gdb: Add debug tracing for bfd cache activity.

This patch adds a new debug flag bfd-cache, which when set to non-zero
produces debugging log messages relating to gdb's bfd cache.

gdb/ChangeLog:

	* gdb_bfd.c (debug_bfd_cache): New variable.
	(show_bfd_cache_debug): New function.
	(gdb_bfd_open): Add debug logging.
	(gdb_bfd_ref): Likewise.
	(gdb_bfd_unref): Likewise.
	(_initialize_gdb_bfd): Add new set/show command.
	* NEWS: Mention new command.

gdb/doc/ChangeLog:

	* gdb.texinfo (File Caching): Document "set/show debug bfd-cache".

gdb/ChangeLog

@@ -1,3 +1,13 @@
+2015-08-18  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb_bfd.c (debug_bfd_cache): New variable.
+	(show_bfd_cache_debug): New function.
+	(gdb_bfd_open): Add debug logging.
+	(gdb_bfd_ref): Likewise.
+	(gdb_bfd_unref): Likewise.
+	(_initialize_gdb_bfd): Add new set/show command.
+	* NEWS: Mention new command.
+
 2015-08-18  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* gdb_bfd.c (bfd_sharing): New variable.

gdb/NEWS

@@ -24,6 +24,10 @@ maint set bfd-sharing
 maint show bfd-sharing
   Control the reuse of bfd objects.
 
+set debug bfd-cache
+show debug bfd-cache
+  Control display of debugging info regarding bfd caching.
+
 * The "disassemble" command accepts a new modifier: /s.
   It prints mixed source+disassembly like /m with two differences:
   - disassembled instructions are now printed in program order, and

gdb/doc/ChangeLog

@@ -1,3 +1,7 @@
+2015-08-18  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.texinfo (File Caching): Document "set/show debug bfd-cache".
+
 2015-08-18  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* gdb.texinfo (Maintenance Commands): Move documentation of "main

gdb/doc/gdb.texinfo

@@ -18371,6 +18371,16 @@ already shared @code{bfd} objects to be unshared, but all future files
 that are opened will create a new @code{bfd} object.  Similarly,
 re-enabling sharing does not cause multiple existing @code{bfd}
 objects to be collapsed into a single shared @code{bfd} object.
+
+@kindex set debug bfd-cache @var{level}
+@kindex bfd caching
+@item set debug bfd-cache @var{level}
+Turns on debugging of the bfd cache, setting the level to @var{level}.
+
+@kindex show debug bfd-cache
+@kindex bfd caching
+@item show debug bfd-cache
+Show the current debugging level of the bfd cache.
 @end table
 
 @node Separate Debug Files

gdb/gdb_bfd.c

@@ -122,6 +122,16 @@ show_bfd_sharing  (struct ui_file *file, int from_tty,
   fprintf_filtered (file, _("BFD sharing is %s.\n"), value);
 }
 
+/* When non-zero debugging of the bfd caches is enabled.  */
+
+static unsigned int debug_bfd_cache;
+static void
+show_bfd_cache_debug (struct ui_file *file, int from_tty,
+		      struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("BFD cache debugging is %s.\n"), value);
+}
+
 /* The type of an object being looked up in gdb_bfd_cache.  We use
    htab's capability of storing one kind of object (BFD in this case)
    and using a different sort of object for searching.  */
@@ -407,6 +417,11 @@ gdb_bfd_open (const char *name, const char *target, int fd)
   abfd = htab_find_with_hash (gdb_bfd_cache, &search, hash);
   if (bfd_sharing && abfd != NULL)
     {
+      if (debug_bfd_cache)
+	fprintf_unfiltered (gdb_stdlog,
+			    "Reusing cached bfd %s for %s\n",
+			    host_address_to_string (abfd),
+			    bfd_get_filename (abfd));
       close (fd);
       gdb_bfd_ref (abfd);
       return abfd;
@@ -416,6 +431,12 @@ gdb_bfd_open (const char *name, const char *target, int fd)
   if (abfd == NULL)
     return NULL;
 
+  if (debug_bfd_cache)
+    fprintf_unfiltered (gdb_stdlog,
+			"Creating new bfd %s for %s\n",
+			host_address_to_string (abfd),
+			bfd_get_filename (abfd));
+
   if (bfd_sharing)
     {
       slot = htab_find_slot_with_hash (gdb_bfd_cache, &search, hash, INSERT);
@@ -484,6 +505,12 @@ gdb_bfd_ref (struct bfd *abfd)
 
   gdata = bfd_usrdata (abfd);
 
+  if (debug_bfd_cache)
+    fprintf_unfiltered (gdb_stdlog,
+			"Increase reference count on bfd %s (%s)\n",
+			host_address_to_string (abfd),
+			bfd_get_filename (abfd));
+
   if (gdata != NULL)
     {
       gdata->refc += 1;
@@ -537,7 +564,20 @@ gdb_bfd_unref (struct bfd *abfd)
 
   gdata->refc -= 1;
   if (gdata->refc > 0)
+    {
+      if (debug_bfd_cache)
+	fprintf_unfiltered (gdb_stdlog,
+			    "Decrease reference count on bfd %s (%s)\n",
+			    host_address_to_string (abfd),
+			    bfd_get_filename (abfd));
       return;
+    }
+
+  if (debug_bfd_cache)
+    fprintf_unfiltered (gdb_stdlog,
+			"Delete final reference count on bfd %s (%s)\n",
+			host_address_to_string (abfd),
+			bfd_get_filename (abfd));
 
   archive_bfd = gdata->archive_bfd;
   search.filename = bfd_get_filename (abfd);
@@ -968,4 +1008,13 @@ filename, file size, file modification time, and file inode."),
 			   &show_bfd_sharing,
 			   &maintenance_set_cmdlist,
 			   &maintenance_show_cmdlist);
+
+  add_setshow_zuinteger_cmd ("bfd-cache", class_maintenance,
+			     &debug_bfd_cache, _("\
+Set bfd cache debugging."), _("\
+Show bfd cache debugging."), _("\
+When non-zero, bfd cache specific debugging is enabled."),
+			     NULL,
+			     &show_bfd_cache_debug,
+			     &setdebuglist, &showdebuglist);
 }