diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1f15ae6..9af328d 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,34 @@
 2015-04-09  Andy Wingo  <wingo@igalia.com>
 
+	* guile/scm-symbol.c (gdbscm_lookup_symbol): Don't error if there
+	is no selected frame and no block is selected; instead, fall back
+	to the current frame.
+	* guile/scm-frame-unwinder.c: New file.
+	* guile/lib/gdb/frame-unwinders.scm: New file.
+	* guile/guile.c (initialize_gdb_module): Call
+	gdbscm_initialize_frame_unwinders.
+	* guile/guile-internal.h (gdbscm_initialize_frame_unwinders): New
+	declaration.
+	* frame.c (get_prev_frame): Detect recursive unwinds, returning
+	NULL in that case.
+	* frame-unwind.h (frame_unwind_got_bytes): Make buf arg const.
+	(frame_unwind_is_unwinding): New declaration.
+	* frame-unwind.c (is_unwinding): New file-local variable.
+	(set_is_unwinding, unset_is_unwinding): New file-local helpers.
+	(frame_unwind_is_unwinding): New exported predicate.
+	(frame_unwind_try_handler): Arrange for
+	frame_unwind_is_unwinding to return true when unwinding the
+	innermost frame.
+	(frame_unwind_got_bytes): Make buf arg const.
+	* data-directory/Makefile.in (GUILE_SOURCE_FILES): Add
+	frame-unwinders.scm.
+	(GUILE_COMPILED_FILES): Add frame-unwinders.go.
+	* Makefile.in (SUBDIR_GUILE_OBS): Add scm-frame-unwinder.o.
+	(SUBDIR_GUILE_SRCS): Add scm-frame-unwinder.c
+	(scm-frame-unwinder.o): New target.
+
+2015-04-09  Andy Wingo  <wingo@igalia.com>
+
 	* guile/scm-frame-filter.c:
 	* guile/lib/gdb/frame-filters.scm: New files.
 	* guile/guile.c (guile_extension_ops): Add the Guile frame
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 4c664ae..08f432b 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -322,6 +322,7 @@ SUBDIR_GUILE_OBS = \
 	scm-exception.o \
 	scm-frame.o \
 	scm-frame-filter.o \
+	scm-frame-unwinder.o \
 	scm-gsmob.o \
 	scm-iterator.o \
 	scm-lazy-string.o \
@@ -349,6 +350,7 @@ SUBDIR_GUILE_SRCS = \
 	guile/scm-exception.c \
 	guile/scm-frame.c \
 	guile/scm-frame-filter.c \
+	guile/scm-frame-unwinder.c \
 	guile/scm-gsmob.c \
 	guile/scm-iterator.c \
 	guile/scm-lazy-string.c \
@@ -2440,6 +2442,10 @@ scm-frame-filter.o: $(srcdir)/guile/scm-frame-filter.c
 	$(COMPILE) $(srcdir)/guile/scm-frame-filter.c
 	$(POSTCOMPILE)
 
+scm-frame-unwinder.o: $(srcdir)/guile/scm-frame-unwinder.c
+	$(COMPILE) $(srcdir)/guile/scm-frame-unwinder.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 21e44b9..b36506c 100644
--- a/gdb/data-directory/Makefile.in
+++ b/gdb/data-directory/Makefile.in
@@ -90,6 +90,7 @@ GUILE_SOURCE_FILES = \
 	gdb/boot.scm \
 	gdb/experimental.scm \
 	gdb/frame-filters.scm \
+	gdb/frame-unwinders.scm \
 	gdb/init.scm \
 	gdb/iterator.scm \
 	gdb/printing.scm \
@@ -102,6 +103,7 @@ GUILE_NO_UNBOUND_WARNING_COMPILED_FILES = \
 GUILE_COMPILED_FILES = \
 	gdb/experimental.go \
 	gdb/frame-filters.go \
+	gdb/frame-unwinders.go \
 	gdb/iterator.go \
 	gdb/printing.go \
 	gdb/support.go \
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index bcff616..d637482 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,5 +1,9 @@
 2015-04-09  Andy Wingo  <wingo@igalia.com>
 
+	* guile.texi (Guile Frame Unwinder API): New section.
+
+2015-04-09  Andy Wingo  <wingo@igalia.com>
+
 	* guile.texi (Guile Frame Filter API)
 	(Writing a Frame Filter in Guile): New sections.
 
diff --git a/gdb/doc/guile.texi b/gdb/doc/guile.texi
index e2826f0..6c850a4 100644
--- a/gdb/doc/guile.texi
+++ b/gdb/doc/guile.texi
@@ -143,6 +143,7 @@ from the Guile interactive prompt.
 * 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.
+* Guile Frame Unwinder API:: Programmatically unwinding stack frames
 * Commands In Guile::        Implementing new commands in Guile
 * Parameters In Guile::      Adding new @value{GDBN} parameters
 * Progspaces In Guile::      Program spaces
@@ -2119,6 +2120,215 @@ also possible to do the job of an decorator with a filter.  Still,
 avoiding the stream interfaces can often be a good reason to use the
 simpler decorator layer.
 
+@node Guile Frame Unwinder API
+@subsubsection Unwinding Frames in Guile
+@cindex frame unwinder api, guile
+
+In @value{GDBN} terminology, ``unwinding'' is the process of finding
+an older (outer) frame on the stack.  Unwinders form the core of
+backtrace computation in @value{GDBN}.  @value{GDBN} comes with
+unwinders for each target architecture that it supports, and these
+usually suffice to unwind the stack.  However, some target programs
+can have non-standard frame layouts that cannot be unwound by the
+standard unwinders.  This is often the case when working with
+just-in-time compilation environments, for example in JavaScript
+implementations.  In such cases, users can define custom code in Guile
+to programmatically unwind the problematic stack frames.
+
+Before getting into the API, we should discuss how unwinders work in
+@value{GDBN}.
+
+As an example, consider a stack in which we have already computed
+frame 0 and we want to compute frame 1.  We say that frame 0 is the
+``inner'' frame, and frame 1 will be the ``outer'' frame.
+
+Unwinding starts with a model of the state of all registers in an
+inner, already unwound frame.  In our case, we start with frame 0.
+@value{GDBN} then constructs a provisional frame object for the outer
+frame that is being built (frame 1) and links it to the inner frame
+(frame 0).  @value{GDBN} then goes through its list of registered
+unwinders, searching for one that knows how to compute the register
+state in frame 1, given the state of frame 0.  @value{GDBN} will then
+ask the chosen unwinder to compute a frame identifier for the outer
+frame.  Once the unwinder has done so, the frame is marked as
+``valid'' and can be accessed using the normal frame API.
+
+A frame identifier (frame ID) consists of code and data pointers
+associated with a frame which will remain valid as long as the frame
+is still alive.  Usually a frame ID is built from the code and stack
+pointers as they were when control entered the function associated
+with the frame, though as described below there are other ways to
+build a frame ID@.  However as you can see, computing the frame ID
+requires some input from the unwinder to determine the start code
+address (PC) and the frame pointer (FP), especially on platforms that
+don't dedicate a register to the FP.
+
+(Given this description, you might wonder how the frame ID for the
+innermost frame (frame 0) is unwound, given that unwinding requires an
+inner frame.  The answer is that internally, @value{GDBN} always has a
+``sentinel'' frame that is inner to the innermost frame, and which has
+a pre-computed unwinder that just returns the registers as they are,
+without unwinding.)
+
+The Guile frame unwinder API loosely follows this protocol as
+described above.  Guile will build a special ``pending frame object''
+corresponding the frame being unwound (in our example, frame 1).  It
+allows the user to read registers from that pending frame, which in
+reality are unwound from the already-existing frame 0.  If the
+unwinder decides that it can handle the frame in question, it then
+creates and returns an ``unwind info'' object for that frame.  The
+unwind info object contains a frame ID for the pending frame.  It also
+records the values of any registers saved in the frame, for use when
+unwinding its outer frame (frame 2).
+
+Frame unwinder objects are managed in Guile much in the same way as
+frame filters.  Indeed, users will often want to implement both frame
+unwinders and frame filters: unwinders will compute the correct
+backtrace and register state, and filters can fill in function names,
+line numbers, and the like.  @xref{Guile Frame Filter API}, for more
+on frame filters.
+
+As with frame filters, there can be multiple frame unwinders
+registered with @value{GDBN}, and each one may be individually enabled
+or disabled at will.  The filters will be tried in priority order,
+from highest to lowest priority, and the first one that sets the frame
+ID will take responsibility for the frame.
+
+To use frame unwinders, first load the @code{(gdb frame-unwinders)} module
+to have access to the procedures that manipulate frame unwinders:
+
+@example
+(use-modules (gdb frame-unwinders))
+@end example
+
+@deffn {Scheme Procedure} make-frame-unwinder name procedure @
+       @r{[}#:priority priority@r{]} @r{[}#:enabled? boolean@r{]}
+Make a new frame unwinder.
+
+The unwinder will be identified by the string @var{name}.
+@var{procedure} should be a function of one argument, taking a pending
+frame object.  If the unwinder procedure decides to handle the frame,
+it should return an unwind info object.  Otherwise if the unwinder
+returns @code{#f}, @value{GDBN} will continue to search its list for
+an unwinder.
+
+The unwinder will be initially enabled, unless the keyword argument
+@code{#:enabled? #f} is given.  Even if the unwinder is marked as
+enabled, it will need to be registered with @value{GDBN} via
+@code{register-frame-unwinder!} in order to take effect.
+@end deffn
+
+@deffn {Scheme Procedure} all-frame-unwinders
+Return a list of all frame unwinders.
+@end deffn
+
+@deffn {Scheme Procedure} register-frame-unwinder! unwinder @
+       @r{[}#:locus locus@r{]}
+Register the frame unwinder @var{unwinder} with @value{GDBN}.
+
+The unwinder will be associated with a specific ``locus'', which may
+be an objfile, a progspace, or the ``global'' locus, indicating that
+the unwinder should run for all progspaces.  The default value of
+@code{#f} for @var{locus} indicates that the unwinder should be
+registered globally.  Pass an objfile or a progspace as the
+@code{#:locus} keyword argument to associate the unwinder with a
+specific objfile or progspace, respectively.
+@end deffn
+
+Registering an unwinder on an objfile or a progspace locus has the
+advantage that the unwinder will go away when the objfile or progspace
+is unloaded.  To explicitly remove an unwinder from GDB, use
+@code{remove-frame-unwinder!}.
+
+@deffn {Scheme Procedure} remove-frame-unwinder! unwinder
+Removes the frame unwinder @var{unwinder} from @value{GDBN}.
+@end deffn
+
+@deffn {Scheme Procedure} set-frame-unwinder-enabled! unwinder enabled?
+Mark a frame unwinder as enabled, if @var{enabled?} is true, or as
+disabled otherwise.
+@end deffn
+
+Unwinders are enabled when they are created, unless @code{#:enabled?
+#f} is passed to @code{make-frame-unwinder}.
+
+@deffn {Scheme Procedure} frame-unwinder-name unwinder
+@deffnx {Scheme Procedure} frame-unwinder-enabled? unwinder
+@deffnx {Scheme Procedure} frame-unwinder-registered? unwinder
+@deffnx {Scheme Procedure} frame-unwinder-priority unwinder
+@deffnx {Scheme Procedure} frame-unwinder-procedure unwinder
+@deffnx {Scheme Procedure} frame-unwinder-locus unwinder
+Accessors for a frame unwinder object's fields.  The
+@code{registered?}  field indicates whether a unwinder has been added
+to @value{GDBN} or not.  @code{locus} is the objfile or progspace in
+which the unwinder was registered, or @code{#f} otherwise.
+@end deffn
+
+Frame unwinders operate on ``pending frames''.  Pending frames are
+valid only while they are being unwound; any access to a pending frame
+outside the extent of their unwind operation will signal an error.
+Currently, pending frames can only be used in two limited ways: to
+read registers from the frame, and to construct an unwind info object
+for a successful unwinder return.
+
+@deffn {Scheme Procedure} pending-frame-read-register frame register
+Return the value of a register in the pending frame @var{frame}.
+@var{register} should be given as a string.
+@end deffn
+
+If an unwinder successfully unwinds a frame, it should return an
+unwind info object created via the @code{make-unwind-info} procedure.
+An unwind info object specifies the frame ID for its associated
+pending frame, and also records values of registers that are saved
+within the frame.
+
+@deffn {Scheme Procedure} make-unwind-info frame frame-id
+Make an unwind info object for the pending frame @var{frame},
+specifying @var{frame-id} as its frame ID.  @var{frame-id} should be
+the result of a call to @code{make-frame-id}.
+@end deffn
+
+@deffn {Scheme Procedure} make-frame-id fp @r{[}#:pc pc@r{]} @r{[}#:special special@r{]}
+Build a frame ID object from the given @var{fp}, @var{pc}, and
+@var{special} values.
+
+A frame ID is a unique name for a frame that remains valid as long as
+the frame itself is valid.  Usually the frame ID is built from from
+the frame's stack address and code address.  The stack address
+@var{fp} should normally be a pointer to the new end of the stack when
+the function was called, as a @value{GDBN} value.  Similarly the code
+address @var{pc} should be given as the address of the entry point of
+the function.
+
+The @var{fp} argument is required.  While it is a good idea to specify
+a @var{pc}, a code address is not required to build a frame ID, and so
+@var{pc} is a keyword argument.  Call @code{make-frame-id} with
+a @code{#:pc @var{pc}} argument to specify a code address.
+
+Some architectures have another stack or some other frame state store;
+currently this is only the case for ia64.  For these odd platforms the
+frame ID needs an additional address, which may be passed as the
+@var{special} argument, via the @code{#:special} keyword.
+@end deffn.
+
+After building an unwind info object for a pending frame, an unwinder
+can call @code{unwind-info-add-saved-register!} to record saved
+registers.  The values of the saved registers logically belong to the
+frame that is older than the pending frame being unwound, not to the
+pending frame itself.
+
+@deffn {Scheme Procedure} unwind-info-add-saved-register! unwind-info register value
+Set the saved value of a register in a pending frame.
+
+@var{register} names a register, and should be a string, for example
+@samp{rip}.  @var{value} is the register value, as a @value{GDBN}
+value.
+@end deffn
+
+Any register whose value is not recorded as saved via
+@code{unwind-info-add-saved-register!} will be marked as ``not saved''
+in the outer frame.
+
 @node Commands In Guile
 @subsubsection Commands In Guile
 
diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
index bba1ae7..4347dca 100644
--- a/gdb/frame-unwind.c
+++ b/gdb/frame-unwind.c
@@ -87,6 +87,34 @@ frame_unwind_append_unwinder (struct gdbarch *gdbarch,
   (*ip)->unwinder = unwinder;
 }
 
+/* Nonzero if we are finding the unwinder for a frame; see
+   frame_unwind_try_handler.  */
+static int is_unwinding = 0;
+
+/* Return nonzero if we are inside a sniffer call.  */
+
+int
+frame_unwind_is_unwinding (void)
+{
+  return is_unwinding;
+}
+
+/* Cleanup helpers for is_unwinding.  */
+
+static void
+unset_is_unwinding (void *unused)
+{
+  is_unwinding = 0;
+}
+
+static struct cleanup*
+set_is_unwinding (void)
+{
+  is_unwinding = 1;
+
+  return make_cleanup (unset_is_unwinding, NULL);
+}
+
 /* Call SNIFFER from UNWINDER.  If it succeeded set UNWINDER for
    THIS_FRAME and return 1.  Otherwise the function keeps THIS_FRAME
    unchanged and returns 0.  */
@@ -98,11 +126,18 @@ frame_unwind_try_unwinder (struct frame_info *this_frame, void **this_cache,
   struct cleanup *old_cleanup;
   int res = 0;
 
+  if (is_unwinding)
+    internal_error (__FILE__, __LINE__,
+		    _("Recursion detected while finding an unwinder."));
   old_cleanup = frame_prepare_for_sniffer (this_frame, unwinder);
 
   TRY
     {
+      struct cleanup *cleanup = set_is_unwinding ();
+
       res = unwinder->sniffer (unwinder, this_frame, this_cache);
+
+      do_cleanups (cleanup);
     }
   CATCH (ex, RETURN_MASK_ERROR)
     {
@@ -252,7 +287,8 @@ frame_unwind_got_constant (struct frame_info *frame, int regnum,
 }
 
 struct value *
-frame_unwind_got_bytes (struct frame_info *frame, int regnum, gdb_byte *buf)
+frame_unwind_got_bytes (struct frame_info *frame, int regnum,
+			const gdb_byte *buf)
 {
   struct gdbarch *gdbarch = frame_unwind_arch (frame);
   struct value *reg_val;
diff --git a/gdb/frame-unwind.h b/gdb/frame-unwind.h
index 44add12..3e322f2 100644
--- a/gdb/frame-unwind.h
+++ b/gdb/frame-unwind.h
@@ -179,6 +179,11 @@ extern void frame_unwind_append_unwinder (struct gdbarch *gdbarch,
 extern void frame_unwind_find_by_frame (struct frame_info *this_frame,
 					void **this_cache);
 
+/* Return nonzero if we are in the process of finding an unwinder for a frame.
+   See the comments in get_current_frame.  */
+
+extern int frame_unwind_is_unwinding (void);
+
 /* Helper functions for value-based register unwinding.  These return
    a (possibly lazy) value of the appropriate type.  */
 
@@ -210,7 +215,7 @@ struct value *frame_unwind_got_constant (struct frame_info *frame, int regnum,
    inside BUF.  */
 
 struct value *frame_unwind_got_bytes (struct frame_info *frame, int regnum,
-                                      gdb_byte *buf);
+                                      const gdb_byte *buf);
 
 /* Return a value which indicates that FRAME's saved version of REGNUM
    has a known constant (computed) value of ADDR.  Convert the
diff --git a/gdb/frame.c b/gdb/frame.c
index b3cbf23..9e63f21 100644
--- a/gdb/frame.c
+++ b/gdb/frame.c
@@ -2212,6 +2212,22 @@ get_prev_frame (struct frame_info *this_frame)
       return NULL;
     }
 
+  /* Unwinders implemented in Python or Scheme could eventually make an API call
+     that would cause GDB to try to unwind a frame while unwinding a frame.
+     Because already-unwound frames will be found in the frame cache, unwinding
+     will only happen at the old end of the stack, which means that any
+     recursive unwinding attempt will surely lead to unbounded recursion.  Ways
+     this can happen include such common functions as `get_current_arch' or
+     `lookup_symbol', via `get_selected_frame', so it's impractical to simply
+     declare these an error.  Instead, we detect this case and return NULL,
+     indicating that the known stack of frames ends here.  */
+  if (frame_unwind_is_unwinding ())
+    {
+      frame_debug_got_null_frame (this_frame,
+				  "get_prev_frame within unwinder sniffer");
+      return NULL;
+    }
+
   return get_prev_frame_always (this_frame);
 }
 
diff --git a/gdb/guile/guile-internal.h b/gdb/guile/guile-internal.h
index d7c166c..9ca807e 100644
--- a/gdb/guile/guile-internal.h
+++ b/gdb/guile/guile-internal.h
@@ -598,6 +598,7 @@ 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_frame_unwinders (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 176e97e..d1850e7 100644
--- a/gdb/guile/guile.c
+++ b/gdb/guile/guile.c
@@ -670,6 +670,7 @@ initialize_gdb_module (void *data)
   gdbscm_initialize_disasm ();
   gdbscm_initialize_frames ();
   gdbscm_initialize_frame_filters ();
+  gdbscm_initialize_frame_unwinders ();
   gdbscm_initialize_iterators ();
   gdbscm_initialize_lazy_strings ();
   gdbscm_initialize_math ();
diff --git a/gdb/guile/lib/gdb/frame-unwinders.scm b/gdb/guile/lib/gdb/frame-unwinders.scm
new file mode 100644
index 0000000..d668d01
--- /dev/null
+++ b/gdb/guile/lib/gdb/frame-unwinders.scm
@@ -0,0 +1,235 @@
+;; Frame unwinder 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 frame-unwinders)
+  #:use-module ((gdb) #:hide (frame? symbol?))
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-9)
+  #:use-module (ice-9 match)
+  #:export (pending-frame-read-register
+
+            make-frame-id
+
+            make-unwind-info
+            unwind-info-add-saved-register!
+
+            make-frame-unwinder
+            frame-unwinder?
+            frame-unwinder-name
+            frame-unwinder-enabled?
+            frame-unwinder-registered?
+            frame-unwinder-procedure
+            frame-unwinder-locus
+
+            find-frame-unwinder-by-name
+
+            register-frame-unwinder!
+            remove-frame-unwinder!
+            set-frame-unwinder-enabled!
+
+            all-frame-unwinders))
+
+(define-record-type <frame-id>
+  (%make-frame-id sp pc special)
+  frame-id?
+  (sp frame-id-sp)
+  (pc frame-id-pc)
+  (special frame-id-special))
+
+(define* (make-frame-id sp #:key pc special)
+  "Make a new frame identifier, or \"frame ID\".
+
+A frame ID is a unique name for a frame that remains valid as long as
+the frame itself is valid.
+
+Usually the frame ID is built from from the frame's stack address and
+code address.  The stack address, SP, should normally be a pointer to
+the new end of the stack when the function was called, as a GDB value.
+
+It is possible to create a frame ID with just an SP, but it's better to
+specify a code address (PC) via the #:pc keyword argument.  The PC
+indicates the address of the entry point of the function.
+
+Some architectures have another stack or some other frame state store,
+like ia64, and they need an additional address, which may be passed as
+the #:special keyword argument."
+  (%make-frame-id sp pc special))
+
+;; Silence unbound-toplevel warnings until we can load the extension.
+(define %make-unwind-info #f)
+
+(define (make-unwind-info pending-frame frame-id)
+  "Make an unwind info object for a given pending frame.  FRAME-ID will
+the frame ID of the frame."
+  (%make-unwind-info pending-frame
+                     (frame-id-sp frame-id)
+                     (frame-id-pc frame-id)
+                     (frame-id-special frame-id)))
+
+(define-record-type <frame-unwinder>
+  (%make-frame-unwinder name enabled? registered? procedure locus)
+  frame-unwinder?
+  ;; string
+  (name frame-unwinder-name)
+  ;; bool
+  (enabled? frame-unwinder-enabled? set-enabled?!)
+  ;; bool
+  (registered? frame-unwinder-registered? set-registered?!)
+  ;; pending-frame -> unwind-info | #f
+  (procedure frame-unwinder-procedure)
+  ;; objfile | progspace | #f
+  (locus frame-unwinder-locus set-locus!))
+
+(define* (make-frame-unwinder name procedure #:key (enabled? #t))
+  "Make and return a new frame unwinder.  NAME and PROCEDURE are
+required arguments.  Specify #:enabled? to set the enabled status of the
+unwinder.
+
+The unwinder must be registered with GDB via `register-frame-unwinder!'
+before it is active."
+  (let ((registered? #f) (locus #f))
+    (%make-frame-unwinder name enabled? registered? procedure locus)))
+
+;; List of frame unwinders.
+(define *frame-unwinders* '())
+
+(define (same-scope? a b)
+  "Return #t if A and B represent the same scope, for the purposes of
+frame unwinder selection."
+  (cond
+   ;; If either is the global locus, they share a scope.
+   ((or (not a) (not b)) #t)
+   ;; If either is an objfile, compare their progspaces, unless the
+   ;; objfile is invalid.
+   ((objfile? a) (and (objfile-valid? a)
+                      (same-scope? (objfile-progspace a) b)))
+   ((objfile? b) (and (objfile-valid? b)
+                      (same-scope? a (objfile-progspace b))))
+   ;; Otherwise they are progspaces.  If they eq?, it's the same scope.
+   (else (eq? a b))))
+
+(define (is-valid? unwinder)
+  "Return #t if the locus of UNWINDER is still valid, or otherwise #f if
+the objfile or progspace has been removed from GDB."
+  (let ((locus (frame-unwinder-locus unwinder)))
+    (cond
+     ((progspace? locus) (progspace-valid? locus))
+     ((objfile? locus) (objfile-valid? locus))
+     (else #t))))
+
+(define (prune-frame-unwinders!)
+  "Prune frame unwinders whose objfile or progspace has gone away."
+  (unless (and-map is-valid? *frame-unwinders*)
+    (set! *frame-unwinders*
+          (let lp ((unwinders *frame-unwinders*))
+            (match unwinders
+              (() '())
+              ((f . unwinders)
+               (cond
+                ((is-valid? f)
+                 (cons f (lp unwinders)))
+                (else
+                 (set-registered?! f #f)
+                 (lp unwinders)))))))))
+
+(define (all-frame-unwinders)
+  "Return a list of all registered frame unwinders."
+  (prune-frame-unwinders!)
+  ;; Copy the list to prevent callers from mutating our state.
+  (list-copy *frame-unwinders*))
+
+(define* (register-frame-unwinder! unwinder #:key locus replace?)
+  "Register a frame unwinder with GDB.  Frame unwinders must be
+registered before they will be used to unwinder backtraces.
+
+By default, the unwinder will be registered globally.  Specify an
+objfile or a progspace as the #:locus keyword argument to instead
+register the unwinder as belonging to a specific objfile or progspace.
+
+The unwinder's name must be unique within its locus.  GDB will raise an
+exception if the locus already has a unwinder registered with the given
+name, unless a true value is passed as the #:replace? keyword argument,
+in which case any existing unwinder will be removed from its locus."
+  (define (check-locus!)
+    (cond
+     ((objfile? locus)
+      (unless (objfile-valid? locus)
+        (error "Objfile is not valid" locus)))
+     ((progspace? locus)
+      (unless (progspace-valid? locus)
+        (error "Progspace is not valid" locus)))
+     (locus
+      (error "Invalid locus" locus))))
+  (define (duplicate-unwinder? other)
+    (and (equal? (frame-unwinder-name other)
+                 (frame-unwinder-name unwinder))
+         (eq? (frame-unwinder-locus other) locus)))
+
+  (when (frame-unwinder-registered? unwinder)
+    (error "Frame unwinder is already registered with GDB" unwinder))
+  (check-locus!)
+  (prune-frame-unwinders!)
+  (let ((found (find duplicate-unwinder? *frame-unwinders*)))
+    (when found
+      (if replace?
+          (remove-frame-unwinder! found)
+          (error "Frame unwinder with this name already present in locus"
+                 (frame-unwinder-name filter)))))
+  (set-registered?! unwinder #t)
+  (set-locus! unwinder locus)
+  (set! *frame-unwinders* (cons unwinder *frame-unwinders*)))
+
+(define (unregister-frame-unwinder! unwinder)
+  "Unregister a frame unwinder."
+  (set-registered?! unwinder #f)
+  (set-locus! unwinder #f)
+  (set! *frame-unwinders* (delq unwinder *frame-unwinders*)))
+
+(define* (find-frame-unwinder-by-name name #:optional locus)
+  (prune-frame-unwinders!)
+  ;; First check for names within the locus, then within the scope.
+  (or (find (lambda (unwinder)
+              (and (equal? name (frame-unwinder-name unwinder))
+                   (eq? (frame-unwinder-locus unwinder) locus)))
+            *frame-unwinders*)
+      (find (lambda (unwinder)
+              (and (equal? name (frame-unwinder-name unwinder))
+                   (same-scope? (frame-unwinder-locus unwinder) locus)))
+            *frame-unwinders*)
+      (error "no frame unwinder found with name" name)))
+
+(define (set-frame-unwinder-enabled! unwinder enabled?)
+  "Enable or disable a frame unwinder."
+  (set-enabled?! unwinder enabled?)
+  *unspecified*)
+
+(define (unwind-frame frame)
+  (define (try-unwind locus)
+    (or-map (lambda (unwinder)
+              (and (frame-unwinder-enabled? unwinder)
+                   (eq? (frame-unwinder-locus unwinder) locus)
+                   ((frame-unwinder-procedure unwinder) frame)))
+            *frame-unwinders*))
+  (prune-frame-unwinders!)
+  (or (try-unwind (current-objfile))
+      (try-unwind (current-progspace))
+      ;; Try global unwinders last.
+      (try-unwind #f)))
+
+(load-extension "gdb" "gdbscm_load_frame_unwinders")
diff --git a/gdb/guile/scm-frame-unwinder.c b/gdb/guile/scm-frame-unwinder.c
new file mode 100644
index 0000000..363830c
--- /dev/null
+++ b/gdb/guile/scm-frame-unwinder.c
@@ -0,0 +1,570 @@
+/* Scheme frame unwinding interface.
+
+   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 "arch-utils.h"
+#include "frame-unwind.h"
+#include "gdb_obstack.h"
+#include "guile-internal.h"
+#include "inferior.h"
+#include "language.h"
+#include "observer.h"
+#include "regcache.h"
+#include "user-regs.h"
+#include "value.h"
+
+/* Non-zero if the (gdb frame-unwinders) module has been loaded.  */
+static int gdbscm_frame_unwinders_loaded = 0;
+
+/* The captured unwind-frame variable.  */
+static SCM unwind_frame = SCM_BOOL_F;
+
+/* Key that we use when associating data with an architecture.  */
+static struct gdbarch_data *uwscm_gdbarch_data;
+
+/* The frame unwinder interface makes pending frame objects when trying
+   to unwind frames, and unwind info objects when unwinding is successful.
+   Here we define the names for the pending frame and unwind info Scheme
+   data types.  */
+static const char pending_frame_smob_name[] = "gdb:pending-frame";
+static const char unwind_info_smob_name[] = "gdb:unwind-info";
+
+/* SMOB tag for pending frames and unwind info.  */
+static scm_t_bits pending_frame_smob_tag;
+static scm_t_bits unwind_info_smob_tag;
+
+/* Data associated with a pending frame.  */
+struct uwscm_pending_frame
+{
+  /* The frame being unwound, used for the read-register interface.  */
+  struct frame_info *this_frame;
+
+  /* The architecture of the frame, here for convenience.  */
+  struct gdbarch *gdbarch;
+};
+
+/* Data associated with an unwind info object.  */
+struct uwscm_unwind_info
+{
+  /* The associated pending frame.  */
+  SCM frame;
+
+  /* The frame_id for the associated pending frame.  */
+  struct frame_id frame_id;
+
+  /* A list of (REGNUM . VALUE) pairs, indicating register values for the
+     associated pending frame.  */
+  SCM registers;
+};
+
+/* Type predicate for pending frames.  */
+
+static int
+uwscm_is_pending_frame (SCM obj)
+{
+  return SCM_SMOB_PREDICATE (pending_frame_smob_tag, obj);
+}
+
+/* Data accessor for pending frames.  */
+
+static struct uwscm_pending_frame *
+uwscm_pending_frame_data (SCM obj)
+{
+  gdb_assert (uwscm_is_pending_frame (obj));
+  return (struct uwscm_pending_frame *) SCM_SMOB_DATA (obj);
+}
+
+/* Type predicate for unwind info.  */
+
+static int
+uwscm_is_unwind_info (SCM obj)
+{
+  return SCM_SMOB_PREDICATE (unwind_info_smob_tag, obj);
+}
+
+/* Data accessor for unwind_info.  */
+
+static struct uwscm_unwind_info *
+uwscm_unwind_info_data (SCM obj)
+{
+  gdb_assert (uwscm_is_unwind_info (obj));
+  return (struct uwscm_unwind_info *) SCM_SMOB_DATA (obj);
+}
+
+/* Build a pending frame.  */
+
+static SCM
+uwscm_make_pending_frame (struct frame_info *this_frame)
+{
+  struct uwscm_pending_frame *data;
+
+  data = scm_gc_malloc (sizeof (*data), pending_frame_smob_name);
+
+  data->this_frame = this_frame;
+  TRY
+    {
+      data->gdbarch = get_frame_arch (this_frame);
+    }
+  CATCH (except, RETURN_MASK_ALL)
+    {
+      GDBSCM_HANDLE_GDB_EXCEPTION (except);
+    }
+  END_CATCH
+
+  SCM_RETURN_NEWSMOB (pending_frame_smob_tag, data);
+}
+
+/* Pending frames may only be accessed from Scheme within the dynamic
+   extent of the unwind callback.  */
+
+static int
+uwscm_pending_frame_is_valid (SCM pending_frame)
+{
+  return uwscm_pending_frame_data (pending_frame)->this_frame != NULL;
+}
+
+/* Is this a pending frame that is accessible from Scheme?  */
+
+static int
+uwscm_is_valid_pending_frame (SCM obj)
+{
+  return uwscm_is_pending_frame (obj) && uwscm_pending_frame_is_valid (obj);
+}
+
+/* Is this an unwind info whose associated pending frame is valid?  */
+
+static int
+uwscm_is_valid_unwind_info (SCM obj)
+{
+  return uwscm_is_unwind_info (obj)
+    && uwscm_pending_frame_is_valid (uwscm_unwind_info_data (obj)->frame);
+}
+
+/* Called as the unwind callback finishes to invalidate the pending
+   frame.  */
+
+static void
+uwscm_invalidate_pending_frame (SCM pending_frame)
+{
+  gdb_assert (uwscm_pending_frame_is_valid (pending_frame));
+  uwscm_pending_frame_data (pending_frame)->this_frame = NULL;
+}
+
+/* Raise a Scheme exception if OBJ is not a valid pending frame.  */
+
+static void
+uwscm_assert_valid_pending_frame (SCM obj, const char *func_name, int pos)
+{
+  if (!uwscm_is_valid_pending_frame (obj))
+    gdbscm_throw (gdbscm_make_type_error (func_name, pos, obj,
+					  "valid <gdb:pending-frame>"));
+}
+
+/* Raise a Scheme exception if OBJ is not an unwind info object whose
+   associated pending frame is valid.  */
+
+static void
+uwscm_assert_valid_unwind_info (SCM obj, const char *func_name, int pos)
+{
+  if (!uwscm_is_valid_unwind_info (obj))
+    gdbscm_throw (gdbscm_make_type_error (func_name, pos, obj,
+					  "valid <gdb:unwind-info>"));
+}
+
+/* Helper to convert a frame ID component to a CORE_ADDR.  */
+
+static CORE_ADDR
+uwscm_value_to_addr (SCM value, int arg)
+{
+  struct value *c_value;
+  CORE_ADDR ret;
+
+  if (!vlscm_is_value (value))
+    gdbscm_throw (gdbscm_make_type_error ("make-unwind-info",
+					  arg, value, "<gdb:value> object"));
+
+  c_value = vlscm_scm_to_value (value);
+
+  TRY
+    {
+      ret = value_as_address (c_value);
+    }
+  CATCH (except, RETURN_MASK_ALL)
+    {
+      GDBSCM_HANDLE_GDB_EXCEPTION (except);
+    }
+  END_CATCH
+
+  return ret;
+}
+
+/* (%make-unwind-info pending-frame sp pc special)
+
+   Create an unwind info structure for this pending frame.  Wrapped in Scheme to
+   take a frame ID record.  */
+
+static SCM
+gdbscm_make_unwind_info (SCM pending_frame, SCM sp, SCM pc, SCM special)
+{
+  struct uwscm_unwind_info *data;
+  struct frame_id frame_id;
+
+  uwscm_assert_valid_pending_frame (pending_frame, FUNC_NAME, SCM_ARG1);
+
+  if (gdbscm_is_false (pc))
+    frame_id = frame_id_build_wild (uwscm_value_to_addr (sp, SCM_ARG2));
+  else if (gdbscm_is_false (special))
+    frame_id = frame_id_build (uwscm_value_to_addr (sp, SCM_ARG2),
+			       uwscm_value_to_addr (pc, SCM_ARG3));
+  else
+    frame_id = frame_id_build_special (uwscm_value_to_addr (sp, SCM_ARG2),
+				       uwscm_value_to_addr (pc, SCM_ARG3),
+				       uwscm_value_to_addr (special, SCM_ARG4));
+
+  data = scm_gc_malloc (sizeof (*data), unwind_info_smob_name);
+
+  data->frame = pending_frame;
+  data->frame_id = frame_id;
+  data->registers = SCM_EOL;
+
+  SCM_RETURN_NEWSMOB (unwind_info_smob_tag, data);
+}
+
+/* Convert the string REGISTER_SCM to a register number for the given
+   architecture.  */
+
+static int
+uwscm_scm_to_regnum (SCM register_scm, struct gdbarch *gdbarch,
+		     const char *func_name, int arg)
+{
+  int regnum;
+  struct cleanup *cleanup;
+  char *register_str;
+
+  gdbscm_parse_function_args (func_name, arg, NULL,
+			      "s", register_scm, &register_str);
+  cleanup = make_cleanup (xfree, register_str);
+
+  TRY
+    {
+      regnum = user_reg_map_name_to_regnum (gdbarch, register_str,
+					    strlen (register_str));
+    }
+  CATCH (except, RETURN_MASK_ALL)
+    {
+      do_cleanups (cleanup);
+      GDBSCM_HANDLE_GDB_EXCEPTION (except);
+    }
+  END_CATCH
+
+  do_cleanups (cleanup);
+
+  if (regnum < 0)
+    gdbscm_out_of_range_error (func_name, arg,
+			       register_scm, _("unknown register"));
+
+  return regnum;
+}
+
+/* (pending-frame-read-register <gdb:pending-frame> string)
+      -> <gdb:value>
+
+   Sniffs a register value from a pending frame.  */
+
+static SCM
+gdbscm_pending_frame_read_register (SCM pending_frame, SCM register_scm)
+{
+  struct uwscm_pending_frame *data;
+  struct value *value = NULL;
+  int regnum;
+
+  uwscm_assert_valid_pending_frame (pending_frame, FUNC_NAME, SCM_ARG1);
+  data = uwscm_pending_frame_data (pending_frame);
+  regnum = uwscm_scm_to_regnum (register_scm, data->gdbarch, FUNC_NAME,
+				SCM_ARG2);
+
+  TRY
+    {
+      value = get_frame_register_value (data->this_frame, regnum);
+    }
+  CATCH (except, RETURN_MASK_ALL)
+    {
+      GDBSCM_HANDLE_GDB_EXCEPTION (except);
+    }
+  END_CATCH
+
+  if (value == NULL)
+    gdbscm_out_of_range_error (FUNC_NAME, SCM_ARG2, register_scm,
+			       _("cannot read register from frame"));
+
+  return vlscm_scm_from_value (value);
+}
+
+/* (unwind-info-add-saved-register! unwind-info register value)
+
+   Records the saved value of a particular register in UNWIND_INFO's
+   corresponding pending frame.  REGISTER_SCM names the register, as a
+   string, and VALUE_SCM is a <gdb:value>.  */
+
+static SCM
+gdbscm_unwind_info_add_saved_register_x (SCM unwind_info, SCM register_scm,
+					 SCM value_scm)
+{
+  struct uwscm_unwind_info *data;
+  struct uwscm_pending_frame *frame_data;
+  struct value *value;
+  int regnum;
+  int value_size;
+
+  uwscm_assert_valid_unwind_info (unwind_info, FUNC_NAME, SCM_ARG1);
+  data = uwscm_unwind_info_data (unwind_info);
+  frame_data = uwscm_pending_frame_data (data->frame);
+  regnum = uwscm_scm_to_regnum (register_scm, frame_data->gdbarch,
+				FUNC_NAME, SCM_ARG2);
+
+  if (!vlscm_is_value (value_scm))
+    gdbscm_throw (gdbscm_make_type_error (FUNC_NAME, SCM_ARG3,
+					  value_scm,
+					  "<gdb:value> object"));
+
+  value = vlscm_scm_to_value (value_scm);
+  value_size = TYPE_LENGTH (value_enclosing_type (value));
+
+  if (value_size != register_size (frame_data->gdbarch, regnum))
+    gdbscm_invalid_object_error ("unwind-info-add-saved-register!",
+				 SCM_ARG3, value_scm,
+				 "wrong sized value for register");
+
+  data->registers = scm_assv_set_x (data->registers,
+				    scm_from_int (regnum),
+				    value_scm);
+
+  return SCM_UNSPECIFIED;
+}
+
+/* frame_unwind.this_id method.  */
+
+static void
+uwscm_this_id (struct frame_info *this_frame, void **cache_ptr,
+	       struct frame_id *this_id)
+{
+  SCM unwind_info = PTR2SCM (*cache_ptr);
+  struct uwscm_unwind_info *data;
+
+  data = uwscm_unwind_info_data (unwind_info);
+  *this_id = data->frame_id;
+}
+
+/* frame_unwind.prev_register.  */
+
+static struct value *
+uwscm_prev_register (struct frame_info *this_frame, void **cache_ptr,
+		     int regnum)
+{
+  SCM unwind_info = PTR2SCM (*cache_ptr);
+  struct uwscm_unwind_info *data;
+  SCM value_scm;
+  struct value *c_value;
+  const gdb_byte *buf;
+
+  data = uwscm_unwind_info_data (unwind_info);
+  value_scm = scm_assv_ref (data->registers, scm_from_int (regnum));
+  if (gdbscm_is_false (value_scm))
+    return frame_unwind_got_optimized (this_frame, regnum);
+
+  c_value = vlscm_scm_to_value (value_scm);
+  buf = value_contents (c_value);
+
+  return frame_unwind_got_bytes (this_frame, regnum, buf);
+}
+
+/* Call unwind-frame on the pending frame and check that the return
+   value is either a valid unwind info object, for a successful unwind, or
+   #f otherwise.  */
+
+static SCM
+do_call_unwind_frame (void *data)
+{
+  SCM pending_frame = PTR2SCM (data);
+  SCM result;
+
+  result = scm_call_1 (scm_variable_ref (unwind_frame), pending_frame);
+
+  if (!gdbscm_is_false (result))
+    uwscm_assert_valid_unwind_info (result, "unwind-frame", 0);
+
+  return result;
+}
+
+/* Sniffer implementation.  */
+
+static int
+uwscm_sniffer (const struct frame_unwind *self, struct frame_info *this_frame,
+	       void **cache_ptr)
+{
+  SCM pending_frame;
+  SCM result;
+
+  /* Note that it's possible to have loaded the Guile interface, but not yet
+     loaded (gdb frame-unwinders), so checking gdb_scheme_initialized is not
+     sufficient.  */
+  if (!gdbscm_frame_unwinders_loaded)
+    return 0;
+
+  pending_frame = uwscm_make_pending_frame (this_frame);
+  /* Recurse through gdbscm_call_guile so that we can just throw
+     exceptions on error.  */
+  result = gdbscm_call_guile (do_call_unwind_frame,
+			      SCM2PTR (pending_frame),
+			      gdbscm_memory_error_p);
+
+  /* Drop the reference to this_frame, so that future use of
+     pending_frame from Scheme will signal an error.  */
+  uwscm_invalidate_pending_frame (pending_frame);
+
+  if (gdbscm_is_exception (result))
+    {
+      gdbscm_print_gdb_exception (SCM_BOOL_F, result);
+      return 0;
+    }
+
+  if (gdbscm_is_false (result))
+    return 0;
+
+  *cache_ptr = SCM2PTR (scm_gc_protect_object (result));
+
+  return 1;
+}
+
+/* Frame cache release shim.  */
+
+static void
+uwscm_dealloc_cache (struct frame_info *this_frame, void *cache)
+{
+  scm_gc_unprotect_object (PTR2SCM (cache));
+}
+
+struct uwscm_gdbarch_data_type
+{
+  /* Has the unwinder shim been prepended? */
+  int unwinder_registered;
+};
+
+static void *
+uwscm_gdbarch_data_init (struct gdbarch *gdbarch)
+{
+  return GDBARCH_OBSTACK_ZALLOC (gdbarch, struct uwscm_gdbarch_data_type);
+}
+
+/* New inferior architecture callback: register the Guile sniffers
+   intermediary.  */
+
+static void
+uwscm_on_new_gdbarch (struct gdbarch *newarch)
+{
+  struct uwscm_gdbarch_data_type *data =
+      gdbarch_data (newarch, uwscm_gdbarch_data);
+
+  if (!data->unwinder_registered)
+    {
+      struct frame_unwind *unwinder
+          = GDBARCH_OBSTACK_ZALLOC (newarch, struct frame_unwind);
+
+      unwinder->type = NORMAL_FRAME;
+      unwinder->stop_reason = default_frame_unwind_stop_reason;
+      unwinder->this_id = uwscm_this_id;
+      unwinder->prev_register = uwscm_prev_register;
+      unwinder->unwind_data = (void *) newarch;
+      unwinder->sniffer = uwscm_sniffer;
+      unwinder->dealloc_cache = uwscm_dealloc_cache;
+      frame_unwind_prepend_unwinder (newarch, unwinder);
+      data->unwinder_registered = 1;
+    }
+}
+
+static const scheme_function unwind_functions[] =
+{
+  { "%make-unwind-info", 4, 0, 0, gdbscm_make_unwind_info,
+    /* Wrapped and documented in Scheme; no need for docs here.  */
+    ""},
+
+  { "pending-frame-read-register", 2, 0, 0,
+    gdbscm_pending_frame_read_register,
+    "\
+Return the value of a register in a pending frame.\n\
+\n\
+  Arguments: <gdb:pending-frame> string" },
+
+  { "unwind-info-add-saved-register!", 3, 0, 0,
+    gdbscm_unwind_info_add_saved_register_x,
+    "\
+Record the saved value of a register for a pending frame.\n\
+\n\
+After reading a pending frame's registers and determining that it\n\
+can handle the frame, an unwinder will create an unwind info object and\n\
+call this function to record saved registers for the frame.  The values\n\
+of the saved registers logically belong to the frame that is older than\n\
+the pending frame being unwound, not to the pending frame itself.\n\
+\n\
+The first argument should be a <gdb:unwind-info> object.  The second\n\
+names a register, and should be a string, for example \"rip\".  The\n\
+third argument is the value, as a GDB value.  By default, any register\n\
+whose value is not added to the unwind info's saved register set\n\
+will be marked as \"not saved\" in the outer frame." },
+
+  END_FUNCTIONS
+};
+
+/* Called by lib/gdb/frame-unwinders.scm.  */
+
+static void
+gdbscm_load_frame_unwinders (void *unused)
+{
+  if (gdbscm_frame_unwinders_loaded)
+    return;
+
+  gdbscm_frame_unwinders_loaded = 1;
+
+  gdbscm_define_functions (unwind_functions, 0);
+
+  unwind_frame = scm_c_lookup ("unwind-frame");
+}
+
+/* Initialize the opaque pending frame and unwind info types and
+   register gdbscm_load_frame_unwinders for calling by (gdb
+   frame-unwinders).  */
+
+void
+gdbscm_initialize_frame_unwinders (void)
+{
+  pending_frame_smob_tag =
+    gdbscm_make_smob_type (pending_frame_smob_name, 0);
+  unwind_info_smob_tag =
+    gdbscm_make_smob_type (unwind_info_smob_name, 0);
+
+  uwscm_gdbarch_data =
+    gdbarch_data_register_post_init (uwscm_gdbarch_data_init);
+  observer_attach_architecture_changed (uwscm_on_new_gdbarch);
+
+  scm_c_register_extension ("gdb", "gdbscm_load_frame_unwinders",
+                            gdbscm_load_frame_unwinders, NULL);
+}
diff --git a/gdb/guile/scm-symbol.c b/gdb/guile/scm-symbol.c
index 99ef928..1ad6d0c 100644
--- a/gdb/guile/scm-symbol.c
+++ b/gdb/guile/scm-symbol.c
@@ -605,7 +605,9 @@ gdbscm_lookup_symbol (SCM name_scm, SCM rest)
 
       TRY
 	{
-	  selected_frame = get_selected_frame (_("no frame selected"));
+	  selected_frame = get_selected_frame_if_set ();
+	  if (selected_frame == NULL)
+	    selected_frame = get_current_frame ();
 	  block = get_frame_block (selected_frame, NULL);
 	}
       CATCH (except, RETURN_MASK_ALL)
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index e156f57..20e6a70 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,12 @@
 2015-04-09  Andy Wingo  <wingo@igalia.com>
 
+	* gdb.guile/scm-frame-unwinder.exp: New file.
+	* gdb.guile/scm-frame-unwinder.c: New file.
+	* gdb.guile/scm-frame-unwinder-gdb.scm.in: New file.
+	* gdb.guile/scm-frame-unwinder.scm: New file.
+
+2015-04-09  Andy Wingo  <wingo@igalia.com>
+
 	* gdb.guile/amd64-scm-frame-filter-invalidarg.S:
 	* gdb.guile/scm-frame-filter-gdb.scm.in:
 	* gdb.guile/scm-frame-filter-invalidarg-gdb.scm.in:
diff --git a/gdb/testsuite/gdb.guile/scm-frame-unwinder-gdb.scm.in b/gdb/testsuite/gdb.guile/scm-frame-unwinder-gdb.scm.in
new file mode 100644
index 0000000..5c658d5
--- /dev/null
+++ b/gdb/testsuite/gdb.guile/scm-frame-unwinder-gdb.scm.in
@@ -0,0 +1,31 @@
+;; Copyright (C) 2015 Free Software Foundation, Inc.
+;;
+;; 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/>.
+
+;; This file is part of the GDB test-suite.  It tests Guile-based frame
+;; filters.
+
+(use-modules (gdb)
+             (gdb frame-unwinders))
+
+(define* (install-unwinders! #:optional (locus (current-objfile)))
+  (define (unwind-frame frame)
+    #f)
+  (define (add-unwinder! name)
+    (register-frame-unwinder! (make-frame-unwinder name unwind-frame)
+                              #:locus locus))
+  (add-unwinder! "Auto-loaded dummy")
+  (add-unwinder! "Auto-loaded dummy 2"))
+
+(install-unwinders!)
diff --git a/gdb/testsuite/gdb.guile/scm-frame-unwinder.c b/gdb/testsuite/gdb.guile/scm-frame-unwinder.c
new file mode 100644
index 0000000..6546c67
--- /dev/null
+++ b/gdb/testsuite/gdb.guile/scm-frame-unwinder.c
@@ -0,0 +1,35 @@
+/* Test file for the Scheme frame unwinding interface.
+
+   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/>.  */
+
+int
+f2 (int a)
+{
+  return ++a;
+}
+
+int
+f1 (int a, int b)
+{
+  return f2 (a) + b;
+}
+
+int main (int argc, char *argv[])
+{
+  return f1 (1, 2);
+}
diff --git a/gdb/testsuite/gdb.guile/scm-frame-unwinder.exp b/gdb/testsuite/gdb.guile/scm-frame-unwinder.exp
new file mode 100644
index 0000000..6fbe48a
--- /dev/null
+++ b/gdb/testsuite/gdb.guile/scm-frame-unwinder.exp
@@ -0,0 +1,90 @@
+# Copyright (C) 2015 Free Software Foundation, Inc.
+
+# 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/>.
+
+# This file is part of the GDB testsuite.  It tests Guile-based
+# frame-filters.
+
+load_lib gdb-guile.exp
+
+standard_testfile
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile}] } {
+    return -1
+}
+
+# Skip all tests if Guile scripting is not enabled.
+if { [skip_guile_tests] } { continue }
+
+# Make the -gdb.scm script available to gdb, it is automagically loaded by gdb.
+# Care is taken to put it in the same directory as the binary so that
+# gdb will find it.
+set remote_obj_guile_file \
+    [remote_download \
+	 host ${srcdir}/${subdir}/${testfile}-gdb.scm.in \
+	 [standard_output_file ${testfile}-gdb.scm]]
+
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_test_no_output "set auto-load safe-path ${remote_obj_guile_file}" \
+    "set auto-load safe-path"
+gdb_load ${binfile}
+# Verify gdb loaded the script.
+gdb_test "info auto-load guile-scripts" "Yes.*/${testfile}-gdb.scm.*" \
+    "Test auto-load had loaded guile scripts"
+
+if ![runto_main] then {
+    return -1
+}
+
+# Load global frame-unwinders
+set remote_guile_file [gdb_remote_download host \
+			    ${srcdir}/${subdir}/${testfile}.scm]
+gdb_scm_load_file ${remote_guile_file}
+
+# Test query
+gdb_test "guile (map frame-unwinder-name (all-frame-unwinders))" \
+    "\\(\"Synthetic\" \"Dummy\" \"Auto-loaded dummy 2\" \"Auto-loaded dummy\"\\)" \
+    "all frame unwinders"
+gdb_test "guile (map frame-unwinder-enabled? (all-frame-unwinders))" \
+    "\\(#f #t #t #t\\)" \
+    "all frame unwinders enabled?"
+
+gdb_test_no_output "guile (set-frame-unwinder-enabled! (find-frame-unwinder-by-name \"Dummy\") #f)" \
+    "disable dummy"
+gdb_test "guile (frame-unwinder-enabled? (find-frame-unwinder-by-name \"Dummy\"))"\
+    "#f" \
+    "dummy not enabled"
+gdb_test_no_output "guile (set-frame-unwinder-enabled! (find-frame-unwinder-by-name \"Dummy\") #t)" \
+    "re-enable dummy"
+gdb_test "guile (frame-unwinder-enabled? (find-frame-unwinder-by-name \"Dummy\"))"\
+    "#t" \
+    "dummy re-enabled"
+
+gdb_test "bt 10" \
+    "\#0  main .*scm-frame-unwinder.c:34" \
+    "backtrace from main"
+
+gdb_test_no_output "guile (set-frame-unwinder-enabled! (find-frame-unwinder-by-name \"Synthetic\") #t)" \
+    "enable synthetic unwinder"
+
+gdb_breakpoint "f2"
+gdb_continue_to_breakpoint "breakpoint at f2"
+
+# It would be nice to the backtrace at this position with and without
+# the unwinder, but currently enabling an unwinder doesn't invalidate
+# the frame cache.
+
+gdb_test "bt 10"\
+    "\#0  f2 .*scm-frame-unwinder.c:23\r\n\#1 .*\#9  0x0*cabba9e5 in \\?\\? \\(\\)\r\n\\(More stack frames follow...\\)" \
+    "backtrace full of cabbages"
diff --git a/gdb/testsuite/gdb.guile/scm-frame-unwinder.scm b/gdb/testsuite/gdb.guile/scm-frame-unwinder.scm
new file mode 100644
index 0000000..8f91527
--- /dev/null
+++ b/gdb/testsuite/gdb.guile/scm-frame-unwinder.scm
@@ -0,0 +1,41 @@
+;; Copyright (C) 2015 Free Software Foundation, Inc.
+;;
+;; 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/>.
+
+;; This file is part of the GDB test-suite.  It tests Guile-based frame
+;; filters.
+
+(use-modules (gdb)
+             (gdb frame-unwinders))
+
+(define (dummy-unwinder frame)
+  #f)
+
+(register-frame-unwinder! (make-frame-unwinder "Dummy" dummy-unwinder))
+
+
+(define (synthetic-unwinder frame)
+  ;; Increment the stack pointer, set IP to 0xdeadbeef
+  (let* ((this-pc (pending-frame-read-register frame "rip"))
+         (this-sp (pending-frame-read-register frame "rsp"))
+         (prev-pc (value-cast (make-value #xcabba9e5) (value-type this-pc)))
+         (prev-sp (value-add this-sp 32))
+         (frame-id (make-frame-id this-sp #:pc this-pc))
+         (unwind-info (make-unwind-info frame frame-id)))
+    (unwind-info-add-saved-register! unwind-info "rip" prev-pc)
+    (unwind-info-add-saved-register! unwind-info "rsp" prev-sp)
+    unwind-info))
+
+(register-frame-unwinder!
+ (make-frame-unwinder "Synthetic" synthetic-unwinder #:enabled? #f))
