3 Pumpkin - Notes on handling the Perl Patch Pumpkin
7 There is no simple synopsis, yet.
11 This document attempts to begin to describe some of the considerations
12 involved in patching, porting, and maintaining perl.
14 This document is still under construction, and still subject to
15 significant changes. Still, I hope parts of it will be useful,
16 so I'm releasing it even though it's not done.
18 For the most part, it's a collection of anecdotal information that
19 already assumes some familiarity with the Perl sources. I really need
20 an introductory section that describes the organization of the sources
21 and all the various auxiliary files that are part of the distribution.
23 =head1 Where Do I Get Perl Sources and Related Material?
25 The Comprehensive Perl Archive Network (or CPAN) is the place to go.
26 There are many mirrors, but the easiest thing to use is probably
27 http://www.perl.com/CPAN/README.html , which automatically points you to a
28 mirror site "close" to you.
30 =head2 Perl5-porters mailing list
32 The mailing list perl5-porters@perl.org
33 is the main group working with the development of perl. If you're
34 interested in all the latest developments, you should definitely
35 subscribe. The list is high volume, but generally has a
36 fairly low noise level.
38 Subscribe by sending the message (in the body of your letter)
40 subscribe perl5-porters
42 to perl5-porters-request@perl.org .
44 Archives of the list are held at:
46 http://www.rosat.mpe-garching.mpg.de/mailing-lists/perl-porters/
48 =head1 How are Perl Releases Numbered?
50 Beginning with v5.6.0, even versions will stand for maintenance releases
51 and odd versions for development releases, i.e., v5.6.x for maintenance
52 releases, and v5.7.x for development releases. Before v5.6.0, subversions
53 _01 through _49 were reserved for bug-fix maintenance releases, and
54 subversions _50 through _99 for unstable development versions.
56 For example, in v5.6.1, the revision number is 5, the version is 6,
57 and 1 is the subversion.
59 For compatibility with the older numbering scheme the composite floating
60 point version number continues to be available as the magic variable $],
61 and amounts to C<$revision + $version/1000 + $subversion/1000000>. This
62 can still be used in comparisons.
64 print "You've got an old perl\n" if $] < 5.005_03;
66 In addition, the version is also available as a string in $^V.
68 print "You've got a new perl\n" if $^V and $^V ge v5.6.0;
70 You can also require particular version (or later) with:
74 or using the new syntax available only from v5.6 onward:
78 At some point in the future, we may need to decide what to call the
79 next big revision. In the .package file used by metaconfig to
80 generate Configure, there are two variables that might be relevant:
81 $baserev=5 and $package=perl5.
83 Perl releases produced by the members of perl5-porters are usually
84 available on CPAN in the F<src/5.0/maint> and F<src/5.0/devel>
87 =head2 Maintenance and Development Subversions
89 The first rule of maintenance work is "First, do no harm."
91 Trial releases of bug-fix maintenance releases are announced on
92 perl5-porters. Trial releases use the new subversion number (to avoid
93 testers installing it over the previous release) and include a 'local
94 patch' entry in patchlevel.h. The distribution file contains the
95 string C<MAINT_TRIAL> to make clear that the file is not meant for
98 In general, the names of official distribution files for the public
99 always match the regular expression:
101 ^perl\d+\.(\d+)\.\d+(-MAINT_TRIAL_\d+)\.tar\.gz$
103 C<$1> in the pattern is always an even number for maintenance
104 versions, and odd for developer releases.
106 In the past it has been observed that pumkings tend to invent new
107 naming conventions on the fly. If you are a pumpking, before you
108 invent a new name for any of the three types of perl distributions,
109 please inform the guys from the CPAN who are doing indexing and
110 provide the trees of symlinks and the like. They will have to know
111 I<in advance> what you decide.
113 =head2 Why is it called the patch pumpkin?
115 Chip Salzenberg gets credit for that, with a nod to his cow orker,
116 David Croy. We had passed around various names (baton, token, hot
117 potato) but none caught on. Then, Chip asked:
121 Who has the patch pumpkin?
123 To explain: David Croy once told me once that at a previous job,
124 there was one tape drive and multiple systems that used it for backups.
125 But instead of some high-tech exclusion software, they used a low-tech
126 method to prevent multiple simultaneous backups: a stuffed pumpkin.
127 No one was allowed to make backups unless they had the "backup pumpkin".
133 =head1 Philosophical Issues in Patching and Porting Perl
135 There are no absolute rules, but there are some general guidelines I
136 have tried to follow as I apply patches to the perl sources.
137 (This section is still under construction.)
139 =head2 Solve problems as generally as possible
141 Never implement a specific restricted solution to a problem when you
142 can solve the same problem in a more general, flexible way.
144 For example, for dynamic loading to work on some SVR4 systems, we had
145 to build a shared libperl.so library. In order to build "FAT" binaries
146 on NeXT 4.0 systems, we had to build a special libperl library. Rather
147 than continuing to build a contorted nest of special cases, I
148 generalized the process of building libperl so that NeXT and SVR4 users
149 could still get their work done, but others could build a shared
150 libperl if they wanted to as well.
152 Contain your changes carefully. Assume nothing about other operating
153 systems, not even closely related ones. Your changes must not affect
156 Spy shamelessly on how similar patching or porting issues have been
159 If feasible, try to keep filenames 8.3-compliant to humor those poor
160 souls that get joy from running Perl under such dire limitations.
162 =head2 Seek consensus on major changes
164 If you are making big changes, don't do it in secret. Discuss the
165 ideas in advance on perl5-porters.
167 =head2 Keep the documentation up-to-date
169 If your changes may affect how users use perl, then check to be sure
170 that the documentation is in sync with your changes. Be sure to
171 check all the files F<pod/*.pod> and also the F<INSTALL> document.
173 Consider writing the appropriate documentation first and then
174 implementing your change to correspond to the documentation.
176 =head2 Avoid machine-specific #ifdef's
178 To the extent reasonable, try to avoid machine-specific #ifdef's in
179 the sources. Instead, use feature-specific #ifdef's. The reason is
180 that the machine-specific #ifdef's may not be valid across major
181 releases of the operating system. Further, the feature-specific tests
182 may help out folks on another platform who have the same problem.
184 =head2 Machine-specific files
190 If you have many machine-specific #defines or #includes, consider
191 creating an "osish.h" (os2ish.h, vmsish.h, and so on) and including
192 that in perl.h. If you have several machine-specific files (function
193 emulations, function stubs, build utility wrappers) you may create a
194 separate subdirectory (djgpp, win32) and put the files in there.
195 Remember to update C<MANIFEST> when you add files.
197 If your system supports dynamic loading but none of the existing
198 methods at F<ext/DynaLoader/dl_*.xs> work for you, you must write
199 a new one. Study the existing ones to see what kind of interface
204 There are two kinds of hints: hints for building Perl and hints for
205 extensions. The former live in the C<hints> subdirectory, the latter
206 in C<ext/*/hints> subdirectories.
208 The top level hints are Bourne-shell scripts that set, modify and
209 unset appropriate Configure variables, based on the Configure command
210 line options and possibly existing config.sh and Policy.sh files from
211 previous Configure runs.
213 The extension hints are written Perl (by the time they are used
214 miniperl has been built) and control the building of their respective
215 extensions. They can be used to for example manipulate compilation
218 =item build and installation Makefiles, scripts, and so forth
220 Sometimes you will also need to tweak the Perl build and installation
221 procedure itself, like for example F<Makefile.SH> and F<installperl>.
222 Tread very carefully, even more than usual. Contain your changes
227 Many of the tests in C<t> subdirectory assume machine-specific things
228 like existence of certain functions, something about filesystem
229 semantics, certain external utilities and their error messages. Use
230 the C<$^O> and the C<Config> module (which contains the results of the
231 Configure run, in effect the C<config.sh> converted to Perl) to either
232 skip (preferably not) or customize (preferable) the tests for your
237 Certain standard modules may need updating if your operating system
238 sports for example a native filesystem naming. You may want to update
239 some or all of the modules File::Basename, File::Spec, File::Path, and
240 File::Copy to become aware of your native filesystem syntax and
245 If your operating system comes from outside UNIX you almost certainly
246 will have differences in the available operating system functionality
247 (missing system calls, different semantics, whatever). Please
248 document these at F<pod/perlport.pod>. If your operating system is
249 the first B<not> to have a system call also update the list of
250 "portability-bewares" at the beginning of F<pod/perlfunc.pod>.
252 A file called F<README.youros> at the top level that explains things
253 like how to install perl at this platform, where to get any possibly
254 required additional software, and for example what test suite errors
255 to expect, is nice too.
257 You may also want to write a separate F<.pod> file for your operating
258 system to tell about existing mailing lists, os-specific modules,
259 documentation, whatever. Please name these along the lines of
260 F<perl>I<youros>.pod. [unfinished: where to put this file (the pod/
261 subdirectory, of course: but more importantly, which/what index files
266 =head2 Allow for lots of testing
268 We should never release a main version without testing it as a
271 =head2 Test popular applications and modules.
273 We should never release a main version without testing whether or not
274 it breaks various popular modules and applications. A partial list of
275 such things would include majordomo, metaconfig, apache, Tk, CGI,
276 libnet, and libwww, to name just a few. Of course it's quite possible
277 that some of those things will be just plain broken and need to be fixed,
278 but, in general, we ought to try to avoid breaking widely-installed
281 =head2 Automated generation of derivative files
283 The F<embed.h>, F<keywords.h>, F<opcode.h>, and F<perltoc.pod> files
284 are all automatically generated by perl scripts. In general, don't
285 patch these directly; patch the data files instead.
287 F<Configure> and F<config_h.SH> are also automatically generated by
288 B<metaconfig>. In general, you should patch the metaconfig units
289 instead of patching these files directly. However, very minor changes
290 to F<Configure> may be made in between major sync-ups with the
291 metaconfig units, which tends to be complicated operations. But be
292 careful, this can quickly spiral out of control. Running metaconfig
295 Also F<Makefile> is automatically produced from F<Makefile.SH>.
296 In general, look out for all F<*.SH> files.
298 Finally, the sample files in the F<Porting/> subdirectory are
299 generated automatically by the script F<U/mksample> included
300 with the metaconfig units. See L<"run metaconfig"> below for
301 information on obtaining the metaconfig units.
303 =head1 How to Make a Distribution
305 There really ought to be a 'make dist' target, but there isn't.
306 The 'dist' suite of tools also contains a number of tools that I haven't
307 learned how to use yet. Some of them may make this all a bit easier.
309 Here are the steps I go through to prepare a patch & distribution.
311 Lots of it could doubtless be automated but isn't. The Porting/makerel
312 (make release) perl script does now help automate some parts of it.
314 =head2 Announce your intentions
316 First, you should volunteer out loud to take the patch pumpkin. It's
317 generally counter-productive to have multiple people working in secret
320 At the same time, announce what you plan to do with the patch pumpkin,
321 to allow folks a chance to object or suggest alternatives, or do it for
322 you. Naturally, the patch pumpkin holder ought to incorporate various
323 bug fixes and documentation improvements that are posted while he or
324 she has the pumpkin, but there might also be larger issues at stake.
326 One of the precepts of the subversion idea is that we shouldn't give
327 the patch pumpkin to anyone unless we have some idea what he or she
328 is going to do with it.
330 =head2 refresh pod/perltoc.pod
332 Presumably, you have done a full C<make> in your working source
333 directory. Before you C<make spotless> (if you do), and if you have
334 changed any documentation in any module or pod file, change to the
335 F<pod> directory and run C<make toc>.
337 =head2 run installhtml to check the validity of the pod files
339 =head2 update patchlevel.h
341 Don't be shy about using the subversion number, even for a relatively
342 modest patch. We've never even come close to using all 99 subversions,
343 and it's better to have a distinctive number for your patch. If you
344 need feedback on your patch, go ahead and issue it and promise to
345 incorporate that feedback quickly (e.g. within 1 week) and send out a
348 =head2 run metaconfig
350 If you need to make changes to Configure or config_h.SH, it may be best to
351 change the appropriate metaconfig units instead, and regenerate Configure.
355 will regenerate Configure and config_h.SH. Much more information
356 on obtaining and running metaconfig is in the F<U/README> file
357 that comes with Perl's metaconfig units. Perl's metaconfig units
358 should be available on CPAN. A set of units that will work with
359 perl5.005 is in the file F<mc_units-5.005_00-01.tar.gz> under
360 http://www.perl.com/CPAN/authors/id/ANDYD/ . The mc_units tar file
361 should be unpacked in your main perl source directory. Note: those
362 units were for use with 5.005. There may have been changes since then.
363 Check for later versions or contact perl5-porters@perl.org to obtain a
364 pointer to the current version.
366 Alternatively, do consider if the F<*ish.h> files might be a better
367 place for your changes.
371 Make sure the MANIFEST is up-to-date. You can use dist's B<manicheck>
372 program for this. You can also use
374 perl -w -MExtUtils::Manifest=fullcheck -e fullcheck
376 Both commands will also list extra files in the directory that are not
379 The MANIFEST is normally sorted.
381 If you are using metaconfig to regenerate Configure, then you should note
382 that metaconfig actually uses MANIFEST.new, so you want to be sure
383 MANIFEST.new is up-to-date too. I haven't found the MANIFEST/MANIFEST.new
384 distinction particularly useful, but that's probably because I still haven't
385 learned how to use the full suite of tools in the dist distribution.
387 =head2 Check permissions
389 All the tests in the t/ directory ought to be executable. The
390 main makefile used to do a 'chmod t/*/*.t', but that resulted in
391 a self-modifying distribution--something some users would strongly
392 prefer to avoid. The F<t/TEST> script will check for this
393 and do the chmod if needed, but the tests still ought to be
396 In all, the following files should probably be executable:
411 vms/ext/Stdio/test.pl
415 Other things ought to be readable, at least :-).
417 Probably, the permissions for the files could be encoded in MANIFEST
418 somehow, but I'm reluctant to change MANIFEST itself because that
419 could break old scripts that use MANIFEST.
421 I seem to recall that some SVR3 systems kept some sort of file that listed
422 permissions for system files; something like that might be appropriate.
426 This will build a config.sh and config.h. You can skip this if you haven't
427 changed Configure or config_h.SH at all. I use the following command
429 sh Configure -Dprefix=/opt/perl -Doptimize=-O -Dusethreads \
431 -Dcf_email='yourname@yourhost.yourplace.com' \
432 -Dperladmin='yourname@yourhost.yourplace.com' \
433 -Dmydomain='.yourplace.com' \
434 -Dmyhostname='yourhost' \
437 =head2 Update Porting/config.sh and Porting/config_H
440 This section needs revision. We're currently working on easing
441 the task of keeping the vms, win32, and plan9 config.sh info
442 up-to-date. The plan is to use keep up-to-date 'canned' config.sh
443 files in the appropriate subdirectories and then generate 'canned'
444 config.h files for vms, win32, etc. from the generic config.sh file.
445 This is to ease maintenance. When Configure gets updated, the parts
446 sometimes get scrambled around, and the changes in config_H can
447 sometimes be very hard to follow. config.sh, on the other hand, can
448 safely be sorted, so it's easy to track (typically very small) changes
449 to config.sh and then propoagate them to a canned 'config.h' by any
450 number of means, including a perl script in win32/ or carrying
451 config.sh and config_h.SH to a Unix system and running sh
455 The Porting/config.sh and Porting/config_H files are provided to
456 help those folks who can't run Configure. It is important to keep
457 them up-to-date. If you have changed config_h.SH, those changes must
458 be reflected in config_H as well. (The name config_H was chosen to
459 distinguish the file from config.h even on case-insensitive file systems.)
460 Simply edit the existing config_H file; keep the first few explanatory
461 lines and then copy your new config.h below.
463 It may also be necessary to update win32/config.?c, vms/config.vms and
464 plan9/config.plan9, though you should be quite careful in doing so if
465 you are not familiar with those systems. You might want to issue your
466 patch with a promise to quickly issue a follow-up that handles those
469 =head2 make run_byacc
471 If you have byacc-1.8.2 (available from CPAN), and if there have been
472 changes to F<perly.y>, you can regenerate the F<perly.c> file. The
473 run_byacc makefile target does this by running byacc and then applying
474 some patches so that byacc dynamically allocates space, rather than
475 having fixed limits. This patch is handled by the F<perly.fixer>
476 script. Depending on the nature of the changes to F<perly.y>, you may
477 or may not have to hand-edit the patch to apply correctly. If you do,
478 you should include the edited patch in the new distribution. If you
479 have byacc-1.9, the patch won't apply cleanly. Changes to the printf
480 output statements mean the patch won't apply cleanly. Long ago I
481 started to fix F<perly.fixer> to detect this, but I never completed the
484 If C<perly.c> changes, make sure you run C<perl vms/vms_yfix.pl> to
485 update the corresponding VMS files. See L<VMS-specific updates>.
487 Some additional notes from Larry on this:
489 Don't forget to regenerate perly_c.diff.
493 patch perly.c <perly_c.diff
494 # manually apply any failed hunks
495 diff -c2 perly.c.orig perly.c >perly_c.diff
497 One chunk of lines that often fails begins with
501 and ends one line before
503 #define YYERRCODE 256
505 This only happens when you add or remove a token type. I suppose this
506 could be automated, but it doesn't happen very often nowadays.
510 =head2 make regen_headers
512 The F<embed.h>, F<keywords.h>, and F<opcode.h> files are all automatically
513 generated by perl scripts. Since the user isn't guaranteed to have a
514 working perl, we can't require the user to generate them. Hence you have
515 to, if you're making a distribution.
517 I used to include rules like the following in the makefile:
519 # The following three header files are generated automatically
520 # The correct versions should be already supplied with the perl kit,
521 # in case you don't have perl or 'sh' available.
522 # The - is to ignore error return codes in case you have the source
523 # installed read-only or you don't have perl yet.
524 keywords.h: keywords.pl
525 @echo "Don't worry if this fails."
529 However, I got B<lots> of mail consisting of people worrying because the
530 command failed. I eventually decided that I would save myself time
531 and effort by manually running C<make regen_headers> myself rather
532 than answering all the questions and complaints about the failing
535 =head2 global.sym, interp.sym and perlio.sym
537 Make sure these files are up-to-date. Read the comments in these
538 files and in perl_exp.SH to see what to do.
540 =head2 Binary compatibility
542 If you do change F<global.sym> or F<interp.sym>, think carefully about
543 what you are doing. To the extent reasonable, we'd like to maintain
544 souce and binary compatibility with older releases of perl. That way,
545 extensions built under one version of perl will continue to work with
546 new versions of perl.
548 Of course, some incompatible changes may well be necessary. I'm just
549 suggesting that we not make any such changes without thinking carefully
550 about them first. If possible, we should provide
551 backwards-compatibility stubs. There's a lot of XS code out there.
552 Let's not force people to keep changing it.
556 Be sure to update the F<Changes> file. Try to include both an overall
557 summary as well as detailed descriptions of the changes. Your
558 audience will include other developers and users, so describe
559 user-visible changes (if any) in terms they will understand, not in
560 code like "initialize foo variable in bar function".
562 There are differing opinions on whether the detailed descriptions
563 ought to go in the Changes file or whether they ought to be available
564 separately in the patch file (or both). There is no disagreement that
565 detailed descriptions ought to be easily available somewhere.
569 The F<Todo> file contains a roughly-catgorized unordered list of
570 aspects of Perl that could use enhancement, features that could be
571 added, areas that could be cleaned up, and so on. During your term as
572 pumpkin-holder, you will probably address some of these issues, and
573 perhaps identify others which, while you decide not to address them
574 this time around, may be tackled in the future. Update the file
575 reflect the situation as it stands when you hand over the pumpkin.
577 You might like, early in your pumpkin-holding career, to see if you
578 can find champions for partiticular issues on the to-do list: an issue
579 owned is an issue more likely to be resolved.
581 There are also some more porting-specific L<Todo> items later in this
584 =head2 OS/2-specific updates
586 In the os2 directory is F<diff.configure>, a set of OS/2-specific
587 diffs against B<Configure>. If you make changes to Configure, you may
588 want to consider regenerating this diff file to save trouble for the
591 You can also consider the OS/2 diffs as reminders of portability
592 things that need to be fixed in Configure.
594 =head2 VMS-specific updates
596 If you have changed F<perly.y> or F<perly.c>, then you most probably want
597 to update F<vms/perly_{h,c}.vms> by running C<perl vms/vms_yfix.pl>.
599 The Perl version number appears in several places under F<vms>.
600 It is courteous to update these versions. For example, if you are
601 making 5.004_42, replace "5.00441" with "5.00442".
603 =head2 Making the new distribution
605 Suppose, for example, that you want to make version 5.004_08. Then you can
606 do something like the following
608 mkdir ../perl5.004_08
609 awk '{print $1}' MANIFEST | cpio -pdm ../perl5.004_08
611 tar cf perl5.004_08.tar perl5.004_08
612 gzip --best perl5.004_08.tar
614 These steps, with extra checks, are automated by the Porting/makerel
617 =head2 Making a new patch
619 I find the F<makepatch> utility quite handy for making patches.
620 You can obtain it from any CPAN archive under
621 http://www.perl.com/CPAN/authors/Johan_Vromans/ . There are a couple
622 of differences between my version and the standard one. I have mine do
625 # Print a reassuring "End of Patch" note so people won't
626 # wonder if their mailer truncated patches.
627 print "\n\nEnd of Patch.\n";
629 at the end. That's because I used to get questions from people asking
630 if their mail was truncated.
632 It also writes Index: lines which include the new directory prefix
633 (change Index: print, approx line 294 or 310 depending on the version,
634 to read: print PATCH ("Index: $newdir$new\n");). That helps patches
635 work with more POSIX conformant patch programs.
637 Here's how I generate a new patch. I'll use the hypothetical
638 5.004_07 to 5.004_08 patch as an example.
640 # unpack perl5.004_07/
641 gzip -d -c perl5.004_07.tar.gz | tar -xof -
642 # unpack perl5.004_08/
643 gzip -d -c perl5.004_08.tar.gz | tar -xof -
644 makepatch perl5.004_07 perl5.004_08 > perl5.004_08.pat
646 Makepatch will automatically generate appropriate B<rm> commands to remove
647 deleted files. Unfortunately, it will not correctly set permissions
648 for newly created files, so you may have to do so manually. For example,
649 patch 5.003_04 created a new test F<t/op/gv.t> which needs to be executable,
650 so at the top of the patch, I inserted the following lines:
656 Now, of course, my patch is now wrong because makepatch didn't know I
657 was going to do that command, and it patched against /dev/null.
659 So, what I do is sort out all such shell commands that need to be in the
660 patch (including possible mv-ing of files, if needed) and put that in the
661 shell commands at the top of the patch. Next, I delete all the patch parts
662 of perl5.004_08.pat, leaving just the shell commands. Then, I do the
666 sh ../perl5.004_08.pat
668 makepatch perl5.004_07 perl5.004_08 >> perl5.004_08.pat
670 (Note the append to preserve my shell commands.)
671 Now, my patch will line up with what the end users are going to do.
673 =head2 Testing your patch
675 It seems obvious, but be sure to test your patch. That is, verify that
676 it produces exactly the same thing as your full distribution.
679 gzip -d -c perl5.004_07.tar.gz | tar -xf -
681 sh ../perl5.004_08.pat
682 patch -p1 -N < ../perl5.004_08.pat
684 gdiff -r perl5.004_07 perl5.004_08
686 where B<gdiff> is GNU diff. Other diff's may also do recursive checking.
690 Again, it's obvious, but you should test your new version as widely as you
691 can. You can be sure you'll hear about it quickly if your version doesn't
692 work on both ANSI and pre-ANSI compilers, and on common systems such as
693 SunOS 4.1.[34], Solaris, and Linux.
695 If your changes include conditional code, try to test the different
696 branches as thoroughly as you can. For example, if your system
697 supports dynamic loading, you can also test static loading with
701 You can also hand-tweak your config.h to try out different #ifdef
706 Purify is a commercial tool that is helpful in identifying memory
707 overruns, wild pointers, memory leaks and other such badness. Perl
708 must be compiled in a specific way for optimal testing with Purify.
710 Use the following commands to test perl with Purify:
712 sh Configure -des -Doptimize=-g -Uusemymalloc -Dusemultiplicity \
714 setenv PURIFYOPTIONS "-chain-length=25"
717 ln -s ../pureperl perl
720 Disabling Perl's malloc allows Purify to monitor allocations and leaks
721 more closely; using Perl's malloc will make Purify report most leaks
722 in the "potential" leaks category. Enabling the multiplicity option
723 allows perl to clean up thoroughly when the interpreter shuts down, which
724 reduces the number of bogus leak reports from Purify. The -DPURIFY
725 enables any Purify-specific debugging code in the sources.
727 Purify outputs messages in "Viewer" windows by default. If you don't have
728 a windowing environment or if you simply want the Purify output to
729 unobtrusively go to a log file instead of to the interactive window,
730 use the following options instead:
732 setenv PURIFYOPTIONS "-chain-length=25 -windows=no -log-file=perl.log \
735 The only currently known leaks happen when there are compile-time errors
736 within eval or require. (Fixing these is non-trivial, unfortunately, but
737 they must be fixed eventually.)
739 =head1 Common Gotcha's
745 The '#elif' preprocessor directive is not understood on all systems.
746 Specifically, I know that Pyramids don't understand it. Thus instead of the
757 You have to do the more Byzantine
769 Incidentally, whitespace between the leading '#' and the preprocessor
770 command is not guaranteed, but is very portable and you may use it freely.
771 I think it makes things a bit more readable, especially once things get
772 rather deeply nested. I also think that things should almost never get
773 too deeply nested, so it ought to be a moot point :-)
775 =item Probably Prefer POSIX
777 It's often the case that you'll need to choose whether to do
778 something the BSD-ish way or the POSIX-ish way. It's usually not
779 a big problem when the two systems use different names for similar
780 functions, such as memcmp() and bcmp(). The perl.h header file
781 handles these by appropriate #defines, selecting the POSIX mem*()
782 functions if available, but falling back on the b*() functions, if
785 More serious is the case where some brilliant person decided to
786 use the same function name but give it a different meaning or
787 calling sequence :-). getpgrp() and setpgrp() come to mind.
788 These are a real problem on systems that aim for conformance to
789 one standard (e.g. POSIX), but still try to support the other way
790 of doing things (e.g. BSD). My general advice (still not really
791 implemented in the source) is to do something like the following.
792 Suppose there are two alternative versions, fooPOSIX() and
796 /* use fooPOSIX(); */
799 /* try to emulate fooPOSIX() with fooBSD();
800 perhaps with the following: */
801 # define fooPOSIX fooBSD
803 # /* Uh, oh. We have to supply our own. */
804 # define fooPOSIX Perl_fooPOSIX
808 =item Think positively
810 If you need to add an #ifdef test, it is usually easier to follow if you
811 think positively, e.g.
813 #ifdef HAS_NEATO_FEATURE
814 /* use neato feature */
816 /* use some fallback mechanism */
819 rather than the more impenetrable
821 #ifndef MISSING_NEATO_FEATURE
822 /* Not missing it, so we must have it, so use it */
824 /* Are missing it, so fall back on something else. */
827 Of course for this toy example, there's not much difference. But when
828 the #ifdef's start spanning a couple of screen fulls, and the #else's
829 are marked something like
831 #else /* !MISSING_NEATO_FEATURE */
833 I find it easy to get lost.
835 =item Providing Missing Functions -- Problem
837 Not all systems have all the neat functions you might want or need, so
838 you might decide to be helpful and provide an emulation. This is
839 sound in theory and very kind of you, but please be careful about what
840 you name the function. Let me use the C<pause()> function as an
843 Perl5.003 has the following in F<perl.h>
846 #define pause() sleep((32767<<16)+32767)
849 Configure sets HAS_PAUSE if the system has the pause() function, so
850 this #define only kicks in if the pause() function is missing.
853 Unfortunately, some systems apparently have a prototype for pause()
854 in F<unistd.h>, but don't actually have the function in the library.
855 (Or maybe they do have it in a library we're not using.)
857 Thus, the compiler sees something like
859 extern int pause(void);
861 #define pause() sleep((32767<<16)+32767)
863 and dies with an error message. (Some compilers don't mind this;
864 others apparently do.)
866 To work around this, 5.003_03 and later have the following in perl.h:
868 /* Some unistd.h's give a prototype for pause() even though
869 HAS_PAUSE ends up undefined. This causes the #define
870 below to be rejected by the compiler. Sigh.
875 # define Pause() sleep((32767<<16)+32767)
880 The curious reader may wonder why I didn't do the following in
886 sleep((32767<<16)+32767);
890 That is, since the function is missing, just provide it.
891 Then things would probably be been alright, it would seem.
893 Well, almost. It could be made to work. The problem arises from the
894 conflicting needs of dynamic loading and namespace protection.
896 For dynamic loading to work on AIX (and VMS) we need to provide a list
897 of symbols to be exported. This is done by the script F<perl_exp.SH>,
898 which reads F<global.sym> and F<interp.sym>. Thus, the C<pause>
899 symbol would have to be added to F<global.sym> So far, so good.
901 On the other hand, one of the goals of Perl5 is to make it easy to
902 either extend or embed perl and link it with other libraries. This
903 means we have to be careful to keep the visible namespace "clean".
904 That is, we don't want perl's global variables to conflict with
905 those in the other application library. Although this work is still
906 in progress, the way it is currently done is via the F<embed.h> file.
907 This file is built from the F<global.sym> and F<interp.sym> files,
908 since those files already list the globally visible symbols. If we
909 had added C<pause> to global.sym, then F<embed.h> would contain the
912 #define pause Perl_pause
914 and calls to C<pause> in the perl sources would now point to
915 C<Perl_pause>. Now, when B<ld> is run to build the F<perl> executable,
916 it will go looking for C<perl_pause>, which probably won't exist in any
917 of the standard libraries. Thus the build of perl will fail.
919 Those systems where C<HAS_PAUSE> is not defined would be ok, however,
920 since they would get a C<Perl_pause> function in util.c. The rest of
921 the world would be in trouble.
923 And yes, this scenario has happened. On SCO, the function C<chsize>
924 is available. (I think it's in F<-lx>, the Xenix compatibility
925 library.) Since the perl4 days (and possibly before), Perl has
926 included a C<chsize> function that gets called something akin to
929 I32 chsize(fd, length)
935 #define chsize Perl_chsize
937 to F<embed.h>, the compile started failing on SCO systems.
939 The "fix" is to give the function a different name. The one
940 implemented in 5.003_05 isn't optimal, but here's what was done:
943 # ifdef my_chsize /* Probably #defined to Perl_my_chsize in embed.h */
946 # define my_chsize chsize
949 My explanatory comment in patch 5.003_05 said:
951 Undef and then re-define my_chsize from Perl_my_chsize to
952 just plain chsize if this system HAS_CHSIZE. This probably only
953 applies to SCO. This shows the perils of having internal
954 functions with the same name as external library functions :-).
956 Now, we can safely put C<my_chsize> in F<global.sym>, export it, and
957 hide it with F<embed.h>.
959 To be consistent with what I did for C<pause>, I probably should have
960 called the new function C<Chsize>, rather than C<my_chsize>.
961 However, the perl sources are quite inconsistent on this (Consider
962 New, Mymalloc, and Myremalloc, to name just a few.)
964 There is a problem with this fix, however, in that C<Perl_chsize>
965 was available as a F<libperl.a> library function in 5.003, but it
966 isn't available any more (as of 5.003_07). This means that we've
967 broken binary compatibility. This is not good.
969 =item Providing missing functions -- some ideas
971 We currently don't have a standard way of handling such missing
972 function names. Right now, I'm effectively thinking aloud about a
973 solution. Some day, I'll try to formally propose a solution.
975 Part of the problem is that we want to have some functions listed as
976 exported but not have their names mangled by embed.h or possibly
977 conflict with names in standard system headers. We actually already
978 have such a list at the end of F<perl_exp.SH> (though that list is
981 # extra globals not included above.
982 cat <<END >> perl.exp
1006 This still needs much thought, but I'm inclined to think that one
1007 possible solution is to prefix all such functions with C<perl_> in the
1008 source and list them along with the other C<perl_*> functions in
1011 Thus, for C<chsize>, we'd do something like the following:
1015 # define perl_chsize chsize
1018 then in some file (e.g. F<util.c> or F<doio.c>) do
1021 I32 perl_chsize(fd, length)
1022 /* implement the function here . . . */
1025 Alternatively, we could just always use C<chsize> everywhere and move
1026 C<chsize> from F<global.sym> to the end of F<perl_exp.SH>. That would
1027 probably be fine as long as our C<chsize> function agreed with all the
1028 C<chsize> function prototypes in the various systems we'll be using.
1029 As long as the prototypes in actual use don't vary that much, this is
1030 probably a good alternative. (As a counter-example, note how Configure
1031 and perl have to go through hoops to find and use get Malloc_t and
1032 Free_t for C<malloc> and C<free>.)
1034 At the moment, this latter option is what I tend to prefer.
1036 =item All the world's a VAX
1038 Sorry, showing my age:-). Still, all the world is not BSD 4.[34],
1039 SVR4, or POSIX. Be aware that SVR3-derived systems are still quite
1040 common (do you have any idea how many systems run SCO?) If you don't
1041 have a bunch of v7 manuals handy, the metaconfig units (by default
1042 installed in F</usr/local/lib/dist/U>) are a good resource to look at
1047 =head1 Miscellaneous Topics
1051 Why does perl use a metaconfig-generated Configure script instead of an
1052 autoconf-generated configure script?
1054 Metaconfig and autoconf are two tools with very similar purposes.
1055 Metaconfig is actually the older of the two, and was originally written
1056 by Larry Wall, while autoconf is probably now used in a wider variety of
1057 packages. The autoconf info file discusses the history of autoconf and
1058 how it came to be. The curious reader is referred there for further
1061 Overall, both tools are quite good, I think, and the choice of which one
1062 to use could be argued either way. In March, 1994, when I was just
1063 starting to work on Configure support for Perl5, I considered both
1064 autoconf and metaconfig, and eventually decided to use metaconfig for the
1069 =item Compatibility with Perl4
1071 Perl4 used metaconfig, so many of the #ifdef's were already set up for
1072 metaconfig. Of course metaconfig had evolved some since Perl4's days,
1073 but not so much that it posed any serious problems.
1075 =item Metaconfig worked for me
1077 My system at the time was Interactive 2.2, a SVR3.2/386 derivative that
1078 also had some POSIX support. Metaconfig-generated Configure scripts
1079 worked fine for me on that system. On the other hand, autoconf-generated
1080 scripts usually didn't. (They did come quite close, though, in some
1081 cases.) At the time, I actually fetched a large number of GNU packages
1082 and checked. Not a single one configured and compiled correctly
1083 out-of-the-box with the system's cc compiler.
1085 =item Configure can be interactive
1087 With both autoconf and metaconfig, if the script works, everything is
1088 fine. However, one of my main problems with autoconf-generated scripts
1089 was that if it guessed wrong about something, it could be B<very> hard to
1090 go back and fix it. For example, autoconf always insisted on passing the
1091 -Xp flag to cc (to turn on POSIX behavior), even when that wasn't what I
1092 wanted or needed for that package. There was no way short of editing the
1093 configure script to turn this off. You couldn't just edit the resulting
1094 Makefile at the end because the -Xp flag influenced a number of other
1097 Metaconfig's Configure scripts, on the other hand, can be interactive.
1098 Thus if Configure is guessing things incorrectly, you can go back and fix
1099 them. This isn't as important now as it was when we were actively
1100 developing Configure support for new features such as dynamic loading,
1101 but it's still useful occasionally.
1105 At the time, autoconf-generated scripts were covered under the GNU Public
1106 License, and hence weren't suitable for inclusion with Perl, which has a
1107 different licensing policy. (Autoconf's licensing has since changed.)
1111 Metaconfig builds up Configure from a collection of discrete pieces
1112 called "units". You can override the standard behavior by supplying your
1113 own unit. With autoconf, you have to patch the standard files instead.
1114 I find the metaconfig "unit" method easier to work with. Others
1115 may find metaconfig's units clumsy to work with.
1119 =head2 Why isn't there a directory to override Perl's library?
1121 Mainly because no one's gotten around to making one. Note that
1122 "making one" involves changing perl.c, Configure, config_h.SH (and
1123 associated files, see above), and I<documenting> it all in the
1126 Apparently, most folks who want to override one of the standard library
1127 files simply do it by overwriting the standard library files.
1131 In the perl.c sources, you'll find an undocumented APPLLIB_EXP
1132 variable, sort of like PRIVLIB_EXP and ARCHLIB_EXP (which are
1133 documented in config_h.SH). Here's what APPLLIB_EXP is for, from
1134 a mail message from Larry:
1136 The main intent of APPLLIB_EXP is for folks who want to send out a
1137 version of Perl embedded in their product. They would set the symbol
1138 to be the name of the library containing the files needed to run or to
1139 support their particular application. This works at the "override"
1140 level to make sure they get their own versions of any library code that
1141 they absolutely must have configuration control over.
1143 As such, I don't see any conflict with a sysadmin using it for a
1144 override-ish sort of thing, when installing a generic Perl. It should
1145 probably have been named something to do with overriding though. Since
1146 it's undocumented we could still change it... :-)
1148 Given that it's already there, you can use it to override
1149 distribution modules. If you do
1151 sh Configure -Dccflags='-DAPPLLIB_EXP=/my/override'
1153 then perl.c will put /my/override ahead of ARCHLIB and PRIVLIB.
1155 =head2 Shared libperl.so location
1157 Why isn't the shared libperl.so installed in /usr/lib/ along
1158 with "all the other" shared libraries? Instead, it is installed
1159 in $archlib, which is typically something like
1161 /usr/local/lib/perl5/archname/5.00404
1163 and is architecture- and version-specific.
1165 The basic reason why a shared libperl.so gets put in $archlib is so that
1166 you can have more than one version of perl on the system at the same time,
1167 and have each refer to its own libperl.so.
1169 Three examples might help. All of these work now; none would work if you
1170 put libperl.so in /usr/lib.
1176 Suppose you want to have both threaded and non-threaded perl versions
1177 around. Configure will name both perl libraries "libperl.so" (so that
1178 you can link to them with -lperl). The perl binaries tell them apart
1179 by having looking in the appropriate $archlib directories.
1183 Suppose you have perl5.004_04 installed and you want to try to compile
1184 it again, perhaps with different options or after applying a patch.
1185 If you already have libperl.so installed in /usr/lib/, then it may be
1186 either difficult or impossible to get ld.so to find the new libperl.so
1187 that you're trying to build. If, instead, libperl.so is tucked away in
1188 $archlib, then you can always just change $archlib in the current perl
1189 you're trying to build so that ld.so won't find your old libperl.so.
1190 (The INSTALL file suggests you do this when building a debugging perl.)
1194 The shared perl library is not a "well-behaved" shared library with
1195 proper major and minor version numbers, so you can't necessarily
1196 have perl5.004_04 and perl5.004_05 installed simultaneously. Suppose
1197 perl5.004_04 were to install /usr/lib/libperl.so.4.4, and perl5.004_05
1198 were to install /usr/lib/libperl.so.4.5. Now, when you try to run
1199 perl5.004_04, ld.so might try to load libperl.so.4.5, since it has
1200 the right "major version" number. If this works at all, it almost
1201 certainly defeats the reason for keeping perl5.004_04 around. Worse,
1202 with development subversions, you certaily can't guarantee that
1203 libperl.so.4.4 and libperl.so.4.55 will be compatible.
1205 Anyway, all this leads to quite obscure failures that are sure to drive
1206 casual users crazy. Even experienced users will get confused :-). Upon
1207 reflection, I'd say leave libperl.so in $archlib.
1211 =head1 Upload Your Work to CPAN
1213 You can upload your work to CPAN if you have a CPAN id. Check out
1214 http://www.perl.com/CPAN/modules/04pause.html for information on
1215 _PAUSE_, the Perl Author's Upload Server.
1217 I typically upload both the patch file, e.g. F<perl5.004_08.pat.gz>
1218 and the full tar file, e.g. F<perl5.004_08.tar.gz>.
1220 If you want your patch to appear in the F<src/5.0/unsupported>
1221 directory on CPAN, send e-mail to the CPAN master librarian. (Check
1222 out http://www.perl.com/CPAN/CPAN.html ).
1224 =head1 Help Save the World
1226 You should definitely announce your patch on the perl5-porters list.
1227 You should also consider announcing your patch on
1228 comp.lang.perl.announce, though you should make it quite clear that a
1229 subversion is not a production release, and be prepared to deal with
1230 people who will not read your disclaimer.
1234 Here, in no particular order, are some Configure and build-related
1235 items that merit consideration. This list isn't exhaustive, it's just
1236 what I came up with off the top of my head.
1238 =head2 Good ideas waiting for round tuits
1242 =item Configure -Dsrc=/blah/blah
1244 We should be able to emulate B<configure --srcdir>. Tom Tromey
1245 tromey@creche.cygnus.com has submitted some patches to
1246 the dist-users mailing list along these lines. They have been folded
1247 back into the main distribution, but various parts of the perl
1248 Configure/build/install process still assume src='.'.
1250 =item Hint file fixes
1252 Various hint files work around Configure problems. We ought to fix
1253 Configure so that most of them aren't needed.
1255 =item Hint file information
1257 Some of the hint file information (particularly dynamic loading stuff)
1258 ought to be fed back into the main metaconfig distribution.
1262 =head2 Probably good ideas waiting for round tuits
1266 =item GNU configure --options
1268 I've received sensible suggestions for --exec_prefix and other
1269 GNU configure --options. It's not always obvious exactly what is
1270 intended, but this merits investigation.
1274 Currently, B<make clean> isn't all that useful, though
1275 B<make realclean> and B<make distclean> are. This needs a bit of
1276 thought and documentation before it gets cleaned up.
1278 =item Try gcc if cc fails
1280 Currently, we just give up.
1282 =item bypassing safe*alloc wrappers
1284 On some systems, it may be safe to call the system malloc directly
1285 without going through the util.c safe* layers. (Such systems would
1286 accept free(0), for example.) This might be a time-saver for systems
1287 that already have a good malloc. (Recent Linux libc's apparently have
1288 a nice malloc that is well-tuned for the system.)
1292 =head2 Vague possibilities
1298 Get some of the Macintosh stuff folded back into the main distribution.
1300 =item gconvert replacement
1302 Maybe include a replacement function that doesn't lose data in rare
1303 cases of coercion between string and numerical values.
1305 =item Improve makedepend
1307 The current makedepend process is clunky and annoyingly slow, but it
1308 works for most folks. Alas, it assumes that there is a filename
1309 $firstmakefile that the B<make> command will try to use before it uses
1310 F<Makefile>. Such may not be the case for all B<make> commands,
1311 particularly those on non-Unix systems.
1313 Probably some variant of the BSD F<.depend> file will be useful.
1314 We ought to check how other packages do this, if they do it at all.
1315 We could probably pre-generate the dependencies (with the exception of
1316 malloc.o, which could probably be determined at F<Makefile.SH>
1319 =item GNU Makefile standard targets
1321 GNU software generally has standardized Makefile targets. Unless we
1322 have good reason to do otherwise, I see no reason not to support them.
1326 Somehow, straighten out, document, and implement lockf(), flock(),
1327 and/or fcntl() file locking. It's a mess.
1333 Original author: Andy Dougherty doughera@lafcol.lafayette.edu .
1334 Additions by Chip Salzenberg chip@perl.com and
1335 Tim Bunce Tim.Bunce@ig.co.uk .
1337 All opinions expressed herein are those of the authorZ<>(s).
1339 =head1 LAST MODIFIED
1341 $Id: pumpkin.pod,v 1.23 2000/01/13 19:45:13 doughera Released $