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[perl5.git] / ext / DynaLoader / DynaLoader.pm
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1package DynaLoader;
2
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3=head1 NAME
4
5DynaLoader - Dynamically load C libraries into Perl code
6
7dl_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;
c2960299 12 @ISA = qw(... DynaLoader ...);
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13
14
15=head1 DESCRIPTION
16
c2960299 17This document defines a standard generic interface to the dynamic
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18linking mechanisms available on many platforms. Its primary purpose is
19to implement automatic dynamic loading of Perl modules.
20
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21This document serves as both a specification for anyone wishing to
22implement the DynaLoader for a new platform and as a guide for
23anyone wishing to use the DynaLoader directly in an application.
24
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25The DynaLoader is designed to be a very simple high-level
26interface that is sufficiently general to cover the requirements
27of SunOS, HP-UX, NeXT, Linux, VMS and other platforms.
28
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29It is also hoped that the interface will cover the needs of OS/2, NT
30etc and also allow pseudo-dynamic linking (using C<ld -A> at runtime).
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31
32It must be stressed that the DynaLoader, by itself, is practically
33useless for accessing non-Perl libraries because it provides almost no
34Perl-to-C 'glue'. There is, for example, no mechanism for calling a C
35library function or supplying arguments. It is anticipated that any
36glue that may be developed in the future will be implemented in a
37separate dynamically loaded module.
38
39DynaLoader 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 $message = dl_error C
54
55=over 4
56
57=item @dl_library_path
58
59The standard/default list of directories in which dl_findfile() will
60search for libraries etc. Directories are searched in order:
61$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
65ensure portability across a wide range of platforms.
66
67@dl_library_path should also be initialised with any other directories
68that can be determined from the environment at runtime (such as
69LD_LIBRARY_PATH for SunOS).
70
71After initialisation @dl_library_path can be manipulated by an
72application using push and unshift before calling dl_findfile().
73Unshift can be used to add directories to the front of the search order
74either to save search time or to override libraries with the same name
75in the 'normal' directories.
76
77The load function that dl_load_file() calls may require an absolute
78pathname. The dl_findfile() function and @dl_library_path can be
79used to search for and return the absolute pathname for the
80library/object that you wish to load.
81
82=item @dl_resolve_using
83
84A list of additional libraries or other shared objects which can be
85used to resolve any undefined symbols that might be generated by a
86later call to load_file().
87
88This is only required on some platforms which do not handle dependent
89libraries automatically. For example the Socket Perl extension library
90(F<auto/Socket/Socket.so>) contains references to many socket functions
91which need to be resolved when it's loaded. Most platforms will
92automatically know where to find the 'dependent' library (e.g.,
93F</usr/lib/libsocket.so>). A few platforms need to to be told the location
94of the dependent library explicitly. Use @dl_resolve_using for this.
95
96Example usage:
97
98 @dl_resolve_using = dl_findfile('-lsocket');
99
100=item @dl_require_symbols
101
102A list of one or more symbol names that are in the library/object file
103to be dynamically loaded. This is only required on some platforms.
104
105=item dl_error()
106
107Syntax:
108
109 $message = dl_error();
110
111Error message text from the last failed DynaLoader function. Note
112that, similar to errno in unix, a successful function call does not
113reset this message.
114
115Implementations should detect the error as soon as it occurs in any of
116the other functions and save the corresponding message for later
117retrieval. This will avoid problems on some platforms (such as SunOS)
118where the error message is very temporary (e.g., dlerror()).
119
120=item $dl_debug
121
122Internal debugging messages are enabled when $dl_debug is set true.
123Currently setting $dl_debug only affects the Perl side of the
124DynaLoader. These messages should help an application developer to
125resolve any DynaLoader usage problems.
126
127$dl_debug is set to C<$ENV{'PERL_DL_DEBUG'}> if defined.
128
129For the DynaLoader developer/porter there is a similar debugging
130variable added to the C code (see dlutils.c) and enabled if Perl was
131built with the B<-DDEBUGGING> flag. This can also be set via the
132PERL_DL_DEBUG environment variable. Set to 1 for minimal information or
133higher for more.
134
135=item dl_findfile()
136
137Syntax:
138
139 @filepaths = dl_findfile(@names)
140
141Determine the full paths (including file suffix) of one or more
142loadable files given their generic names and optionally one or more
143directories. Searches directories in @dl_library_path by default and
144returns an empty list if no files were found.
145
146Names can be specified in a variety of platform independent forms. Any
147names in the form B<-lname> are converted into F<libname.*>, where F<.*> is
148an appropriate suffix for the platform.
149
150If a name does not already have a suitable prefix and/or suffix then
151the corresponding file will be searched for by trying combinations of
152prefix and suffix appropriate to the platform: "$name.o", "lib$name.*"
153and "$name".
154
155If 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
157names are treated as filenames to be searched for.
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158
159Using arguments of the form C<-Ldir> and C<-lname> is recommended.
160
161Example:
162
163 @dl_resolve_using = dl_findfile(qw(-L/usr/5lib -lposix));
164
165
166=item dl_expandspec()
167
168Syntax:
169
170 $filepath = dl_expandspec($spec)
171
172Some unusual systems, such as VMS, require special filename handling in
173order to deal with symbolic names for files (i.e., VMS's Logical Names).
174
175To support these systems a dl_expandspec() function can be implemented
176either in the F<dl_*.xs> file or code can be added to the autoloadable
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177dl_expandspec() function in F<DynaLoader.pm>. See F<DynaLoader.pm> for
178more information.
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179
180=item dl_load_file()
181
182Syntax:
183
184 $libref = dl_load_file($filename)
185
186Dynamically load $filename, which must be the path to a shared object
187or library. An opaque 'library reference' is returned as a handle for
188the loaded object. Returns undef on error.
189
190(On systems that provide a handle for the loaded object such as SunOS
191and HPUX, $libref will be that handle. On other systems $libref will
192typically be $filename or a pointer to a buffer containing $filename.
193The application should not examine or alter $libref in any way.)
194
195This is function that does the real work. It should use the current
196values of @dl_require_symbols and @dl_resolve_using if required.
197
198 SunOS: dlopen($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
207Syntax:
208
209 $symref = dl_find_symbol($libref, $symbol)
210
211Return the address of the symbol $symbol or C<undef> if not found. If the
212target system has separate functions to search for symbols of different
213types then dl_find_symbol() should search for function symbols first and
214then other types.
215
216The exact manner in which the address is returned in $symref is not
217currently defined. The only initial requirement is that $symref can
218be passed to, and understood by, dl_install_xsub().
219
220 SunOS: dlsym($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,$symbol)
225
226
227=item dl_undef_symbols()
228
229Example
230
231 @symbols = dl_undef_symbols()
232
233Return a list of symbol names which remain undefined after load_file().
234Returns C<()> if not known. Don't worry if your platform does not provide
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235a mechanism for this. Most do not need it and hence do not provide it,
236they just return an empty list.
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237
238
239=item dl_install_xsub()
240
241Syntax:
242
243 dl_install_xsub($perl_name, $symref [, $filename])
244
245Create a new Perl external subroutine named $perl_name using $symref as
246a pointer to the function which implements the routine. This is simply
247a direct call to newXSUB(). Returns a reference to the installed
248function.
249
250The $filename parameter is used by Perl to identify the source file for
251the function if required by die(), caller() or the debugger. If
252$filename is not defined then "DynaLoader" will be used.
253
254
255=item boostrap()
256
257Syntax:
258
259bootstrap($module)
260
261This is the normal entry point for automatic dynamic loading in Perl.
262
263It performs the following actions:
264
265=over 8
266
267=item *
268
269locates an auto/$module directory by searching @INC
270
271=item *
272
273uses dl_findfile() to determine the filename to load
274
275=item *
276
277sets @dl_require_symbols to C<("boot_$module")>
278
279=item *
280
281executes an F<auto/$module/$module.bs> file if it exists
282(typically used to add to @dl_resolve_using any files which
283are required to load the module on the current platform)
284
285=item *
286
287calls dl_load_file() to load the file
288
289=item *
290
291calls dl_undef_symbols() and warns if any symbols are undefined
292
293=item *
294
295calls dl_find_symbol() for "boot_$module"
296
297=item *
298
299calls dl_install_xsub() to install it as "${module}::bootstrap"
300
301=item *
302
303calls &{"${module}::bootstrap"} to bootstrap the module
304
305=back
306
307=back
308
309
310=head1 AUTHOR
311
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312Tim Bunce, 11 August 1994.
313
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314This interface is based on the work and comments of (in no particular
315order): Larry Wall, Robert Sanders, Dean Roehrich, Jeff Okamoto, Anno
c2960299 316Siegel, Thomas Neumann, Paul Marquess, Charles Bailey, myself and others.
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317
318Larry Wall designed the elegant inherited bootstrap mechanism and
319implemented 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#
c2960299 332# Read ext/DynaLoader/README for detailed information.
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333#
334# Tim.Bunce@ig.co.uk, August 1994
335
336use Config;
337use Carp;
338use AutoLoader;
339
fec02dd3 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 $Config{'dlsrc'} eq "dl_dld.xs";
363
364# Initialise @dl_library_path with the 'standard' library path
365# for this platform as determined by Configure
366push(@dl_library_path, split(' ',$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.
371push(@dl_library_path, split(/:/, $ENV{'LD_LIBRARY_PATH'}))
372 if $ENV{'LD_LIBRARY_PATH'};
373
374
375# No prizes for guessing why we don't say 'bootstrap DynaLoader;' here.
75f92628 376boot_DynaLoader() if defined(&boot_DynaLoader);
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379if ($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
3851; # End of main code
386
387
388# The bootstrap function cannot be autoloaded (without complications)
389# so we define it here:
390
391sub 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
c2960299 397 confess "Usage: DynaLoader::bootstrap(module)" unless $module;
a0d0e21e 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 $bs) { # only read file if it's not empty
a0d0e21e 437 local($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
467sub _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
479sub 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; }
c2960299 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, $_); next; }
c2960299 506
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507 # VMS: we may be using native VMS directry syntax instead of
508 # Unix emulation, so check this as well
509 if ($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 $found[0] unless wantarray;
545 @found;
546}
547
548
549sub dl_expandspec{
550 my($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}