Fix: tracepoint.h incorrect assumption about constructor order

Incorrect assumption about constructor execution order can trigger a
segfault when trying to execute tracepoint_register_lib.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/include/lttng/tracepoint.h b/include/lttng/tracepoint.h
index fb635c111327e86a20a6898d364f3e175acb9a85..0629af23e67e21f121478e1da3cbaff869c249e6 100644 (file)
--- a/include/lttng/tracepoint.h
+++ b/include/lttng/tracepoint.h
@@ -227,6 +227,41 @@ int __tracepoint_ptrs_registered
 struct tracepoint_dlopen tracepoint_dlopen
        __attribute__((weak, visibility("hidden")));
 
+#ifndef _LGPL_SOURCE
+static inline void lttng_ust_notrace
+__tracepoint__init_urcu_sym(void);
+static inline void
+__tracepoint__init_urcu_sym(void)
+{
+       /*
+        * 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 =
+                       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 =
+                       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 =
+                       URCU_FORCE_CAST(void *(*)(void *p),
+                               dlsym(tracepoint_dlopen.liblttngust_handle,
+                                       "tp_rcu_dereference_sym_bp"));
+}
+#else
+static inline void lttng_ust_notrace
+__tracepoint__init_urcu_sym(void);
+static inline void
+__tracepoint__init_urcu_sym(void)
+{
+}
+#endif
+
 static void lttng_ust_notrace __attribute__((constructor))
 __tracepoints__init(void);
 static void
@@ -240,28 +275,7 @@ __tracepoints__init(void)
                        dlopen("liblttng-ust-tracepoint.so.0", RTLD_NOW | RTLD_GLOBAL);
        if (!tracepoint_dlopen.liblttngust_handle)
                return;
-       tracepoint_dlopen.tracepoint_register_lib =
-               URCU_FORCE_CAST(int (*)(struct tracepoint * const *, int),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
-                                       "tracepoint_register_lib"));
-       tracepoint_dlopen.tracepoint_unregister_lib =
-               URCU_FORCE_CAST(int (*)(struct tracepoint * const *),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
-                                       "tracepoint_unregister_lib"));
-#ifndef _LGPL_SOURCE
-       tracepoint_dlopen.rcu_read_lock_sym_bp =
-               URCU_FORCE_CAST(void (*)(void),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
-                                       "tp_rcu_read_lock_bp"));
-       tracepoint_dlopen.rcu_read_unlock_sym_bp =
-               URCU_FORCE_CAST(void (*)(void),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
-                                       "tp_rcu_read_unlock_bp"));
-       tracepoint_dlopen.rcu_dereference_sym_bp =
-               URCU_FORCE_CAST(void *(*)(void *p),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
-                                       "tp_rcu_dereference_sym_bp"));
-#endif
+       __tracepoint__init_urcu_sym();
 }
 
 static void lttng_ust_notrace __attribute__((destructor))
@@ -346,9 +360,20 @@ __tracepoints__ptrs_init(void)
                        dlopen("liblttng-ust-tracepoint.so.0", RTLD_NOW | RTLD_GLOBAL);
        if (!tracepoint_dlopen.liblttngust_handle)
                return;
-       tracepoint_dlopen.tracepoint_register_lib(__start___tracepoints_ptrs,
+       tracepoint_dlopen.tracepoint_register_lib =
+               URCU_FORCE_CAST(int (*)(struct tracepoint * const *, int),
+                               dlsym(tracepoint_dlopen.liblttngust_handle,
+                                       "tracepoint_register_lib"));
+       tracepoint_dlopen.tracepoint_unregister_lib =
+               URCU_FORCE_CAST(int (*)(struct tracepoint * const *),
+                               dlsym(tracepoint_dlopen.liblttngust_handle,
+                                       "tracepoint_unregister_lib"));
+       __tracepoint__init_urcu_sym();
+       if (tracepoint_dlopen.tracepoint_register_lib) {
+               tracepoint_dlopen.tracepoint_register_lib(__start___tracepoints_ptrs,
                                __stop___tracepoints_ptrs -
                                __start___tracepoints_ptrs);
+       }
 }
 
 static void lttng_ust_notrace __attribute__((destructor))