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 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.xray.mpe.mpg.de/mailing-lists/perl5-porters/
48 =head1 How are Perl Releases Numbered?
50 Beginning with v5.6.0, even versions will stand for maintenance releases
51 and odd versions for development releases, i.e., v5.6.x for maintenance
52 releases, and v5.7.x for development releases. Before v5.6.0, subversions
53 _01 through _49 were reserved for bug-fix maintenance releases, and
54 subversions _50 through _99 for unstable development versions.
56 For example, in v5.6.1, the revision number is 5, the version is 6,
57 and 1 is the subversion.
59 For compatibility with the older numbering scheme the composite floating
60 point version number continues to be available as the magic variable $],
61 and amounts to C<$revision + $version/1000 + $subversion/100000>. This
62 can still be used in comparisons.
64 print "You've got an old perl\n" if $] < 5.005_03;
66 In addition, the version is also available as a string in $^V.
68 print "You've got a new perl\n" if $^V and $^V ge v5.6.0;
70 You can also require particular version (or later) with:
74 or using the new syntax available only from v5.6 onward:
78 At some point in the future, we may need to decide what to call the
79 next big revision. In the .package file used by metaconfig to
80 generate Configure, there are two variables that might be relevant:
81 $baserev=5 and $package=perl5.
83 Perl releases produced by the members of perl5-porters are usually
84 available on CPAN in the F<src/5.0/maint> and F<src/5.0/devel>
87 =head2 Maintenance and Development Subversions
89 The first rule of maintenance work is "First, do no harm."
91 Trial releases of bug-fix maintenance releases are announced on
92 perl5-porters. Trial releases use the new subversion number (to avoid
93 testers installing it over the previous release) and include a 'local
94 patch' entry in F<patchlevel.h>. The distribution file contains the
95 string C<MAINT_TRIAL> to make clear that the file is not meant for
98 In general, the names of official distribution files for the public
99 always match the regular expression:
101 ^perl\d+\.(\d+)\.\d+(-MAINT_TRIAL_\d+)\.tar\.gz$
103 C<$1> in the pattern is always an even number for maintenance
104 versions, and odd for developer releases.
106 In the past it has been observed that pumpkings tend to invent new
107 naming conventions on the fly. If you are a pumpking, before you
108 invent a new name for any of the three types of perl distributions,
109 please inform the guys from the CPAN who are doing indexing and
110 provide the trees of symlinks and the like. They will have to know
111 I<in advance> what you decide.
113 =head2 Why is it called the patch pumpkin?
115 Chip Salzenberg gets credit for that, with a nod to his cow orker,
116 David Croy. We had passed around various names (baton, token, hot
117 potato) but none caught on. Then, Chip asked:
121 Who has the patch pumpkin?
123 To explain: David Croy once told me once that at a previous job,
124 there was one tape drive and multiple systems that used it for backups.
125 But instead of some high-tech exclusion software, they used a low-tech
126 method to prevent multiple simultaneous backups: a stuffed pumpkin.
127 No one was allowed to make backups unless they had the "backup pumpkin".
133 =head1 Philosophical Issues in Patching and Porting Perl
135 There are no absolute rules, but there are some general guidelines I
136 have tried to follow as I apply patches to the perl sources.
137 (This section is still under construction.)
139 =head2 Solve problems as generally as possible
141 Never implement a specific restricted solution to a problem when you
142 can solve the same problem in a more general, flexible way.
144 For example, for dynamic loading to work on some SVR4 systems, we had
145 to build a shared libperl.so library. In order to build "FAT" binaries
146 on NeXT 4.0 systems, we had to build a special libperl library. Rather
147 than continuing to build a contorted nest of special cases, I
148 generalized the process of building libperl so that NeXT and SVR4 users
149 could still get their work done, but others could build a shared
150 libperl if they wanted to as well.
152 Contain your changes carefully. Assume nothing about other operating
153 systems, not even closely related ones. Your changes must not affect
156 Spy shamelessly on how similar patching or porting issues have been
159 If feasible, try to keep filenames 8.3-compliant to humor those poor
160 souls that get joy from running Perl under such dire limitations.
161 There's a script, F<check83.pl>, for keeping your nose 8.3-clean.
162 In a similar vein, do not create files or directories which differ only
163 in case (upper versus lower).
165 =head2 Seek consensus on major changes
167 If you are making big changes, don't do it in secret. Discuss the
168 ideas in advance on perl5-porters.
170 =head2 Keep the documentation up-to-date
172 If your changes may affect how users use perl, then check to be sure
173 that the documentation is in sync with your changes. Be sure to
174 check all the files F<pod/*.pod> and also the F<INSTALL> document.
176 Consider writing the appropriate documentation first and then
177 implementing your change to correspond to the documentation.
179 =head2 Avoid machine-specific #ifdef's
181 To the extent reasonable, try to avoid machine-specific #ifdef's in
182 the sources. Instead, use feature-specific #ifdef's. The reason is
183 that the machine-specific #ifdef's may not be valid across major
184 releases of the operating system. Further, the feature-specific tests
185 may help out folks on another platform who have the same problem.
187 =head2 Machine-specific files
193 If you have many machine-specific #defines or #includes, consider
194 creating an "osish.h" (F<os2ish.h>, F<vmsish.h>, and so on) and including
195 that in F<perl.h>. If you have several machine-specific files (function
196 emulations, function stubs, build utility wrappers) you may create a
197 separate subdirectory (djgpp, win32) and put the files in there.
198 Remember to update C<MANIFEST> when you add files.
200 If your system supports dynamic loading but none of the existing
201 methods at F<ext/DynaLoader/dl_*.xs> work for you, you must write
202 a new one. Study the existing ones to see what kind of interface
207 There are two kinds of hints: hints for building Perl and hints for
208 extensions. The former live in the C<hints> subdirectory, the latter
209 in C<ext/*/hints> subdirectories.
211 The top level hints are Bourne-shell scripts that set, modify and
212 unset appropriate Configure variables, based on the Configure command
213 line options and possibly existing config.sh and Policy.sh files from
214 previous Configure runs.
216 The extension hints are written in Perl (by the time they are used
217 miniperl has been built) and control the building of their respective
218 extensions. They can be used to for example manipulate compilation
221 =item build and installation Makefiles, scripts, and so forth
223 Sometimes you will also need to tweak the Perl build and installation
224 procedure itself, like for example F<Makefile.SH> and F<installperl>.
225 Tread very carefully, even more than usual. Contain your changes
230 Many of the tests in C<t> subdirectory assume machine-specific things
231 like existence of certain functions, something about filesystem
232 semantics, certain external utilities and their error messages. Use
233 the C<$^O> and the C<Config> module (which contains the results of the
234 Configure run, in effect the C<config.sh> converted to Perl) to either
235 skip (preferably not) or customize (preferable) the tests for your
240 Certain standard modules may need updating if your operating system
241 sports for example a native filesystem naming. You may want to update
242 some or all of the modules File::Basename, File::Spec, File::Path, and
243 File::Copy to become aware of your native filesystem syntax and
246 Remember to have a $VERSION in the modules. You can use the
247 F<Porting/checkVERSION.pl> script for checking this.
251 If your operating system comes from outside UNIX you almost certainly
252 will have differences in the available operating system functionality
253 (missing system calls, different semantics, whatever). Please
254 document these at F<pod/perlport.pod>. If your operating system is
255 the first B<not> to have a system call also update the list of
256 "portability-bewares" at the beginning of F<pod/perlfunc.pod>.
258 A file called F<README.youros> at the top level that explains things
259 like how to install perl at this platform, where to get any possibly
260 required additional software, and for example what test suite errors
261 to expect, is nice too. Such files are in the process of being written
262 in pod format and will eventually be renamed F<INSTALL.youros>.
264 You may also want to write a separate F<.pod> file for your operating
265 system to tell about existing mailing lists, os-specific modules,
266 documentation, whatever. Please name these along the lines of
267 F<perl>I<youros>.pod. [unfinished: where to put this file (the pod/
268 subdirectory, of course: but more importantly, which/what index files
273 =head2 Allow for lots of testing
275 We should never release a main version without testing it as a
278 =head2 Test popular applications and modules.
280 We should never release a main version without testing whether or not
281 it breaks various popular modules and applications. A partial list of
282 such things would include majordomo, metaconfig, apache, Tk, CGI,
283 libnet, and libwww, to name just a few. Of course it's quite possible
284 that some of those things will be just plain broken and need to be fixed,
285 but, in general, we ought to try to avoid breaking widely-installed
288 =head2 Automated generation of derivative files
290 The F<embed.h>, F<keywords.h>, F<opcode.h>, F<regcharclass.h>,
291 F<l1_char_class_tab.h>, and F<perltoc.pod> files
292 are all automatically generated by perl scripts. In general, don't
293 patch these directly; patch the data files instead.
295 Also F<Makefile> is automatically produced from F<Makefile.SH>.
296 In general, look out for all F<*.SH> files.
298 Finally, the sample files F<config.sh> and F<config_H> in the
299 F<Porting/> subdirectory are generated by the script F<Porting/mksample>.
301 =head3 Files generated by metaconfig
303 F<Configure>, F<config_h.SH> and F<Porting/Glossary> are generated by
304 B<metaconfig> (see below for more information on how to use this system)
305 and direct changes to these files should in general not be pushed to blead.
317 changes pre-approved by the metaconfig maintainers
321 Such changes should also be notified to the metaconfig maintainers.
323 Alternatively, do consider if the F<*ish.h> files or the hint files might
324 be a better place for your changes.
326 =head1 Working with metaconfig
328 Information about how to use metaconfig can be found in the F<README>
329 and F<README_U> files in the metaconfig repository containing Perl's
333 git clone https://github.com/perl5-metaconfig/metaconfig.git
334 # or using a registered github.com identity with ssh
335 git clone github.com:perl5-metaconfig/metaconfig metaconfig
337 Since metaconfig is hard to change, running correction scripts after
338 this generation is sometimes needed. Configure gained complexity over
339 time, and the order in which config_h.SH is generated can cause havoc
340 when compiling perl. Therefor, you need to run Porting/config_h.pl
341 after that generation. All that and more is described in the README
342 files that come with the metaunits.
344 =head1 How to Make a Distribution
346 This section has now been expanded and moved into its own file,
347 F<Porting/release_managers_guide.pod>.
349 I've kept some of the subsections here for now, as they don't directly
350 relate to building a release any more, but still contain what might be
351 useful information - DAPM 7/2009.
355 If you are using metaconfig to regenerate Configure, then you should note
356 that metaconfig actually uses MANIFEST.new, so you want to be sure
357 MANIFEST.new is up-to-date too. I haven't found the MANIFEST/MANIFEST.new
358 distinction particularly useful, but that's probably because I still haven't
359 learned how to use the full suite of tools in the dist distribution.
364 This will build a config.sh and config.h. You can skip this if you haven't
365 changed Configure or config_h.SH at all. I use the following command
367 sh Configure -Dprefix=/opt/perl -Doptimize=-O -Dusethreads \
369 -Dcf_email='yourname@yourhost.yourplace.com' \
370 -Dperladmin='yourname@yourhost.yourplace.com' \
371 -Dmydomain='.yourplace.com' \
372 -Dmyhostname='yourhost' \
375 =head2 Update Porting/config.sh and Porting/config_H
378 This section needs revision. We're currently working on easing
379 the task of keeping the vms, win32, and plan9 config.sh info
380 up-to-date. The plan is to use keep up-to-date 'canned' config.sh
381 files in the appropriate subdirectories and then generate 'canned'
382 config.h files for vms, win32, etc. from the generic config.sh file.
383 This is to ease maintenance. When Configure gets updated, the parts
384 sometimes get scrambled around, and the changes in config_H can
385 sometimes be very hard to follow. config.sh, on the other hand, can
386 safely be sorted, so it's easy to track (typically very small) changes
387 to config.sh and then propagate them to a canned 'config.h' by any
388 number of means, including a perl script in win32/ or carrying
389 F<config.sh> and F<config_h.SH> to a Unix system and running sh
390 config_h.SH.) Vms uses F<configure.com> to generate its own F<config.sh>
391 and F<config.h>. If you want to add a new variable to F<config.sh> check
392 with vms folk how to add it to configure.com too.
395 The F<Porting/config.sh> and F<Porting/config_H> files are provided to
396 help those folks who can't run Configure. It is important to keep
397 them up-to-date. If you have changed F<config_h.SH>, those changes must
398 be reflected in config_H as well. (The name config_H was chosen to
399 distinguish the file from config.h even on case-insensitive file systems.)
400 Simply edit the existing config_H file; keep the first few explanatory
401 lines and then copy your new config.h below.
403 It may also be necessary to update win32/config.?c, and
404 F<plan9/config.plan9>, though you should be quite careful in doing so if
405 you are not familiar with those systems. You might want to issue your
406 patch with a promise to quickly issue a follow-up that handles those
409 =head2 make regen_perly
411 If F<perly.y> has been edited, it is necessary to run this target to rebuild
412 F<perly.h>, F<perly.act> and F<perly.tab>. In fact this target just runs the Perl
413 script F<regen_perly.pl>. Note that F<perly.c> is I<not> rebuilt; this is just a
414 plain static file now.
416 This target relies on you having Bison installed on your system. Running
417 the target will tell you if you haven't got the right version, and if so,
418 where to get the right one. Or if you prefer, you could hack
419 F<regen_perly.pl> to work with your version of Bison. The important things
420 are that the regexes can still extract out the right chunks of the Bison
421 output into F<perly.act> and F<perly.tab>, and that the contents of those two
422 files, plus F<perly.h>, are functionally equivalent to those produced by the
423 supported version of Bison.
425 Note that in the old days, you had to do C<make run_byacc> instead.
427 =head2 make regen_all
429 This target takes care of the regen_headers target.
430 (It used to also call the regen_pods target, but that has been eliminated.)
432 =head2 make regen_headers
434 The F<embed.h>, F<keywords.h>, and F<opcode.h> files are all automatically
435 generated by perl scripts. Since the user isn't guaranteed to have a
436 working perl, we can't require the user to generate them. Hence you have
437 to, if you're making a distribution.
439 I used to include rules like the following in the makefile:
441 # The following three header files are generated automatically
442 # The correct versions should be already supplied with the perl kit,
443 # in case you don't have perl or 'sh' available.
444 # The - is to ignore error return codes in case you have the source
445 # installed read-only or you don't have perl yet.
446 keywords.h: keywords.pl
447 @echo "Don't worry if this fails."
451 However, I got B<lots> of mail consisting of people worrying because the
452 command failed. I eventually decided that I would save myself time
453 and effort by manually running C<make regen_headers> myself rather
454 than answering all the questions and complaints about the failing
457 =head2 globvar.sym, and perlio.sym
459 Make sure these files are up-to-date. Read the comments in these
460 files and in F<perl_exp.SH> to see what to do.
462 =head2 Binary compatibility
464 If you do change F<embed.fnc> think carefully about
465 what you are doing. To the extent reasonable, we'd like to maintain
466 source and binary compatibility with older releases of perl. That way,
467 extensions built under one version of perl will continue to work with
468 new versions of perl.
470 Of course, some incompatible changes may well be necessary. I'm just
471 suggesting that we not make any such changes without thinking carefully
472 about them first. If possible, we should provide
473 backwards-compatibility stubs. There's a lot of XS code out there.
474 Let's not force people to keep changing it.
478 F<dist/Devel-PPPort/PPPort.pm> needs to be synchronized to include all
479 new macros added to .h files (normally F<perl.h> and F<XSUB.h>, but others
480 as well). Since chances are that when a new macro is added the
481 committer will forget to update F<PPPort.pm>, it's the best to diff for
482 changes in .h files when making a new release and making sure that
483 F<PPPort.pm> contains them all.
485 The pumpking can delegate the synchronization responsibility to anybody
486 else, but the release process is the only place where we can make sure
487 that no new macros fell through the cracks.
492 The F<Porting/todo.pod> file contains a roughly-categorized unordered
493 list of aspects of Perl that could use enhancement, features that could
494 be added, areas that could be cleaned up, and so on. During your term
495 as pumpkin-holder, you will probably address some of these issues, and
496 perhaps identify others which, while you decide not to address them this
497 time around, may be tackled in the future. Update the file to reflect
498 the situation as it stands when you hand over the pumpkin.
500 You might like, early in your pumpkin-holding career, to see if you
501 can find champions for particular issues on the to-do list: an issue
502 owned is an issue more likely to be resolved.
504 There are also some more porting-specific L</Todo> items later in this
507 =head2 OS/2-specific updates
509 In the os2 directory is F<diff.configure>, a set of OS/2-specific
510 diffs against B<Configure>. If you make changes to Configure, you may
511 want to consider regenerating this diff file to save trouble for the
514 You can also consider the OS/2 diffs as reminders of portability
515 things that need to be fixed in Configure.
517 =head2 VMS-specific updates
519 The Perl revision number appears as "perl5" in F<configure.com>.
520 It is courteous to update that if necessary.
523 =head2 Making a new patch
525 I find the F<makepatch> utility quite handy for making patches.
526 You can obtain it from any CPAN archive under
527 L<http://www.cpan.org/authors/Johan_Vromans/>. There are a couple
528 of differences between my version and the standard one. I have mine do
531 # Print a reassuring "End of Patch" note so people won't
532 # wonder if their mailer truncated patches.
533 print "\n\nEnd of Patch.\n";
535 at the end. That's because I used to get questions from people asking
536 if their mail was truncated.
538 It also writes Index: lines which include the new directory prefix
539 (change Index: print, approx line 294 or 310 depending on the version,
540 to read: print PATCH ("Index: $newdir$new\n");). That helps patches
541 work with more POSIX conformant patch programs.
543 Here's how I generate a new patch. I'll use the hypothetical
544 5.004_07 to 5.004_08 patch as an example.
546 # unpack perl5.004_07/
547 gzip -d -c perl5.004_07.tar.gz | tar -xof -
548 # unpack perl5.004_08/
549 gzip -d -c perl5.004_08.tar.gz | tar -xof -
550 makepatch perl5.004_07 perl5.004_08 > perl5.004_08.pat
552 Makepatch will automatically generate appropriate B<rm> commands to remove
553 deleted files. Unfortunately, it will not correctly set permissions
554 for newly created files, so you may have to do so manually. For example,
555 patch 5.003_04 created a new test F<t/op/gv.t> which needs to be executable,
556 so at the top of the patch, I inserted the following lines:
562 Now, of course, my patch is now wrong because makepatch didn't know I
563 was going to do that command, and it patched against /dev/null.
565 So, what I do is sort out all such shell commands that need to be in the
566 patch (including possible mv-ing of files, if needed) and put that in the
567 shell commands at the top of the patch. Next, I delete all the patch parts
568 of perl5.004_08.pat, leaving just the shell commands. Then, I do the
572 sh ../perl5.004_08.pat
574 makepatch perl5.004_07 perl5.004_08 >> perl5.004_08.pat
576 (Note the append to preserve my shell commands.)
577 Now, my patch will line up with what the end users are going to do.
579 =head2 Testing your patch
581 It seems obvious, but be sure to test your patch. That is, verify that
582 it produces exactly the same thing as your full distribution.
585 gzip -d -c perl5.004_07.tar.gz | tar -xf -
587 sh ../perl5.004_08.pat
588 patch -p1 -N < ../perl5.004_08.pat
590 gdiff -r perl5.004_07 perl5.004_08
592 where B<gdiff> is GNU diff. Other diff's may also do recursive checking.
596 Again, it's obvious, but you should test your new version as widely as you
597 can. You can be sure you'll hear about it quickly if your version doesn't
598 work on both ANSI and pre-ANSI compilers, and on common systems such as
599 SunOS 4.1.[34], Solaris, and Linux.
601 If your changes include conditional code, try to test the different
602 branches as thoroughly as you can. For example, if your system
603 supports dynamic loading, you can also test static loading with
607 You can also hand-tweak your config.h to try out different #ifdef
614 =item gcc -ansi -pedantic
616 Configure -Dgccansipedantic [ -Dcc=gcc ] will enable (via the cflags script,
617 not $Config{ccflags}) the gcc strict ANSI C flags -ansi and -pedantic for
618 the compilation of the core files on platforms where it knows it can
619 do so (like Linux, see cflags.SH for the full list), and on some
620 platforms only one (Solaris can do only -pedantic, not -ansi).
621 The flag -DPERL_GCC_PEDANTIC also gets added, since gcc does not add
622 any internal cpp flag to signify that -pedantic is being used, as it
623 does for -ansi (__STRICT_ANSI__).
625 Note that the -ansi and -pedantic are enabled only for version 3 (and
626 later) of gcc, since even gcc version 2.95.4 finds lots of seemingly
627 false "value computed not used" errors from Perl.
629 The -ansi and -pedantic are useful in catching at least the following
630 nonportable practices:
636 gcc-specific extensions
652 The -Dgccansipedantic should be used only when cleaning up the code,
653 not for production builds, since otherwise gcc cannot inline certain
658 =head1 Common Gotchas
662 =item Probably Prefer POSIX
664 It's often the case that you'll need to choose whether to do
665 something the BSD-ish way or the POSIX-ish way. It's usually not
666 a big problem when the two systems use different names for similar
667 functions, such as memcmp() and bcmp(). The perl.h header file
668 handles these by appropriate #defines, selecting the POSIX mem*()
669 functions if available, but falling back on the b*() functions, if
672 More serious is the case where some brilliant person decided to
673 use the same function name but give it a different meaning or
674 calling sequence :-). getpgrp() and setpgrp() come to mind.
675 These are a real problem on systems that aim for conformance to
676 one standard (e.g. POSIX), but still try to support the other way
677 of doing things (e.g. BSD). My general advice (still not really
678 implemented in the source) is to do something like the following.
679 Suppose there are two alternative versions, fooPOSIX() and
683 /* use fooPOSIX(); */
686 /* try to emulate fooPOSIX() with fooBSD();
687 perhaps with the following: */
688 # define fooPOSIX fooBSD
690 # /* Uh, oh. We have to supply our own. */
691 # define fooPOSIX Perl_fooPOSIX
695 =item Think positively
697 If you need to add an #ifdef test, it is usually easier to follow if you
698 think positively, e.g.
700 #ifdef HAS_NEATO_FEATURE
701 /* use neato feature */
703 /* use some fallback mechanism */
706 rather than the more impenetrable
708 #ifndef MISSING_NEATO_FEATURE
709 /* Not missing it, so we must have it, so use it */
711 /* Are missing it, so fall back on something else. */
714 Of course for this toy example, there's not much difference. But when
715 the #ifdef's start spanning a couple of screen fulls, and the #else's
716 are marked something like
718 #else /* !MISSING_NEATO_FEATURE */
720 I find it easy to get lost.
722 =item Providing Missing Functions -- Problem
724 Not all systems have all the neat functions you might want or need, so
725 you might decide to be helpful and provide an emulation. This is
726 sound in theory and very kind of you, but please be careful about what
727 you name the function. Let me use the C<pause()> function as an
730 Perl5.003 has the following in F<perl.h>
733 #define pause() sleep((32767<<16)+32767)
736 Configure sets HAS_PAUSE if the system has the pause() function, so
737 this #define only kicks in if the pause() function is missing.
740 Unfortunately, some systems apparently have a prototype for pause()
741 in F<unistd.h>, but don't actually have the function in the library.
742 (Or maybe they do have it in a library we're not using.)
744 Thus, the compiler sees something like
746 extern int pause(void);
748 #define pause() sleep((32767<<16)+32767)
750 and dies with an error message. (Some compilers don't mind this;
751 others apparently do.)
753 To work around this, 5.003_03 and later have the following in perl.h:
755 /* Some unistd.h's give a prototype for pause() even though
756 HAS_PAUSE ends up undefined. This causes the #define
757 below to be rejected by the compiler. Sigh.
762 # define Pause() sleep((32767<<16)+32767)
767 The curious reader may wonder why I didn't do the following in
773 sleep((32767<<16)+32767);
777 That is, since the function is missing, just provide it.
778 Then things would probably be been alright, it would seem.
780 Well, almost. It could be made to work. The problem arises from the
781 conflicting needs of dynamic loading and namespace protection.
783 For dynamic loading to work on AIX (and VMS) we need to provide a list
784 of symbols to be exported. This is done by the script F<perl_exp.SH>,
785 which reads F<embed.fnc>. Thus, the C<pause>
786 symbol would have to be added to F<embed.fnc> So far, so good.
788 On the other hand, one of the goals of Perl5 is to make it easy to
789 either extend or embed perl and link it with other libraries. This
790 means we have to be careful to keep the visible namespace "clean".
791 That is, we don't want perl's global variables to conflict with
792 those in the other application library. Although this work is still
793 in progress, the way it is currently done is via the F<embed.h> file.
794 This file is built from the F<embed.fnc> file,
795 since those files already list the globally visible symbols. If we
796 had added C<pause> to F<embed.fnc>, then F<embed.h> would contain the
799 #define pause Perl_pause
801 and calls to C<pause> in the perl sources would now point to
802 C<Perl_pause>. Now, when B<ld> is run to build the F<perl> executable,
803 it will go looking for C<perl_pause>, which probably won't exist in any
804 of the standard libraries. Thus the build of perl will fail.
806 Those systems where C<HAS_PAUSE> is not defined would be ok, however,
807 since they would get a C<Perl_pause> function in util.c. The rest of
808 the world would be in trouble.
810 And yes, this scenario has happened. On SCO, the function C<chsize>
811 is available. (I think it's in F<-lx>, the Xenix compatibility
812 library.) Since the perl4 days (and possibly before), Perl has
813 included a C<chsize> function that gets called something akin to
816 I32 chsize(fd, length)
822 #define chsize Perl_chsize
824 to F<embed.h>, the compile started failing on SCO systems.
826 The "fix" is to give the function a different name. The one
827 implemented in 5.003_05 isn't optimal, but here's what was done:
830 # ifdef my_chsize /* Probably #defined to Perl_my_chsize */
831 # undef my_chsize /* in embed.h */
833 # define my_chsize chsize
836 My explanatory comment in patch 5.003_05 said:
838 Undef and then re-define my_chsize from Perl_my_chsize to
839 just plain chsize if this system HAS_CHSIZE. This probably only
840 applies to SCO. This shows the perils of having internal
841 functions with the same name as external library functions :-).
843 Now, we can safely put C<my_chsize> in C<embed.fnc>, export it, and
844 hide it with F<embed.h>.
846 To be consistent with what I did for C<pause>, I probably should have
847 called the new function C<Chsize>, rather than C<my_chsize>.
848 However, the perl sources are quite inconsistent on this (Consider
849 New, Mymalloc, and Myremalloc, to name just a few.)
851 There is a problem with this fix, however, in that C<Perl_chsize>
852 was available as a F<libperl.a> library function in 5.003, but it
853 isn't available any more (as of 5.003_07). This means that we've
854 broken binary compatibility. This is not good.
856 =item Providing missing functions -- some ideas
858 We currently don't have a standard way of handling such missing
859 function names. Right now, I'm effectively thinking aloud about a
860 solution. Some day, I'll try to formally propose a solution.
862 Part of the problem is that we want to have some functions listed as
863 exported but not have their names mangled by embed.h or possibly
864 conflict with names in standard system headers. We actually already
865 have such a list at the end of F<perl_exp.SH> (though that list is
868 # extra globals not included above.
869 cat <<END >> perl.exp
893 This still needs much thought, but I'm inclined to think that one
894 possible solution is to prefix all such functions with C<perl_> in the
895 source and list them along with the other C<perl_*> functions in
898 Thus, for C<chsize>, we'd do something like the following:
902 # define perl_chsize chsize
905 then in some file (e.g. F<util.c> or F<doio.c>) do
908 I32 perl_chsize(fd, length)
909 /* implement the function here . . . */
912 Alternatively, we could just always use C<chsize> everywhere and move
913 C<chsize> from F<embed.fnc> to the end of F<perl_exp.SH>. That would
914 probably be fine as long as our C<chsize> function agreed with all the
915 C<chsize> function prototypes in the various systems we'll be using.
916 As long as the prototypes in actual use don't vary that much, this is
917 probably a good alternative. (As a counter-example, note how Configure
918 and perl have to go through hoops to find and use get Malloc_t and
919 Free_t for C<malloc> and C<free>.)
921 At the moment, this latter option is what I tend to prefer.
923 =item All the world's a VAX
925 Sorry, showing my age:-). Still, all the world is not BSD 4.[34],
926 SVR4, or POSIX. Be aware that SVR3-derived systems are still quite
927 common (do you have any idea how many systems run SCO?) If you don't
928 have a bunch of v7 manuals handy, the metaconfig units (by default
929 installed in F</usr/local/lib/dist/U>) are a good resource to look at
934 =head1 Miscellaneous Topics
938 Why does perl use a metaconfig-generated Configure script instead of an
939 autoconf-generated configure script?
941 Metaconfig and autoconf are two tools with very similar purposes.
942 Metaconfig is actually the older of the two, and was originally written
943 by Larry Wall, while autoconf is probably now used in a wider variety of
944 packages. The autoconf info file discusses the history of autoconf and
945 how it came to be. The curious reader is referred there for further
948 Overall, both tools are quite good, I think, and the choice of which one
949 to use could be argued either way. In March, 1994, when I was just
950 starting to work on Configure support for Perl5, I considered both
951 autoconf and metaconfig, and eventually decided to use metaconfig for the
956 =item Compatibility with Perl4
958 Perl4 used metaconfig, so many of the #ifdef's were already set up for
959 metaconfig. Of course metaconfig had evolved some since Perl4's days,
960 but not so much that it posed any serious problems.
962 =item Metaconfig worked for me
964 My system at the time was Interactive 2.2, an SVR3.2/386 derivative that
965 also had some POSIX support. Metaconfig-generated Configure scripts
966 worked fine for me on that system. On the other hand, autoconf-generated
967 scripts usually didn't. (They did come quite close, though, in some
968 cases.) At the time, I actually fetched a large number of GNU packages
969 and checked. Not a single one configured and compiled correctly
970 out-of-the-box with the system's cc compiler.
972 =item Configure can be interactive
974 With both autoconf and metaconfig, if the script works, everything is
975 fine. However, one of my main problems with autoconf-generated scripts
976 was that if it guessed wrong about something, it could be B<very> hard to
977 go back and fix it. For example, autoconf always insisted on passing the
978 -Xp flag to cc (to turn on POSIX behavior), even when that wasn't what I
979 wanted or needed for that package. There was no way short of editing the
980 configure script to turn this off. You couldn't just edit the resulting
981 Makefile at the end because the -Xp flag influenced a number of other
984 Metaconfig's Configure scripts, on the other hand, can be interactive.
985 Thus if Configure is guessing things incorrectly, you can go back and fix
986 them. This isn't as important now as it was when we were actively
987 developing Configure support for new features such as dynamic loading,
988 but it's still useful occasionally.
992 At the time, autoconf-generated scripts were covered under the GNU Public
993 License, and hence weren't suitable for inclusion with Perl, which has a
994 different licensing policy. (Autoconf's licensing has since changed.)
998 Metaconfig builds up Configure from a collection of discrete pieces
999 called "units". You can override the standard behavior by supplying your
1000 own unit. With autoconf, you have to patch the standard files instead.
1001 I find the metaconfig "unit" method easier to work with. Others
1002 may find metaconfig's units clumsy to work with.
1006 =head2 Why isn't there a directory to override Perl's library?
1008 Mainly because no one's gotten around to making one. Note that
1009 "making one" involves changing perl.c, Configure, config_h.SH (and
1010 associated files, see above), and I<documenting> it all in the
1013 Apparently, most folks who want to override one of the standard library
1014 files simply do it by overwriting the standard library files.
1018 In the perl.c sources, you'll find an undocumented APPLLIB_EXP
1019 variable, sort of like PRIVLIB_EXP and ARCHLIB_EXP (which are
1020 documented in config_h.SH). Here's what APPLLIB_EXP is for, from
1021 a mail message from Larry:
1023 The main intent of APPLLIB_EXP is for folks who want to send out a
1024 version of Perl embedded in their product. They would set the
1025 symbol to be the name of the library containing the files needed
1026 to run or to support their particular application. This works at
1027 the "override" level to make sure they get their own versions of
1028 any library code that they absolutely must have configuration
1031 As such, I don't see any conflict with a sysadmin using it for a
1032 override-ish sort of thing, when installing a generic Perl. It
1033 should probably have been named something to do with overriding
1034 though. Since it's undocumented we could still change it... :-)
1036 Given that it's already there, you can use it to override distribution modules.
1037 One way to do that is to add
1039 ccflags="$ccflags -DAPPLLIB_EXP=\"/my/override\""
1041 to your config.over file. (You have to be particularly careful to get the
1042 double quotes in. APPLLIB_EXP must be a valid C string. It might
1043 actually be easier to just #define it yourself in perl.c.)
1045 Then perl.c will put /my/override ahead of ARCHLIB and PRIVLIB. Perl will
1046 also search architecture-specific and version-specific subdirectories of
1049 =head2 Shared libperl.so location
1051 Why isn't the shared libperl.so installed in /usr/lib/ along
1052 with "all the other" shared libraries? Instead, it is installed
1053 in $archlib, which is typically something like
1055 /usr/local/lib/perl5/archname/5.00404
1057 and is architecture- and version-specific.
1059 The basic reason why a shared libperl.so gets put in $archlib is so that
1060 you can have more than one version of perl on the system at the same time,
1061 and have each refer to its own libperl.so.
1063 Three examples might help. All of these work now; none would work if you
1064 put libperl.so in /usr/lib.
1070 Suppose you want to have both threaded and non-threaded perl versions
1071 around. Configure will name both perl libraries "libperl.so" (so that
1072 you can link to them with -lperl). The perl binaries tell them apart
1073 by having looking in the appropriate $archlib directories.
1077 Suppose you have perl5.004_04 installed and you want to try to compile
1078 it again, perhaps with different options or after applying a patch.
1079 If you already have libperl.so installed in /usr/lib/, then it may be
1080 either difficult or impossible to get ld.so to find the new libperl.so
1081 that you're trying to build. If, instead, libperl.so is tucked away in
1082 $archlib, then you can always just change $archlib in the current perl
1083 you're trying to build so that ld.so won't find your old libperl.so.
1084 (The INSTALL file suggests you do this when building a debugging perl.)
1088 The shared perl library is not a "well-behaved" shared library with
1089 proper major and minor version numbers, so you can't necessarily
1090 have perl5.004_04 and perl5.004_05 installed simultaneously. Suppose
1091 perl5.004_04 were to install /usr/lib/libperl.so.4.4, and perl5.004_05
1092 were to install /usr/lib/libperl.so.4.5. Now, when you try to run
1093 perl5.004_04, ld.so might try to load libperl.so.4.5, since it has
1094 the right "major version" number. If this works at all, it almost
1095 certainly defeats the reason for keeping perl5.004_04 around. Worse,
1096 with development subversions, you certainly can't guarantee that
1097 libperl.so.4.4 and libperl.so.4.55 will be compatible.
1099 Anyway, all this leads to quite obscure failures that are sure to drive
1100 casual users crazy. Even experienced users will get confused :-). Upon
1101 reflection, I'd say leave libperl.so in $archlib.
1105 =head2 Indentation style
1107 Over the years Perl has become a mishmash of
1108 various indentation styles, but the original "Larry style" can
1109 probably be restored with (GNU) indent somewhat like this:
1111 indent -kr -nce -psl -sc
1113 A more ambitious solution would also specify a list of Perl specific
1114 types with -TSV -TAV -THV .. -TMAGIC -TPerlIO ... but that list would
1115 be quite ungainly. Also note that GNU indent also doesn't do aligning
1116 of consecutive assignments, which would truly wreck the layout in
1117 places like sv.c:Perl_sv_upgrade() or sv.c:Perl_clone_using().
1118 Similarly nicely aligned &&s, ||s and ==s would not be respected.
1120 =head1 Upload Your Work to CPAN
1122 You can upload your work to CPAN if you have a CPAN id. Check out
1123 L<http://www.cpan.org/modules/04pause.html> for information on
1124 _PAUSE_, the Perl Author's Upload Server.
1126 I typically upload both the patch file, e.g. F<perl5.004_08.pat.gz>
1127 and the full tar file, e.g. F<perl5.004_08.tar.gz>.
1129 If you want your patch to appear in the F<src/5.0/unsupported>
1130 directory on CPAN, send e-mail to the CPAN master librarian. (Check
1131 out L<http://www.cpan.org/CPAN.html> ).
1133 =head1 Help Save the World
1135 You should definitely announce your patch on the perl5-porters list.
1139 Here, in no particular order, are some Configure and build-related
1140 items that merit consideration. This list isn't exhaustive, it's just
1141 what I came up with off the top of my head.
1143 =head2 Adding missing library functions to Perl
1145 The perl Configure script automatically determines which headers and
1146 functions you have available on your system and arranges for them to be
1147 included in the compilation and linking process. Occasionally, when porting
1148 perl to an operating system for the first time, you may find that the
1149 operating system is missing a key function. While perl may still build
1150 without this function, no perl program will be able to reference the missing
1151 function. You may be able to write the missing function yourself, or you
1152 may be able to find the missing function in the distribution files for
1153 another software package. In this case, you need to instruct the perl
1154 configure-and-build process to use your function. Perform these steps.
1160 Code and test the function you wish to add. Test it carefully; you will
1161 have a much easier time debugging your code independently than when it is a
1166 Here is an implementation of the POSIX truncate function for an operating
1167 system (VOS) that does not supply one, but which does supply the ftruncate()
1170 /* Beginning of modification history */
1171 /* Written 02-01-02 by Nick Ing-Simmons (nick@ing-simmons.net) */
1172 /* End of modification history */
1174 /* VOS doesn't supply a truncate function, so we build one up
1175 from the available POSIX functions. */
1178 #include <sys/types.h>
1182 truncate(const char *path, off_t len)
1184 int fd = open(path,O_WRONLY);
1187 code = ftruncate(fd,len);
1193 Place this file into a subdirectory that has the same name as the operating
1194 system. This file is named perl/vos/vos.c
1198 If your operating system has a hints file (in perl/hints/XXX.sh for an
1199 operating system named XXX), then start with it. If your operating system
1200 has no hints file, then create one. You can use a hints file for a similar
1201 operating system, if one exists, as a template.
1205 Add lines like the following to your hints file. The first line
1206 (d_truncate="define") instructs Configure that the truncate() function
1207 exists. The second line (archobjs="vos.o") instructs the makefiles that the
1208 perl executable depends on the existence of a file named "vos.o". (Make
1209 will automatically look for "vos.c" and compile it with the same options as
1210 the perl source code). The final line ("test -h...") adds a symbolic link
1211 to the top-level directory so that make can find vos.c. Of course, you
1212 should use your own operating system name for the source file of extensions,
1215 # VOS does not have truncate() but we supply one in vos.c
1219 # Help gmake find vos.c
1220 test -h vos.c || ln -s vos/vos.c vos.c
1222 The hints file is a series of shell commands that are run in the top-level
1223 directory (the "perl" directory). Thus, these commands are simply executed
1224 by Configure at an appropriate place during its execution.
1228 At this point, you can run the Configure script and rebuild perl. Carefully
1229 test the newly-built perl to ensure that normal paths, and error paths,
1230 behave as you expect.
1234 =head2 Good ideas waiting for round tuits
1238 =item Configure -Dsrc=/blah/blah
1240 We should be able to emulate B<configure --srcdir>. Tom Tromey
1241 tromey@creche.cygnus.com has submitted some patches to
1242 the dist-users mailing list along these lines. They have been folded
1243 back into the main distribution, but various parts of the perl
1244 Configure/build/install process still assume src='.'.
1246 =item Hint file fixes
1248 Various hint files work around Configure problems. We ought to fix
1249 Configure so that most of them aren't needed.
1251 =item Hint file information
1253 Some of the hint file information (particularly dynamic loading stuff)
1254 ought to be fed back into the main metaconfig distribution.
1258 =head2 Probably good ideas waiting for round tuits
1262 =item GNU configure --options
1264 I've received sensible suggestions for --exec_prefix and other
1265 GNU configure --options. It's not always obvious exactly what is
1266 intended, but this merits investigation.
1268 =item Try gcc if cc fails
1270 Currently, we just give up.
1272 =item bypassing safe*alloc wrappers
1274 On some systems, it may be safe to call the system malloc directly
1275 without going through the util.c safe* layers. (Such systems would
1276 accept free(0), for example.) This might be a time-saver for systems
1277 that already have a good malloc. (Recent Linux libc's apparently have
1278 a nice malloc that is well-tuned for the system.)
1282 =head2 Vague possibilities
1286 =item gconvert replacement
1288 Maybe include a replacement function that doesn't lose data in rare
1289 cases of coercion between string and numerical values.
1291 =item Improve makedepend
1293 The current makedepend process is clunky and annoyingly slow, but it
1294 works for most folks. Alas, it assumes that there is a filename
1295 $firstmakefile that the B<make> command will try to use before it uses
1296 F<Makefile>. Such may not be the case for all B<make> commands,
1297 particularly those on non-Unix systems.
1299 Probably some variant of the BSD F<.depend> file will be useful.
1300 We ought to check how other packages do this, if they do it at all.
1301 We could probably pre-generate the dependencies (with the exception of
1302 malloc.o, which could probably be determined at F<Makefile.SH>
1305 =item GNU Makefile standard targets
1307 GNU software generally has standardized Makefile targets. Unless we
1308 have good reason to do otherwise, I see no reason not to support them.
1312 Somehow, straighten out, document, and implement lockf(), flock(),
1313 and/or fcntl() file locking. It's a mess. See $d_fcntl_can_lock
1314 in recent config.sh files though.
1318 =head2 Copyright Issues
1320 The following is based on the consensus of a couple of IPR lawyers,
1321 but it is of course not a legally binding statement, just a common
1328 Tacking on copyright statements is unnecessary to begin with because
1329 of the Berne convention. But assuming you want to go ahead...
1333 The right form of a copyright statement is
1335 Copyright (C) Year, Year, ... by Someone
1337 The (C) is not required everywhere but it doesn't hurt and in certain
1338 jurisdictions it is required, so let's leave it in. (Yes, it's true
1339 that in some jurisdictions the "(C)" is not legally binding, one should
1340 use the true ringed-C. But we don't have that character available for
1341 Perl's source code.)
1343 The years must be listed out separately. Year-Year is not correct.
1344 Only the years when the piece has changed 'significantly' may be added.
1348 One cannot give away one's copyright trivially. One can give one's
1349 copyright away by using public domain, but even that requires a little
1350 bit more than just saying 'this is in public domain'. (What it
1351 exactly requires depends on your jurisdiction.) But barring public
1352 domain, one cannot "transfer" one's copyright to another person or
1353 entity. In the context of software, it means that contributors cannot
1354 give away their copyright or "transfer" it to the "owner" of the software.
1356 Also remember that in many cases if you are employed by someone,
1357 your work may be copyrighted to your employer, even when you are
1358 contributing on your own time (this all depends on too many things
1359 to list here). But the bottom line is that you definitely can't give
1360 away a copyright you may not even have.
1362 What is possible, however, is that the software can simply state
1364 Copyright (C) Year, Year, ... by Someone and others
1366 and then list the "others" somewhere in the distribution.
1367 And this is exactly what Perl does. (The "somewhere" is
1368 AUTHORS and the Changes* files.)
1372 Split files, merged files, and generated files are problematic.
1373 The rule of thumb: in split files, copy the copyright years of
1374 the original file to all the new files; in merged files make
1375 an union of the copyright years of all the old files; in generated
1376 files propagate the copyright years of the generating file(s).
1380 The files of Perl source code distribution do carry a lot of
1381 copyrights, by various people. (There are many copyrights embedded in
1382 perl.c, for example.) The most straightforward thing for pumpkings to
1383 do is to simply update Larry's copyrights at the beginning of the
1384 *.[hcy], *.pl, and README files, and leave all other
1385 copyrights alone. Doing more than that requires quite a bit of tracking.
1391 Original author: Andy Dougherty doughera@lafayette.edu .
1392 Additions by Chip Salzenberg chip@perl.com, Tim Bunce and the perl5
1395 All opinions expressed herein are those of the authorZ<>(s).
1397 =head1 LAST MODIFIED
1399 2017-10-13 Dominic Hargreaves