DEBUG
+#define tor_trace(subsystem, event_name, ...)           \
+  do {                                                  \
+    TOR_TRACE_LOG_DEBUG(tor_ ## subsystem, event_name); \
+  } while (0)
+
+/* This corresponds to the --enable-tracing-instrumentation-log-debug
+ * configure option which maps all tracepoints to a log_debug() statement. */
 #include "lib/trace/debug.h"
-#endif
 
-#else /* !defined(TOR_EVENT_TRACING_ENABLED) */
+#else /* !defined(HAVE_TRACING) */
 
-/* Reaching this point, we NOP every event declaration because event tracing
- * is not been enabled at compile time. */
-#define tor_trace(subsystem, name, args...)
+/* Reaching this point, tracing is disabled thus we NOP every tracepoints
+ * declaration so we have no execution cost at runtime. */
+#define tor_trace(subsystem, name, ...)
 
-#endif /* defined(TOR_EVENT_TRACING_ENABLED) */
+#endif /* defined(HAVE_TRACING) */
 
-#endif /* !defined(TOR_TRACE_EVENTS_H) */
+#endif /* !defined(TOR_LIB_TRACE_EVENTS_H) */

src/lib/trace/include.am

@@ -2,18 +2,20 @@
 noinst_LIBRARIES += \
 	src/lib/libtor-trace.a
 
+# ADD_C_FILE: INSERT SOURCES HERE.
+LIBTOR_TRACE_A_SOURCES = \
+	src/lib/trace/trace.c
+
 # ADD_C_FILE: INSERT HEADERS HERE.
 TRACEHEADERS = \
 	src/lib/trace/trace.h \
 	src/lib/trace/events.h
 
-if USE_EVENT_TRACING_DEBUG
+if USE_TRACING_INSTRUMENTATION_LOG_DEBUG
 TRACEHEADERS += \
 	src/lib/trace/debug.h
 endif
 
-# ADD_C_FILE: INSERT SOURCES HERE.
-src_lib_libtor_trace_a_SOURCES = \
-	src/lib/trace/trace.c
+src_lib_libtor_trace_a_SOURCES = $(LIBTOR_TRACE_A_SOURCES)
 
 noinst_HEADERS+= $(TRACEHEADERS)