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, with one exception. Perl includes
303 both a F<Configure> script and a F<configure> script. The
304 F<configure> script is a front-end to the main F<Configure>, but
305 is there to aid folks who use autoconf-generated F<configure> files
306 for other software. The problem is that F<Configure> and F<configure>
307 are the same on case-insensitive file systems, so I deliberately put
308 F<configure> first in the MANIFEST so that the extraction of
309 F<Configure> will overwrite F<configure> and leave you with the
310 correct script. (The F<configure> script must also have write
311 permission for this to work, so it's the only file in the distribution
312 I normally have with write permission.)
314 If you are using metaconfig to regenerate Configure, then you should note
315 that metaconfig actually uses MANIFEST.new, so you want to be sure
316 MANIFEST.new is up-to-date too. I haven't found the MANIFEST/MANIFEST.new
317 distinction particularly useful, but that's probably because I still haven't
318 learned how to use the full suite of tools in the dist distribution.
320 =head2 Check permissions
322 All the tests in the t/ directory ought to be executable. The
323 main makefile used to do a 'chmod t/*/*.t', but that resulted in
324 a self-modifying distribution--something some users would strongly
325 prefer to avoid. Probably, the F<t/TEST> script should check for this
326 and do the chmod if needed, but it doesn't currently.
328 In all, the following files should probably be executable:
343 vms/ext/Stdio/test.pl
348 Other things ought to be readable, at least :-).
350 Probably, the permissions for the files could be encoded in MANIFEST
351 somehow, but I'm reluctant to change MANIFEST itself because that
352 could break old scripts that use MANIFEST.
354 I seem to recall that some SVR3 systems kept some sort of file that listed
355 permissions for system files; something like that might be appropriate.
359 This will build a config.sh and config.h. You can skip this if you haven't
360 changed Configure or config_h.SH at all. I use the following command
362 sh Configure -Dprefix=/opt/perl -Doptimize=-O -Dusethreads \
364 -Dcf_email='yourname@yourhost.yourplace.com' \
365 -Dperladmin='yourname@yourhost.yourplace.com' \
366 -Dmydomain='.yourplace.com' \
367 -Dmyhostname='yourhost' \
370 =head2 Update Porting/config.sh and Porting/config_H
373 This section needs revision. We're currently working on easing
374 the task of keeping the vms, win32, and plan9 config.sh info
375 up-to-date. The plan is to use keep up-to-date 'canned' config.sh
376 files in the appropriate subdirectories and then generate 'canned'
377 config.h files for vms, win32, etc. from the generic config.sh file.
378 This is to ease maintenance. When Configure gets updated, the parts
379 sometimes get scrambled around, and the changes in config_H can
380 sometimes be very hard to follow. config.sh, on the other hand, can
381 safely be sorted, so it's easy to track (typically very small) changes
382 to config.sh and then propoagate them to a canned 'config.h' by any
383 number of means, including a perl script in win32/ or carrying
384 config.sh and config_h.SH to a Unix system and running sh
388 The Porting/config.sh and Porting/config_H files are provided to
389 help those folks who can't run Configure. It is important to keep
390 them up-to-date. If you have changed config_h.SH, those changes must
391 be reflected in config_H as well. (The name config_H was chosen to
392 distinguish the file from config.h even on case-insensitive file systems.)
393 Simply edit the existing config_H file; keep the first few explanatory
394 lines and then copy your new config.h below.
396 It may also be necessary to update vms/config.vms and
397 plan9/config.plan9, though you should be quite careful in doing so if
398 you are not familiar with those systems. You might want to issue your
399 patch with a promise to quickly issue a follow-up that handles those
402 =head2 make run_byacc
404 If you have byacc-1.8.2 (available from CPAN), and if there have been
405 changes to F<perly.y>, you can regenerate the F<perly.c> file. The
406 run_byacc makefile target does this by running byacc and then applying
407 some patches so that byacc dynamically allocates space, rather than
408 having fixed limits. This patch is handled by the F<perly.fixer>
409 script. Depending on the nature of the changes to F<perly.y>, you may
410 or may not have to hand-edit the patch to apply correctly. If you do,
411 you should include the edited patch in the new distribution. If you
412 have byacc-1.9, the patch won't apply cleanly. Changes to the printf
413 output statements mean the patch won't apply cleanly. Long ago I
414 started to fix F<perly.fixer> to detect this, but I never completed the
417 Some additional notes from Larry on this:
419 Don't forget to regenerate perly.c.diff.
423 patch perly.c <perly.c.diff
424 # manually apply any failed hunks
425 diff -c2 perly.c.orig perly.c >perly.c.diff
427 One chunk of lines that often fails begins with
431 and ends one line before
433 #define YYERRCODE 256
435 This only happens when you add or remove a token type. I suppose this
436 could be automated, but it doesn't happen very often nowadays.
440 =head2 make regen_headers
442 The F<embed.h>, F<keywords.h>, and F<opcode.h> files are all automatically
443 generated by perl scripts. Since the user isn't guaranteed to have a
444 working perl, we can't require the user to generate them. Hence you have
445 to, if you're making a distribution.
447 I used to include rules like the following in the makefile:
449 # The following three header files are generated automatically
450 # The correct versions should be already supplied with the perl kit,
451 # in case you don't have perl or 'sh' available.
452 # The - is to ignore error return codes in case you have the source
453 # installed read-only or you don't have perl yet.
454 keywords.h: keywords.pl
455 @echo "Don't worry if this fails."
459 However, I got B<lots> of mail consisting of people worrying because the
460 command failed. I eventually decided that I would save myself time
461 and effort by manually running C<make regen_headers> myself rather
462 than answering all the questions and complaints about the failing
465 =head2 global.sym, interp.sym and perlio.sym
467 Make sure these files are up-to-date. Read the comments in these
468 files and in perl_exp.SH to see what to do.
470 =head2 Binary compatibility
472 If you do change F<global.sym> or F<interp.sym>, think carefully about
473 what you are doing. To the extent reasonable, we'd like to maintain
474 souce and binary compatibility with older releases of perl. That way,
475 extensions built under one version of perl will continue to work with
476 new versions of perl.
478 Of course, some incompatible changes may well be necessary. I'm just
479 suggesting that we not make any such changes without thinking carefully
480 about them first. If possible, we should provide
481 backwards-compatibility stubs. There's a lot of XS code out there.
482 Let's not force people to keep changing it.
486 Be sure to update the F<Changes> file. Try to include both an overall
487 summary as well as detailed descriptions of the changes. Your
488 audience will include other developers and users, so describe
489 user-visible changes (if any) in terms they will understand, not in
490 code like "initialize foo variable in bar function".
492 There are differing opinions on whether the detailed descriptions
493 ought to go in the Changes file or whether they ought to be available
494 separately in the patch file (or both). There is no disagreement that
495 detailed descriptions ought to be easily available somewhere.
499 The F<Todo> file contains a roughly-catgorized unordered list of
500 aspects of Perl that could use enhancement, features that could be
501 added, areas that could be cleaned up, and so on. During your term as
502 pumpkin-holder, you will probably address some of these issues, and
503 perhaps identify others which, while you decide not to address them
504 this time around, may be tackled in the future. Update the file
505 reflect the situation as it stands when you hand over the pumpkin.
507 You might like, early in your pumpkin-holding career, to see if you
508 can find champions for partiticular issues on the to-do list: an issue
509 owned is an issue more likely to be resolved.
511 =head2 OS/2-specific updates
513 In the os2 directory is F<diff.configure>, a set of OS/2-specific
514 diffs against B<Configure>. If you make changes to Configure, you may
515 want to consider regenerating this diff file to save trouble for the
518 You can also consider the OS/2 diffs as reminders of portability
519 things that need to be fixed in Configure.
521 =head2 VMS-specific updates
523 If you have changed F<perly.y>, then you may want to update
524 F<vms/perly_{h,c}.vms> by running C<perl vms/vms_yfix.pl>.
526 The Perl version number appears in several places under F<vms>.
527 It is courteous to update these versions. For example, if you are
528 making 5.004_42, replace "5.00441" with "5.00442".
530 =head2 Making the new distribution
532 Suppose, for example, that you want to make version 5.004_08. Then you can
533 do something like the following
535 mkdir ../perl5.004_08
536 awk '{print $1}' MANIFEST | cpio -pdm ../perl5.004_08
538 tar cf perl5.004_08.tar perl5.004_08
539 gzip --best perl5.004_08.tar
541 These steps, with extra checks, are automated by the Porting/makerel
544 =head2 Making a new patch
546 I find the F<makepatch> utility quite handy for making patches.
547 You can obtain it from any CPAN archive under
548 http://www.perl.com/CPAN/authors/Johan_Vromans/ . There are a couple
549 of differences between my version and the standard one. I have mine do
552 # Print a reassuring "End of Patch" note so people won't
553 # wonder if their mailer truncated patches.
554 print "\n\nEnd of Patch.\n";
556 at the end. That's because I used to get questions from people asking
557 if their mail was truncated.
559 It also writes Index: lines which include the new directory prefix
560 (change Index: print, approx line 294 or 310 depending on the version,
561 to read: print PATCH ("Index: $newdir$new\n");). That helps patches
562 work with more POSIX conformant patch programs.
564 Here's how I generate a new patch. I'll use the hypothetical
565 5.004_07 to 5.004_08 patch as an example.
567 # unpack perl5.004_07/
568 gzip -d -c perl5.004_07.tar.gz | tar -xof -
569 # unpack perl5.004_08/
570 gzip -d -c perl5.004_08.tar.gz | tar -xof -
571 makepatch perl5.004_07 perl5.004_08 > perl5.004_08.pat
573 Makepatch will automatically generate appropriate B<rm> commands to remove
574 deleted files. Unfortunately, it will not correctly set permissions
575 for newly created files, so you may have to do so manually. For example,
576 patch 5.003_04 created a new test F<t/op/gv.t> which needs to be executable,
577 so at the top of the patch, I inserted the following lines:
583 Now, of course, my patch is now wrong because makepatch didn't know I
584 was going to do that command, and it patched against /dev/null.
586 So, what I do is sort out all such shell commands that need to be in the
587 patch (including possible mv-ing of files, if needed) and put that in the
588 shell commands at the top of the patch. Next, I delete all the patch parts
589 of perl5.004_08.pat, leaving just the shell commands. Then, I do the
593 sh ../perl5.004_08.pat
595 makepatch perl5.004_07 perl5.004_08 >> perl5.004_08.pat
597 (Note the append to preserve my shell commands.)
598 Now, my patch will line up with what the end users are going to do.
600 =head2 Testing your patch
602 It seems obvious, but be sure to test your patch. That is, verify that
603 it produces exactly the same thing as your full distribution.
606 gzip -d -c perl5.004_07.tar.gz | tar -xf -
608 sh ../perl5.004_08.pat
609 patch -p1 -N < ../perl5.004_08.pat
611 gdiff -r perl5.004_07 perl5.004_08
613 where B<gdiff> is GNU diff. Other diff's may also do recursive checking.
617 Again, it's obvious, but you should test your new version as widely as you
618 can. You can be sure you'll hear about it quickly if your version doesn't
619 work on both ANSI and pre-ANSI compilers, and on common systems such as
620 SunOS 4.1.[34], Solaris, and Linux.
622 If your changes include conditional code, try to test the different
623 branches as thoroughly as you can. For example, if your system
624 supports dynamic loading, you can also test static loading with
628 You can also hand-tweak your config.h to try out different #ifdef
631 =head1 Common Gotcha's
637 The '#elif' preprocessor directive is not understood on all systems.
638 Specifically, I know that Pyramids don't understand it. Thus instead of the
649 You have to do the more Byzantine
661 Incidentally, whitespace between the leading '#' and the preprocessor
662 command is not guaranteed, but is very portable and you may use it freely.
663 I think it makes things a bit more readable, especially once things get
664 rather deeply nested. I also think that things should almost never get
665 too deeply nested, so it ought to be a moot point :-)
667 =item Probably Prefer POSIX
669 It's often the case that you'll need to choose whether to do
670 something the BSD-ish way or the POSIX-ish way. It's usually not
671 a big problem when the two systems use different names for similar
672 functions, such as memcmp() and bcmp(). The perl.h header file
673 handles these by appropriate #defines, selecting the POSIX mem*()
674 functions if available, but falling back on the b*() functions, if
677 More serious is the case where some brilliant person decided to
678 use the same function name but give it a different meaning or
679 calling sequence :-). getpgrp() and setpgrp() come to mind.
680 These are a real problem on systems that aim for conformance to
681 one standard (e.g. POSIX), but still try to support the other way
682 of doing things (e.g. BSD). My general advice (still not really
683 implemented in the source) is to do something like the following.
684 Suppose there are two alternative versions, fooPOSIX() and
688 /* use fooPOSIX(); */
691 /* try to emulate fooPOSIX() with fooBSD();
692 perhaps with the following: */
693 # define fooPOSIX fooBSD
695 # /* Uh, oh. We have to supply our own. */
696 # define fooPOSIX Perl_fooPOSIX
700 =item Think positively
702 If you need to add an #ifdef test, it is usually easier to follow if you
703 think positively, e.g.
705 #ifdef HAS_NEATO_FEATURE
706 /* use neato feature */
708 /* use some fallback mechanism */
711 rather than the more impenetrable
713 #ifndef MISSING_NEATO_FEATURE
714 /* Not missing it, so we must have it, so use it */
716 /* Are missing it, so fall back on something else. */
719 Of course for this toy example, there's not much difference. But when
720 the #ifdef's start spanning a couple of screen fulls, and the #else's
721 are marked something like
723 #else /* !MISSING_NEATO_FEATURE */
725 I find it easy to get lost.
727 =item Providing Missing Functions -- Problem
729 Not all systems have all the neat functions you might want or need, so
730 you might decide to be helpful and provide an emulation. This is
731 sound in theory and very kind of you, but please be careful about what
732 you name the function. Let me use the C<pause()> function as an
735 Perl5.003 has the following in F<perl.h>
738 #define pause() sleep((32767<<16)+32767)
741 Configure sets HAS_PAUSE if the system has the pause() function, so
742 this #define only kicks in if the pause() function is missing.
745 Unfortunately, some systems apparently have a prototype for pause()
746 in F<unistd.h>, but don't actually have the function in the library.
747 (Or maybe they do have it in a library we're not using.)
749 Thus, the compiler sees something like
751 extern int pause(void);
753 #define pause() sleep((32767<<16)+32767)
755 and dies with an error message. (Some compilers don't mind this;
756 others apparently do.)
758 To work around this, 5.003_03 and later have the following in perl.h:
760 /* Some unistd.h's give a prototype for pause() even though
761 HAS_PAUSE ends up undefined. This causes the #define
762 below to be rejected by the compiler. Sigh.
767 # define Pause() sleep((32767<<16)+32767)
772 The curious reader may wonder why I didn't do the following in
778 sleep((32767<<16)+32767);
782 That is, since the function is missing, just provide it.
783 Then things would probably be been alright, it would seem.
785 Well, almost. It could be made to work. The problem arises from the
786 conflicting needs of dynamic loading and namespace protection.
788 For dynamic loading to work on AIX (and VMS) we need to provide a list
789 of symbols to be exported. This is done by the script F<perl_exp.SH>,
790 which reads F<global.sym> and F<interp.sym>. Thus, the C<pause>
791 symbol would have to be added to F<global.sym> So far, so good.
793 On the other hand, one of the goals of Perl5 is to make it easy to
794 either extend or embed perl and link it with other libraries. This
795 means we have to be careful to keep the visible namespace "clean".
796 That is, we don't want perl's global variables to conflict with
797 those in the other application library. Although this work is still
798 in progress, the way it is currently done is via the F<embed.h> file.
799 This file is built from the F<global.sym> and F<interp.sym> files,
800 since those files already list the globally visible symbols. If we
801 had added C<pause> to global.sym, then F<embed.h> would contain the
804 #define pause Perl_pause
806 and calls to C<pause> in the perl sources would now point to
807 C<Perl_pause>. Now, when B<ld> is run to build the F<perl> executable,
808 it will go looking for C<perl_pause>, which probably won't exist in any
809 of the standard libraries. Thus the build of perl will fail.
811 Those systems where C<HAS_PAUSE> is not defined would be ok, however,
812 since they would get a C<Perl_pause> function in util.c. The rest of
813 the world would be in trouble.
815 And yes, this scenario has happened. On SCO, the function C<chsize>
816 is available. (I think it's in F<-lx>, the Xenix compatibility
817 library.) Since the perl4 days (and possibly before), Perl has
818 included a C<chsize> function that gets called something akin to
821 I32 chsize(fd, length)
827 #define chsize Perl_chsize
829 to F<embed.h>, the compile started failing on SCO systems.
831 The "fix" is to give the function a different name. The one
832 implemented in 5.003_05 isn't optimal, but here's what was done:
835 # ifdef my_chsize /* Probably #defined to Perl_my_chsize in embed.h */
838 # define my_chsize chsize
841 My explanatory comment in patch 5.003_05 said:
843 Undef and then re-define my_chsize from Perl_my_chsize to
844 just plain chsize if this system HAS_CHSIZE. This probably only
845 applies to SCO. This shows the perils of having internal
846 functions with the same name as external library functions :-).
848 Now, we can safely put C<my_chsize> in F<global.sym>, export it, and
849 hide it with F<embed.h>.
851 To be consistent with what I did for C<pause>, I probably should have
852 called the new function C<Chsize>, rather than C<my_chsize>.
853 However, the perl sources are quite inconsistent on this (Consider
854 New, Mymalloc, and Myremalloc, to name just a few.)
856 There is a problem with this fix, however, in that C<Perl_chsize>
857 was available as a F<libperl.a> library function in 5.003, but it
858 isn't available any more (as of 5.003_07). This means that we've
859 broken binary compatibility. This is not good.
861 =item Providing missing functions -- some ideas
863 We currently don't have a standard way of handling such missing
864 function names. Right now, I'm effectively thinking aloud about a
865 solution. Some day, I'll try to formally propose a solution.
867 Part of the problem is that we want to have some functions listed as
868 exported but not have their names mangled by embed.h or possibly
869 conflict with names in standard system headers. We actually already
870 have such a list at the end of F<perl_exp.SH> (though that list is
873 # extra globals not included above.
874 cat <<END >> perl.exp
898 This still needs much thought, but I'm inclined to think that one
899 possible solution is to prefix all such functions with C<perl_> in the
900 source and list them along with the other C<perl_*> functions in
903 Thus, for C<chsize>, we'd do something like the following:
907 # define perl_chsize chsize
910 then in some file (e.g. F<util.c> or F<doio.c>) do
913 I32 perl_chsize(fd, length)
914 /* implement the function here . . . */
917 Alternatively, we could just always use C<chsize> everywhere and move
918 C<chsize> from F<global.sym> to the end of F<perl_exp.SH>. That would
919 probably be fine as long as our C<chsize> function agreed with all the
920 C<chsize> function prototypes in the various systems we'll be using.
921 As long as the prototypes in actual use don't vary that much, this is
922 probably a good alternative. (As a counter-example, note how Configure
923 and perl have to go through hoops to find and use get Malloc_t and
924 Free_t for C<malloc> and C<free>.)
926 At the moment, this latter option is what I tend to prefer.
928 =item All the world's a VAX
930 Sorry, showing my age:-). Still, all the world is not BSD 4.[34],
931 SVR4, or POSIX. Be aware that SVR3-derived systems are still quite
932 common (do you have any idea how many systems run SCO?) If you don't
933 have a bunch of v7 manuals handy, the metaconfig units (by default
934 installed in F</usr/local/lib/dist/U>) are a good resource to look at
939 =head1 Miscellaneous Topics
943 Why does perl use a metaconfig-generated Configure script instead of an
944 autoconf-generated configure script?
946 Metaconfig and autoconf are two tools with very similar purposes.
947 Metaconfig is actually the older of the two, and was originally written
948 by Larry Wall, while autoconf is probably now used in a wider variety of
949 packages. The autoconf info file discusses the history of autoconf and
950 how it came to be. The curious reader is referred there for further
953 Overall, both tools are quite good, I think, and the choice of which one
954 to use could be argued either way. In March, 1994, when I was just
955 starting to work on Configure support for Perl5, I considered both
956 autoconf and metaconfig, and eventually decided to use metaconfig for the
961 =item Compatibility with Perl4
963 Perl4 used metaconfig, so many of the #ifdef's were already set up for
964 metaconfig. Of course metaconfig had evolved some since Perl4's days,
965 but not so much that it posed any serious problems.
967 =item Metaconfig worked for me
969 My system at the time was Interactive 2.2, a SVR3.2/386 derivative that
970 also had some POSIX support. Metaconfig-generated Configure scripts
971 worked fine for me on that system. On the other hand, autoconf-generated
972 scripts usually didn't. (They did come quite close, though, in some
973 cases.) At the time, I actually fetched a large number of GNU packages
974 and checked. Not a single one configured and compiled correctly
975 out-of-the-box with the system's cc compiler.
977 =item Configure can be interactive
979 With both autoconf and metaconfig, if the script works, everything is
980 fine. However, one of my main problems with autoconf-generated scripts
981 was that if it guessed wrong about something, it could be B<very> hard to
982 go back and fix it. For example, autoconf always insisted on passing the
983 -Xp flag to cc (to turn on POSIX behavior), even when that wasn't what I
984 wanted or needed for that package. There was no way short of editing the
985 configure script to turn this off. You couldn't just edit the resulting
986 Makefile at the end because the -Xp flag influenced a number of other
989 Metaconfig's Configure scripts, on the other hand, can be interactive.
990 Thus if Configure is guessing things incorrectly, you can go back and fix
991 them. This isn't as important now as it was when we were actively
992 developing Configure support for new features such as dynamic loading,
993 but it's still useful occasionally.
997 At the time, autoconf-generated scripts were covered under the GNU Public
998 License, and hence weren't suitable for inclusion with Perl, which has a
999 different licensing policy. (Autoconf's licensing has since changed.)
1003 Metaconfig builds up Configure from a collection of discrete pieces
1004 called "units". You can override the standard behavior by supplying your
1005 own unit. With autoconf, you have to patch the standard files instead.
1006 I find the metaconfig "unit" method easier to work with. Others
1007 may find metaconfig's units clumsy to work with.
1011 =head2 @INC search order
1013 By default, the list of perl library directories in @INC is the
1021 Specifically, on my Solaris/x86 system, I run
1022 B<sh Configure -Dprefix=/opt/perl> and I have the following
1025 /opt/perl/lib/i86pc-solaris/5.00307
1027 /opt/perl/lib/site_perl/i86pc-solaris
1028 /opt/perl/lib/site_perl
1030 That is, perl's directories come first, followed by the site-specific
1033 The site libraries come second to support the usage of extensions
1034 across perl versions. Read the relevant section in F<INSTALL> for
1035 more information. If we ever make $sitearch version-specific, this
1036 topic could be revisited.
1038 =head2 Why isn't there a directory to override Perl's library?
1040 Mainly because no one's gotten around to making one. Note that
1041 "making one" involves changing perl.c, Configure, config_h.SH (and
1042 associated files, see above), and I<documenting> it all in the
1045 Apparently, most folks who want to override one of the standard library
1046 files simply do it by overwriting the standard library files.
1050 In the perl.c sources, you'll find an undocumented APPLLIB_EXP
1051 variable, sort of like PRIVLIB_EXP and ARCHLIB_EXP (which are
1052 documented in config_h.SH). Here's what APPLLIB_EXP is for, from
1053 a mail message from Larry:
1055 The main intent of APPLLIB_EXP is for folks who want to send out a
1056 version of Perl embedded in their product. They would set the symbol
1057 to be the name of the library containing the files needed to run or to
1058 support their particular application. This works at the "override"
1059 level to make sure they get their own versions of any library code that
1060 they absolutely must have configuration control over.
1062 As such, I don't see any conflict with a sysadmin using it for a
1063 override-ish sort of thing, when installing a generic Perl. It should
1064 probably have been named something to do with overriding though. Since
1065 it's undocumented we could still change it... :-)
1067 Given that it's already there, you can use it to override
1068 distribution modules. If you do
1070 sh Configure -Dccflags='-DAPPLLIB_EXP=/my/override'
1072 then perl.c will put /my/override ahead of ARCHLIB and PRIVLIB.
1074 =head1 Upload Your Work to CPAN
1076 You can upload your work to CPAN if you have a CPAN id. Check out
1077 http://www.perl.com/CPAN/modules/04pause.html for information on
1078 _PAUSE_, the Perl Author's Upload Server.
1080 I typically upload both the patch file, e.g. F<perl5.004_08.pat.gz>
1081 and the full tar file, e.g. F<perl5.004_08.tar.gz>.
1083 If you want your patch to appear in the F<src/5.0/unsupported>
1084 directory on CPAN, send e-mail to the CPAN master librarian. (Check
1085 out http://www.perl.com/CPAN/CPAN.html ).
1087 =head1 Help Save the World
1089 You should definitely announce your patch on the perl5-porters list.
1090 You should also consider announcing your patch on
1091 comp.lang.perl.announce, though you should make it quite clear that a
1092 subversion is not a production release, and be prepared to deal with
1093 people who will not read your disclaimer.
1097 Here, in no particular order, are some Configure and build-related
1098 items that merit consideration. This list isn't exhaustive, it's just
1099 what I came up with off the top of my head.
1101 =head2 Good ideas waiting for round tuits
1107 I think we ought to support
1109 Configure -Dinstallprefix=/blah/blah
1111 Currently, we support B<-Dprefix=/blah/blah>, but the changing the install
1112 location has to be handled by something like the F<config.over> trick
1113 described in F<INSTALL>. AFS users also are treated specially.
1114 We should probably duplicate the metaconfig prefix stuff for an
1117 =item Configure -Dsrcdir=/blah/blah
1119 We should be able to emulate B<configure --srcdir>. Tom Tromey
1120 tromey@creche.cygnus.com has submitted some patches to
1121 the dist-users mailing list along these lines. Eventually, they ought
1122 to get folded back into the main distribution.
1124 =item Hint file fixes
1126 Various hint files work around Configure problems. We ought to fix
1127 Configure so that most of them aren't needed.
1129 =item Hint file information
1131 Some of the hint file information (particularly dynamic loading stuff)
1132 ought to be fed back into the main metaconfig distribution.
1136 =head2 Probably good ideas waiting for round tuits
1140 =item GNU configure --options
1142 I've received sensible suggestions for --exec_prefix and other
1143 GNU configure --options. It's not always obvious exactly what is
1144 intended, but this merits investigation.
1148 Currently, B<make clean> isn't all that useful, though
1149 B<make realclean> and B<make distclean> are. This needs a bit of
1150 thought and documentation before it gets cleaned up.
1152 =item Try gcc if cc fails
1154 Currently, we just give up.
1156 =item bypassing safe*alloc wrappers
1158 On some systems, it may be safe to call the system malloc directly
1159 without going through the util.c safe* layers. (Such systems would
1160 accept free(0), for example.) This might be a time-saver for systems
1161 that already have a good malloc. (Recent Linux libc's apparently have
1162 a nice malloc that is well-tuned for the system.)
1166 =head2 Vague possibilities
1172 Get some of the Macintosh stuff folded back into the main distribution.
1174 =item gconvert replacement
1176 Maybe include a replacement function that doesn't lose data in rare
1177 cases of coercion between string and numerical values.
1181 Can we support C<long long> on systems where C<long long> is larger
1182 than what we've been using for C<IV>? What if you can't C<sprintf>
1185 =item Improve makedepend
1187 The current makedepend process is clunky and annoyingly slow, but it
1188 works for most folks. Alas, it assumes that there is a filename
1189 $firstmakefile that the B<make> command will try to use before it uses
1190 F<Makefile>. Such may not be the case for all B<make> commands,
1191 particularly those on non-Unix systems.
1193 Probably some variant of the BSD F<.depend> file will be useful.
1194 We ought to check how other packages do this, if they do it at all.
1195 We could probably pre-generate the dependencies (with the exception of
1196 malloc.o, which could probably be determined at F<Makefile.SH>
1199 =item GNU Makefile standard targets
1201 GNU software generally has standardized Makefile targets. Unless we
1202 have good reason to do otherwise, I see no reason not to support them.
1206 Somehow, straighten out, document, and implement lockf(), flock(),
1207 and/or fcntl() file locking. It's a mess.
1213 Original author: Andy Dougherty doughera@lafcol.lafayette.edu .
1214 Additions by Chip Salzenberg chip@perl.com and
1215 Tim Bunce Tim.Bunce@ig.co.uk .
1217 All opinions expressed herein are those of the authorZ<>(s).
1219 =head1 LAST MODIFIED
1221 $Id: pumpkin.pod,v 1.14 1998/03/03 17:14:47 doughera Released $