From: Jan Blunck <jblunck@suse.de>
Date: Tue, 27 Oct 2009 10:07:39 +0000 (+0100)
Subject: Make references to __{start,stop}___{markers,tracepoints} weak
X-Git-Tag: v0.1~53
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=55994a672106ec794f292d747206542067a27584;p=ust.git

Make references to __{start,stop}___{markers,tracepoints} weak

When using the linker script approach for initialization of the libust
library we unconditionally call __markers_init()/__tracepoints_init().
If one is using only tracepoints or only markers the init call fails
because of undefined references to the linker generated symbols for the
__markers or __tracepoints section (__start___markers, ...). Since we use
the symbols just for the size and the start of the section it is safe to
use weak symbols in this case: if the size if zero nothing get read anyway.

Signed-off-by: Jan Blunck <jblunck@suse.de>
---

diff --git a/include/ust/marker.h b/include/ust/marker.h
index 0c32586..bbd9187 100644
--- a/include/ust/marker.h
+++ b/include/ust/marker.h
@@ -309,18 +309,20 @@ struct lib {
 	struct list_head list;
 };
 
-extern int marker_register_lib(struct marker *markers_start, struct marker_addr *marker_addr_start, int markers_count);
-
-#define MARKER_LIB										\
-extern struct marker __start___markers[] __attribute__((visibility("hidden")));			\
-extern struct marker __stop___markers[] __attribute__((visibility("hidden")));			\
-extern struct marker_addr __start___marker_addr[] __attribute__((visibility("hidden")));	\
-extern struct marker_addr __stop___marker_addr[] __attribute__((visibility("hidden")));		\
-												\
-static void __attribute__((constructor)) __markers__init(void)					\
-{												\
-	marker_register_lib(__start___markers, __start___marker_addr, (((long)__stop___markers)-((long)__start___markers))/sizeof(struct marker)); \
-}
+extern int marker_register_lib(struct marker *markers_start,
+			       struct marker_addr *marker_addr_start,
+			       int markers_count);
+
+#define MARKER_LIB							\
+	extern struct marker __start___markers[] __attribute__((weak, visibility("hidden"))); \
+	extern struct marker __stop___markers[] __attribute__((weak, visibility("hidden"))); \
+	extern struct marker_addr __start___marker_addr[] __attribute__((weak, visibility("hidden"))); \
+	extern struct marker_addr __stop___marker_addr[] __attribute__((weak, visibility("hidden"))); \
+									\
+	static void __attribute__((constructor)) __markers__init(void)	\
+	{								\
+		marker_register_lib(__start___markers, __start___marker_addr, (((long)__stop___markers)-((long)__start___markers))/sizeof(struct marker)); \
+	}
 
 extern void marker_set_new_marker_cb(void (*cb)(struct marker *));
 extern void init_markers(void);
diff --git a/include/ust/tracepoint.h b/include/ust/tracepoint.h
index 56c62b0..b0ccbad 100644
--- a/include/ust/tracepoint.h
+++ b/include/ust/tracepoint.h
@@ -202,8 +202,8 @@ extern int tracepoint_register_lib(struct tracepoint *tracepoints_start,
 				   int tracepoints_count);
 
 #define TRACEPOINT_LIB							\
-	extern struct tracepoint __start___tracepoints[] __attribute__((visibility("hidden")));	\
-	extern struct tracepoint __stop___tracepoints[] __attribute__((visibility("hidden"))); \
+	extern struct tracepoint __start___tracepoints[] __attribute__((weak, visibility("hidden"))); \
+	extern struct tracepoint __stop___tracepoints[] __attribute__((weak, visibility("hidden"))); \
 	static void __attribute__((constructor)) __tracepoints__init(void) \
 	{								\
 		tracepoint_register_lib(__start___tracepoints,		\