Move to kernel style SPDX license identifiers
[lttng-ust.git] / include / lttng / tracepoint.h
index 4b7473eee49a7c6866e33cb001464b73e2a7b181..bcab5e2d7b0fa3c2ac0efb71b2c4f2ed3a68f2fe 100644 (file)
@@ -1,54 +1,61 @@
-#ifndef _LTTNG_TRACEPOINT_H
-#define _LTTNG_TRACEPOINT_H
-
 /*
- * Copyright 2011-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
- * SOFTWARE.
+ * SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  */
 
+#ifndef _LTTNG_TRACEPOINT_H
+#define _LTTNG_TRACEPOINT_H
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <lttng/tracepoint-types.h>
 #include <lttng/tracepoint-rcu.h>
 #include <urcu/compiler.h>
+#include <urcu/system.h>
 #include <dlfcn.h>     /* for dlopen */
 #include <string.h>    /* for memset */
 #include <lttng/ust-config.h>  /* for sdt */
 #include <lttng/ust-compiler.h>
 
 #ifdef LTTNG_UST_HAVE_SDT_INTEGRATION
-#define SDT_USE_VARIADIC
+/*
+ * Instead of using SDT_USE_VARIADIC from 'sys/sdt.h', use our own namespaced
+ * macros since the instrumented application might already have included
+ * 'sys/sdt.h' without variadic support.
+ */
 #include <sys/sdt.h>
+
+#define _LTTNG_SDT_NARG(...) \
+       __LTTNG_SDT_NARG(__VA_ARGS__, 12,11,10,9,8,7,6,5,4,3,2,1,0)
+
+#define __LTTNG_SDT_NARG(_0,_1,_2,_3,_4,_5,_6,_7,_8,_9,_10,_11,_12, N, ...) N
+
+#define _LTTNG_SDT_PROBE_N(provider, name, N, ...) \
+       _SDT_PROBE(provider, name, N, (__VA_ARGS__))
+
+#define LTTNG_STAP_PROBEV(provider, name, ...) \
+       _LTTNG_SDT_PROBE_N(provider, name, _LTTNG_SDT_NARG(0, ##__VA_ARGS__), ##__VA_ARGS__)
+
 #else
-#define STAP_PROBEV(...)
+#define LTTNG_STAP_PROBEV(...)
 #endif
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+#define tracepoint_enabled(provider, name) \
+       caa_unlikely(CMM_LOAD_SHARED(__tracepoint_##provider##___##name.state))
+
+#define do_tracepoint(provider, name, ...) \
+       __tracepoint_cb_##provider##___##name(__VA_ARGS__)
+
 #define tracepoint(provider, name, ...)                                            \
        do {                                                                \
-               STAP_PROBEV(provider, name, ## __VA_ARGS__);                \
-               if (caa_unlikely(__tracepoint_##provider##___##name.state)) \
-                       __tracepoint_cb_##provider##___##name(__VA_ARGS__); \
+               LTTNG_STAP_PROBEV(provider, name, ## __VA_ARGS__);          \
+               if (tracepoint_enabled(provider, name))                     \
+                       do_tracepoint(provider, name, __VA_ARGS__);         \
        } while (0)
 
 #define TP_ARGS(...)       __VA_ARGS__
@@ -151,29 +158,29 @@ extern "C" {
  * address.
  */
 #define _DECLARE_TRACEPOINT(_provider, _name, ...)                                     \
-extern struct tracepoint __tracepoint_##_provider##___##_name;                         \
+extern struct lttng_ust_tracepoint __tracepoint_##_provider##___##_name;               \
 static inline __attribute__((always_inline, unused)) lttng_ust_notrace                 \
 void __tracepoint_cb_##_provider##___##_name(_TP_ARGS_PROTO(__VA_ARGS__));             \
 static                                                                                 \
 void __tracepoint_cb_##_provider##___##_name(_TP_ARGS_PROTO(__VA_ARGS__))              \
 {                                                                                      \
-       struct tracepoint_probe *__tp_probe;                                            \
+       struct lttng_ust_tracepoint_probe *__tp_probe;                                  \
                                                                                        \
        if (caa_unlikely(!TP_RCU_LINK_TEST()))                                          \
                return;                                                                 \
-       tp_rcu_read_lock_bp();                                                          \
-       __tp_probe = tp_rcu_dereference_bp(__tracepoint_##_provider##___##_name.probes); \
+       tp_rcu_read_lock();                                                             \
+       __tp_probe = tp_rcu_dereference(__tracepoint_##_provider##___##_name.probes);   \
        if (caa_unlikely(!__tp_probe))                                                  \
                goto end;                                                               \
        do {                                                                            \
-               void (*__tp_cb)(void) = __tp_probe->func;                                       \
+               void (*__tp_cb)(void) = __tp_probe->func;                               \
                void *__tp_data = __tp_probe->data;                                     \
                                                                                        \
                URCU_FORCE_CAST(void (*)(_TP_ARGS_DATA_PROTO(__VA_ARGS__)), __tp_cb)    \
                                (_TP_ARGS_DATA_VAR(__VA_ARGS__));                       \
        } while ((++__tp_probe)->func);                                                 \
 end:                                                                                   \
-       tp_rcu_read_unlock_bp();                                                        \
+       tp_rcu_read_unlock();                                                           \
 }                                                                                      \
 static inline lttng_ust_notrace                                                                \
 void __tracepoint_register_##_provider##___##_name(char *name,                         \
@@ -204,22 +211,19 @@ extern int __tracepoint_probe_unregister(const char *name, void (*func)(void),
  * tracepoint dynamic linkage handling (callbacks). Hidden visibility:
  * shared across objects in a module/main executable.
  */
-struct tracepoint_dlopen {
+struct lttng_ust_tracepoint_dlopen {
        void *liblttngust_handle;
 
-       int (*tracepoint_register_lib)(struct tracepoint * const *tracepoints_start,
+       int (*tracepoint_register_lib)(struct lttng_ust_tracepoint * const *tracepoints_start,
                int tracepoints_count);
-       int (*tracepoint_unregister_lib)(struct tracepoint * const *tracepoints_start);
-#ifndef _LGPL_SOURCE
-       void (*rcu_read_lock_sym_bp)(void);
-       void (*rcu_read_unlock_sym_bp)(void);
-       void *(*rcu_dereference_sym_bp)(void *p);
-#endif
+       int (*tracepoint_unregister_lib)(struct lttng_ust_tracepoint * const *tracepoints_start);
+       void (*rcu_read_lock_sym)(void);
+       void (*rcu_read_unlock_sym)(void);
+       void *(*rcu_dereference_sym)(void *p);
 };
 
-extern struct tracepoint_dlopen tracepoint_dlopen;
-
-#if defined(TRACEPOINT_DEFINE) || defined(TRACEPOINT_CREATE_PROBES)
+extern struct lttng_ust_tracepoint_dlopen tracepoint_dlopen;
+extern struct lttng_ust_tracepoint_dlopen *tracepoint_dlopen_ptr;
 
 /*
  * These weak symbols, the constructor, and destructor take care of
@@ -230,34 +234,77 @@ int __tracepoint_registered
        __attribute__((weak, visibility("hidden")));
 int __tracepoint_ptrs_registered
        __attribute__((weak, visibility("hidden")));
-struct tracepoint_dlopen tracepoint_dlopen
+struct lttng_ust_tracepoint_dlopen tracepoint_dlopen
+       __attribute__((weak, visibility("hidden")));
+/*
+ * Deal with gcc O1 optimisation issues with weak hidden symbols. gcc
+ * 4.8 and prior does not have the same behavior for symbol scoping on
+ * 32-bit powerpc depending on the object size: symbols for objects of 8
+ * bytes or less have the same address throughout a module, whereas they
+ * have different addresses between compile units for objects larger
+ * than 8 bytes. Add this pointer indirection to ensure that the symbol
+ * scoping match that of the other weak hidden symbols found in this
+ * header.
+ */
+struct lttng_ust_tracepoint_dlopen *tracepoint_dlopen_ptr
+       __attribute__((weak, visibility("hidden")));
+
+/*
+ * Tracepoint dynamic linkage handling (callbacks). Hidden visibility: shared
+ * across objects in a module/main executable. The callbacks are used to
+ * control and check if the destructors should be executed.
+ */
+struct lttng_ust_tracepoint_destructors_syms {
+       void (*tracepoint_disable_destructors)(void);
+       int (*tracepoint_get_destructors_state)(void);
+};
+
+extern struct lttng_ust_tracepoint_destructors_syms tracepoint_destructors_syms;
+extern struct lttng_ust_tracepoint_destructors_syms *tracepoint_destructors_syms_ptr;
+
+struct lttng_ust_tracepoint_destructors_syms tracepoint_destructors_syms
+       __attribute__((weak, visibility("hidden")));
+struct lttng_ust_tracepoint_destructors_syms *tracepoint_destructors_syms_ptr
        __attribute__((weak, visibility("hidden")));
 
+static inline void tracepoint_disable_destructors(void)
+{
+       if (!tracepoint_dlopen_ptr)
+               tracepoint_dlopen_ptr = &tracepoint_dlopen;
+       if (!tracepoint_destructors_syms_ptr)
+               tracepoint_destructors_syms_ptr = &tracepoint_destructors_syms;
+       if (tracepoint_dlopen_ptr->liblttngust_handle
+                       && tracepoint_destructors_syms_ptr->tracepoint_disable_destructors)
+               tracepoint_destructors_syms_ptr->tracepoint_disable_destructors();
+}
+
 #ifndef _LGPL_SOURCE
 static inline void lttng_ust_notrace
 __tracepoint__init_urcu_sym(void);
 static inline void
 __tracepoint__init_urcu_sym(void)
 {
+       if (!tracepoint_dlopen_ptr)
+               tracepoint_dlopen_ptr = &tracepoint_dlopen;
        /*
         * Symbols below are needed by tracepoint call sites and probe
         * providers.
         */
-       if (!tracepoint_dlopen.rcu_read_lock_sym_bp)
-               tracepoint_dlopen.rcu_read_lock_sym_bp =
+       if (!tracepoint_dlopen_ptr->rcu_read_lock_sym)
+               tracepoint_dlopen_ptr->rcu_read_lock_sym =
                        URCU_FORCE_CAST(void (*)(void),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
-                                       "tp_rcu_read_lock_bp"));
-       if (!tracepoint_dlopen.rcu_read_unlock_sym_bp)
-               tracepoint_dlopen.rcu_read_unlock_sym_bp =
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
+                                       "tp_rcu_read_lock"));
+       if (!tracepoint_dlopen_ptr->rcu_read_unlock_sym)
+               tracepoint_dlopen_ptr->rcu_read_unlock_sym =
                        URCU_FORCE_CAST(void (*)(void),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
-                                       "tp_rcu_read_unlock_bp"));
-       if (!tracepoint_dlopen.rcu_dereference_sym_bp)
-               tracepoint_dlopen.rcu_dereference_sym_bp =
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
+                                       "tp_rcu_read_unlock"));
+       if (!tracepoint_dlopen_ptr->rcu_dereference_sym)
+               tracepoint_dlopen_ptr->rcu_dereference_sym =
                        URCU_FORCE_CAST(void *(*)(void *p),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
-                                       "tp_rcu_dereference_sym_bp"));
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
+                                       "tp_rcu_dereference_sym"));
 }
 #else
 static inline void lttng_ust_notrace
@@ -273,13 +320,19 @@ __tracepoints__init(void);
 static void
 __tracepoints__init(void)
 {
-       if (__tracepoint_registered++)
+       if (__tracepoint_registered++) {
+               if (!tracepoint_dlopen_ptr->liblttngust_handle)
+                       return;
+               __tracepoint__init_urcu_sym();
                return;
+       }
 
-       if (!tracepoint_dlopen.liblttngust_handle)
-               tracepoint_dlopen.liblttngust_handle =
-                       dlopen("liblttng-ust-tracepoint.so.0", RTLD_NOW | RTLD_GLOBAL);
-       if (!tracepoint_dlopen.liblttngust_handle)
+       if (!tracepoint_dlopen_ptr)
+               tracepoint_dlopen_ptr = &tracepoint_dlopen;
+       if (!tracepoint_dlopen_ptr->liblttngust_handle)
+               tracepoint_dlopen_ptr->liblttngust_handle =
+                       dlopen("liblttng-ust-tracepoint.so.1", RTLD_NOW | RTLD_GLOBAL);
+       if (!tracepoint_dlopen_ptr->liblttngust_handle)
                return;
        __tracepoint__init_urcu_sym();
 }
@@ -293,18 +346,34 @@ __tracepoints__destroy(void)
 
        if (--__tracepoint_registered)
                return;
-       if (tracepoint_dlopen.liblttngust_handle && !__tracepoint_ptrs_registered) {
-               ret = dlclose(tracepoint_dlopen.liblttngust_handle);
-               if (ret) {
-                       fprintf(stderr, "Error (%d) in dlclose\n", ret);
-                       abort();
-               }
-               memset(&tracepoint_dlopen, 0, sizeof(tracepoint_dlopen));
+       if (!tracepoint_dlopen_ptr)
+               tracepoint_dlopen_ptr = &tracepoint_dlopen;
+       if (!tracepoint_destructors_syms_ptr)
+               tracepoint_destructors_syms_ptr = &tracepoint_destructors_syms;
+       if (!tracepoint_dlopen_ptr->liblttngust_handle)
+               return;
+       if (__tracepoint_ptrs_registered)
+               return;
+       /*
+        * Lookup if destructors must be executed using the new method.
+        */
+       if (tracepoint_destructors_syms_ptr->tracepoint_get_destructors_state
+               && !tracepoint_destructors_syms_ptr->tracepoint_get_destructors_state()) {
+               /*
+                * The tracepoint_get_destructors_state symbol was found with
+                * dlsym but its returned value is 0 meaning that destructors
+                * must not be executed.
+                */
+               return;
+       }
+       ret = dlclose(tracepoint_dlopen_ptr->liblttngust_handle);
+       if (ret) {
+               fprintf(stderr, "Error (%d) in dlclose\n", ret);
+               abort();
        }
+       memset(tracepoint_dlopen_ptr, 0, sizeof(*tracepoint_dlopen_ptr));
 }
 
-#endif
-
 #ifdef TRACEPOINT_DEFINE
 
 /*
@@ -312,9 +381,9 @@ __tracepoints__destroy(void)
  * registering only _one_ instance of the tracepoints per shared-ojbect
  * (or for the whole main program).
  */
-extern struct tracepoint * const __start___tracepoints_ptrs[]
+extern struct lttng_ust_tracepoint * const __start___tracepoints_ptrs[]
        __attribute__((weak, visibility("hidden")));
-extern struct tracepoint * const __stop___tracepoints_ptrs[]
+extern struct lttng_ust_tracepoint * const __stop___tracepoints_ptrs[]
        __attribute__((weak, visibility("hidden")));
 
 /*
@@ -344,7 +413,7 @@ extern struct tracepoint * const __stop___tracepoints_ptrs[]
        static const char __tp_strtab_##_provider##___##_name[]                 \
                __attribute__((section("__tracepoints_strings"))) =             \
                        #_provider ":" #_name;                                  \
-       struct tracepoint __tracepoint_##_provider##___##_name                  \
+       struct lttng_ust_tracepoint __tracepoint_##_provider##___##_name        \
                __attribute__((section("__tracepoints"))) =                     \
                {                                                               \
                        __tp_strtab_##_provider##___##_name,                    \
@@ -354,8 +423,10 @@ extern struct tracepoint * const __stop___tracepoints_ptrs[]
                        _TP_EXTRACT_STRING(_args),                              \
                        { },                                                    \
                };                                                              \
-       static struct tracepoint * __tracepoint_ptr_##_provider##___##_name     \
-               __attribute__((used, section("__tracepoints_ptrs"))) =          \
+       static struct lttng_ust_tracepoint *                                    \
+               __tracepoint_ptr_##_provider##___##_name                        \
+               __attribute__((section("__tracepoints_ptrs"), used))            \
+               __lttng_ust_variable_attribute_no_sanitize_address =            \
                        &__tracepoint_##_provider##___##_name;
 
 static void lttng_ust_notrace __attribute__((constructor))
@@ -365,22 +436,34 @@ __tracepoints__ptrs_init(void)
 {
        if (__tracepoint_ptrs_registered++)
                return;
-       if (!tracepoint_dlopen.liblttngust_handle)
-               tracepoint_dlopen.liblttngust_handle =
-                       dlopen("liblttng-ust-tracepoint.so.0", RTLD_NOW | RTLD_GLOBAL);
-       if (!tracepoint_dlopen.liblttngust_handle)
+       if (!tracepoint_dlopen_ptr)
+               tracepoint_dlopen_ptr = &tracepoint_dlopen;
+       if (!tracepoint_dlopen_ptr->liblttngust_handle)
+               tracepoint_dlopen_ptr->liblttngust_handle =
+                       dlopen("liblttng-ust-tracepoint.so.1", RTLD_NOW | RTLD_GLOBAL);
+       if (!tracepoint_dlopen_ptr->liblttngust_handle)
                return;
-       tracepoint_dlopen.tracepoint_register_lib =
-               URCU_FORCE_CAST(int (*)(struct tracepoint * const *, int),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
+       if (!tracepoint_destructors_syms_ptr)
+               tracepoint_destructors_syms_ptr = &tracepoint_destructors_syms;
+       tracepoint_dlopen_ptr->tracepoint_register_lib =
+               URCU_FORCE_CAST(int (*)(struct lttng_ust_tracepoint * const *, int),
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
                                        "tracepoint_register_lib"));
-       tracepoint_dlopen.tracepoint_unregister_lib =
-               URCU_FORCE_CAST(int (*)(struct tracepoint * const *),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
+       tracepoint_dlopen_ptr->tracepoint_unregister_lib =
+               URCU_FORCE_CAST(int (*)(struct lttng_ust_tracepoint * const *),
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
                                        "tracepoint_unregister_lib"));
+       tracepoint_destructors_syms_ptr->tracepoint_disable_destructors =
+               URCU_FORCE_CAST(void (*)(void),
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
+                                       "tp_disable_destructors"));
+       tracepoint_destructors_syms_ptr->tracepoint_get_destructors_state =
+               URCU_FORCE_CAST(int (*)(void),
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
+                                       "tp_get_destructors_state"));
        __tracepoint__init_urcu_sym();
-       if (tracepoint_dlopen.tracepoint_register_lib) {
-               tracepoint_dlopen.tracepoint_register_lib(__start___tracepoints_ptrs,
+       if (tracepoint_dlopen_ptr->tracepoint_register_lib) {
+               tracepoint_dlopen_ptr->tracepoint_register_lib(__start___tracepoints_ptrs,
                                __stop___tracepoints_ptrs -
                                __start___tracepoints_ptrs);
        }
@@ -395,15 +478,22 @@ __tracepoints__ptrs_destroy(void)
 
        if (--__tracepoint_ptrs_registered)
                return;
-       if (tracepoint_dlopen.tracepoint_unregister_lib)
-               tracepoint_dlopen.tracepoint_unregister_lib(__start___tracepoints_ptrs);
-       if (tracepoint_dlopen.liblttngust_handle && !__tracepoint_registered) {
-               ret = dlclose(tracepoint_dlopen.liblttngust_handle);
+       if (!tracepoint_dlopen_ptr)
+               tracepoint_dlopen_ptr = &tracepoint_dlopen;
+       if (!tracepoint_destructors_syms_ptr)
+               tracepoint_destructors_syms_ptr = &tracepoint_destructors_syms;
+       if (tracepoint_dlopen_ptr->tracepoint_unregister_lib)
+               tracepoint_dlopen_ptr->tracepoint_unregister_lib(__start___tracepoints_ptrs);
+       if (tracepoint_dlopen_ptr->liblttngust_handle
+                       && tracepoint_destructors_syms_ptr->tracepoint_get_destructors_state
+                       && tracepoint_destructors_syms_ptr->tracepoint_get_destructors_state()
+                       && !__tracepoint_ptrs_registered) {
+               ret = dlclose(tracepoint_dlopen_ptr->liblttngust_handle);
                if (ret) {
                        fprintf(stderr, "Error (%d) in dlclose\n", ret);
                        abort();
                }
-               memset(&tracepoint_dlopen, 0, sizeof(tracepoint_dlopen));
+               memset(tracepoint_dlopen_ptr, 0, sizeof(*tracepoint_dlopen_ptr));
        }
 }
 
@@ -421,13 +511,57 @@ __tracepoints__ptrs_destroy(void)
 
 /* The following declarations must be outside re-inclusion protection. */
 
+#ifndef TRACEPOINT_ENUM
+
+/*
+ * Tracepoint Enumerations
+ *
+ * The enumeration is a mapping between an integer, or range of integers, and
+ * a string. It can be used to have a more compact trace in cases where the
+ * possible values for a field are limited:
+ *
+ * An example:
+ *
+ * TRACEPOINT_ENUM(someproject_component, enumname,
+ *     TP_ENUM_VALUES(
+ *             ctf_enum_value("even", 0)
+ *             ctf_enum_value("uneven", 1)
+ *             ctf_enum_range("twoto4", 2, 4)
+ *             ctf_enum_value("five", 5)
+ *     )
+ * )
+ *
+ * Where "someproject_component" is the name of the component this enumeration
+ * belongs to and "enumname" identifies this enumeration. Inside the
+ * TP_ENUM_VALUES macro is the actual mapping. Each string value can map
+ * to either a single value with ctf_enum_value or a range of values
+ * with ctf_enum_range.
+ *
+ * Enumeration ranges may overlap, but the behavior is implementation-defined,
+ * each trace reader will handle overlapping as it wishes.
+ *
+ * That enumeration can then be used in a field inside the TP_FIELD macro using
+ * the following line:
+ *
+ * ctf_enum(someproject_component, enumname, enumtype, enumfield, enumval)
+ *
+ * Where "someproject_component" and "enumname" match those in the
+ * TRACEPOINT_ENUM, "enumtype" is a signed or unsigned integer type
+ * backing the enumeration, "enumfield" is the name of the field and
+ * "enumval" is the value.
+ */
+
+#define TRACEPOINT_ENUM(provider, name, values)
+
+#endif /* #ifndef TRACEPOINT_ENUM */
+
 #ifndef TRACEPOINT_EVENT
 
 /*
  * How to use the TRACEPOINT_EVENT macro:
  *
  * An example:
- * 
+ *
  * TRACEPOINT_EVENT(someproject_component, event_name,
  *
  *     * TP_ARGS takes from 0 to 10 "type, field_name" pairs *
@@ -438,20 +572,23 @@ __tracepoints__ptrs_destroy(void)
  *     * TP_FIELDS describes the event payload layout in the trace *
  *
  *     TP_FIELDS(
- *         * Integer, printed in base 10 * 
+ *         * Integer, printed in base 10 *
  *         ctf_integer(int, field_a, arg0)
  *
- *         * Integer, printed with 0x base 16 * 
+ *         * Integer, printed with 0x base 16 *
  *         ctf_integer_hex(unsigned long, field_d, arg1)
  *
- *         * Array Sequence, printed as UTF8-encoded array of bytes * 
+ *         * Enumeration *
+ *         ctf_enum(someproject_component, enum_name, int, field_e, arg0)
+ *
+ *         * Array Sequence, printed as UTF8-encoded array of bytes *
  *         ctf_array_text(char, field_b, string, FIXED_LEN)
  *         ctf_sequence_text(char, field_c, string, size_t, strlen)
  *
- *         * String, printed as UTF8-encoded string * 
+ *         * String, printed as UTF8-encoded string *
  *         ctf_string(field_e, string)
  *
- *         * Array sequence of signed integer values * 
+ *         * Array sequence of signed integer values *
  *         ctf_array(long, field_f, arg4, FIXED_LEN4)
  *         ctf_sequence(long, field_g, arg4, size_t, arg4_len)
  *     )
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