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

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(-)

> From: Andrew Burgess <andrew.burgess@embecosm.com>
> Cc: Andrew Burgess <andrew.burgess@embecosm.com>
> Date: Thu, 13 Aug 2015 13:44:59 +0100
> 
> 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".

OK for the documentation parts, with one comment:

> +Control whether @code{bfd} objects can be shared.  When sharing is
> +enabled @value{GDBN} will reuse already open @code{bfd} objects rather
          ^
Please insert a comma where indicated.

Thanks.

On 08/13/2015 01:44 PM, Andrew Burgess wrote:
> 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.


>  * 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.

typo "beaviour".  (While at it, I think the manual is meant to
standardize on USA spelling, thus "behavior".)

> +
> +@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

I believe present tense is preferred in the manual, like:

s/will reuse/reuses/

> +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}

...re-enabling sharing does not cause...


> +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.


> @@ -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;

Initialize it here?  Like:

 static int bfd_sharing = 1;

>    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,

Please add a show hook, for i18n.

> +			   &maintenance_set_cmdlist,
> +			   &maintenance_show_cmdlist);
> +  bfd_sharing = 1;

See above.

>  }
> 

Otherwise LGTM.

Thanks,
Pedro Alves