Only call {set,clear}_semaphore probe function if they are not NULL

This patch is a response to what I commented on:

  <https://sourceware.org/ml/gdb-patches/2014-10/msg00046.html>

When reviewing Jose's USDT probe support patches.  Basically, in his
patch he had to create dummy functions for the set_semaphore and the
clear_semaphore methods of probe_ops (gdb/probe.h), because those
functions were called inconditionally from inside gdb/breakpoint.c and
gdb/tracepoint.c.  However, the semaphore concept may not apply to all
types of probes, and this is the case here: USDT probes do not have
semaphores (although SDT probes do).

Anyway, this is a simple (almost obvious) patch to guard the call to
{set,clear}_semaphore.  It does not introduce any regression on a
Fedora 20 x86_64.

I will apply it in a few days in case there is no comment.

gdb/ChangeLog:
2014-10-14  Sergio Durigan Junior  <sergiodj@redhat.com>

	* breakpoint.c (bkpt_probe_insert_location): Call set_semaphore
	only if it is not NULL.
	(bkpt_probe_remove_location): Likewise, for clear_semaphore.
	* probe.h (struct probe_ops) <set_semaphore>: Update comment.
	(struct probe_ops) <clear_semaphore>: Likewise.
	* tracepoint.c (start_tracing): Call set_semaphore only if it is
	not NULL.
	(stop_tracing): Likewise, for clear_semaphore.

4 files changed, 25 insertions, 10 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index ec05028..57ddd7b 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,16 @@
 2014-10-14  Sergio Durigan Junior  <sergiodj@redhat.com>
 
+	* breakpoint.c (bkpt_probe_insert_location): Call set_semaphore
+	only if it is not NULL.
+	(bkpt_probe_remove_location): Likewise, for clear_semaphore.
+	* probe.h (struct probe_ops) <set_semaphore>: Update comment.
+	(struct probe_ops) <clear_semaphore>: Likewise.
+	* tracepoint.c (start_tracing): Call set_semaphore only if it is
+	not NULL.
+	(stop_tracing): Likewise, for clear_semaphore.
+
+2014-10-14  Sergio Durigan Junior  <sergiodj@redhat.com>
+
 	* stap-probe.c (stap_parse_argument): Initialize expout explicitly
 	using language_c, instead of current_language.
 
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index a144a7e..dc2e297 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -13696,9 +13696,10 @@ bkpt_probe_insert_location (struct bp_location *bl)
     {
       /* The insertion was successful, now let's set the probe's semaphore
 	 if needed.  */
-      bl->probe.probe->pops->set_semaphore (bl->probe.probe,
-					    bl->probe.objfile,
-					    bl->gdbarch);
+      if (bl->probe.probe->pops->set_semaphore != NULL)
+	bl->probe.probe->pops->set_semaphore (bl->probe.probe,
+					      bl->probe.objfile,
+					      bl->gdbarch);
     }
 
   return v;
@@ -13708,9 +13709,10 @@ static int
 bkpt_probe_remove_location (struct bp_location *bl)
 {
   /* Let's clear the semaphore before removing the location.  */
-  bl->probe.probe->pops->clear_semaphore (bl->probe.probe,
-					  bl->probe.objfile,
-					  bl->gdbarch);
+  if (bl->probe.probe->pops->clear_semaphore != NULL)
+    bl->probe.probe->pops->clear_semaphore (bl->probe.probe,
+					    bl->probe.objfile,
+					    bl->gdbarch);
 
   return bkpt_remove_location (bl);
 }
diff --git a/gdb/probe.h b/gdb/probe.h
index b4ff0a6..a128151 100644
--- a/gdb/probe.h
+++ b/gdb/probe.h
@@ -96,14 +96,14 @@ struct probe_ops
 
     /* Set the semaphore associated with the PROBE.  This function only makes
        sense if the probe has a concept of semaphore associated to a
-       probe.  */
+       probe, otherwise it can be set to NULL.  */
 
     void (*set_semaphore) (struct probe *probe, struct objfile *objfile,
 			   struct gdbarch *gdbarch);
 
     /* Clear the semaphore associated with the PROBE.  This function only
        makes sense if the probe has a concept of semaphore associated to
-       a probe.  */
+       a probe, otherwise it can be set to NULL.  */
 
     void (*clear_semaphore) (struct probe *probe, struct objfile *objfile,
 			     struct gdbarch *gdbarch);
diff --git a/gdb/tracepoint.c b/gdb/tracepoint.c
index 51af2af..fc20063 100644
--- a/gdb/tracepoint.c
+++ b/gdb/tracepoint.c
@@ -1858,7 +1858,8 @@ start_tracing (char *notes)
       t->number_on_target = b->number;
 
       for (loc = b->loc; loc; loc = loc->next)
-	if (loc->probe.probe != NULL)
+	if (loc->probe.probe != NULL
+	    && loc->probe.probe->pops->set_semaphore != NULL)
 	  loc->probe.probe->pops->set_semaphore (loc->probe.probe,
 						 loc->probe.objfile,
 						 loc->gdbarch);
@@ -1957,7 +1958,8 @@ stop_tracing (char *note)
 	     but we don't really care if this semaphore goes out of sync.
 	     That's why we are decrementing it here, but not taking care
 	     in other places.  */
-	  if (loc->probe.probe != NULL)
+	  if (loc->probe.probe != NULL
+	      && loc->probe.probe->pops->clear_semaphore != NULL)
 	    loc->probe.probe->pops->clear_semaphore (loc->probe.probe,
 						     loc->probe.objfile,
 						     loc->gdbarch);