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   1  
   2  # Generated from DynaLoader_pm.PL
   3  
   4  package DynaLoader;
   5  
   6  #   And Gandalf said: 'Many folk like to know beforehand what is to
   7  #   be set on the table; but those who have laboured to prepare the
   8  #   feast like to keep their secret; for wonder makes the words of
   9  #   praise louder.'
  10  
  11  #   (Quote from Tolkien suggested by Anno Siegel.)
  12  #
  13  # See pod text at end of file for documentation.
  14  # See also ext/DynaLoader/README in source tree for other information.
  15  #
  16  # Tim.Bunce@ig.co.uk, August 1994
  17  
  18  BEGIN {
  19      $VERSION = '1.08';
  20  }
  21  
  22  require AutoLoader;
  23  *AUTOLOAD = \&AutoLoader::AUTOLOAD;
  24  
  25  use Config;
  26  
  27  # enable debug/trace messages from DynaLoader perl code
  28  $dl_debug = $ENV{PERL_DL_DEBUG} || 0 unless defined $dl_debug;
  29  
  30  #
  31  # Flags to alter dl_load_file behaviour.  Assigned bits:
  32  #   0x01  make symbols available for linking later dl_load_file's.
  33  #         (only known to work on Solaris 2 using dlopen(RTLD_GLOBAL))
  34  #         (ignored under VMS; effect is built-in to image linking)
  35  #
  36  # This is called as a class method $module->dl_load_flags.  The
  37  # definition here will be inherited and result on "default" loading
  38  # behaviour unless a sub-class of DynaLoader defines its own version.
  39  #
  40  
  41  sub dl_load_flags { 0x00 }
  42  
  43  # ($dl_dlext, $dlsrc)
  44  #         = @Config::Config{'dlext', 'dlsrc'};
  45    ($dl_dlext, $dlsrc) = ('so', 'dl_dlopen.xs')
  46  ;
  47  
  48  $do_expand = 0;
  49  
  50  
  51  
  52  @dl_require_symbols = ();       # names of symbols we need
  53  @dl_resolve_using   = ();       # names of files to link with
  54  @dl_library_path    = ();       # path to look for files
  55  
  56  #XSLoader.pm may have added elements before we were required
  57  #@dl_shared_objects  = ();       # shared objects for symbols we have 
  58  #@dl_librefs         = ();       # things we have loaded
  59  #@dl_modules         = ();       # Modules we have loaded
  60  
  61  # This is a fix to support DLD's unfortunate desire to relink -lc
  62  @dl_resolve_using = dl_findfile('-lc') if $dlsrc eq "dl_dld.xs";
  63  
  64  # Initialise @dl_library_path with the 'standard' library path
  65  # for this platform as determined by Configure.
  66  
  67  push(@dl_library_path, split(' ', $Config::Config{libpth}));
  68  
  69  
  70  my $ldlibpthname         = $Config::Config{ldlibpthname};
  71  my $ldlibpthname_defined = defined $Config::Config{ldlibpthname};
  72  my $pthsep               = $Config::Config{path_sep};
  73  
  74  # Add to @dl_library_path any extra directories we can gather from environment
  75  # during runtime.
  76  
  77  if ($ldlibpthname_defined &&
  78      exists $ENV{$ldlibpthname}) {
  79      push(@dl_library_path, split(/$pthsep/, $ENV{$ldlibpthname}));
  80  }
  81  
  82  # E.g. HP-UX supports both its native SHLIB_PATH *and* LD_LIBRARY_PATH.
  83  
  84  if ($ldlibpthname_defined &&
  85      $ldlibpthname ne 'LD_LIBRARY_PATH' &&
  86      exists $ENV{LD_LIBRARY_PATH}) {
  87      push(@dl_library_path, split(/$pthsep/, $ENV{LD_LIBRARY_PATH}));
  88  }
  89  
  90  
  91  # No prizes for guessing why we don't say 'bootstrap DynaLoader;' here.
  92  # NOTE: All dl_*.xs (including dl_none.xs) define a dl_error() XSUB
  93  boot_DynaLoader('DynaLoader') if defined(&boot_DynaLoader) &&
  94                                  !defined(&dl_error);
  95  
  96  if ($dl_debug) {
  97      print STDERR "DynaLoader.pm loaded (@INC, @dl_library_path)\n";
  98      print STDERR "DynaLoader not linked into this perl\n"
  99          unless defined(&boot_DynaLoader);
 100  }
 101  
 102  1; # End of main code
 103  
 104  
 105  sub croak   { require Carp; Carp::croak(@_)   }
 106  
 107  sub bootstrap_inherit {
 108      my $module = $_[0];
 109      local *isa = *{"$module\::ISA"};
 110      local @isa = (@isa, 'DynaLoader');
 111      # Cannot goto due to delocalization.  Will report errors on a wrong line?
 112      bootstrap(@_);
 113  }
 114  
 115  # The bootstrap function cannot be autoloaded (without complications)
 116  # so we define it here:
 117  
 118  sub bootstrap {
 119      # use local vars to enable $module.bs script to edit values
 120      local(@args) = @_;
 121      local($module) = $args[0];
 122      local(@dirs, $file);
 123  
 124      unless ($module) {
 125      require Carp;
 126      Carp::confess("Usage: DynaLoader::bootstrap(module)");
 127      }
 128  
 129      # A common error on platforms which don't support dynamic loading.
 130      # Since it's fatal and potentially confusing we give a detailed message.
 131      croak("Can't load module $module, dynamic loading not available in this perl.\n".
 132      "  (You may need to build a new perl executable which either supports\n".
 133      "  dynamic loading or has the $module module statically linked into it.)\n")
 134      unless defined(&dl_load_file);
 135  
 136  
 137      
 138      my @modparts = split(/::/,$module);
 139      my $modfname = $modparts[-1];
 140  
 141      # Some systems have restrictions on files names for DLL's etc.
 142      # mod2fname returns appropriate file base name (typically truncated)
 143      # It may also edit @modparts if required.
 144      $modfname = &mod2fname(\@modparts) if defined &mod2fname;
 145  
 146      
 147  
 148      my $modpname = join('/',@modparts);
 149  
 150      print STDERR "DynaLoader::bootstrap for $module ",
 151                 "(auto/$modpname/$modfname.so)\n"
 152      if $dl_debug;
 153  
 154      foreach (@INC) {
 155      
 156      
 157          my $dir = "$_/auto/$modpname";
 158      
 159      
 160      next unless -d $dir; # skip over uninteresting directories
 161      
 162      # check for common cases to avoid autoload of dl_findfile
 163      my $try =  "$dir/$modfname.so";
 164      last if $file = (-f $try) && $try;
 165      
 166      
 167      # no luck here, save dir for possible later dl_findfile search
 168      push @dirs, $dir;
 169      }
 170      # last resort, let dl_findfile have a go in all known locations
 171      $file = dl_findfile(map("-L$_",@dirs,@INC), $modfname) unless $file;
 172  
 173      croak("Can't locate loadable object for module $module in \@INC (\@INC contains: @INC)")
 174      unless $file;    # wording similar to error from 'require'
 175  
 176      
 177      my $bootname = "boot_$module";
 178      $bootname =~ s/\W/_/g;
 179      @dl_require_symbols = ($bootname);
 180  
 181      # Execute optional '.bootstrap' perl script for this module.
 182      # The .bs file can be used to configure @dl_resolve_using etc to
 183      # match the needs of the individual module on this architecture.
 184      my $bs = $file;
 185      $bs =~ s/(\.\w+)?(;\d*)?$/\.bs/; # look for .bs 'beside' the library
 186      if (-s $bs) { # only read file if it's not empty
 187          print STDERR "BS: $bs ($^O, $dlsrc)\n" if $dl_debug;
 188          eval { do $bs; };
 189          warn "$bs: $@\n" if $@;
 190      }
 191  
 192      my $boot_symbol_ref;
 193  
 194      
 195  
 196      # Many dynamic extension loading problems will appear to come from
 197      # this section of code: XYZ failed at line 123 of DynaLoader.pm.
 198      # Often these errors are actually occurring in the initialisation
 199      # C code of the extension XS file. Perl reports the error as being
 200      # in this perl code simply because this was the last perl code
 201      # it executed.
 202  
 203      my $libref = dl_load_file($file, $module->dl_load_flags) or
 204      croak("Can't load '$file' for module $module: ".dl_error());
 205  
 206      push(@dl_librefs,$libref);  # record loaded object
 207  
 208      my @unresolved = dl_undef_symbols();
 209      if (@unresolved) {
 210      require Carp;
 211      Carp::carp("Undefined symbols present after loading $file: @unresolved\n");
 212      }
 213  
 214      $boot_symbol_ref = dl_find_symbol($libref, $bootname) or
 215           croak("Can't find '$bootname' symbol in $file\n");
 216  
 217      push(@dl_modules, $module); # record loaded module
 218  
 219    boot:
 220      my $xs = dl_install_xsub("$module}::bootstrap", $boot_symbol_ref, $file);
 221  
 222      # See comment block above
 223  
 224      push(@dl_shared_objects, $file); # record files loaded
 225  
 226      &$xs(@args);
 227  }
 228  
 229  
 230  #sub _check_file {   # private utility to handle dl_expandspec vs -f tests
 231  #    my($file) = @_;
 232  #    return $file if (!$do_expand && -f $file); # the common case
 233  #    return $file if ( $do_expand && ($file=dl_expandspec($file)));
 234  #    return undef;
 235  #}
 236  
 237  
 238  # Let autosplit and the autoloader deal with these functions:
 239  __END__
 240  
 241  
 242  sub dl_findfile {
 243      # Read ext/DynaLoader/DynaLoader.doc for detailed information.
 244      # This function does not automatically consider the architecture
 245      # or the perl library auto directories.
 246      my (@args) = @_;
 247      my (@dirs,  $dir);   # which directories to search
 248      my (@found);         # full paths to real files we have found
 249      #my $dl_ext= 'so'; # $Config::Config{'dlext'} suffix for perl extensions
 250      #my $dl_so = 'so'; # $Config::Config{'so'} suffix for shared libraries
 251  
 252      print STDERR "dl_findfile(@args)\n" if $dl_debug;
 253  
 254      # accumulate directories but process files as they appear
 255      arg: foreach(@args) {
 256          #  Special fast case: full filepath requires no search
 257      
 258      
 259      
 260          if (m:/: && -f $_) {
 261          push(@found,$_);
 262          last arg unless wantarray;
 263          next;
 264      }
 265      
 266  
 267          # Deal with directories first:
 268          #  Using a -L prefix is the preferred option (faster and more robust)
 269          if (m:^-L:) { s/^-L//; push(@dirs, $_); next; }
 270  
 271      
 272      
 273          #  Otherwise we try to try to spot directories by a heuristic
 274          #  (this is a more complicated issue than it first appears)
 275          if (m:/: && -d $_) {   push(@dirs, $_); next; }
 276  
 277      
 278  
 279          #  Only files should get this far...
 280          my(@names, $name);    # what filenames to look for
 281          if (m:-l: ) {          # convert -lname to appropriate library name
 282              s/-l//;
 283              push(@names,"lib$_.so");
 284              push(@names,"lib$_.a");
 285          } else {                # Umm, a bare name. Try various alternatives:
 286              # these should be ordered with the most likely first
 287              push(@names,"$_.so")    unless m/\.so$/o;
 288              push(@names,"$_.so")     unless m/\.so$/o;
 289              push(@names,"lib$_.so")  unless m:/:;
 290              push(@names,"$_.a")          if !m/\.a$/ and $dlsrc eq "dl_dld.xs";
 291              push(@names, $_);
 292          }
 293      my $dirsep = '/';
 294      
 295          foreach $dir (@dirs, @dl_library_path) {
 296              next unless -d $dir;
 297          
 298              foreach $name (@names) {
 299          my($file) = "$dir$dirsep$name";
 300                  print STDERR " checking in $dir for $name\n" if $dl_debug;
 301          $file = ($do_expand) ? dl_expandspec($file) : (-f $file && $file);
 302          #$file = _check_file($file);
 303          if ($file) {
 304                      push(@found, $file);
 305                      next arg; # no need to look any further
 306                  }
 307              }
 308          }
 309      }
 310      if ($dl_debug) {
 311          foreach(@dirs) {
 312              print STDERR " dl_findfile ignored non-existent directory: $_\n" unless -d $_;
 313          }
 314          print STDERR "dl_findfile found: @found\n";
 315      }
 316      return $found[0] unless wantarray;
 317      @found;
 318  }
 319  
 320  
 321  sub dl_expandspec {
 322      my($spec) = @_;
 323      # Optional function invoked if DynaLoader.pm sets $do_expand.
 324      # Most systems do not require or use this function.
 325      # Some systems may implement it in the dl_*.xs file in which case
 326      # this autoload version will not be called but is harmless.
 327  
 328      # This function is designed to deal with systems which treat some
 329      # 'filenames' in a special way. For example VMS 'Logical Names'
 330      # (something like unix environment variables - but different).
 331      # This function should recognise such names and expand them into
 332      # full file paths.
 333      # Must return undef if $spec is invalid or file does not exist.
 334  
 335      my $file = $spec; # default output to input
 336  
 337      
 338      return undef unless -f $file;
 339      
 340      print STDERR "dl_expandspec($spec) => $file\n" if $dl_debug;
 341      $file;
 342  }
 343  
 344  sub dl_find_symbol_anywhere
 345  {
 346      my $sym = shift;
 347      my $libref;
 348      foreach $libref (@dl_librefs) {
 349      my $symref = dl_find_symbol($libref,$sym);
 350      return $symref if $symref;
 351      }
 352      return undef;
 353  }
 354  
 355  =head1 NAME
 356  
 357  DynaLoader - Dynamically load C libraries into Perl code
 358  
 359  =head1 SYNOPSIS
 360  
 361      package YourPackage;
 362      require DynaLoader;
 363      @ISA = qw(... DynaLoader ...);
 364      bootstrap YourPackage;
 365  
 366      # optional method for 'global' loading
 367      sub dl_load_flags { 0x01 }     
 368  
 369  
 370  =head1 DESCRIPTION
 371  
 372  This document defines a standard generic interface to the dynamic
 373  linking mechanisms available on many platforms.  Its primary purpose is
 374  to implement automatic dynamic loading of Perl modules.
 375  
 376  This document serves as both a specification for anyone wishing to
 377  implement the DynaLoader for a new platform and as a guide for
 378  anyone wishing to use the DynaLoader directly in an application.
 379  
 380  The DynaLoader is designed to be a very simple high-level
 381  interface that is sufficiently general to cover the requirements
 382  of SunOS, HP-UX, NeXT, Linux, VMS and other platforms.
 383  
 384  It is also hoped that the interface will cover the needs of OS/2, NT
 385  etc and also allow pseudo-dynamic linking (using C<ld -A> at runtime).
 386  
 387  It must be stressed that the DynaLoader, by itself, is practically
 388  useless for accessing non-Perl libraries because it provides almost no
 389  Perl-to-C 'glue'.  There is, for example, no mechanism for calling a C
 390  library function or supplying arguments.  A C::DynaLib module
 391  is available from CPAN sites which performs that function for some
 392  common system types.  And since the year 2000, there's also Inline::C,
 393  a module that allows you to write Perl subroutines in C.  Also available
 394  from your local CPAN site.
 395  
 396  DynaLoader Interface Summary
 397  
 398    @dl_library_path
 399    @dl_resolve_using
 400    @dl_require_symbols
 401    $dl_debug
 402    @dl_librefs
 403    @dl_modules
 404    @dl_shared_objects
 405                                                    Implemented in:
 406    bootstrap($modulename)                               Perl
 407    @filepaths = dl_findfile(@names)                     Perl
 408    $flags = $modulename->dl_load_flags                  Perl
 409    $symref  = dl_find_symbol_anywhere($symbol)          Perl
 410  
 411    $libref  = dl_load_file($filename, $flags)           C
 412    $status  = dl_unload_file($libref)                   C
 413    $symref  = dl_find_symbol($libref, $symbol)          C
 414    @symbols = dl_undef_symbols()                        C
 415    dl_install_xsub($name, $symref [, $filename])        C
 416    $message = dl_error                                  C
 417  
 418  =over 4
 419  
 420  =item @dl_library_path
 421  
 422  The standard/default list of directories in which dl_findfile() will
 423  search for libraries etc.  Directories are searched in order:
 424  $dl_library_path[0], [1], ... etc
 425  
 426  @dl_library_path is initialised to hold the list of 'normal' directories
 427  (F</usr/lib>, etc) determined by B<Configure> (C<$Config{'libpth'}>).  This should
 428  ensure portability across a wide range of platforms.
 429  
 430  @dl_library_path should also be initialised with any other directories
 431  that can be determined from the environment at runtime (such as
 432  LD_LIBRARY_PATH for SunOS).
 433  
 434  After initialisation @dl_library_path can be manipulated by an
 435  application using push and unshift before calling dl_findfile().
 436  Unshift can be used to add directories to the front of the search order
 437  either to save search time or to override libraries with the same name
 438  in the 'normal' directories.
 439  
 440  The load function that dl_load_file() calls may require an absolute
 441  pathname.  The dl_findfile() function and @dl_library_path can be
 442  used to search for and return the absolute pathname for the
 443  library/object that you wish to load.
 444  
 445  =item @dl_resolve_using
 446  
 447  A list of additional libraries or other shared objects which can be
 448  used to resolve any undefined symbols that might be generated by a
 449  later call to load_file().
 450  
 451  This is only required on some platforms which do not handle dependent
 452  libraries automatically.  For example the Socket Perl extension
 453  library (F<auto/Socket/Socket.so>) contains references to many socket
 454  functions which need to be resolved when it's loaded.  Most platforms
 455  will automatically know where to find the 'dependent' library (e.g.,
 456  F</usr/lib/libsocket.so>).  A few platforms need to be told the
 457  location of the dependent library explicitly.  Use @dl_resolve_using
 458  for this.
 459  
 460  Example usage:
 461  
 462      @dl_resolve_using = dl_findfile('-lsocket');
 463  
 464  =item @dl_require_symbols
 465  
 466  A list of one or more symbol names that are in the library/object file
 467  to be dynamically loaded.  This is only required on some platforms.
 468  
 469  =item @dl_librefs
 470  
 471  An array of the handles returned by successful calls to dl_load_file(),
 472  made by bootstrap, in the order in which they were loaded.
 473  Can be used with dl_find_symbol() to look for a symbol in any of
 474  the loaded files.
 475  
 476  =item @dl_modules
 477  
 478  An array of module (package) names that have been bootstrap'ed.
 479  
 480  =item @dl_shared_objects
 481  
 482  An array of file names for the shared objects that were loaded.
 483  
 484  =item dl_error()
 485  
 486  Syntax:
 487  
 488      $message = dl_error();
 489  
 490  Error message text from the last failed DynaLoader function.  Note
 491  that, similar to errno in unix, a successful function call does not
 492  reset this message.
 493  
 494  Implementations should detect the error as soon as it occurs in any of
 495  the other functions and save the corresponding message for later
 496  retrieval.  This will avoid problems on some platforms (such as SunOS)
 497  where the error message is very temporary (e.g., dlerror()).
 498  
 499  =item $dl_debug
 500  
 501  Internal debugging messages are enabled when $dl_debug is set true.
 502  Currently setting $dl_debug only affects the Perl side of the
 503  DynaLoader.  These messages should help an application developer to
 504  resolve any DynaLoader usage problems.
 505  
 506  $dl_debug is set to C<$ENV{'PERL_DL_DEBUG'}> if defined.
 507  
 508  For the DynaLoader developer/porter there is a similar debugging
 509  variable added to the C code (see dlutils.c) and enabled if Perl was
 510  built with the B<-DDEBUGGING> flag.  This can also be set via the
 511  PERL_DL_DEBUG environment variable.  Set to 1 for minimal information or
 512  higher for more.
 513  
 514  =item dl_findfile()
 515  
 516  Syntax:
 517  
 518      @filepaths = dl_findfile(@names)
 519  
 520  Determine the full paths (including file suffix) of one or more
 521  loadable files given their generic names and optionally one or more
 522  directories.  Searches directories in @dl_library_path by default and
 523  returns an empty list if no files were found.
 524  
 525  Names can be specified in a variety of platform independent forms.  Any
 526  names in the form B<-lname> are converted into F<libname.*>, where F<.*> is
 527  an appropriate suffix for the platform.
 528  
 529  If a name does not already have a suitable prefix and/or suffix then
 530  the corresponding file will be searched for by trying combinations of
 531  prefix and suffix appropriate to the platform: "$name.o", "lib$name.*"
 532  and "$name".
 533  
 534  If any directories are included in @names they are searched before
 535  @dl_library_path.  Directories may be specified as B<-Ldir>.  Any other
 536  names are treated as filenames to be searched for.
 537  
 538  Using arguments of the form C<-Ldir> and C<-lname> is recommended.
 539  
 540  Example: 
 541  
 542      @dl_resolve_using = dl_findfile(qw(-L/usr/5lib -lposix));
 543  
 544  
 545  =item dl_expandspec()
 546  
 547  Syntax:
 548  
 549      $filepath = dl_expandspec($spec)
 550  
 551  Some unusual systems, such as VMS, require special filename handling in
 552  order to deal with symbolic names for files (i.e., VMS's Logical Names).
 553  
 554  To support these systems a dl_expandspec() function can be implemented
 555  either in the F<dl_*.xs> file or code can be added to the autoloadable
 556  dl_expandspec() function in F<DynaLoader.pm>.  See F<DynaLoader.pm> for
 557  more information.
 558  
 559  =item dl_load_file()
 560  
 561  Syntax:
 562  
 563      $libref = dl_load_file($filename, $flags)
 564  
 565  Dynamically load $filename, which must be the path to a shared object
 566  or library.  An opaque 'library reference' is returned as a handle for
 567  the loaded object.  Returns undef on error.
 568  
 569  The $flags argument to alters dl_load_file behaviour.  
 570  Assigned bits:
 571  
 572   0x01  make symbols available for linking later dl_load_file's.
 573         (only known to work on Solaris 2 using dlopen(RTLD_GLOBAL))
 574         (ignored under VMS; this is a normal part of image linking)
 575  
 576  (On systems that provide a handle for the loaded object such as SunOS
 577  and HPUX, $libref will be that handle.  On other systems $libref will
 578  typically be $filename or a pointer to a buffer containing $filename.
 579  The application should not examine or alter $libref in any way.)
 580  
 581  This is the function that does the real work.  It should use the
 582  current values of @dl_require_symbols and @dl_resolve_using if required.
 583  
 584      SunOS: dlopen($filename)
 585      HP-UX: shl_load($filename)
 586      Linux: dld_create_reference(@dl_require_symbols); dld_link($filename)
 587      NeXT:  rld_load($filename, @dl_resolve_using)
 588      VMS:   lib$find_image_symbol($filename,$dl_require_symbols[0])
 589  
 590  (The dlopen() function is also used by Solaris and some versions of
 591  Linux, and is a common choice when providing a "wrapper" on other
 592  mechanisms as is done in the OS/2 port.)
 593  
 594  =item dl_unload_file()
 595  
 596  Syntax:
 597  
 598      $status = dl_unload_file($libref)
 599  
 600  Dynamically unload $libref, which must be an opaque 'library reference' as
 601  returned from dl_load_file.  Returns one on success and zero on failure.
 602  
 603  This function is optional and may not necessarily be provided on all platforms.
 604  If it is defined, it is called automatically when the interpreter exits for
 605  every shared object or library loaded by DynaLoader::bootstrap.  All such
 606  library references are stored in @dl_librefs by DynaLoader::Bootstrap as it
 607  loads the libraries.  The files are unloaded in last-in, first-out order.
 608  
 609  This unloading is usually necessary when embedding a shared-object perl (e.g.
 610  one configured with -Duseshrplib) within a larger application, and the perl
 611  interpreter is created and destroyed several times within the lifetime of the
 612  application.  In this case it is possible that the system dynamic linker will
 613  unload and then subsequently reload the shared libperl without relocating any
 614  references to it from any files DynaLoaded by the previous incarnation of the
 615  interpreter.  As a result, any shared objects opened by DynaLoader may point to
 616  a now invalid 'ghost' of the libperl shared object, causing apparently random
 617  memory corruption and crashes.  This behaviour is most commonly seen when using
 618  Apache and mod_perl built with the APXS mechanism.
 619  
 620      SunOS: dlclose($libref)
 621      HP-UX: ???
 622      Linux: ???
 623      NeXT:  ???
 624      VMS:   ???
 625  
 626  (The dlclose() function is also used by Solaris and some versions of
 627  Linux, and is a common choice when providing a "wrapper" on other
 628  mechanisms as is done in the OS/2 port.)
 629  
 630  =item dl_load_flags()
 631  
 632  Syntax:
 633  
 634      $flags = dl_load_flags $modulename;
 635  
 636  Designed to be a method call, and to be overridden by a derived class
 637  (i.e. a class which has DynaLoader in its @ISA).  The definition in
 638  DynaLoader itself returns 0, which produces standard behavior from
 639  dl_load_file().
 640  
 641  =item dl_find_symbol()
 642  
 643  Syntax:
 644  
 645      $symref = dl_find_symbol($libref, $symbol)
 646  
 647  Return the address of the symbol $symbol or C<undef> if not found.  If the
 648  target system has separate functions to search for symbols of different
 649  types then dl_find_symbol() should search for function symbols first and
 650  then other types.
 651  
 652  The exact manner in which the address is returned in $symref is not
 653  currently defined.  The only initial requirement is that $symref can
 654  be passed to, and understood by, dl_install_xsub().
 655  
 656      SunOS: dlsym($libref, $symbol)
 657      HP-UX: shl_findsym($libref, $symbol)
 658      Linux: dld_get_func($symbol) and/or dld_get_symbol($symbol)
 659      NeXT:  rld_lookup("_$symbol")
 660      VMS:   lib$find_image_symbol($libref,$symbol)
 661  
 662  
 663  =item dl_find_symbol_anywhere()
 664  
 665  Syntax:
 666  
 667      $symref = dl_find_symbol_anywhere($symbol)
 668  
 669  Applies dl_find_symbol() to the members of @dl_librefs and returns
 670  the first match found.
 671  
 672  =item dl_undef_symbols()
 673  
 674  Example
 675  
 676      @symbols = dl_undef_symbols()
 677  
 678  Return a list of symbol names which remain undefined after load_file().
 679  Returns C<()> if not known.  Don't worry if your platform does not provide
 680  a mechanism for this.  Most do not need it and hence do not provide it,
 681  they just return an empty list.
 682  
 683  
 684  =item dl_install_xsub()
 685  
 686  Syntax:
 687  
 688      dl_install_xsub($perl_name, $symref [, $filename])
 689  
 690  Create a new Perl external subroutine named $perl_name using $symref as
 691  a pointer to the function which implements the routine.  This is simply
 692  a direct call to newXSUB().  Returns a reference to the installed
 693  function.
 694  
 695  The $filename parameter is used by Perl to identify the source file for
 696  the function if required by die(), caller() or the debugger.  If
 697  $filename is not defined then "DynaLoader" will be used.
 698  
 699  
 700  =item bootstrap()
 701  
 702  Syntax:
 703  
 704  bootstrap($module)
 705  
 706  This is the normal entry point for automatic dynamic loading in Perl.
 707  
 708  It performs the following actions:
 709  
 710  =over 8
 711  
 712  =item *
 713  
 714  locates an auto/$module directory by searching @INC
 715  
 716  =item *
 717  
 718  uses dl_findfile() to determine the filename to load
 719  
 720  =item *
 721  
 722  sets @dl_require_symbols to C<("boot_$module")>
 723  
 724  =item *
 725  
 726  executes an F<auto/$module/$module.bs> file if it exists
 727  (typically used to add to @dl_resolve_using any files which
 728  are required to load the module on the current platform)
 729  
 730  =item *
 731  
 732  calls dl_load_flags() to determine how to load the file.
 733  
 734  =item *
 735  
 736  calls dl_load_file() to load the file
 737  
 738  =item *
 739  
 740  calls dl_undef_symbols() and warns if any symbols are undefined
 741  
 742  =item *
 743  
 744  calls dl_find_symbol() for "boot_$module"
 745  
 746  =item *
 747  
 748  calls dl_install_xsub() to install it as "$module}::bootstrap"
 749  
 750  =item *
 751  
 752  calls &{"$module}::bootstrap"} to bootstrap the module (actually
 753  it uses the function reference returned by dl_install_xsub for speed)
 754  
 755  =back
 756  
 757  =back
 758  
 759  
 760  =head1 AUTHOR
 761  
 762  Tim Bunce, 11 August 1994.
 763  
 764  This interface is based on the work and comments of (in no particular
 765  order): Larry Wall, Robert Sanders, Dean Roehrich, Jeff Okamoto, Anno
 766  Siegel, Thomas Neumann, Paul Marquess, Charles Bailey, myself and others.
 767  
 768  Larry Wall designed the elegant inherited bootstrap mechanism and
 769  implemented the first Perl 5 dynamic loader using it.
 770  
 771  Solaris global loading added by Nick Ing-Simmons with design/coding
 772  assistance from Tim Bunce, January 1996.
 773  
 774  =cut