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
12 considerations involved in patching 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 Perl version numbers are floating point numbers, such as 5.004.
51 (Observations about the imprecision of floating point numbers for
52 representing reality probably have more relevance than you might
53 imagine :-) The major version number is 5 and the '004' is the
54 patchlevel. (Questions such as whether or not '004' is really a minor
55 version number can safely be ignored.:)
57 The version number is available as the magic variable $],
58 and can be used in comparisons, e.g.
60 print "You've got an old perl\n" if $] < 5.002;
62 You can also require particular version (or later) with
66 At some point in the future, we may need to decide what to call the
67 next big revision. In the .package file used by metaconfig to
68 generate Configure, there are two variables that might be relevant:
69 $baserev=5.0 and $package=perl5. At various times, I have suggested
70 we might change them to $baserev=5.1 and $package=perl5.1 if want
71 to signify a fairly major update. Or, we might want to jump to perl6.
72 Let's worry about that problem when we get there.
76 In addition, there may be "developer" sub-versions available. These
77 are not official releases. They may contain unstable experimental
78 features, and are subject to rapid change. Such developer
79 sub-versions are numbered with sub-version numbers. For example,
80 version 5.003_04 is the 4'th developer version built on top of
81 5.003. It might include the _01, _02, and _03 changes, but it
82 also might not. Sub-versions are allowed to be subversive. (But see
83 the next section for recent changes.)
85 These sub-versions can also be used as floating point numbers, so
86 you can do things such as
88 print "You've got an unstable perl\n" if $] == 5.00303;
90 You can also require particular version (or later) with
92 use 5.003_03; # the "_" is optional
94 Sub-versions produced by the members of perl5-porters are usually
95 available on CPAN in the F<src/5.0/unsupported> directory.
97 =head2 Maintenance and Development Subversions
99 As an experiment, starting with version 5.004, subversions _01 through
100 _49 will be reserved for bug-fix maintenance releases, and subversions
101 _50 through _99 will be available for unstable development versions.
103 The separate bug-fix track is being established to allow us an easy
104 way to distribute important bug fixes without waiting for the
105 developers to untangle all the other problems in the current
108 Trial releases of bug-fix maintenance releases are announced on
109 perl5-porters. Trial releases use the new subversion number (to avoid
110 testers installing it over the previous release) and include a 'local
111 patch' entry in patchlevel.h.
113 Watch for announcements of maintenance subversions in
114 comp.lang.perl.announce.
116 =head2 Why such a complicated scheme?
118 Two reasons, really. At least.
120 First, we need some way to identify and release collections of patches
121 that are known to have new features that need testing and exploration. The
122 subversion scheme does that nicely while fitting into the
125 Second, since most of the folks who help maintain perl do so on a
126 free-time voluntary basis, perl development does not proceed at a
127 precise pace, though it always seems to be moving ahead quickly.
128 We needed some way to pass around the "patch pumpkin" to allow
129 different people chances to work on different aspects of the
130 distribution without getting in each other's way. It wouldn't be
131 constructive to have multiple people working on incompatible
132 implementations of the same idea. Instead what was needed was
133 some kind of "baton" or "token" to pass around so everyone knew
136 =head2 Why is it called the patch pumpkin?
138 Chip Salzenberg gets credit for that, with a nod to his cow orker,
139 David Croy. We had passed around various names (baton, token, hot
140 potato) but none caught on. Then, Chip asked:
144 Who has the patch pumpkin?
146 To explain: David Croy once told me once that at a previous job,
147 there was one tape drive and multiple systems that used it for backups.
148 But instead of some high-tech exclusion software, they used a low-tech
149 method to prevent multiple simultaneous backups: a stuffed pumpkin.
150 No one was allowed to make backups unless they had the "backup pumpkin".
156 =head1 Philosophical Issues in Patching Perl
158 There are no absolute rules, but there are some general guidelines I
159 have tried to follow as I apply patches to the perl sources.
160 (This section is still under construction.)
162 =head2 Solve problems as generally as possible
164 Never implement a specific restricted solution to a problem when you
165 can solve the same problem in a more general, flexible way.
167 For example, for dynamic loading to work on some SVR4 systems, we had
168 to build a shared libperl.so library. In order to build "FAT" binaries
169 on NeXT 4.0 systems, we had to build a special libperl library. Rather
170 than continuing to build a contorted nest of special cases, I
171 generalized the process of building libperl so that NeXT and SVR4 users
172 could still get their work done, but others could build a shared
173 libperl if they wanted to as well.
175 =head2 Seek consensus on major changes
177 If you are making big changes, don't do it in secret. Discuss the
178 ideas in advance on perl5-porters.
180 =head2 Keep the documentation up-to-date
182 If your changes may affect how users use perl, then check to be sure
183 that the documentation is in sync with your changes. Be sure to
184 check all the files F<pod/*.pod> and also the F<INSTALL> document.
186 Consider writing the appropriate documentation first and then
187 implementing your change to correspond to the documentation.
189 =head2 Avoid machine-specific #ifdef's
191 To the extent reasonable, try to avoid machine-specific #ifdef's in
192 the sources. Instead, use feature-specific #ifdef's. The reason is
193 that the machine-specific #ifdef's may not be valid across major
194 releases of the operating system. Further, the feature-specific tests
195 may help out folks on another platform who have the same problem.
197 =head2 Allow for lots of testing
199 We should never release a main version without testing it as a
202 =head2 Test popular applications and modules.
204 We should never release a main version without testing whether or not
205 it breaks various popular modules and applications. A partial list of
206 such things would include majordomo, metaconfig, apache, Tk, CGI,
207 libnet, and libwww, to name just a few. Of course it's quite possible
208 that some of those things will be just plain broken and need to be fixed,
209 but, in general, we ought to try to avoid breaking widely-installed
212 =head2 Automate generation of derivative files
214 The F<embed.h>, F<keywords.h>, F<opcode.h>, and F<perltoc.pod> files
215 are all automatically generated by perl scripts. In general, don't
216 patch these directly; patch the data files instead.
218 F<Configure> and F<config_h.SH> are also automatically generated by
219 B<metaconfig>. In general, you should patch the metaconfig units
220 instead of patching these files directly. However, very minor changes to
221 F<Configure> may be made in between major sync-ups with the metaconfig
222 units, which tends to be complicated operations. But be careful, this
223 can quickly spiral out of control. Running metaconfig is not really
226 =head1 How to Make a Distribution
228 There really ought to be a 'make dist' target, but there isn't.
229 The 'dist' suite of tools also contains a number of tools that I haven't
230 learned how to use yet. Some of them may make this all a bit easier.
232 Here are the steps I go through to prepare a patch & distribution.
234 Lots of it could doubtless be automated but isn't. The Porting/makerel
235 (make release) perl script does now help automate some parts of it.
237 =head2 Announce your intentions
239 First, you should volunteer out loud to take the patch pumpkin. It's
240 generally counter-productive to have multiple people working in secret
243 At the same time, announce what you plan to do with the patch pumpkin,
244 to allow folks a chance to object or suggest alternatives, or do it for
245 you. Naturally, the patch pumpkin holder ought to incorporate various
246 bug fixes and documentation improvements that are posted while he or
247 she has the pumpkin, but there might also be larger issues at stake.
249 One of the precepts of the subversion idea is that we shouldn't give
250 the patch pumpkin to anyone unless we have some idea what he or she
251 is going to do with it.
253 =head2 refresh pod/perltoc.pod
255 Presumably, you have done a full C<make> in your working source
256 directory. Before you C<make spotless> (if you do), and if you have
257 changed any documentation in any module or pod file, change to the
258 F<pod> directory and run C<make toc>.
260 =head2 run installhtml to check the validity of the pod files
262 =head2 update patchlevel.h
264 Don't be shy about using the subversion number, even for a relatively
265 modest patch. We've never even come close to using all 99 subversions,
266 and it's better to have a distinctive number for your patch. If you
267 need feedback on your patch, go ahead and issue it and promise to
268 incorporate that feedback quickly (e.g. within 1 week) and send out a
271 =head2 run metaconfig
273 If you need to make changes to Configure or config_h.SH, it may be best to
274 change the appropriate metaconfig units instead, and regenerate Configure.
278 will regenerate Configure and config_h.SH. More information on
279 obtaining and running metaconfig is in the F<U/README> file that comes
280 with Perl's metaconfig units. Perl's metaconfig units should be
281 available the same place you found this file. On CPAN, look under my
282 directory F<authors/id/ANDYD/> for a file such as F<5.003_07-02.U.tar.gz>.
283 That file should be unpacked in your main perl source directory. It
284 contains the files needed to run B<metaconfig> to reproduce Perl's
285 Configure script. (Those units are for 5.003_07. There have been
286 changes since then; please contact me if you want more recent
287 versions, and I will try to point you in the right direction.)
289 Alternatively, do consider if the F<*ish.h> files might be a better
290 place for your changes.
294 Make sure the MANIFEST is up-to-date. You can use dist's B<manicheck>
295 program for this. You can also use
297 perl -w -MExtUtils::Manifest=fullcheck -e fullcheck
299 Both commands will also list extra files in the directory that are not
302 The MANIFEST is normally sorted.
304 If you are using metaconfig to regenerate Configure, then you should note
305 that metaconfig actually uses MANIFEST.new, so you want to be sure
306 MANIFEST.new is up-to-date too. I haven't found the MANIFEST/MANIFEST.new
307 distinction particularly useful, but that's probably because I still haven't
308 learned how to use the full suite of tools in the dist distribution.
310 =head2 Check permissions
312 All the tests in the t/ directory ought to be executable. The
313 main makefile used to do a 'chmod t/*/*.t', but that resulted in
314 a self-modifying distribution--something some users would strongly
315 prefer to avoid. Probably, the F<t/TEST> script should check for this
316 and do the chmod if needed, but it doesn't currently.
318 In all, the following files should probably be executable:
333 vms/ext/Stdio/test.pl
337 Other things ought to be readable, at least :-).
339 Probably, the permissions for the files could be encoded in MANIFEST
340 somehow, but I'm reluctant to change MANIFEST itself because that
341 could break old scripts that use MANIFEST.
343 I seem to recall that some SVR3 systems kept some sort of file that listed
344 permissions for system files; something like that might be appropriate.
348 This will build a config.sh and config.h. You can skip this if you haven't
349 changed Configure or config_h.SH at all. I use the following command
351 sh Configure -Dprefix=/opt/perl -Doptimize=-O -Dusethreads \
353 -Dcf_email='yourname@yourhost.yourplace.com' \
354 -Dperladmin='yourname@yourhost.yourplace.com' \
355 -Dmydomain='.yourplace.com' \
356 -Dmyhostname='yourhost' \
359 =head2 Update Porting/config.sh and Porting/config_H
362 This section needs revision. We're currently working on easing
363 the task of keeping the vms, win32, and plan9 config.sh info
364 up-to-date. The plan is to use keep up-to-date 'canned' config.sh
365 files in the appropriate subdirectories and then generate 'canned'
366 config.h files for vms, win32, etc. from the generic config.sh file.
367 This is to ease maintenance. When Configure gets updated, the parts
368 sometimes get scrambled around, and the changes in config_H can
369 sometimes be very hard to follow. config.sh, on the other hand, can
370 safely be sorted, so it's easy to track (typically very small) changes
371 to config.sh and then propoagate them to a canned 'config.h' by any
372 number of means, including a perl script in win32/ or carrying
373 config.sh and config_h.SH to a Unix system and running sh
377 The Porting/config.sh and Porting/config_H files are provided to
378 help those folks who can't run Configure. It is important to keep
379 them up-to-date. If you have changed config_h.SH, those changes must
380 be reflected in config_H as well. (The name config_H was chosen to
381 distinguish the file from config.h even on case-insensitive file systems.)
382 Simply edit the existing config_H file; keep the first few explanatory
383 lines and then copy your new config.h below.
385 It may also be necessary to update vms/config.vms and
386 plan9/config.plan9, though you should be quite careful in doing so if
387 you are not familiar with those systems. You might want to issue your
388 patch with a promise to quickly issue a follow-up that handles those
391 =head2 make run_byacc
393 If you have byacc-1.8.2 (available from CPAN), and if there have been
394 changes to F<perly.y>, you can regenerate the F<perly.c> file. The
395 run_byacc makefile target does this by running byacc and then applying
396 some patches so that byacc dynamically allocates space, rather than
397 having fixed limits. This patch is handled by the F<perly.fixer>
398 script. Depending on the nature of the changes to F<perly.y>, you may
399 or may not have to hand-edit the patch to apply correctly. If you do,
400 you should include the edited patch in the new distribution. If you
401 have byacc-1.9, the patch won't apply cleanly. Changes to the printf
402 output statements mean the patch won't apply cleanly. Long ago I
403 started to fix F<perly.fixer> to detect this, but I never completed the
406 Some additional notes from Larry on this:
408 Don't forget to regenerate perly.c.diff.
412 patch perly.c <perly.c.diff
413 # manually apply any failed hunks
414 diff -c2 perly.c.orig perly.c >perly.c.diff
416 One chunk of lines that often fails begins with
420 and ends one line before
422 #define YYERRCODE 256
424 This only happens when you add or remove a token type. I suppose this
425 could be automated, but it doesn't happen very often nowadays.
429 =head2 make regen_headers
431 The F<embed.h>, F<keywords.h>, and F<opcode.h> files are all automatically
432 generated by perl scripts. Since the user isn't guaranteed to have a
433 working perl, we can't require the user to generate them. Hence you have
434 to, if you're making a distribution.
436 I used to include rules like the following in the makefile:
438 # The following three header files are generated automatically
439 # The correct versions should be already supplied with the perl kit,
440 # in case you don't have perl or 'sh' available.
441 # The - is to ignore error return codes in case you have the source
442 # installed read-only or you don't have perl yet.
443 keywords.h: keywords.pl
444 @echo "Don't worry if this fails."
448 However, I got B<lots> of mail consisting of people worrying because the
449 command failed. I eventually decided that I would save myself time
450 and effort by manually running C<make regen_headers> myself rather
451 than answering all the questions and complaints about the failing
454 =head2 global.sym, interp.sym and perlio.sym
456 Make sure these files are up-to-date. Read the comments in these
457 files and in perl_exp.SH to see what to do.
459 =head2 Binary compatibility
461 If you do change F<global.sym> or F<interp.sym>, think carefully about
462 what you are doing. To the extent reasonable, we'd like to maintain
463 souce and binary compatibility with older releases of perl. That way,
464 extensions built under one version of perl will continue to work with
465 new versions of perl.
467 Of course, some incompatible changes may well be necessary. I'm just
468 suggesting that we not make any such changes without thinking carefully
469 about them first. If possible, we should provide
470 backwards-compatibility stubs. There's a lot of XS code out there.
471 Let's not force people to keep changing it.
475 Be sure to update the F<Changes> file. Try to include both an overall
476 summary as well as detailed descriptions of the changes. Your
477 audience will include other developers and users, so describe
478 user-visible changes (if any) in terms they will understand, not in
479 code like "initialize foo variable in bar function".
481 There are differing opinions on whether the detailed descriptions
482 ought to go in the Changes file or whether they ought to be available
483 separately in the patch file (or both). There is no disagreement that
484 detailed descriptions ought to be easily available somewhere.
488 The F<Todo> file contains a roughly-catgorized unordered list of
489 aspects of Perl that could use enhancement, features that could be
490 added, areas that could be cleaned up, and so on. During your term as
491 pumpkin-holder, you will probably address some of these issues, and
492 perhaps identify others which, while you decide not to address them
493 this time around, may be tackled in the future. Update the file
494 reflect the situation as it stands when you hand over the pumpkin.
496 You might like, early in your pumpkin-holding career, to see if you
497 can find champions for partiticular issues on the to-do list: an issue
498 owned is an issue more likely to be resolved.
500 There are also some more porting-specific L<Todo> items later in this
503 =head2 OS/2-specific updates
505 In the os2 directory is F<diff.configure>, a set of OS/2-specific
506 diffs against B<Configure>. If you make changes to Configure, you may
507 want to consider regenerating this diff file to save trouble for the
510 You can also consider the OS/2 diffs as reminders of portability
511 things that need to be fixed in Configure.
513 =head2 VMS-specific updates
515 If you have changed F<perly.y>, then you may want to update
516 F<vms/perly_{h,c}.vms> by running C<perl vms/vms_yfix.pl>.
518 The Perl version number appears in several places under F<vms>.
519 It is courteous to update these versions. For example, if you are
520 making 5.004_42, replace "5.00441" with "5.00442".
522 =head2 Making the new distribution
524 Suppose, for example, that you want to make version 5.004_08. Then you can
525 do something like the following
527 mkdir ../perl5.004_08
528 awk '{print $1}' MANIFEST | cpio -pdm ../perl5.004_08
530 tar cf perl5.004_08.tar perl5.004_08
531 gzip --best perl5.004_08.tar
533 These steps, with extra checks, are automated by the Porting/makerel
536 =head2 Making a new patch
538 I find the F<makepatch> utility quite handy for making patches.
539 You can obtain it from any CPAN archive under
540 http://www.perl.com/CPAN/authors/Johan_Vromans/ . There are a couple
541 of differences between my version and the standard one. I have mine do
544 # Print a reassuring "End of Patch" note so people won't
545 # wonder if their mailer truncated patches.
546 print "\n\nEnd of Patch.\n";
548 at the end. That's because I used to get questions from people asking
549 if their mail was truncated.
551 It also writes Index: lines which include the new directory prefix
552 (change Index: print, approx line 294 or 310 depending on the version,
553 to read: print PATCH ("Index: $newdir$new\n");). That helps patches
554 work with more POSIX conformant patch programs.
556 Here's how I generate a new patch. I'll use the hypothetical
557 5.004_07 to 5.004_08 patch as an example.
559 # unpack perl5.004_07/
560 gzip -d -c perl5.004_07.tar.gz | tar -xof -
561 # unpack perl5.004_08/
562 gzip -d -c perl5.004_08.tar.gz | tar -xof -
563 makepatch perl5.004_07 perl5.004_08 > perl5.004_08.pat
565 Makepatch will automatically generate appropriate B<rm> commands to remove
566 deleted files. Unfortunately, it will not correctly set permissions
567 for newly created files, so you may have to do so manually. For example,
568 patch 5.003_04 created a new test F<t/op/gv.t> which needs to be executable,
569 so at the top of the patch, I inserted the following lines:
575 Now, of course, my patch is now wrong because makepatch didn't know I
576 was going to do that command, and it patched against /dev/null.
578 So, what I do is sort out all such shell commands that need to be in the
579 patch (including possible mv-ing of files, if needed) and put that in the
580 shell commands at the top of the patch. Next, I delete all the patch parts
581 of perl5.004_08.pat, leaving just the shell commands. Then, I do the
585 sh ../perl5.004_08.pat
587 makepatch perl5.004_07 perl5.004_08 >> perl5.004_08.pat
589 (Note the append to preserve my shell commands.)
590 Now, my patch will line up with what the end users are going to do.
592 =head2 Testing your patch
594 It seems obvious, but be sure to test your patch. That is, verify that
595 it produces exactly the same thing as your full distribution.
598 gzip -d -c perl5.004_07.tar.gz | tar -xf -
600 sh ../perl5.004_08.pat
601 patch -p1 -N < ../perl5.004_08.pat
603 gdiff -r perl5.004_07 perl5.004_08
605 where B<gdiff> is GNU diff. Other diff's may also do recursive checking.
609 Again, it's obvious, but you should test your new version as widely as you
610 can. You can be sure you'll hear about it quickly if your version doesn't
611 work on both ANSI and pre-ANSI compilers, and on common systems such as
612 SunOS 4.1.[34], Solaris, and Linux.
614 If your changes include conditional code, try to test the different
615 branches as thoroughly as you can. For example, if your system
616 supports dynamic loading, you can also test static loading with
620 You can also hand-tweak your config.h to try out different #ifdef
623 =head1 Common Gotcha's
629 The '#elif' preprocessor directive is not understood on all systems.
630 Specifically, I know that Pyramids don't understand it. Thus instead of the
641 You have to do the more Byzantine
653 Incidentally, whitespace between the leading '#' and the preprocessor
654 command is not guaranteed, but is very portable and you may use it freely.
655 I think it makes things a bit more readable, especially once things get
656 rather deeply nested. I also think that things should almost never get
657 too deeply nested, so it ought to be a moot point :-)
659 =item Probably Prefer POSIX
661 It's often the case that you'll need to choose whether to do
662 something the BSD-ish way or the POSIX-ish way. It's usually not
663 a big problem when the two systems use different names for similar
664 functions, such as memcmp() and bcmp(). The perl.h header file
665 handles these by appropriate #defines, selecting the POSIX mem*()
666 functions if available, but falling back on the b*() functions, if
669 More serious is the case where some brilliant person decided to
670 use the same function name but give it a different meaning or
671 calling sequence :-). getpgrp() and setpgrp() come to mind.
672 These are a real problem on systems that aim for conformance to
673 one standard (e.g. POSIX), but still try to support the other way
674 of doing things (e.g. BSD). My general advice (still not really
675 implemented in the source) is to do something like the following.
676 Suppose there are two alternative versions, fooPOSIX() and
680 /* use fooPOSIX(); */
683 /* try to emulate fooPOSIX() with fooBSD();
684 perhaps with the following: */
685 # define fooPOSIX fooBSD
687 # /* Uh, oh. We have to supply our own. */
688 # define fooPOSIX Perl_fooPOSIX
692 =item Think positively
694 If you need to add an #ifdef test, it is usually easier to follow if you
695 think positively, e.g.
697 #ifdef HAS_NEATO_FEATURE
698 /* use neato feature */
700 /* use some fallback mechanism */
703 rather than the more impenetrable
705 #ifndef MISSING_NEATO_FEATURE
706 /* Not missing it, so we must have it, so use it */
708 /* Are missing it, so fall back on something else. */
711 Of course for this toy example, there's not much difference. But when
712 the #ifdef's start spanning a couple of screen fulls, and the #else's
713 are marked something like
715 #else /* !MISSING_NEATO_FEATURE */
717 I find it easy to get lost.
719 =item Providing Missing Functions -- Problem
721 Not all systems have all the neat functions you might want or need, so
722 you might decide to be helpful and provide an emulation. This is
723 sound in theory and very kind of you, but please be careful about what
724 you name the function. Let me use the C<pause()> function as an
727 Perl5.003 has the following in F<perl.h>
730 #define pause() sleep((32767<<16)+32767)
733 Configure sets HAS_PAUSE if the system has the pause() function, so
734 this #define only kicks in if the pause() function is missing.
737 Unfortunately, some systems apparently have a prototype for pause()
738 in F<unistd.h>, but don't actually have the function in the library.
739 (Or maybe they do have it in a library we're not using.)
741 Thus, the compiler sees something like
743 extern int pause(void);
745 #define pause() sleep((32767<<16)+32767)
747 and dies with an error message. (Some compilers don't mind this;
748 others apparently do.)
750 To work around this, 5.003_03 and later have the following in perl.h:
752 /* Some unistd.h's give a prototype for pause() even though
753 HAS_PAUSE ends up undefined. This causes the #define
754 below to be rejected by the compiler. Sigh.
759 # define Pause() sleep((32767<<16)+32767)
764 The curious reader may wonder why I didn't do the following in
770 sleep((32767<<16)+32767);
774 That is, since the function is missing, just provide it.
775 Then things would probably be been alright, it would seem.
777 Well, almost. It could be made to work. The problem arises from the
778 conflicting needs of dynamic loading and namespace protection.
780 For dynamic loading to work on AIX (and VMS) we need to provide a list
781 of symbols to be exported. This is done by the script F<perl_exp.SH>,
782 which reads F<global.sym> and F<interp.sym>. Thus, the C<pause>
783 symbol would have to be added to F<global.sym> So far, so good.
785 On the other hand, one of the goals of Perl5 is to make it easy to
786 either extend or embed perl and link it with other libraries. This
787 means we have to be careful to keep the visible namespace "clean".
788 That is, we don't want perl's global variables to conflict with
789 those in the other application library. Although this work is still
790 in progress, the way it is currently done is via the F<embed.h> file.
791 This file is built from the F<global.sym> and F<interp.sym> files,
792 since those files already list the globally visible symbols. If we
793 had added C<pause> to global.sym, then F<embed.h> would contain the
796 #define pause Perl_pause
798 and calls to C<pause> in the perl sources would now point to
799 C<Perl_pause>. Now, when B<ld> is run to build the F<perl> executable,
800 it will go looking for C<perl_pause>, which probably won't exist in any
801 of the standard libraries. Thus the build of perl will fail.
803 Those systems where C<HAS_PAUSE> is not defined would be ok, however,
804 since they would get a C<Perl_pause> function in util.c. The rest of
805 the world would be in trouble.
807 And yes, this scenario has happened. On SCO, the function C<chsize>
808 is available. (I think it's in F<-lx>, the Xenix compatibility
809 library.) Since the perl4 days (and possibly before), Perl has
810 included a C<chsize> function that gets called something akin to
813 I32 chsize(fd, length)
819 #define chsize Perl_chsize
821 to F<embed.h>, the compile started failing on SCO systems.
823 The "fix" is to give the function a different name. The one
824 implemented in 5.003_05 isn't optimal, but here's what was done:
827 # ifdef my_chsize /* Probably #defined to Perl_my_chsize in embed.h */
830 # define my_chsize chsize
833 My explanatory comment in patch 5.003_05 said:
835 Undef and then re-define my_chsize from Perl_my_chsize to
836 just plain chsize if this system HAS_CHSIZE. This probably only
837 applies to SCO. This shows the perils of having internal
838 functions with the same name as external library functions :-).
840 Now, we can safely put C<my_chsize> in F<global.sym>, export it, and
841 hide it with F<embed.h>.
843 To be consistent with what I did for C<pause>, I probably should have
844 called the new function C<Chsize>, rather than C<my_chsize>.
845 However, the perl sources are quite inconsistent on this (Consider
846 New, Mymalloc, and Myremalloc, to name just a few.)
848 There is a problem with this fix, however, in that C<Perl_chsize>
849 was available as a F<libperl.a> library function in 5.003, but it
850 isn't available any more (as of 5.003_07). This means that we've
851 broken binary compatibility. This is not good.
853 =item Providing missing functions -- some ideas
855 We currently don't have a standard way of handling such missing
856 function names. Right now, I'm effectively thinking aloud about a
857 solution. Some day, I'll try to formally propose a solution.
859 Part of the problem is that we want to have some functions listed as
860 exported but not have their names mangled by embed.h or possibly
861 conflict with names in standard system headers. We actually already
862 have such a list at the end of F<perl_exp.SH> (though that list is
865 # extra globals not included above.
866 cat <<END >> perl.exp
890 This still needs much thought, but I'm inclined to think that one
891 possible solution is to prefix all such functions with C<perl_> in the
892 source and list them along with the other C<perl_*> functions in
895 Thus, for C<chsize>, we'd do something like the following:
899 # define perl_chsize chsize
902 then in some file (e.g. F<util.c> or F<doio.c>) do
905 I32 perl_chsize(fd, length)
906 /* implement the function here . . . */
909 Alternatively, we could just always use C<chsize> everywhere and move
910 C<chsize> from F<global.sym> to the end of F<perl_exp.SH>. That would
911 probably be fine as long as our C<chsize> function agreed with all the
912 C<chsize> function prototypes in the various systems we'll be using.
913 As long as the prototypes in actual use don't vary that much, this is
914 probably a good alternative. (As a counter-example, note how Configure
915 and perl have to go through hoops to find and use get Malloc_t and
916 Free_t for C<malloc> and C<free>.)
918 At the moment, this latter option is what I tend to prefer.
920 =item All the world's a VAX
922 Sorry, showing my age:-). Still, all the world is not BSD 4.[34],
923 SVR4, or POSIX. Be aware that SVR3-derived systems are still quite
924 common (do you have any idea how many systems run SCO?) If you don't
925 have a bunch of v7 manuals handy, the metaconfig units (by default
926 installed in F</usr/local/lib/dist/U>) are a good resource to look at
931 =head1 Miscellaneous Topics
935 Why does perl use a metaconfig-generated Configure script instead of an
936 autoconf-generated configure script?
938 Metaconfig and autoconf are two tools with very similar purposes.
939 Metaconfig is actually the older of the two, and was originally written
940 by Larry Wall, while autoconf is probably now used in a wider variety of
941 packages. The autoconf info file discusses the history of autoconf and
942 how it came to be. The curious reader is referred there for further
945 Overall, both tools are quite good, I think, and the choice of which one
946 to use could be argued either way. In March, 1994, when I was just
947 starting to work on Configure support for Perl5, I considered both
948 autoconf and metaconfig, and eventually decided to use metaconfig for the
953 =item Compatibility with Perl4
955 Perl4 used metaconfig, so many of the #ifdef's were already set up for
956 metaconfig. Of course metaconfig had evolved some since Perl4's days,
957 but not so much that it posed any serious problems.
959 =item Metaconfig worked for me
961 My system at the time was Interactive 2.2, a SVR3.2/386 derivative that
962 also had some POSIX support. Metaconfig-generated Configure scripts
963 worked fine for me on that system. On the other hand, autoconf-generated
964 scripts usually didn't. (They did come quite close, though, in some
965 cases.) At the time, I actually fetched a large number of GNU packages
966 and checked. Not a single one configured and compiled correctly
967 out-of-the-box with the system's cc compiler.
969 =item Configure can be interactive
971 With both autoconf and metaconfig, if the script works, everything is
972 fine. However, one of my main problems with autoconf-generated scripts
973 was that if it guessed wrong about something, it could be B<very> hard to
974 go back and fix it. For example, autoconf always insisted on passing the
975 -Xp flag to cc (to turn on POSIX behavior), even when that wasn't what I
976 wanted or needed for that package. There was no way short of editing the
977 configure script to turn this off. You couldn't just edit the resulting
978 Makefile at the end because the -Xp flag influenced a number of other
981 Metaconfig's Configure scripts, on the other hand, can be interactive.
982 Thus if Configure is guessing things incorrectly, you can go back and fix
983 them. This isn't as important now as it was when we were actively
984 developing Configure support for new features such as dynamic loading,
985 but it's still useful occasionally.
989 At the time, autoconf-generated scripts were covered under the GNU Public
990 License, and hence weren't suitable for inclusion with Perl, which has a
991 different licensing policy. (Autoconf's licensing has since changed.)
995 Metaconfig builds up Configure from a collection of discrete pieces
996 called "units". You can override the standard behavior by supplying your
997 own unit. With autoconf, you have to patch the standard files instead.
998 I find the metaconfig "unit" method easier to work with. Others
999 may find metaconfig's units clumsy to work with.
1003 =head2 @INC search order
1005 By default, the list of perl library directories in @INC is the
1013 Specifically, on my Solaris/x86 system, I run
1014 B<sh Configure -Dprefix=/opt/perl> and I have the following
1017 /opt/perl/lib/i86pc-solaris/5.00307
1019 /opt/perl/lib/site_perl/i86pc-solaris
1020 /opt/perl/lib/site_perl
1022 That is, perl's directories come first, followed by the site-specific
1025 The site libraries come second to support the usage of extensions
1026 across perl versions. Read the relevant section in F<INSTALL> for
1027 more information. If we ever make $sitearch version-specific, this
1028 topic could be revisited.
1030 =head2 Why isn't there a directory to override Perl's library?
1032 Mainly because no one's gotten around to making one. Note that
1033 "making one" involves changing perl.c, Configure, config_h.SH (and
1034 associated files, see above), and I<documenting> it all in the
1037 Apparently, most folks who want to override one of the standard library
1038 files simply do it by overwriting the standard library files.
1042 In the perl.c sources, you'll find an undocumented APPLLIB_EXP
1043 variable, sort of like PRIVLIB_EXP and ARCHLIB_EXP (which are
1044 documented in config_h.SH). Here's what APPLLIB_EXP is for, from
1045 a mail message from Larry:
1047 The main intent of APPLLIB_EXP is for folks who want to send out a
1048 version of Perl embedded in their product. They would set the symbol
1049 to be the name of the library containing the files needed to run or to
1050 support their particular application. This works at the "override"
1051 level to make sure they get their own versions of any library code that
1052 they absolutely must have configuration control over.
1054 As such, I don't see any conflict with a sysadmin using it for a
1055 override-ish sort of thing, when installing a generic Perl. It should
1056 probably have been named something to do with overriding though. Since
1057 it's undocumented we could still change it... :-)
1059 Given that it's already there, you can use it to override
1060 distribution modules. If you do
1062 sh Configure -Dccflags='-DAPPLLIB_EXP=/my/override'
1064 then perl.c will put /my/override ahead of ARCHLIB and PRIVLIB.
1066 =head2 Shared libperl.so location
1068 Why isn't the shared libperl.so installed in /usr/lib/ along
1069 with "all the other" shared libraries? Instead, it is installed
1070 in $archlib, which is typically something like
1072 /usr/local/lib/perl5/archname/5.00404
1074 and is architecture- and version-specific.
1076 The basic reason why a shared libperl.so gets put in $archlib is so that
1077 you can have more than one version of perl on the system at the same time,
1078 and have each refer to its own libperl.so.
1080 Three examples might help. All of these work now; none would work if you
1081 put libperl.so in /usr/lib.
1087 Suppose you want to have both threaded and non-threaded perl versions
1088 around. Configure will name both perl libraries "libperl.so" (so that
1089 you can link to them with -lperl). The perl binaries tell them apart
1090 by having looking in the appropriate $archlib directories.
1094 Suppose you have perl5.004_04 installed and you want to try to compile
1095 it again, perhaps with different options or after applying a patch.
1096 If you already have libperl.so installed in /usr/lib/, then it may be
1097 either difficult or impossible to get ld.so to find the new libperl.so
1098 that you're trying to build. If, instead, libperl.so is tucked away in
1099 $archlib, then you can always just change $archlib in the current perl
1100 you're trying to build so that ld.so won't find your old libperl.so.
1101 (The INSTALL file suggests you do this when building a debugging perl.)
1105 The shared perl library is not a "well-behaved" shared library with
1106 proper major and minor version numbers, so you can't necessarily
1107 have perl5.004_04 and perl5.004_05 installed simultaneously. Suppose
1108 perl5.004_04 were to install /usr/lib/libperl.so.4.4, and perl5.004_05
1109 were to install /usr/lib/libperl.so.4.5. Now, when you try to run
1110 perl5.004_04, ld.so might try to load libperl.so.4.5, since it has
1111 the right "major version" number. If this works at all, it almost
1112 certainly defeats the reason for keeping perl5.004_04 around. Worse,
1113 with development subversions, you certaily can't guarantee that
1114 libperl.so.4.4 and libperl.so.4.55 will be compatible.
1116 Anyway, all this leads to quite obscure failures that are sure to drive
1117 casual users crazy. Even experienced users will get confused :-). Upon
1118 reflection, I'd say leave libperl.so in $archlib.
1122 =head1 Upload Your Work to CPAN
1124 You can upload your work to CPAN if you have a CPAN id. Check out
1125 http://www.perl.com/CPAN/modules/04pause.html for information on
1126 _PAUSE_, the Perl Author's Upload Server.
1128 I typically upload both the patch file, e.g. F<perl5.004_08.pat.gz>
1129 and the full tar file, e.g. F<perl5.004_08.tar.gz>.
1131 If you want your patch to appear in the F<src/5.0/unsupported>
1132 directory on CPAN, send e-mail to the CPAN master librarian. (Check
1133 out http://www.perl.com/CPAN/CPAN.html ).
1135 =head1 Help Save the World
1137 You should definitely announce your patch on the perl5-porters list.
1138 You should also consider announcing your patch on
1139 comp.lang.perl.announce, though you should make it quite clear that a
1140 subversion is not a production release, and be prepared to deal with
1141 people who will not read your disclaimer.
1145 Here, in no particular order, are some Configure and build-related
1146 items that merit consideration. This list isn't exhaustive, it's just
1147 what I came up with off the top of my head.
1149 =head2 Good ideas waiting for round tuits
1155 I think we ought to support
1157 Configure -Dinstallprefix=/blah/blah
1159 Currently, we support B<-Dprefix=/blah/blah>, but the changing the install
1160 location has to be handled by something like the F<config.over> trick
1161 described in F<INSTALL>. AFS users also are treated specially.
1162 We should probably duplicate the metaconfig prefix stuff for an
1165 =item Configure -Dsrc=/blah/blah
1167 We should be able to emulate B<configure --srcdir>. Tom Tromey
1168 tromey@creche.cygnus.com has submitted some patches to
1169 the dist-users mailing list along these lines. They have been folded
1170 back into the main distribution, but various parts of the perl
1171 Configure/build/install process still assume src='.'.
1173 =item Hint file fixes
1175 Various hint files work around Configure problems. We ought to fix
1176 Configure so that most of them aren't needed.
1178 =item Hint file information
1180 Some of the hint file information (particularly dynamic loading stuff)
1181 ought to be fed back into the main metaconfig distribution.
1183 =item Catch GNU Libc "Stub" functions
1185 Some functions (such as lchown()) are present in libc, but are
1186 unimplmented. That is, they always fail and set errno=ENOSYS.
1188 Thomas Bushnell provided the following sample code and the explanation
1191 /* System header to define __stub macros and hopefully few prototypes,
1192 which can conflict with char FOO(); below. */
1194 /* Override any gcc2 internal prototype to avoid an error. */
1195 /* We use char because int might match the return type of a gcc2
1196 builtin and then its argument prototype would still apply. */
1201 /* The GNU C library defines this for functions which it implements
1202 to always fail with ENOSYS. Some functions are actually named
1203 something starting with __ and the normal name is an alias. */
1204 #if defined (__stub_FOO) || defined (__stub___FOO)
1212 The choice of <assert.h> is essentially arbitrary. The GNU libc
1213 macros are found in <gnu/stubs.h>. You can include that file instead
1214 of <assert.h> (which itself includes <gnu/stubs.h>) if you test for
1215 its existence first. <assert.h> is assumed to exist on every system,
1216 which is why it's used here. Any GNU libc header file will include
1217 the stubs macros. If either __stub_NAME or __stub___NAME is defined,
1218 then the function doesn't actually exist. Tests using <assert.h> work
1219 on every system around.
1221 The declaration of FOO is there to override builtin prototypes for
1226 =head2 Probably good ideas waiting for round tuits
1230 =item GNU configure --options
1232 I've received sensible suggestions for --exec_prefix and other
1233 GNU configure --options. It's not always obvious exactly what is
1234 intended, but this merits investigation.
1238 Currently, B<make clean> isn't all that useful, though
1239 B<make realclean> and B<make distclean> are. This needs a bit of
1240 thought and documentation before it gets cleaned up.
1242 =item Try gcc if cc fails
1244 Currently, we just give up.
1246 =item bypassing safe*alloc wrappers
1248 On some systems, it may be safe to call the system malloc directly
1249 without going through the util.c safe* layers. (Such systems would
1250 accept free(0), for example.) This might be a time-saver for systems
1251 that already have a good malloc. (Recent Linux libc's apparently have
1252 a nice malloc that is well-tuned for the system.)
1256 =head2 Vague possibilities
1262 Get some of the Macintosh stuff folded back into the main distribution.
1264 =item gconvert replacement
1266 Maybe include a replacement function that doesn't lose data in rare
1267 cases of coercion between string and numerical values.
1269 =item Improve makedepend
1271 The current makedepend process is clunky and annoyingly slow, but it
1272 works for most folks. Alas, it assumes that there is a filename
1273 $firstmakefile that the B<make> command will try to use before it uses
1274 F<Makefile>. Such may not be the case for all B<make> commands,
1275 particularly those on non-Unix systems.
1277 Probably some variant of the BSD F<.depend> file will be useful.
1278 We ought to check how other packages do this, if they do it at all.
1279 We could probably pre-generate the dependencies (with the exception of
1280 malloc.o, which could probably be determined at F<Makefile.SH>
1283 =item GNU Makefile standard targets
1285 GNU software generally has standardized Makefile targets. Unless we
1286 have good reason to do otherwise, I see no reason not to support them.
1290 Somehow, straighten out, document, and implement lockf(), flock(),
1291 and/or fcntl() file locking. It's a mess.
1297 Original author: Andy Dougherty doughera@lafcol.lafayette.edu .
1298 Additions by Chip Salzenberg chip@perl.com and
1299 Tim Bunce Tim.Bunce@ig.co.uk .
1301 All opinions expressed herein are those of the authorZ<>(s).
1303 =head1 LAST MODIFIED
1305 $Id: pumpkin.pod,v 1.17 1998/06/30 17:00:06 doughera Released $