Fix: work-around gcc optimisation oddness on 32-bit powerpc

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 tracepoint.h.

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

diff --git a/include/lttng/tracepoint.h b/include/lttng/tracepoint.h
index ed20594497ab65bab366b594bb965e740d3e9b29..418857a8d6cd2cbaab98f9f65c391deac641dbff 100644 (file)
--- a/include/lttng/tracepoint.h
+++ b/include/lttng/tracepoint.h
@@ -255,6 +255,18 @@ int __tracepoint_ptrs_registered
        __attribute__((weak, visibility("hidden")));
 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")));
 
 #ifndef _LGPL_SOURCE
 static inline void lttng_ust_notrace
@@ -262,24 +274,26 @@ __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_bp)
+               tracepoint_dlopen_ptr->rcu_read_lock_sym_bp =
                        URCU_FORCE_CAST(void (*)(void),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
                                        "tp_rcu_read_lock_bp"));
-       if (!tracepoint_dlopen.rcu_read_unlock_sym_bp)
-               tracepoint_dlopen.rcu_read_unlock_sym_bp =
+       if (!tracepoint_dlopen_ptr->rcu_read_unlock_sym_bp)
+               tracepoint_dlopen_ptr->rcu_read_unlock_sym_bp =
                        URCU_FORCE_CAST(void (*)(void),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
                                        "tp_rcu_read_unlock_bp"));
-       if (!tracepoint_dlopen.rcu_dereference_sym_bp)
-               tracepoint_dlopen.rcu_dereference_sym_bp =
+       if (!tracepoint_dlopen_ptr->rcu_dereference_sym_bp)
+               tracepoint_dlopen_ptr->rcu_dereference_sym_bp =
                        URCU_FORCE_CAST(void *(*)(void *p),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
                                        "tp_rcu_dereference_sym_bp"));
 }
 #else
@@ -299,10 +313,12 @@ __tracepoints__init(void)
        if (__tracepoint_registered++)
                return;
 
-       if (!tracepoint_dlopen.liblttngust_handle)
-               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.0", RTLD_NOW | RTLD_GLOBAL);
-       if (!tracepoint_dlopen.liblttngust_handle)
+       if (!tracepoint_dlopen_ptr->liblttngust_handle)
                return;
        __tracepoint__init_urcu_sym();
 }
@@ -316,15 +332,17 @@ __tracepoints__destroy(void)
 
        if (--__tracepoint_registered)
                return;
+       if (!tracepoint_dlopen_ptr)
+               tracepoint_dlopen_ptr = &tracepoint_dlopen;
        if (!__tracepoints__disable_destructors
-                       && tracepoint_dlopen.liblttngust_handle
+                       && tracepoint_dlopen_ptr->liblttngust_handle
                        && !__tracepoint_ptrs_registered) {
-               ret = dlclose(tracepoint_dlopen.liblttngust_handle);
+               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));
        }
 }
 
@@ -391,22 +409,24 @@ __tracepoints__ptrs_init(void)
 {
        if (__tracepoint_ptrs_registered++)
                return;
-       if (!tracepoint_dlopen.liblttngust_handle)
-               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.0", RTLD_NOW | RTLD_GLOBAL);
-       if (!tracepoint_dlopen.liblttngust_handle)
+       if (!tracepoint_dlopen_ptr->liblttngust_handle)
                return;
-       tracepoint_dlopen.tracepoint_register_lib =
+       tracepoint_dlopen_ptr->tracepoint_register_lib =
                URCU_FORCE_CAST(int (*)(struct lttng_ust_tracepoint * const *, int),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
                                        "tracepoint_register_lib"));
-       tracepoint_dlopen.tracepoint_unregister_lib =
+       tracepoint_dlopen_ptr->tracepoint_unregister_lib =
                URCU_FORCE_CAST(int (*)(struct lttng_ust_tracepoint * const *),
-                               dlsym(tracepoint_dlopen.liblttngust_handle,
+                               dlsym(tracepoint_dlopen_ptr->liblttngust_handle,
                                        "tracepoint_unregister_lib"));
        __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);
        }
@@ -421,17 +441,19 @@ __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_ptr)
+               tracepoint_dlopen_ptr = &tracepoint_dlopen;
+       if (tracepoint_dlopen_ptr->tracepoint_unregister_lib)
+               tracepoint_dlopen_ptr->tracepoint_unregister_lib(__start___tracepoints_ptrs);
        if (!__tracepoints__disable_destructors
-                       && tracepoint_dlopen.liblttngust_handle
+                       && tracepoint_dlopen_ptr->liblttngust_handle
                        && !__tracepoint_ptrs_registered) {
-               ret = dlclose(tracepoint_dlopen.liblttngust_handle);
+               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));
        }
 }