Re: [PATCH, doc RFA] Add guile gdb command support

[Doug Evans <xdje42@gmail.com>]

Hi.

Here is what I committed.
Thanks.

commit e698b8c41cbb2648a11a2ae806922c44d1482aed
Author: Doug Evans <xdje42@gmail.com>
Date:   Tue Jun 3 00:29:49 2014 -0700

    Add command support for Guile.
    
    	* Makefile.in (SUBDIR_GUILE_OBS): Add scm-cmd.o.
    	(SUBDIR_GUILE_SRCS): Add scm-cmd.c.
    	(scm-cmd.o): New rule.
    	* guile/guile-internal.h (gdbscm_gc_xstrdup): Declare.
    	(gdbscm_user_error_p): Declare.
    	(gdbscm_parse_command_name): Declare.
    	(gdbscm_valid_command_class_p): Declare.
    	(gdbscm_initialize_commands): Declare.
    	* guile/guile.c (initialize_gdb_module): Call
    	gdbscm_initialize_commands.
    	* guile/lib/gdb.scm: Export command symbols.
    	* guile/lib/gdb/init.scm (%exception-keys): Add gdb:user-error.
    	(throw-user-error): New function.
    	* guile/scm-cmd.c: New file.
    	* guile/scm-exception.c (user_error_symbol): New static global.
    	(gdbscm_user_error_p): New function.
    	(gdbscm_initialize_exceptions): Set user_error_symbol.
    	* scm-utils.c (gdbscm_gc_xstrdup): New function.
    
    	testsuite/
    	* gdb.guile/scm-cmd.c: New file.
    	* gdb.guile/scm-cmd.exp: New file.
    
    	doc/
    	* guile.texi (Guile API): Add entry for Commands In Guile.
    	(Basic Guile) <parse-and-eval>: Add reference.
    	(Basic Guile) <string->argv>: Move definition to Commands In Guile.
    	(GDB Scheme Data Types): Mention <gdb:command> object.
    	(Commands In Guile): New node.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 414ac6d..ff829fc 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,25 @@
+2014-06-02  Doug Evans  <xdje42@gmail.com>
+
+	Add command support for Guile.
+	* Makefile.in (SUBDIR_GUILE_OBS): Add scm-cmd.o.
+	(SUBDIR_GUILE_SRCS): Add scm-cmd.c.
+	(scm-cmd.o): New rule.
+	* guile/guile-internal.h (gdbscm_gc_xstrdup): Declare.
+	(gdbscm_user_error_p): Declare.
+	(gdbscm_parse_command_name): Declare.
+	(gdbscm_valid_command_class_p): Declare.
+	(gdbscm_initialize_commands): Declare.
+	* guile/guile.c (initialize_gdb_module): Call
+	gdbscm_initialize_commands.
+	* guile/lib/gdb.scm: Export command symbols.
+	* guile/lib/gdb/init.scm (%exception-keys): Add gdb:user-error.
+	(throw-user-error): New function.
+	* guile/scm-cmd.c: New file.
+	* guile/scm-exception.c (user_error_symbol): New static global.
+	(gdbscm_user_error_p): New function.
+	(gdbscm_initialize_exceptions): Set user_error_symbol.
+	* scm-utils.c (gdbscm_gc_xstrdup): New function.
+
 2014-06-02  Phil Muldoon  <pmuldoon@redhat.com>
 
 	* top.c (command_loop): Handle comments here...
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index 51aeeb3..6159918 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -288,6 +288,7 @@ SUBDIR_GUILE_OBS = \
 	scm-auto-load.o \
 	scm-block.o \
 	scm-breakpoint.o \
+	scm-cmd.o \
 	scm-disasm.o \
 	scm-exception.o \
 	scm-frame.o \
@@ -312,6 +313,7 @@ SUBDIR_GUILE_SRCS = \
 	guile/scm-auto-load.c \
 	guile/scm-block.c \
 	guile/scm-breakpoint.c \
+	guile/scm-cmd.c \
 	guile/scm-disasm.c \
 	guile/scm-exception.c \
 	guile/scm-frame.c \
@@ -2272,6 +2274,10 @@ scm-breakpoint.o: $(srcdir)/guile/scm-breakpoint.c
 	$(COMPILE) $(srcdir)/guile/scm-breakpoint.c
 	$(POSTCOMPILE)
 
+scm-cmd.o: $(srcdir)/guile/scm-cmd.c
+	$(COMPILE) $(srcdir)/guile/scm-cmd.c
+	$(POSTCOMPILE)
+
 scm-disasm.o: $(srcdir)/guile/scm-disasm.c
 	$(COMPILE) $(srcdir)/guile/scm-disasm.c
 	$(POSTCOMPILE)
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index cbe00db..f2dafe3 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,5 +1,13 @@
 2014-06-02  Doug Evans  <xdje42@gmail.com>
 
+	* guile.texi (Guile API): Add entry for Commands In Guile.
+	(Basic Guile) <parse-and-eval>: Add reference.
+	(Basic Guile) <string->argv>: Move definition to Commands In Guile.
+	(GDB Scheme Data Types): Mention <gdb:command> object.
+	(Commands In Guile): New node.
+
+2014-06-02  Doug Evans  <xdje42@gmail.com>
+
 	* guile.texi (Guile API): Add entry for Progspaces In Guile.
 	(GDB Scheme Data Types): Mention <gdb:progspace> object.
 	(Progspaces In Guile): New node.
diff --git a/gdb/doc/guile.texi b/gdb/doc/guile.texi
index 23c8398..70fbd16 100644
--- a/gdb/doc/guile.texi
+++ b/gdb/doc/guile.texi
@@ -141,6 +141,7 @@ 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
+* Commands In Guile::        Implementing new commands in Guile
 * Progspaces In Guile::      Program spaces
 * Objfiles In Guile::        Object files in Guile
 * Frames In Guile::          Accessing inferior stack frames from Guile
@@ -293,16 +294,14 @@ Parse @var{expression} as an expression in the current language,
 evaluate it, and return the result as a @code{<gdb:value>}.
 The @var{expression} must be a string.
 
-This function is useful when computing values.
+This function can be useful when implementing a new command
+(@pxref{Commands In Guile}), as it provides a way to parse the
+command's arguments as an expression.
+It is also is useful when computing values.
 For example, it is the only way to get the value of a
 convenience variable (@pxref{Convenience Vars}) as a @code{<gdb:value>}.
 @end deffn
 
-@deffn {Scheme Procedure} string->argv string
-Convert a string to a list of strings split up according to
-@value{GDBN}'s argv parsing rules.
-@end deffn
-
 @node Guile Configuration
 @subsubsection Guile Configuration
 @cindex guile configuration
@@ -358,6 +357,9 @@ as a symbol.
 @item <gdb:breakpoint>
 @xref{Breakpoints In Guile}.
 
+@item <gdb:command>
+@xref{Commands In Guile}.
+
 @item <gdb:exception>
 @xref{Guile Exception Handling}.
 
@@ -1665,6 +1667,285 @@ my_library.so:
     bar
 @end smallexample
 
+@node Commands In Guile
+@subsubsection Commands In Guile
+
+@cindex commands in guile
+@cindex guile commands
+You can implement new @value{GDBN} CLI commands in Guile.  A CLI
+command object is created with the @code{make-command} Guile function,
+and added to @value{GDBN} with the @code{register-command!} Guile function.
+This two-step approach is taken to separate out the side-effect of adding
+the command to @value{GDBN} from @code{make-command}.
+
+There is no support for multi-line commands, that is commands that
+consist of multiple lines and are terminated with @code{end}.
+
+@c TODO: line length
+@deffn {Scheme Procedure} (make-command name @r{[}#:invoke invoke{]} @r{[}#:command-class command-class@r{]} @r{[}#:completer-class completer{]} @r{[}#:prefix? prefix@r{]} @r{[}#:doc doc-string{]})
+
+The argument @var{name} is the name of the command.  If @var{name} consists of
+multiple words, then the initial words are looked for as prefix
+commands.  In this case, if one of the prefix commands does not exist,
+an exception is raised.
+
+The result is the @code{<gdb:command>} object representing the command.
+The command is not usable until it has been registered with @value{GDBN}
+with @code{register-command!}.
+
+The rest of the arguments are optional.
+
+The argument @var{invoke} is a procedure of three arguments: @var{self},
+@var{args} and @var{from-tty}.  The argument @var{self} is the
+@code{<gdb:command>} object representing the command.
+The argument @var{args} is a string representing the arguments passed to
+the command, after leading and trailing whitespace has been stripped.
+The argument @var{from-tty} is a boolean flag and specifies whether the
+command should consider itself to have been originated from the user
+invoking it interactively.  If this function throws an exception,
+it is turned into a @value{GDBN} @code{error} call.
+Otherwise, the return value is ignored.
+
+The argument @var{command-class} is one of the @samp{COMMAND_} constants
+defined below.  This argument tells @value{GDBN} how to categorize the
+new command in the help system.  The default is @code{COMMAND_NONE}.
+
+The argument @var{completer} is either @code{#f}, one of the @samp{COMPLETE_}
+constants defined below, or a procedure, also defined below.
+This argument tells @value{GDBN} how to perform completion
+for this command.  If not provided or if the value is @code{#f},
+then no completion is performed on the command.
+
+The argument @var{prefix} is a boolean flag indicating whether the new
+command is a prefix command; sub-commands of this command may be
+registered.
+
+The argument @var{doc-string} is help text for the new command.
+If no documentation string is provided, the default value ``This command is
+not documented.'' is used.
+@end deffn
+
+@deffn {Scheme Procedure} register-command! command
+Add @var{command}, a @code{<gdb:command>} object, to @value{GDBN}'s
+list of commands.
+It is an error to register a command more than once.
+The result is unspecified.
+@end deffn
+
+@deffn {Scheme Procedure} command? object
+Return @code{#t} if @var{object} is a @code{<gdb:command>} object.
+Otherwise return @code{#f}.
+@end deffn
+
+@cindex don't repeat Guile command
+@deffn {Scheme Procedure} dont-repeat
+By default, a @value{GDBN} command is repeated when the user enters a
+blank line at the command prompt.  A command can suppress this
+behavior by invoking the @code{dont-repeat} function.  This is similar
+to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
+@end deffn
+
+@deffn {Scheme Procedure} string->argv string
+Convert a string to a list of strings split up according to
+@value{GDBN}'s argv parsing rules.
+It is recommended to use this for consistency.
+Arguments are separated by spaces and may be quoted.
+Example:
+
+@smallexample
+scheme@@(guile-user)> (string->argv "1 2\\ \\\"3 '4 \"5' \"6 '7\"")
+$1 = ("1" "2 \"3" "4 \"5" "6 '7")
+@end smallexample
+@end deffn
+
+@deffn {Scheme Procedure} throw-user-error message . args
+Throw a @code{gdb:user-error} exception.
+The argument @var{message} is the error message as a format string, like the 
+@var{fmt} argument to the @code{format} Scheme function.
+@xref{Formatted Output,,, guile, GNU Guile Reference Manual}.
+The argument @var{args} is a list of the optional arguments of @var{message}.
+
+This is used when the command detects a user error of some kind,
+say a bad command argument.
+
+@smallexample
+(gdb) guile (use-modules (gdb))
+(gdb) guile
+(register-command! (make-command "test-user-error"
+  #:command-class COMMAND_OBSCURE
+  #:invoke (lambda (self arg from-tty)
+    (throw-user-error "Bad argument ~a" arg))))
+end
+(gdb) test-user-error ugh
+ERROR: Bad argument ugh
+@end smallexample
+@end deffn
+
+@cindex completion of Guile commands
+@deffn completer self text word
+If the @var{completer} option to @code{make-command} is a procedure,
+it takes three arguments: @var{self} which is the @code{<gdb:command>}
+object, and @var{text} and @var{word} which are both strings.
+The argument @var{text} holds the complete command line up to the cursor's
+location.  The argument @var{word} holds the last word of the command line;
+this is computed using a word-breaking heuristic.
+
+All forms of completion are handled by this function, that is,
+the @key{TAB} and @key{M-?} key bindings (@pxref{Completion}),
+and the @code{complete} command (@pxref{Help, complete}).
+
+This procedure can return several kinds of values:
+
+@itemize @bullet
+@item
+If the return value is a list, the contents of the list are used as the
+completions.  It is up to @var{completer} to ensure that the
+contents actually do complete the word.  An empty list is
+allowed, it means that there were no completions available.  Only
+string elements of the list are used; other elements in the
+list are ignored.
+
+@item
+If the return value is a @code{<gdb:iterator>} object, it is iterated over to
+obtain the completions.  It is up to @code{completer-procedure} to ensure
+that the results actually do complete the word.  Only
+string elements of the result are used; other elements in the
+sequence are ignored.
+
+@item
+All other results are treated as though there were no available
+completions.
+@end itemize
+@end deffn
+
+When a new command is registered, it will have been declared as a member of
+some general class of commands.  This is used to classify top-level
+commands in the on-line help system; note that prefix commands are not
+listed under their own category but rather that of their top-level
+command.  The available classifications are represented by constants
+defined in the @code{gdb} module:
+
+@vtable @code
+@item COMMAND_NONE
+The command does not belong to any particular class.  A command in
+this category will not be displayed in any of the help categories.
+This is the default.
+
+@item COMMAND_RUNNING
+The command is related to running the inferior.  For example,
+@code{start}, @code{step}, and @code{continue} are in this category.
+Type @kbd{help running} at the @value{GDBN} prompt to see a list of
+commands in this category.
+
+@item COMMAND_DATA
+The command is related to data or variables.  For example,
+@code{call}, @code{find}, and @code{print} are in this category.  Type
+@kbd{help data} at the @value{GDBN} prompt to see a list of commands
+in this category.
+
+@item COMMAND_STACK
+The command has to do with manipulation of the stack.  For example,
+@code{backtrace}, @code{frame}, and @code{return} are in this
+category.  Type @kbd{help stack} at the @value{GDBN} prompt to see a
+list of commands in this category.
+
+@item COMMAND_FILES
+This class is used for file-related commands.  For example,
+@code{file}, @code{list} and @code{section} are in this category.
+Type @kbd{help files} at the @value{GDBN} prompt to see a list of
+commands in this category.
+
+@item COMMAND_SUPPORT
+This should be used for ``support facilities'', generally meaning
+things that are useful to the user when interacting with @value{GDBN},
+but not related to the state of the inferior.  For example,
+@code{help}, @code{make}, and @code{shell} are in this category.  Type
+@kbd{help support} at the @value{GDBN} prompt to see a list of
+commands in this category.
+
+@item COMMAND_STATUS
+The command is an @samp{info}-related command, that is, related to the
+state of @value{GDBN} itself.  For example, @code{info}, @code{macro},
+and @code{show} are in this category.  Type @kbd{help status} at the
+@value{GDBN} prompt to see a list of commands in this category.
+
+@item COMMAND_BREAKPOINTS
+The command has to do with breakpoints.  For example, @code{break},
+@code{clear}, and @code{delete} are in this category.  Type @kbd{help
+breakpoints} at the @value{GDBN} prompt to see a list of commands in
+this category.
+
+@item COMMAND_TRACEPOINTS
+The command has to do with tracepoints.  For example, @code{trace},
+@code{actions}, and @code{tfind} are in this category.  Type
+@kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
+commands in this category.
+
+@item COMMAND_USER
+The command is a general purpose command for the user, and typically
+does not fit in one of the other categories.
+Type @kbd{help user-defined} at the @value{GDBN} prompt to see
+a list of commands in this category, as well as the list of gdb macros
+(@pxref{Sequences}).
+
+@item COMMAND_OBSCURE
+The command is only used in unusual circumstances, or is not of
+general interest to users.  For example, @code{checkpoint},
+@code{fork}, and @code{stop} are in this category.  Type @kbd{help
+obscure} at the @value{GDBN} prompt to see a list of commands in this
+category.
+
+@item COMMAND_MAINTENANCE
+The command is only useful to @value{GDBN} maintainers.  The
+@code{maintenance} and @code{flushregs} commands are in this category.
+Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
+commands in this category.
+@end vtable
+
+A new command can use a predefined completion function, either by
+specifying it via an argument at initialization, or by returning it
+from the @code{completer} procedure.  These predefined completion
+constants are all defined in the @code{gdb} module:
+
+@vtable @code
+@item COMPLETE_NONE
+This constant means that no completion should be done.
+
+@item COMPLETE_FILENAME
+This constant means that filename completion should be performed.
+
+@item COMPLETE_LOCATION
+This constant means that location completion should be done.
+@xref{Specify Location}.
+
+@item COMPLETE_COMMAND
+This constant means that completion should examine @value{GDBN}
+command names.
+
+@item COMPLETE_SYMBOL
+This constant means that completion should be done using symbol names
+as the source.
+
+@item COMPLETE_EXPRESSION
+This constant means that completion should be done on expressions.
+Often this means completing on symbol names, but some language
+parsers also have support for completing on field names.
+@end vtable
+
+The following code snippet shows how a trivial CLI command can be
+implemented in Guile:
+
+@smallexample
+(gdb) guile
+(register-command! (make-command "hello-world"
+  #:command-class COMMAND_USER
+  #:doc "Greet the whole world."
+  #:invoke (lambda (self args from-tty) (display "Hello, World!\n"))))
+end
+(gdb) hello-world
+Hello, World!
+@end smallexample
+
 @node Progspaces In Guile
 @subsubsection Program Spaces In Guile
 
diff --git a/gdb/guile/guile-internal.h b/gdb/guile/guile-internal.h
index 9f6a886..042ece9 100644
--- a/gdb/guile/guile-internal.h
+++ b/gdb/guile/guile-internal.h
@@ -164,6 +164,8 @@ extern ULONGEST gdbscm_scm_to_ulongest (SCM u);
 extern void gdbscm_dynwind_xfree (void *ptr);
 
 extern int gdbscm_is_procedure (SCM proc);
+
+extern char *gdbscm_gc_xstrdup (const char *);
 \f
 /* GDB smobs, from scm-gsmob.c */
 
@@ -315,6 +317,8 @@ extern char *gdbscm_exception_message_to_string (SCM exception);
 
 extern excp_matcher_func gdbscm_memory_error_p;
 
+extern excp_matcher_func gdbscm_user_error_p;
+
 extern SCM gdbscm_make_memory_error (const char *subr, const char *msg,
 				     SCM args);
 
@@ -375,6 +379,15 @@ extern SCM bkscm_scm_from_block (const struct block *block,
 extern const struct block *bkscm_scm_to_block
   (SCM block_scm, int arg_pos, const char *func_name, SCM *excp);
 
+/* scm-cmd.c */
+
+extern char *gdbscm_parse_command_name (const char *name,
+					const char *func_name, int arg_pos,
+					struct cmd_list_element ***base_list,
+					struct cmd_list_element **start_list);
+
+extern int gdbscm_valid_command_class_p (int command_class);
+
 /* scm-frame.c */
 
 typedef struct _frame_smob frame_smob;
@@ -543,6 +556,7 @@ extern void gdbscm_initialize_arches (void);
 extern void gdbscm_initialize_auto_load (void);
 extern void gdbscm_initialize_blocks (void);
 extern void gdbscm_initialize_breakpoints (void);
+extern void gdbscm_initialize_commands (void);
 extern void gdbscm_initialize_disasm (void);
 extern void gdbscm_initialize_exceptions (void);
 extern void gdbscm_initialize_frames (void);
diff --git a/gdb/guile/guile.c b/gdb/guile/guile.c
index 51919de..c4e5832 100644
--- a/gdb/guile/guile.c
+++ b/gdb/guile/guile.c
@@ -537,6 +537,7 @@ initialize_gdb_module (void *data)
   gdbscm_initialize_auto_load ();
   gdbscm_initialize_blocks ();
   gdbscm_initialize_breakpoints ();
+  gdbscm_initialize_commands ();
   gdbscm_initialize_disasm ();
   gdbscm_initialize_frames ();
   gdbscm_initialize_iterators ();
diff --git a/gdb/guile/lib/gdb.scm b/gdb/guile/lib/gdb.scm
index 646ca81..a3f43a4 100644
--- a/gdb/guile/lib/gdb.scm
+++ b/gdb/guile/lib/gdb.scm
@@ -141,6 +141,34 @@
  set-breakpoint-stop!
  breakpoint-commands
 
+ ;; scm-cmd.c
+
+ make-command
+ register-command!
+ command?
+ command-valid?
+ dont-repeat
+
+ COMPLETE_NONE
+ COMPLETE_FILENAME
+ COMPLETE_LOCATION
+ COMPLETE_COMMAND
+ COMPLETE_SYMBOL
+ COMPLETE_EXPRESSION
+
+ COMMAND_NONE
+ COMMAND_RUNNING
+ COMMAND_DATA
+ COMMAND_STACK
+ COMMAND_FILES
+ COMMAND_SUPPORT
+ COMMAND_STATUS
+ COMMAND_BREAKPOINTS
+ COMMAND_TRACEPOINTS
+ COMMAND_OBSCURE
+ COMMAND_MAINTENANCE
+ COMMAND_USER
+
  ;; scm-disasm.c
 
  arch-disassemble
@@ -457,4 +485,5 @@
  orig-input-port
  orig-output-port
  orig-error-port
+ throw-user-error
 )
diff --git a/gdb/guile/lib/gdb/init.scm b/gdb/guile/lib/gdb/init.scm
index 12ad67d..1e90790 100644
--- a/gdb/guile/lib/gdb/init.scm
+++ b/gdb/guile/lib/gdb/init.scm
@@ -37,7 +37,8 @@
 (define %exception-keys '(gdb:error
 			  gdb:invalid-object-error
 			  gdb:memory-error
-			  gdb:pp-type-error))
+			  gdb:pp-type-error
+			  gdb:user-error))
 
 ;; Printer for gdb exceptions, used when Scheme tries to print them directly.
 
@@ -171,3 +172,10 @@
 (define-public (orig-input-port) %orig-input-port)
 (define-public (orig-output-port) %orig-output-port)
 (define-public (orig-error-port) %orig-error-port)
+
+;; Utility to throw gdb:user-error for use in writing gdb commands.
+;; The requirements for the arguments to "throw" are a bit obscure,
+;; so give the user something simpler.
+
+(define-public (throw-user-error message . args)
+  (throw 'gdb:user-error #f message args))
diff --git a/gdb/guile/scm-cmd.c b/gdb/guile/scm-cmd.c
new file mode 100644
index 0000000..ee3674c
--- /dev/null
+++ b/gdb/guile/scm-cmd.c
@@ -0,0 +1,893 @@
+/* GDB commands implemented in Scheme.
+
+   Copyright (C) 2008-2014 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 <ctype.h>
+#include "exceptions.h"
+#include "charset.h"
+#include "gdbcmd.h"
+#include "cli/cli-decode.h"
+#include "completer.h"
+#include "guile-internal.h"
+
+/* The <gdb:command> smob.
+
+   Note: Commands are added to gdb using a two step process:
+   1) Call make-command to create a <gdb:command> object.
+   2) Call register-command! to add the command to gdb.
+   It is done this way so that the constructor, make-command, doesn't have
+   any side-effects.  This means that the smob needs to store everything
+   that was passed to make-command.  */
+
+typedef struct _command_smob
+{
+  /* This always appears first.  */
+  gdb_smob base;
+
+  /* The name of the command, as passed to make-command.  */
+  char *name;
+
+  /* The last word of the command.
+     This is needed because add_cmd requires us to allocate space
+     for it. :-(  */
+  char *cmd_name;
+
+  /* Non-zero if this is a prefix command.  */
+  int is_prefix;
+
+  /* One of the COMMAND_* constants.  */
+  enum command_class cmd_class;
+
+  /* The documentation for the command.  */
+  char *doc;
+
+  /* The corresponding gdb command object.
+     This is NULL if the command has not been registered yet, or
+     is no longer registered.  */
+  struct cmd_list_element *command;
+
+  /* A prefix command requires storage for a list of its sub-commands.
+     A pointer to this is passed to add_prefix_command, and to add_cmd
+     for sub-commands of that prefix.
+     This is NULL if the command has not been registered yet, or
+     is no longer registered.  If this command is not a prefix
+     command, then this field is unused.  */
+  struct cmd_list_element *sub_list;
+
+  /* The procedure to call to invoke the command.
+     (lambda (self arg from-tty) ...).
+     Its result is unspecified.  */
+  SCM invoke;
+
+  /* Either #f, one of the COMPLETE_* constants, or a procedure to call to
+     perform command completion.  Called as (lambda (self text word) ...).  */
+  SCM complete;
+
+  /* The <gdb:command> object we are contained in, needed to protect/unprotect
+     the object since a reference to it comes from non-gc-managed space
+     (the command context pointer).  */
+  SCM containing_scm;
+} command_smob;
+
+static const char command_smob_name[] = "gdb:command";
+
+/* The tag Guile knows the objfile smob by.  */
+static scm_t_bits command_smob_tag;
+
+/* Keywords used by make-command.  */
+static SCM invoke_keyword;
+static SCM command_class_keyword;
+static SCM completer_class_keyword;
+static SCM prefix_p_keyword;
+static SCM doc_keyword;
+
+/* Struct representing built-in completion types.  */
+struct cmdscm_completer
+{
+  /* Scheme symbol name.  */
+  const char *name;
+  /* Completion function.  */
+  completer_ftype *completer;
+};
+
+static const struct cmdscm_completer cmdscm_completers[] =
+{
+  { "COMPLETE_NONE", noop_completer },
+  { "COMPLETE_FILENAME", filename_completer },
+  { "COMPLETE_LOCATION", location_completer },
+  { "COMPLETE_COMMAND", command_completer },
+  { "COMPLETE_SYMBOL", make_symbol_completion_list_fn },
+  { "COMPLETE_EXPRESSION", expression_completer },
+};
+
+#define N_COMPLETERS (sizeof (cmdscm_completers) \
+		      / sizeof (cmdscm_completers[0]))
+
+static int cmdscm_is_valid (command_smob *);
+\f
+/* Administrivia for command smobs.  */
+
+/* The smob "print" function for <gdb:command>.  */
+
+static int
+cmdscm_print_command_smob (SCM self, SCM port, scm_print_state *pstate)
+{
+  command_smob *c_smob = (command_smob *) SCM_SMOB_DATA (self);
+
+  gdbscm_printf (port, "#<%s", command_smob_name);
+
+  gdbscm_printf (port, " %s",
+		 c_smob->name != NULL ? c_smob->name : "{unnamed}");
+
+  if (! cmdscm_is_valid (c_smob))
+    scm_puts (" {invalid}", port);
+
+  scm_puts (">", port);
+
+  scm_remember_upto_here_1 (self);
+
+  /* Non-zero means success.  */
+  return 1;
+}
+
+/* Low level routine to create a <gdb:command> object.
+   It's empty in the sense that a command still needs to be associated
+   with it.  */
+
+static SCM
+cmdscm_make_command_smob (void)
+{
+  command_smob *c_smob = (command_smob *)
+    scm_gc_malloc (sizeof (command_smob), command_smob_name);
+  SCM c_scm;
+
+  memset (c_smob, 0, sizeof (*c_smob));
+  c_smob->cmd_class = no_class;
+  c_smob->invoke = SCM_BOOL_F;
+  c_smob->complete = SCM_BOOL_F;
+  c_scm = scm_new_smob (command_smob_tag, (scm_t_bits) c_smob);
+  c_smob->containing_scm = c_scm;
+  gdbscm_init_gsmob (&c_smob->base);
+
+  return c_scm;
+}
+
+/* Clear the COMMAND pointer in C_SMOB and unprotect the object from GC.  */
+
+static void
+cmdscm_release_command (command_smob *c_smob)
+{
+  c_smob->command = NULL;
+  scm_gc_unprotect_object (c_smob->containing_scm);
+}
+
+/* Return non-zero if SCM is a command smob.  */
+
+static int
+cmdscm_is_command (SCM scm)
+{
+  return SCM_SMOB_PREDICATE (command_smob_tag, scm);
+}
+
+/* (command? scm) -> boolean */
+
+static SCM
+gdbscm_command_p (SCM scm)
+{
+  return scm_from_bool (cmdscm_is_command (scm));
+}
+
+/* Returns the <gdb:command> object in SELF.
+   Throws an exception if SELF is not a <gdb:command> object.  */
+
+static SCM
+cmdscm_get_command_arg_unsafe (SCM self, int arg_pos, const char *func_name)
+{
+  SCM_ASSERT_TYPE (cmdscm_is_command (self), self, arg_pos, func_name,
+		   command_smob_name);
+
+  return self;
+}
+
+/* Returns a pointer to the command smob of SELF.
+   Throws an exception if SELF is not a <gdb:command> object.  */
+
+static command_smob *
+cmdscm_get_command_smob_arg_unsafe (SCM self, int arg_pos,
+				    const char *func_name)
+{
+  SCM c_scm = cmdscm_get_command_arg_unsafe (self, arg_pos, func_name);
+  command_smob *c_smob = (command_smob *) SCM_SMOB_DATA (c_scm);
+
+  return c_smob;
+}
+
+/* Return non-zero if command C_SMOB is valid.  */
+
+static int
+cmdscm_is_valid (command_smob *c_smob)
+{
+  return c_smob->command != NULL;
+}
+
+/* Returns a pointer to the command smob of SELF.
+   Throws an exception if SELF is not a valid <gdb:command> object.  */
+
+static command_smob *
+cmdscm_get_valid_command_smob_arg_unsafe (SCM self, int arg_pos,
+					  const char *func_name)
+{
+  command_smob *c_smob
+    = cmdscm_get_command_smob_arg_unsafe (self, arg_pos, func_name);
+
+  if (!cmdscm_is_valid (c_smob))
+    {
+      gdbscm_invalid_object_error (func_name, arg_pos, self,
+				   _("<gdb:command>"));
+    }
+
+  return c_smob;
+}
+\f
+/* Scheme functions for GDB commands.  */
+
+/* (command-valid? <gdb:command>) -> boolean
+   Returns #t if SELF is still valid.  */
+
+static SCM
+gdbscm_command_valid_p (SCM self)
+{
+  command_smob *c_smob
+    = cmdscm_get_command_smob_arg_unsafe (self, SCM_ARG1, FUNC_NAME);
+
+  return scm_from_bool (cmdscm_is_valid (c_smob));
+}
+
+/* (dont-repeat cmd) -> unspecified
+   Scheme function which wraps dont_repeat.  */
+
+static SCM
+gdbscm_dont_repeat (SCM self)
+{
+  /* We currently don't need anything from SELF, but still verify it.  */
+  command_smob *c_smob
+    = cmdscm_get_valid_command_smob_arg_unsafe (self, SCM_ARG1, FUNC_NAME);
+
+  dont_repeat ();
+
+  return SCM_UNSPECIFIED;
+}
+\f
+/* The make-command function.  */
+
+/* Called if the gdb cmd_list_element is destroyed.  */
+
+static void
+cmdscm_destroyer (struct cmd_list_element *self, void *context)
+{
+  command_smob *c_smob = (command_smob *) context;
+
+  cmdscm_release_command (c_smob);
+
+  /* We allocated the name, doc string, and perhaps the prefix name.  */
+  xfree ((char *) self->name);
+  xfree (self->doc);
+  xfree (self->prefixname);
+}
+
+/* Called by gdb to invoke the command.  */
+
+static void
+cmdscm_function (struct cmd_list_element *command, char *args, int from_tty)
+{
+  command_smob *c_smob/*obj*/ = (command_smob *) get_cmd_context (command);
+  SCM arg_scm, tty_scm, result;
+
+  gdb_assert (c_smob != NULL);
+
+  if (args == NULL)
+    args = "";
+  arg_scm = gdbscm_scm_from_string (args, strlen (args), host_charset (), 1);
+  if (gdbscm_is_exception (arg_scm))
+    error (_("Could not convert arguments to Scheme string."));
+
+  tty_scm = scm_from_bool (from_tty);
+
+  result = gdbscm_safe_call_3 (c_smob->invoke, c_smob->containing_scm,
+			       arg_scm, tty_scm, gdbscm_user_error_p);
+
+  if (gdbscm_is_exception (result))
+    {
+      /* Don't print the stack if this was an error signalled by the command
+	 itself.  */
+      if (gdbscm_user_error_p (gdbscm_exception_key (result)))
+	{
+	  char *msg = gdbscm_exception_message_to_string (result);
+
+	  make_cleanup (xfree, msg);
+	  error ("%s", msg);
+	}
+      else
+	{
+	  gdbscm_print_gdb_exception (SCM_BOOL_F, result);
+	  error (_("Error occurred in Scheme-implemented GDB command."));
+	}
+    }
+}
+
+/* Subroutine of cmdscm_completer to simplify it.
+   Print an error message indicating that COMPLETION is a bad completion
+   result.  */
+
+static void
+cmdscm_bad_completion_result (const char *msg, SCM completion)
+{
+  SCM port = scm_current_error_port ();
+
+  scm_puts (msg, port);
+  scm_display (completion, port);
+  scm_newline (port);
+}
+
+/* Subroutine of cmdscm_completer to simplify it.
+   Validate COMPLETION and add to RESULT.
+   If an error occurs print an error message.
+   The result is a boolean indicating success.  */
+
+static int
+cmdscm_add_completion (SCM completion, VEC (char_ptr) **result)
+{
+  char *item;
+  SCM except_scm;
+
+  if (!scm_is_string (completion))
+    {
+      /* Inform the user, but otherwise ignore the entire result.  */
+      cmdscm_bad_completion_result (_("Bad text from completer: "),
+				    completion);
+      return 0;
+    }
+
+  item = gdbscm_scm_to_string (completion, NULL, host_charset (), 1,
+			       &except_scm);
+  if (item == NULL)
+    {
+      /* Inform the user, but otherwise ignore the entire result.  */
+      gdbscm_print_gdb_exception (SCM_BOOL_F, except_scm);
+      return 0;
+    }
+
+  VEC_safe_push (char_ptr, *result, item);
+
+  return 1;
+}
+
+/* Called by gdb for command completion.  */
+
+static VEC (char_ptr) *
+cmdscm_completer (struct cmd_list_element *command,
+		  const char *text, const char *word)
+{
+  command_smob *c_smob/*obj*/ = (command_smob *) get_cmd_context (command);
+  SCM completer_result_scm;
+  SCM text_scm, word_scm, result_scm;
+  VEC (char_ptr) *result = NULL;
+
+  gdb_assert (c_smob != NULL);
+  gdb_assert (gdbscm_is_procedure (c_smob->complete));
+
+  text_scm = gdbscm_scm_from_string (text, strlen (text), host_charset (),
+				     1);
+  if (gdbscm_is_exception (text_scm))
+    error (_("Could not convert \"text\" argument to Scheme string."));
+  word_scm = gdbscm_scm_from_string (word, strlen (word), host_charset (),
+				     1);
+  if (gdbscm_is_exception (word_scm))
+    error (_("Could not convert \"word\" argument to Scheme string."));
+
+  completer_result_scm
+    = gdbscm_safe_call_3 (c_smob->complete, c_smob->containing_scm,
+			  text_scm, word_scm, NULL);
+
+  if (gdbscm_is_exception (completer_result_scm))
+    {
+      /* Inform the user, but otherwise ignore.  */
+      gdbscm_print_gdb_exception (SCM_BOOL_F, completer_result_scm);
+      goto done;
+    }
+
+  if (gdbscm_is_true (scm_list_p (completer_result_scm)))
+    {
+      SCM list = completer_result_scm;
+
+      while (!scm_is_eq (list, SCM_EOL))
+	{
+	  SCM next = scm_car (list);
+
+	  if (!cmdscm_add_completion (next, &result))
+	    {
+	      VEC_free (char_ptr, result);
+	      goto done;
+	    }
+
+	  list = scm_cdr (list);
+	}
+    }
+  else if (itscm_is_iterator (completer_result_scm))
+    {
+      SCM iter = completer_result_scm;
+      SCM next = itscm_safe_call_next_x (iter, NULL);
+
+      while (gdbscm_is_true (next))
+	{
+	  if (gdbscm_is_exception (next))
+	    {
+	      /* Inform the user, but otherwise ignore the entire result.  */
+	      gdbscm_print_gdb_exception (SCM_BOOL_F, completer_result_scm);
+	      VEC_free (char_ptr, result);
+	      goto done;
+	    }
+
+	  if (!cmdscm_add_completion (next, &result))
+	    {
+	      VEC_free (char_ptr, result);
+	      goto done;
+	    }
+
+	  next = itscm_safe_call_next_x (iter, NULL);
+	}
+    }
+  else
+    {
+      /* Inform the user, but otherwise ignore.  */
+      cmdscm_bad_completion_result (_("Bad completer result: "),
+				    completer_result_scm);
+    }
+
+ done:
+  return result;
+}
+
+/* Helper for gdbscm_make_command which locates the command list to use and
+   pulls out the command name.
+
+   NAME is the command name list.  The final word in the list is the
+   name of the new command.  All earlier words must be existing prefix
+   commands.
+
+   *BASE_LIST is set to the final prefix command's list of
+   *sub-commands.
+
+   START_LIST is the list in which the search starts.
+
+   This function returns the xmalloc()d name of the new command.
+   On error a Scheme exception is thrown.  */
+
+char *
+gdbscm_parse_command_name (const char *name,
+			   const char *func_name, int arg_pos,
+			   struct cmd_list_element ***base_list,
+			   struct cmd_list_element **start_list)
+{
+  struct cmd_list_element *elt;
+  int len = strlen (name);
+  int i, lastchar;
+  char *prefix_text;
+  const char *prefix_text2;
+  char *result, *msg;
+
+  /* Skip trailing whitespace.  */
+  for (i = len - 1; i >= 0 && (name[i] == ' ' || name[i] == '\t'); --i)
+    ;
+  if (i < 0)
+    {
+      gdbscm_out_of_range_error (func_name, arg_pos,
+				 gdbscm_scm_from_c_string (name),
+				 _("no command name found"));
+    }
+  lastchar = i;
+
+  /* Find first character of the final word.  */
+  for (; i > 0 && (isalnum (name[i - 1])
+		   || name[i - 1] == '-'
+		   || name[i - 1] == '_');
+       --i)
+    ;
+  result = xmalloc (lastchar - i + 2);
+  memcpy (result, &name[i], lastchar - i + 1);
+  result[lastchar - i + 1] = '\0';
+
+  /* Skip whitespace again.  */
+  for (--i; i >= 0 && (name[i] == ' ' || name[i] == '\t'); --i)
+    ;
+  if (i < 0)
+    {
+      *base_list = start_list;
+      return result;
+    }
+
+  prefix_text = xmalloc (i + 2);
+  memcpy (prefix_text, name, i + 1);
+  prefix_text[i + 1] = '\0';
+
+  prefix_text2 = prefix_text;
+  elt = lookup_cmd_1 (&prefix_text2, *start_list, NULL, 1);
+  if (!elt || elt == (struct cmd_list_element *) -1)
+    {
+      msg = xstrprintf (_("could not find command prefix '%s'"), prefix_text);
+      xfree (prefix_text);
+      xfree (result);
+      scm_dynwind_begin (0);
+      gdbscm_dynwind_xfree (msg);
+      gdbscm_out_of_range_error (func_name, arg_pos,
+				 gdbscm_scm_from_c_string (name), msg);
+    }
+
+  if (elt->prefixlist)
+    {
+      xfree (prefix_text);
+      *base_list = elt->prefixlist;
+      return result;
+    }
+
+  msg = xstrprintf (_("'%s' is not a prefix command"), prefix_text);
+  xfree (prefix_text);
+  xfree (result);
+  scm_dynwind_begin (0);
+  gdbscm_dynwind_xfree (msg);
+  gdbscm_out_of_range_error (func_name, arg_pos,
+			     gdbscm_scm_from_c_string (name), msg);
+  /* NOTREACHED */
+}
+
+static const scheme_integer_constant command_classes[] =
+{
+  /* Note: alias and user are special; pseudo appears to be unused,
+     and there is no reason to expose tui or xdb, I think.  */
+  { "COMMAND_NONE", no_class },
+  { "COMMAND_RUNNING", class_run },
+  { "COMMAND_DATA", class_vars },
+  { "COMMAND_STACK", class_stack },
+  { "COMMAND_FILES", class_files },
+  { "COMMAND_SUPPORT", class_support },
+  { "COMMAND_STATUS", class_info },
+  { "COMMAND_BREAKPOINTS", class_breakpoint },
+  { "COMMAND_TRACEPOINTS", class_trace },
+  { "COMMAND_OBSCURE", class_obscure },
+  { "COMMAND_MAINTENANCE", class_maintenance },
+  { "COMMAND_USER", class_user },
+
+  END_INTEGER_CONSTANTS
+};
+
+/* Return non-zero if command_class is a valid command class.  */
+
+int
+gdbscm_valid_command_class_p (int command_class)
+{
+  int i;
+
+  for (i = 0; command_classes[i].name != NULL; ++i)
+    {
+      if (command_classes[i].value == command_class)
+	return 1;
+    }
+
+  return 0;
+}
+
+/* Return a normalized form of command NAME.
+   That is tabs are replaced with spaces and multiple spaces are replaced
+   with a single space.
+   If WANT_TRAILING_SPACE is non-zero, add one space at the end.  This is for
+   prefix commands.
+   but that is the caller's responsibility.
+   Space for the result is allocated on the GC heap.  */
+
+static char *
+cmdscm_canonicalize_name (const char *name, int want_trailing_space)
+{
+  int i, out, seen_word;
+  char *result = scm_gc_malloc_pointerless (strlen (name) + 2, FUNC_NAME);
+
+  i = out = seen_word = 0;
+  while (name[i])
+    {
+      /* Skip whitespace.  */
+      while (name[i] == ' ' || name[i] == '\t')
+	++i;
+      /* Copy non-whitespace characters.  */
+      if (name[i])
+	{
+	  if (seen_word)
+	    result[out++] = ' ';
+	  while (name[i] && name[i] != ' ' && name[i] != '\t')
+	    result[out++] = name[i++];
+	  seen_word = 1;
+	}
+    }
+  if (want_trailing_space)
+    result[out++] = ' ';
+  result[out] = '\0';
+
+  return result;
+}
+
+/* (make-command name [#:invoke lambda]
+     [#:command-class class] [#:completer-class completer]
+     [#:prefix? <bool>] [#:doc <string>]) -> <gdb:command>
+
+   NAME is the name of the command.  It may consist of multiple words,
+   in which case the final word is the name of the new command, and
+   earlier words must be prefix commands.
+
+   INVOKE is a procedure of three arguments that performs the command when
+   invoked: (lambda (self arg from-tty) ...).
+   Its result is unspecified.
+
+   CLASS is the kind of command.  It must be one of the COMMAND_*
+   constants defined in the gdb module.  If not specified, "no_class" is used.
+
+   COMPLETER is the kind of completer.  It must be either:
+     #f - completion is not supported for this command.
+     One of the COMPLETE_* constants defined in the gdb module.
+     A procedure of three arguments: (lambda (self text word) ...).
+       Its result is one of:
+         A list of strings.
+         A <gdb:iterator> object that returns the set of possible completions,
+         ending with #f.
+	 TODO(dje): Once PR 16699 is fixed, add support for returning
+	 a COMPLETE_* constant.
+   If not specified, then completion is not supported for this command.
+
+   If PREFIX is #t, then this command is a prefix command.
+
+   DOC is the doc string for the command.
+
+   The result is the <gdb:command> Scheme object.
+   The command is not available to be used yet, however.
+   It must still be added to gdb with register-command!.  */
+
+static SCM
+gdbscm_make_command (SCM name_scm, SCM rest)
+{
+  const SCM keywords[] = {
+    invoke_keyword, command_class_keyword, completer_class_keyword,
+    prefix_p_keyword, doc_keyword, SCM_BOOL_F
+  };
+  int invoke_arg_pos = -1, command_class_arg_pos = 1;
+  int completer_class_arg_pos = -1, is_prefix_arg_pos = -1;
+  int doc_arg_pos = -1;
+  char *s;
+  char *name;
+  int command_class = no_class;
+  SCM completer_class = SCM_BOOL_F;
+  int is_prefix = 0;
+  char *doc = NULL;
+  SCM invoke = SCM_BOOL_F;
+  SCM c_scm;
+  command_smob *c_smob;
+
+  gdbscm_parse_function_args (FUNC_NAME, SCM_ARG1, keywords, "s#OiOts",
+			      name_scm, &name, rest,
+			      &invoke_arg_pos, &invoke,
+			      &command_class_arg_pos, &command_class,
+			      &completer_class_arg_pos, &completer_class,
+			      &is_prefix_arg_pos, &is_prefix,
+			      &doc_arg_pos, &doc);
+
+  if (doc == NULL)
+    doc = xstrdup (_("This command is not documented."));
+
+  s = name;
+  name = cmdscm_canonicalize_name (s, is_prefix);
+  xfree (s);
+  s = doc;
+  doc = gdbscm_gc_xstrdup (s);
+  xfree (s);
+
+  if (is_prefix
+      ? name[0] == ' '
+      : name[0] == '\0')
+    {
+      gdbscm_out_of_range_error (FUNC_NAME, SCM_ARG1, name_scm,
+				 _("no command name found"));
+    }
+
+  if (gdbscm_is_true (invoke))
+    {
+      SCM_ASSERT_TYPE (gdbscm_is_procedure (invoke), invoke,
+		       invoke_arg_pos, FUNC_NAME, _("procedure"));
+    }
+
+  if (!gdbscm_valid_command_class_p (command_class))
+    {
+      gdbscm_out_of_range_error (FUNC_NAME, command_class_arg_pos,
+				 scm_from_int (command_class),
+				 _("invalid command class argument"));
+    }
+
+  SCM_ASSERT_TYPE (gdbscm_is_false (completer_class)
+		   || scm_is_integer (completer_class)
+		   || gdbscm_is_procedure (completer_class),
+		   completer_class, completer_class_arg_pos, FUNC_NAME,
+		   _("integer or procedure"));
+  if (scm_is_integer (completer_class)
+      && !scm_is_signed_integer (completer_class, 0, N_COMPLETERS - 1))
+    {
+      gdbscm_out_of_range_error (FUNC_NAME, completer_class_arg_pos,
+				 completer_class,
+				 _("invalid completion type argument"));
+    }
+
+  c_scm = cmdscm_make_command_smob ();
+  c_smob = (command_smob *) SCM_SMOB_DATA (c_scm);
+  c_smob->name = name;
+  c_smob->is_prefix = is_prefix;
+  c_smob->cmd_class = command_class;
+  c_smob->doc = doc;
+  c_smob->invoke = invoke;
+  c_smob->complete = completer_class;
+
+  return c_scm;
+}
+
+/* (register-command! <gdb:command>) -> unspecified
+
+   It is an error to register a command more than once.  */
+
+static SCM
+gdbscm_register_command_x (SCM self)
+{
+  command_smob *c_smob
+    = cmdscm_get_command_smob_arg_unsafe (self, SCM_ARG1, FUNC_NAME);
+  char *cmd_name, *pfx_name;
+  struct cmd_list_element **cmd_list;
+  struct cmd_list_element *cmd = NULL;
+  volatile struct gdb_exception except;
+
+  if (cmdscm_is_valid (c_smob))
+    scm_misc_error (FUNC_NAME, _("command is already registered"), SCM_EOL);
+
+  cmd_name = gdbscm_parse_command_name (c_smob->name, FUNC_NAME, SCM_ARG1,
+					&cmd_list, &cmdlist);
+  c_smob->cmd_name = gdbscm_gc_xstrdup (cmd_name);
+  xfree (cmd_name);
+
+  TRY_CATCH (except, RETURN_MASK_ALL)
+    {
+      if (c_smob->is_prefix)
+	{
+	  /* If we have our own "invoke" method, then allow unknown
+	     sub-commands.  */
+	  int allow_unknown = gdbscm_is_true (c_smob->invoke);
+
+	  cmd = add_prefix_cmd (c_smob->cmd_name, c_smob->cmd_class,
+				NULL, c_smob->doc, &c_smob->sub_list,
+				c_smob->name, allow_unknown, cmd_list);
+	}
+      else
+	{
+	  cmd = add_cmd (c_smob->cmd_name, c_smob->cmd_class,
+			 NULL, c_smob->doc, cmd_list);
+	}
+    }
+  GDBSCM_HANDLE_GDB_EXCEPTION (except);
+
+  /* Note: At this point the command exists in gdb.
+     So no more errors after this point.  */
+
+  /* There appears to be no API to set this.  */
+  cmd->func = cmdscm_function;
+  cmd->destroyer = cmdscm_destroyer;
+
+  c_smob->command = cmd;
+  set_cmd_context (cmd, c_smob);
+
+  if (gdbscm_is_true (c_smob->complete))
+    {
+      set_cmd_completer (cmd,
+			 scm_is_integer (c_smob->complete)
+			 ? cmdscm_completers[scm_to_int (c_smob->complete)].completer
+			 : cmdscm_completer);
+    }
+
+  /* The owner of this command is not in GC-controlled memory, so we need
+     to protect it from GC until the command is deleted.  */
+  scm_gc_protect_object (c_smob->containing_scm);
+
+  return SCM_UNSPECIFIED;
+}
+\f
+/* Initialize the Scheme command support.  */
+
+static const scheme_function command_functions[] =
+{
+  { "make-command", 1, 0, 1, gdbscm_make_command,
+    "\
+Make a GDB command object.\n\
+\n\
+  Arguments: name [#:invoke lambda]\n\
+      [#:command-class <class>] [#:completer-class <completer>]\n\
+      [#:prefix? <bool>] [#:doc string]\n\
+    name: The name of the command.  It may consist of multiple words,\n\
+      in which case the final word is the name of the new command, and\n\
+      earlier words must be prefix commands.\n\
+    invoke: A procedure of three arguments to perform the command.\n\
+      (lambda (self arg from-tty) ...)\n\
+      Its result is unspecified.\n\
+    class: The class of the command, one of COMMAND_*.\n\
+      The default is COMMAND_NONE.\n\
+    completer: The kind of completer, #f, one of COMPLETE_*, or a procedure\n\
+      to perform the completion: (lambda (self text word) ...).\n\
+    prefix?: If true then the command is a prefix command.\n\
+    doc: The \"doc string\" of the command.\n\
+  Returns: <gdb:command> object" },
+
+  { "register-command!", 1, 0, 0, gdbscm_register_command_x,
+    "\
+Register a <gdb:command> object with GDB." },
+
+  { "command?", 1, 0, 0, gdbscm_command_p,
+    "\
+Return #t if the object is a <gdb:command> object." },
+
+  { "command-valid?", 1, 0, 0, gdbscm_command_valid_p,
+    "\
+Return #t if the <gdb:command> object is valid." },
+
+  { "dont-repeat", 1, 0, 0, gdbscm_dont_repeat,
+    "\
+Prevent command repetition when user enters an empty line.\n\
+\n\
+  Arguments: <gdb:command>\n\
+  Returns: unspecified" },
+
+  END_FUNCTIONS
+};
+
+/* Initialize the 'commands' code.  */
+
+void
+gdbscm_initialize_commands (void)
+{
+  int i;
+
+  command_smob_tag
+    = gdbscm_make_smob_type (command_smob_name, sizeof (command_smob));
+  scm_set_smob_print (command_smob_tag, cmdscm_print_command_smob);
+
+  gdbscm_define_integer_constants (command_classes, 1);
+  gdbscm_define_functions (command_functions, 1);
+
+  for (i = 0; i < N_COMPLETERS; ++i)
+    {
+      scm_c_define (cmdscm_completers[i].name, scm_from_int (i));
+      scm_c_export (cmdscm_completers[i].name, NULL);
+    }
+
+  invoke_keyword = scm_from_latin1_keyword ("invoke");
+  command_class_keyword = scm_from_latin1_keyword ("command-class");
+  completer_class_keyword = scm_from_latin1_keyword ("completer-class");
+  prefix_p_keyword = scm_from_latin1_keyword ("prefix?");
+  doc_keyword = scm_from_latin1_keyword ("doc");
+}
diff --git a/gdb/guile/scm-exception.c b/gdb/guile/scm-exception.c
index f773a7d..0f3c875 100644
--- a/gdb/guile/scm-exception.c
+++ b/gdb/guile/scm-exception.c
@@ -64,6 +64,9 @@ static SCM memory_error_symbol;
 /* User interrupt, e.g., RETURN_QUIT in struct gdb_exception.  */
 static SCM signal_symbol;
 
+/* A user error, e.g., bad arg to gdb command.  */
+static SCM user_error_symbol;
+
 /* Printing the stack is done by first capturing the stack and recording it in
    a <gdb:exception> object with this key and with the ARGS field set to
    (cons real-key (cons stack real-args)).
@@ -391,6 +394,15 @@ gdbscm_memory_error_p (SCM key)
   return scm_is_eq (key, memory_error_symbol);
 }
 
+/* Return non-zero if KEY is gdb:user-error.
+   Note: This is an excp_matcher_func function.  */
+
+int
+gdbscm_user_error_p (SCM key)
+{
+  return scm_is_eq (key, user_error_symbol);
+}
+
 /* Wrapper around scm_throw to throw a gdb:exception.
    This function does not return.
    This function cannot be called from inside TRY_CATCH.  */
@@ -663,6 +675,8 @@ gdbscm_initialize_exceptions (void)
 
   memory_error_symbol = scm_from_latin1_symbol ("gdb:memory-error");
 
+  user_error_symbol = scm_from_latin1_symbol ("gdb:user-error");
+
   gdbscm_invalid_object_error_symbol
     = scm_from_latin1_symbol ("gdb:invalid-object-error");
 
diff --git a/gdb/guile/scm-utils.c b/gdb/guile/scm-utils.c
index 9e9901d..918a51b 100644
--- a/gdb/guile/scm-utils.c
+++ b/gdb/guile/scm-utils.c
@@ -583,3 +583,15 @@ gdbscm_is_procedure (SCM proc)
 {
   return gdbscm_is_true (scm_procedure_p (proc));
 }
+
+/* Same as xstrdup, but the string is allocated on the GC heap.  */
+
+char *
+gdbscm_gc_xstrdup (const char *str)
+{
+  size_t len = strlen (str);
+  char *result = scm_gc_malloc_pointerless (len + 1, "gdbscm_gc_xstrdup");
+
+  strcpy (result, str);
+  return result;
+}
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 718ce24..bec3ce4 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2014-06-02  Doug Evans  <xdje42@gmail.com>
 
+	* gdb.guile/scm-cmd.c: New file.
+	* gdb.guile/scm-cmd.exp: New file.
+
+2014-06-02  Doug Evans  <xdje42@gmail.com>
+
 	* gdb.guile/scm-pretty-print.exp: Add tests for objfile and progspace
 	pretty-printer lookup.
 	* gdb.guile/scm-pretty-print.scm (pp_s-printer): New function.
diff --git a/gdb/testsuite/gdb.guile/scm-cmd.c b/gdb/testsuite/gdb.guile/scm-cmd.c
new file mode 100644
index 0000000..7f0dc59
--- /dev/null
+++ b/gdb/testsuite/gdb.guile/scm-cmd.c
@@ -0,0 +1,29 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2013 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/>.  */
+
+struct foo
+{
+  int ij;
+  int bc;
+};
+
+int
+main (void)
+{
+  struct foo bar;
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.guile/scm-cmd.exp b/gdb/testsuite/gdb.guile/scm-cmd.exp
new file mode 100644
index 0000000..a407f63
--- /dev/null
+++ b/gdb/testsuite/gdb.guile/scm-cmd.exp
@@ -0,0 +1,198 @@
+# Copyright (C) 2009-2013 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 the mechanism
+# for defining new GDB commands in Scheme.
+
+load_lib gdb-guile.exp
+
+standard_testfile
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile}] } {
+    return
+}
+
+# Skip all tests if Guile scripting is not enabled.
+if { [skip_guile_tests] } { continue }
+
+if ![gdb_guile_runto_main] {
+    fail "Can't run to main"
+    return
+}
+
+# Test a simple command, and command? while we're at it.
+
+gdb_test_multiline "input simple command" \
+    "guile" "" \
+    "(define test-cmd" "" \
+    " (make-command \"test-cmd\"" "" \
+    "  #:command-class COMMAND_OBSCURE" "" \
+    "  #:invoke (lambda (self arg from-tty)" "" \
+    "    (display (format #f \"test-cmd output, arg = ~a\\n\" arg)))))" "" \
+    "(register-command! test-cmd)" "" \
+    "end" ""
+
+gdb_test "guile (print (command? test-cmd))" "= #t"
+gdb_test "guile (print (command? 42))" "= #f"
+
+gdb_test "test-cmd ugh" "test-cmd output, arg = ugh" "call simple command"
+
+# Test a prefix command, and a subcommand within it.
+
+gdb_test_multiline "input prefix command" \
+    "guile" "" \
+    "(register-command! (make-command \"prefix-cmd\"" "" \
+    "  #:command-class COMMAND_OBSCURE" "" \
+    "  #:completer-class COMPLETE_NONE" "" \
+    "  #:prefix? #t" "" \
+    "  #:invoke (lambda (self arg from-tty)" "" \
+    "    (display (format #f \"prefix-cmd output, arg = ~a\\n\" arg)))))" "" \
+    "end" ""
+
+gdb_test "prefix-cmd ugh" "prefix-cmd output, arg = ugh" "call prefix command"
+
+gdb_test_multiline "input subcommand" \
+    "guile" "" \
+    "(register-command! (make-command \"prefix-cmd subcmd\"" "" \
+    "  #:command-class COMMAND_OBSCURE" "" \
+    "  #:invoke (lambda (self arg from-tty)" "" \
+    "    (display (format #f \"subcmd output, arg = ~a\\n\" arg)))))" "" \
+    "end" ""
+
+gdb_test "prefix-cmd subcmd ugh" "subcmd output, arg = ugh" "call subcmd"
+
+# Test a subcommand in an existing GDB prefix.
+
+gdb_test_multiline "input new subcommand" \
+    "guile" "" \
+    "(register-command! (make-command \"info newsubcmd\"" "" \
+    "  #:command-class COMMAND_OBSCURE" "" \
+    "  #:invoke (lambda (self arg from-tty)" "" \
+    "    (display (format #f \"newsubcmd output, arg = ~a\\n\" arg)))))" "" \
+    "end" ""
+
+gdb_test "info newsubcmd ugh" "newsubcmd output, arg = ugh" "call newsubcmd"
+
+# Test a command that throws gdb:user-error.
+
+gdb_test_multiline "input command to throw error" \
+    "guile" "" \
+    "(register-command! (make-command \"test-error-cmd\"" "" \
+    "  #:command-class COMMAND_OBSCURE" "" \
+    "  #:invoke (lambda (self arg from-tty)" "" \
+    "    (throw-user-error \"you lose! ~a\" arg))))" "" \
+    "end" ""
+
+gdb_test "test-error-cmd ugh" "ERROR: you lose! ugh" "call error command"
+
+# Test string->argv.
+
+gdb_test "guile (raw-print (string->argv \"1 2 3\"))" \
+    {= \("1" "2" "3"\)} \
+    "(string->argv \"1 2 3\")"
+
+gdb_test "guile (raw-print (string->argv \"'1 2' 3\"))" \
+    {= \("1 2" "3"\)} \
+    "(string->argv \"'1 2' 3\")"
+
+gdb_test "guile (raw-print (string->argv \"\\\"1 2\\\" 3\"))" \
+    {= \("1 2" "3"\)} \
+    "(string->argv (\"\\\"1 2\\\" 3\")"
+
+gdb_test "guile (raw-print (string->argv \"1\\\\ 2 3\"))" \
+    {= \("1 2" "3"\)} \
+    "(string->argv \"1\\\\ 2 3\")"
+
+# Test user-defined guile commands.
+
+gdb_test_multiline "input simple user-defined command" \
+    "guile" "" \
+    "(register-command! (make-command \"test-help\"" "" \
+    "  #:doc \"Docstring\"" "" \
+    "  #:command-class COMMAND_USER" "" \
+    "  #:invoke (lambda (self arg from-tty)" "" \
+    "    (display (format #f \"test-cmd output, arg = ~a\\n\" arg)))))" "" \
+    "end" ""
+
+gdb_test "test-help ugh" "test-cmd output, arg = ugh" \
+    "call simple user-defined command"
+
+# Make sure the command shows up in `help user-defined`.
+gdb_test "help user-defined" \
+    "User-defined commands.\[\r\n\]+The commands in this class are those defined by the user.\[\r\n\]+Use the \"define\" command to define a command.\[\r\n\]+List of commands:\[\r\n\]+test-help -- Docstring\[\r\n\]+Type \"help\" followed by command name for full documentation.\[\r\n\]+Type \"apropos word\" to search for commands related to \"word\".\[\r\n\]+Command name abbreviations are allowed if unambiguous.\[\r\n\]+" \
+    "see user-defined command in `help user-defined`"
+
+# Test expression completion on fields.
+
+gdb_test_multiline "expression completion command" \
+    "guile" "" \
+    "(register-command! (make-command \"expr-test\"" "" \
+    "  #:command-class COMMAND_USER" ""\
+    "  #:completer-class COMPLETE_EXPRESSION" "" \
+    "  #:invoke (lambda (self arg from-tty)" "" \
+    "    (display (format #f \"invoked on = ~a\\n\" arg)))))" "" \
+    "end" ""
+
+gdb_test "complete expr-test bar\." \
+    "expr-test bar\.bc.*expr-test bar\.ij.*" \
+    "test completion through complete command"
+
+set test "complete 'expr-test bar.i'"
+send_gdb "expr-test bar\.i\t\t"
+gdb_test_multiple "" "$test" {
+    -re "expr-test bar\.ij \\\x07$" {
+	send_gdb "\n"
+	gdb_test_multiple "" $test {
+	    -re "invoked on = bar.ij.*$gdb_prompt $" {
+		pass "$test"
+	    }
+	}
+    }
+}
+
+# Test using a function for completion.
+
+gdb_test_multiline "completer-as-function command" \
+    "guile" "" \
+    "(register-command! (make-command \"completer-as-function\"" "" \
+    "  #:command-class COMMAND_USER" ""\
+    "  #:completer-class (lambda (self text word)" "" \
+    "    (list \"1\" \"2\" \"3\"))" "" \
+    "  #:invoke (lambda (self arg from-tty)" "" \
+    "    (display (format #f \"invoked on = ~a\\n\" arg)))))" "" \
+    "end" ""
+
+gdb_test "complete completer-as-function 42\." \
+    "completer-as-function 42\.1.*completer-as-function 42\.2.*completer-as-function 42\.3" \
+    "test completion with completion function"
+
+# Test Scheme error in invoke function.
+
+gdb_test_multiline "input command with Scheme error" \
+    "guile" "" \
+    "(register-command! (make-command \"test-scheme-error-cmd\"" "" \
+    "  #:command-class COMMAND_OBSCURE" "" \
+    "  #:invoke (lambda (self arg from-tty)" "" \
+    "    oops-bad-spelling)))" "" \
+    "end" ""
+
+gdb_test "test-scheme-error-cmd ugh" \
+    "Error occurred in Scheme-implemented GDB command." \
+    "call scheme-error command"
+
+# If there is a problem with object management, this can often trigger it.
+# It is useful to do this last, after we've created a bunch of command objects.
+
+gdb_test_no_output "guile (gc)"