1 \input texinfo @c -*-texinfo-*-
4 @setfilename ../info/emodules.info
5 @settitle Extending Emacs using C Modules
9 @c Use some macros so that we can format for either XEmacs
10 @c or (shudder) GNU Emacs.
31 This file documents the module loading technology of @value{emacs}.
33 Copyright @copyright{} 1998 J. Kean Johnston.
35 Permission is granted to make and distribute verbatim copies of this
36 manual provided the copyright notice and this permission notice are
37 preserved on all copies.
40 Permission is granted to process this file through TeX and print the
41 results, provided the printed document carries copying permission notice
42 identical to this one except for the removal of this paragraph (this
43 paragraph not being relevant to the printed manual).
46 Permission is granted to copy and distribute modified versions of this
47 manual under the conditions for verbatim copying, provided that the
48 entire resulting derived work is distributed under the terms of a
49 permission notice identical to this one.
51 Permission is granted to copy and distribute translations of this manual
52 into another language, under the above conditions for modified versions,
53 except that this permission notice may be stated in a translation
54 approved by the Foundation.
56 Permission is granted to copy and distribute modified versions of this
57 manual under the conditions for verbatim copying, provided also that the
58 section entitled ``GNU General Public License'' is included exactly as
59 in the original, and provided that the entire resulting derived work is
60 distributed under the terms of a permission notice identical to this
63 Permission is granted to copy and distribute translations of this manual
64 into another language, under the above conditions for modified versions,
65 except that the section entitled ``GNU General Public License'' may be
66 included in a translation approved by the Free Software Foundation
67 instead of in the original English.
77 @setchapternewpage odd
81 @title Extending @value{emacs} using C and C++
82 @subtitle Version 1.0, September 1998
84 @author J. Kean Johnston
89 Copyright @copyright{} 1998 J. Kean Johnston. @*
95 Permission is granted to make and distribute verbatim copies of this
96 manual provided the copyright notice and this permission notice are
97 preserved on all copies.
99 Permission is granted to copy and distribute modified versions of this
100 manual under the conditions for verbatim copying, provided also that the
101 section entitled ``GNU General Public License'' is included
102 exactly as in the original, and provided that the entire resulting
103 derived work is distributed under the terms of a permission notice
104 identical to this one.
106 Permission is granted to copy and distribute translations of this manual
107 into another language, under the above conditions for modified versions,
108 except that the section entitled ``GNU General Public License'' may be
109 included in a translation approved by the Free Software Foundation
110 instead of in the original English.
115 @node Top, Introduction, (dir), (dir)
116 This Info file contains v1.0 of the @value{emacs} dynamic loadable module
117 support documentation.
119 * Introduction:: Introducing Emacs Modules
120 * Anatomy of a Module:: Basic module layout and technology
121 * Using ellcc:: How to use the module compiler
122 * Defining Functions:: Creating new Lisp primitives
123 * Defining Variables:: Creating new Lisp variables
124 * Index:: Concept Index
126 --- The Detailed Node Listing ---
130 * Required Header File:: Always include <emodules.h>
131 * Required Functions:: Functions you must always provide
132 * Required Variables:: Variables whose values you must provide
133 * Loading other Modules:: How to load dependent modules
137 * Compile Mode:: Compiling modules using ellcc
138 * Initialization Mode:: Generating documentation and variables
139 * Link Mode:: Creating the final loadable module
140 * Other ellcc options:: Other useful options
141 * Environment Variables:: How to control ellcc
145 * Using DEFUN:: Using the DEFUN macro to define functions
146 * Declaring Functions:: Declaring functions to the Lisp reader
151 @node Introduction, Anatomy of a Module, Top, Top
152 @chapter Introduction
154 @value{emacs} is a powerful, extensible editor. The traditional way of
155 extending the functionality of @value{emacs} is to use its built-in Lisp
156 language (called Emacs Lisp, or Elisp for short). However, while Elisp
157 is a full programming language and capable of extending @value{emacs} in more
158 ways than you can imagine, it does have its short-comings.
160 Firstly, Elisp is an interpreted language, and this has serious speed
161 implications. Like all other interpreted languages (like Java), Elisp
162 is often suitable only for certain types of application or extension.
163 So although Elisp is a general purpose language, and very high level,
164 there are times when it is desirable to descend to a lower level compiled
165 language for speed purposes.
167 Secondly, Elisp (or Lisp in general) is not a very common language any
168 more, except for certain circles in the computer industry. C is a far
169 more commonly known language, and because it is compiled, more suited to
170 a wider range of applications, especially those that require low level
171 access to a system or need to be as quick as possible.
173 @cindex Emacs Modules
176 @cindex shared object
177 This manual describes a new way of extending @value{emacs}, by using dynamic
178 loadable modules (also known as dynamically loadable libraries (DLLs),
179 dynamic shared objects (DSOs) or just simply shared objects), which can
180 be written in C or C++ and loaded into @value{emacs} at any time. I sometimes
181 refer to this technology as @dfn{CEmacs}, which is short for @dfn{C
184 @value{emacs} modules are configured into and installed with @value{emacs} by
185 default on all systems that support loading of shared objects. From a
186 users perspective, the internals of @value{emacs} modules are irrelevant.
187 All a user will ever need to know about shared objects is the name of
188 the shared object when they want to load a given module. From a
189 developers perspective though, a lot more is provided.
196 Of primary interest is the @code{ellcc} program. This program is
197 created during compile time, and is intended to abstract compiler
198 specific characteristics from the developer. This program is called to
199 compile and link all objects that will make up the final shared object,
200 and accepts all common C compiler flags. @code{ellcc} also sets up the
201 correct environment for compiling modules by enabling any special
202 compiler modes (such as PIC mode), setting the correct include paths for
203 the location of @value{emacs} internal header files etc. The program will also
204 invoke the linker correctly to created the final shared object which is
205 loaded into @value{emacs}.
209 CEmacs also makes all of the relevant @value{emacs} internal header files
210 available for module authors to use. This is often required to get data
211 structure definitions and external variable declarations. The header
212 files installed include the module specific header file
213 @file{emodules.h}. Due to the nature of dynamic modules, most of the
214 internals of @value{emacs} are exposed.
215 @xref{Top,,,internals,@value{emacs} Internals Manual}, for a
216 more complete discussion on how to extend and understand @value{emacs}. All of
217 the rules for C modules are discussed there.
221 Part of the @value{emacs} distribution is a set of sample modules. These are
222 not installed when @value{emacs} is, but remain in the @value{emacs} source tree.
223 These modules live in the directory @file{modules}, which is a
224 sub-directory of the main @value{emacs} source code directory. Please look at
225 the samples carefully, and maybe even use them as a basis for making
226 your own modules. Most of the concepts required for writing extension
227 modules are covered in the samples.
230 @cindex documentation
232 Last, but not least is this manual. This can be viewed from within
233 @value{emacs}, and it can be printed out as well. It is the intention of this
234 document that it will describe everything you need to know about
235 extending @value{emacs} in C. If you do not find this to be the case, please
236 contact the author(s).
239 The rest of this document will discuss the actual mechanics of
240 @value{emacs} modules and work through several of the samples. Please be
241 sure that you have read the @value{emacs} Internals Manual and understand
242 everything in it. The concepts there apply to all modules. This
243 document may have some overlap, but it is the internals manual which
244 should be considered the final authority. It will also help a great
245 deal to look at the actual @value{emacs} source code to see how things are
248 @node Anatomy of a Module, Using ellcc, Introduction, Top
249 @chapter Anatomy of a Module
251 @cindex module skeleton
252 @cindex skeleton, module
253 @cindex module format
254 @cindex format, module
256 Each dynamically loadable @value{emacs} extension (hereafter referred to as a
257 module) has a certain compulsory format, and must contain several
258 pieces of information and several mandatory functions. This chapter
259 describes the basic layout of a module, and provides a very simple
260 sample. The source for this sample can be found in the file
261 @file{modules/simple/sample.c} in the main @value{emacs} source code tree.
264 * Required Header File:: Always include <emodules.h>
265 * Required Functions:: Functions you must always provide
266 * Required Variables:: Variables whose values you must provide
267 * Loading other Modules:: How to load dependent modules
270 @node Required Header File, Required Functions, Anatomy of a Module, Anatomy of a Module
271 @section Required Header File
272 @cindex required header
273 @cindex include files
277 Every module must include the file @file{<emodules.h>}. This
278 will include several other @value{emacs} internal header files, and will set up
279 certain vital macros. One of the most important files included by
280 @file{emodules.h} is the generated @file{config.h} file, which contains
281 all of the required system abstraction macros and definitions. Most
282 modules will probably require some pre-processor conditionals based on
283 constants defined in @file{config.h}. Please read that file to
284 familiarize yourself with the macros defined there.
286 Depending on exactly what your module will be doing, you will probably
287 need to include one or more of the @value{emacs} internal header files. When
288 you @code{#include <emodules.h>}, you will get a few of the most important
289 @value{emacs} header files included automatically for you. The files included
294 This file contains most of the macros required for declaring Lisp object
295 types, macros for accessing Lisp objects, and global variable
299 All system dependent declarations and abstraction macros live here. You
300 should never call low level system functions directly. Rather, you
301 should use the abstraction macros provided in this header file.
304 This header file defines the window structures and Lisp types, and
305 provides functions and macros for manipulating multiple @value{emacs} windows.
308 All macros and function declarations for manipulating internal and user
309 visible buffers appear in this file.
312 This header provides the information required for performing text
313 insertion and deletion.
316 Provides the required structure, macro and function definitions for
317 manipulating @value{emacs} frames.
320 @node Required Functions, Required Variables, Required Header File, Anatomy of a Module
321 @section Required Functions
322 @cindex initialization
323 @cindex functions, required
324 @cindex required functions
326 Every module requires several initialization functions. It is the
327 responsibility of these functions to load in any dependent modules, and to
328 declare all variables and functions which are to be made visible to the
329 @value{emacs} Lisp reader. Each of these functions performs a very specific
330 task, and they are executed in the correct order by @value{emacs}. All of
331 these functions are @code{void} functions which take no arguments.
332 Here, briefly, are the required module functions. Note that the actual
333 function names do not end with the string @code{_module}, but rather
334 they end with the abbreviated module name by which the module is known.
335 More on the module name and its importance later. Just bear in mind
336 that the text @code{_module} in the functions below is simply a
337 place-holder, not an actual function name.
341 @findex syms_of_module
342 This required function is responsible for introducing to the Lisp reader
343 all functions that you have defined in your module using
344 @code{DEFUN()}. Note that @emph{only} functions are declared here, using
345 the @code{DEFSUBR()} macro. No variables are declared.
348 @findex vars_of_module
349 This required function contains calls to macros such as
350 @code{DEFVAR_LISP()}, @code{DEFVAR_BOOL()} etc, and its purpose is to
351 declare and initialize all and any variables that your module defines.
352 They syntax for declaring variables is identical to the syntax used for
353 all internal @value{emacs} source code. If the module is intended to be
354 usable statically linked into XEmacs, the actions of this function are
355 severely restricted. @xref{General Coding Rules,,,internals,
356 @value{emacs} Internals Manual}. Also see the comments in
357 @file{src/emacs.c} (@code{main_1}). Modules which perform
358 initializations not permitted by these rules will probably work, but
359 dual-use (dynamic loading and static linking) modules will require very
360 careful, and possibly fragile, coding.
362 @item modules_of_module
363 @findex modules_of_module
364 This optional function should be used to load in any modules which your
365 module depends on. The @value{emacs} module loading code makes sure that the
366 same module is not loaded twice, so several modules can safely call the
367 module load function for the same module. Only one copy of each module
368 (at a given version) will ever be loaded.
371 @findex docs_of_module
372 This is a required function, but not one which you need ever write.
373 This function is created automatically by @code{ellcc} when the module
374 initialization code is produced. It is required to document all
375 functions and variables declared in your module.
378 @node Required Variables, Loading other Modules, Required Functions, Anatomy of a Module
379 @section Required Variables
380 @cindex initialization
381 @cindex variables, required
382 @cindex required variables
384 Not only does a module need to declare the initialization functions
385 mentioned above, it is also required to provide certain variables which
386 the module loading code searches for in order to determine the viability
387 of a module. You are @emph{not} required to provide these variables in
388 your source files. They are automatically set up in the module
389 initialization file by the @code{ellcc} compiler. These variables are
390 discussed here simply for the sake of completeness.
393 @item emodules_compiler
394 This is a variable of type @code{long}, and is used to indicate the
395 version of the @value{emacs} loading technology that was used to produce the
396 module being loaded. This version number is completely unrelated to
397 the @value{emacs} version number, as a given module may quite well work
398 regardless of the version of @value{emacs} that was installed at the time the
401 The @value{emacs} modules version is used to differentiate between major
402 changes in the module loading technology, not versions of @value{emacs}.
405 This is a short (typically 10 characters or less) name for the module,
406 and it is used as a suffix for all of the required functions. This is
407 also the name by which the module is recognized when loading dependent
408 modules. The name does not necessarily have to be the same as the
409 physical file name, although keeping the two names in sync is a pretty
410 good idea. The name must not be empty, and it must be a valid part of a
411 C function name. The value of this variable is appended to the function
412 names @code{syms_of_}, @code{vars_of_}, @code{modules_of_} and
413 @code{docs_of_} to form the actual function names that the module
414 loading code looks for when loading a module.
416 This variable is set by the @code{--mod-name} argument to @code{ellcc}.
418 @item emodules_version
419 This string variable is used to load specific versions of a module.
420 Rarely will two or more versions of a module be left lying around, but
421 just in case this does happen, this variable can be used to control
422 exactly which module should be loaded. See the Lisp function
423 @code{load-module} for more details. This variable is set by the
424 @code{--mod-version} argument to @code{ellcc}.
427 This is a string which describes the module, and can contain spaces or
428 other special characters. It is used solely for descriptive purposes,
429 and does not affect the loading of the module. The value is set by the
430 @code{--mod-title} argument to @code{ellcc}.
433 @node Loading other Modules, , Required Variables, Anatomy of a Module
434 @section Loading other Modules
436 @findex modules_of_module
437 @findex emodules_load
439 During the loading of a module, it is the responsibility of the function
440 @code{modules_of_module} to load in any modules which the current module
441 depends on. If the module is stand-alone, and does not depend on other
442 modules, then this function can be left empty or even undeclared.
443 However, if it does have dependencies, it must call
444 @code{emodules_load}:
448 int emodules_load (const char *module,
454 The first argument @var{module} is the name of the actual shared object
455 or DLL. You can omit the @file{.so}, @file{.ell} or @file{.dll}
456 extension of you wish. If you do not specify an absolute path name,
457 then the same rules as apply to loading Lisp modules are applied when
458 searching for the module. If the module cannot be found in any of the
459 standard places, and an absolute path name was not specified,
460 @code{emodules_load} will signal an error and loading of the module
463 The second argument (@var{modname}) is the module name to load, and
464 must match the contents of the variable @var{emodule_name} in the
465 module to be loaded. A mis-match will cause the module load to fail. If
466 this parameter is @code{NULL} or empty, then no checks are performed
467 against the target module's @var{emodule_name} variable.
469 The last argument, @var{modver}, is the desired version of the module
470 to load, and is compared to the target module's
471 @var{emodule_version} value. If this parameter is not @code{NULL}
472 or empty, and the match fails, then the load of the module will fail.
474 @code{emodules_load} can be called recursively. If, at any point
475 during the loading of modules a failure is encountered, then all modules
476 that were loaded since the top level call to @code{emodules_load}
477 will be unloaded. This means that if any child modules fail to load,
478 then their parents will also fail to load. This does not include
479 previous successful calls to @code{emodules_load} at the top level.
481 @node Using ellcc, Defining Functions, Anatomy of a Module, Top
482 @chapter Using @code{ellcc}
484 @cindex module compiler
486 Before discussing the anatomy of a module in greater detail, you should
487 be aware of the steps required in order to correctly compile and link a
488 module for use within @value{emacs}. There is little difference between
489 compiling normal C code and compiling a module. In fact, all that
490 changes is the command used to compile the module, and a few extra
491 arguments to the compiler.
493 @value{emacs} now ships with a new user utility, called @code{ellcc}. This
494 is the @dfn{Emacs Loadable Library C Compiler}. This is a wrapper
495 program that will invoke the real C compiler with the correct arguments
496 to compile and link your module. With the exception of a few command
497 line options, this program can be considered a replacement for your C
498 compiler. It accepts all of the same flags and arguments that your C
499 compiler does, so in many cases you can simply set the @code{make}
500 variable @code{CC} to @code{ellcc} and your code will be compiled as
501 an Emacs module rather than a static C object.
503 @code{ellcc} has three distinct modes of operation. It can be run in
504 compile, link or initialization mode. These modes are discussed in more
505 detail below. If you want @code{ellcc} to show the commands it is
506 executing, you can specify the option @code{--mode=verbose} to
507 @code{ellcc}. Specifying this option twice will enable certain extra
508 debugging messages to be displayed on the standard output.
511 * Compile Mode:: Compiling modules using ellcc
512 * Initialization Mode:: Generating documentation and variables
513 * Link Mode:: Creating the final loadable module
514 * Other ellcc options:: Other useful options
515 * Environment Variables:: How to control ellcc
518 @node Compile Mode, Initialization Mode, Using ellcc, Using ellcc
519 @section Compile Mode
522 By default, @code{ellcc} is in @dfn{compile} mode. This means that it
523 assumes that all of the command line arguments are C compiler arguments,
524 and that you want to compile the specified source file or files. You
525 can force compile mode by specifying the @code{--mode=compile} argument
528 In this mode, @code{ellcc} is simply a front-end to the same C compiler
529 that was used to create the @value{emacs} binary itself. All @code{ellcc}
530 does in this mode is insert a few extra command line arguments before
531 the arguments you specify to @code{ellcc} itself. @code{ellcc} will
532 then invoke the C compiler to compile your module, and will return the
533 same exit codes and messages that your C compiler does.
535 By far the easiest way to compile modules is to construct a
536 @file{Makefile} as you would for a normal program, and simply insert, at
537 some appropriate place something similar to:
541 CC=ellcc --mode=compile
544 $(CC) $(CFLAGS) -c $<
548 After this, all you need to do is provide simple @code{make} rules for
549 compiling your module source files. Since modules are most useful when
550 they are small and self-contained, most modules will have a single
551 source file, aside from the module specific initialization file (see
554 @node Initialization Mode, Link Mode, Compile Mode, Using ellcc
555 @section Initialization Mode
556 @cindex initialization
557 @cindex documentation
559 @value{emacs} uses a rather bizarre way of documenting variables and
560 functions. Rather than have the documentation for compiled functions
561 and variables passed as static strings in the source code, the
562 documentation is included as a C comment. A special program, called
563 @file{make-docfile}, is used to scan the source code files and extract
564 the documentation from these comments, producing the @value{emacs} @file{DOC}
565 file, which the internal help engine scans when the documentation for a
566 function or variable is requested.
568 Due to the internal construction of Lisp objects, subrs and other such
569 things, adding documentation for a compiled function or variable in a
570 compiled module, at any time after @value{emacs} has been @dfn{dumped} is
571 somewhat problematic. Fortunately, as a module writer you are insulated
572 from the difficulties thanks to your friend @code{ellcc} and some
573 internal trickery in the module loading code. This is all done using
574 the @dfn{initialization} mode of @code{ellcc}.
576 The result of running @code{ellcc} in initialization mode is a C source
577 file which you compile with (you guessed it) @code{ellcc} in compile
578 mode. Initialization mode is where you set the module name, version,
579 title and gather together all of the documentation strings for the
580 functions and variables in your module. There are several options that
581 you are required to pass @code{ellcc} in initialization mode, the first
582 of which is the mode switch itself, @code{--mode=init}.
584 Next, you need to specify the name of the C source code file that
585 @code{ellcc} will produce, and you specify this using the
586 @code{--mod-output=FILENAME} argument. @var{FILENAME} is the name of
587 the C source code file that will contain the module variables and
588 @code{docs_of_module} function.
590 As discussed previously, each module requires a short @dfn{handle} or
591 module name. This is specified with the @code{--mod-name=NAME} option,
592 where @var{NAME} is the abbreviated module name. This @var{NAME} must
593 consist only of characters that are valid in C function and variable
596 The module version is specified using @code{--mod-version=VERSION}
597 argument, with @var{VERSION} being any arbitrary version string. This
598 version can be passed as an optional second argument to the Lisp
599 function @code{load-module}, and as the third argument to the internal
600 module loading command @code{emodules_load}. This version string is
601 used to distinguish between different versions of the same module, and
602 to ensure that the module is loaded at a specific version.
604 Last, but not least, is the module title. Specified using the
605 @code{--mod-title=TITLE} option, the specified @var{TITLE} is used when
606 the list of loaded modules is displayed. The module title serves no
607 purpose other than to inform the user of the function of the module.
608 This string should be brief, as it has to be formatted to fit the
611 Following all of these parameters, you need to provide the list of all
612 source code modules that make up your module. These are the files which
613 are scanned by @file{make-docfile}, and provide the information required
614 to populate the @code{docs_of_module} function. Below is a sample
615 @file{Makefile} fragment which indicates how all of this is used.
619 CC=ellcc --mode=compile
621 MODINIT=ellcc --mode=init
622 CFLAGS=-O2 -DSOME_STUFF
625 $(CC) $(CFLAGS) -c $<
629 MODTITLE="Small sample module"
631 SRCS=modfile1.c modfile2.c modfile3.c
636 rm -f $(OBJS) sample_init.o sample.ell
639 mkdir `ellcc --mod-location`/mymods > /dev/null
640 cp sample.ell `ellcc --mod-location`/mymods/sample.ell
642 sample.ell: $(OBJS) sample_init.o
643 $(LD) --mod-output=$@ $(OBJS) sample_init.o
645 sample_init.o: sample_init.c
646 sample_init.c: $(SRCS)
647 $(MODINIT) --mod-name=$(MODNAME) --mod-version=$(MODVER) \
648 --mod-title=$(MODTITLE) --mod-output=$@ $(SRCS)
652 The above @file{Makefile} is, in fact, complete, and would compile the
653 sample module, and optionally install it. The @code{--mod-location}
654 argument to @code{ellcc} will produce, on the standard output, the base
655 location of the @value{emacs} module directory. Each sub-directory of that
656 directory is automatically searched for for modules when they are loaded
657 with @code{load-module}. An alternative location would be
658 @file{/usr/local/lib/xemacs/site-modules}. That path can change
659 depending on the options the person who compiled @value{emacs} chose, so you
660 can always determine the correct site location using the
661 @code{--mod-site-location} option. This directory is treated the same
662 way as the main module directory. Each sub-directory within it is
663 searched for a given module when the user attempts to load it. The
664 valid extensions that the loader attempts to use are @file{.so},
665 @file{.ell} and @file{.dll}. You can use any of these extensions,
666 although @file{.ell} is the preferred extension.
668 @node Link Mode, Other ellcc options, Initialization Mode, Using ellcc
672 Once all of your source code files have been compiled (including the
673 generated init file) you need to link them all together to create the
674 loadable module. To do this, you invoke @code{ellcc} in link mode, by
675 passing the @code{--mode=link} option. You need to specify the final
676 output file using the @code{--mod-output=NAME} option, but other than
677 that all other arguments are passed on directly to the system compiler
678 or linker, along with any other required arguments to create the
681 The module has complete access to all symbols that were present in the
682 dumped @value{emacs}, so you do not need to link against libraries that were
683 linked in with the main executable. If your library uses some other
684 extra libraries, you will need to link with those. There is nothing
685 particularly complicated about link mode. All you need to do is make
686 sure you invoke it correctly in the @file{Makefile}. See the sample
687 @file{Makefile} above for an example of a well constructed
688 @file{Makefile} that invoked the linker correctly.
690 @node Other ellcc options, Environment Variables, Link Mode, Using ellcc
691 @section Other @code{ellcc} options
694 Aside from the three main @code{ellcc} modes described above,
695 @code{ellcc} can accept several other options. These are typically used
696 in a @file{Makefile} to determine installation paths. @code{ellcc} also
697 allows you to over-ride several of its built-in compiler and linker
698 options using environment variables. Here is the complete list of
699 options that @code{ellcc} accepts.
703 Enables compilation mode. Use this to compile source modules.
706 Enabled link edit mode. Use this to create the final module.
709 Used to create the documentation function and to initialize other
710 required variables. Produces a C source file that must be compiled with
711 @code{ellcc} in compile mode before linking the final module.
714 Enables verbose mode. This will show you the commands that are being
715 executed, as well as the version number of @code{ellcc}. If you specify
716 this option twice, then some extra debugging information is displayed.
718 @item --mod-name=NAME
719 Sets the short internal module @var{NAME} to the string specified,
720 which must consist only of valid C identifiers. Required during
723 @item --mod-version=VERSION
724 Sets the internal module @var{VERSION} to the specified string.
725 Required during initialization mode.
727 @item --mod-title=TITLE
728 Sets the module descriptive @var{TITLE} to the string specified. This
729 string can contain any printable characters, but should not be too
730 long. It is required during initialization mode.
732 @item --mod-output=FILENAME
733 Used to control the output file name. This is used during
734 initialization mode to set the name of the C source file that will be
735 created to @var{FILENAME}. During link mode, it sets the name of the
736 final loadable module to @var{FILENAME}.
739 This will print the name of the standard module installation path on the
740 standard output and immediately exit @code{ellcc}. Use this option to
741 determine the directory prefix of where you should install your modules.
743 @item --mod-site-location
744 This will print the name of the site specific module location and exit.
747 Prints the name of the root of the architecture-dependent directory that
748 @value{emacs} searches for architecture-dependent files.
751 Prints the name of the configuration for which @value{emacs} and @code{ellcc}
755 @node Environment Variables, , Other ellcc options, Using ellcc
756 @section Environment Variables
757 @cindex environment variables
759 During its normal operation, @code{ellcc} uses the compiler and linker
760 flags that were determined at the time @value{emacs} was configured. In
761 certain rare circumstances you may wish to over-ride the flags passed to
762 the compiler or linker, and you can do so using environment variables.
763 The table below lists all of the environment variables that @code{ellcc}
769 This is used to over-ride the name of the C compiler that is invoked by
774 Sets the name of the link editor to use to created the final module.
777 @cindex @code{ELLCFLAGS}
778 Sets the compiler flags passed on when compiling source modules. This
779 only sets the basic C compiler flags. There are certain hard-coded
780 flags that will always be passed.
783 @cindex @code{ELLLDFLAGS}
784 Sets the flags passed on to the linker. This does @strong{not} include
785 the flags for enabling PIC mode. This just sets basic linker flags.
788 @cindex @code{ELLDLLFLAGS}
789 Sets the flags passed to the linker that are required to created shared
790 and loadable objects.
793 @cindex @code{ELLPICFLAGS}
794 Sets the C compiler option required to produce an object file that is
795 suitable for including in a shared library. This option should turn on
796 PIC mode, or the moral equivalent thereof on the target system.
799 @cindex @code{ELLMAKEDOC}
800 Sets the name of the @file{make-docfile} program to use. Usually
801 @code{ellcc} will use the version that was compiled and installed with
802 @value{emacs}, but this option allows you to specify an alternative path.
803 Used during the compile phase of @value{emacs} itself.
806 @node Defining Functions, Defining Variables, Using ellcc, Top
807 @chapter Defining Functions
808 @cindex defining functions
810 One of the main reasons you would ever write a module is to
811 provide one or more @dfn{functions} for the user or the editor to use.
813 @dfn{function} is a bit overloaded here, as it refers to both a C
814 function and the way it appears to Lisp, which is a @dfn{subroutine}, or
815 simply a @dfn{subr}. A Lisp subr is also known as a Lisp primitive, but
816 that term applies less to dynamic modules. @xref{Writing Lisp
817 Primitives,,,internals,@value{emacs} Internals Manual}, for details on how to
818 declare functions. You should familiarize yourself with the
819 instructions there. The format of the function declaration is identical
822 Normal Lisp primitives document the functions they defining by including
823 the documentation as a C comment. During the build process, a program
824 called @file{make-docfile} is run, which will extract all of these
825 comments, build up a single large documentation file, and will store
826 pointers to the start of each documentation entry in the dumped @value{emacs}.
827 This, of course, will not work for dynamic modules, as they are loaded
828 long after @value{emacs} has been dumped. For this reason, we require a
829 special means for adding documentation for new subrs. This is what the
830 macro @code{CDOCSUBR} is used for, and this is used extensively during
831 @code{ellcc} initialization mode.
833 When using @code{DEFUN} in normal @value{emacs} C code, the sixth
834 ``parameter'' is a C comment which documents the function. For a
835 dynamic module, we of course need to convert the C comment to a usable
836 string, and we need to set the documentation pointer of the subr to this
837 string. As a module programmer, you don't actually need to do any work
838 for this to happen. It is all taken care of in the
839 @code{docs_of_module} function created by @code{ellcc}.
842 * Using DEFUN:: Using the DEFUN macro to define functions
843 * Declaring Functions:: Declaring functions to the Lisp reader
846 @node Using DEFUN, Declaring Functions, Defining Functions, Defining Functions
847 @section Using @code{DEFUN}
850 @cindex functions, Lisp
851 @cindex functions, defining
853 Although the full syntax of a function declaration is discussed in the
854 @value{emacs} internals manual in greater depth, what follows is a brief
855 description of how to define and implement a new Lisp primitive in a
856 module. This is done using the @code{DEFUN} macro. Here is a small
861 DEFUN ("my-function", Fmy_function, 1, 1, "FFile name: ", /*
862 Sample Emacs primitive function.
864 The specified FILE is frobnicated before it is fnozzled.
873 filename = (char *)XSTRING_DATA(file);
880 The first argument is the name of the function as it will appear to the
881 Lisp reader. This must be provided as a string. The second argument is
882 the name of the actual C function that will be created. This is
883 typically the Lisp function name with a preceding capital @code{F}, with
884 hyphens converted to underscores. This must be a valid C function
885 name. Next come the minimum and maximum number of arguments,
886 respectively. This is used to ensure that the correct number of
887 arguments are passed to the function. Next is the @code{interactive}
888 definition. If this function is meant to be run by a user
889 interactively, then you need to specify the argument types and prompts
890 in this string. Please consult the @value{emacs} Lisp manual for more
891 details. Next comes a C comment that is the documentation for this
892 function. This comment @strong{must} exist. Last comes the list of
893 function argument names, if any.
895 @node Declaring Functions, , Using DEFUN, Defining Functions
896 @section Declaring Functions
898 @cindex functions, declaring
900 Simply writing the code for a function is not enough to make it
901 available to the Lisp reader. You have to, during module
902 initialization, let the Lisp reader know about the new function. This
903 is done by calling @code{DEFSUBR} with the name of the function. This
904 is the sole purpose of the initialization function
905 @code{syms_of_module}. @xref{Required Functions}, for more details.
907 Each call to @code{DEFSUBR} takes as its only argument the name of the
908 function, which is the same as the second argument to the call to
909 @code{DEFUN}. Using the example function above, you would insert the
910 following code in the @code{syms_of_module} function:
914 DEFSUBR(Fmy_function);
918 This call will instruct @value{emacs} to make the function visible to the Lisp
919 reader and will prepare for the insertion of the documentation into
920 the right place. Once this is done, the user can call the Lisp
921 function @code{my-function}, if it was defined as an interactive
922 function (which in this case it was).
924 Thats all there is to defining and announcing new functions. The rules
925 for what goes inside the functions, and how to write good modules, is
926 beyond the scope of this document. Please consult the @value{emacs}
927 internals manual for more details.
929 @node Defining Variables, Index, Defining Functions, Top
930 @chapter Defining Variables
931 @cindex defining variables
932 @cindex defining objects
936 @cindex variables, Lisp
937 @cindex variables, defining
938 @cindex objects, defining
939 @cindex objects, Lisp
941 Rarely will you write a module that only contains functions. It is
942 common to also provide variables which can be used to control the
943 behavior of the function, or store the results of the function being
944 executed. The actual C variable types are the same for modules
945 and internal @value{emacs} primitives, and the declaration of the variables
948 @xref{Adding Global Lisp Variables,,,internals,XEmacs Internals Manual},
949 for more information on variables and naming conventions.
951 Once your variables are defined, you need to initialize them and make
952 the Lisp reader aware of them. This is done in the
953 @code{vars_of_module} initialization function using special @value{emacs}
954 macros such as @code{DEFVAR_LISP}, @code{DEFVAR_BOOL}, @code{DEFVAR_INT}
955 etc. The best way to see how to use these macros is to look at existing
956 source code, or read the internals manual.
958 One @emph{very} important difference between @value{emacs} variables and
959 module variables is how you use pure space. Simply put, you
960 @strong{never} use pure space in @value{emacs} modules. The pure space
961 storage is of a limited size, and is initialized properly during the
962 dumping of @value{emacs}. Because variables are being added dynamically to
963 an already running @value{emacs} when you load a module, you cannot use pure
964 space. Be warned: @strong{do not use pure space in modules. Repeat, do
965 not use pure space in modules.} Once again, to remove all doubts:
966 @strong{DO NOT USE PURE SPACE IN MODULES!!!}
968 Below is a small example which declares and initializes two
969 variables. You will note that this code takes into account the fact
970 that this module may very well be compiled into @value{emacs} itself. This
971 is a prudent thing to do.
975 Lisp_Object Vsample_string;
981 DEFVAR_LISP ("sample-string", &Vsample_string /*
982 This is a sample string, declared in a module.
984 Nothing magical about it.
987 DEFVAR_BOOL("sample-boolean", &sample_boolean /*
988 *Sample user-settable boolean.
992 Vsample_string = build_string("My string");
997 @c Print the tables of contents
1001 @node Index, , Defining Variables, Top