Fix: tracepoint instrumentation constructor order issue

If the linker decides to run a constructor from a tracepoint probe
before the constructor from the application, a recent modification
(commit 558b9d86247004f8e9bbaf8c982f3b2b182093d1) allowed that the wrong
constructor execution order could prohibit the program's tracepoints
from being registered.

Fix this by making two separate constructors.

Fixes #487

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

diff --git a/include/lttng/tracepoint.h b/include/lttng/tracepoint.h
index 785c87e516904017948d0227e034a2b5f2b5711f..fb635c111327e86a20a6898d364f3e175acb9a85 100644 (file)
--- a/include/lttng/tracepoint.h
+++ b/include/lttng/tracepoint.h
@@ -213,6 +213,75 @@ struct tracepoint_dlopen {
 
 extern struct tracepoint_dlopen tracepoint_dlopen;
 
+#if defined(TRACEPOINT_DEFINE) || defined(TRACEPOINT_CREATE_PROBES)
+
+/*
+ * These weak symbols, the constructor, and destructor take care of
+ * registering only _one_ instance of the tracepoints per shared-ojbect
+ * (or for the whole main program).
+ */
+int __tracepoint_registered
+       __attribute__((weak, visibility("hidden")));
+int __tracepoint_ptrs_registered
+       __attribute__((weak, visibility("hidden")));
+struct tracepoint_dlopen tracepoint_dlopen
+       __attribute__((weak, visibility("hidden")));
+
+static void lttng_ust_notrace __attribute__((constructor))
+__tracepoints__init(void);
+static void
+__tracepoints__init(void)
+{
+       if (__tracepoint_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)
+               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
+}
+
+static void lttng_ust_notrace __attribute__((destructor))
+__tracepoints__destroy(void);
+static void
+__tracepoints__destroy(void)
+{
+       int ret;
+
+       if (--__tracepoint_registered)
+               return;
+       if (tracepoint_dlopen.liblttngust_handle && !__tracepoint_ptrs_registered) {
+               ret = dlclose(tracepoint_dlopen.liblttngust_handle);
+               assert(!ret);
+               memset(&tracepoint_dlopen, 0, sizeof(tracepoint_dlopen));
+       }
+}
+
+#endif
+
 #ifdef TRACEPOINT_DEFINE
 
 /*
@@ -265,101 +334,46 @@ extern struct tracepoint * const __stop___tracepoints_ptrs[]
                __attribute__((used, section("__tracepoints_ptrs"))) =          \
                        &__tracepoint_##_provider##___##_name;
 
-static inline void __tracepoints__init_define(void)
-{
-       tracepoint_dlopen.tracepoint_register_lib(__start___tracepoints_ptrs,
-                               __stop___tracepoints_ptrs -
-                               __start___tracepoints_ptrs);
-}
-
-static inline void __tracepoints__destroy_define(void)
-{
-       if (tracepoint_dlopen.tracepoint_unregister_lib)
-               tracepoint_dlopen.tracepoint_unregister_lib(__start___tracepoints_ptrs);
-}
-
-
-#else /* TRACEPOINT_DEFINE */
-
-#define _DEFINE_TRACEPOINT(_provider, _name, _args)
-
-static inline void __tracepoints__init_define(void)
-{
-}
-
-static inline void __tracepoints__destroy_define(void)
-{
-}
-
-#endif /* #else TRACEPOINT_DEFINE */
-
-#if defined(TRACEPOINT_DEFINE) || defined(TRACEPOINT_CREATE_PROBES)
-
-/*
- * These weak symbols, the constructor, and destructor take care of
- * registering only _one_ instance of the tracepoints per shared-ojbect
- * (or for the whole main program).
- */
-int __tracepoint_registered
-       __attribute__((weak, visibility("hidden")));
-struct tracepoint_dlopen tracepoint_dlopen
-       __attribute__((weak, visibility("hidden")));
-
 static void lttng_ust_notrace __attribute__((constructor))
-__tracepoints__init(void);
+__tracepoints__ptrs_init(void);
 static void
-__tracepoints__init(void)
+__tracepoints__ptrs_init(void)
 {
-       if (__tracepoint_registered++)
+       if (__tracepoint_ptrs_registered++)
                return;
-
-       tracepoint_dlopen.liblttngust_handle =
-               dlopen("liblttng-ust-tracepoint.so.0", RTLD_NOW | RTLD_GLOBAL);
+       if (!tracepoint_dlopen.liblttngust_handle)
+               tracepoint_dlopen.liblttngust_handle =
+                       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
-       __tracepoints__init_define();
+       tracepoint_dlopen.tracepoint_register_lib(__start___tracepoints_ptrs,
+                               __stop___tracepoints_ptrs -
+                               __start___tracepoints_ptrs);
 }
 
 static void lttng_ust_notrace __attribute__((destructor))
-__tracepoints__destroy(void);
+__tracepoints__ptrs_destroy(void);
 static void
-__tracepoints__destroy(void)
+__tracepoints__ptrs_destroy(void)
 {
        int ret;
 
-       if (--__tracepoint_registered)
+       if (--__tracepoint_ptrs_registered)
                return;
-       __tracepoints__destroy_define();
-       if (tracepoint_dlopen.liblttngust_handle) {
+       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);
                assert(!ret);
                memset(&tracepoint_dlopen, 0, sizeof(tracepoint_dlopen));
        }
 }
 
-#endif
+#else /* TRACEPOINT_DEFINE */
+
+#define _DEFINE_TRACEPOINT(_provider, _name, _args)
+
+#endif /* #else TRACEPOINT_DEFINE */
 
 #ifdef __cplusplus
 }