3 Pumpkin - Notes on handling the Perl Patch Pumpkin And Porting Perl
7 There is no simple synopsis, yet.
11 This document attempts to begin to describe some of the considerations
12 involved in patching, porting, and maintaining perl.
14 This document is still under construction, and still subject to
15 significant changes. Still, I hope parts of it will be useful,
16 so I'm releasing it even though it's not done.
18 For the most part, it's a collection of anecdotal information that
19 already assumes some familiarity with the Perl sources. I really need
20 an introductory section that describes the organization of the sources
21 and all the various auxiliary files that are part of the distribution.
23 =head1 Where Do I Get Perl Sources and Related Material?
25 The Comprehensive Perl Archive Network (or CPAN) is the place to go.
26 There are many mirrors, but the easiest thing to use is probably
27 L<http://www.cpan.org/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 To subscribe to perl5-porters, send an email to
40 perl5-porters-subscribe@perl.org
42 Archives of the list are held at:
44 https://lists.perl.org/list/perl5-porters.html
46 =head1 How are Perl Releases Numbered?
48 Beginning with v5.6.0, even versions will stand for maintenance releases
49 and odd versions for development releases, i.e., v5.6.x for maintenance
50 releases, and v5.7.x for development releases. Before v5.6.0, subversions
51 _01 through _49 were reserved for bug-fix maintenance releases, and
52 subversions _50 through _99 for unstable development versions.
54 For example, in v5.6.1, the revision number is 5, the version is 6,
55 and 1 is the subversion.
57 For compatibility with the older numbering scheme the composite floating
58 point version number continues to be available as the magic variable $],
59 and amounts to C<$revision + $version/1000 + $subversion/100000>. This
60 can still be used in comparisons.
62 print "You've got an old perl\n" if $] < 5.005_03;
64 In addition, the version is also available as a string in $^V.
66 print "You've got a new perl\n" if $^V and $^V ge v5.6.0;
68 You can also require particular version (or later) with:
72 or using the new syntax available only from v5.6 onward:
76 At some point in the future, we may need to decide what to call the
77 next big revision. In the .package file used by metaconfig to
78 generate Configure, there are two variables that might be relevant:
79 $baserev=5 and $package=perl5.
81 Perl releases produced by the members of perl5-porters are usually
82 available on CPAN in the F<src/5.0/maint> and F<src/5.0/devel>
85 =head2 Maintenance and Development Subversions
87 The first rule of maintenance work is "First, do no harm."
89 Trial releases of bug-fix maintenance releases are announced on
90 perl5-porters. Trial releases use the new subversion number (to avoid
91 testers installing it over the previous release) and include a 'local
92 patch' entry in F<patchlevel.h>. The distribution file contains the
93 string C<MAINT_TRIAL> to make clear that the file is not meant for
96 In general, the names of official distribution files for the public
97 always match the regular expression:
99 ^perl\d+\.(\d+)\.\d+(-MAINT_TRIAL_\d+)\.tar\.gz$
101 C<$1> in the pattern is always an even number for maintenance
102 versions, and odd for developer releases.
104 In the past it has been observed that pumpkings tend to invent new
105 naming conventions on the fly. If you are a pumpking, before you
106 invent a new name for any of the three types of perl distributions,
107 please inform the guys from the CPAN who are doing indexing and
108 provide the trees of symlinks and the like. They will have to know
109 I<in advance> what you decide.
111 =head2 Why is it called the patch pumpkin?
113 Chip Salzenberg gets credit for that, with a nod to his cow orker,
114 David Croy. We had passed around various names (baton, token, hot
115 potato) but none caught on. Then, Chip asked:
119 Who has the patch pumpkin?
121 To explain: David Croy once told me once that at a previous job,
122 there was one tape drive and multiple systems that used it for backups.
123 But instead of some high-tech exclusion software, they used a low-tech
124 method to prevent multiple simultaneous backups: a stuffed pumpkin.
125 No one was allowed to make backups unless they had the "backup pumpkin".
131 =head1 Philosophical Issues in Patching and Porting Perl
133 There are no absolute rules, but there are some general guidelines I
134 have tried to follow as I apply patches to the perl sources.
135 (This section is still under construction.)
137 =head2 Solve problems as generally as possible
139 Never implement a specific restricted solution to a problem when you
140 can solve the same problem in a more general, flexible way.
142 For example, for dynamic loading to work on some SVR4 systems, we had
143 to build a shared libperl.so library. In order to build "FAT" binaries
144 on NeXT 4.0 systems, we had to build a special libperl library. Rather
145 than continuing to build a contorted nest of special cases, I
146 generalized the process of building libperl so that NeXT and SVR4 users
147 could still get their work done, but others could build a shared
148 libperl if they wanted to as well.
150 Contain your changes carefully. Assume nothing about other operating
151 systems, not even closely related ones. Your changes must not affect
154 Spy shamelessly on how similar patching or porting issues have been
157 If feasible, try to keep filenames 8.3-compliant to humor those poor
158 souls that get joy from running Perl under such dire limitations.
159 There's a script, F<check83.pl>, for keeping your nose 8.3-clean.
160 In a similar vein, do not create files or directories which differ only
161 in case (upper versus lower).
163 =head2 Seek consensus on major changes
165 If you are making big changes, don't do it in secret. Discuss the
166 ideas in advance on perl5-porters.
168 =head2 Keep the documentation up-to-date
170 If your changes may affect how users use perl, then check to be sure
171 that the documentation is in sync with your changes. Be sure to
172 check all the files F<pod/*.pod> and also the F<INSTALL> document.
174 Consider writing the appropriate documentation first and then
175 implementing your change to correspond to the documentation.
177 =head2 Avoid machine-specific #ifdef's
179 To the extent reasonable, try to avoid machine-specific #ifdef's in
180 the sources. Instead, use feature-specific #ifdef's. The reason is
181 that the machine-specific #ifdef's may not be valid across major
182 releases of the operating system. Further, the feature-specific tests
183 may help out folks on another platform who have the same problem.
185 =head2 Machine-specific files
191 If you have many machine-specific #defines or #includes, consider
192 creating an "osish.h" (F<os2ish.h>, F<vmsish.h>, and so on) and including
193 that in F<perl.h>. If you have several machine-specific files (function
194 emulations, function stubs, build utility wrappers) you may create a
195 separate subdirectory (djgpp, win32) and put the files in there.
196 Remember to update C<MANIFEST> when you add files.
198 If your system supports dynamic loading but none of the existing
199 methods at F<ext/DynaLoader/dl_*.xs> work for you, you must write
200 a new one. Study the existing ones to see what kind of interface
205 There are two kinds of hints: hints for building Perl and hints for
206 extensions. The former live in the C<hints> subdirectory, the latter
207 in C<ext/*/hints> subdirectories.
209 The top level hints are Bourne-shell scripts that set, modify and
210 unset appropriate Configure variables, based on the Configure command
211 line options and possibly existing config.sh and Policy.sh files from
212 previous Configure runs.
214 The extension hints are written in Perl (by the time they are used
215 miniperl has been built) and control the building of their respective
216 extensions. They can be used to for example manipulate compilation
219 =item build and installation Makefiles, scripts, and so forth
221 Sometimes you will also need to tweak the Perl build and installation
222 procedure itself, like for example F<Makefile.SH> and F<installperl>.
223 Tread very carefully, even more than usual. Contain your changes
228 Many of the tests in C<t> subdirectory assume machine-specific things
229 like existence of certain functions, something about filesystem
230 semantics, certain external utilities and their error messages. Use
231 the C<$^O> and the C<Config> module (which contains the results of the
232 Configure run, in effect the C<config.sh> converted to Perl) to either
233 skip (preferably not) or customize (preferable) the tests for your
238 Certain standard modules may need updating if your operating system
239 sports for example a native filesystem naming. You may want to update
240 some or all of the modules File::Basename, File::Spec, File::Path, and
241 File::Copy to become aware of your native filesystem syntax and
244 Remember to have a $VERSION in the modules. You can use the
245 F<Porting/checkVERSION.pl> script for checking this.
249 If your operating system comes from outside UNIX you almost certainly
250 will have differences in the available operating system functionality
251 (missing system calls, different semantics, whatever). Please
252 document these at F<pod/perlport.pod>. If your operating system is
253 the first B<not> to have a system call also update the list of
254 "portability-bewares" at the beginning of F<pod/perlfunc.pod>.
256 A file called F<README.youros> at the top level that explains things
257 like how to install perl at this platform, where to get any possibly
258 required additional software, and for example what test suite errors
259 to expect, is nice too. Such files are in the process of being written
260 in pod format and will eventually be renamed F<INSTALL.youros>.
262 You may also want to write a separate F<.pod> file for your operating
263 system to tell about existing mailing lists, os-specific modules,
264 documentation, whatever. Please name these along the lines of
265 F<perl>I<youros>.pod. [unfinished: where to put this file (the pod/
266 subdirectory, of course: but more importantly, which/what index files
271 =head2 Allow for lots of testing
273 We should never release a main version without testing it as a
276 =head2 Test popular applications and modules.
278 We should never release a main version without testing whether or not
279 it breaks various popular modules and applications. A partial list of
280 such things would include majordomo, metaconfig, apache, Tk, CGI,
281 libnet, and libwww, to name just a few. Of course it's quite possible
282 that some of those things will be just plain broken and need to be fixed,
283 but, in general, we ought to try to avoid breaking widely-installed
286 =head2 Automated generation of derivative files
288 The F<embed.h>, F<keywords.h>, F<opcode.h>, F<regcharclass.h>,
289 F<l1_char_class_tab.h>, and F<perltoc.pod> files
290 are all automatically generated by perl scripts. In general, don't
291 patch these directly; patch the data files instead.
293 Also F<Makefile> is automatically produced from F<Makefile.SH>.
294 In general, look out for all F<*.SH> files.
296 Finally, the sample files F<config.sh> and F<config_H> in the
297 F<Porting/> subdirectory are generated by the script F<Porting/mksample>.
299 =head3 Files generated by metaconfig
301 F<Configure>, F<config_h.SH> and F<Porting/Glossary> are generated by
302 B<metaconfig> (see below for more information on how to use this system)
303 and direct changes to these files should in general not be pushed to blead.
315 changes pre-approved by the metaconfig maintainers
319 Such changes should also be notified to the metaconfig maintainers by
320 creating an issue at <https://github.com/Perl/metaconfig/issues>.
322 Alternatively, do consider if the F<*ish.h> files or the hint files might
323 be a better place for your changes.
325 =head1 Working with metaconfig
327 Information about how to use metaconfig can be found in the F<README>
328 and F<README_U> files in the metaconfig repository containing Perl's
332 git clone https://github.com/Perl/metaconfig.git
333 # or using a registered github.com identity with ssh
334 git clone github.com:Perl/metaconfig.git
336 Since metaconfig is hard to change, running correction scripts after
337 this generation is sometimes needed. Configure gained complexity over
338 time, and the order in which config_h.SH is generated can cause havoc
339 when compiling perl. Therefor, you need to run Porting/config_h.pl
340 after that generation. All that and more is described in the README
341 files that come with the metaunits.
343 =head1 How to Make a Distribution
345 This section has now been expanded and moved into its own file,
346 F<Porting/release_managers_guide.pod>.
348 I've kept some of the subsections here for now, as they don't directly
349 relate to building a release any more, but still contain what might be
350 useful information - DAPM 7/2009.
354 If you are using metaconfig to regenerate Configure, then you should note
355 that metaconfig actually uses MANIFEST.new, so you want to be sure
356 MANIFEST.new is up-to-date too. I haven't found the MANIFEST/MANIFEST.new
357 distinction particularly useful, but that's probably because I still haven't
358 learned how to use the full suite of tools in the dist distribution.
363 This will build a config.sh and config.h. You can skip this if you haven't
364 changed Configure or config_h.SH at all. I use the following command
366 sh Configure -Dprefix=/opt/perl -Doptimize=-O -Dusethreads \
368 -Dcf_email='yourname@yourhost.yourplace.com' \
369 -Dperladmin='yourname@yourhost.yourplace.com' \
370 -Dmydomain='.yourplace.com' \
371 -Dmyhostname='yourhost' \
374 =head2 Update Porting/config.sh and Porting/config_H
377 This section needs revision. We're currently working on easing
378 the task of keeping the vms, win32, and plan9 config.sh info
379 up-to-date. The plan is to use keep up-to-date 'canned' config.sh
380 files in the appropriate subdirectories and then generate 'canned'
381 config.h files for vms, win32, etc. from the generic config.sh file.
382 This is to ease maintenance. When Configure gets updated, the parts
383 sometimes get scrambled around, and the changes in config_H can
384 sometimes be very hard to follow. config.sh, on the other hand, can
385 safely be sorted, so it's easy to track (typically very small) changes
386 to config.sh and then propagate them to a canned 'config.h' by any
387 number of means, including a perl script in win32/ or carrying
388 F<config.sh> and F<config_h.SH> to a Unix system and running sh
389 config_h.SH.) Vms uses F<configure.com> to generate its own F<config.sh>
390 and F<config.h>. If you want to add a new variable to F<config.sh> check
391 with vms folk how to add it to configure.com too.
394 The F<Porting/config.sh> and F<Porting/config_H> files are provided to
395 help those folks who can't run Configure. It is important to keep
396 them up-to-date. If you have changed F<config_h.SH>, those changes must
397 be reflected in config_H as well. (The name config_H was chosen to
398 distinguish the file from config.h even on case-insensitive file systems.)
399 Simply edit the existing config_H file; keep the first few explanatory
400 lines and then copy your new config.h below.
402 It may also be necessary to update win32/config.?c, and
403 F<plan9/config.plan9>, though you should be quite careful in doing so if
404 you are not familiar with those systems. You might want to issue your
405 patch with a promise to quickly issue a follow-up that handles those
408 =head2 make regen_perly
410 If F<perly.y> has been edited, it is necessary to run this target to rebuild
411 F<perly.h>, F<perly.act> and F<perly.tab>. In fact this target just runs the Perl
412 script F<regen_perly.pl>. Note that F<perly.c> is I<not> rebuilt; this is just a
413 plain static file now.
415 This target relies on you having Bison installed on your system. Running
416 the target will tell you if you haven't got the right version, and if so,
417 where to get the right one. Or if you prefer, you could hack
418 F<regen_perly.pl> to work with your version of Bison. The important things
419 are that the regexes can still extract out the right chunks of the Bison
420 output into F<perly.act> and F<perly.tab>, and that the contents of those two
421 files, plus F<perly.h>, are functionally equivalent to those produced by the
422 supported version of Bison.
424 Note that in the old days, you had to do C<make run_byacc> instead.
426 =head2 make regen_all
428 This target takes care of the regen_headers target.
429 (It used to also call the regen_pods target, but that has been eliminated.)
431 =head2 make regen_headers
433 The F<embed.h>, F<keywords.h>, and F<opcode.h> files are all automatically
434 generated by perl scripts. Since the user isn't guaranteed to have a
435 working perl, we can't require the user to generate them. Hence you have
436 to, if you're making a distribution.
438 I used to include rules like the following in the makefile:
440 # The following three header files are generated automatically
441 # The correct versions should be already supplied with the perl kit,
442 # in case you don't have perl or 'sh' available.
443 # The - is to ignore error return codes in case you have the source
444 # installed read-only or you don't have perl yet.
445 keywords.h: keywords.pl
446 @echo "Don't worry if this fails."
450 However, I got B<lots> of mail consisting of people worrying because the
451 command failed. I eventually decided that I would save myself time
452 and effort by manually running C<make regen_headers> myself rather
453 than answering all the questions and complaints about the failing
456 =head2 globvar.sym, and perlio.sym
458 Make sure these files are up-to-date. Read the comments in these
459 files and in F<perl_exp.SH> to see what to do.
461 =head2 Binary compatibility
463 If you do change F<embed.fnc> think carefully about
464 what you are doing. To the extent reasonable, we'd like to maintain
465 source and binary compatibility with older releases of perl. That way,
466 extensions built under one version of perl will continue to work with
467 new versions of perl.
469 Of course, some incompatible changes may well be necessary. I'm just
470 suggesting that we not make any such changes without thinking carefully
471 about them first. If possible, we should provide
472 backwards-compatibility stubs. There's a lot of XS code out there.
473 Let's not force people to keep changing it.
477 F<dist/Devel-PPPort/PPPort.pm> needs to be synchronized to include all
478 new macros added to .h files (normally F<perl.h> and F<XSUB.h>, but others
479 as well). Since chances are that when a new macro is added the
480 committer will forget to update F<PPPort.pm>, it's the best to diff for
481 changes in .h files when making a new release and making sure that
482 F<PPPort.pm> contains them all.
484 The pumpking can delegate the synchronization responsibility to anybody
485 else, but the release process is the only place where we can make sure
486 that no new macros fell through the cracks.
491 The F<Porting/todo.pod> file contains a roughly-categorized unordered
492 list of aspects of Perl that could use enhancement, features that could
493 be added, areas that could be cleaned up, and so on. During your term
494 as pumpkin-holder, you will probably address some of these issues, and
495 perhaps identify others which, while you decide not to address them this
496 time around, may be tackled in the future. Update the file to reflect
497 the situation as it stands when you hand over the pumpkin.
499 You might like, early in your pumpkin-holding career, to see if you
500 can find champions for particular issues on the to-do list: an issue
501 owned is an issue more likely to be resolved.
503 There are also some more porting-specific L</Todo> items later in this
506 =head2 OS/2-specific updates
508 In the os2 directory is F<diff.configure>, a set of OS/2-specific
509 diffs against B<Configure>. If you make changes to Configure, you may
510 want to consider regenerating this diff file to save trouble for the
513 You can also consider the OS/2 diffs as reminders of portability
514 things that need to be fixed in Configure.
516 =head2 VMS-specific updates
518 The Perl revision number appears as "perl5" in F<configure.com>.
519 It is courteous to update that if necessary.
522 =head2 Making a new patch
524 I find the F<makepatch> utility quite handy for making patches.
525 You can obtain it from any CPAN archive under
526 L<https://www.cpan.org/authors/id/J/JV/JV/>. There are a couple
527 of differences between my version and the standard one. I have mine do
530 # Print a reassuring "End of Patch" note so people won't
531 # wonder if their mailer truncated patches.
532 print "\n\nEnd of Patch.\n";
534 at the end. That's because I used to get questions from people asking
535 if their mail was truncated.
537 It also writes Index: lines which include the new directory prefix
538 (change Index: print, approx line 294 or 310 depending on the version,
539 to read: print PATCH ("Index: $newdir$new\n");). That helps patches
540 work with more POSIX conformant patch programs.
542 Here's how I generate a new patch. I'll use the hypothetical
543 5.004_07 to 5.004_08 patch as an example.
545 # unpack perl5.004_07/
546 gzip -d -c perl5.004_07.tar.gz | tar -xof -
547 # unpack perl5.004_08/
548 gzip -d -c perl5.004_08.tar.gz | tar -xof -
549 makepatch perl5.004_07 perl5.004_08 > perl5.004_08.pat
551 Makepatch will automatically generate appropriate B<rm> commands to remove
552 deleted files. Unfortunately, it will not correctly set permissions
553 for newly created files, so you may have to do so manually. For example,
554 patch 5.003_04 created a new test F<t/op/gv.t> which needs to be executable,
555 so at the top of the patch, I inserted the following lines:
561 Now, of course, my patch is now wrong because makepatch didn't know I
562 was going to do that command, and it patched against /dev/null.
564 So, what I do is sort out all such shell commands that need to be in the
565 patch (including possible mv-ing of files, if needed) and put that in the
566 shell commands at the top of the patch. Next, I delete all the patch parts
567 of perl5.004_08.pat, leaving just the shell commands. Then, I do the
571 sh ../perl5.004_08.pat
573 makepatch perl5.004_07 perl5.004_08 >> perl5.004_08.pat
575 (Note the append to preserve my shell commands.)
576 Now, my patch will line up with what the end users are going to do.
578 =head2 Testing your patch
580 It seems obvious, but be sure to test your patch. That is, verify that
581 it produces exactly the same thing as your full distribution.
584 gzip -d -c perl5.004_07.tar.gz | tar -xf -
586 sh ../perl5.004_08.pat
587 patch -p1 -N < ../perl5.004_08.pat
589 gdiff -r perl5.004_07 perl5.004_08
591 where B<gdiff> is GNU diff. Other diff's may also do recursive checking.
595 Again, it's obvious, but you should test your new version as widely as you
596 can. You can be sure you'll hear about it quickly if your version doesn't
597 work on both ANSI and pre-ANSI compilers, and on common systems such as
598 SunOS 4.1.[34], Solaris, and Linux.
600 If your changes include conditional code, try to test the different
601 branches as thoroughly as you can. For example, if your system
602 supports dynamic loading, you can also test static loading with
606 You can also hand-tweak your config.h to try out different #ifdef
613 =item gcc -ansi -pedantic
615 Configure -Dgccansipedantic [ -Dcc=gcc ] will enable (via the cflags script,
616 not $Config{ccflags}) the gcc strict ANSI C flags -ansi and -pedantic for
617 the compilation of the core files on platforms where it knows it can
618 do so (like Linux, see cflags.SH for the full list), and on some
619 platforms only one (Solaris can do only -pedantic, not -ansi).
620 The flag -DPERL_GCC_PEDANTIC also gets added, since gcc does not add
621 any internal cpp flag to signify that -pedantic is being used, as it
622 does for -ansi (__STRICT_ANSI__).
624 Note that the -ansi and -pedantic are enabled only for version 3 (and
625 later) of gcc, since even gcc version 2.95.4 finds lots of seemingly
626 false "value computed not used" errors from Perl.
628 The -ansi and -pedantic are useful in catching at least the following
629 nonportable practices:
635 gcc-specific extensions
651 The -Dgccansipedantic should be used only when cleaning up the code,
652 not for production builds, since otherwise gcc cannot inline certain
657 =head1 Common Gotchas
661 =item Probably Prefer POSIX
663 It's often the case that you'll need to choose whether to do
664 something the BSD-ish way or the POSIX-ish way. It's usually not
665 a big problem when the two systems use different names for similar
666 functions, such as memcmp() and bcmp(). The perl.h header file
667 handles these by appropriate #defines, selecting the POSIX mem*()
668 functions if available, but falling back on the b*() functions, if
671 More serious is the case where some brilliant person decided to
672 use the same function name but give it a different meaning or
673 calling sequence :-). getpgrp() and setpgrp() come to mind.
674 These are a real problem on systems that aim for conformance to
675 one standard (e.g. POSIX), but still try to support the other way
676 of doing things (e.g. BSD). My general advice (still not really
677 implemented in the source) is to do something like the following.
678 Suppose there are two alternative versions, fooPOSIX() and
682 /* use fooPOSIX(); */
685 /* try to emulate fooPOSIX() with fooBSD();
686 perhaps with the following: */
687 # define fooPOSIX fooBSD
689 # /* Uh, oh. We have to supply our own. */
690 # define fooPOSIX Perl_fooPOSIX
694 =item Think positively
696 If you need to add an #ifdef test, it is usually easier to follow if you
697 think positively, e.g.
699 #ifdef HAS_NEATO_FEATURE
700 /* use neato feature */
702 /* use some fallback mechanism */
705 rather than the more impenetrable
707 #ifndef MISSING_NEATO_FEATURE
708 /* Not missing it, so we must have it, so use it */
710 /* Are missing it, so fall back on something else. */
713 Of course for this toy example, there's not much difference. But when
714 the #ifdef's start spanning a couple of screen fulls, and the #else's
715 are marked something like
717 #else /* !MISSING_NEATO_FEATURE */
719 I find it easy to get lost.
721 =item Providing Missing Functions -- Problem
723 Not all systems have all the neat functions you might want or need, so
724 you might decide to be helpful and provide an emulation. This is
725 sound in theory and very kind of you, but please be careful about what
726 you name the function. Let me use the C<pause()> function as an
729 Perl5.003 has the following in F<perl.h>
732 #define pause() sleep((32767<<16)+32767)
735 Configure sets HAS_PAUSE if the system has the pause() function, so
736 this #define only kicks in if the pause() function is missing.
739 Unfortunately, some systems apparently have a prototype for pause()
740 in F<unistd.h>, but don't actually have the function in the library.
741 (Or maybe they do have it in a library we're not using.)
743 Thus, the compiler sees something like
745 extern int pause(void);
747 #define pause() sleep((32767<<16)+32767)
749 and dies with an error message. (Some compilers don't mind this;
750 others apparently do.)
752 To work around this, 5.003_03 and later have the following in perl.h:
754 /* Some unistd.h's give a prototype for pause() even though
755 HAS_PAUSE ends up undefined. This causes the #define
756 below to be rejected by the compiler. Sigh.
761 # define Pause() sleep((32767<<16)+32767)
766 The curious reader may wonder why I didn't do the following in
772 sleep((32767<<16)+32767);
776 That is, since the function is missing, just provide it.
777 Then things would probably be been alright, it would seem.
779 Well, almost. It could be made to work. The problem arises from the
780 conflicting needs of dynamic loading and namespace protection.
782 For dynamic loading to work on AIX (and VMS) we need to provide a list
783 of symbols to be exported. This is done by the script F<perl_exp.SH>,
784 which reads F<embed.fnc>. Thus, the C<pause>
785 symbol would have to be added to F<embed.fnc> So far, so good.
787 On the other hand, one of the goals of Perl5 is to make it easy to
788 either extend or embed perl and link it with other libraries. This
789 means we have to be careful to keep the visible namespace "clean".
790 That is, we don't want perl's global variables to conflict with
791 those in the other application library. Although this work is still
792 in progress, the way it is currently done is via the F<embed.h> file.
793 This file is built from the F<embed.fnc> file,
794 since those files already list the globally visible symbols. If we
795 had added C<pause> to F<embed.fnc>, then F<embed.h> would contain the
798 #define pause Perl_pause
800 and calls to C<pause> in the perl sources would now point to
801 C<Perl_pause>. Now, when B<ld> is run to build the F<perl> executable,
802 it will go looking for C<perl_pause>, which probably won't exist in any
803 of the standard libraries. Thus the build of perl will fail.
805 Those systems where C<HAS_PAUSE> is not defined would be ok, however,
806 since they would get a C<Perl_pause> function in util.c. The rest of
807 the world would be in trouble.
809 And yes, this scenario has happened. On SCO, the function C<chsize>
810 is available. (I think it's in F<-lx>, the Xenix compatibility
811 library.) Since the perl4 days (and possibly before), Perl has
812 included a C<chsize> function that gets called something akin to
815 I32 chsize(fd, length)
821 #define chsize Perl_chsize
823 to F<embed.h>, the compile started failing on SCO systems.
825 The "fix" is to give the function a different name. The one
826 implemented in 5.003_05 isn't optimal, but here's what was done:
829 # ifdef my_chsize /* Probably #defined to Perl_my_chsize */
830 # undef my_chsize /* in embed.h */
832 # define my_chsize chsize
835 My explanatory comment in patch 5.003_05 said:
837 Undef and then re-define my_chsize from Perl_my_chsize to
838 just plain chsize if this system HAS_CHSIZE. This probably only
839 applies to SCO. This shows the perils of having internal
840 functions with the same name as external library functions :-).
842 Now, we can safely put C<my_chsize> in C<embed.fnc>, export it, and
843 hide it with F<embed.h>.
845 To be consistent with what I did for C<pause>, I probably should have
846 called the new function C<Chsize>, rather than C<my_chsize>.
847 However, the perl sources are quite inconsistent on this (Consider
848 New, Mymalloc, and Myremalloc, to name just a few.)
850 There is a problem with this fix, however, in that C<Perl_chsize>
851 was available as a F<libperl.a> library function in 5.003, but it
852 isn't available any more (as of 5.003_07). This means that we've
853 broken binary compatibility. This is not good.
855 =item Providing missing functions -- some ideas
857 We currently don't have a standard way of handling such missing
858 function names. Right now, I'm effectively thinking aloud about a
859 solution. Some day, I'll try to formally propose a solution.
861 Part of the problem is that we want to have some functions listed as
862 exported but not have their names mangled by embed.h or possibly
863 conflict with names in standard system headers. We actually already
864 have such a list at the end of F<perl_exp.SH> (though that list is
867 # extra globals not included above.
868 cat <<END >> perl.exp
892 This still needs much thought, but I'm inclined to think that one
893 possible solution is to prefix all such functions with C<perl_> in the
894 source and list them along with the other C<perl_*> functions in
897 Thus, for C<chsize>, we'd do something like the following:
901 # define perl_chsize chsize
904 then in some file (e.g. F<util.c> or F<doio.c>) do
907 I32 perl_chsize(fd, length)
908 /* implement the function here . . . */
911 Alternatively, we could just always use C<chsize> everywhere and move
912 C<chsize> from F<embed.fnc> to the end of F<perl_exp.SH>. That would
913 probably be fine as long as our C<chsize> function agreed with all the
914 C<chsize> function prototypes in the various systems we'll be using.
915 As long as the prototypes in actual use don't vary that much, this is
916 probably a good alternative. (As a counter-example, note how Configure
917 and perl have to go through hoops to find and use get Malloc_t and
918 Free_t for C<malloc> and C<free>.)
920 At the moment, this latter option is what I tend to prefer.
922 =item All the world's a VAX
924 Sorry, showing my age:-). Still, all the world is not BSD 4.[34],
925 SVR4, or POSIX. Be aware that SVR3-derived systems are still quite
926 common (do you have any idea how many systems run SCO?) If you don't
927 have a bunch of v7 manuals handy, the metaconfig units (by default
928 installed in F</usr/local/lib/dist/U>) are a good resource to look at
933 =head1 Miscellaneous Topics
937 Why does perl use a metaconfig-generated Configure script instead of an
938 autoconf-generated configure script?
940 Metaconfig and autoconf are two tools with very similar purposes.
941 Metaconfig is actually the older of the two, and was originally written
942 by Larry Wall, while autoconf is probably now used in a wider variety of
943 packages. The autoconf info file discusses the history of autoconf and
944 how it came to be. The curious reader is referred there for further
947 Overall, both tools are quite good, I think, and the choice of which one
948 to use could be argued either way. In March, 1994, when I was just
949 starting to work on Configure support for Perl5, I considered both
950 autoconf and metaconfig, and eventually decided to use metaconfig for the
955 =item Compatibility with Perl4
957 Perl4 used metaconfig, so many of the #ifdef's were already set up for
958 metaconfig. Of course metaconfig had evolved some since Perl4's days,
959 but not so much that it posed any serious problems.
961 =item Metaconfig worked for me
963 My system at the time was Interactive 2.2, an SVR3.2/386 derivative that
964 also had some POSIX support. Metaconfig-generated Configure scripts
965 worked fine for me on that system. On the other hand, autoconf-generated
966 scripts usually didn't. (They did come quite close, though, in some
967 cases.) At the time, I actually fetched a large number of GNU packages
968 and checked. Not a single one configured and compiled correctly
969 out-of-the-box with the system's cc compiler.
971 =item Configure can be interactive
973 With both autoconf and metaconfig, if the script works, everything is
974 fine. However, one of my main problems with autoconf-generated scripts
975 was that if it guessed wrong about something, it could be B<very> hard to
976 go back and fix it. For example, autoconf always insisted on passing the
977 -Xp flag to cc (to turn on POSIX behavior), even when that wasn't what I
978 wanted or needed for that package. There was no way short of editing the
979 configure script to turn this off. You couldn't just edit the resulting
980 Makefile at the end because the -Xp flag influenced a number of other
983 Metaconfig's Configure scripts, on the other hand, can be interactive.
984 Thus if Configure is guessing things incorrectly, you can go back and fix
985 them. This isn't as important now as it was when we were actively
986 developing Configure support for new features such as dynamic loading,
987 but it's still useful occasionally.
991 At the time, autoconf-generated scripts were covered under the GNU Public
992 License, and hence weren't suitable for inclusion with Perl, which has a
993 different licensing policy. (Autoconf's licensing has since changed.)
997 Metaconfig builds up Configure from a collection of discrete pieces
998 called "units". You can override the standard behavior by supplying your
999 own unit. With autoconf, you have to patch the standard files instead.
1000 I find the metaconfig "unit" method easier to work with. Others
1001 may find metaconfig's units clumsy to work with.
1005 =head2 Why isn't there a directory to override Perl's library?
1007 Mainly because no one's gotten around to making one. Note that
1008 "making one" involves changing perl.c, Configure, config_h.SH (and
1009 associated files, see above), and I<documenting> it all in the
1012 Apparently, most folks who want to override one of the standard library
1013 files simply do it by overwriting the standard library files.
1017 In the perl.c sources, you'll find an undocumented APPLLIB_EXP
1018 variable, sort of like PRIVLIB_EXP and ARCHLIB_EXP (which are
1019 documented in config_h.SH). Here's what APPLLIB_EXP is for, from
1020 a mail message from Larry:
1022 The main intent of APPLLIB_EXP is for folks who want to send out a
1023 version of Perl embedded in their product. They would set the
1024 symbol to be the name of the library containing the files needed
1025 to run or to support their particular application. This works at
1026 the "override" level to make sure they get their own versions of
1027 any library code that they absolutely must have configuration
1030 As such, I don't see any conflict with a sysadmin using it for a
1031 override-ish sort of thing, when installing a generic Perl. It
1032 should probably have been named something to do with overriding
1033 though. Since it's undocumented we could still change it... :-)
1035 Given that it's already there, you can use it to override distribution modules.
1036 One way to do that is to add
1038 ccflags="$ccflags -DAPPLLIB_EXP=\"/my/override\""
1040 to your config.over file. (You have to be particularly careful to get the
1041 double quotes in. APPLLIB_EXP must be a valid C string. It might
1042 actually be easier to just #define it yourself in perl.c.)
1044 Then perl.c will put /my/override ahead of ARCHLIB and PRIVLIB. Perl will
1045 also search architecture-specific and version-specific subdirectories of
1048 =head2 Shared libperl.so location
1050 Why isn't the shared libperl.so installed in /usr/lib/ along
1051 with "all the other" shared libraries? Instead, it is installed
1052 in $archlib, which is typically something like
1054 /usr/local/lib/perl5/archname/5.00404
1056 and is architecture- and version-specific.
1058 The basic reason why a shared libperl.so gets put in $archlib is so that
1059 you can have more than one version of perl on the system at the same time,
1060 and have each refer to its own libperl.so.
1062 Three examples might help. All of these work now; none would work if you
1063 put libperl.so in /usr/lib.
1069 Suppose you want to have both threaded and non-threaded perl versions
1070 around. Configure will name both perl libraries "libperl.so" (so that
1071 you can link to them with -lperl). The perl binaries tell them apart
1072 by having looking in the appropriate $archlib directories.
1076 Suppose you have perl5.004_04 installed and you want to try to compile
1077 it again, perhaps with different options or after applying a patch.
1078 If you already have libperl.so installed in /usr/lib/, then it may be
1079 either difficult or impossible to get ld.so to find the new libperl.so
1080 that you're trying to build. If, instead, libperl.so is tucked away in
1081 $archlib, then you can always just change $archlib in the current perl
1082 you're trying to build so that ld.so won't find your old libperl.so.
1083 (The INSTALL file suggests you do this when building a debugging perl.)
1087 The shared perl library is not a "well-behaved" shared library with
1088 proper major and minor version numbers, so you can't necessarily
1089 have perl5.004_04 and perl5.004_05 installed simultaneously. Suppose
1090 perl5.004_04 were to install /usr/lib/libperl.so.4.4, and perl5.004_05
1091 were to install /usr/lib/libperl.so.4.5. Now, when you try to run
1092 perl5.004_04, ld.so might try to load libperl.so.4.5, since it has
1093 the right "major version" number. If this works at all, it almost
1094 certainly defeats the reason for keeping perl5.004_04 around. Worse,
1095 with development subversions, you certainly can't guarantee that
1096 libperl.so.4.4 and libperl.so.4.55 will be compatible.
1098 Anyway, all this leads to quite obscure failures that are sure to drive
1099 casual users crazy. Even experienced users will get confused :-). Upon
1100 reflection, I'd say leave libperl.so in $archlib.
1104 =head2 Indentation style
1106 Over the years Perl has become a mishmash of
1107 various indentation styles, but the original "Larry style" can
1108 probably be restored with (GNU) indent somewhat like this:
1110 indent -kr -nce -psl -sc
1112 A more ambitious solution would also specify a list of Perl specific
1113 types with -TSV -TAV -THV .. -TMAGIC -TPerlIO ... but that list would
1114 be quite ungainly. Also note that GNU indent also doesn't do aligning
1115 of consecutive assignments, which would truly wreck the layout in
1116 places like sv.c:Perl_sv_upgrade() or sv.c:Perl_clone_using().
1117 Similarly nicely aligned &&s, ||s and ==s would not be respected.
1119 =head1 Upload Your Work to CPAN
1121 You can upload your work to CPAN if you have a CPAN id. Check out
1122 L<http://www.cpan.org/modules/04pause.html> for information on
1123 _PAUSE_, the Perl Author's Upload Server.
1125 I typically upload both the patch file, e.g. F<perl5.004_08.pat.gz>
1126 and the full tar file, e.g. F<perl5.004_08.tar.gz>.
1128 If you want your patch to appear in the F<src/5.0/unsupported>
1129 directory on CPAN, send e-mail to the CPAN master librarian. (Check
1130 out L<http://www.cpan.org/CPAN.html> ).
1132 =head1 Help Save the World
1134 You should definitely announce your patch on the perl5-porters list.
1138 Here, in no particular order, are some Configure and build-related
1139 items that merit consideration. This list isn't exhaustive, it's just
1140 what I came up with off the top of my head.
1142 =head2 Adding missing library functions to Perl
1144 The perl Configure script automatically determines which headers and
1145 functions you have available on your system and arranges for them to be
1146 included in the compilation and linking process. Occasionally, when porting
1147 perl to an operating system for the first time, you may find that the
1148 operating system is missing a key function. While perl may still build
1149 without this function, no perl program will be able to reference the missing
1150 function. You may be able to write the missing function yourself, or you
1151 may be able to find the missing function in the distribution files for
1152 another software package. In this case, you need to instruct the perl
1153 configure-and-build process to use your function. Perform these steps.
1159 Code and test the function you wish to add. Test it carefully; you will
1160 have a much easier time debugging your code independently than when it is a
1165 Here is an implementation of the POSIX truncate function for an operating
1166 system (VOS) that does not supply one, but which does supply the ftruncate()
1169 /* Beginning of modification history */
1170 /* Written 02-01-02 by Nick Ing-Simmons (nick@ing-simmons.net) */
1171 /* End of modification history */
1173 /* VOS doesn't supply a truncate function, so we build one up
1174 from the available POSIX functions. */
1177 #include <sys/types.h>
1181 truncate(const char *path, off_t len)
1183 int fd = open(path,O_WRONLY);
1186 code = ftruncate(fd,len);
1192 Place this file into a subdirectory that has the same name as the operating
1193 system. This file is named perl/vos/vos.c
1197 If your operating system has a hints file (in perl/hints/XXX.sh for an
1198 operating system named XXX), then start with it. If your operating system
1199 has no hints file, then create one. You can use a hints file for a similar
1200 operating system, if one exists, as a template.
1204 Add lines like the following to your hints file. The first line
1205 (d_truncate="define") instructs Configure that the truncate() function
1206 exists. The second line (archobjs="vos.o") instructs the makefiles that the
1207 perl executable depends on the existence of a file named "vos.o". (Make
1208 will automatically look for "vos.c" and compile it with the same options as
1209 the perl source code). The final line ("test -h...") adds a symbolic link
1210 to the top-level directory so that make can find vos.c. Of course, you
1211 should use your own operating system name for the source file of extensions,
1214 # VOS does not have truncate() but we supply one in vos.c
1218 # Help gmake find vos.c
1219 test -h vos.c || ln -s vos/vos.c vos.c
1221 The hints file is a series of shell commands that are run in the top-level
1222 directory (the "perl" directory). Thus, these commands are simply executed
1223 by Configure at an appropriate place during its execution.
1227 At this point, you can run the Configure script and rebuild perl. Carefully
1228 test the newly-built perl to ensure that normal paths, and error paths,
1229 behave as you expect.
1233 =head2 Good ideas waiting for round tuits
1237 =item Configure -Dsrc=/blah/blah
1239 We should be able to emulate B<configure --srcdir>. Tom Tromey
1240 tromey@creche.cygnus.com has submitted some patches to
1241 the dist-users mailing list along these lines. They have been folded
1242 back into the main distribution, but various parts of the perl
1243 Configure/build/install process still assume src='.'.
1245 =item Hint file fixes
1247 Various hint files work around Configure problems. We ought to fix
1248 Configure so that most of them aren't needed.
1250 =item Hint file information
1252 Some of the hint file information (particularly dynamic loading stuff)
1253 ought to be fed back into the main metaconfig distribution.
1257 =head2 Probably good ideas waiting for round tuits
1261 =item GNU configure --options
1263 I've received sensible suggestions for --exec_prefix and other
1264 GNU configure --options. It's not always obvious exactly what is
1265 intended, but this merits investigation.
1267 =item Try gcc if cc fails
1269 Currently, we just give up.
1271 =item bypassing safe*alloc wrappers
1273 On some systems, it may be safe to call the system malloc directly
1274 without going through the util.c safe* layers. (Such systems would
1275 accept free(0), for example.) This might be a time-saver for systems
1276 that already have a good malloc. (Recent Linux libc's apparently have
1277 a nice malloc that is well-tuned for the system.)
1281 =head2 Vague possibilities
1285 =item gconvert replacement
1287 Maybe include a replacement function that doesn't lose data in rare
1288 cases of coercion between string and numerical values.
1290 =item Improve makedepend
1292 The current makedepend process is clunky and annoyingly slow, but it
1293 works for most folks. Alas, it assumes that there is a filename
1294 $firstmakefile that the B<make> command will try to use before it uses
1295 F<Makefile>. Such may not be the case for all B<make> commands,
1296 particularly those on non-Unix systems.
1298 Probably some variant of the BSD F<.depend> file will be useful.
1299 We ought to check how other packages do this, if they do it at all.
1300 We could probably pre-generate the dependencies (with the exception of
1301 malloc.o, which could probably be determined at F<Makefile.SH>
1304 =item GNU Makefile standard targets
1306 GNU software generally has standardized Makefile targets. Unless we
1307 have good reason to do otherwise, I see no reason not to support them.
1311 Somehow, straighten out, document, and implement lockf(), flock(),
1312 and/or fcntl() file locking. It's a mess. See $d_fcntl_can_lock
1313 in recent config.sh files though.
1317 =head2 Copyright Issues
1319 The following is based on the consensus of a couple of IPR lawyers,
1320 but it is of course not a legally binding statement, just a common
1327 Tacking on copyright statements is unnecessary to begin with because
1328 of the Berne convention. But assuming you want to go ahead...
1332 The right form of a copyright statement is
1334 Copyright (C) Year, Year, ... by Someone
1336 The (C) is not required everywhere but it doesn't hurt and in certain
1337 jurisdictions it is required, so let's leave it in. (Yes, it's true
1338 that in some jurisdictions the "(C)" is not legally binding, one should
1339 use the true ringed-C. But we don't have that character available for
1340 Perl's source code.)
1342 The years must be listed out separately. Year-Year is not correct.
1343 Only the years when the piece has changed 'significantly' may be added.
1347 One cannot give away one's copyright trivially. One can give one's
1348 copyright away by using public domain, but even that requires a little
1349 bit more than just saying 'this is in public domain'. (What it
1350 exactly requires depends on your jurisdiction.) But barring public
1351 domain, one cannot "transfer" one's copyright to another person or
1352 entity. In the context of software, it means that contributors cannot
1353 give away their copyright or "transfer" it to the "owner" of the software.
1355 Also remember that in many cases if you are employed by someone,
1356 your work may be copyrighted to your employer, even when you are
1357 contributing on your own time (this all depends on too many things
1358 to list here). But the bottom line is that you definitely can't give
1359 away a copyright you may not even have.
1361 What is possible, however, is that the software can simply state
1363 Copyright (C) Year, Year, ... by Someone and others
1365 and then list the "others" somewhere in the distribution.
1366 And this is exactly what Perl does. (The "somewhere" is
1367 AUTHORS and the Changes* files.)
1371 Split files, merged files, and generated files are problematic.
1372 The rule of thumb: in split files, copy the copyright years of
1373 the original file to all the new files; in merged files make
1374 an union of the copyright years of all the old files; in generated
1375 files propagate the copyright years of the generating file(s).
1379 The files of Perl source code distribution do carry a lot of
1380 copyrights, by various people. (There are many copyrights embedded in
1381 perl.c, for example.) The most straightforward thing for pumpkings to
1382 do is to simply update Larry's copyrights at the beginning of the
1383 *.[hcy], *.pl, and README files, and leave all other
1384 copyrights alone. Doing more than that requires quite a bit of tracking.
1390 Original author: Andy Dougherty doughera@lafayette.edu .
1391 Additions by Chip Salzenberg chip@perl.com, Tim Bunce and the perl5
1394 All opinions expressed herein are those of the authorZ<>(s).
1396 =head1 LAST MODIFIED
1398 2017-10-13 Dominic Hargreaves