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Pumpkin - Notes on handling the Perl Patch Pumpkin
There is no simple synopsis, yet.
This document attempts to begin to describe some of the considerations involved in patching, porting, 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.
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.
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 .
Archives of the list are held at: http://www.rosat.mpe-garching.mpg.de/mailing-lists/perl-porters/
Beginning with v5.6.0, even versions will stand for maintenance releases and odd versions for development releases, i.e., v5.6.x for maintenance releases, and v5.7.x for development releases. Before v5.6.0, subversions _01 through _49 were reserved for bug-fix maintenance releases, and subversions _50 through _99 for unstable development versions.
For example, in v5.6.1, the revision number is 5, the version is 6, and 1 is the subversion.
For compatibility with the older numbering scheme the composite floating
point version number continues to be available as the magic variable $],
and amounts to $revision + $version/1000 + $subversion/100000
. This
can still be used in comparisons.
print "You've got an old perl\n" if $] < 5.005_03;
In addition, the version is also available as a string in $^V. print "You've got a new perl\n" if $^V and $^V ge v5.6.0;
You can also require particular version (or later) with: use 5.006;
or using the new syntax available only from v5.6 onward: use v5.6.0;
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 and $package=perl5.
Perl releases produced by the members of perl5-porters are usually
available on CPAN in the src/5.0/maint
and src/5.0/devel
directories.
The first rule of maintenance work is "First, do no harm."
Trial releases of bug-fix maintenance releases are announced on
perl5-porters. Trial releases use the new subversion number (to avoid
testers installing it over the previous release) and include a 'local
patch' entry in patchlevel.h. The distribution file contains the
string MAINT_TRIAL
to make clear that the file is not meant for
public consumption.
In general, the names of official distribution files for the public always match the regular expression: ^perl\d+\.(\d+)\.\d+(-MAINT_TRIAL_\d+)\.tar\.gz$
$1
in the pattern is always an even number for maintenance
versions, and odd for developer releases.
In the past it has been observed that pumkings tend to invent new naming conventions on the fly. If you are a pumpking, before you invent a new name for any of the three types of perl distributions, please inform the guys from the CPAN who are doing indexing and provide the trees of symlinks and the like. They will have to know in advance what you decide.
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.
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.)
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.
Contain your changes carefully. Assume nothing about other operating systems, not even closely related ones. Your changes must not affect other platforms.
Spy shamelessly on how similar patching or porting issues have been settled elsewhere.
If feasible, try to keep filenames 8.3-compliant to humor those poor souls that get joy from running Perl under such dire limitations.
If you are making big changes, don't do it in secret. Discuss the ideas in advance on perl5-porters.
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 pod/*.pod
and also the INSTALL
document.
Consider writing the appropriate documentation first and then implementing your change to correspond to the documentation.
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.
MANIFEST
when you add files.
If your system supports dynamic loading but none of the existing
methods at ext/DynaLoader/dl_*.xs
work for you, you must write
a new one. Study the existing ones to see what kind of interface
you must supply.
hints
subdirectory, the latter
in ext/*/hints
subdirectories.
The top level hints are Bourne-shell scripts that set, modify and unset appropriate Configure variables, based on the Configure command line options and possibly existing config.sh and Policy.sh files from previous Configure runs.
The extension hints are written in Perl (by the time they are used miniperl has been built) and control the building of their respective extensions. They can be used to for example manipulate compilation and linking flags.
Makefile.SH
and installperl
.
Tread very carefully, even more than usual. Contain your changes
with utmost care.
t
subdirectory assume machine-specific things
like existence of certain functions, something about filesystem
semantics, certain external utilities and their error messages. Use
the $^O
and the Config
module (which contains the results of the
Configure run, in effect the config.sh
converted to Perl) to either
skip (preferably not) or customize (preferable) the tests for your
platform.
pod/perlport.pod
. If your operating system is
the first not to have a system call also update the list of
"portability-bewares" at the beginning of pod/perlfunc.pod
.
A file called README.youros
at the top level that explains things
like how to install perl at this platform, where to get any possibly
required additional software, and for example what test suite errors
to expect, is nice too. Such files are in the process of being written
in pod format and will eventually be renamed INSTALL.youros
.
You may also want to write a separate .pod
file for your operating
system to tell about existing mailing lists, os-specific modules,
documentation, whatever. Please name these along the lines of
perl
youros.pod. [unfinished: where to put this file (the pod/
subdirectory, of course: but more importantly, which/what index files
should be updated?)]
We should never release a main version without testing it as a subversion first.
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.
The embed.h
, keywords.h
, opcode.h
, and perltoc.pod
files
are all automatically generated by perl scripts. In general, don't
patch these directly; patch the data files instead.
Configure
and config_h.SH
are also automatically generated by
metaconfig. In general, you should patch the metaconfig units
instead of patching these files directly. However, very minor changes
to Configure
may be made in between major sync-ups with the
metaconfig units, which tends to be complicated operations. But be
careful, this can quickly spiral out of control. Running metaconfig
is not really hard.
Also Makefile
is automatically produced from Makefile.SH
.
In general, look out for all *.SH
files.
Finally, the sample files in the Porting/
subdirectory are
generated automatically by the script U/mksample
included
with the metaconfig units. See the section on run metaconfig elsewhere in this document below for
information on obtaining the metaconfig units.
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.
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.
Presumably, you have done a full make
in your working source
directory. Before you make spotless
(if you do), and if you have
changed any documentation in any module or pod file, change to the
pod
directory and run make toc
.
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.
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. Much more information
on obtaining and running metaconfig is in the U/README
file
that comes with Perl's metaconfig units. Perl's metaconfig units
should be available on CPAN. A set of units that will work with
perl5.005 is in the file mc_units-5.005_00-01.tar.gz
under
http://www.perl.com/CPAN/authors/id/ANDYD/ . The mc_units tar file
should be unpacked in your main perl source directory. Note: those
units were for use with 5.005. There may have been changes since then.
Check for later versions or contact perl5-porters@perl.org to obtain a
pointer to the current version.
Alternatively, do consider if the *ish.h
files might be a better
place for your changes.
Make sure the MANIFEST is up-to-date. You can use dist's manicheck 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.
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.
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. The t/TEST
script will check for this
and do the chmod if needed, but the tests still ought to be
executable.
In all, the following files should probably be executable: Configure configpm configure.gnu 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 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.
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. I use the following command sh Configure -Dprefix=/opt/perl -Doptimize=-O -Dusethreads \ -Dcf_by='yourname' \ -Dcf_email='yourname@yourhost.yourplace.com' \ -Dperladmin='yourname@yourhost.yourplace.com' \ -Dmydomain='.yourplace.com' \ -Dmyhostname='yourhost' \ -des
[XXX This section needs revision. We're currently working on easing the task of keeping the vms, win32, and plan9 config.sh info up-to-date. The plan is to use keep up-to-date 'canned' config.sh files in the appropriate subdirectories and then generate 'canned' config.h files for vms, win32, etc. from the generic config.sh file. This is to ease maintenance. When Configure gets updated, the parts sometimes get scrambled around, and the changes in config_H can sometimes be very hard to follow. config.sh, on the other hand, can safely be sorted, so it's easy to track (typically very small) changes to config.sh and then propoagate them to a canned 'config.h' by any number of means, including a perl script in win32/ or carrying config.sh and config_h.SH to a Unix system and running sh config_h.SH.) Vms uses configure.com to generate its own config.sh and config.h. If you want to add a new variable to config.sh check with vms folk how to add it to configure.com too. XXX]
The Porting/config.sh and Porting/config_H files are provided to help those folks who can't run Configure. It is important to keep them 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 win32/config.?c, 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.
If you have byacc-1.8.2 (available from CPAN), and if there have been
changes to perly.y
, you can regenerate the perly.c
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 perly.fixer
script. Depending on the nature of the changes to perly.y
, 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 perly.fixer
to detect this, but I never completed the
task.
If perly.c
or perly.h
changes, make sure you run perl vms/vms_yfix.pl
to update the corresponding VMS files. This could be taken care of by
the regen_all target in the Unix Makefile. See also
the VMS-specific updates entry elsewhere in this document.
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 # manually apply any failed hunks diff -c2 perly.c.orig 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
This target takes care of the PERLYVMS, regen_headers, and regen_pods targets.
The embed.h
, keywords.h
, and opcode.h
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 lots of mail consisting of people worrying because the
command failed. I eventually decided that I would save myself time
and effort by manually running make regen_headers
myself rather
than answering all the questions and complaints about the failing
command.
Will run `make regen_pods` in the pod directory for indexing.
Make sure these files are up-to-date. Read the comments in these files and in perl_exp.SH to see what to do.
If you do change global.sym
or interp.sym
, think carefully about
what you are doing. To the extent reasonable, we'd like to maintain
source 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.
Be sure to update the Changes
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.
The Todo
file contains a roughly-catgorized unordered list of
aspects of Perl that could use enhancement, features that could be
added, areas that could be cleaned up, and so on. During your term as
pumpkin-holder, you will probably address some of these issues, and
perhaps identify others which, while you decide not to address them
this time around, may be tackled in the future. Update the file
reflect the situation as it stands when you hand over the pumpkin.
You might like, early in your pumpkin-holding career, to see if you can find champions for partiticular issues on the to-do list: an issue owned is an issue more likely to be resolved.
There are also some more porting-specific the Todo manpage items later in this file.
In the os2 directory is diff.configure
, a set of OS/2-specific
diffs against Configure. 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.
If you have changed perly.y
or perly.c
, then you most probably want
to update vms/perly_{h,c}.vms
by running perl vms/vms_yfix.pl
, or
by running `make regen_all` which will run that script for you.
The Perl revision number appears as "perl5" in configure.com. It is courteous to update that if necessary.
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.
I find the makepatch
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 rm 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 t/op/gv.t
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.
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 gdiff is GNU diff. Other diff's may also do recursive checking.
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.
Configure
with
-Dccflags='-DCHECK_FORMAT -Wformat' and run make
. The compiler
will produce warning of incorrect use of format arguments. CHECK_FORMAT
changes perl-defined formats to common formats, so DO NOT USE the executable
produced by this process.
A more accurate approach is the following commands: sh Configure -des -Dccflags=-Wformat ... make miniperl # without -DCHECK_FORMAT perl -i.orig -pwe 's/-Wformat/-DCHECK_FORMAT $&/' config.sh sh Configure -S make >& make.log # build from correct miniperl make clean make miniperl >& mini.log # build miniperl with -DCHECK_FORMAT perl -nwe 'print if /^\S+:/ and not /^make\b/' mini.log make.log make clean
(-Wformat support by Robin Barker.)
Purify is a commercial tool that is helpful in identifying memory overruns, wild pointers, memory leaks and other such badness. Perl must be compiled in a specific way for optimal testing with Purify.
Use the following commands to test perl with Purify: sh Configure -des -Doptimize=-g -Uusemymalloc -Dusemultiplicity \ -Accflags=-DPURIFY setenv PURIFYOPTIONS "-chain-length=25" make all pureperl cd t ln -s ../pureperl perl setenv PERL_DESTRUCT_LEVEL 5 ./perl TEST
Disabling Perl's malloc allows Purify to monitor allocations and leaks more closely; using Perl's malloc will make Purify report most leaks in the "potential" leaks category. Enabling the multiplicity option allows perl to clean up thoroughly when the interpreter shuts down, which reduces the number of bogus leak reports from Purify. The -DPURIFY enables any Purify-specific debugging code in the sources.
Purify outputs messages in "Viewer" windows by default. If you don't have a windowing environment or if you simply want the Purify output to unobtrusively go to a log file instead of to the interactive window, use the following options instead: setenv PURIFYOPTIONS "-chain-length=25 -windows=no -log-file=perl.log \ -append-logfile=yes"
The only currently known leaks happen when there are compile-time errors within eval or require. (Fixing these is non-trivial, unfortunately, but they must be fixed eventually.)
#if defined(I_FOO) # include <foo.h> #elif defined(I_BAR) # include <bar.h> #else # include <fubar.h> #endif
You have to do the more Byzantine #if defined(I_FOO) # include <foo.h> #else # if defined(I_BAR) # include <bar.h> # else # include <fubar.h> # 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 :-)
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
#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.
pause()
function as an
illustration.
Perl5.003 has the following in perl.h
#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 unistd.h
, 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
util.c
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 perl_exp.SH
,
which reads global.sym
and interp.sym
. Thus, the pause
symbol would have to be added to global.sym
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 theembed.h
file. This file is built from theglobal.sym
andinterp.sym
files, since those files already list the globally visible symbols. If we had addedpause
to global.sym, thenembed.h
would contain the line #define pause Perl_pause
and calls to pause
in the perl sources would now point to
Perl_pause
. Now, when ld is run to build the perl
executable,
it will go looking for perl_pause
, which probably won't exist in any
of the standard libraries. Thus the build of perl will fail.
Those systems where HAS_PAUSE
is not defined would be ok, however,
since they would get a Perl_pause
function in util.c. The rest of
the world would be in trouble.
And yes, this scenario has happened. On SCO, the functionchsize
is available. (I think it's in-lx
, the Xenix compatibility library.) Since the perl4 days (and possibly before), Perl has included achsize
function that gets called something akin to #ifndef HAS_CHSIZE I32 chsize(fd, length) /* . . . */ #endif
When 5.003 added #define chsize Perl_chsize
to embed.h
, 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 my_chsize
in global.sym
, export it, and
hide it with embed.h
.
To be consistent with what I did for pause
, I probably should have
called the new function Chsize
, rather than my_chsize
.
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 Perl_chsize
was available as a libperl.a
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.
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 perl_exp.SH
(though that list is
out-of-date):
# extra globals not included above.
cat <<END >> 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 perl_
in the
source and list them along with the other perl_*
functions in
perl_exp.SH
.
Thus, for chsize
, we'd do something like the following:
/* in perl.h */
#ifdef HAS_CHSIZE
# define perl_chsize chsize
#endif
then in some file (e.g.util.c
ordoio.c
) do #ifndef HAS_CHSIZE I32 perl_chsize(fd, length) /* implement the function here . . . */ #endif
Alternatively, we could just always use chsize
everywhere and move
chsize
from global.sym
to the end of perl_exp.SH
. That would
probably be fine as long as our chsize
function agreed with all the
chsize
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 malloc
and free
.)
At the moment, this latter option is what I tend to prefer.
/usr/local/lib/dist/U
) are a good resource to look at
for portability.
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:
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.
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 documenting 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.
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.
Why isn't the shared libperl.so installed in /usr/lib/ along with "all the other" shared libraries? Instead, it is installed in $archlib, which is typically something like /usr/local/lib/perl5/archname/5.00404
and is architecture- and version-specific.
The basic reason why a shared libperl.so gets put in $archlib is so that you can have more than one version of perl on the system at the same time, and have each refer to its own libperl.so.
Three examples might help. All of these work now; none would work if you put libperl.so in /usr/lib.
Anyway, all this leads to quite obscure failures that are sure to drive casual users crazy. Even experienced users will get confused :-). Upon reflection, I'd say leave libperl.so in $archlib.
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. perl5.004_08.pat.gz
and the full tar file, e.g. perl5.004_08.tar.gz
.
If you want your patch to appear in the src/5.0/unsupported
directory on CPAN, send e-mail to the CPAN master librarian. (Check
out http://www.perl.com/CPAN/CPAN.html ).
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.
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.
Makefile
. Such may not be the case for all make commands,
particularly those on non-Unix systems.
Probably some variant of the BSD .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 Makefile.SH
extraction time.
Original author: Andy Dougherty doughera@lafcol.lafayette.edu . Additions by Chip Salzenberg chip@perl.com and Tim Bunce Tim.Bunce@ig.co.uk .
All opinions expressed herein are those of the author(s).
$Id: pumpkin.pod,v 1.23 2000/01/13 19:45:13 doughera Released $