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| 128 | .rm #[ #] #H #V #F C |
| 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. |