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1 | package DynaLoader; |
2 | |
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3 | =head1 NAME |
4 | |
5 | DynaLoader - Dynamically load C libraries into Perl code |
6 | |
7 | dl_error(), dl_findfile(), dl_expandspec(), dl_load_file(), dl_find_symbol(), dl_undef_symbols(), dl_install_xsub(), boostrap() - routines used by DynaLoader modules |
8 | |
9 | =head1 SYNOPSIS |
10 | |
11 | require DynaLoader; |
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12 | @ISA = qw(... DynaLoader ...); |
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13 | |
14 | |
15 | =head1 DESCRIPTION |
16 | |
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17 | This document defines a standard generic interface to the dynamic |
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18 | linking mechanisms available on many platforms. Its primary purpose is |
19 | to implement automatic dynamic loading of Perl modules. |
20 | |
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21 | This document serves as both a specification for anyone wishing to |
22 | implement the DynaLoader for a new platform and as a guide for |
23 | anyone wishing to use the DynaLoader directly in an application. |
24 | |
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25 | The DynaLoader is designed to be a very simple high-level |
26 | interface that is sufficiently general to cover the requirements |
27 | of SunOS, HP-UX, NeXT, Linux, VMS and other platforms. |
28 | |
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29 | It is also hoped that the interface will cover the needs of OS/2, NT |
30 | etc and also allow pseudo-dynamic linking (using C<ld -A> at runtime). |
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31 | |
32 | It must be stressed that the DynaLoader, by itself, is practically |
33 | useless for accessing non-Perl libraries because it provides almost no |
34 | Perl-to-C 'glue'. There is, for example, no mechanism for calling a C |
35 | library function or supplying arguments. It is anticipated that any |
36 | glue that may be developed in the future will be implemented in a |
37 | separate dynamically loaded module. |
38 | |
39 | DynaLoader Interface Summary |
40 | |
41 | @dl_library_path |
42 | @dl_resolve_using |
43 | @dl_require_symbols |
44 | $dl_debug |
45 | Implemented in: |
46 | bootstrap($modulename) Perl |
47 | @filepaths = dl_findfile(@names) Perl |
48 | |
49 | $libref = dl_load_file($filename) C |
50 | $symref = dl_find_symbol($libref, $symbol) C |
51 | @symbols = dl_undef_symbols() C |
52 | dl_install_xsub($name, $symref [, $filename]) C |
53 | $message = dl_error C |
54 | |
55 | =over 4 |
56 | |
57 | =item @dl_library_path |
58 | |
59 | The standard/default list of directories in which dl_findfile() will |
60 | search for libraries etc. Directories are searched in order: |
61 | $dl_library_path[0], [1], ... etc |
62 | |
63 | @dl_library_path is initialised to hold the list of 'normal' directories |
64 | (F</usr/lib>, etc) determined by B<Configure> (C<$Config{'libpth'}>). This should |
65 | ensure portability across a wide range of platforms. |
66 | |
67 | @dl_library_path should also be initialised with any other directories |
68 | that can be determined from the environment at runtime (such as |
69 | LD_LIBRARY_PATH for SunOS). |
70 | |
71 | After initialisation @dl_library_path can be manipulated by an |
72 | application using push and unshift before calling dl_findfile(). |
73 | Unshift can be used to add directories to the front of the search order |
74 | either to save search time or to override libraries with the same name |
75 | in the 'normal' directories. |
76 | |
77 | The load function that dl_load_file() calls may require an absolute |
78 | pathname. The dl_findfile() function and @dl_library_path can be |
79 | used to search for and return the absolute pathname for the |
80 | library/object that you wish to load. |
81 | |
82 | =item @dl_resolve_using |
83 | |
84 | A list of additional libraries or other shared objects which can be |
85 | used to resolve any undefined symbols that might be generated by a |
86 | later call to load_file(). |
87 | |
88 | This is only required on some platforms which do not handle dependent |
89 | libraries automatically. For example the Socket Perl extension library |
90 | (F<auto/Socket/Socket.so>) contains references to many socket functions |
91 | which need to be resolved when it's loaded. Most platforms will |
92 | automatically know where to find the 'dependent' library (e.g., |
93 | F</usr/lib/libsocket.so>). A few platforms need to to be told the location |
94 | of the dependent library explicitly. Use @dl_resolve_using for this. |
95 | |
96 | Example usage: |
97 | |
98 | @dl_resolve_using = dl_findfile('-lsocket'); |
99 | |
100 | =item @dl_require_symbols |
101 | |
102 | A list of one or more symbol names that are in the library/object file |
103 | to be dynamically loaded. This is only required on some platforms. |
104 | |
105 | =item dl_error() |
106 | |
107 | Syntax: |
108 | |
109 | $message = dl_error(); |
110 | |
111 | Error message text from the last failed DynaLoader function. Note |
112 | that, similar to errno in unix, a successful function call does not |
113 | reset this message. |
114 | |
115 | Implementations should detect the error as soon as it occurs in any of |
116 | the other functions and save the corresponding message for later |
117 | retrieval. This will avoid problems on some platforms (such as SunOS) |
118 | where the error message is very temporary (e.g., dlerror()). |
119 | |
120 | =item $dl_debug |
121 | |
122 | Internal debugging messages are enabled when $dl_debug is set true. |
123 | Currently setting $dl_debug only affects the Perl side of the |
124 | DynaLoader. These messages should help an application developer to |
125 | resolve any DynaLoader usage problems. |
126 | |
127 | $dl_debug is set to C<$ENV{'PERL_DL_DEBUG'}> if defined. |
128 | |
129 | For the DynaLoader developer/porter there is a similar debugging |
130 | variable added to the C code (see dlutils.c) and enabled if Perl was |
131 | built with the B<-DDEBUGGING> flag. This can also be set via the |
132 | PERL_DL_DEBUG environment variable. Set to 1 for minimal information or |
133 | higher for more. |
134 | |
135 | =item dl_findfile() |
136 | |
137 | Syntax: |
138 | |
139 | @filepaths = dl_findfile(@names) |
140 | |
141 | Determine the full paths (including file suffix) of one or more |
142 | loadable files given their generic names and optionally one or more |
143 | directories. Searches directories in @dl_library_path by default and |
144 | returns an empty list if no files were found. |
145 | |
146 | Names can be specified in a variety of platform independent forms. Any |
147 | names in the form B<-lname> are converted into F<libname.*>, where F<.*> is |
148 | an appropriate suffix for the platform. |
149 | |
150 | If a name does not already have a suitable prefix and/or suffix then |
151 | the corresponding file will be searched for by trying combinations of |
152 | prefix and suffix appropriate to the platform: "$name.o", "lib$name.*" |
153 | and "$name". |
154 | |
155 | If any directories are included in @names they are searched before |
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156 | @dl_library_path. Directories may be specified as B<-Ldir>. Any other |
157 | names are treated as filenames to be searched for. |
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158 | |
159 | Using arguments of the form C<-Ldir> and C<-lname> is recommended. |
160 | |
161 | Example: |
162 | |
163 | @dl_resolve_using = dl_findfile(qw(-L/usr/5lib -lposix)); |
164 | |
165 | |
166 | =item dl_expandspec() |
167 | |
168 | Syntax: |
169 | |
170 | $filepath = dl_expandspec($spec) |
171 | |
172 | Some unusual systems, such as VMS, require special filename handling in |
173 | order to deal with symbolic names for files (i.e., VMS's Logical Names). |
174 | |
175 | To support these systems a dl_expandspec() function can be implemented |
176 | either in the F<dl_*.xs> file or code can be added to the autoloadable |
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177 | dl_expandspec() function in F<DynaLoader.pm>. See F<DynaLoader.pm> for |
178 | more information. |
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179 | |
180 | =item dl_load_file() |
181 | |
182 | Syntax: |
183 | |
184 | $libref = dl_load_file($filename) |
185 | |
186 | Dynamically load $filename, which must be the path to a shared object |
187 | or library. An opaque 'library reference' is returned as a handle for |
188 | the loaded object. Returns undef on error. |
189 | |
190 | (On systems that provide a handle for the loaded object such as SunOS |
191 | and HPUX, $libref will be that handle. On other systems $libref will |
192 | typically be $filename or a pointer to a buffer containing $filename. |
193 | The application should not examine or alter $libref in any way.) |
194 | |
195 | This is function that does the real work. It should use the current |
196 | values of @dl_require_symbols and @dl_resolve_using if required. |
197 | |
198 | SunOS: dlopen($filename) |
199 | HP-UX: shl_load($filename) |
200 | Linux: dld_create_reference(@dl_require_symbols); dld_link($filename) |
201 | NeXT: rld_load($filename, @dl_resolve_using) |
202 | VMS: lib$find_image_symbol($filename,$dl_require_symbols[0]) |
203 | |
204 | |
205 | =item dl_find_symbol() |
206 | |
207 | Syntax: |
208 | |
209 | $symref = dl_find_symbol($libref, $symbol) |
210 | |
211 | Return the address of the symbol $symbol or C<undef> if not found. If the |
212 | target system has separate functions to search for symbols of different |
213 | types then dl_find_symbol() should search for function symbols first and |
214 | then other types. |
215 | |
216 | The exact manner in which the address is returned in $symref is not |
217 | currently defined. The only initial requirement is that $symref can |
218 | be passed to, and understood by, dl_install_xsub(). |
219 | |
220 | SunOS: dlsym($libref, $symbol) |
221 | HP-UX: shl_findsym($libref, $symbol) |
222 | Linux: dld_get_func($symbol) and/or dld_get_symbol($symbol) |
223 | NeXT: rld_lookup("_$symbol") |
224 | VMS: lib$find_image_symbol($libref,$symbol) |
225 | |
226 | |
227 | =item dl_undef_symbols() |
228 | |
229 | Example |
230 | |
231 | @symbols = dl_undef_symbols() |
232 | |
233 | Return a list of symbol names which remain undefined after load_file(). |
234 | Returns C<()> if not known. Don't worry if your platform does not provide |
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235 | a mechanism for this. Most do not need it and hence do not provide it, |
236 | they just return an empty list. |
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237 | |
238 | |
239 | =item dl_install_xsub() |
240 | |
241 | Syntax: |
242 | |
243 | dl_install_xsub($perl_name, $symref [, $filename]) |
244 | |
245 | Create a new Perl external subroutine named $perl_name using $symref as |
246 | a pointer to the function which implements the routine. This is simply |
247 | a direct call to newXSUB(). Returns a reference to the installed |
248 | function. |
249 | |
250 | The $filename parameter is used by Perl to identify the source file for |
251 | the function if required by die(), caller() or the debugger. If |
252 | $filename is not defined then "DynaLoader" will be used. |
253 | |
254 | |
255 | =item boostrap() |
256 | |
257 | Syntax: |
258 | |
259 | bootstrap($module) |
260 | |
261 | This is the normal entry point for automatic dynamic loading in Perl. |
262 | |
263 | It performs the following actions: |
264 | |
265 | =over 8 |
266 | |
267 | =item * |
268 | |
269 | locates an auto/$module directory by searching @INC |
270 | |
271 | =item * |
272 | |
273 | uses dl_findfile() to determine the filename to load |
274 | |
275 | =item * |
276 | |
277 | sets @dl_require_symbols to C<("boot_$module")> |
278 | |
279 | =item * |
280 | |
281 | executes an F<auto/$module/$module.bs> file if it exists |
282 | (typically used to add to @dl_resolve_using any files which |
283 | are required to load the module on the current platform) |
284 | |
285 | =item * |
286 | |
287 | calls dl_load_file() to load the file |
288 | |
289 | =item * |
290 | |
291 | calls dl_undef_symbols() and warns if any symbols are undefined |
292 | |
293 | =item * |
294 | |
295 | calls dl_find_symbol() for "boot_$module" |
296 | |
297 | =item * |
298 | |
299 | calls dl_install_xsub() to install it as "${module}::bootstrap" |
300 | |
301 | =item * |
302 | |
303 | calls &{"${module}::bootstrap"} to bootstrap the module |
304 | |
305 | =back |
306 | |
307 | =back |
308 | |
309 | |
310 | =head1 AUTHOR |
311 | |
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312 | Tim Bunce, 11 August 1994. |
313 | |
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314 | This interface is based on the work and comments of (in no particular |
315 | order): Larry Wall, Robert Sanders, Dean Roehrich, Jeff Okamoto, Anno |
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316 | Siegel, Thomas Neumann, Paul Marquess, Charles Bailey, myself and others. |
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317 | |
318 | Larry Wall designed the elegant inherited bootstrap mechanism and |
319 | implemented the first Perl 5 dynamic loader using it. |
320 | |
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321 | =cut |
322 | |
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323 | # |
324 | # And Gandalf said: 'Many folk like to know beforehand what is to |
325 | # be set on the table; but those who have laboured to prepare the |
326 | # feast like to keep their secret; for wonder makes the words of |
327 | # praise louder.' |
328 | # |
329 | |
330 | # Quote from Tolkien sugested by Anno Siegel. |
331 | # |
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332 | # Read ext/DynaLoader/README for detailed information. |
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333 | # |
334 | # Tim.Bunce@ig.co.uk, August 1994 |
335 | |
336 | use Config; |
337 | use Carp; |
338 | use AutoLoader; |
339 | |
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340 | @ISA=qw(AutoLoader); |
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341 | |
342 | |
343 | # enable messages from DynaLoader perl code |
344 | $dl_debug = 0 unless $dl_debug; |
345 | $dl_debug = $ENV{'PERL_DL_DEBUG'} if $ENV{'PERL_DL_DEBUG'}; |
346 | |
347 | $dl_so = $dl_dlext = ""; # avoid typo warnings |
348 | $dl_so = $Config{'so'}; # suffix for shared libraries |
349 | $dl_dlext = $Config{'dlext'}; # suffix for dynamic modules |
350 | |
351 | # Some systems need special handling to expand file specifications |
352 | # (VMS support by Charles Bailey <bailey@HMIVAX.HUMGEN.UPENN.EDU>) |
353 | # See dl_expandspec() for more details. Should be harmless but |
354 | # inefficient to define on systems that don't need it. |
355 | $do_expand = ($Config{'osname'} eq 'VMS'); |
356 | |
357 | @dl_require_symbols = (); # names of symbols we need |
358 | @dl_resolve_using = (); # names of files to link with |
359 | @dl_library_path = (); # path to look for files |
360 | |
361 | # This is a fix to support DLD's unfortunate desire to relink -lc |
362 | @dl_resolve_using = dl_findfile('-lc') if $Config{'dlsrc'} eq "dl_dld.xs"; |
363 | |
364 | # Initialise @dl_library_path with the 'standard' library path |
365 | # for this platform as determined by Configure |
366 | push(@dl_library_path, split(' ',$Config{'libpth'})); |
367 | |
368 | # Add to @dl_library_path any extra directories we can gather from |
369 | # environment variables. So far LD_LIBRARY_PATH is the only known |
370 | # variable used for this purpose. Others may be added later. |
371 | push(@dl_library_path, split(/:/, $ENV{'LD_LIBRARY_PATH'})) |
372 | if $ENV{'LD_LIBRARY_PATH'}; |
373 | |
374 | |
375 | # No prizes for guessing why we don't say 'bootstrap DynaLoader;' here. |
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376 | boot_DynaLoader() if defined(&boot_DynaLoader); |
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377 | |
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378 | |
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379 | if ($dl_debug){ |
380 | print STDERR "DynaLoader.pm loaded (@dl_library_path)\n"; |
381 | print STDERR "DynaLoader not linked into this perl\n" |
382 | unless defined(&boot_DynaLoader); |
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383 | } |
384 | |
385 | 1; # End of main code |
386 | |
387 | |
388 | # The bootstrap function cannot be autoloaded (without complications) |
389 | # so we define it here: |
390 | |
391 | sub bootstrap { |
392 | # use local vars to enable $module.bs script to edit values |
393 | local(@args) = @_; |
394 | local($module) = $args[0]; |
395 | local(@dirs, $file); |
396 | |
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397 | confess "Usage: DynaLoader::bootstrap(module)" unless $module; |
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398 | |
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399 | # A common error on platforms which don't support dynamic loading. |
400 | # Since it's fatal and potentially confusing we give a detailed message. |
401 | croak("Can't load module $module, dynamic loading not available in this perl.\n". |
402 | " (You may need to build a new perl executable which either supports\n". |
403 | " dynamic loading or has the $module module statically linked into it.)\n") |
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404 | unless defined(&dl_load_file); |
405 | |
406 | print STDERR "DynaLoader::bootstrap($module)\n" if $dl_debug; |
407 | |
408 | my(@modparts) = split(/::/,$module); |
409 | my($modfname) = $modparts[-1]; |
410 | my($modpname) = join('/',@modparts); |
411 | foreach (@INC) { |
412 | my $dir = "$_/auto/$modpname"; |
413 | next unless -d $dir; # skip over uninteresting directories |
414 | |
415 | # check for common cases to avoid autoload of dl_findfile |
416 | last if ($file=_check_file("$dir/$modfname.$dl_dlext")); |
417 | |
418 | # no luck here, save dir for possible later dl_findfile search |
419 | push(@dirs, "-L$dir"); |
420 | } |
421 | # last resort, let dl_findfile have a go in all known locations |
422 | $file = dl_findfile(@dirs, map("-L$_",@INC), $modfname) unless $file; |
423 | |
424 | croak "Can't find loadable object for module $module in \@INC" |
425 | unless $file; |
426 | |
427 | my($bootname) = "boot_$module"; |
428 | $bootname =~ s/\W/_/g; |
429 | @dl_require_symbols = ($bootname); |
430 | |
431 | # Execute optional '.bootstrap' perl script for this module. |
432 | # The .bs file can be used to configure @dl_resolve_using etc to |
433 | # match the needs of the individual module on this architecture. |
434 | my $bs = $file; |
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435 | $bs =~ s/(\.\w+)?$/\.bs/; # look for .bs 'beside' the library |
436 | if (-s $bs) { # only read file if it's not empty |
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437 | local($osname, $dlsrc) = @Config{'osname','dlsrc'}; |
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438 | print STDERR "BS: $bs ($osname, $dlsrc)\n" if $dl_debug; |
439 | eval { do $bs; }; |
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440 | warn "$bs: $@\n" if $@; |
441 | } |
442 | |
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443 | # Many dynamic extension loading problems will appear to come from |
444 | # this section of code: XYZ failed at line 123 of DynaLoader.pm. |
445 | # Often these errors are actually occurring in the initialisation |
446 | # C code of the extension XS file. Perl reports the error as being |
447 | # in this perl code simply because this was the last perl code |
448 | # it executed. |
449 | |
450 | my $libref = dl_load_file($file) or |
451 | croak "Can't load '$file' for module $module: ".dl_error()."\n"; |
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452 | |
453 | my(@unresolved) = dl_undef_symbols(); |
454 | carp "Undefined symbols present after loading $file: @unresolved\n" |
455 | if (@unresolved); |
456 | |
457 | my $boot_symbol_ref = dl_find_symbol($libref, $bootname) or |
458 | croak "Can't find '$bootname' symbol in $file\n"; |
459 | |
460 | dl_install_xsub("${module}::bootstrap", $boot_symbol_ref, $file); |
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461 | |
462 | # See comment block above |
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463 | &{"${module}::bootstrap"}(@args); |
464 | } |
465 | |
466 | |
467 | sub _check_file{ # private utility to handle dl_expandspec vs -f tests |
468 | my($file) = @_; |
469 | return $file if (!$do_expand && -f $file); # the common case |
470 | return $file if ( $do_expand && ($file=dl_expandspec($file))); |
471 | return undef; |
472 | } |
473 | |
474 | |
475 | # Let autosplit and the autoloader deal with these functions: |
476 | __END__ |
477 | |
478 | |
479 | sub dl_findfile { |
480 | # Read ext/DynaLoader/DynaLoader.doc for detailed information. |
481 | # This function does not automatically consider the architecture |
482 | # or the perl library auto directories. |
483 | my (@args) = @_; |
484 | my (@dirs, $dir); # which directories to search |
485 | my (@found); # full paths to real files we have found |
486 | my ($vms) = ($Config{'osname'} eq 'VMS'); |
487 | |
488 | print STDERR "dl_findfile(@args)\n" if $dl_debug; |
489 | |
490 | # accumulate directories but process files as they appear |
491 | arg: foreach(@args) { |
492 | # Special fast case: full filepath requires no search |
493 | if (m:/: && -f $_ && !$do_expand){ |
494 | push(@found,$_); |
495 | last arg unless wantarray; |
496 | next; |
497 | } |
498 | |
499 | # Deal with directories first: |
500 | # Using a -L prefix is the preferred option (faster and more robust) |
501 | if (m:^-L:){ s/^-L//; push(@dirs, $_); next; } |
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502 | |
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503 | # Otherwise we try to try to spot directories by a heuristic |
504 | # (this is a more complicated issue than it first appears) |
505 | if (m:/: && -d $_){ push(@dirs, $_); next; } |
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506 | |
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507 | # VMS: we may be using native VMS directry syntax instead of |
508 | # Unix emulation, so check this as well |
509 | if ($vms && /[:>\]]/ && -d $_){ push(@dirs, $_); next; } |
510 | |
511 | # Only files should get this far... |
512 | my(@names, $name); # what filenames to look for |
513 | if (m:-l: ){ # convert -lname to appropriate library name |
514 | s/-l//; |
515 | push(@names,"lib$_.$dl_so"); |
516 | push(@names,"lib$_.a"); |
517 | }else{ # Umm, a bare name. Try various alternatives: |
518 | # these should be ordered with the most likely first |
519 | push(@names,"$_.$dl_so") unless m/\.$dl_so$/o; |
520 | push(@names,"lib$_.$dl_so") unless m:/:; |
521 | push(@names,"$_.o") unless m/\.(o|$dl_so)$/o; |
522 | push(@names,"$_.a") unless m/\.a$/; |
523 | push(@names, $_); |
524 | } |
525 | foreach $dir (@dirs, @dl_library_path) { |
526 | next unless -d $dir; |
527 | foreach $name (@names) { |
528 | my($file) = "$dir/$name"; |
529 | print STDERR " checking in $dir for $name\n" if $dl_debug; |
530 | $file = _check_file($file); |
531 | if ($file){ |
532 | push(@found, $file); |
533 | next arg; # no need to look any further |
534 | } |
535 | } |
536 | } |
537 | } |
538 | if ($dl_debug) { |
539 | foreach(@dirs) { |
540 | print STDERR " dl_findfile ignored non-existent directory: $_\n" unless -d $_; |
541 | } |
542 | print STDERR "dl_findfile found: @found\n"; |
543 | } |
544 | return $found[0] unless wantarray; |
545 | @found; |
546 | } |
547 | |
548 | |
549 | sub dl_expandspec{ |
550 | my($spec) = @_; |
551 | # Optional function invoked if DynaLoader.pm sets $do_expand. |
552 | # Most systems do not require or use this function. |
553 | # Some systems may implement it in the dl_*.xs file in which case |
554 | # this autoload version will not be called but is harmless. |
555 | |
556 | # This function is designed to deal with systems which treat some |
557 | # 'filenames' in a special way. For example VMS 'Logical Names' |
558 | # (something like unix environment variables - but different). |
559 | # This function should recognise such names and expand them into |
560 | # full file paths. |
561 | # Must return undef if $spec is invalid or file does not exist. |
562 | |
563 | my($file) = $spec; # default output to input |
564 | my($osname) = $Config{'osname'}; |
565 | |
566 | if ($osname eq 'VMS'){ # dl_expandspec should be defined in dl_vms.xs |
567 | croak "dl_expandspec: should be defined in XS file!\n"; |
568 | }else{ |
569 | return undef unless -f $file; |
570 | } |
571 | print STDERR "dl_expandspec($spec) => $file\n" if $dl_debug; |
572 | $file; |
573 | } |