Allow weak binding from instrumented apps to liblttng-ust

[lttng-ust.git] / include / lttng / tracepoint.h

diff --git a/include/lttng/tracepoint.h b/include/lttng/tracepoint.h
index dc7832cb25531b1912d2e0449976da8a58ce5cd3..831447dd64643dc754ec0aa6ad9cd39a12ce7d36 100644 (file)
--- a/include/lttng/tracepoint.h
+++ b/include/lttng/tracepoint.h
@@ -17,6 +17,7 @@
 #include <urcu-bp.h>
 #include <tracepoint-types.h>
 #include <urcu/compiler.h>
+#include <dlfcn.h>     /* for dlopen */
 
 #ifdef __cplusplus
 extern "C" {
@@ -108,8 +109,10 @@ static inline void __tracepoint_cb_##provider##___##name(_TP_ARGS_PROTO(__VA_ARG
 {                                                                                      \
        struct tracepoint_probe *__tp_probe;                                            \
                                                                                        \
+       if (!rcu_read_lock_bp)                                                          \
+               return;                                                                 \
        rcu_read_lock_bp();                                                             \
-       __tp_probe = rcu_dereference(__tracepoint_##provider##___##name.probes);        \
+       __tp_probe = rcu_dereference_bp(__tracepoint_##provider##___##name.probes);     \
        if (caa_unlikely(!__tp_probe))                                                  \
                goto end;                                                               \
        do {                                                                            \
@@ -133,6 +136,11 @@ static inline void __tracepoint_unregister_##provider##___##name(char *name,               \
        __tracepoint_probe_unregister(name, func, data);                                \
 }
 
+extern int __tracepoint_probe_register(const char *name, void *func, void *data);
+extern int __tracepoint_probe_unregister(const char *name, void *func, void *data);
+
+#ifdef TRACEPOINT_DEFINE
+
 /*
  * Note: to allow PIC code, we need to allow the linker to update the pointers
  * in the __tracepoints_ptrs section.
@@ -149,11 +157,10 @@ static inline void __tracepoint_unregister_##provider##___##name(char *name,              \
                __attribute__((used, section("__tracepoints_ptrs"))) =          \
                        &__tracepoint_##provider##___##name;
 
-extern int __tracepoint_probe_register(const char *name, void *func, void *data);
-extern int __tracepoint_probe_unregister(const char *name, void *func, void *data);
-extern int tracepoint_register_lib(struct tracepoint * const *tracepoints_start,
+static int (*tracepoint_register_lib)(struct tracepoint * const *tracepoints_start,
                int tracepoints_count);
-extern int tracepoint_unregister_lib(struct tracepoint * const *tracepoints_start);
+static int (*tracepoint_unregister_lib)(struct tracepoint * const *tracepoints_start);
+static void *liblttngust_handle;
 
 /*
  * These weak symbols, the constructor, and destructor take care of
@@ -171,6 +178,14 @@ static void __attribute__((constructor)) __tracepoints__init(void)
 {
        if (__tracepoint_registered++)
                return;
+
+       liblttngust_handle = dlopen("liblttng-ust.so", RTLD_NOW | RTLD_GLOBAL);
+       if (!liblttngust_handle)
+               return;
+       tracepoint_register_lib = dlsym(liblttngust_handle,
+                                       "tracepoint_register_lib");
+       tracepoint_unregister_lib = dlsym(liblttngust_handle,
+                                       "tracepoint_unregister_lib");
        tracepoint_register_lib(__start___tracepoints_ptrs,
                                __stop___tracepoints_ptrs -
                                __start___tracepoints_ptrs);
@@ -178,11 +193,25 @@ static void __attribute__((constructor)) __tracepoints__init(void)
 
 static void __attribute__((destructor)) __tracepoints__destroy(void)
 {
+       int ret;
        if (--__tracepoint_registered)
                return;
-       tracepoint_unregister_lib(__start___tracepoints_ptrs);
+       if (tracepoint_unregister_lib)
+               tracepoint_unregister_lib(__start___tracepoints_ptrs);
+       if (liblttngust_handle) {
+               tracepoint_unregister_lib = NULL;
+               tracepoint_register_lib = NULL;
+               ret = dlclose(liblttngust_handle);
+               assert(!ret);
+       }
 }
 
+#else /* TRACEPOINT_DEFINE */
+
+#define _DEFINE_TRACEPOINT(provider, name)
+
+#endif /* #else TRACEPOINT_DEFINE */
+
 #ifdef __cplusplus
 }
 #endif
@@ -273,12 +302,14 @@ static void __attribute__((destructor)) __tracepoints__destroy(void)
  */
 
 #define TRACEPOINT_EVENT(provider, name, args, fields)                 \
-       _DECLARE_TRACEPOINT(provider, name, _TP_PARAMS(args))
+       _DECLARE_TRACEPOINT(provider, name, _TP_PARAMS(args))           \
+       _DEFINE_TRACEPOINT(provider, name)
 
 #define TRACEPOINT_EVENT_CLASS(provider, name, args, fields)
 
 #define TRACEPOINT_EVENT_INSTANCE(provider, _template, name, args)     \
-       _DECLARE_TRACEPOINT(provider, name, _TP_PARAMS(args))
+       _DECLARE_TRACEPOINT(provider, name, _TP_PARAMS(args))           \
+       _DEFINE_TRACEPOINT(provider, name)
 
 #endif /* #ifndef TRACEPOINT_EVENT */