From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 26 Apr 2011 16:18:45 +0000 (-0400)
Subject: Tracepoint: make tracepoint ptrs section rw
X-Git-Tag: v1.9.1~382
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=332b3a18ea9e3be7ec5d65a4d75c5cf2b6a59525;p=lttng-ust.git

Tracepoint: make tracepoint ptrs section rw

The pointer section needs to be rw so that the linker can update the
pointers at link-time, thus allowing the code to be compiled with -fPIC.

The previous behavior would cause section flag mismatch, because
TRACEPOINT_LIB declared the ptr with "= NULL", which is not a void *
const, but rather a void *, which forces the element it is assigned to
to become non-const.

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

diff --git a/include/ust/tracepoint.h b/include/ust/tracepoint.h
index b9557d57..b11d69d7 100644
--- a/include/ust/tracepoint.h
+++ b/include/ust/tracepoint.h
@@ -116,13 +116,17 @@ struct tracepoint {
 						   data);		\
 	}
 
+/*
+ * __tracepoints_ptrs section is not const (read-only) to let the linker update
+ * the pointer, allowing PIC code.
+ */
 #define DEFINE_TRACEPOINT_FN(name, reg, unreg)				\
 	static const char __tpstrtab_##name[]				\
 	__attribute__((section("__tracepoints_strings"))) = #name;	\
 	struct tracepoint __tracepoint_##name				\
 	__attribute__((section("__tracepoints"))) =			\
 		{ __tpstrtab_##name, 0, NULL };				\
-	static struct tracepoint * const __tracepoint_ptr_##name	\
+	static struct tracepoint * __tracepoint_ptr_##name		\
 	__attribute__((used, section("__tracepoints_ptrs"))) =		\
 		&__tracepoint_##name;
 
@@ -231,8 +235,8 @@ extern int tracepoint_unregister_lib(struct tracepoint * const *tracepoints_star
 #define TRACEPOINT_LIB							\
 	extern struct tracepoint * const __start___tracepoints_ptrs[] __attribute__((weak, visibility("hidden"))); \
 	extern struct tracepoint * const __stop___tracepoints_ptrs[] __attribute__((weak, visibility("hidden"))); \
-	static struct tracepoint * const __tracepoint_ptr_dummy		\
-	__attribute__((used, section("__tracepoints_ptrs"))) = NULL;	\
+	static struct tracepoint * __tracepoint_ptr_dummy		\
+	__attribute__((used, section("__tracepoints_ptrs")));		\
 	static void __attribute__((constructor)) __tracepoints__init(void)	\
 	{									\
 		tracepoint_register_lib(__start___tracepoints_ptrs,			\
@@ -388,8 +392,8 @@ extern int trace_event_unregister_lib(struct trace_event * const *start_trace_ev
 	__attribute__((weak, visibility("hidden")));			\
 	extern struct trace_event * const __stop___trace_events_ptrs[]	\
 	__attribute__((weak, visibility("hidden")));			\
-	static struct trace_event * const __event_ptrs_dummy		\
-	__attribute__((used, section("__trace_events_ptrs"))) =	NULL;	\
+	static struct trace_event * __event_ptrs_dummy			\
+	__attribute__((used, section("__trace_events_ptrs")));		\
 	static void __attribute__((constructor))			\
 	__trace_events__init(void)					\
 	{								\