=head1 NAME Pumpkin - Notes on handling the Perl Patch Pumpkin =head1 SYNOPSIS There is no simple synopsis, yet. =head1 DESCRIPTION This document attempts to begin to describe some of the considerations involved in patching and maintaining perl. This document is still under construction, and still subject to significant changes. Still, I hope parts of it will be useful, so I'm releasing it even though it's not done. For the most part, it's a collection of anecdotal information that already assumes some familiarity with the Perl sources. I really need an introductory section that describes the organization of the sources and all the various auxiliary files that are part of the distribution. =head1 Where Do I Get Perl Sources and Related Material? The Comprehensive Perl Archive Network (or CPAN) is the place to go. There are many mirrors, but the easiest thing to use is probably http://www.perl.com/CPAN/README.html , which automatically points you to a mirror site "close" to you. =head2 Perl5-porters mailing list The mailing list perl5-porters@perl.org is the main group working with the development of perl. If you're interested in all the latest developments, you should definitely subscribe. The list is high volume, but generally has a fairly low noise level. Subscribe by sending the message (in the body of your letter) subscribe perl5-porters to perl5-porters-request@perl.org . =head1 How are Perl Releases Numbered? Perl version numbers are floating point numbers, such as 5.004. (Observations about the imprecision of floating point numbers for representing reality probably have more relevance than you might imagine :-) The major version number is 5 and the '004' is the patchlevel. (Questions such as whether or not '004' is really a minor version number can safely be ignored.:) The version number is available as the magic variable $], and can be used in comparisons, e.g. print "You've got an old perl\n" if $] < 5.002; You can also require particular version (or later) with use 5.002; At some point in the future, we may need to decide what to call the next big revision. In the .package file used by metaconfig to generate Configure, there are two variables that might be relevant: $baserev=5.0 and $package=perl5. At various times, I have suggested we might change them to $baserev=5.1 and $package=perl5.1 if want to signify a fairly major update. Or, we might want to jump to perl6. Let's worry about that problem when we get there. =head2 Subversions In addition, there may be "developer" sub-versions available. These are not official releases. They may contain unstable experimental features, and are subject to rapid change. Such developer sub-versions are numbered with sub-version numbers. For example, version 5.004_04 is the 4'th developer version built on top of 5.004. It might include the _01, _02, and _03 changes, but it also might not. Sub-versions are allowed to be subversive. These sub-versions can also be used as floating point numbers, so you can do things such as print "You've got an unstable perl\n" if $] == 5.00303; You can also require particular version (or later) with use 5.003_03; # the "_" is optional Sub-versions produced by the members of perl5-porters are usually available on CPAN in the F directory. =head2 Maintenance and Development Subversions As an experiment, starting with version 5.004, subversions _01 through _49 will be reserved for bug-fix maintenance releases, and subversions _50 through _99 will be available for unstable development versions. The separate bug-fix track is being established to allow us an easy way to distribute important bug fixes without waiting for the developers to untangle all the other problems in the current developer's release. Watch for announcements of maintenance subversions in comp.lang.perl.announce. =head2 Why such a complicated scheme? Two reasons, really. At least. First, we need some way to identify and release collections of patches that are known to have new features that need testing and exploration. The subversion scheme does that nicely while fitting into the C mold. Second, since most of the folks who help maintain perl do so on a free-time voluntary basis, perl development does not proceed at a precise pace, though it always seems to be moving ahead quickly. We needed some way to pass around the "patch pumpkin" to allow different people chances to work on different aspects of the distribution without getting in each other's way. It wouldn't be constructive to have multiple people working on incompatible implementations of the same idea. Instead what was needed was some kind of "baton" or "token" to pass around so everyone knew whose turn was next. =head2 Why is it called the patch pumpkin? Chip Salzenberg gets credit for that, with a nod to his cow orker, David Croy. We had passed around various names (baton, token, hot potato) but none caught on. Then, Chip asked: [begin quote] Who has the patch pumpkin? To explain: David Croy once told me once that at a previous job, there was one tape drive and multiple systems that used it for backups. But instead of some high-tech exclusion software, they used a low-tech method to prevent multiple simultaneous backups: a stuffed pumpkin. No one was allowed to make backups unless they had the "backup pumpkin". [end quote] The name has stuck. =head1 Philosophical Issues in Patching Perl There are no absolute rules, but there are some general guidelines I have tried to follow as I apply patches to the perl sources. (This section is still under construction.) =head2 Solve problems as generally as possible Never implement a specific restricted solution to a problem when you can solve the same problem in a more general, flexible way. For example, for dynamic loading to work on some SVR4 systems, we had to build a shared libperl.so library. In order to build "FAT" binaries on NeXT 4.0 systems, we had to build a special libperl library. Rather than continuing to build a contorted nest of special cases, I generalized the process of building libperl so that NeXT and SVR4 users could still get their work done, but others could build a shared libperl if they wanted to as well. =head2 Seek consensus on major changes If you are making big changes, don't do it in secret. Discuss the ideas in advance on perl5-porters. =head2 Keep the documentation up-to-date If your changes may affect how users use perl, then check to be sure that the documentation is in sync with your changes. Be sure to check all the files F and also the F document. Consider writing the appropriate documentation first and then implementing your change to correspond to the documentation. =head2 Avoid machine-specific #ifdef's To the extent reasonable, try to avoid machine-specific #ifdef's in the sources. Instead, use feature-specific #ifdef's. The reason is that the machine-specific #ifdef's may not be valid across major releases of the operating system. Further, the feature-specific tests may help out folks on another platform who have the same problem. =head2 Allow for lots of testing We should never release a main version without testing it as a subversion first. =head2 Test popular applications and modules. We should never release a main version without testing whether or not it breaks various popular modules and applications. A partial list of such things would include majordomo, metaconfig, apache, Tk, CGI, libnet, and libwww, to name just a few. Of course it's quite possible that some of those things will be just plain broken and need to be fixed, but, in general, we ought to try to avoid breaking widely-installed things. =head2 Automate generation of derivative files The F, F, F, and F files are all automatically generated by perl scripts. In general, don't patch these directly; patch the data files instead. F and F are also automatically generated by B. In general, you should patch the metaconfig units instead of patching these files directly. However, minor changes to F may be made in between major sync-ups with the metaconfig units, which tends to be complicated operations. =head1 How to Make a Distribution There really ought to be a 'make dist' target, but there isn't. The 'dist' suite of tools also contains a number of tools that I haven't learned how to use yet. Some of them may make this all a bit easier. Here are the steps I go through to prepare a patch & distribution. Lots of it could doubtless be automated but isn't. The Porting/makerel (make release) perl script does now help automate some parts of it. =head2 Announce your intentions First, you should volunteer out loud to take the patch pumpkin. It's generally counter-productive to have multiple people working in secret on the same thing. At the same time, announce what you plan to do with the patch pumpkin, to allow folks a chance to object or suggest alternatives, or do it for you. Naturally, the patch pumpkin holder ought to incorporate various bug fixes and documentation improvements that are posted while he or she has the pumpkin, but there might also be larger issues at stake. One of the precepts of the subversion idea is that we shouldn't give the patch pumpkin to anyone unless we have some idea what he or she is going to do with it. =head2 refresh pod/perltoc.pod Presumably, you have done a full C in your working source directory. Before you C (if you do), and if you have changed any documentation in any module or pod file, change to the F directory and run C. =head2 run installhtml to check the validity of the pod files =head2 update patchlevel.h Don't be shy about using the subversion number, even for a relatively modest patch. We've never even come close to using all 99 subversions, and it's better to have a distinctive number for your patch. If you need feedback on your patch, go ahead and issue it and promise to incorporate that feedback quickly (e.g. within 1 week) and send out a second patch. =head2 run metaconfig If you need to make changes to Configure or config_h.SH, it may be best to change the appropriate metaconfig units instead, and regenerate Configure. metaconfig -m will regenerate Configure and config_h.SH. More information on obtaining and running metaconfig is in the F file that comes with Perl's metaconfig units. Perl's metaconfig units should be available the same place you found this file. On CPAN, look under my directory F for a file such as F<5.003_07-02.U.tar.gz>. That file should be unpacked in your main perl source directory. It contains the files needed to run B to reproduce Perl's Configure script. (Those units are for 5.003_07. There have been changes since then; please contact me if you want more recent versions, and I will try to point you in the right direction.) Alternatively, do consider if the F<*ish.h> files might be a better place for your changes. =head2 MANIFEST Make sure the MANIFEST is up-to-date. You can use dist's B program for this. You can also use perl -w -MExtUtils::Manifest=fullcheck -e fullcheck Both commands will also list extra files in the directory that are not listed in MANIFEST. The MANIFEST is normally sorted, with one exception. Perl includes both a F script and a F script. The F script is a front-end to the main F, but is there to aid folks who use autoconf-generated F files for other software. The problem is that F and F are the same on case-insensitive file systems, so I deliberately put F first in the MANIFEST so that the extraction of F will overwrite F and leave you with the correct script. (The F script must also have write permission for this to work, so it's the only file in the distribution I normally have with write permission.) If you are using metaconfig to regenerate Configure, then you should note that metaconfig actually uses MANIFEST.new, so you want to be sure MANIFEST.new is up-to-date too. I haven't found the MANIFEST/MANIFEST.new distinction particularly useful, but that's probably because I still haven't learned how to use the full suite of tools in the dist distribution. =head2 Check permissions All the tests in the t/ directory ought to be executable. The main makefile used to do a 'chmod t/*/*.t', but that resulted in a self-modifying distribution--something some users would strongly prefer to avoid. Probably, the F script should check for this and do the chmod if needed, but it doesn't currently. In all, the following files should probably be executable: Configure configpm configure embed.pl installperl installman keywords.pl myconfig opcode.pl perly.fixer t/TEST t/*/*.t *.SH vms/ext/Stdio/test.pl vms/ext/filespec.t vms/fndvers.com x2p/*.SH Other things ought to be readable, at least :-). Probably, the permissions for the files could be encoded in MANIFEST somehow, but I'm reluctant to change MANIFEST itself because that could break old scripts that use MANIFEST. I seem to recall that some SVR3 systems kept some sort of file that listed permissions for system files; something like that might be appropriate. =head2 Run Configure This will build a config.sh and config.h. You can skip this if you haven't changed Configure or config_h.SH at all. =head2 Update config_H The config_H file is provided to help those folks who can't run Configure. It is important to keep it up-to-date. If you have changed config_h.SH, those changes must be reflected in config_H as well. (The name config_H was chosen to distinguish the file from config.h even on case-insensitive file systems.) Simply edit the existing config_H file; keep the first few explanatory lines and then copy your new config.h below. It may also be necessary to update vms/config.vms and plan9/config.plan9, though you should be quite careful in doing so if you are not familiar with those systems. You might want to issue your patch with a promise to quickly issue a follow-up that handles those directories. =head2 make run_byacc If you have byacc-1.8.2 (available from CPAN), and if there have been changes to F, you can regenerate the F file. The run_byacc makefile target does this by running byacc and then applying some patches so that byacc dynamically allocates space, rather than having fixed limits. This patch is handled by the F script. Depending on the nature of the changes to F, you may or may not have to hand-edit the patch to apply correctly. If you do, you should include the edited patch in the new distribution. If you have byacc-1.9, the patch won't apply cleanly. Changes to the printf output statements mean the patch won't apply cleanly. Long ago I started to fix F to detect this, but I never completed the task. Some additional notes from Larry on this: Don't forget to regenerate perly.c.diff. byacc -d perly.y mv y.tab.c perly.c patch perly.c perly.c.diff One chunk of lines that often fails begins with #line 29 "perly.y" and ends one line before #define YYERRCODE 256 This only happens when you add or remove a token type. I suppose this could be automated, but it doesn't happen very often nowadays. Larry =head2 make regen_headers The F, F, and F files are all automatically generated by perl scripts. Since the user isn't guaranteed to have a working perl, we can't require the user to generate them. Hence you have to, if you're making a distribution. I used to include rules like the following in the makefile: # The following three header files are generated automatically # The correct versions should be already supplied with the perl kit, # in case you don't have perl or 'sh' available. # The - is to ignore error return codes in case you have the source # installed read-only or you don't have perl yet. keywords.h: keywords.pl @echo "Don't worry if this fails." - perl keywords.pl However, I got B of mail consisting of people worrying because the command failed. I eventually decided that I would save myself time and effort by manually running C myself rather than answering all the questions and complaints about the failing command. =head2 global.sym, interp.sym and perlio.sym Make sure these files are up-to-date. Read the comments in these files and in perl_exp.SH to see what to do. =head2 Binary compatibility If you do change F or F, think carefully about what you are doing. To the extent reasonable, we'd like to maintain souce and binary compatibility with older releases of perl. That way, extensions built under one version of perl will continue to work with new versions of perl. Of course, some incompatible changes may well be necessary. I'm just suggesting that we not make any such changes without thinking carefully about them first. If possible, we should provide backwards-compatibility stubs. There's a lot of XS code out there. Let's not force people to keep changing it. =head2 Changes Be sure to update the F file. Try to include both an overall summary as well as detailed descriptions of the changes. Your audience will include other developers and users, so describe user-visible changes (if any) in terms they will understand, not in code like "initialize foo variable in bar function". There are differing opinions on whether the detailed descriptions ought to go in the Changes file or whether they ought to be available separately in the patch file (or both). There is no disagreement that detailed descriptions ought to be easily available somewhere. =head2 OS/2-specific updates In the os2 directory is F, a set of OS/2-specific diffs against B. If you make changes to Configure, you may want to consider regenerating this diff file to save trouble for the OS/2 maintainer. You can also consider the OS/2 diffs as reminders of portability things that need to be fixed in Configure. =head2 VMS-specific updates If you have changed F, then you may want to update F by running C. The Perl version number appears in several places under F. It is courteous to update these versions. For example, if you are making 5.004_42, replace "5.00441" with "5.00442". =head2 Making the new distribution Suppose, for example, that you want to make version 5.004_08. Then you can do something like the following mkdir ../perl5.004_08 awk '{print $1}' MANIFEST | cpio -pdm ../perl5.004_08 cd ../ tar cf perl5.004_08.tar perl5.004_08 gzip --best perl5.004_08.tar These steps, with extra checks, are automated by the Porting/makerel script. =head2 Making a new patch I find the F utility quite handy for making patches. You can obtain it from any CPAN archive under http://www.perl.com/CPAN/authors/Johan_Vromans/ . There are a couple of differences between my version and the standard one. I have mine do a # Print a reassuring "End of Patch" note so people won't # wonder if their mailer truncated patches. print "\n\nEnd of Patch.\n"; at the end. That's because I used to get questions from people asking if their mail was truncated. It also writes Index: lines which include the new directory prefix (change Index: print, approx line 294 or 310 depending on the version, to read: print PATCH ("Index: $newdir$new\n");). That helps patches work with more POSIX conformant patch programs. Here's how I generate a new patch. I'll use the hypothetical 5.004_07 to 5.004_08 patch as an example. # unpack perl5.004_07/ gzip -d -c perl5.004_07.tar.gz | tar -xof - # unpack perl5.004_08/ gzip -d -c perl5.004_08.tar.gz | tar -xof - makepatch perl5.004_07 perl5.004_08 > perl5.004_08.pat Makepatch will automatically generate appropriate B commands to remove deleted files. Unfortunately, it will not correctly set permissions for newly created files, so you may have to do so manually. For example, patch 5.003_04 created a new test F which needs to be executable, so at the top of the patch, I inserted the following lines: # Make a new test touch t/op/gv.t chmod +x t/opt/gv.t Now, of course, my patch is now wrong because makepatch didn't know I was going to do that command, and it patched against /dev/null. So, what I do is sort out all such shell commands that need to be in the patch (including possible mv-ing of files, if needed) and put that in the shell commands at the top of the patch. Next, I delete all the patch parts of perl5.004_08.pat, leaving just the shell commands. Then, I do the following: cd perl5.004_07 sh ../perl5.004_08.pat cd .. makepatch perl5.004_07 perl5.004_08 >> perl5.004_08.pat (Note the append to preserve my shell commands.) Now, my patch will line up with what the end users are going to do. =head2 Testing your patch It seems obvious, but be sure to test your patch. That is, verify that it produces exactly the same thing as your full distribution. rm -rf perl5.004_07 gzip -d -c perl5.004_07.tar.gz | tar -xf - cd perl5.004_07 sh ../perl5.004_08.pat patch -p1 -N < ../perl5.004_08.pat cd .. gdiff -r perl5.004_07 perl5.004_08 where B is GNU diff. Other diff's may also do recursive checking. =head2 More testing Again, it's obvious, but you should test your new version as widely as you can. You can be sure you'll hear about it quickly if your version doesn't work on both ANSI and pre-ANSI compilers, and on common systems such as SunOS 4.1.[34], Solaris, and Linux. If your changes include conditional code, try to test the different branches as thoroughly as you can. For example, if your system supports dynamic loading, you can also test static loading with sh Configure -Uusedl You can also hand-tweak your config.h to try out different #ifdef branches. =head1 Common Gotcha's =over 4 =item #elif The '#elif' preprocessor directive is not understood on all systems. Specifically, I know that Pyramids don't understand it. Thus instead of the simple #if defined(I_FOO) # include #elif defined(I_BAR) # include #else # include #endif You have to do the more Byzantine #if defined(I_FOO) # include #else # if defined(I_BAR) # include # else # include # endif #endif Incidentally, whitespace between the leading '#' and the preprocessor command is not guaranteed, but is very portable and you may use it freely. I think it makes things a bit more readable, especially once things get rather deeply nested. I also think that things should almost never get too deeply nested, so it ought to be a moot point :-) =item Probably Prefer POSIX It's often the case that you'll need to choose whether to do something the BSD-ish way or the POSIX-ish way. It's usually not a big problem when the two systems use different names for similar functions, such as memcmp() and bcmp(). The perl.h header file handles these by appropriate #defines, selecting the POSIX mem*() functions if available, but falling back on the b*() functions, if need be. More serious is the case where some brilliant person decided to use the same function name but give it a different meaning or calling sequence :-). getpgrp() and setpgrp() come to mind. These are a real problem on systems that aim for conformance to one standard (e.g. POSIX), but still try to support the other way of doing things (e.g. BSD). My general advice (still not really implemented in the source) is to do something like the following. Suppose there are two alternative versions, fooPOSIX() and fooBSD(). #ifdef HAS_FOOPOSIX /* use fooPOSIX(); */ #else # ifdef HAS_FOOBSD /* try to emulate fooPOSIX() with fooBSD(); perhaps with the following: */ # define fooPOSIX fooBSD # else # /* Uh, oh. We have to supply our own. */ # define fooPOSIX Perl_fooPOSIX # endif #endif =item Think positively If you need to add an #ifdef test, it is usually easier to follow if you think positively, e.g. #ifdef HAS_NEATO_FEATURE /* use neato feature */ #else /* use some fallback mechanism */ #endif rather than the more impenetrable #ifndef MISSING_NEATO_FEATURE /* Not missing it, so we must have it, so use it */ #else /* Are missing it, so fall back on something else. */ #endif Of course for this toy example, there's not much difference. But when the #ifdef's start spanning a couple of screen fulls, and the #else's are marked something like #else /* !MISSING_NEATO_FEATURE */ I find it easy to get lost. =item Providing Missing Functions -- Problem Not all systems have all the neat functions you might want or need, so you might decide to be helpful and provide an emulation. This is sound in theory and very kind of you, but please be careful about what you name the function. Let me use the C function as an illustration. Perl5.003 has the following in F #ifndef HAS_PAUSE #define pause() sleep((32767<<16)+32767) #endif Configure sets HAS_PAUSE if the system has the pause() function, so this #define only kicks in if the pause() function is missing. Nice idea, right? Unfortunately, some systems apparently have a prototype for pause() in F, but don't actually have the function in the library. (Or maybe they do have it in a library we're not using.) Thus, the compiler sees something like extern int pause(void); /* . . . */ #define pause() sleep((32767<<16)+32767) and dies with an error message. (Some compilers don't mind this; others apparently do.) To work around this, 5.003_03 and later have the following in perl.h: /* Some unistd.h's give a prototype for pause() even though HAS_PAUSE ends up undefined. This causes the #define below to be rejected by the compiler. Sigh. */ #ifdef HAS_PAUSE # define Pause pause #else # define Pause() sleep((32767<<16)+32767) #endif This works. The curious reader may wonder why I didn't do the following in F instead: #ifndef HAS_PAUSE void pause() { sleep((32767<<16)+32767); } #endif That is, since the function is missing, just provide it. Then things would probably be been alright, it would seem. Well, almost. It could be made to work. The problem arises from the conflicting needs of dynamic loading and namespace protection. For dynamic loading to work on AIX (and VMS) we need to provide a list of symbols to be exported. This is done by the script F, which reads F and F. Thus, the C symbol would have to be added to F So far, so good. On the other hand, one of the goals of Perl5 is to make it easy to either extend or embed perl and link it with other libraries. This means we have to be careful to keep the visible namespace "clean". That is, we don't want perl's global variables to conflict with those in the other application library. Although this work is still in progress, the way it is currently done is via the F file. This file is built from the F and F files, since those files already list the globally visible symbols. If we had added C to global.sym, then F would contain the line #define pause Perl_pause and calls to C in the perl sources would now point to C. Now, when B is run to build the F executable, it will go looking for C, which probably won't exist in any of the standard libraries. Thus the build of perl will fail. Those systems where C is not defined would be ok, however, since they would get a C function in util.c. The rest of the world would be in trouble. And yes, this scenario has happened. On SCO, the function C is available. (I think it's in F<-lx>, the Xenix compatibility library.) Since the perl4 days (and possibly before), Perl has included a C function that gets called something akin to #ifndef HAS_CHSIZE I32 chsize(fd, length) /* . . . */ #endif When 5.003 added #define chsize Perl_chsize to F, the compile started failing on SCO systems. The "fix" is to give the function a different name. The one implemented in 5.003_05 isn't optimal, but here's what was done: #ifdef HAS_CHSIZE # ifdef my_chsize /* Probably #defined to Perl_my_chsize in embed.h */ # undef my_chsize # endif # define my_chsize chsize #endif My explanatory comment in patch 5.003_05 said: Undef and then re-define my_chsize from Perl_my_chsize to just plain chsize if this system HAS_CHSIZE. This probably only applies to SCO. This shows the perils of having internal functions with the same name as external library functions :-). Now, we can safely put C in F, export it, and hide it with F. To be consistent with what I did for C, I probably should have called the new function C, rather than C. However, the perl sources are quite inconsistent on this (Consider New, Mymalloc, and Myremalloc, to name just a few.) There is a problem with this fix, however, in that C was available as a F library function in 5.003, but it isn't available any more (as of 5.003_07). This means that we've broken binary compatibility. This is not good. =item Providing missing functions -- some ideas We currently don't have a standard way of handling such missing function names. Right now, I'm effectively thinking aloud about a solution. Some day, I'll try to formally propose a solution. Part of the problem is that we want to have some functions listed as exported but not have their names mangled by embed.h or possibly conflict with names in standard system headers. We actually already have such a list at the end of F (though that list is out-of-date): # extra globals not included above. cat <> perl.exp perl_init_ext perl_init_fold perl_init_i18nl14n perl_alloc perl_construct perl_destruct perl_free perl_parse perl_run perl_get_sv perl_get_av perl_get_hv perl_get_cv perl_call_argv perl_call_pv perl_call_method perl_call_sv perl_requirepv safecalloc safemalloc saferealloc safefree This still needs much thought, but I'm inclined to think that one possible solution is to prefix all such functions with C in the source and list them along with the other C functions in F. Thus, for C, we'd do something like the following: /* in perl.h */ #ifdef HAS_CHSIZE # define perl_chsize chsize #endif then in some file (e.g. F or F) do #ifndef HAS_CHSIZE I32 perl_chsize(fd, length) /* implement the function here . . . */ #endif Alternatively, we could just always use C everywhere and move C from F to the end of F. That would probably be fine as long as our C function agreed with all the C function prototypes in the various systems we'll be using. As long as the prototypes in actual use don't vary that much, this is probably a good alternative. (As a counter-example, note how Configure and perl have to go through hoops to find and use get Malloc_t and Free_t for C and C.) At the moment, this latter option is what I tend to prefer. =item All the world's a VAX Sorry, showing my age:-). Still, all the world is not BSD 4.[34], SVR4, or POSIX. Be aware that SVR3-derived systems are still quite common (do you have any idea how many systems run SCO?) If you don't have a bunch of v7 manuals handy, the metaconfig units (by default installed in F) are a good resource to look at for portability. =back =head1 Miscellaneous Topics =head2 Autoconf Why does perl use a metaconfig-generated Configure script instead of an autoconf-generated configure script? Metaconfig and autoconf are two tools with very similar purposes. Metaconfig is actually the older of the two, and was originally written by Larry Wall, while autoconf is probably now used in a wider variety of packages. The autoconf info file discusses the history of autoconf and how it came to be. The curious reader is referred there for further information. Overall, both tools are quite good, I think, and the choice of which one to use could be argued either way. In March, 1994, when I was just starting to work on Configure support for Perl5, I considered both autoconf and metaconfig, and eventually decided to use metaconfig for the following reasons: =over 4 =item Compatibility with Perl4 Perl4 used metaconfig, so many of the #ifdef's were already set up for metaconfig. Of course metaconfig had evolved some since Perl4's days, but not so much that it posed any serious problems. =item Metaconfig worked for me My system at the time was Interactive 2.2, a SVR3.2/386 derivative that also had some POSIX support. Metaconfig-generated Configure scripts worked fine for me on that system. On the other hand, autoconf-generated scripts usually didn't. (They did come quite close, though, in some cases.) At the time, I actually fetched a large number of GNU packages and checked. Not a single one configured and compiled correctly out-of-the-box with the system's cc compiler. =item Configure can be interactive With both autoconf and metaconfig, if the script works, everything is fine. However, one of my main problems with autoconf-generated scripts was that if it guessed wrong about something, it could be B hard to go back and fix it. For example, autoconf always insisted on passing the -Xp flag to cc (to turn on POSIX behavior), even when that wasn't what I wanted or needed for that package. There was no way short of editing the configure script to turn this off. You couldn't just edit the resulting Makefile at the end because the -Xp flag influenced a number of other configure tests. Metaconfig's Configure scripts, on the other hand, can be interactive. Thus if Configure is guessing things incorrectly, you can go back and fix them. This isn't as important now as it was when we were actively developing Configure support for new features such as dynamic loading, but it's still useful occasionally. =item GPL At the time, autoconf-generated scripts were covered under the GNU Public License, and hence weren't suitable for inclusion with Perl, which has a different licensing policy. (Autoconf's licensing has since changed.) =item Modularity Metaconfig builds up Configure from a collection of discrete pieces called "units". You can override the standard behavior by supplying your own unit. With autoconf, you have to patch the standard files instead. I find the metaconfig "unit" method easier to work with. Others may find metaconfig's units clumsy to work with. =back =head2 @INC search order By default, the list of perl library directories in @INC is the following: $archlib $privlib $sitearch $sitelib Specifically, on my Solaris/x86 system, I run B and I have the following directories: /opt/perl/lib/i86pc-solaris/5.00307 /opt/perl/lib /opt/perl/lib/site_perl/i86pc-solaris /opt/perl/lib/site_perl That is, perl's directories come first, followed by the site-specific directories. The site libraries come second to support the usage of extensions across perl versions. Read the relevant section in F for more information. If we ever make $sitearch version-specific, this topic could be revisited. =head2 Why isn't there a directory to override Perl's library? Mainly because no one's gotten around to making one. Note that "making one" involves changing perl.c, Configure, config_h.SH (and associated files, see above), and I it all in the INSTALL file. Apparently, most folks who want to override one of the standard library files simply do it by overwriting the standard library files. =head2 APPLLIB In the perl.c sources, you'll find an undocumented APPLLIB_EXP variable, sort of like PRIVLIB_EXP and ARCHLIB_EXP (which are documented in config_h.SH). Here's what APPLLIB_EXP is for, from a mail message from Larry: The main intent of APPLLIB_EXP is for folks who want to send out a version of Perl embedded in their product. They would set the symbol to be the name of the library containing the files needed to run or to support their particular application. This works at the "override" level to make sure they get their own versions of any library code that they absolutely must have configuration control over. As such, I don't see any conflict with a sysadmin using it for a override-ish sort of thing, when installing a generic Perl. It should probably have been named something to do with overriding though. Since it's undocumented we could still change it... :-) Given that it's already there, you can use it to override distribution modules. If you do sh Configure -Dccflags='-DAPPLLIB_EXP=/my/override' then perl.c will put /my/override ahead of ARCHLIB and PRIVLIB. =head1 Upload Your Work to CPAN You can upload your work to CPAN if you have a CPAN id. Check out http://www.perl.com/CPAN/modules/04pause.html for information on _PAUSE_, the Perl Author's Upload Server. I typically upload both the patch file, e.g. F and the full tar file, e.g. F. If you want your patch to appear in the F directory on CPAN, send e-mail to the CPAN master librarian. (Check out http://www.perl.com/CPAN/CPAN.html ). =head1 Help Save the World You should definitely announce your patch on the perl5-porters list. You should also consider announcing your patch on comp.lang.perl.announce, though you should make it quite clear that a subversion is not a production release, and be prepared to deal with people who will not read your disclaimer. =head1 Todo Here, in no particular order, are some Configure and build-related items that merit consideration. This list isn't exhaustive, it's just what I came up with off the top of my head. =head2 Good ideas waiting for round tuits =over 4 =item installprefix I think we ought to support Configure -Dinstallprefix=/blah/blah Currently, we support B<-Dprefix=/blah/blah>, but the changing the install location has to be handled by something like the F trick described in F. AFS users also are treated specially. We should probably duplicate the metaconfig prefix stuff for an install prefix. =item Configure -Dsrcdir=/blah/blah We should be able to emulate B. Tom Tromey tromey@creche.cygnus.com has submitted some patches to the dist-users mailing list along these lines. Eventually, they ought to get folded back into the main distribution. =item Hint file fixes Various hint files work around Configure problems. We ought to fix Configure so that most of them aren't needed. =item Hint file information Some of the hint file information (particularly dynamic loading stuff) ought to be fed back into the main metaconfig distribution. =back =head2 Probably good ideas waiting for round tuits =over 4 =item GNU configure --options I've received sensible suggestions for --exec_prefix and other GNU configure --options. It's not always obvious exactly what is intended, but this merits investigation. =item make clean Currently, B isn't all that useful, though B and B are. This needs a bit of thought and documentation before it gets cleaned up. =item Try gcc if cc fails Currently, we just give up. =item bypassing safe*alloc wrappers On some systems, it may be safe to call the system malloc directly without going through the util.c safe* layers. (Such systems would accept free(0), for example.) This might be a time-saver for systems that already have a good malloc. (Recent Linux libc's apparently have a nice malloc that is well-tuned for the system.) =back =head2 Vague possibilities =over 4 =item MacPerl Get some of the Macintosh stuff folded back into the main distribution. =item gconvert replacement Maybe include a replacement function that doesn't lose data in rare cases of coercion between string and numerical values. =item long long Can we support C on systems where C is larger than what we've been using for C? What if you can't C a C? =item Improve makedepend The current makedepend process is clunky and annoyingly slow, but it works for most folks. Alas, it assumes that there is a filename $firstmakefile that the B command will try to use before it uses F. Such may not be the case for all B commands, particularly those on non-Unix systems. Probably some variant of the BSD F<.depend> file will be useful. We ought to check how other packages do this, if they do it at all. We could probably pre-generate the dependencies (with the exception of malloc.o, which could probably be determined at F extraction time. =item GNU Makefile standard targets GNU software generally has standardized Makefile targets. Unless we have good reason to do otherwise, I see no reason not to support them. =item File locking Somehow, straighten out, document, and implement lockf(), flock(), and/or fcntl() file locking. It's a mess. =back =head1 AUTHOR Andy Dougherty . Additions by Chip Salzenberg . All opinions expressed herein are those of the authorZ<>(s). =head1 LAST MODIFIED $Id: pumpkin.pod,v 1.10.1.1 1997/06/10 20:46:47 timbo Exp $