Some library might want to generate events in their ctor/dtor. If
LTTng initialize/finalize its tracepoints/events at the wrong time,
events are lost.
Order of execution of the ctor/dtor is determined by priority. When
some priorities are equal, the order of execution seems to be
determined by:
a) Order of appearance if in the same compilation unit
b) Order of link if in different compilation units
c) Order of load by ld-linux.so or dlopen(3) for
share objects
Also, using the constructor/destructor attributes without any priority
will default to the _lowest_ priority 65535, at least for GCC.
Thus, Providing the LTTNG_*_PRIO definitions allows users to set their
ctor/dtor priority like so:
----------------------------------------------------------------------
...
__attribute__((constructor(LTTNG_CTOR_PRIO + 1)))
...
__attribute__((destructor(LTTNG_DTOR_PRIO + 1)))
...
----------------------------------------------------------------------
or without any priority, that would also work.
Note that LTTNG_*_PRIO are set to 101 because it is the _highest_
priority and 0 to 100 are reserved.
Signed-off-by: Olivier Dion <olivier.d...@polymtl.ca>
---
include/lttng/tracepoint.h | 8 ++++----
include/lttng/ust-compiler.h | 7 +++++++
include/lttng/ust-tracepoint-event.h | 4 ++--
3 files changed, 13 insertions(+), 6 deletions(-)
diff --git a/include/lttng/tracepoint.h b/include/lttng/tracepoint.h
index d77a2fb2..70903757 100644
--- a/include/lttng/tracepoint.h
+++ b/include/lttng/tracepoint.h
@@ -318,7 +318,7 @@ __tracepoint__init_urcu_sym(void)
}
#endif
-static void lttng_ust_notrace __attribute__((constructor))
+static void lttng_ust_notrace __attribute__((constructor(LTTNG_CTOR_PRIO)))
__tracepoints__init(void);
static void
__tracepoints__init(void)
@@ -340,7 +340,7 @@ __tracepoints__init(void)
__tracepoint__init_urcu_sym();
}
-static void lttng_ust_notrace __attribute__((destructor))
+static void lttng_ust_notrace __attribute__((destructor(LTTNG_DTOR_PRIO)))
__tracepoints__destroy(void);
static void
__tracepoints__destroy(void)
@@ -444,7 +444,7 @@ extern struct lttng_ust_tracepoint * const
__stop___tracepoints_ptrs[]
__attribute__((used, section("__tracepoints_ptrs"))) =
\
&__tracepoint_##_provider##___##_name;
-static void lttng_ust_notrace __attribute__((constructor))
+static void lttng_ust_notrace __attribute__((constructor(LTTNG_CTOR_PRIO)))
__tracepoints__ptrs_init(void);
static void
__tracepoints__ptrs_init(void)
@@ -488,7 +488,7 @@ __tracepoints__ptrs_init(void)
}
}
-static void lttng_ust_notrace __attribute__((destructor))
+static void lttng_ust_notrace __attribute__((destructor(LTTNG_DTOR_PRIO)))
__tracepoints__ptrs_destroy(void);
static void
__tracepoints__ptrs_destroy(void)
diff --git a/include/lttng/ust-compiler.h b/include/lttng/ust-compiler.h
index 1d04da1a..4f1b1a40 100644
--- a/include/lttng/ust-compiler.h
+++ b/include/lttng/ust-compiler.h
@@ -27,4 +27,11 @@
#define lttng_ust_notrace __attribute__((no_instrument_function))
#define LTTNG_PACKED __attribute__((__packed__))
+/*
+ * Value in range [0, 100] are reserved. Thus 101 is the higest
+ * priority that can be used.
+ */
+#define LTTNG_CTOR_PRIO 101
+#define LTTNG_DTOR_PRIO 101
+
#endif /* _LTTNG_UST_COMPILER_H */
diff --git a/include/lttng/ust-tracepoint-event.h
b/include/lttng/ust-tracepoint-event.h
index 7890c247..cd45ae08 100644
--- a/include/lttng/ust-tracepoint-event.h
+++ b/include/lttng/ust-tracepoint-event.h
@@ -1009,7 +1009,7 @@ static int
_TP_COMBINE_TOKENS(__probe_register_refcount___, TRACEPOINT_PROVIDER)
/* Reset all macros within TRACEPOINT_EVENT */
#include <lttng/ust-tracepoint-event-reset.h>
-static void lttng_ust_notrace __attribute__((constructor))
+static void lttng_ust_notrace __attribute__((constructor(LTTNG_CTOR_PRIO)))
_TP_COMBINE_TOKENS(__lttng_events_init__, TRACEPOINT_PROVIDER)(void);
static void
_TP_COMBINE_TOKENS(__lttng_events_init__, TRACEPOINT_PROVIDER)(void)
@@ -1036,7 +1036,7 @@ _TP_COMBINE_TOKENS(__lttng_events_init__,
TRACEPOINT_PROVIDER)(void)
}
}
-static void lttng_ust_notrace __attribute__((destructor))
+static void lttng_ust_notrace __attribute__((destructor(LTTNG_DTOR_PRIO)))
_TP_COMBINE_TOKENS(__lttng_events_exit__, TRACEPOINT_PROVIDER)(void);
static void
_TP_COMBINE_TOKENS(__lttng_events_exit__, TRACEPOINT_PROVIDER)(void)
--
2.27.0
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