[PATCH v2 2/3] gdb: New maintenance command to disable bfd sharing.

[Andrew Burgess <andrew dot burgess at embecosm dot com>]

In some rare maintainer cases it is desirable to be able to disable bfd
sharing.  This patch adds new commands maintenance set/show commands for
bfd-sharing, allowing gdb's bfd cache to be turned off.

gdb/ChangeLog:

	* gdb_bfd.c (bfd_sharing): New variable.
	(gdb_bfd_open): Check bfd_sharing variable.
	(_initialize_gdb_bfd): Add new set/show command.
	* NEWS: Mention new command.

gdb/doc/ChangeLog:

	* gdb.texinfo (Maintenance Commands): Move documentation of "main
	info bfds" to...
	(File Caching): A New section.  Outline bfd caching, and add new
	description for "main set/show bfd-sharing".
---
 gdb/ChangeLog       |  7 +++++++
 gdb/NEWS            |  4 ++++
 gdb/doc/ChangeLog   |  7 +++++++
 gdb/doc/gdb.texinfo | 35 ++++++++++++++++++++++++++++++-----
 gdb/gdb_bfd.c       | 29 +++++++++++++++++++++++++----
 5 files changed, 73 insertions(+), 9 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d920ea0..0f73f08 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,12 @@
 2015-08-11  Andrew Burgess  <andrew.burgess@embecosm.com>
 
+	* gdb_bfd.c (bfd_sharing): New variable.
+	(gdb_bfd_open): Check bfd_sharing variable.
+	(_initialize_gdb_bfd): Add new set/show command.
+	* NEWS: Mention new command.
+
+2015-08-11  Andrew Burgess  <andrew.burgess@embecosm.com>
+
 	* gdb_bfd.c (struct gdb_bfd_data): Add size, inode, and device id
 	field.
 	(struct gdb_bfd_cache_search): Likewise.
diff --git a/gdb/NEWS b/gdb/NEWS
index 3fe6036..87fc14e 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -16,6 +16,10 @@ maint show target-non-stop
   "set non-stop" is "off".  The default is "auto", meaning non-stop
   mode is enabled if supported by the target.
 
+maint set bfd-sharing
+maint show bfd-sharing
+  Control the reuse of bfd objects.
+
 *** Changes in GDB 7.10
 
 * Support for process record-replay and reverse debugging on aarch64*-linux*
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 846ac24..9d553db 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,10 @@
+2015-08-11  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.texinfo (Maintenance Commands): Move documentation of "main
+	info bfds" to...
+	(File Caching): A New section.  Outline bfd caching, and add new
+	description for "main set/show bfd-sharing".
+
 2015-08-07  Pedro Alves  <palves@redhat.com>
 
 	* gdb.texinfo (Maintenance Commands): Document "maint set/show
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 900970b..3cfb1a7 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -18190,6 +18190,36 @@ Set whether a source file may have multiple base names.
 Show whether a source file may have multiple base names.
 @end table
 
+@node File Caching
+@section File Caching
+@cindex caching of opened files
+@cindex caching of bfd objects
+
+To speed up file loading, and reduce memory usage, @value{GDBN} will
+reuse the @code{bfd} objects used to track open files.  @xref{Top, ,
+BFD, bfd, The Binary File Descriptor Library}.  The following commands
+allow visibility and control of the caching beaviour.
+
+@table @code
+@kindex maint info bfds
+@item maint info bfds
+This prints information about each @code{bfd} object that is known to
+@value{GDBN}.
+
+@kindex maint set bfd-sharing
+@kindex maint show bfd-sharing
+@kindex bfd caching
+@item maint set bfd-sharing
+@item maint show bfd-sharing
+Control whether @code{bfd} objects can be shared.  When sharing is
+enabled @value{GDBN} will reuse already open @code{bfd} objects rather
+than reopening the same file.  Turning sharing off does not cause
+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 will not cause multiple existing @code{bfd}
+objects to be collapsed into a single shared @code{bfd} object.
+@end table
+
 @node Separate Debug Files
 @section Debugging Information in Separate Files
 @cindex separate debugging information files
@@ -33987,11 +34017,6 @@ Shared library events.
 
 @end table
 
-@kindex maint info bfds
-@item maint info bfds
-This prints information about each @code{bfd} object that is known to
-@value{GDBN}.  @xref{Top, , BFD, bfd, The Binary File Descriptor Library}.
-
 @kindex maint info btrace
 @item maint info btrace
 Pint information about raw branch tracing data.
diff --git a/gdb/gdb_bfd.c b/gdb/gdb_bfd.c
index ee29531..14fdf43 100644
--- a/gdb/gdb_bfd.c
+++ b/gdb/gdb_bfd.c
@@ -111,6 +111,11 @@ DEFINE_REGISTRY (bfd, GDB_BFD_DATA_ACCESSOR)
 
 static htab_t gdb_bfd_cache;
 
+/* When true gdb will reuse an existing bfd object if the filename,
+   modification time, and file size all match.  */
+
+static int bfd_sharing;
+
 /* 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.  */
@@ -394,7 +399,7 @@ gdb_bfd_open (const char *name, const char *target, int fd)
      opening the BFD may fail; and this would violate hashtab
      invariants.  */
   abfd = htab_find_with_hash (gdb_bfd_cache, &search, hash);
-  if (abfd != NULL)
+  if (bfd_sharing && abfd != NULL)
     {
       close (fd);
       gdb_bfd_ref (abfd);
@@ -405,9 +410,12 @@ gdb_bfd_open (const char *name, const char *target, int fd)
   if (abfd == NULL)
     return NULL;
 
-  slot = htab_find_slot_with_hash (gdb_bfd_cache, &search, hash, INSERT);
-  gdb_assert (!*slot);
-  *slot = abfd;
+  if (bfd_sharing)
+    {
+      slot = htab_find_slot_with_hash (gdb_bfd_cache, &search, hash, INSERT);
+      gdb_assert (!*slot);
+      *slot = abfd;
+    }
 
   gdb_bfd_ref (abfd);
   return abfd;
@@ -942,4 +950,17 @@ _initialize_gdb_bfd (void)
   add_cmd ("bfds", class_maintenance, maintenance_info_bfds, _("\
 List the BFDs that are currently open."),
 	   &maintenanceinfolist);
+
+  add_setshow_boolean_cmd ("bfd-sharing", no_class,
+			   &bfd_sharing, _("\
+Set whether gdb will share bfds that appear to be the same file."), _("\
+Show whether gdb will share bfds that appear to be the same file."), _("\
+When enabled gdb will reuse existing bfds rather than reopening the\n\
+same file.  To decide if two files are the same then gdb compares the\n\
+filename, file size, file modification time, and file inode."),
+			   NULL,
+			   NULL,
+			   &maintenance_set_cmdlist,
+			   &maintenance_show_cmdlist);
+  bfd_sharing = 1;
 }
-- 
2.4.0