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[PATCH] Add Guile frame filter interface


Hi,

The attached patch exposes the frame filter interface to Guile.  It's
mostly modelled on the Python interface, but has a more functional
flavor.  No test cases yet, but I figure there will be a round of
comments so it's probably worth getting this out early.

Thoughts?

Andy

>From b8d2c47e351cfe28802001d0315657c807bf73c4 Mon Sep 17 00:00:00 2001
From: Andy Wingo <wingo@igalia.com>
Date: Sun, 15 Feb 2015 12:17:23 +0100
Subject: [PATCH] Add Guile frame filter interface.

gdb/ChangeLog:
	* guile/scm-frame-filter.c:
	* guile/lib/gdb/frames.scm: New files.
	* guile/guile.c (guile_extension_ops): Add the Guile frame
	filter.
	(initialize_gdb_module): Initialize the Guile frame filter
	module.
	* guile/guile-internal.h (frscm_scm_from_frame)
	(gdbscm_apply_frame_filter, gdbscm_initialize_frame_filters): New
	declarations.
	* Makefile.in: Add scm-frame-filter.c.
	* data-directory/Makefile.in: Add frames.scm.
	* guile/scm-frame.c (frscm_scm_from_frame): Export.

gdb/doc/ChangeLog:
	* guile.texi (Guile Frame Filter API)
	(Writing a Frame Filter in Guile): New sections.
---
 gdb/ChangeLog                  |   15 +
 gdb/Makefile.in                |    6 +
 gdb/data-directory/Makefile.in |    2 +
 gdb/doc/ChangeLog              |    5 +
 gdb/doc/guile.texi             |  379 +++++++++++++++
 gdb/guile/guile-internal.h     |   10 +
 gdb/guile/guile.c              |    3 +-
 gdb/guile/lib/gdb/frames.scm   |  326 +++++++++++++
 gdb/guile/scm-frame-filter.c   | 1001 ++++++++++++++++++++++++++++++++++++++++
 gdb/guile/scm-frame.c          |    2 +-
 10 files changed, 1747 insertions(+), 2 deletions(-)
 create mode 100644 gdb/guile/lib/gdb/frames.scm
 create mode 100644 gdb/guile/scm-frame-filter.c

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 0b7b4b7..8003dab 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,18 @@
+2015-02-15  Andy Wingo  <wingo@igalia.com>
+
+	* guile/scm-frame-filter.c:
+	* guile/lib/gdb/frames.scm: New files.
+	* guile/guile.c (guile_extension_ops): Add the Guile frame
+	filter.
+	(initialize_gdb_module): Initialize the Guile frame filter
+	module.
+	* guile/guile-internal.h (frscm_scm_from_frame)
+	(gdbscm_apply_frame_filter, gdbscm_initialize_frame_filters): New
+	declarations.
+	* Makefile.in: Add scm-frame-filter.c.
+	* data-directory/Makefile.in: Add frames.scm.
+	* guile/scm-frame.c (frscm_scm_from_frame): Export.
+
 2015-02-10  Andy Wingo  <wingo@igalia.com>
 
 	* guile/guile.c (_initialize_guile): Disable automatic
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 00fb2cd..49bd2d2 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -310,6 +310,7 @@ SUBDIR_GUILE_OBS = \
 	scm-disasm.o \
 	scm-exception.o \
 	scm-frame.o \
+	scm-frame-filter.o \
 	scm-gsmob.o \
 	scm-iterator.o \
 	scm-lazy-string.o \
@@ -336,6 +337,7 @@ SUBDIR_GUILE_SRCS = \
 	guile/scm-disasm.c \
 	guile/scm-exception.c \
 	guile/scm-frame.c \
+	guile/scm-frame-filter.c \
 	guile/scm-gsmob.c \
 	guile/scm-iterator.c \
 	guile/scm-lazy-string.c \
@@ -2405,6 +2407,10 @@ scm-frame.o: $(srcdir)/guile/scm-frame.c
 	$(COMPILE) $(srcdir)/guile/scm-frame.c
 	$(POSTCOMPILE)
 
+scm-frame-filter.o: $(srcdir)/guile/scm-frame-filter.c
+	$(COMPILE) $(srcdir)/guile/scm-frame-filter.c
+	$(POSTCOMPILE)
+
 scm-gsmob.o: $(srcdir)/guile/scm-gsmob.c
 	$(COMPILE) $(srcdir)/guile/scm-gsmob.c
 	$(POSTCOMPILE)
diff --git a/gdb/data-directory/Makefile.in b/gdb/data-directory/Makefile.in
index c01b86d..e406e9e 100644
--- a/gdb/data-directory/Makefile.in
+++ b/gdb/data-directory/Makefile.in
@@ -87,6 +87,7 @@ GUILE_SOURCE_FILES = \
 	./gdb.scm \
 	gdb/boot.scm \
 	gdb/experimental.scm \
+	gdb/frames.scm \
 	gdb/init.scm \
 	gdb/iterator.scm \
 	gdb/printing.scm \
@@ -96,6 +97,7 @@ GUILE_SOURCE_FILES = \
 GUILE_COMPILED_FILES = \
 	./gdb.go \
 	gdb/experimental.go \
+	gdb/frames.go \
 	gdb/iterator.go \
 	gdb/printing.go \
 	gdb/support.go \
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index b8e1f7f..c7f6470 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,8 @@
+2015-02-15  Andy Wingo  <wingo@igalia.com>
+
+	* guile.texi (Guile Frame Filter API)
+	(Writing a Frame Filter in Guile): New sections.
+
 2015-02-09  Markus Metzger  <markus.t.metzger@intel.com>
 
 	* gdb.texinfo (Branch Trace Configuration Format): Add size.
diff --git a/gdb/doc/guile.texi b/gdb/doc/guile.texi
index 53e69f2..d9b3638 100644
--- a/gdb/doc/guile.texi
+++ b/gdb/doc/guile.texi
@@ -141,6 +141,8 @@ from the Guile interactive prompt.
 * Guile Pretty Printing API:: Pretty-printing values with Guile
 * Selecting Guile Pretty-Printers:: How GDB chooses a pretty-printer
 * Writing a Guile Pretty-Printer:: Writing a pretty-printer
+* Guile Frame Filter API::   Filtering frames.
+* Writing a Frame Filter in Guile:: Writing a frame filter.
 * Commands In Guile::        Implementing new commands in Guile
 * Parameters In Guile::      Adding new @value{GDBN} parameters
 * Progspaces In Guile::      Program spaces
@@ -1693,6 +1695,383 @@ my_library.so:
     bar
 @end smallexample
 
+@node Guile Frame Filter API
+@subsubsection Filtering Frames in Guile
+@cindex frame filters api
+
+Frame filters allow the user to programmatically alter the way a
+backtrace (@pxref{Backtrace}) prints.  Frame filters can reorganize,
+annotate, insert, and remove frames in a backtrace.
+
+Only commands that print a backtrace, or, in the case of @sc{gdb/mi}
+commands (@pxref{GDB/MI}), those that return a collection of frames
+are affected.  The commands that work with frame filters are:
+
+@code{backtrace} (@pxref{backtrace-command,, The backtrace command}),
+@code{-stack-list-frames}
+(@pxref{-stack-list-frames,, The -stack-list-frames command}),
+@code{-stack-list-variables} (@pxref{-stack-list-variables,, The
+-stack-list-variables command}), @code{-stack-list-arguments}
+@pxref{-stack-list-arguments,, The -stack-list-arguments command}) and
+@code{-stack-list-locals} (@pxref{-stack-list-locals,, The
+-stack-list-locals command}).
+
+A frame filter is a function that takes a SRFI-41 stream of annotated
+frame objects as an argument, and returns a potentially modified
+stream of annotated frame objects.  @xref{SRFI-41,,,guile,The Guile
+Reference Manual}, for more on the SRFI-41 specification for lazy
+streams.  Operating over a stream allows frame filters to inspect,
+reorganize, insert, and remove frames.  @value{GDBN} also provides a
+more simple @dfn{frame annotator} API that works on individual frames,
+for the common case in which the user does not need to reorganize the
+backtrace.  Both APIs are described below.
+
+There can be multiple frame filters registered with @value{GDBN}, and
+each one may be individually enabled or disabled at will.  Multiple
+frame filters can be enabled at the same time.  Frame filters have an
+associated @dfn{priority} which determines the order in which they are
+applied over the annotated frame stream.  For example, if there are
+two filters registered and enabled, @var{f1} and @var{f2}, and the
+priority of @var{f2} is greater than that of @var{f1}, then the result
+of frame filtering will be @code{(@var{f2} (@var{f1} @var{stream}))}.
+In this way, higher-priority frame filters get the last word on the
+backtrace that is ultimately printed.
+
+An important consideration when designing frame filters, and well
+worth reflecting upon, is that frame filters should avoid unwinding
+the call stack if possible.  Some stacks can run very deep, into the
+tens of thousands in some cases.  To search every frame when a frame
+filter executes may be too expensive at that step.  The frame filter
+cannot know how many frames it has to iterate over, and it may have to
+iterate through them all.  This ends up duplicating effort as
+@value{GDBN} performs this iteration when it prints the frames.
+Therefore a frame filter should avoid peeking ahead in the frame
+stream, if possible.  @xref{Writing a Frame Filter}, for examples on
+how to write a good frame filter.
+
+To use frame filters, first load the @code{(gdb frames)} module to
+have access to the procedures that manipulate frame filters:
+
+@example
+(use-modules (gdb frames))
+@end example
+
+@deffn {Scheme Procedure} add-frame-filter! name filter @
+       @r{[}#:priority priority@r{]} @
+       @r{[}#:objfile objfile@r{]} @r{[}#:progspace progspace@r{]}
+Register the frame filter procedure @var{filter} with @value{GDBN}.
+@var{filter} should be a function of one argument, taking a SRFI-41
+stream of annotated frames and returning a possibily modified stream
+of annotated frames.  The filter is identified by @var{name}, which
+should be unique among all known filters.
+
+The filter will be registered with the given @var{priority}, which
+should be a number, and which defaults to 20 if not given.  By
+default, the filter is @dfn{global}, meaning that it is associated
+with all objfiles and progspaces.  Pass one of @code{#:objfile} or
+@code{#:progspace} to instead associate the filter with a specific
+objfile or progspace, respectively.
+
+The filter will be initially enabled.
+@end deffn
+
+@deffn {Scheme Procedure} all-frame-filters
+Return a list of the names of all frame filters.
+@end deffn
+
+@deffn {Scheme Procedure} remove-frame-filter! name
+@deffnx {Scheme Procedure} enable-frame-filter! name
+@deffnx {Scheme Procedure} disable-frame-filter! name
+Remove, enable, or disable a frame filter, respectively.  @var{name}
+should correspond to the name of a filter previously added with
+@code{add-frame-filter!}.  If no such filter is found, an error is
+signalled.
+@end deffn
+
+When a command is executed from @value{GDBN} that is compatible with
+frame filters, @value{GDBN} selects all filters registered in the
+current progspace, filters for all objfiles, and filters with no
+associated objfile or progspace.  That list is then sorted by
+priority, as described above, and applied to the annotated frame
+stream.
+
+An annotated frame is a Guile record type that holds information about
+a frame: its function name, its arguments, its locals, and so on.  An
+annotated frame is always associated with a GDB frame object.  To
+add, remove, or otherwise alter information associated with an
+annotated frame, use the @code{reannotate-frame} procedure.
+
+@deffn {Scheme Procedure} reannotate-frame! ann @
+       @r{[}#:function-name function-name@r{]} @
+       @r{[}#:address address@r{]} @
+       @r{[}#:filename filename@r{]} @
+       @r{[}#:line line@r{]} @
+       @r{[}#:arguments arguments@r{]} @
+       @r{[}#:locals locals@r{]} @
+       @r{[}#:children children@r{]}
+Take the annotated frame object @var{ann} and return a new annotated
+frame object, replacing the fields specified by the keyword arguments
+with their new values.  For example, calling @code{(reannotate-frame
+@var{x} #:function-name "foo")} will create a new annotated frame
+object that inherits all fields from @var{x}, but whose function name
+has been set to @code{"foo"}.
+@end deffn
+
+The @code{(gdb frames)} module defines accessors for the various
+fields of annotated frame objects.
+
+@deffn {Scheme Procedure} annotated-frame-frame ann
+Return the GDB frame object associated with the annotated frame
+@var{ann}.  @xref{Frames In Guile}.
+@end deffn
+
+@deffn {Scheme Procedure} annotated-frame-function-name ann
+Return the function name associated with the annotated frame
+@var{ann}, as a string, or @code{#f} if not available.
+@end deffn
+
+@deffn {Scheme Procedure} annotated-frame-address ann
+Return the address associated with the annotated frame @var{ann}, as
+an integer.
+@end deffn
+
+@deffn {Scheme Procedure} annotated-frame-filename ann
+Return the file name associated with the annotated frame @var{ann}, as
+a string, or @code{#f} if not available.
+@end deffn
+
+@deffn {Scheme Procedure} annotated-frame-line ann
+Return the line number associated with the annotated frame @var{ann},
+as an integer, or @code{#f} if not available.
+@end deffn
+
+@deffn {Scheme Procedure} annotated-frame-arguments ann
+Return a list of the function arguments associated with the annotated
+frame @var{ann}.  Each item of the list should either be a GDB symbol
+(@pxref{Symbols In Guile}), a pair of a GDB symbol and a GDB value
+(@pxref{Values From Inferior In Guile}, or a pair of a string and a
+GDB value.  In the first case, the value will be loaded from the frame
+if needed.
+@end deffn
+
+@deffn {Scheme Procedure} annotated-frame-locals ann
+Return a list of the function arguments associated with the annotated
+frame @var{ann}, in the same format as for
+@code{annotated-frame-arguments}.
+@end deffn
+
+Annotated frames may also have @dfn{child frames}.  By default, no
+frame has a child frame, but filters may reorganize the frame stream
+into a stream of frame trees, by populating the child list.  Of
+course, such a reorganization is ultimately cosmetic, as it doesn't
+alter the stack of frames seen by @value{GDBN} and navigable by the
+user, for example by using the @code{frame} command.  Still, nesting
+frames may lead to a more understandable presentation of a backtrace.
+
+@deffn {Scheme Procedure} annotated-frame-children ann
+Return a list of the @dfn{child frames} function name associated with
+the annotated frame @var{ann}.  Each item of the list should be an
+annotated frame object.
+@end deffn
+
+While frame filters can both reorganize and reannotate the frame
+stream, it is often the case that one only wants to reannotate the
+frames in a stream, without reorganizing then.  In that case there is
+a simpler API for @dfn{frame annotators} that simply maps annotated
+frames to annotated frames.
+
+@deffn {Scheme Procedure} add-frame-annotator! name annotator @
+       @r{[}#:priority priority@r{]} @
+       @r{[}#:objfile objfile@r{]} @r{[}#:progspace progspace@r{]}
+Register the frame annotator procedure @var{annotator} with
+@value{GDBN}.  @var{annotator} should be a function of one argument,
+takingn annotated frame object and returning a possibily modified
+annotated frame.  The annotator is identified by @var{name}, which
+should be unique among all known annotators.
+
+The annotator has an associated priority, as with frame filters.  See
+the documentation on @code{add-frame-filter!}, for more.
+
+The annotator will be initially enabled.
+@end deffn
+
+@deffn {Scheme Procedure} all-frame-annotators
+Return a list of the names of all frame annotators.
+@end deffn
+
+@deffn {Scheme Procedure} remove-frame-annotator! name
+@deffnx {Scheme Procedure} enable-frame-annotator! name
+@deffnx {Scheme Procedure} disable-frame-annotator! name
+Remove, enable, or disable a frame annotator, respectively.
+@var{name} should correspond to the name of a annotator previously
+added with @code{add-frame-annotator!}.  If no such annotator is
+found, an error is signalled.
+@end deffn
+
+@node Writing a Frame Filter in Guile
+@subsubsection Writing a Frame Filter in Guile
+@cindex writing a frame filter
+
+The simplest kind of frame filter just takes the incoming stream of
+frames and produces an identical stream of values.  For example:
+
+@example
+(use-modules (gdb frames))
+
+(define (identity-frame-filter stream)
+  (cond
+   ((stream-null? stream)
+    ;; End of stream?  Then return end-of-stream.
+    stream-null)
+   (else
+    ;; Otherwise recurse on the tail of the stream.
+    (stream-cons (stream-car stream)
+                 (identity-frame-filter (stream-cdr stream))))))
+@end example
+
+If you are not familiar with SRFI-41 streams, you might think that
+this would eagerly traverse the whole stack of frames.  This would be
+bad because we don't want to produce an entire backtrace at once when
+the user might cancel after only seeing one page.  However this is not
+the case, because unlike normal Scheme procedures, @code{stream-cons}
+is @dfn{lazy} in its arguments, which is to say that its arguments are
+only evaluated when they are accessed via @code{stream-car} and
+@code{stream-cdr}.  In this way the stream looks infinite, but in
+reality only produces values as they are requested by the caller.
+
+To use this frame filter, we have to register it with @value{GDBN}.
+
+@example
+(add-frame-filter! "identity" identity-frame-filter)
+@end example
+
+Now our filter will run each time a backtrace is printed, or in
+general for any GDB command that uses the frame filter interface.
+
+Filters are enabled when they are added.  You can control the enabled
+or disabled state of a filter using the appropriate procedures:
+
+@example
+(disable-frame-filter! "identity")
+(enable-frame-filter! "identity")
+@end example
+
+Finally, we can remove all filters with a simple application of
+@code{for-each}:
+
+@example
+(for-each remove-frame-filter! (all-frame-filters))
+@end example
+
+The same general mechanics apply to frame annotators as well.
+
+Let us define a more interesting example.  For example, in Guile there
+is a function @code{scm_call_n}, which may be invoked directly but is
+often invoked via well-known wrappers like @code{scm_call_0},
+@code{scm_call_1}, and so on.  For example here is part of a backtrace
+of an optimized Guile build, when you first start a Guile REPL:
+
+@smallexample
+#10 0x00007ffff7b6ed91 in vm_debug_engine ([...]) at vm-engine.c:815
+#11 0x00007ffff7b74380 in scm_call_n ([...]) at vm.c:1258
+#12 0x00007ffff7afb9d9 in scm_call_0 ([...]) at eval.c:475
+#13 0x00007ffff7b74a0e in sf_fill_input ([...]) at vports.c:94
+@end smallexample
+
+For the sake of the example, the arguments to each have been
+abbreviated to @code{[...]}.  Now, it might be nice if we could nest
+@code{scm_call_n} inside @code{scm_call_0}, so let's do that:
+
+@smallexample
+(use-modules (gdb) (gdb frames) (srfi srfi-41))
+
+(define (nest-scm-call-filter stream)
+  (cond
+   ((stream-null? stream)
+    ;; No frames.
+    stream)
+   (else
+    (let ((ann (stream-car stream))
+          (stream* (stream-cdr stream)))
+      ;; A base case, for when the head frame does not match.
+      (define (continue)
+        (stream-cons ann (nest-scm-call-filter stream*)))
+
+      (cond
+       ;; Is this a call to scm_call_n and is there a next frame?
+       ((and (equal? (annotated-frame-function-name ann) "scm_call_n")
+             (not (stream-null? stream*)))
+        (let* ((next (stream-car stream*))
+               (next-name (annotated-frame-function-name next)))
+          (cond
+           ;; Does the next frame have a function name and
+           ;; does it start with "scm_call_"?
+           ((and next-name
+                 (string-prefix? "scm_call_" next-name))
+            ;; A match!  Reorganize the first two frames into
+            ;; one annotated frame with a child.
+            (let* ((children (cons ann
+                                   (annotated-frame-children next)))
+                   (next (reannotate-frame next #:children children)))
+              (stream-cons next
+                           (nest-scm-call-filter (stream-cdr stream*)))))
+           (else (continue)))))
+       (else (continue)))))))
+
+(add-frame-filter! "nest-scm-call" nest-scm-call-filter)
+@end smallexample
+
+With this filter in place, the resulting backtrace looks like:
+
+@smallexample
+#10 0x00007ffff7b6ed91 in vm_debug_engine ([...]) at vm-engine.c:815
+#12 0x00007ffff7afb9d9 in scm_call_0 ([...]) at eval.c:475
+    #11 0x00007ffff7b74380 in scm_call_n ([...]) at vm.c:1258
+#13 0x00007ffff7b74a0e in sf_fill_input ([...]) at vports.c:94
+@end smallexample
+
+As you can see, frame #11 has been nested below frame #12.
+
+Sometimes, though, all this stream processing and stream recursion can
+be too complicated if your desire is just to annotate individual
+frames.  In that situation, the frame annotator API can be more
+appropriate.  For example, if we know that there are some C procedures
+that have ``aliases'' in some other language, like Scheme, then we can
+annotate them in the backtrace with their Scheme names.
+
+@smallexample
+(use-modules (gdb frames))
+
+(define *function-name-aliases*
+  '(("scm_primitive_eval" . "primitive-eval")))
+
+(define (alias-annotator ann)
+  (let* ((name (annotated-frame-function-name ann))
+         (alias (assoc-ref *function-name-aliases* name)))
+    (if alias
+        (reannotate-frame ann #:function-name
+                              (string-append "[" alias "] " name))
+        ann)))
+
+(add-frame-annotator! "alias-annotator" alias-annotator)
+@end smallexample
+
+A backtrace with this annotator in place produces:
+
+@smallexample
+#19 [...] in vm_debug_engine ([...]) at vm-engine.c:806
+#20 [...] in scm_call_n ([...]) at vm.c:1258
+#21 [...] in [primitive-eval] scm_primitive_eval ([...]) at eval.c:656
+#22 [...] in scm_eval ([...]) at eval.c:690
+#23 [...] in scm_shell ([...]) at script.c:454
+@end smallexample
+
+Again, parts have been elided with @code{[...]}.
+
+It is possible to do the job of an annotator with a filter, but if the
+task is simple enough for an annotator, it's much less code, as the
+above example shows.
+
 @node Commands In Guile
 @subsubsection Commands In Guile
 
diff --git a/gdb/guile/guile-internal.h b/gdb/guile/guile-internal.h
index 7b7f592..9733e20 100644
--- a/gdb/guile/guile-internal.h
+++ b/gdb/guile/guile-internal.h
@@ -32,6 +32,7 @@ struct block;
 struct frame_info;
 struct objfile;
 struct symbol;
+struct inferior;
 
 /* A function to pass to the safe-call routines to ignore things like
    memory errors.  */
@@ -421,6 +422,9 @@ typedef struct _frame_smob frame_smob;
 
 extern int frscm_is_frame (SCM scm);
 
+extern SCM frscm_scm_from_frame (struct frame_info *frame,
+				 struct inferior *inferior);
+
 extern frame_smob *frscm_get_frame_smob_arg_unsafe (SCM frame_scm, int arg_pos,
 						    const char *func_name);
 
@@ -578,6 +582,11 @@ extern enum ext_lang_rc gdbscm_apply_val_pretty_printer
    const struct value_print_options *options,
    const struct language_defn *language);
 
+extern enum ext_lang_bt_status gdbscm_apply_frame_filter
+  (const struct extension_language_defn *,
+   struct frame_info *frame, int flags, enum ext_lang_frame_args args_type,
+   struct ui_out *out, int frame_low, int frame_high);
+
 extern int gdbscm_breakpoint_has_cond (const struct extension_language_defn *,
 				       struct breakpoint *b);
 
@@ -594,6 +603,7 @@ extern void gdbscm_initialize_commands (void);
 extern void gdbscm_initialize_disasm (void);
 extern void gdbscm_initialize_exceptions (void);
 extern void gdbscm_initialize_frames (void);
+extern void gdbscm_initialize_frame_filters (void);
 extern void gdbscm_initialize_iterators (void);
 extern void gdbscm_initialize_lazy_strings (void);
 extern void gdbscm_initialize_math (void);
diff --git a/gdb/guile/guile.c b/gdb/guile/guile.c
index e9d2aae..3ad362b 100644
--- a/gdb/guile/guile.c
+++ b/gdb/guile/guile.c
@@ -147,7 +147,7 @@ static const struct extension_language_ops guile_extension_ops =
 
   gdbscm_apply_val_pretty_printer,
 
-  NULL, /* gdbscm_apply_frame_filter, */
+  gdbscm_apply_frame_filter,
 
   gdbscm_preserve_values,
 
@@ -663,6 +663,7 @@ initialize_gdb_module (void *data)
   gdbscm_initialize_commands ();
   gdbscm_initialize_disasm ();
   gdbscm_initialize_frames ();
+  gdbscm_initialize_frame_filters ();
   gdbscm_initialize_iterators ();
   gdbscm_initialize_lazy_strings ();
   gdbscm_initialize_math ();
diff --git a/gdb/guile/lib/gdb/frames.scm b/gdb/guile/lib/gdb/frames.scm
new file mode 100644
index 0000000..9bab59f
--- /dev/null
+++ b/gdb/guile/lib/gdb/frames.scm
@@ -0,0 +1,326 @@
+;; Frame filter support.
+;;
+;; Copyright (C) 2015 Free Software Foundation, Inc.
+;;
+;; This file is part of GDB.
+;;
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 3 of the License, or
+;; (at your option) any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gdb frames)
+  #:use-module ((gdb) #:hide (frame? symbol?))
+  #:use-module ((gdb) #:select ((frame? . gdb:frame?) (symbol? . gdb:symbol?)))
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-9)
+  #:use-module (srfi srfi-26)
+  #:use-module (srfi srfi-41)
+  #:export (reannotate-frame
+            annotated-frame?
+            annotated-frame-frame
+            annotated-frame-function-name
+            annotated-frame-address
+            annotated-frame-filename
+            annotated-frame-line
+            annotated-frame-arguments
+            annotated-frame-locals
+            annotated-frame-children
+
+            add-frame-annotator!
+            all-frame-annotators
+            remove-frame-annotator!
+            enable-frame-annotator!
+            disable-frame-annotator!
+
+            add-frame-filter!
+            all-frame-filters
+            remove-frame-filter!
+            enable-frame-filter!
+            disable-frame-filter!))
+
+(define-record-type <annotated-frame>
+  (make-annotated-frame frame function-name address filename line
+                        arguments locals children)
+  annotated-frame?
+  (frame annotated-frame-frame)            ; frame
+  (function-name annotated-frame-function-name) ; string
+  (address annotated-frame-address)        ; int
+  (filename annotated-frame-filename)      ; string
+  (line annotated-frame-line)              ; int
+  ;; local := symbol | (string . value)
+  (arguments annotated-frame-arguments)    ; (local  ...)
+  (locals annotated-frame-locals)          ; (local ...)
+  (children annotated-frame-children)      ; (annotated-frame ...)
+  )
+
+(define (frame-function-name frame)
+  (let ((f (frame-function frame)))
+    (cond
+     ((not f) f)
+     ((gdb:symbol? f) (symbol-print-name f))
+     (else (object->string f)))))
+
+(define (frame-filename frame)
+  (or (and=> (frame-sal frame)
+             (lambda (sal)
+               (and=> (sal-symtab sal) symtab-filename)))
+      ;; FIXME: Fall back to (solib-name (frame-pc frame)) if present.
+      #f))
+
+(define (frame-line frame)
+  (and=> (frame-sal frame) sal-line))
+
+(define (frame-arguments frame)
+  (let lp ((block (false-if-exception (frame-block frame))))
+    (cond
+     ((not block) '())
+     ((not (block-function block)) (lp (block-superblock block)))
+     (else
+      (filter symbol-argument? (block-symbols block))))))
+
+(define (frame-locals frame)
+  (let lp ((block (false-if-exception (frame-block frame))))
+    (if (or (not block) (block-global? block) (block-static? block))
+        '()
+        (append (remove symbol-argument? (block-symbols block))
+                (lp (block-superblock block))))))
+
+;; frame -> annotated-frame
+(define (annotate-frame frame)
+  (make-annotated-frame frame
+                        (frame-function-name frame)
+                        (frame-pc frame)
+                        (frame-filename frame)
+                        (frame-line frame)
+                        (frame-arguments frame)
+                        (frame-locals frame)
+                        '()))
+
+(define* (reannotate-frame ann #:key
+                           (function-name (annotated-frame-function-name ann))
+                           (address (annotated-frame-address ann))
+                           (filename (annotated-frame-filename ann))
+                           (line (annotated-frame-line ann))
+                           (arguments (annotated-frame-arguments ann))
+                           (locals (annotated-frame-locals ann))
+                           (children (annotated-frame-children ann)))
+  (define (valid-local? x)
+    (or (gdb:symbol? x)
+        (and (pair? x)
+             (or (gdb:symbol? (car x)) (string? (car x)))
+             (value? (cdr x)))))
+  (define (list-of? pred x)
+    (and (list? x) (and-map pred x)))
+  (unless (or (not function-name) (string? function-name))
+    (error "function-name should be a string or #f"))
+  (unless (and (exact-integer? address) (not (negative? address)))
+    (error "address should be an non-negative integer"))
+  (unless (or (not filename) (string? filename))
+    (error "filename should be a string or #f"))
+  (unless (or (not line) (and (exact-integer? line) (positive? line)))
+    (error "line expected to a positive integer or #f"))
+  (unless (list-of? valid-local? arguments)
+    (error "arguments should be a list of symbol-value pairs, \
+string-value pairs, or symbols"))
+  (unless (list-of? valid-local? locals)
+    (error "locals should be a list of symbol-value pairs, \
+string-value pairs, or symbols"))
+  (unless (and-map annotated-frame? children)
+    (error "children should be annotated frames" children))
+  (make-annotated-frame (annotated-frame-frame ann)
+                        function-name address filename line arguments locals
+                        children))
+
+(define-record-type <scoped-priority-item>
+  (make-scoped-priority-item name priority enabled? entry scope)
+  priority-item?
+  (name &name)
+  (priority &priority)
+  (enabled? &enabled? set-enabled?!)
+  (entry &entry)
+  (scope &scope))
+
+(define (add-to-priority-list priority-list name priority enabled? entry scope)
+  (when (find (lambda (x) (equal? (&name x) name)) priority-list)
+    (error "Name already present in list" name))
+  (sort (cons (make-scoped-priority-item name priority enabled? entry scope)
+              priority-list)
+        (lambda (a b)
+          (>= (&priority a) (&priority b)))))
+
+(define (remove-from-priority-list priority-list name)
+  (remove (lambda (x) (equal? (&name x) name)) priority-list))
+
+(define (priority-list-enable! priority-list name)
+  (let ((item (find (lambda (x) (equal? (&name x) name)) priority-list)))
+    (unless item
+      (error "Name not found in list" name))
+    (set-enabled?! item #t)))
+
+(define (priority-list-disable! priority-list name)
+  (let ((item (find (lambda (x) (equal? (&name x) name)) priority-list)))
+    (unless item
+      (error "Name not found in list" name))
+    (set-enabled?! item #f)))
+
+(define-syntax-rule (define-scoped-priority-list *priority-list*
+                      all-names active-entries add! remove! enable! disable!)
+  (begin
+    (define *priority-list* '())
+
+    ;; -> (name ...), from low to high priority
+    (define (all-names)
+      (reverse (map &name *priority-list*)))
+
+    ;; -> (entry ...), from low to high priority
+    (define* (active-entries progspace)
+      (reverse (filter-map (lambda (item)
+                             (and (&enabled? item)
+                                  ;; The entry matches if its progspace
+                                  ;; matches, its objfile is still
+                                  ;; valid, or if it is not associated
+                                  ;; with a specific progspace or
+                                  ;; objfile.
+                                  (let ((scope (&scope item)))
+                                    (or (not scope)
+                                        (if (progspace? scope)
+                                            (eq? progspace scope)
+                                            (objfile-valid? scope))))
+                                  (&entry item)))
+                           *priority-list*)))
+
+    (define* (add! name entry #:key objfile progspace (priority 20))
+      ;; scope := objfile | progspace | #f
+      (define (compute-scope objfile progspace)
+        (cond
+         (objfile
+          (when progspace
+            (error "Only one of #:objfile or #:progspace may be given"))
+          (unless (objfile? objfile)
+            (error "Not an objfile" objfile))
+          objfile)
+         (progspace
+          (unless (progspace? progspace)
+            (error "Not a progspace" progspace))
+          progspace)
+         (else #f)))
+      (let ((scope (compute-scope objfile progspace)))
+        (set! *priority-list*
+              (add-to-priority-list *priority-list*
+                                    name priority #t entry scope))))
+
+    (define (remove! name)
+      (set! *priority-list*
+            (remove-from-priority-list *priority-list* name)))
+
+    (define (enable! name)
+      (priority-list-enable! *priority-list* name))
+
+    (define (disable! name)
+      (priority-list-disable! *priority-list* name))))
+
+;; frame-annotator := annotated-frame -> annotated-frame
+(define-scoped-priority-list *frame-annotators*
+  all-frame-annotators
+  active-frame-annotators
+  add-frame-annotator!
+  remove-frame-annotator!
+  enable-frame-annotator!
+  disable-frame-annotator!)
+
+(define (apply-fold functions seed)
+  (fold (lambda (f seed) (f seed)) seed functions))
+
+(define (apply-frame-annotators ann)
+  (apply-fold (active-frame-annotators (current-progspace)) ann))
+
+;; frame-filter := Stream annotated-frame -> Stream annotated-frame
+(define-scoped-priority-list *frame-filters*
+  all-frame-filters
+  active-frame-filters
+  add-frame-filter!
+  remove-frame-filter!
+  enable-frame-filter!
+  disable-frame-filter!)
+
+(define (apply-frame-filters ann)
+  (apply-fold (active-frame-filters (current-progspace)) ann))
+
+;; frame int int -> Stream annotated-frame
+(define (frame-stream frame frame-low frame-high)
+  (define (make-stream frame index count)
+    (let ((frames (stream-unfold annotate-frame gdb:frame? frame-older frame)))
+      (if count
+          (stream-take frames count)
+          frames)))
+  (if (negative? frame-low)
+      ;; Traverse the stack to find the outermost N frames.
+      (let ((count (- frame-low)))
+        (let lp ((older frame) (n 0))
+          (cond
+           ((not older)
+            (make-stream frame 0 n))
+           ((< n count)
+            (lp (frame-older frame) (1+ n)))
+           (else
+            ;; "older" is now "count" frames older than "frame".  Keep
+            ;; going until we hit the oldest frame.
+            (let lp ((frame frame) (older older) (newer-index 0))
+              (if older
+                  (lp (frame-older frame) (frame-older older) (1+ newer-index))
+                  (make-stream frame newer-index count)))))))
+      (let lp ((frame frame) (frame-low frame-low) (newer-index 0))
+        ;; Cut the innermost N frames.
+        (cond
+         ((not frame) 'no-frames)
+         ((zero? frame-low)
+          (let ((count (if (eqv? frame-high -1)
+                           #f
+                           (1+ (max (- frame-high newer-index) 0)))))
+            (make-stream frame newer-index count)))
+         (else
+          (lp (frame-older frame) (1- frame-low) (1+ newer-index)))))))
+
+(define (stream->gdb-iterator stream lower)
+  (make-iterator stream stream
+                 (lambda (iter)
+                   (let ((stream (iterator-progress iter)))
+                     (cond
+                      ((stream-null? stream)
+                       (end-of-iteration))
+                      (else
+                       (set-iterator-progress! iter (stream-cdr stream))
+                       (lower (stream-car stream))))))))
+
+(define (annotated-frame->vector ann)
+  ;; C can't deal so nicely with record types, so lower to a more simple
+  ;; data structure.
+  (vector (annotated-frame-frame ann)
+          (annotated-frame-function-name ann)
+          (annotated-frame-address ann)
+          (annotated-frame-filename ann)
+          (annotated-frame-line ann)
+          (annotated-frame-arguments ann)
+          (annotated-frame-locals ann)
+          (map annotated-frame->vector (annotated-frame-children ann))))
+
+(define (apply-frame-filter frame frame-low frame-high)
+  (and (or (pair? (active-frame-filters (current-progspace)))
+           (pair? (active-frame-annotators (current-progspace))))
+       (stream->gdb-iterator
+        (apply-frame-filters
+         (stream-map
+          apply-frame-annotators
+          (frame-stream frame frame-low frame-high)))
+        annotated-frame->vector)))
+
+(load-extension "gdb" "gdbscm_load_frame_filters")
diff --git a/gdb/guile/scm-frame-filter.c b/gdb/guile/scm-frame-filter.c
new file mode 100644
index 0000000..0c9687b
--- /dev/null
+++ b/gdb/guile/scm-frame-filter.c
@@ -0,0 +1,1001 @@
+/* Scheme interface to frame filter.
+
+   Copyright (C) 2015 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* See README file in this directory for implementation notes, coding
+   conventions, et.al.  */
+
+#include "defs.h"
+#include "annotate.h"
+#include "block.h"
+#include "demangle.h"
+#include "frame.h"
+#include "inferior.h"
+#include "language.h"
+#include "objfiles.h"
+#include "symfile.h"
+#include "symtab.h"
+#include "stack.h"
+#include "valprint.h"
+#include "value.h"
+#include "guile-internal.h"
+
+/* Non-zero if the (gdb frames) module has been loaded.  */
+static int gdbscm_frame_filters_loaded = 0;
+
+/* The captured apply-frame-filter variable.  */
+static SCM apply_frame_filter = SCM_BOOL_F;
+
+/* Called by lib/gdb/frames.scm.  */
+static void
+gdbscm_load_frame_filters (void *unused)
+{
+  if (gdbscm_frame_filters_loaded)
+    return;
+
+  gdbscm_frame_filters_loaded = 1;
+
+  apply_frame_filter = scm_c_lookup ("apply-frame-filter");
+}
+
+/* Helper to throw type errors as Scheme exceptions.  */
+static void
+gdbscm_throw_type_error (const char *subr, int arg_pos, SCM val,
+                         const char *expected_type)
+{
+  gdbscm_throw (gdbscm_make_type_error (subr, arg_pos, val, expected_type));
+}
+
+/* We surround TRY_CATCH blocks with Scheme dynwinds, so that Scheme
+   exceptions can interoperate with GDB exceptions.  Since GDB's
+   TRY_CATCH saves and restores cleanups around its body, and
+   automatically runs inner cleanups on exception, we arrange to do the
+   same on Scheme exceptions.  */
+static void
+dynwind_restore_cleanups (void *data)
+{
+  struct cleanup *cleanups = data;
+  restore_cleanups (cleanups);
+}
+
+static void
+dynwind_do_cleanups (void *data)
+{
+  struct cleanup *cleanups = data;
+  do_cleanups (cleanups);
+}
+
+/* Use BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS instead of TRY_CATCH when
+   you are inside gdbscm_safe_call, and close it with
+   RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND.  This will cause
+   GDB exceptions raised within the block to be re-raised as Scheme
+   exceptions.  Leaving the block in any way -- whether normally, via a
+   GDB exception, or a Scheme exception -- will cause any cleanups that
+   were registered within the block to run.
+
+   Given that almost all code in this file is dynamically within one of
+   these blocks, when should you add a new one?  There are only a few
+   cases:
+
+     1. You need to call make_cleanup_ui_out_tuple_begin_end or
+        some other bracketed UI operation.
+     2. You are allocating something "big" that should be cleaned up
+        promptly, like make_cleanup_ui_file_delete.
+     3. You want to register a Scheme unwind procedure, and need to
+        prevent GDB exceptions from passing your dynwind.  */
+
+#define BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS()                        \
+  do {                                                                  \
+    volatile struct gdb_exception __except;                             \
+    /* Any cleanup pushed within the TRY_CATCH will be run on GDB       \
+       exception.  We will have to run them manually on normal exit or  \
+       Scheme exception.  */                                            \
+    scm_dynwind_begin (0);                                              \
+    /* Save the cleanup stack, and arrange to restore it after any exit \
+       from the TRY_CATCH, local or non-local.  */                      \
+    scm_dynwind_unwind_handler (dynwind_restore_cleanups,               \
+                                save_cleanups (),                       \
+                                SCM_F_WIND_EXPLICITLY);                 \
+    TRY_CATCH (__except, RETURN_MASK_ALL)                               \
+      {                                                                 \
+        struct cleanup *__cleanups = make_cleanup (null_cleanup, NULL); \
+        /* Ensure cleanups run on Scheme exception.  */                 \
+        scm_dynwind_unwind_handler (dynwind_do_cleanups, __cleanups, 0);\
+        do
+
+#define RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND()              \
+        while (0);                                                      \
+        /* Ensure cleanups run on normal exit.  */                      \
+        do_cleanups (__cleanups);                                       \
+      }                                                                 \
+    /* Pop the dynwind and restore the saved cleanup stack.  */         \
+    scm_dynwind_end ();                                                 \
+    if (__except.reason < 0)                                            \
+      /* Rethrow GDB exception as Scheme exception.  */                 \
+      gdbscm_throw_gdb_exception (__except);                            \
+  } while (0)
+
+
+/* Helper function to extract a symbol, a name, a language definition,
+   and a value from ITEM, which is an element of a Scheme "arguments" or
+   "locals" list.
+
+   ITEM will either be a pair of a string and a value, a pair of a
+   symbol and a value, or just a symbol.  NAME is a pass-through
+   argument where the name of the symbol will be written.  NAME is
+   allocated in this function, and a cleanup handler is registered if
+   needed.  SYM is a pass-through argument where the symbol will be
+   written.  If the name is a string and not a symbol, SYM will be set
+   to NULL.  LANGUAGE is also a pass-through argument denoting the
+   language attributed to the symbol.  In the case of SYM being NULL,
+   this will be set to the current language.  Finally, VALUE will be set
+   to the unwrapped GDB value, if ITEM is a pair, and otherwise
+   NULL.  */
+static void
+extract_sym_and_value (SCM item, const char **name, struct symbol **sym,
+                       const struct language_defn **language,
+                       struct value **value, struct gdbarch *gdbarch)
+{
+  if (scm_is_pair (item))
+    {
+      SCM symbol_scm = scm_car (item), value_scm = scm_cdr (item);
+      SCM exception = SCM_BOOL_F;
+
+      if (scm_is_string (symbol_scm))
+        {
+          *name = gdbscm_scm_to_host_string (symbol_scm, NULL,
+					     &exception);
+          if (!*name)
+            gdbscm_throw (exception);
+          make_cleanup (xfree, name);
+
+          *sym = NULL;
+          *language = current_language;
+        }
+      else
+        {
+          *sym = syscm_get_valid_symbol_arg_unsafe (symbol_scm,
+						    GDBSCM_ARG_NONE,
+                                                    "print-frame");
+          *name = SYMBOL_PRINT_NAME (*sym);
+
+          if (language_mode == language_mode_auto)
+            *language = language_def (SYMBOL_LANGUAGE (*sym));
+          else
+            *language = current_language;
+        }
+
+      *value = vlscm_convert_value_from_scheme ("print-frame",
+                                                GDBSCM_ARG_NONE,
+                                                value_scm,
+                                                &exception,
+                                                gdbarch,
+                                                *language);
+      if (!*value)
+        gdbscm_throw (exception);
+    }
+  else
+    {
+      *sym = syscm_get_valid_symbol_arg_unsafe (item, GDBSCM_ARG_NONE,
+                                                "print-frame");
+      *name = SYMBOL_PRINT_NAME (*sym);
+
+      if (language_mode == language_mode_auto)
+        *language = language_def (SYMBOL_LANGUAGE (*sym));
+      else
+        *language = current_language;
+
+      *value = NULL;
+    }
+}
+
+enum mi_print_types
+{
+  MI_PRINT_ARGS,
+  MI_PRINT_LOCALS
+};
+
+/* MI prints only certain values according to the type of symbol and
+   also what the user has specified.  SYM is the symbol to check, and
+   MI_PRINT_TYPES is an enum specifying what the user wants emitted
+   for the MI command in question.  */
+static int
+mi_should_print (struct symbol *sym, enum mi_print_types type)
+{
+  int print_me = 0;
+
+  switch (SYMBOL_CLASS (sym))
+    {
+    default:
+    case LOC_UNDEF:     /* catches errors        */
+    case LOC_CONST:     /* constant              */
+    case LOC_TYPEDEF:   /* local typedef         */
+    case LOC_LABEL:     /* local label           */
+    case LOC_BLOCK:     /* local function        */
+    case LOC_CONST_BYTES:       /* loc. byte seq.        */
+    case LOC_UNRESOLVED:        /* unresolved static     */
+    case LOC_OPTIMIZED_OUT:     /* optimized out         */
+      print_me = 0;
+      break;
+
+    case LOC_ARG:       /* argument              */
+    case LOC_REF_ARG:   /* reference arg         */
+    case LOC_REGPARM_ADDR:      /* indirect register arg */
+    case LOC_LOCAL:     /* stack local           */
+    case LOC_STATIC:    /* static                */
+    case LOC_REGISTER:  /* register              */
+    case LOC_COMPUTED:  /* computed location     */
+      if (type == MI_PRINT_LOCALS)
+        print_me = ! SYMBOL_IS_ARGUMENT (sym);
+      else
+        print_me = SYMBOL_IS_ARGUMENT (sym);
+    }
+  return print_me;
+}
+
+/* Helper function which outputs a type name extracted from VAL to a
+   "type" field in the output stream OUT.  OUT is the ui-out structure
+   the type name will be output too, and VAL is the value that the
+   type will be extracted from.  */
+static void
+gdbscm_print_type (struct ui_out *out, struct value *val)
+{
+  struct type *type;
+
+  BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS ()
+    {
+      struct ui_file *stb = mem_fileopen ();
+      make_cleanup_ui_file_delete (stb);
+      type = check_typedef (value_type (val));
+      type_print (value_type (val), "", stb, -1);
+      ui_out_field_stream (out, "type", stb);
+    }
+  RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND ();
+}
+
+/* Helper function which outputs a value to an output field in a
+   stream.  OUT is the ui-out structure the value will be output to,
+   VAL is the value that will be printed, OPTS contains the value
+   printing options, ARGS_TYPE is an enumerator describing the
+   argument format, and LANGUAGE is the language_defn that the value
+   will be printed with. */
+static void
+gdbscm_print_value (struct ui_out *out, struct value *val,
+                    const struct value_print_options *opts,
+                    int indent,
+                    enum ext_lang_frame_args args_type,
+                    const struct language_defn *language)
+{
+  int should_print = 0;
+  int local_indent = (4 * indent);
+
+  /* Never set an indent level for common_val_print if MI.  */
+  if (ui_out_is_mi_like_p (out))
+    local_indent = 0;
+
+  /* MI does not print certain values, differentiated by type,
+     depending on what ARGS_TYPE indicates.  Test type against option.
+     For CLI print all values.  */
+  if (args_type == MI_PRINT_SIMPLE_VALUES
+      || args_type == MI_PRINT_ALL_VALUES)
+    {
+      struct type *type = check_typedef (value_type (val));
+
+      if (args_type == MI_PRINT_ALL_VALUES)
+        should_print = 1;
+      else if (args_type == MI_PRINT_SIMPLE_VALUES
+               && TYPE_CODE (type) != TYPE_CODE_ARRAY
+               && TYPE_CODE (type) != TYPE_CODE_STRUCT
+               && TYPE_CODE (type) != TYPE_CODE_UNION)
+        should_print = 1;
+    }
+  else if (args_type != NO_VALUES)
+    should_print = 1;
+
+  if (should_print)
+    {
+      BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS ()
+        {
+          struct ui_file *stb = mem_fileopen ();
+          make_cleanup_ui_file_delete (stb);
+          common_val_print (val, stb, indent, opts, language);
+          ui_out_field_stream (out, "value", stb);
+        }
+      RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND ();
+    }
+}
+
+enum print_args_field
+{
+  WITH_ARGS_FIELD,
+  WITHOUT_ARGS_FIELD
+};
+
+/* Helper function to output a single frame argument and value to an
+   output stream.  This function will account for entry values if the FV
+   parameter is populated, the frame argument has entry values
+   associated with them, and the appropriate "set entry-value" options
+   are set.  Will output in CLI or MI like format depending on the type
+   of output stream detected.  OUT is the output stream, SYM_NAME is the
+   name of the symbol.  If SYM_NAME is populated then it must have an
+   accompanying value in the parameter FV.  FA is a frame argument
+   structure.  If FA is populated, both SYM_NAME and FV are ignored.
+   OPTS contains the value printing options, ARGS_TYPE is an enumerator
+   describing the argument format, PRINT_ARGS_FIELD is a flag which
+   indicates if we output "ARGS=1" in MI output in commands where both
+   arguments and locals are printed.  */
+static void
+gdbscm_print_single_arg (struct ui_out *out,
+                         const char *sym_name,
+                         struct frame_arg *fa,
+                         struct value *fv,
+                         const struct value_print_options *opts,
+                         enum ext_lang_frame_args args_type,
+			 enum print_args_field print_args_field,
+                         const struct language_defn *language)
+{
+  struct value *val;
+
+  if (fa != NULL)
+    {
+      if (fa->val == NULL && fa->error == NULL)
+        return;
+      language = language_def (SYMBOL_LANGUAGE (fa->sym));
+      val = fa->val;
+    }
+  else
+    val = fv;
+
+  BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS ()
+    {
+      /*  MI has varying rules for tuples, but generally if there is
+          only one element in each item in the list, do not start a
+          tuple.  The exception is -stack-list-variables which emits an
+          ARGS="1" field if the value is a frame argument.  This is
+          denoted in this function with PRINT_ARGS_FIELD which is flag
+          from the caller to emit the ARGS field.  */
+      if (ui_out_is_mi_like_p (out))
+        {
+          if (print_args_field == WITH_ARGS_FIELD
+	      || args_type != NO_VALUES)
+            make_cleanup_ui_out_tuple_begin_end (out, NULL);
+        }
+
+      annotate_arg_begin ();
+
+      /* If frame argument is populated, check for entry-values and the
+         entry value options.  */
+      if (fa != NULL)
+        {
+          struct ui_file *stb;
+
+          stb = mem_fileopen ();
+          make_cleanup_ui_file_delete (stb);
+          fprintf_symbol_filtered (stb, SYMBOL_PRINT_NAME (fa->sym),
+                                   SYMBOL_LANGUAGE (fa->sym),
+                                   DMGL_PARAMS | DMGL_ANSI);
+          if (fa->entry_kind == print_entry_values_compact)
+            {
+              fputs_filtered ("=", stb);
+
+              fprintf_symbol_filtered (stb, SYMBOL_PRINT_NAME (fa->sym),
+                                       SYMBOL_LANGUAGE (fa->sym),
+                                       DMGL_PARAMS | DMGL_ANSI);
+            }
+          if (fa->entry_kind == print_entry_values_only
+              || fa->entry_kind == print_entry_values_compact)
+            {
+              fputs_filtered ("@entry", stb);
+            }
+          ui_out_field_stream (out, "name", stb);
+        }
+      else
+        /* Otherwise, just output the name.  */
+        ui_out_field_string (out, "name", sym_name);
+
+      annotate_arg_name_end ();
+
+      if (! ui_out_is_mi_like_p (out))
+        ui_out_text (out, "=");
+
+      if (print_args_field == WITH_ARGS_FIELD)
+        ui_out_field_int (out, "arg", 1);
+
+      /* For MI print the type, but only for simple values.  This seems
+         weird, but this is how MI choose to format the various output
+         types.  */
+      if (args_type == MI_PRINT_SIMPLE_VALUES && val != NULL)
+        gdbscm_print_type (out, val);
+
+      if (val != NULL)
+        annotate_arg_value (value_type (val));
+
+      /* If the output is to the CLI, and the user option "set print
+         frame-arguments" is set to none, just output "...".  */
+      if (! ui_out_is_mi_like_p (out) && args_type == NO_VALUES)
+        ui_out_field_string (out, "value", "...");
+      else
+        {
+          /* Otherwise, print the value for both MI and the CLI, except
+             for the case of MI_PRINT_NO_VALUES.  */
+          if (args_type != NO_VALUES)
+            {
+              if (val == NULL)
+                {
+                  gdb_assert (fa != NULL && fa->error != NULL);
+                  ui_out_field_fmt (out, "value",
+                                    _("<error reading variable: %s>"),
+                                    fa->error);
+                }
+              else
+                gdbscm_print_value (out, val, opts, 0, args_type,
+				    language);
+            }
+        }
+    }
+  RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND ();
+}
+
+/* Helper function to print one local.  LOCAL is the pair or symbol that
+   is compatible with extract_sym_and_value, OUT is the output stream,
+   INDENT is whether we should indent the output (for CLI), ARGS_TYPE is
+   an enumerator describing the argument format, PRINT_ARGS_FIELD is
+   flag which indicates whether to output the ARGS field in the case of
+   -stack-list-variables and FRAME is the backing frame.  */
+static void
+gdbscm_print_local (SCM local,
+                    struct ui_out *out,
+                    int indent,
+                    enum ext_lang_frame_args args_type,
+                    struct frame_info *frame,
+		    enum print_args_field print_args_field,
+                    struct gdbarch *gdbarch)
+{
+  struct value_print_options opts;
+  const struct language_defn *language;
+  const char *sym_name;
+  struct value *val;
+  struct symbol *sym;
+  int local_indent = 8 + (8 * indent);
+  int out_is_mi = ui_out_is_mi_like_p (out);
+
+  get_user_print_options (&opts);
+  opts.deref_ref = 1;
+
+  extract_sym_and_value (local, &sym_name, &sym, &language, &val,
+			 gdbarch);
+
+  if (sym && out_is_mi && ! mi_should_print (sym, MI_PRINT_LOCALS))
+    return;
+
+  if (!val)
+    /* If the object did not provide a value, read it.  */
+    val = read_var_value (sym, frame);
+
+  BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS ()
+    {
+      /* With PRINT_NO_VALUES, MI does not emit a tuple normally as each
+         output contains only one field.  The exception is
+         -stack-list-variables, which always provides a tuple.  */
+      if (out_is_mi)
+        {
+          if (print_args_field == WITH_ARGS_FIELD
+	      || args_type != NO_VALUES)
+            make_cleanup_ui_out_tuple_begin_end (out, NULL);
+        }
+      else
+        {
+          /* If the output is not MI we indent locals.  */
+          ui_out_spaces (out, local_indent);
+        }
+
+      ui_out_field_string (out, "name", sym_name);
+
+      if (! out_is_mi)
+        ui_out_text (out, " = ");
+
+      if (args_type == MI_PRINT_SIMPLE_VALUES)
+        gdbscm_print_type (out, val);
+
+      /* CLI always prints values for locals.  MI uses the
+         simple/no/all system.  */
+      if (! out_is_mi)
+        {
+          int val_indent = (indent + 1) * 4;
+
+          gdbscm_print_value (out, val, &opts, val_indent, args_type,
+			      language);
+        }
+      else
+        {
+          if (args_type != NO_VALUES)
+            gdbscm_print_value (out, val, &opts, 0, args_type, language);
+        }
+    }
+  RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND ();
+
+  ui_out_text (out, "\n");
+}
+
+/* Helper function for printing locals.  This function largely just
+   creates the wrapping tuple, and calls enumerate_locals.  Returns
+   EXT_LANG_BT_ERROR on error, or EXT_LANG_BT_OK on success.  */
+static void
+gdbscm_print_locals (SCM locals,
+                     struct ui_out *out,
+                     enum ext_lang_frame_args args_type,
+                     int indent,
+                     struct frame_info *frame,
+		     enum print_args_field print_args_field,
+                     struct gdbarch *gdbarch)
+{
+  BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS ()
+    {
+      make_cleanup_ui_out_list_begin_end (out, "locals");
+
+      for (; scm_is_pair (locals); locals = scm_cdr (locals))
+        {
+          SCM local = scm_car (locals);
+
+          gdbscm_print_local (local, out, indent, args_type, frame,
+			      print_args_field, gdbarch);
+        }
+
+      if (!scm_is_null (locals))
+        gdbscm_throw_type_error ("print-locals", GDBSCM_ARG_NONE,
+                                 locals, "null-terminated locals list");
+    }
+  RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND ();
+}
+
+/* Helper function to print an argument.  ARG is a pair or a symbol, in
+   the format expected by extract_sym_and_value, OUT is the output
+   stream, ARGS_TYPE is an enumerator describing the argument format,
+   PRINT_ARGS_FIELD is a flag which indicates if we output "ARGS=1" in
+   MI output in commands where both arguments and locals are printed,
+   and FRAME is the backing frame.  */
+static void
+gdbscm_print_arg (SCM arg, struct ui_out *out,
+                  enum ext_lang_frame_args args_type,
+                  struct frame_info *frame,
+		  enum print_args_field print_args_field,
+                  struct gdbarch *gdbarch)
+{
+  struct value_print_options opts;
+  const struct language_defn *language;
+  const char *sym_name;
+  struct symbol *sym;
+  struct value *val;
+
+  get_user_print_options (&opts);
+  if (args_type == CLI_SCALAR_VALUES)
+    opts.summary = 1;
+  opts.deref_ref = 1;
+
+  extract_sym_and_value (arg, &sym_name, &sym, &language, &val, gdbarch);
+
+  if (sym && ui_out_is_mi_like_p (out)
+      && ! mi_should_print (sym, MI_PRINT_ARGS))
+    return;
+
+  annotate_arg_begin ();
+
+  if (val)
+    {
+      /* If the annotated frame provides a value, just print that.  */
+      gdbscm_print_single_arg (out, sym_name, NULL, val, &opts,
+                               args_type, print_args_field,
+                               language);
+    }
+  else
+    {
+      struct frame_arg arg, entryarg;
+
+      /* Otherwise, the annotated frame did not provide a value, so this
+         is a frame argument to be read by GDB.  In this case we have to
+         account for entry-values.  */
+      read_frame_arg (sym, frame, &arg, &entryarg);
+      make_cleanup (xfree, arg.error);
+      make_cleanup (xfree, entryarg.error);
+
+      if (arg.entry_kind != print_entry_values_only)
+        gdbscm_print_single_arg (out, NULL, &arg, NULL, &opts,
+                                 args_type, print_args_field, NULL);
+
+      if (entryarg.entry_kind != print_entry_values_no)
+        {
+          if (arg.entry_kind != print_entry_values_only)
+            {
+              /* Delimit the two arguments that we are printing.  */
+              ui_out_text (out, ", ");
+              ui_out_wrap_hint (out, "    ");
+            }
+
+          gdbscm_print_single_arg (out, NULL, &entryarg, NULL, &opts,
+                                   args_type, print_args_field, NULL);
+        }
+    }
+
+
+  annotate_arg_end ();
+}
+
+/* Helper function for printing frame arguments.  */
+static void
+gdbscm_print_args (SCM args, struct ui_out *out,
+                   enum ext_lang_frame_args args_type,
+                   struct frame_info *frame,
+		   enum print_args_field print_args_field,
+                   struct gdbarch *gdbarch)
+{
+  BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS ()
+    {
+      int arg_index = 0;
+
+      make_cleanup_ui_out_list_begin_end (out, "args");
+
+      annotate_frame_args ();
+      if (! ui_out_is_mi_like_p (out))
+        ui_out_text (out, " (");
+
+      for (; scm_is_pair (args); args = scm_cdr (args), arg_index++)
+        {
+          SCM arg = scm_car (args);
+
+          if (arg_index > 0)
+            ui_out_text (out, ", ");
+
+          gdbscm_print_arg (arg, out, args_type, frame,
+			    print_args_field, gdbarch);
+        }
+
+      if (!scm_is_null (args))
+        gdbscm_throw_type_error ("print-args", GDBSCM_ARG_NONE,
+                                 args, "null-terminated argument list");
+
+      if (! ui_out_is_mi_like_p (out))
+        ui_out_text (out, ")");
+    }
+  RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND ();
+}
+
+/*  Print a single frame to the designated output stream, detecting
+    whether the output is MI or console, and formatting the output
+    according to the conventions of that protocol.  ANN is the annotated
+    frame object, as a vector.  FLAGS is an integer describing the
+    various print options.  The FLAGS variables is described in
+    "apply_frame_filter" function.  ARGS_TYPE is an enumerator
+    describing the argument format.  OUT is the output stream to print,
+    INDENT is the level of indention for this frame, in the case of
+    child frames. */
+static void
+gdbscm_print_frame (SCM ann, int flags, enum ext_lang_frame_args args_type,
+                    struct ui_out *out, int indent)
+{
+  struct gdbarch *gdbarch;
+  struct frame_info *frame;
+  struct value_print_options opts;
+  int print_level, print_frame_info, print_args, print_locals;
+  SCM frame_scm, function_name_scm, address_scm, filename_scm, line_scm;
+  SCM arguments_scm, locals_scm, children_scm;
+
+  /* Extract print settings from FLAGS.  */
+  print_level = (flags & PRINT_LEVEL) ? 1 : 0;
+  print_frame_info = (flags & PRINT_FRAME_INFO) ? 1 : 0;
+  print_args = (flags & PRINT_ARGS) ? 1 : 0;
+  print_locals = (flags & PRINT_LOCALS) ? 1 : 0;
+
+  get_user_print_options (&opts);
+
+  frame_scm = scm_c_vector_ref (ann, 0);
+  function_name_scm = scm_c_vector_ref (ann, 1);
+  address_scm = scm_c_vector_ref (ann, 2);
+  filename_scm = scm_c_vector_ref (ann, 3);
+  line_scm = scm_c_vector_ref (ann, 4);
+  arguments_scm = scm_c_vector_ref (ann, 5);
+  locals_scm = scm_c_vector_ref (ann, 6);
+  children_scm = scm_c_vector_ref (ann, 7);
+
+  {
+    frame_smob *smob =
+      frscm_get_frame_smob_arg_unsafe (frame_scm, 0, "print-frame");
+    frame = frscm_frame_smob_to_frame (smob);
+  }
+
+  /* stack-list-variables.  */
+  if (print_locals && print_args && ! print_frame_info)
+    {
+      BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS ()
+        {
+          /* Getting the frame arch needs to happen within a dynwind.  */
+          gdbarch = get_frame_arch (frame);
+
+          make_cleanup_ui_out_list_begin_end (out, "variables");
+          gdbscm_print_args (arguments_scm, out, args_type, frame,
+			     WITH_ARGS_FIELD, gdbarch);
+          gdbscm_print_locals (locals_scm, out, args_type, indent, frame,
+			       WITH_ARGS_FIELD, gdbarch);
+        }
+      RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND ();
+      /* FIXME: Print variables for child frames?  */
+      return;
+    }
+
+  BEGIN_DYNWIND_AND_CATCH_GDB_EXCEPTIONS ()
+    {
+      /* Getting the frame arch needs to happen within a dynwind.  */
+      gdbarch = get_frame_arch (frame);
+
+      /* -stack-list-locals does not require a wrapping frame
+          attribute.  */
+      if (print_frame_info || (print_args && ! print_locals))
+        make_cleanup_ui_out_list_begin_end (out, "frame");
+
+      if (print_frame_info && indent > 0)
+        {
+          /* Child frames are also printed with this function
+             (recursively) and are printed with indention.  */
+          ui_out_spaces (out, indent * 4);
+        }
+
+      /* Print frame level.  MI does not require the level if
+         locals/variables only are being printed.  */
+      if ((print_frame_info || print_args) && print_level)
+        {
+          CORE_ADDR address = 0;
+          int level = frame_relative_level (frame);
+
+          if (gdbscm_is_true (address_scm))
+            address = gdbscm_scm_to_ulongest (address_scm);
+
+          annotate_frame_begin (print_level ? level : 0, gdbarch,
+				address);
+          ui_out_text (out, "#");
+          ui_out_field_fmt_int (out, 2, ui_left, "level", level);
+        }
+
+      if (print_frame_info)
+        {
+          /* Print address to the address field.  If an address is not
+             provided, print nothing.  */
+          if (opts.addressprint && gdbscm_is_true (address_scm))
+            {
+              CORE_ADDR address = gdbscm_scm_to_ulongest (address_scm);
+              annotate_frame_address ();
+              ui_out_field_core_addr (out, "addr", gdbarch, address);
+              annotate_frame_address_end ();
+              ui_out_text (out, " in ");
+            }
+
+          /* Print frame function name.  */
+          if (gdbscm_is_false (function_name_scm))
+            {
+              annotate_frame_function_name ();
+              ui_out_field_skip (out, "func");
+            }
+          else if (scm_is_string (function_name_scm))
+            {
+              SCM exception = SCM_BOOL_F;
+              char *function;
+
+              function = gdbscm_scm_to_host_string (function_name_scm,
+						    NULL,
+                                                    &exception);
+              if (!function)
+                gdbscm_throw (exception);
+              make_cleanup (xfree, function);
+
+              annotate_frame_function_name ();
+              ui_out_field_string (out, "func", function);
+            }
+          else
+            {
+              gdbscm_throw_type_error ("print-frame", GDBSCM_ARG_NONE,
+                                       function_name_scm,
+                                       "string or false");
+            }
+        }
+
+      /* Frame arguments.  Check the result, and error if something went
+         wrong.  */
+      if (print_args)
+        gdbscm_print_args (arguments_scm, out, args_type, frame,
+			   WITHOUT_ARGS_FIELD, gdbarch);
+
+      /* File name/source/line number information.  */
+      if (print_frame_info)
+        {
+          char *filename = NULL;
+
+          annotate_frame_source_begin ();
+
+          if (gdbscm_is_true (filename_scm))
+            {
+              SCM exception = SCM_BOOL_F;
+
+              filename = gdbscm_scm_to_host_string (filename_scm, NULL,
+						    &exception);
+
+              if (!filename)
+                gdbscm_throw (exception);
+
+              make_cleanup (xfree, filename);
+
+              ui_out_wrap_hint (out, "   ");
+              ui_out_text (out, " at ");
+              annotate_frame_source_file ();
+              ui_out_field_string (out, "file", filename);
+              annotate_frame_source_file_end ();
+
+              if (gdbscm_is_true (line_scm))
+                {
+                  int line = scm_to_int (line_scm);
+                  ui_out_text (out, ":");
+                  annotate_frame_source_line ();
+                  ui_out_field_int (out, "line", line);
+                }
+            }
+        }
+
+      /* For MI we need to deal with child frames, so if MI output
+         detected do not send newline.  */
+      if (! ui_out_is_mi_like_p (out))
+        {
+          annotate_frame_end ();
+          ui_out_text (out, "\n");
+        }
+
+      if (print_locals)
+        gdbscm_print_locals (locals_scm, out, args_type, indent, frame,
+			     WITHOUT_ARGS_FIELD, gdbarch);
+
+      /* Finally recursively print child frames, if any.  */
+      if (! ui_out_is_mi_like_p (out))
+        indent++;
+
+      /* No need for another dynwind; since we're at the end of the
+         function, the RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND
+         below will close the "children" list just fine.  */
+      make_cleanup_ui_out_list_begin_end (out, "children");
+      for (;
+	   scm_is_pair (children_scm);
+	   children_scm = scm_cdr (children_scm))
+        {
+          SCM child = scm_car (children_scm);
+
+          gdbscm_print_frame (child, flags, args_type, out, indent);
+        }
+
+      if (!scm_is_null (children_scm))
+        gdbscm_throw_type_error ("print-frame", GDBSCM_ARG_NONE,
+                                 children_scm,
+                                 "null-terminated child list");
+    }
+  RETHROW_GDB_EXCEPTIONS_TO_SCHEME_AND_END_DYNWIND ();
+}
+
+/* Iterate through the frame stream, printing each one.  Throws Scheme
+   exceptions on error.  */
+static void
+print_annotated_frame_stream (SCM iter, int flags,
+                              enum ext_lang_frame_args args_type,
+                              struct ui_out *out)
+{
+  while (1)
+    {
+      SCM ann = itscm_safe_call_next_x (iter, gdbscm_memory_error_p);
+
+      if (itscm_is_end_of_iteration (ann))
+        break;
+
+      /* Since we handle all exceptions via gdbscm_safe_call, really
+         we'd like an itcm_call_next_x method that propagates the
+         exception, but lacking that we manually re-throw as needed.  */
+      if (gdbscm_is_exception (ann))
+        gdbscm_throw (ann);
+
+      gdbscm_print_frame (ann, flags, args_type, out, 0);
+    }
+}
+
+struct print_args {
+  SCM iter;
+  int flags;
+  enum ext_lang_frame_args args_type;
+  struct ui_out *out;
+};
+
+/* Returns normally if successful, or otherwise throws an exception.  */
+static SCM
+do_print_annotated_frame_stream (void *data)
+{
+  struct print_args *args = data;
+
+  print_annotated_frame_stream (args->iter, args->flags, args->args_type,
+                                args->out);
+
+  return SCM_BOOL_T;
+}
+
+/*  This is the only publicly exported function in this file.  FRAME is
+    the source frame to start frame-filter invocation.  FLAGS is an
+    integer holding the flags for printing.  The following elements of
+    the FRAME_FILTER_FLAGS enum denotes the make-up of FLAGS:
+    PRINT_LEVEL is a flag indicating whether to print the frame's
+    relative level in the output.  PRINT_FRAME_INFO is a flag that
+    indicates whether this function should print the frame information,
+    PRINT_ARGS is a flag that indicates whether to print frame
+    arguments, and PRINT_LOCALS, likewise, with frame local variables.
+    ARGS_TYPE is an enumerator describing the argument format, OUT is
+    the output stream to print.  FRAME_LOW is the beginning of the slice
+    of frames to print, and FRAME_HIGH is the upper limit of the frames
+    to count.  Returns EXT_LANG_BT_ERROR on error, or
+    EXT_LANG_BT_COMPLETED on success.  */
+
+enum ext_lang_bt_status
+gdbscm_apply_frame_filter (const struct extension_language_defn *extlang,
+                          struct frame_info *frame, int flags,
+                          enum ext_lang_frame_args args_type,
+                          struct ui_out *out, int frame_low,
+			   int frame_high)
+{
+  struct inferior *inferior;
+  SCM result;
+
+  /* Note that it's possible to have loaded the Guile interface, but not
+     yet loaded (gdb frames), so checking gdb_scheme_initialized is not
+     sufficient.  */
+  if (!gdbscm_frame_filters_loaded)
+    return EXT_LANG_BT_NO_FILTERS;
+
+  inferior = current_inferior();
+  result = gdbscm_safe_call_3 (scm_variable_ref (apply_frame_filter),
+			       frscm_scm_from_frame (frame, inferior),
+                               scm_from_int (frame_low),
+                               scm_from_int (frame_high),
+                               gdbscm_memory_error_p);
+
+  if (gdbscm_is_false (result))
+    return EXT_LANG_BT_NO_FILTERS;
+
+  if (itscm_is_iterator (result))
+    {
+      struct print_args args = { result, flags, args_type, out };
+
+      /* Recurse through gdbscm_call_guile so that we can just throw
+         exceptions on error.  */
+      result = gdbscm_call_guile (do_print_annotated_frame_stream, &args,
+                                  gdbscm_memory_error_p);
+    }
+
+  if (gdbscm_is_exception (result))
+    {
+      gdbscm_print_gdb_exception (SCM_BOOL_F, result);
+      return EXT_LANG_BT_ERROR;
+    }
+
+  return EXT_LANG_BT_COMPLETED;
+}
+
+/* Register gdbscm_load_frame_filters for calling by (gdb frames).  */
+void
+gdbscm_initialize_frame_filters (void)
+{
+  scm_c_register_extension ("gdb", "gdbscm_load_frame_filters",
+                            gdbscm_load_frame_filters, NULL);
+}
diff --git a/gdb/guile/scm-frame.c b/gdb/guile/scm-frame.c
index a30c093..3927714 100644
--- a/gdb/guile/scm-frame.c
+++ b/gdb/guile/scm-frame.c
@@ -213,7 +213,7 @@ gdbscm_frame_p (SCM scm)
 /* Create a new <gdb:frame> object that encapsulates FRAME.
    Returns a <gdb:exception> object if there is an error.  */
 
-static SCM
+SCM
 frscm_scm_from_frame (struct frame_info *frame, struct inferior *inferior)
 {
   frame_smob *f_smob, f_smob_for_lookup;
-- 
2.1.4


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