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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "DynaLoader 3" | |
132 | .TH DynaLoader 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | DynaLoader \- Dynamically load C libraries into Perl code | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 4 | |
138 | \& package YourPackage; | |
139 | \& require DynaLoader; | |
140 | \& @ISA = qw(... DynaLoader ...); | |
141 | \& bootstrap YourPackage; | |
142 | .Ve | |
143 | .PP | |
144 | .Vb 2 | |
145 | \& # optional method for 'global' loading | |
146 | \& sub dl_load_flags { 0x01 } | |
147 | .Ve | |
148 | .SH "DESCRIPTION" | |
149 | .IX Header "DESCRIPTION" | |
150 | This document defines a standard generic interface to the dynamic | |
151 | linking mechanisms available on many platforms. Its primary purpose is | |
152 | to implement automatic dynamic loading of Perl modules. | |
153 | .PP | |
154 | This document serves as both a specification for anyone wishing to | |
155 | implement the DynaLoader for a new platform and as a guide for | |
156 | anyone wishing to use the DynaLoader directly in an application. | |
157 | .PP | |
158 | The DynaLoader is designed to be a very simple high-level | |
159 | interface that is sufficiently general to cover the requirements | |
160 | of SunOS, \s-1HP\-UX\s0, NeXT, Linux, \s-1VMS\s0 and other platforms. | |
161 | .PP | |
162 | It is also hoped that the interface will cover the needs of \s-1OS/2\s0, \s-1NT\s0 | |
163 | etc and also allow pseudo-dynamic linking (using \f(CW\*(C`ld \-A\*(C'\fR at runtime). | |
164 | .PP | |
165 | It must be stressed that the DynaLoader, by itself, is practically | |
166 | useless for accessing non-Perl libraries because it provides almost no | |
167 | Perl-to-C 'glue'. There is, for example, no mechanism for calling a C | |
168 | library function or supplying arguments. A C::DynaLib module | |
169 | is available from \s-1CPAN\s0 sites which performs that function for some | |
170 | common system types. And since the year 2000, there's also Inline::C, | |
171 | a module that allows you to write Perl subroutines in C. Also available | |
172 | from your local \s-1CPAN\s0 site. | |
173 | .PP | |
174 | DynaLoader Interface Summary | |
175 | .PP | |
176 | .Vb 12 | |
177 | \& @dl_library_path | |
178 | \& @dl_resolve_using | |
179 | \& @dl_require_symbols | |
180 | \& $dl_debug | |
181 | \& @dl_librefs | |
182 | \& @dl_modules | |
183 | \& @dl_shared_objects | |
184 | \& Implemented in: | |
185 | \& bootstrap($modulename) Perl | |
186 | \& @filepaths = dl_findfile(@names) Perl | |
187 | \& $flags = $modulename->dl_load_flags Perl | |
188 | \& $symref = dl_find_symbol_anywhere($symbol) Perl | |
189 | .Ve | |
190 | .PP | |
191 | .Vb 6 | |
192 | \& $libref = dl_load_file($filename, $flags) C | |
193 | \& $status = dl_unload_file($libref) C | |
194 | \& $symref = dl_find_symbol($libref, $symbol) C | |
195 | \& @symbols = dl_undef_symbols() C | |
196 | \& dl_install_xsub($name, $symref [, $filename]) C | |
197 | \& $message = dl_error C | |
198 | .Ve | |
199 | .IP "@dl_library_path" 4 | |
200 | .IX Item "@dl_library_path" | |
201 | The standard/default list of directories in which \fIdl_findfile()\fR will | |
202 | search for libraries etc. Directories are searched in order: | |
203 | \&\f(CW$dl_library_path\fR[0], [1], ... etc | |
204 | .Sp | |
205 | @dl_library_path is initialised to hold the list of 'normal' directories | |
206 | (\fI/usr/lib\fR, etc) determined by \fBConfigure\fR (\f(CW$Config{'libpth'}\fR). This should | |
207 | ensure portability across a wide range of platforms. | |
208 | .Sp | |
209 | @dl_library_path should also be initialised with any other directories | |
210 | that can be determined from the environment at runtime (such as | |
211 | \&\s-1LD_LIBRARY_PATH\s0 for SunOS). | |
212 | .Sp | |
213 | After initialisation \f(CW@dl_library_path\fR can be manipulated by an | |
214 | application using push and unshift before calling \fIdl_findfile()\fR. | |
215 | Unshift can be used to add directories to the front of the search order | |
216 | either to save search time or to override libraries with the same name | |
217 | in the 'normal' directories. | |
218 | .Sp | |
219 | The load function that \fIdl_load_file()\fR calls may require an absolute | |
220 | pathname. The \fIdl_findfile()\fR function and \f(CW@dl_library_path\fR can be | |
221 | used to search for and return the absolute pathname for the | |
222 | library/object that you wish to load. | |
223 | .IP "@dl_resolve_using" 4 | |
224 | .IX Item "@dl_resolve_using" | |
225 | A list of additional libraries or other shared objects which can be | |
226 | used to resolve any undefined symbols that might be generated by a | |
227 | later call to \fIload_file()\fR. | |
228 | .Sp | |
229 | This is only required on some platforms which do not handle dependent | |
230 | libraries automatically. For example the Socket Perl extension | |
231 | library (\fIauto/Socket/Socket.so\fR) contains references to many socket | |
232 | functions which need to be resolved when it's loaded. Most platforms | |
233 | will automatically know where to find the 'dependent' library (e.g., | |
234 | \&\fI/usr/lib/libsocket.so\fR). A few platforms need to be told the | |
235 | location of the dependent library explicitly. Use \f(CW@dl_resolve_using\fR | |
236 | for this. | |
237 | .Sp | |
238 | Example usage: | |
239 | .Sp | |
240 | .Vb 1 | |
241 | \& @dl_resolve_using = dl_findfile('-lsocket'); | |
242 | .Ve | |
243 | .IP "@dl_require_symbols" 4 | |
244 | .IX Item "@dl_require_symbols" | |
245 | A list of one or more symbol names that are in the library/object file | |
246 | to be dynamically loaded. This is only required on some platforms. | |
247 | .IP "@dl_librefs" 4 | |
248 | .IX Item "@dl_librefs" | |
249 | An array of the handles returned by successful calls to \fIdl_load_file()\fR, | |
250 | made by bootstrap, in the order in which they were loaded. | |
251 | Can be used with \fIdl_find_symbol()\fR to look for a symbol in any of | |
252 | the loaded files. | |
253 | .IP "@dl_modules" 4 | |
254 | .IX Item "@dl_modules" | |
255 | An array of module (package) names that have been bootstrap'ed. | |
256 | .IP "@dl_shared_objects" 4 | |
257 | .IX Item "@dl_shared_objects" | |
258 | An array of file names for the shared objects that were loaded. | |
259 | .IP "\fIdl_error()\fR" 4 | |
260 | .IX Item "dl_error()" | |
261 | Syntax: | |
262 | .Sp | |
263 | .Vb 1 | |
264 | \& $message = dl_error(); | |
265 | .Ve | |
266 | .Sp | |
267 | Error message text from the last failed DynaLoader function. Note | |
268 | that, similar to errno in unix, a successful function call does not | |
269 | reset this message. | |
270 | .Sp | |
271 | Implementations should detect the error as soon as it occurs in any of | |
272 | the other functions and save the corresponding message for later | |
273 | retrieval. This will avoid problems on some platforms (such as SunOS) | |
274 | where the error message is very temporary (e.g., \fIdlerror()\fR). | |
275 | .IP "$dl_debug" 4 | |
276 | .IX Item "$dl_debug" | |
277 | Internal debugging messages are enabled when \f(CW$dl_debug\fR is set true. | |
278 | Currently setting \f(CW$dl_debug\fR only affects the Perl side of the | |
279 | DynaLoader. These messages should help an application developer to | |
280 | resolve any DynaLoader usage problems. | |
281 | .Sp | |
282 | $dl_debug is set to \f(CW$ENV{'PERL_DL_DEBUG'}\fR if defined. | |
283 | .Sp | |
284 | For the DynaLoader developer/porter there is a similar debugging | |
285 | variable added to the C code (see dlutils.c) and enabled if Perl was | |
286 | built with the \fB\-DDEBUGGING\fR flag. This can also be set via the | |
287 | \&\s-1PERL_DL_DEBUG\s0 environment variable. Set to 1 for minimal information or | |
288 | higher for more. | |
289 | .IP "\fIdl_findfile()\fR" 4 | |
290 | .IX Item "dl_findfile()" | |
291 | Syntax: | |
292 | .Sp | |
293 | .Vb 1 | |
294 | \& @filepaths = dl_findfile(@names) | |
295 | .Ve | |
296 | .Sp | |
297 | Determine the full paths (including file suffix) of one or more | |
298 | loadable files given their generic names and optionally one or more | |
299 | directories. Searches directories in \f(CW@dl_library_path\fR by default and | |
300 | returns an empty list if no files were found. | |
301 | .Sp | |
302 | Names can be specified in a variety of platform independent forms. Any | |
303 | names in the form \fB\-lname\fR are converted into \fIlibname.*\fR, where \fI.*\fR is | |
304 | an appropriate suffix for the platform. | |
305 | .Sp | |
306 | If a name does not already have a suitable prefix and/or suffix then | |
307 | the corresponding file will be searched for by trying combinations of | |
308 | prefix and suffix appropriate to the platform: \*(L"$name.o\*(R", \*(L"lib$name.*\*(R" | |
309 | and \*(L"$name\*(R". | |
310 | .Sp | |
311 | If any directories are included in \f(CW@names\fR they are searched before | |
312 | \&\f(CW@dl_library_path\fR. Directories may be specified as \fB\-Ldir\fR. Any other | |
313 | names are treated as filenames to be searched for. | |
314 | .Sp | |
315 | Using arguments of the form \f(CW\*(C`\-Ldir\*(C'\fR and \f(CW\*(C`\-lname\*(C'\fR is recommended. | |
316 | .Sp | |
317 | Example: | |
318 | .Sp | |
319 | .Vb 1 | |
320 | \& @dl_resolve_using = dl_findfile(qw(-L/usr/5lib -lposix)); | |
321 | .Ve | |
322 | .IP "\fIdl_expandspec()\fR" 4 | |
323 | .IX Item "dl_expandspec()" | |
324 | Syntax: | |
325 | .Sp | |
326 | .Vb 1 | |
327 | \& $filepath = dl_expandspec($spec) | |
328 | .Ve | |
329 | .Sp | |
330 | Some unusual systems, such as \s-1VMS\s0, require special filename handling in | |
331 | order to deal with symbolic names for files (i.e., \s-1VMS\s0's Logical Names). | |
332 | .Sp | |
333 | To support these systems a \fIdl_expandspec()\fR function can be implemented | |
334 | either in the \fIdl_*.xs\fR file or code can be added to the autoloadable | |
335 | \&\fIdl_expandspec()\fR function in \fIDynaLoader.pm\fR. See \fIDynaLoader.pm\fR for | |
336 | more information. | |
337 | .IP "\fIdl_load_file()\fR" 4 | |
338 | .IX Item "dl_load_file()" | |
339 | Syntax: | |
340 | .Sp | |
341 | .Vb 1 | |
342 | \& $libref = dl_load_file($filename, $flags) | |
343 | .Ve | |
344 | .Sp | |
345 | Dynamically load \f(CW$filename\fR, which must be the path to a shared object | |
346 | or library. An opaque 'library reference' is returned as a handle for | |
347 | the loaded object. Returns undef on error. | |
348 | .Sp | |
349 | The \f(CW$flags\fR argument to alters dl_load_file behaviour. | |
350 | Assigned bits: | |
351 | .Sp | |
352 | .Vb 3 | |
353 | \& 0x01 make symbols available for linking later dl_load_file's. | |
354 | \& (only known to work on Solaris 2 using dlopen(RTLD_GLOBAL)) | |
355 | \& (ignored under VMS; this is a normal part of image linking) | |
356 | .Ve | |
357 | .Sp | |
358 | (On systems that provide a handle for the loaded object such as SunOS | |
359 | and \s-1HPUX\s0, \f(CW$libref\fR will be that handle. On other systems \f(CW$libref\fR will | |
360 | typically be \f(CW$filename\fR or a pointer to a buffer containing \f(CW$filename\fR. | |
361 | The application should not examine or alter \f(CW$libref\fR in any way.) | |
362 | .Sp | |
363 | This is the function that does the real work. It should use the | |
364 | current values of \f(CW@dl_require_symbols\fR and \f(CW@dl_resolve_using\fR if required. | |
365 | .Sp | |
366 | .Vb 5 | |
367 | \& SunOS: dlopen($filename) | |
368 | \& HP-UX: shl_load($filename) | |
369 | \& Linux: dld_create_reference(@dl_require_symbols); dld_link($filename) | |
370 | \& NeXT: rld_load($filename, @dl_resolve_using) | |
371 | \& VMS: lib$find_image_symbol($filename,$dl_require_symbols[0]) | |
372 | .Ve | |
373 | .Sp | |
374 | (The \fIdlopen()\fR function is also used by Solaris and some versions of | |
375 | Linux, and is a common choice when providing a \*(L"wrapper\*(R" on other | |
376 | mechanisms as is done in the \s-1OS/2\s0 port.) | |
377 | .IP "\fIdl_unload_file()\fR" 4 | |
378 | .IX Item "dl_unload_file()" | |
379 | Syntax: | |
380 | .Sp | |
381 | .Vb 1 | |
382 | \& $status = dl_unload_file($libref) | |
383 | .Ve | |
384 | .Sp | |
385 | Dynamically unload \f(CW$libref\fR, which must be an opaque 'library reference' as | |
386 | returned from dl_load_file. Returns one on success and zero on failure. | |
387 | .Sp | |
388 | This function is optional and may not necessarily be provided on all platforms. | |
389 | If it is defined, it is called automatically when the interpreter exits for | |
390 | every shared object or library loaded by DynaLoader::bootstrap. All such | |
391 | library references are stored in \f(CW@dl_librefs\fR by DynaLoader::Bootstrap as it | |
392 | loads the libraries. The files are unloaded in last\-in, first-out order. | |
393 | .Sp | |
394 | This unloading is usually necessary when embedding a shared-object perl (e.g. | |
395 | one configured with \-Duseshrplib) within a larger application, and the perl | |
396 | interpreter is created and destroyed several times within the lifetime of the | |
397 | application. In this case it is possible that the system dynamic linker will | |
398 | unload and then subsequently reload the shared libperl without relocating any | |
399 | references to it from any files DynaLoaded by the previous incarnation of the | |
400 | interpreter. As a result, any shared objects opened by DynaLoader may point to | |
401 | a now invalid 'ghost' of the libperl shared object, causing apparently random | |
402 | memory corruption and crashes. This behaviour is most commonly seen when using | |
403 | Apache and mod_perl built with the \s-1APXS\s0 mechanism. | |
404 | .Sp | |
405 | .Vb 5 | |
406 | \& SunOS: dlclose($libref) | |
407 | \& HP-UX: ??? | |
408 | \& Linux: ??? | |
409 | \& NeXT: ??? | |
410 | \& VMS: ??? | |
411 | .Ve | |
412 | .Sp | |
413 | (The \fIdlclose()\fR function is also used by Solaris and some versions of | |
414 | Linux, and is a common choice when providing a \*(L"wrapper\*(R" on other | |
415 | mechanisms as is done in the \s-1OS/2\s0 port.) | |
416 | .IP "\fIdl_load_flags()\fR" 4 | |
417 | .IX Item "dl_load_flags()" | |
418 | Syntax: | |
419 | .Sp | |
420 | .Vb 1 | |
421 | \& $flags = dl_load_flags $modulename; | |
422 | .Ve | |
423 | .Sp | |
424 | Designed to be a method call, and to be overridden by a derived class | |
425 | (i.e. a class which has DynaLoader in its \f(CW@ISA\fR). The definition in | |
426 | DynaLoader itself returns 0, which produces standard behavior from | |
427 | \&\fIdl_load_file()\fR. | |
428 | .IP "\fIdl_find_symbol()\fR" 4 | |
429 | .IX Item "dl_find_symbol()" | |
430 | Syntax: | |
431 | .Sp | |
432 | .Vb 1 | |
433 | \& $symref = dl_find_symbol($libref, $symbol) | |
434 | .Ve | |
435 | .Sp | |
436 | Return the address of the symbol \f(CW$symbol\fR or \f(CW\*(C`undef\*(C'\fR if not found. If the | |
437 | target system has separate functions to search for symbols of different | |
438 | types then \fIdl_find_symbol()\fR should search for function symbols first and | |
439 | then other types. | |
440 | .Sp | |
441 | The exact manner in which the address is returned in \f(CW$symref\fR is not | |
442 | currently defined. The only initial requirement is that \f(CW$symref\fR can | |
443 | be passed to, and understood by, \fIdl_install_xsub()\fR. | |
444 | .Sp | |
445 | .Vb 5 | |
446 | \& SunOS: dlsym($libref, $symbol) | |
447 | \& HP-UX: shl_findsym($libref, $symbol) | |
448 | \& Linux: dld_get_func($symbol) and/or dld_get_symbol($symbol) | |
449 | \& NeXT: rld_lookup("_$symbol") | |
450 | \& VMS: lib$find_image_symbol($libref,$symbol) | |
451 | .Ve | |
452 | .IP "\fIdl_find_symbol_anywhere()\fR" 4 | |
453 | .IX Item "dl_find_symbol_anywhere()" | |
454 | Syntax: | |
455 | .Sp | |
456 | .Vb 1 | |
457 | \& $symref = dl_find_symbol_anywhere($symbol) | |
458 | .Ve | |
459 | .Sp | |
460 | Applies \fIdl_find_symbol()\fR to the members of \f(CW@dl_librefs\fR and returns | |
461 | the first match found. | |
462 | .IP "\fIdl_undef_symbols()\fR" 4 | |
463 | .IX Item "dl_undef_symbols()" | |
464 | Example | |
465 | .Sp | |
466 | .Vb 1 | |
467 | \& @symbols = dl_undef_symbols() | |
468 | .Ve | |
469 | .Sp | |
470 | Return a list of symbol names which remain undefined after \fIload_file()\fR. | |
471 | Returns \f(CW\*(C`()\*(C'\fR if not known. Don't worry if your platform does not provide | |
472 | a mechanism for this. Most do not need it and hence do not provide it, | |
473 | they just return an empty list. | |
474 | .IP "\fIdl_install_xsub()\fR" 4 | |
475 | .IX Item "dl_install_xsub()" | |
476 | Syntax: | |
477 | .Sp | |
478 | .Vb 1 | |
479 | \& dl_install_xsub($perl_name, $symref [, $filename]) | |
480 | .Ve | |
481 | .Sp | |
482 | Create a new Perl external subroutine named \f(CW$perl_name\fR using \f(CW$symref\fR as | |
483 | a pointer to the function which implements the routine. This is simply | |
484 | a direct call to \fInewXSUB()\fR. Returns a reference to the installed | |
485 | function. | |
486 | .Sp | |
487 | The \f(CW$filename\fR parameter is used by Perl to identify the source file for | |
488 | the function if required by \fIdie()\fR, \fIcaller()\fR or the debugger. If | |
489 | \&\f(CW$filename\fR is not defined then \*(L"DynaLoader\*(R" will be used. | |
490 | .IP "\fIbootstrap()\fR" 4 | |
491 | .IX Item "bootstrap()" | |
492 | Syntax: | |
493 | .Sp | |
494 | bootstrap($module) | |
495 | .Sp | |
496 | This is the normal entry point for automatic dynamic loading in Perl. | |
497 | .Sp | |
498 | It performs the following actions: | |
499 | .RS 4 | |
500 | .IP "*" 8 | |
501 | locates an auto/$module directory by searching \f(CW@INC\fR | |
502 | .IP "*" 8 | |
503 | uses \fIdl_findfile()\fR to determine the filename to load | |
504 | .IP "*" 8 | |
505 | sets \f(CW@dl_require_symbols\fR to \f(CW\*(C`("boot_$module")\*(C'\fR | |
506 | .IP "*" 8 | |
507 | executes an \fIauto/$module/$module.bs\fR file if it exists | |
508 | (typically used to add to \f(CW@dl_resolve_using\fR any files which | |
509 | are required to load the module on the current platform) | |
510 | .IP "*" 8 | |
511 | calls \fIdl_load_flags()\fR to determine how to load the file. | |
512 | .IP "*" 8 | |
513 | calls \fIdl_load_file()\fR to load the file | |
514 | .IP "*" 8 | |
515 | calls \fIdl_undef_symbols()\fR and warns if any symbols are undefined | |
516 | .IP "*" 8 | |
517 | calls \fIdl_find_symbol()\fR for \*(L"boot_$module\*(R" | |
518 | .IP "*" 8 | |
519 | calls \fIdl_install_xsub()\fR to install it as \*(L"${module}::bootstrap\*(R" | |
520 | .IP "*" 8 | |
521 | calls &{\*(L"${module}::bootstrap\*(R"} to bootstrap the module (actually | |
522 | it uses the function reference returned by dl_install_xsub for speed) | |
523 | .RE | |
524 | .RS 4 | |
525 | .RE | |
526 | .SH "AUTHOR" | |
527 | .IX Header "AUTHOR" | |
528 | Tim Bunce, 11 August 1994. | |
529 | .PP | |
530 | This interface is based on the work and comments of (in no particular | |
531 | order): Larry Wall, Robert Sanders, Dean Roehrich, Jeff Okamoto, Anno | |
532 | Siegel, Thomas Neumann, Paul Marquess, Charles Bailey, myself and others. | |
533 | .PP | |
534 | Larry Wall designed the elegant inherited bootstrap mechanism and | |
535 | implemented the first Perl 5 dynamic loader using it. | |
536 | .PP | |
537 | Solaris global loading added by Nick Ing-Simmons with design/coding | |
538 | assistance from Tim Bunce, January 1996. |