3 # And Gandalf said: 'Many folk like to know beforehand what is to
4 # be set on the table; but those who have laboured to prepare the
5 # feast like to keep their secret; for wonder makes the words of
8 # (Quote from Tolkien sugested by Anno Siegel.)
10 # See pod text at end of file for documentation.
11 # See also ext/DynaLoader/README in source tree for other information.
13 # Tim.Bunce@ig.co.uk, August 1994
22 sub import { } # override import inherited from AutoLoader
24 # enable debug/trace messages from DynaLoader perl code
25 $dl_debug = $ENV{PERL_DL_DEBUG} || 0 unless defined $dl_debug;
27 ($dl_dlext, $dlsrc, $osname)
28 = @Config::Config{'dlext', 'dlsrc', 'osname'};
30 # Some systems need special handling to expand file specifications
31 # (VMS support by Charles Bailey <bailey@HMIVAX.HUMGEN.UPENN.EDU>)
32 # See dl_expandspec() for more details. Should be harmless but
33 # inefficient to define on systems that don't need it.
34 $do_expand = ($osname eq 'VMS');
36 @dl_require_symbols = (); # names of symbols we need
37 @dl_resolve_using = (); # names of files to link with
38 @dl_library_path = (); # path to look for files
40 # This is a fix to support DLD's unfortunate desire to relink -lc
41 @dl_resolve_using = dl_findfile('-lc') if $dlsrc eq "dl_dld.xs";
43 # Initialise @dl_library_path with the 'standard' library path
44 # for this platform as determined by Configure
45 push(@dl_library_path, split(' ',$Config::Config{'libpth'}));
47 # Add to @dl_library_path any extra directories we can gather from
48 # environment variables. So far LD_LIBRARY_PATH is the only known
49 # variable used for this purpose. Others may be added later.
50 push(@dl_library_path, split(/:/, $ENV{LD_LIBRARY_PATH}))
51 if $ENV{LD_LIBRARY_PATH};
54 # No prizes for guessing why we don't say 'bootstrap DynaLoader;' here.
55 boot_DynaLoader() if defined(&boot_DynaLoader);
59 print STDERR "DynaLoader.pm loaded (@INC, @dl_library_path)\n";
60 print STDERR "DynaLoader not linked into this perl\n"
61 unless defined(&boot_DynaLoader);
67 # The bootstrap function cannot be autoloaded (without complications)
68 # so we define it here:
71 # use local vars to enable $module.bs script to edit values
73 local($module) = $args[0];
76 Carp::confess "Usage: DynaLoader::bootstrap(module)" unless $module;
78 # A common error on platforms which don't support dynamic loading.
79 # Since it's fatal and potentially confusing we give a detailed message.
80 Carp::croak("Can't load module $module, dynamic loading not available in this perl.\n".
81 " (You may need to build a new perl executable which either supports\n".
82 " dynamic loading or has the $module module statically linked into it.)\n")
83 unless defined(&dl_load_file);
85 my @modparts = split(/::/,$module);
86 my $modfname = $modparts[-1];
88 # Some systems have restrictions on files names for DLL's etc.
89 # mod2fname returns appropriate file base name (typically truncated)
90 # It may also edit @modparts if required.
91 $modfname = &mod2fname(\@modparts) if defined &mod2fname;
93 my $modpname = join('/',@modparts);
95 print STDERR "DynaLoader::bootstrap for $module ",
96 "(auto/$modpname/$modfname.$dl_dlext)\n" if $dl_debug;
99 my $dir = "$_/auto/$modpname";
100 next unless -d $dir; # skip over uninteresting directories
102 # check for common cases to avoid autoload of dl_findfile
103 last if ($file=_check_file("$dir/$modfname.$dl_dlext"));
105 # no luck here, save dir for possible later dl_findfile search
106 push(@dirs, "-L$dir");
108 # last resort, let dl_findfile have a go in all known locations
109 $file = dl_findfile(@dirs, map("-L$_",@INC), $modfname) unless $file;
111 Carp::croak "Can't find loadable object for module $module in \@INC (@INC)"
114 my $bootname = "boot_$module";
115 $bootname =~ s/\W/_/g;
116 @dl_require_symbols = ($bootname);
118 # Execute optional '.bootstrap' perl script for this module.
119 # The .bs file can be used to configure @dl_resolve_using etc to
120 # match the needs of the individual module on this architecture.
122 $bs =~ s/(\.\w+)?$/\.bs/; # look for .bs 'beside' the library
123 if (-s $bs) { # only read file if it's not empty
124 print STDERR "BS: $bs ($osname, $dlsrc)\n" if $dl_debug;
126 warn "$bs: $@\n" if $@;
129 # Many dynamic extension loading problems will appear to come from
130 # this section of code: XYZ failed at line 123 of DynaLoader.pm.
131 # Often these errors are actually occurring in the initialisation
132 # C code of the extension XS file. Perl reports the error as being
133 # in this perl code simply because this was the last perl code
136 my $libref = dl_load_file($file) or
137 Carp::croak "Can't load '$file' for module $module: ".dl_error()."\n";
139 my @unresolved = dl_undef_symbols();
140 Carp::carp "Undefined symbols present after loading $file: @unresolved\n"
143 my $boot_symbol_ref = dl_find_symbol($libref, $bootname) or
144 Carp::croak "Can't find '$bootname' symbol in $file\n";
146 my $xs = dl_install_xsub("${module}::bootstrap", $boot_symbol_ref, $file);
148 # See comment block above
153 sub _check_file { # private utility to handle dl_expandspec vs -f tests
155 return $file if (!$do_expand && -f $file); # the common case
156 return $file if ( $do_expand && ($file=dl_expandspec($file)));
161 # Let autosplit and the autoloader deal with these functions:
166 # Read ext/DynaLoader/DynaLoader.doc for detailed information.
167 # This function does not automatically consider the architecture
168 # or the perl library auto directories.
170 my (@dirs, $dir); # which directories to search
171 my (@found); # full paths to real files we have found
172 my $vms = ($osname eq 'VMS');
173 my $dl_so = $Config::Config{'so'}; # suffix for shared libraries
175 print STDERR "dl_findfile(@args)\n" if $dl_debug;
177 # accumulate directories but process files as they appear
178 arg: foreach(@args) {
179 # Special fast case: full filepath requires no search
180 if (m:/: && -f $_ && !$do_expand) {
182 last arg unless wantarray;
186 # Deal with directories first:
187 # Using a -L prefix is the preferred option (faster and more robust)
188 if (m:^-L:) { s/^-L//; push(@dirs, $_); next; }
190 # Otherwise we try to try to spot directories by a heuristic
191 # (this is a more complicated issue than it first appears)
192 if (m:/: && -d $_) { push(@dirs, $_); next; }
194 # VMS: we may be using native VMS directry syntax instead of
195 # Unix emulation, so check this as well
196 if ($vms && /[:>\]]/ && -d $_) { push(@dirs, $_); next; }
198 # Only files should get this far...
199 my(@names, $name); # what filenames to look for
200 if (m:-l: ) { # convert -lname to appropriate library name
202 push(@names,"lib$_.$dl_so");
203 push(@names,"lib$_.a");
204 } else { # Umm, a bare name. Try various alternatives:
205 # these should be ordered with the most likely first
206 push(@names,"$_.$dl_so") unless m/\.$dl_so$/o;
207 push(@names,"lib$_.$dl_so") unless m:/:;
208 push(@names,"$_.o") unless m/\.(o|$dl_so)$/o;
209 push(@names,"$_.a") if !m/\.a$/ and $dlsrc eq "dl_dld.xs";
212 foreach $dir (@dirs, @dl_library_path) {
214 foreach $name (@names) {
215 my($file) = "$dir/$name";
216 print STDERR " checking in $dir for $name\n" if $dl_debug;
217 $file = _check_file($file);
220 next arg; # no need to look any further
227 print STDERR " dl_findfile ignored non-existent directory: $_\n" unless -d $_;
229 print STDERR "dl_findfile found: @found\n";
231 return $found[0] unless wantarray;
238 # Optional function invoked if DynaLoader.pm sets $do_expand.
239 # Most systems do not require or use this function.
240 # Some systems may implement it in the dl_*.xs file in which case
241 # this autoload version will not be called but is harmless.
243 # This function is designed to deal with systems which treat some
244 # 'filenames' in a special way. For example VMS 'Logical Names'
245 # (something like unix environment variables - but different).
246 # This function should recognise such names and expand them into
248 # Must return undef if $spec is invalid or file does not exist.
250 my $file = $spec; # default output to input
252 if ($osname eq 'VMS') { # dl_expandspec should be defined in dl_vms.xs
253 Carp::croak "dl_expandspec: should be defined in XS file!\n";
255 return undef unless -f $file;
257 print STDERR "dl_expandspec($spec) => $file\n" if $dl_debug;
264 DynaLoader - Dynamically load C libraries into Perl code
266 dl_error(), dl_findfile(), dl_expandspec(), dl_load_file(), dl_find_symbol(), dl_undef_symbols(), dl_install_xsub(), boostrap() - routines used by DynaLoader modules
272 @ISA = qw(... DynaLoader ...);
273 bootstrap YourPackage;
278 This document defines a standard generic interface to the dynamic
279 linking mechanisms available on many platforms. Its primary purpose is
280 to implement automatic dynamic loading of Perl modules.
282 This document serves as both a specification for anyone wishing to
283 implement the DynaLoader for a new platform and as a guide for
284 anyone wishing to use the DynaLoader directly in an application.
286 The DynaLoader is designed to be a very simple high-level
287 interface that is sufficiently general to cover the requirements
288 of SunOS, HP-UX, NeXT, Linux, VMS and other platforms.
290 It is also hoped that the interface will cover the needs of OS/2, NT
291 etc and also allow pseudo-dynamic linking (using C<ld -A> at runtime).
293 It must be stressed that the DynaLoader, by itself, is practically
294 useless for accessing non-Perl libraries because it provides almost no
295 Perl-to-C 'glue'. There is, for example, no mechanism for calling a C
296 library function or supplying arguments. It is anticipated that any
297 glue that may be developed in the future will be implemented in a
298 separate dynamically loaded module.
300 DynaLoader Interface Summary
307 bootstrap($modulename) Perl
308 @filepaths = dl_findfile(@names) Perl
310 $libref = dl_load_file($filename) C
311 $symref = dl_find_symbol($libref, $symbol) C
312 @symbols = dl_undef_symbols() C
313 dl_install_xsub($name, $symref [, $filename]) C
314 $message = dl_error C
318 =item @dl_library_path
320 The standard/default list of directories in which dl_findfile() will
321 search for libraries etc. Directories are searched in order:
322 $dl_library_path[0], [1], ... etc
324 @dl_library_path is initialised to hold the list of 'normal' directories
325 (F</usr/lib>, etc) determined by B<Configure> (C<$Config{'libpth'}>). This should
326 ensure portability across a wide range of platforms.
328 @dl_library_path should also be initialised with any other directories
329 that can be determined from the environment at runtime (such as
330 LD_LIBRARY_PATH for SunOS).
332 After initialisation @dl_library_path can be manipulated by an
333 application using push and unshift before calling dl_findfile().
334 Unshift can be used to add directories to the front of the search order
335 either to save search time or to override libraries with the same name
336 in the 'normal' directories.
338 The load function that dl_load_file() calls may require an absolute
339 pathname. The dl_findfile() function and @dl_library_path can be
340 used to search for and return the absolute pathname for the
341 library/object that you wish to load.
343 =item @dl_resolve_using
345 A list of additional libraries or other shared objects which can be
346 used to resolve any undefined symbols that might be generated by a
347 later call to load_file().
349 This is only required on some platforms which do not handle dependent
350 libraries automatically. For example the Socket Perl extension library
351 (F<auto/Socket/Socket.so>) contains references to many socket functions
352 which need to be resolved when it's loaded. Most platforms will
353 automatically know where to find the 'dependent' library (e.g.,
354 F</usr/lib/libsocket.so>). A few platforms need to to be told the location
355 of the dependent library explicitly. Use @dl_resolve_using for this.
359 @dl_resolve_using = dl_findfile('-lsocket');
361 =item @dl_require_symbols
363 A list of one or more symbol names that are in the library/object file
364 to be dynamically loaded. This is only required on some platforms.
370 $message = dl_error();
372 Error message text from the last failed DynaLoader function. Note
373 that, similar to errno in unix, a successful function call does not
376 Implementations should detect the error as soon as it occurs in any of
377 the other functions and save the corresponding message for later
378 retrieval. This will avoid problems on some platforms (such as SunOS)
379 where the error message is very temporary (e.g., dlerror()).
383 Internal debugging messages are enabled when $dl_debug is set true.
384 Currently setting $dl_debug only affects the Perl side of the
385 DynaLoader. These messages should help an application developer to
386 resolve any DynaLoader usage problems.
388 $dl_debug is set to C<$ENV{'PERL_DL_DEBUG'}> if defined.
390 For the DynaLoader developer/porter there is a similar debugging
391 variable added to the C code (see dlutils.c) and enabled if Perl was
392 built with the B<-DDEBUGGING> flag. This can also be set via the
393 PERL_DL_DEBUG environment variable. Set to 1 for minimal information or
400 @filepaths = dl_findfile(@names)
402 Determine the full paths (including file suffix) of one or more
403 loadable files given their generic names and optionally one or more
404 directories. Searches directories in @dl_library_path by default and
405 returns an empty list if no files were found.
407 Names can be specified in a variety of platform independent forms. Any
408 names in the form B<-lname> are converted into F<libname.*>, where F<.*> is
409 an appropriate suffix for the platform.
411 If a name does not already have a suitable prefix and/or suffix then
412 the corresponding file will be searched for by trying combinations of
413 prefix and suffix appropriate to the platform: "$name.o", "lib$name.*"
416 If any directories are included in @names they are searched before
417 @dl_library_path. Directories may be specified as B<-Ldir>. Any other
418 names are treated as filenames to be searched for.
420 Using arguments of the form C<-Ldir> and C<-lname> is recommended.
424 @dl_resolve_using = dl_findfile(qw(-L/usr/5lib -lposix));
427 =item dl_expandspec()
431 $filepath = dl_expandspec($spec)
433 Some unusual systems, such as VMS, require special filename handling in
434 order to deal with symbolic names for files (i.e., VMS's Logical Names).
436 To support these systems a dl_expandspec() function can be implemented
437 either in the F<dl_*.xs> file or code can be added to the autoloadable
438 dl_expandspec() function in F<DynaLoader.pm>. See F<DynaLoader.pm> for
445 $libref = dl_load_file($filename)
447 Dynamically load $filename, which must be the path to a shared object
448 or library. An opaque 'library reference' is returned as a handle for
449 the loaded object. Returns undef on error.
451 (On systems that provide a handle for the loaded object such as SunOS
452 and HPUX, $libref will be that handle. On other systems $libref will
453 typically be $filename or a pointer to a buffer containing $filename.
454 The application should not examine or alter $libref in any way.)
456 This is function that does the real work. It should use the current
457 values of @dl_require_symbols and @dl_resolve_using if required.
459 SunOS: dlopen($filename)
460 HP-UX: shl_load($filename)
461 Linux: dld_create_reference(@dl_require_symbols); dld_link($filename)
462 NeXT: rld_load($filename, @dl_resolve_using)
463 VMS: lib$find_image_symbol($filename,$dl_require_symbols[0])
466 =item dl_find_symbol()
470 $symref = dl_find_symbol($libref, $symbol)
472 Return the address of the symbol $symbol or C<undef> if not found. If the
473 target system has separate functions to search for symbols of different
474 types then dl_find_symbol() should search for function symbols first and
477 The exact manner in which the address is returned in $symref is not
478 currently defined. The only initial requirement is that $symref can
479 be passed to, and understood by, dl_install_xsub().
481 SunOS: dlsym($libref, $symbol)
482 HP-UX: shl_findsym($libref, $symbol)
483 Linux: dld_get_func($symbol) and/or dld_get_symbol($symbol)
484 NeXT: rld_lookup("_$symbol")
485 VMS: lib$find_image_symbol($libref,$symbol)
488 =item dl_undef_symbols()
492 @symbols = dl_undef_symbols()
494 Return a list of symbol names which remain undefined after load_file().
495 Returns C<()> if not known. Don't worry if your platform does not provide
496 a mechanism for this. Most do not need it and hence do not provide it,
497 they just return an empty list.
500 =item dl_install_xsub()
504 dl_install_xsub($perl_name, $symref [, $filename])
506 Create a new Perl external subroutine named $perl_name using $symref as
507 a pointer to the function which implements the routine. This is simply
508 a direct call to newXSUB(). Returns a reference to the installed
511 The $filename parameter is used by Perl to identify the source file for
512 the function if required by die(), caller() or the debugger. If
513 $filename is not defined then "DynaLoader" will be used.
522 This is the normal entry point for automatic dynamic loading in Perl.
524 It performs the following actions:
530 locates an auto/$module directory by searching @INC
534 uses dl_findfile() to determine the filename to load
538 sets @dl_require_symbols to C<("boot_$module")>
542 executes an F<auto/$module/$module.bs> file if it exists
543 (typically used to add to @dl_resolve_using any files which
544 are required to load the module on the current platform)
548 calls dl_load_file() to load the file
552 calls dl_undef_symbols() and warns if any symbols are undefined
556 calls dl_find_symbol() for "boot_$module"
560 calls dl_install_xsub() to install it as "${module}::bootstrap"
564 calls &{"${module}::bootstrap"} to bootstrap the module (actually
565 it uses the function reference returned by dl_install_xsub for speed)
574 Tim Bunce, 11 August 1994.
576 This interface is based on the work and comments of (in no particular
577 order): Larry Wall, Robert Sanders, Dean Roehrich, Jeff Okamoto, Anno
578 Siegel, Thomas Neumann, Paul Marquess, Charles Bailey, myself and others.
580 Larry Wall designed the elegant inherited bootstrap mechanism and
581 implemented the first Perl 5 dynamic loader using it.