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, 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.
224 =head1 How to Make a Distribution
226 There really ought to be a 'make dist' target, but there isn't.
227 The 'dist' suite of tools also contains a number of tools that I haven't
228 learned how to use yet. Some of them may make this all a bit easier.
230 Here are the steps I go through to prepare a patch & distribution.
232 Lots of it could doubtless be automated but isn't. The Porting/makerel
233 (make release) perl script does now help automate some parts of it.
235 =head2 Announce your intentions
237 First, you should volunteer out loud to take the patch pumpkin. It's
238 generally counter-productive to have multiple people working in secret
241 At the same time, announce what you plan to do with the patch pumpkin,
242 to allow folks a chance to object or suggest alternatives, or do it for
243 you. Naturally, the patch pumpkin holder ought to incorporate various
244 bug fixes and documentation improvements that are posted while he or
245 she has the pumpkin, but there might also be larger issues at stake.
247 One of the precepts of the subversion idea is that we shouldn't give
248 the patch pumpkin to anyone unless we have some idea what he or she
249 is going to do with it.
251 =head2 refresh pod/perltoc.pod
253 Presumably, you have done a full C<make> in your working source
254 directory. Before you C<make spotless> (if you do), and if you have
255 changed any documentation in any module or pod file, change to the
256 F<pod> directory and run C<make toc>.
258 =head2 run installhtml to check the validity of the pod files
260 =head2 update patchlevel.h
262 Don't be shy about using the subversion number, even for a relatively
263 modest patch. We've never even come close to using all 99 subversions,
264 and it's better to have a distinctive number for your patch. If you
265 need feedback on your patch, go ahead and issue it and promise to
266 incorporate that feedback quickly (e.g. within 1 week) and send out a
269 =head2 run metaconfig
271 If you need to make changes to Configure or config_h.SH, it may be best to
272 change the appropriate metaconfig units instead, and regenerate Configure.
276 will regenerate Configure and config_h.SH. More information on
277 obtaining and running metaconfig is in the F<U/README> file that comes
278 with Perl's metaconfig units. Perl's metaconfig units should be
279 available the same place you found this file. On CPAN, look under my
280 directory F<authors/id/ANDYD/> for a file such as F<5.003_07-02.U.tar.gz>.
281 That file should be unpacked in your main perl source directory. It
282 contains the files needed to run B<metaconfig> to reproduce Perl's
283 Configure script. (Those units are for 5.003_07. There have been
284 changes since then; please contact me if you want more recent
285 versions, and I will try to point you in the right direction.)
287 Alternatively, do consider if the F<*ish.h> files might be a better
288 place for your changes.
292 Make sure the MANIFEST is up-to-date. You can use dist's B<manicheck>
293 program for this. You can also use
295 perl -w -MExtUtils::Manifest=fullcheck -e fullcheck
297 Both commands will also list extra files in the directory that are not
300 The MANIFEST is normally sorted, with one exception. Perl includes
301 both a F<Configure> script and a F<configure> script. The
302 F<configure> script is a front-end to the main F<Configure>, but
303 is there to aid folks who use autoconf-generated F<configure> files
304 for other software. The problem is that F<Configure> and F<configure>
305 are the same on case-insensitive file systems, so I deliberately put
306 F<configure> first in the MANIFEST so that the extraction of
307 F<Configure> will overwrite F<configure> and leave you with the
308 correct script. (The F<configure> script must also have write
309 permission for this to work, so it's the only file in the distribution
310 I normally have with write permission.)
312 If you are using metaconfig to regenerate Configure, then you should note
313 that metaconfig actually uses MANIFEST.new, so you want to be sure
314 MANIFEST.new is up-to-date too. I haven't found the MANIFEST/MANIFEST.new
315 distinction particularly useful, but that's probably because I still haven't
316 learned how to use the full suite of tools in the dist distribution.
318 =head2 Check permissions
320 All the tests in the t/ directory ought to be executable. The
321 main makefile used to do a 'chmod t/*/*.t', but that resulted in
322 a self-modifying distribution--something some users would strongly
323 prefer to avoid. Probably, the F<t/TEST> script should check for this
324 and do the chmod if needed, but it doesn't currently.
326 In all, the following files should probably be executable:
341 vms/ext/Stdio/test.pl
346 Other things ought to be readable, at least :-).
348 Probably, the permissions for the files could be encoded in MANIFEST
349 somehow, but I'm reluctant to change MANIFEST itself because that
350 could break old scripts that use MANIFEST.
352 I seem to recall that some SVR3 systems kept some sort of file that listed
353 permissions for system files; something like that might be appropriate.
357 This will build a config.sh and config.h. You can skip this if you haven't
358 changed Configure or config_h.SH at all.
360 =head2 Update config_H
362 The config_H file is provided to help those folks who can't run Configure.
363 It is important to keep it up-to-date. If you have changed config_h.SH,
364 those changes must be reflected in config_H as well. (The name config_H was
365 chosen to distinguish the file from config.h even on case-insensitive file
366 systems.) Simply edit the existing config_H file; keep the first few
367 explanatory lines and then copy your new config.h below.
369 It may also be necessary to update vms/config.vms and
370 plan9/config.plan9, though you should be quite careful in doing so if
371 you are not familiar with those systems. You might want to issue your
372 patch with a promise to quickly issue a follow-up that handles those
375 =head2 make run_byacc
377 If you have byacc-1.8.2 (available from CPAN), and if there have been
378 changes to F<perly.y>, you can regenerate the F<perly.c> file. The
379 run_byacc makefile target does this by running byacc and then applying
380 some patches so that byacc dynamically allocates space, rather than
381 having fixed limits. This patch is handled by the F<perly.fixer>
382 script. Depending on the nature of the changes to F<perly.y>, you may
383 or may not have to hand-edit the patch to apply correctly. If you do,
384 you should include the edited patch in the new distribution. If you
385 have byacc-1.9, the patch won't apply cleanly. Changes to the printf
386 output statements mean the patch won't apply cleanly. Long ago I
387 started to fix F<perly.fixer> to detect this, but I never completed the
390 Some additional notes from Larry on this:
392 Don't forget to regenerate perly.c.diff.
396 patch perly.c <perly.c.diff
397 # manually apply any failed hunks
398 diff -c2 perly.c.orig perly.c >perly.c.diff
400 One chunk of lines that often fails begins with
404 and ends one line before
406 #define YYERRCODE 256
408 This only happens when you add or remove a token type. I suppose this
409 could be automated, but it doesn't happen very often nowadays.
413 =head2 make regen_headers
415 The F<embed.h>, F<keywords.h>, and F<opcode.h> files are all automatically
416 generated by perl scripts. Since the user isn't guaranteed to have a
417 working perl, we can't require the user to generate them. Hence you have
418 to, if you're making a distribution.
420 I used to include rules like the following in the makefile:
422 # The following three header files are generated automatically
423 # The correct versions should be already supplied with the perl kit,
424 # in case you don't have perl or 'sh' available.
425 # The - is to ignore error return codes in case you have the source
426 # installed read-only or you don't have perl yet.
427 keywords.h: keywords.pl
428 @echo "Don't worry if this fails."
432 However, I got B<lots> of mail consisting of people worrying because the
433 command failed. I eventually decided that I would save myself time
434 and effort by manually running C<make regen_headers> myself rather
435 than answering all the questions and complaints about the failing
438 =head2 global.sym, interp.sym and perlio.sym
440 Make sure these files are up-to-date. Read the comments in these
441 files and in perl_exp.SH to see what to do.
443 =head2 Binary compatibility
445 If you do change F<global.sym> or F<interp.sym>, think carefully about
446 what you are doing. To the extent reasonable, we'd like to maintain
447 souce and binary compatibility with older releases of perl. That way,
448 extensions built under one version of perl will continue to work with
449 new versions of perl.
451 Of course, some incompatible changes may well be necessary. I'm just
452 suggesting that we not make any such changes without thinking carefully
453 about them first. If possible, we should provide
454 backwards-compatibility stubs. There's a lot of XS code out there.
455 Let's not force people to keep changing it.
459 Be sure to update the F<Changes> file. Try to include both an overall
460 summary as well as detailed descriptions of the changes. Your
461 audience will include other developers and users, so describe
462 user-visible changes (if any) in terms they will understand, not in
463 code like "initialize foo variable in bar function".
465 There are differing opinions on whether the detailed descriptions
466 ought to go in the Changes file or whether they ought to be available
467 separately in the patch file (or both). There is no disagreement that
468 detailed descriptions ought to be easily available somewhere.
470 =head2 OS/2-specific updates
472 In the os2 directory is F<diff.configure>, a set of OS/2-specific
473 diffs against B<Configure>. If you make changes to Configure, you may
474 want to consider regenerating this diff file to save trouble for the
477 You can also consider the OS/2 diffs as reminders of portability
478 things that need to be fixed in Configure.
480 =head2 VMS-specific updates
482 If you have changed F<perly.y>, then you may want to update
483 F<vms/perly_{h,c}.vms> by running C<perl vms/vms_yfix.pl>.
485 The Perl version number appears in several places under F<vms>.
486 It is courteous to update these versions. For example, if you are
487 making 5.004_42, replace "5.00441" with "5.00442".
489 =head2 Making the new distribution
491 Suppose, for example, that you want to make version 5.004_08. Then you can
492 do something like the following
494 mkdir ../perl5.004_08
495 awk '{print $1}' MANIFEST | cpio -pdm ../perl5.004_08
497 tar cf perl5.004_08.tar perl5.004_08
498 gzip --best perl5.004_08.tar
500 These steps, with extra checks, are automated by the Porting/makerel
503 =head2 Making a new patch
505 I find the F<makepatch> utility quite handy for making patches.
506 You can obtain it from any CPAN archive under
507 http://www.perl.com/CPAN/authors/Johan_Vromans/ . There are a couple
508 of differences between my version and the standard one. I have mine do
511 # Print a reassuring "End of Patch" note so people won't
512 # wonder if their mailer truncated patches.
513 print "\n\nEnd of Patch.\n";
515 at the end. That's because I used to get questions from people asking
516 if their mail was truncated.
518 It also writes Index: lines which include the new directory prefix
519 (change Index: print, approx line 294 or 310 depending on the version,
520 to read: print PATCH ("Index: $newdir$new\n");). That helps patches
521 work with more POSIX conformant patch programs.
523 Here's how I generate a new patch. I'll use the hypothetical
524 5.004_07 to 5.004_08 patch as an example.
526 # unpack perl5.004_07/
527 gzip -d -c perl5.004_07.tar.gz | tar -xof -
528 # unpack perl5.004_08/
529 gzip -d -c perl5.004_08.tar.gz | tar -xof -
530 makepatch perl5.004_07 perl5.004_08 > perl5.004_08.pat
532 Makepatch will automatically generate appropriate B<rm> commands to remove
533 deleted files. Unfortunately, it will not correctly set permissions
534 for newly created files, so you may have to do so manually. For example,
535 patch 5.003_04 created a new test F<t/op/gv.t> which needs to be executable,
536 so at the top of the patch, I inserted the following lines:
542 Now, of course, my patch is now wrong because makepatch didn't know I
543 was going to do that command, and it patched against /dev/null.
545 So, what I do is sort out all such shell commands that need to be in the
546 patch (including possible mv-ing of files, if needed) and put that in the
547 shell commands at the top of the patch. Next, I delete all the patch parts
548 of perl5.004_08.pat, leaving just the shell commands. Then, I do the
552 sh ../perl5.004_08.pat
554 makepatch perl5.004_07 perl5.004_08 >> perl5.004_08.pat
556 (Note the append to preserve my shell commands.)
557 Now, my patch will line up with what the end users are going to do.
559 =head2 Testing your patch
561 It seems obvious, but be sure to test your patch. That is, verify that
562 it produces exactly the same thing as your full distribution.
565 gzip -d -c perl5.004_07.tar.gz | tar -xf -
567 sh ../perl5.004_08.pat
568 patch -p1 -N < ../perl5.004_08.pat
570 gdiff -r perl5.004_07 perl5.004_08
572 where B<gdiff> is GNU diff. Other diff's may also do recursive checking.
576 Again, it's obvious, but you should test your new version as widely as you
577 can. You can be sure you'll hear about it quickly if your version doesn't
578 work on both ANSI and pre-ANSI compilers, and on common systems such as
579 SunOS 4.1.[34], Solaris, and Linux.
581 If your changes include conditional code, try to test the different
582 branches as thoroughly as you can. For example, if your system
583 supports dynamic loading, you can also test static loading with
587 You can also hand-tweak your config.h to try out different #ifdef
590 =head1 Common Gotcha's
596 The '#elif' preprocessor directive is not understood on all systems.
597 Specifically, I know that Pyramids don't understand it. Thus instead of the
608 You have to do the more Byzantine
620 Incidentally, whitespace between the leading '#' and the preprocessor
621 command is not guaranteed, but is very portable and you may use it freely.
622 I think it makes things a bit more readable, especially once things get
623 rather deeply nested. I also think that things should almost never get
624 too deeply nested, so it ought to be a moot point :-)
626 =item Probably Prefer POSIX
628 It's often the case that you'll need to choose whether to do
629 something the BSD-ish way or the POSIX-ish way. It's usually not
630 a big problem when the two systems use different names for similar
631 functions, such as memcmp() and bcmp(). The perl.h header file
632 handles these by appropriate #defines, selecting the POSIX mem*()
633 functions if available, but falling back on the b*() functions, if
636 More serious is the case where some brilliant person decided to
637 use the same function name but give it a different meaning or
638 calling sequence :-). getpgrp() and setpgrp() come to mind.
639 These are a real problem on systems that aim for conformance to
640 one standard (e.g. POSIX), but still try to support the other way
641 of doing things (e.g. BSD). My general advice (still not really
642 implemented in the source) is to do something like the following.
643 Suppose there are two alternative versions, fooPOSIX() and
647 /* use fooPOSIX(); */
650 /* try to emulate fooPOSIX() with fooBSD();
651 perhaps with the following: */
652 # define fooPOSIX fooBSD
654 # /* Uh, oh. We have to supply our own. */
655 # define fooPOSIX Perl_fooPOSIX
659 =item Think positively
661 If you need to add an #ifdef test, it is usually easier to follow if you
662 think positively, e.g.
664 #ifdef HAS_NEATO_FEATURE
665 /* use neato feature */
667 /* use some fallback mechanism */
670 rather than the more impenetrable
672 #ifndef MISSING_NEATO_FEATURE
673 /* Not missing it, so we must have it, so use it */
675 /* Are missing it, so fall back on something else. */
678 Of course for this toy example, there's not much difference. But when
679 the #ifdef's start spanning a couple of screen fulls, and the #else's
680 are marked something like
682 #else /* !MISSING_NEATO_FEATURE */
684 I find it easy to get lost.
686 =item Providing Missing Functions -- Problem
688 Not all systems have all the neat functions you might want or need, so
689 you might decide to be helpful and provide an emulation. This is
690 sound in theory and very kind of you, but please be careful about what
691 you name the function. Let me use the C<pause()> function as an
694 Perl5.003 has the following in F<perl.h>
697 #define pause() sleep((32767<<16)+32767)
700 Configure sets HAS_PAUSE if the system has the pause() function, so
701 this #define only kicks in if the pause() function is missing.
704 Unfortunately, some systems apparently have a prototype for pause()
705 in F<unistd.h>, but don't actually have the function in the library.
706 (Or maybe they do have it in a library we're not using.)
708 Thus, the compiler sees something like
710 extern int pause(void);
712 #define pause() sleep((32767<<16)+32767)
714 and dies with an error message. (Some compilers don't mind this;
715 others apparently do.)
717 To work around this, 5.003_03 and later have the following in perl.h:
719 /* Some unistd.h's give a prototype for pause() even though
720 HAS_PAUSE ends up undefined. This causes the #define
721 below to be rejected by the compiler. Sigh.
726 # define Pause() sleep((32767<<16)+32767)
731 The curious reader may wonder why I didn't do the following in
737 sleep((32767<<16)+32767);
741 That is, since the function is missing, just provide it.
742 Then things would probably be been alright, it would seem.
744 Well, almost. It could be made to work. The problem arises from the
745 conflicting needs of dynamic loading and namespace protection.
747 For dynamic loading to work on AIX (and VMS) we need to provide a list
748 of symbols to be exported. This is done by the script F<perl_exp.SH>,
749 which reads F<global.sym> and F<interp.sym>. Thus, the C<pause>
750 symbol would have to be added to F<global.sym> So far, so good.
752 On the other hand, one of the goals of Perl5 is to make it easy to
753 either extend or embed perl and link it with other libraries. This
754 means we have to be careful to keep the visible namespace "clean".
755 That is, we don't want perl's global variables to conflict with
756 those in the other application library. Although this work is still
757 in progress, the way it is currently done is via the F<embed.h> file.
758 This file is built from the F<global.sym> and F<interp.sym> files,
759 since those files already list the globally visible symbols. If we
760 had added C<pause> to global.sym, then F<embed.h> would contain the
763 #define pause Perl_pause
765 and calls to C<pause> in the perl sources would now point to
766 C<Perl_pause>. Now, when B<ld> is run to build the F<perl> executable,
767 it will go looking for C<perl_pause>, which probably won't exist in any
768 of the standard libraries. Thus the build of perl will fail.
770 Those systems where C<HAS_PAUSE> is not defined would be ok, however,
771 since they would get a C<Perl_pause> function in util.c. The rest of
772 the world would be in trouble.
774 And yes, this scenario has happened. On SCO, the function C<chsize>
775 is available. (I think it's in F<-lx>, the Xenix compatibility
776 library.) Since the perl4 days (and possibly before), Perl has
777 included a C<chsize> function that gets called something akin to
780 I32 chsize(fd, length)
786 #define chsize Perl_chsize
788 to F<embed.h>, the compile started failing on SCO systems.
790 The "fix" is to give the function a different name. The one
791 implemented in 5.003_05 isn't optimal, but here's what was done:
794 # ifdef my_chsize /* Probably #defined to Perl_my_chsize in embed.h */
797 # define my_chsize chsize
800 My explanatory comment in patch 5.003_05 said:
802 Undef and then re-define my_chsize from Perl_my_chsize to
803 just plain chsize if this system HAS_CHSIZE. This probably only
804 applies to SCO. This shows the perils of having internal
805 functions with the same name as external library functions :-).
807 Now, we can safely put C<my_chsize> in F<global.sym>, export it, and
808 hide it with F<embed.h>.
810 To be consistent with what I did for C<pause>, I probably should have
811 called the new function C<Chsize>, rather than C<my_chsize>.
812 However, the perl sources are quite inconsistent on this (Consider
813 New, Mymalloc, and Myremalloc, to name just a few.)
815 There is a problem with this fix, however, in that C<Perl_chsize>
816 was available as a F<libperl.a> library function in 5.003, but it
817 isn't available any more (as of 5.003_07). This means that we've
818 broken binary compatibility. This is not good.
820 =item Providing missing functions -- some ideas
822 We currently don't have a standard way of handling such missing
823 function names. Right now, I'm effectively thinking aloud about a
824 solution. Some day, I'll try to formally propose a solution.
826 Part of the problem is that we want to have some functions listed as
827 exported but not have their names mangled by embed.h or possibly
828 conflict with names in standard system headers. We actually already
829 have such a list at the end of F<perl_exp.SH> (though that list is
832 # extra globals not included above.
833 cat <<END >> perl.exp
857 This still needs much thought, but I'm inclined to think that one
858 possible solution is to prefix all such functions with C<perl_> in the
859 source and list them along with the other C<perl_*> functions in
862 Thus, for C<chsize>, we'd do something like the following:
866 # define perl_chsize chsize
869 then in some file (e.g. F<util.c> or F<doio.c>) do
872 I32 perl_chsize(fd, length)
873 /* implement the function here . . . */
876 Alternatively, we could just always use C<chsize> everywhere and move
877 C<chsize> from F<global.sym> to the end of F<perl_exp.SH>. That would
878 probably be fine as long as our C<chsize> function agreed with all the
879 C<chsize> function prototypes in the various systems we'll be using.
880 As long as the prototypes in actual use don't vary that much, this is
881 probably a good alternative. (As a counter-example, note how Configure
882 and perl have to go through hoops to find and use get Malloc_t and
883 Free_t for C<malloc> and C<free>.)
885 At the moment, this latter option is what I tend to prefer.
887 =item All the world's a VAX
889 Sorry, showing my age:-). Still, all the world is not BSD 4.[34],
890 SVR4, or POSIX. Be aware that SVR3-derived systems are still quite
891 common (do you have any idea how many systems run SCO?) If you don't
892 have a bunch of v7 manuals handy, the metaconfig units (by default
893 installed in F</usr/local/lib/dist/U>) are a good resource to look at
898 =head1 Miscellaneous Topics
902 Why does perl use a metaconfig-generated Configure script instead of an
903 autoconf-generated configure script?
905 Metaconfig and autoconf are two tools with very similar purposes.
906 Metaconfig is actually the older of the two, and was originally written
907 by Larry Wall, while autoconf is probably now used in a wider variety of
908 packages. The autoconf info file discusses the history of autoconf and
909 how it came to be. The curious reader is referred there for further
912 Overall, both tools are quite good, I think, and the choice of which one
913 to use could be argued either way. In March, 1994, when I was just
914 starting to work on Configure support for Perl5, I considered both
915 autoconf and metaconfig, and eventually decided to use metaconfig for the
920 =item Compatibility with Perl4
922 Perl4 used metaconfig, so many of the #ifdef's were already set up for
923 metaconfig. Of course metaconfig had evolved some since Perl4's days,
924 but not so much that it posed any serious problems.
926 =item Metaconfig worked for me
928 My system at the time was Interactive 2.2, a SVR3.2/386 derivative that
929 also had some POSIX support. Metaconfig-generated Configure scripts
930 worked fine for me on that system. On the other hand, autoconf-generated
931 scripts usually didn't. (They did come quite close, though, in some
932 cases.) At the time, I actually fetched a large number of GNU packages
933 and checked. Not a single one configured and compiled correctly
934 out-of-the-box with the system's cc compiler.
936 =item Configure can be interactive
938 With both autoconf and metaconfig, if the script works, everything is
939 fine. However, one of my main problems with autoconf-generated scripts
940 was that if it guessed wrong about something, it could be B<very> hard to
941 go back and fix it. For example, autoconf always insisted on passing the
942 -Xp flag to cc (to turn on POSIX behavior), even when that wasn't what I
943 wanted or needed for that package. There was no way short of editing the
944 configure script to turn this off. You couldn't just edit the resulting
945 Makefile at the end because the -Xp flag influenced a number of other
948 Metaconfig's Configure scripts, on the other hand, can be interactive.
949 Thus if Configure is guessing things incorrectly, you can go back and fix
950 them. This isn't as important now as it was when we were actively
951 developing Configure support for new features such as dynamic loading,
952 but it's still useful occasionally.
956 At the time, autoconf-generated scripts were covered under the GNU Public
957 License, and hence weren't suitable for inclusion with Perl, which has a
958 different licensing policy. (Autoconf's licensing has since changed.)
962 Metaconfig builds up Configure from a collection of discrete pieces
963 called "units". You can override the standard behavior by supplying your
964 own unit. With autoconf, you have to patch the standard files instead.
965 I find the metaconfig "unit" method easier to work with. Others
966 may find metaconfig's units clumsy to work with.
970 =head2 @INC search order
972 By default, the list of perl library directories in @INC is the
980 Specifically, on my Solaris/x86 system, I run
981 B<sh Configure -Dprefix=/opt/perl> and I have the following
984 /opt/perl/lib/i86pc-solaris/5.00307
986 /opt/perl/lib/site_perl/i86pc-solaris
987 /opt/perl/lib/site_perl
989 That is, perl's directories come first, followed by the site-specific
992 The site libraries come second to support the usage of extensions
993 across perl versions. Read the relevant section in F<INSTALL> for
994 more information. If we ever make $sitearch version-specific, this
995 topic could be revisited.
997 =head2 Why isn't there a directory to override Perl's library?
999 Mainly because no one's gotten around to making one. Note that
1000 "making one" involves changing perl.c, Configure, config_h.SH (and
1001 associated files, see above), and I<documenting> it all in the
1004 Apparently, most folks who want to override one of the standard library
1005 files simply do it by overwriting the standard library files.
1009 In the perl.c sources, you'll find an undocumented APPLLIB_EXP
1010 variable, sort of like PRIVLIB_EXP and ARCHLIB_EXP (which are
1011 documented in config_h.SH). Here's what APPLLIB_EXP is for, from
1012 a mail message from Larry:
1014 The main intent of APPLLIB_EXP is for folks who want to send out a
1015 version of Perl embedded in their product. They would set the symbol
1016 to be the name of the library containing the files needed to run or to
1017 support their particular application. This works at the "override"
1018 level to make sure they get their own versions of any library code that
1019 they absolutely must have configuration control over.
1021 As such, I don't see any conflict with a sysadmin using it for a
1022 override-ish sort of thing, when installing a generic Perl. It should
1023 probably have been named something to do with overriding though. Since
1024 it's undocumented we could still change it... :-)
1026 Given that it's already there, you can use it to override
1027 distribution modules. If you do
1029 sh Configure -Dccflags='-DAPPLLIB_EXP=/my/override'
1031 then perl.c will put /my/override ahead of ARCHLIB and PRIVLIB.
1033 =head1 Upload Your Work to CPAN
1035 You can upload your work to CPAN if you have a CPAN id. Check out
1036 http://www.perl.com/CPAN/modules/04pause.html for information on
1037 _PAUSE_, the Perl Author's Upload Server.
1039 I typically upload both the patch file, e.g. F<perl5.004_08.pat.gz>
1040 and the full tar file, e.g. F<perl5.004_08.tar.gz>.
1042 If you want your patch to appear in the F<src/5.0/unsupported>
1043 directory on CPAN, send e-mail to the CPAN master librarian. (Check
1044 out http://www.perl.com/CPAN/CPAN.html ).
1046 =head1 Help Save the World
1048 You should definitely announce your patch on the perl5-porters list.
1049 You should also consider announcing your patch on
1050 comp.lang.perl.announce, though you should make it quite clear that a
1051 subversion is not a production release, and be prepared to deal with
1052 people who will not read your disclaimer.
1056 Here, in no particular order, are some Configure and build-related
1057 items that merit consideration. This list isn't exhaustive, it's just
1058 what I came up with off the top of my head.
1060 =head2 Good ideas waiting for round tuits
1066 I think we ought to support
1068 Configure -Dinstallprefix=/blah/blah
1070 Currently, we support B<-Dprefix=/blah/blah>, but the changing the install
1071 location has to be handled by something like the F<config.over> trick
1072 described in F<INSTALL>. AFS users also are treated specially.
1073 We should probably duplicate the metaconfig prefix stuff for an
1076 =item Configure -Dsrcdir=/blah/blah
1078 We should be able to emulate B<configure --srcdir>. Tom Tromey
1079 tromey@creche.cygnus.com has submitted some patches to
1080 the dist-users mailing list along these lines. Eventually, they ought
1081 to get folded back into the main distribution.
1083 =item Hint file fixes
1085 Various hint files work around Configure problems. We ought to fix
1086 Configure so that most of them aren't needed.
1088 =item Hint file information
1090 Some of the hint file information (particularly dynamic loading stuff)
1091 ought to be fed back into the main metaconfig distribution.
1095 =head2 Probably good ideas waiting for round tuits
1099 =item GNU configure --options
1101 I've received sensible suggestions for --exec_prefix and other
1102 GNU configure --options. It's not always obvious exactly what is
1103 intended, but this merits investigation.
1107 Currently, B<make clean> isn't all that useful, though
1108 B<make realclean> and B<make distclean> are. This needs a bit of
1109 thought and documentation before it gets cleaned up.
1111 =item Try gcc if cc fails
1113 Currently, we just give up.
1115 =item bypassing safe*alloc wrappers
1117 On some systems, it may be safe to call the system malloc directly
1118 without going through the util.c safe* layers. (Such systems would
1119 accept free(0), for example.) This might be a time-saver for systems
1120 that already have a good malloc. (Recent Linux libc's apparently have
1121 a nice malloc that is well-tuned for the system.)
1125 =head2 Vague possibilities
1131 Get some of the Macintosh stuff folded back into the main distribution.
1133 =item gconvert replacement
1135 Maybe include a replacement function that doesn't lose data in rare
1136 cases of coercion between string and numerical values.
1140 Can we support C<long long> on systems where C<long long> is larger
1141 than what we've been using for C<IV>? What if you can't C<sprintf>
1144 =item Improve makedepend
1146 The current makedepend process is clunky and annoyingly slow, but it
1147 works for most folks. Alas, it assumes that there is a filename
1148 $firstmakefile that the B<make> command will try to use before it uses
1149 F<Makefile>. Such may not be the case for all B<make> commands,
1150 particularly those on non-Unix systems.
1152 Probably some variant of the BSD F<.depend> file will be useful.
1153 We ought to check how other packages do this, if they do it at all.
1154 We could probably pre-generate the dependencies (with the exception of
1155 malloc.o, which could probably be determined at F<Makefile.SH>
1158 =item GNU Makefile standard targets
1160 GNU software generally has standardized Makefile targets. Unless we
1161 have good reason to do otherwise, I see no reason not to support them.
1165 Somehow, straighten out, document, and implement lockf(), flock(),
1166 and/or fcntl() file locking. It's a mess.
1172 Original author: Andy Dougherty doughera@lafcol.lafayette.edu .
1173 Additions by Chip Salzenberg chip@perl.com and
1174 Tim Bunce Tim.Bunce@ig.co.uk .
1176 All opinions expressed herein are those of the authorZ<>(s).
1178 =head1 LAST MODIFIED
1180 $Id: pumpkin.pod,v 1.13 1997/08/28 18:26:40 doughera Released $