Fix tracepoint.h multiple .o within module/core exec linkage bug

We need all symbols looked up with dlopen to share the same linkage
property as the __tracepoint_registered variable (shared across .o in a
module/executable), otherwise only the first .o which runs its
constructor will have those defined.

Caused some tracepoints not to be traced in non-_LGPL_SOURCE
applications, due to the check:

if (!TP_RCU_LINK_TEST())   \
    return;

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

diff --git a/include/lttng/tracepoint-rcu.h b/include/lttng/tracepoint-rcu.h
index 852cfe48d55ee630d588a7ed64d822142e3c7561..23dab7d6c9b47e9838e719d00a479dff315d4cfc 100644 (file)
--- a/include/lttng/tracepoint-rcu.h
+++ b/include/lttng/tracepoint-rcu.h
@@ -23,27 +23,25 @@
 
 #include <urcu-bp.h>
 
-#define TP_RCU_LINK_TEST()     1
 #define tp_rcu_read_lock_bp    rcu_read_lock_bp
 #define tp_rcu_read_unlock_bp  rcu_read_unlock_bp
 #define tp_rcu_dereference_bp  rcu_dereference_bp
+#define TP_RCU_LINK_TEST()     1
 
 #else  /* _LGPL_SOURCE */
 
-#define TP_RCU_LINK_TEST()     tp_rcu_read_lock_bp
-
-/* Symbols looked up with dlsym */
-static void (*tp_rcu_read_lock_bp)(void) __attribute__((unused));
-static void (*tp_rcu_read_unlock_bp)(void) __attribute__((unused));
-static void *(*tp_rcu_dereference_sym_bp)(void *p) __attribute__((unused));
+#define tp_rcu_read_lock_bp    tracepoint_dlopen.rcu_read_lock_sym_bp
+#define tp_rcu_read_unlock_bp  tracepoint_dlopen.rcu_read_unlock_sym_bp
 
 #define tp_rcu_dereference_bp(p)                                            \
        ({                                                                   \
                typeof(p) _________p1 = URCU_FORCE_CAST(typeof(p),           \
-                       tp_rcu_dereference_sym_bp(URCU_FORCE_CAST(void *, p))); \
+                       tracepoint_dlopen.rcu_dereference_sym_bp(URCU_FORCE_CAST(void *, p))); \
                (_________p1);                                               \
        })
 
+#define TP_RCU_LINK_TEST()     tp_rcu_read_lock_bp
+
 #endif /* _LGPL_SOURCE */
 
 #endif /* _LTTNG_TRACEPOINT_RCU_H */

diff --git a/include/lttng/tracepoint.h b/include/lttng/tracepoint.h
index fe18c5b7e4a60a78d9fd721bdcfb5276912696fe..e4941b5a575d35402798c8f9cef65a541d7ed689 100644 (file)
--- a/include/lttng/tracepoint.h
+++ b/include/lttng/tracepoint.h
@@ -18,6 +18,7 @@
 #include <lttng/tracepoint-rcu.h>
 #include <urcu/compiler.h>
 #include <dlfcn.h>     /* for dlopen */
+#include <string.h>    /* for memset */
 #include <assert.h>
 
 #ifdef __cplusplus
@@ -150,6 +151,25 @@ static inline void __tracepoint_unregister_##_provider##___##_name(char *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);
 
+/*
+ * tracepoint dynamic linkage handling (callbacks). Hidden visibility:
+ * shared across objects in a module/main executable.
+ */
+struct tracepoint_dlopen {
+       void *liblttngust_handle;
+
+       int (*tracepoint_register_lib)(struct 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
+};
+
+extern struct tracepoint_dlopen tracepoint_dlopen;
+
 #ifdef TRACEPOINT_DEFINE
 
 /*
@@ -185,11 +205,6 @@ extern int __tracepoint_probe_unregister(const char *name, void *func, void *dat
                __attribute__((used, section("__tracepoints_ptrs"))) =          \
                        &__tracepoint_##provider##___##name;
 
-static int (*tracepoint_register_lib)(struct tracepoint * const *tracepoints_start,
-               int tracepoints_count);
-static int (*tracepoint_unregister_lib)(struct tracepoint * const *tracepoints_start);
-static void *liblttngust_handle;
-
 /*
  * These weak symbols, the constructor, and destructor take care of
  * registering only _one_ instance of the tracepoints per shared-ojbect
@@ -201,38 +216,41 @@ extern struct tracepoint * const __stop___tracepoints_ptrs[]
        __attribute__((weak, visibility("hidden")));
 int __tracepoint_registered
        __attribute__((weak, visibility("hidden")));
+struct tracepoint_dlopen tracepoint_dlopen
+       __attribute__((weak, visibility("hidden")));
 
 static void __attribute__((constructor)) __tracepoints__init(void)
 {
        if (__tracepoint_registered++)
                return;
 
-       liblttngust_handle = dlopen("liblttng-ust-tracepoint.so.0", RTLD_NOW | RTLD_GLOBAL);
-       if (!liblttngust_handle)
+       tracepoint_dlopen.liblttngust_handle =
+               dlopen("liblttng-ust-tracepoint.so.0", RTLD_NOW | RTLD_GLOBAL);
+       if (!tracepoint_dlopen.liblttngust_handle)
                return;
-       tracepoint_register_lib =
+       tracepoint_dlopen.tracepoint_register_lib =
                URCU_FORCE_CAST(int (*)(struct tracepoint * const *, int),
-                               dlsym(liblttngust_handle,
+                               dlsym(tracepoint_dlopen.liblttngust_handle,
                                        "tracepoint_register_lib"));
-       tracepoint_unregister_lib =
+       tracepoint_dlopen.tracepoint_unregister_lib =
                URCU_FORCE_CAST(int (*)(struct tracepoint * const *),
-                               dlsym(liblttngust_handle,
+                               dlsym(tracepoint_dlopen.liblttngust_handle,
                                        "tracepoint_unregister_lib"));
 #ifndef _LGPL_SOURCE
-       tp_rcu_read_lock_bp =
+       tracepoint_dlopen.rcu_read_lock_sym_bp =
                URCU_FORCE_CAST(void (*)(void),
-                               dlsym(liblttngust_handle,
+                               dlsym(tracepoint_dlopen.liblttngust_handle,
                                        "tp_rcu_read_lock_bp"));
-       tp_rcu_read_unlock_bp =
+       tracepoint_dlopen.rcu_read_unlock_sym_bp =
                URCU_FORCE_CAST(void (*)(void),
-                               dlsym(liblttngust_handle,
+                               dlsym(tracepoint_dlopen.liblttngust_handle,
                                        "tp_rcu_read_unlock_bp"));
-       tp_rcu_dereference_sym_bp =
+       tracepoint_dlopen.rcu_dereference_sym_bp =
                URCU_FORCE_CAST(void *(*)(void *p),
-                               dlsym(liblttngust_handle,
+                               dlsym(tracepoint_dlopen.liblttngust_handle,
                                        "tp_rcu_dereference_sym_bp"));
 #endif
-       tracepoint_register_lib(__start___tracepoints_ptrs,
+       tracepoint_dlopen.tracepoint_register_lib(__start___tracepoints_ptrs,
                                __stop___tracepoints_ptrs -
                                __start___tracepoints_ptrs);
 }
@@ -240,15 +258,15 @@ static void __attribute__((constructor)) __tracepoints__init(void)
 static void __attribute__((destructor)) __tracepoints__destroy(void)
 {
        int ret;
+
        if (--__tracepoint_registered)
                return;
-       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);
+       if (tracepoint_dlopen.tracepoint_unregister_lib)
+               tracepoint_dlopen.tracepoint_unregister_lib(__start___tracepoints_ptrs);
+       if (tracepoint_dlopen.liblttngust_handle) {
+               ret = dlclose(tracepoint_dlopen.liblttngust_handle);
                assert(!ret);
+               memset(&tracepoint_dlopen, 0, sizeof(tracepoint_dlopen));
        }
 }