=head1 NAME
Pumpkin - Notes on handling the Perl Patch Pumpkin And Porting Perl
=head1 SYNOPSIS
There is
no
simple synopsis, yet.
=head1 DESCRIPTION
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.
=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
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 .
Archives of the list are held at:
=head1 How are Perl Releases Numbered?
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 C<
$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:
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
$package
=perl5.
Perl releases produced by the members of perl5-porters are usually
available on CPAN in the F<src/5.0/maint> and F<src/5.0/devel>
directories.
=head2 Maintenance and Development Subversions
The first rule of maintenance work is
"First, do no harm."
Trial releases of bug-fix maintenance releases are announced on
perl5-porters. Trial releases
use
the new subversion number (to avoid
testers installing it over the previous release) and include a '
local
patch' entry in F<patchlevel.h>. The distribution file contains the
string C<MAINT_TRIAL> to make clear that the file is not meant
for
public consumption.
In general, the names of official distribution files
for
the public
always match the regular expression:
^perl\d+\.(\d+)\.\d+(-MAINT_TRIAL_\d+)\.tar\.gz$
C<$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 pumpkings 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
I<in advance> what you decide.
=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 and Porting 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.
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.
There's a script, F<check83.pl>,
for
keeping your nose 8.3-clean.
In a similar vein,
do
not create files or directories which differ only
in case (upper versus lower).
=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<pod/*.pod> and also the F<INSTALL> document.
Consider writing the appropriate documentation first and then
implementing your change to correspond to the documentation.
=head2 Avoid machine-specific
To the extent reasonable,
try
to avoid machine-specific
the sources. Instead,
use
feature-specific
that the machine-specific
releases of the operating
system
. Further, the feature-specific tests
may help out folks on another platform who have the same problem.
=head2 Machine-specific files
=over 4
=item source code
If you have many machine-specific
creating an
"osish.h"
(F<os2ish.h>, F<vmsish.h>, and so on) and including
that in F<perl.h>. If you have several machine-specific files (function
emulations, function stubs, build utility wrappers) you may create a
separate subdirectory (djgpp, win32) and put the files in there.
Remember to update C<MANIFEST>
when
you add files.
If your
system
supports dynamic loading but none of the existing
methods at F<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.
=item build hints
There are two kinds of hints: hints
for
building Perl and hints
for
extensions. The former live in the C<hints> subdirectory, the latter
in C<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.
=item build and installation Makefiles, scripts, and so forth
Sometimes you will also need to tweak the Perl build and installation
procedure itself, like
for
example F<Makefile.SH> and F<installperl>.
Tread very carefully, even more than usual. Contain your changes
with
utmost care.
=item test suite
Many of the tests in C<t> subdirectory assume machine-specific things
like existence of certain functions, something about filesystem
semantics, certain external utilities and their error messages. Use
the C<$^O> and the C<Config> module (which contains the results of the
Configure run, in effect the C<config.sh> converted to Perl) to either
skip (preferably not) or customize (preferable) the tests
for
your
platform.
=item modules
Certain standard modules may need updating
if
your operating
system
sports
for
example a native filesystem naming. You may want to update
some or all of the modules File::Basename, File::Spec, File::Path, and
File::Copy to become aware of your native filesystem syntax and
peculiarities.
Remember to have a
$VERSION
in the modules. You can
use
the
F<Porting/checkVERSION.pl> script
for
checking this.
=item documentation
If your operating
system
comes from outside UNIX you almost certainly
will have differences in the available operating
system
functionality
(missing
system
calls, different semantics, whatever). Please
document these at F<pod/perlport.pod>. If your operating
system
is
the first B<not> to have a
system
call also update the list of
"portability-bewares"
at the beginning of F<pod/perlfunc.pod>.
A file called F<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 F<INSTALL.youros>.
You may also want to
write
a separate F<.pod> file
for
your operating
system
to
tell
about existing mailing lists, os-specific modules,
documentation, whatever. Please name these along the lines of
F<perl>I<youros>.pod. [unfinished: where to put this file (the pod/
subdirectory, of course: but more importantly, which/what
index
files
should be updated?)]
=back
=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 Automated generation of derivative files
The F<embed.h>, F<keywords.h>, F<opcode.h>, F<regcharclass.h>,
F<l1_char_class_tab.h>, and F<perltoc.pod> files
are all automatically generated by perl scripts. In general, don't
patch these directly; patch the data files instead.
F<Configure> and F<config_h.SH> are also automatically generated by
B<metaconfig>. In general, you should patch the metaconfig units
instead of patching these files directly. However, very minor changes
to F<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 F<Makefile> is automatically produced from F<Makefile.SH>.
In general, look out
for
all F<*.SH> files.
Finally, the sample files in the F<Porting/> subdirectory are
generated automatically by the script F<U/mksample> included
with
the metaconfig units. See L<
"run metaconfig"
> below
for
information on obtaining the metaconfig units.
=head1 How to Make a Distribution
This section
has
now been expanded and moved into its own file,
F<Porting/release_managers_guide.pod>.
I
've kept some of the subsections here for now, as they don'
t directly
relate to building a release any more, but still contain what might be
useful information - DAPM 7/2009.
=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 F<Configure> and F<config_h.SH>. Much more information
on obtaining and running metaconfig is in the F<U/README> file
that comes
with
Perl's metaconfig units.
Since metaconfig is hard to change, running correction scripts
after
this generation is sometimes needed. Configure gained complexity over
time
, and the order in which config_h.SH is generated can cause havoc
when
compiling perl. Therefor, you need to run Porting/config_h.pl
after
that generation. All that and more is described in the README
files that come
with
the metaunits.
Perl's metaconfig units should be available on CPAN. A set of units
that will work
with
perl5.9.x is in a file
with
a name similar to
The mc_units tar file should be unpacked in your main perl source directory.
Note: those units were
for
use
with
5.9.x. 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 F<
*ish
.h> files or the hint files might be
a better place
for
your changes.
=head2 MANIFEST
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 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. 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
=head2 Update Porting/config.sh and Porting/config_H
[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 propagate them to a canned
'config.h'
by any
number of means, including a perl script in win32/ or carrying
F<config.sh> and F<config_h.SH> to a Unix
system
and running sh
config_h.SH.) Vms uses F<configure.com> to generate its own F<config.sh>
and F<config.h>. If you want to add a new variable to F<config.sh> check
with
vms folk how to add it to configure.com too.
XXX]
The F<Porting/config.sh> and F<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 F<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
F<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 regen_perly
If F<perly.y>
has
been edited, it is necessary to run this target to rebuild
F<perly.h>, F<perly.act> and F<perly.tab>. In fact this target just runs the Perl
script F<regen_perly.pl>. Note that F<perly.c> is I<not> rebuilt; this is just a
plain static file now.
This target relies on you having Bison installed on your
system
. Running
the target will
tell
you
if
you haven't got the right version, and
if
so,
where to get the right one. Or
if
you prefer, you could hack
F<regen_perly.pl> to work
with
your version of Bison. The important things
are that the regexes can still extract out the right chunks of the Bison
output into F<perly.act> and F<perly.tab>, and that the contents of those two
files, plus F<perly.h>, are functionally equivalent to those produced by the
supported version of Bison.
Note that in the old days, you had to
do
C<make run_byacc> instead.
=head2 make regen_all
This target takes care of the regen_headers target.
(It used to also call the regen_pods target, but that
has
been eliminated.)
=head2 make regen_headers
The F<embed.h>, F<keywords.h>, and F<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:
keywords.h: keywords.pl
@echo
"Don't worry if this fails."
- perl keywords.pl
However, I got B<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 C<make regen_headers> myself rather
than answering all the questions and complaints about the failing
command.
=head2 globvar.sym, and perlio.sym
Make sure these files are up-to-date. Read the comments in these
files and in F<perl_exp.SH> to see what to
do
.
=head2 Binary compatibility
If you
do
change F<embed.fnc> 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.
=head2 PPPort
F<cpan/Devel-PPPort/PPPort.pm> needs to be synchronized to include all
new macros added to .h files (normally F<perl.h> and F<XSUB.h>, but others
as well). Since chances are that
when
a new macro is added the
committer will forget to update F<PPPort.pm>, it's the best to diff
for
changes in .h files
when
making a new release and making sure that
F<PPPort.pm> contains them all.
The pumpking can delegate the synchronization responsibility to anybody
else
, but the release process is the only place where we can make sure
that
no
new macros fell through the cracks.
=head2 Todo
The F<Porting/todo.pod> file contains a roughly-categorized 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 to 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
particular issues on the to-
do
list: an issue
owned is an issue more likely to be resolved.
There are also some more porting-specific L</Todo> items later in this
file.
=head2 OS/2-specific updates
In the os2 directory is F<diff.configure>, a set of OS/2-specific
diffs against B<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.
=head2 VMS-specific updates
The Perl revision number appears as
"perl5"
in F<configure.com>.
It is courteous to update that
if
necessary.
=head2 Making a new patch
I find the F<makepatch> utility quite handy
for
making patches.
You can obtain it from any CPAN archive under
of differences between
my
version and the standard one. I have mine
do
a
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.
gzip -d -c perl5.004_07.tar.gz | tar -xof -
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<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 F<t/op/gv.t> which needs to be executable,
so at the top of the patch, I inserted the following lines:
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<gdiff> 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
branches.
=head2 Other tests
=over 4
=item gcc -ansi -pedantic
Configure -Dgccansipedantic [ -Dcc=gcc ] will enable (via the cflags script,
not
$Config
{ccflags}) the gcc strict ANSI C flags -ansi and -pedantic
for
the compilation of the core files on platforms where it knows it can
do
so (like Linux, see cflags.SH
for
the full list), and on some
platforms only one (Solaris can
do
only -pedantic, not -ansi).
The flag -DPERL_GCC_PEDANTIC also gets added, since gcc does not add
any internal cpp flag to signify that -pedantic is being used, as it
does
for
-ansi (__STRICT_ANSI__).
Note that the -ansi and -pedantic are enabled only
for
version 3 (and
later) of gcc, since even gcc version 2.95.4 finds lots of seemingly
false
"value computed not used"
errors from Perl.
The -ansi and -pedantic are useful in catching at least the following
nonportable practices:
=over 4
=item *
gcc-specific extensions
=item *
lvalue casts
=item *
// C++ comments
=item *
enum trailing commas
=back
The -Dgccansipedantic should be used only
when
cleaning up the code,
not
for
production builds, since otherwise gcc cannot inline certain
things.
=back
=head1 Running Purify
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 2
./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.)
=head1 Common Gotchas
=over 4
=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
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().
/*
try
to emulate fooPOSIX()
with
fooBSD();
perhaps
with
the following: */
=item Think positively
If you need to add an
think positively, e.g.
/*
use
some fallback mechanism */
rather than the more impenetrable
/* Not missing it, so we must have it, so
use
it */
/* Are missing it, so fall back on something
else
. */
Of course
for
this toy example, there's not much difference. But
when
the
are marked something like
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<pause()> function as an
illustration.
Perl5.003
has
the following in F<perl.h>
Configure sets HAS_PAUSE
if
the
system
has
the pause() function, so
this
Nice idea, right?
Unfortunately, some systems apparently have a
prototype
for
pause()
in F<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);
/* . . . */
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
below to be rejected by the compiler. Sigh.
*/
This works.
The curious reader may wonder why I didn't
do
the following in
F<util.c> instead:
void pause()
{
sleep
((32767<<16)+32767);
}
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<perl_exp.SH>,
which reads F<embed.fnc>. Thus, the C<pause>
symbol would have to be added to F<embed.fnc> 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<embed.h> file.
This file is built from the F<embed.fnc> file,
since those files already list the globally visible symbols. If we
had added C<pause> to F<embed.fnc>, then F<embed.h> would contain the
line
and calls to C<pause> in the perl sources would now point to
C<Perl_pause>. Now,
when
B<ld> is run to build the F<perl> executable,
it will go looking
for
C<perl_pause>, which probably won't exist in any
of the standard libraries. Thus the build of perl will fail.
Those systems where C<HAS_PAUSE> is not
defined
would be ok, however,
since they would get a C<Perl_pause> function in util.c. The rest of
the world would be in trouble.
And yes, this scenario
has
happened. On SCO, the function C<chsize>
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<chsize> function that gets called something akin to
I32 chsize(fd,
length
)
/* . . . */
When 5.003 added
to F<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:
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<my_chsize> in C<embed.fnc>, export it, and
hide it
with
F<embed.h>.
To be consistent
with
what I did
for
C<pause>, I probably should have
called the new function C<Chsize>, rather than C<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 C<Perl_chsize>
was available as a F<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.
=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<perl_exp.SH> (though that list is
out-of-date):
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
C<perl_> in the
source and list them along
with
the other C<perl_*> functions in
F<perl_exp.SH>.
Thus,
for
C<chsize>, we'd
do
something like the following:
/* in perl.h */
then in some file (e.g. F<util.c> or F<doio.c>)
do
I32 perl_chsize(fd,
length
)
/* implement the function here . . . */
Alternatively, we could just always
use
C<chsize> everywhere and move
C<chsize> from F<embed.fnc> to the end of F<perl_exp.SH>. That would
probably be fine as long as
our
C<chsize> function agreed
with
all the
C<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
C<malloc> and C<free>.)
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</usr/
local
/lib/dist/U>) 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
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, an 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<very> 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 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<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.
=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.
One way to
do
that is to add
ccflags=
"$ccflags -DAPPLLIB_EXP=\"/my/override\""
to your config.over file. (You have to be particularly careful to get the
double quotes in. APPLLIB_EXP must be a valid C string. It might
actually be easier to just
Then perl.c will put /
my
/
override
ahead of ARCHLIB and PRIVLIB. Perl will
also search architecture-specific and version-specific subdirectories of
APPLLIB_EXP.
=head2 Shared libperl.so location
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.
=over
=item 1.
Suppose you want to have both threaded and non-threaded perl versions
around
. Configure will name both perl libraries
"libperl.so"
(so that
you can
link
to them
with
-lperl). The perl binaries
tell
them apart
by having looking in the appropriate
$archlib
directories.
=item 2.
Suppose you have perl5.004_04 installed and you want to
try
to compile
it again, perhaps
with
different options or
after
applying a patch.
If you already have libperl.so installed in /usr/lib/, then it may be
either difficult or impossible to get ld.so to find the new libperl.so
that you're trying to build. If, instead, libperl.so is tucked away in
$archlib
, then you can always just change
$archlib
in the current perl
you
're trying to build so that ld.so won'
t find your old libperl.so.
(The INSTALL file suggests you
do
this
when
building a debugging perl.)
=item 3.
The shared perl library is not a
"well-behaved"
shared library
with
proper major and minor version numbers, so you can't necessarily
have perl5.004_04 and perl5.004_05 installed simultaneously. Suppose
perl5.004_04 were to install /usr/lib/libperl.so.4.4, and perl5.004_05
were to install /usr/lib/libperl.so.4.5. Now,
when
you
try
to run
perl5.004_04, ld.so might
try
to load libperl.so.4.5, since it
has
the right
"major version"
number. If this works at all, it almost
certainly defeats the reason
for
keeping perl5.004_04
around
. Worse,
with
development subversions, you certainly can't guarantee that
libperl.so.4.4 and libperl.so.4.55 will be compatible.
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
.
=back
=head2 Indentation style
Over the years Perl
has
become a mishmash of
various indentation styles, but the original
"Larry style"
can
probably be restored
with
(GNU) indent somewhat like this:
indent -kr -nce -psl -sc
A more ambitious solution would also specify a list of Perl specific
types
with
-TSV -TAV -THV .. -TMAGIC -TPerlIO ... but that list would
be quite ungainly. Also note that GNU indent also doesn't
do
aligning
of consecutive assignments, which would truly wreck the layout in
places like sv.c:Perl_sv_upgrade() or sv.c:Perl_clone_using().
Similarly nicely aligned &
&s
, ||s and ==s would not be respected.
=head1 Upload Your Work to CPAN
You can upload your work to CPAN
if
you have a CPAN id. Check out
_PAUSE_, the Perl Author's Upload Server.
I typically upload both the patch file, e.g. F<perl5.004_08.pat.gz>
and the full tar file, e.g. F<perl5.004_08.tar.gz>.
If you want your patch to appear in the F<src/5.0/unsupported>
directory on CPAN,
send
e-mail to the CPAN master librarian. (Check
=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 Adding missing library functions to Perl
The perl Configure script automatically determines which headers and
functions you have available on your
system
and arranges
for
them to be
included in the compilation and linking process. Occasionally,
when
porting
perl to an operating
system
for
the first
time
, you may find that the
operating
system
is missing a key function. While perl may still build
without this function,
no
perl program will be able to reference the missing
function. You may be able to
write
the missing function yourself, or you
may be able to find the missing function in the distribution files
for
another software
package
. In this case, you need to instruct the perl
configure-and-build process to
use
your function. Perform these steps.
=over 3
=item *
Code and test the function you wish to add. Test it carefully; you will
have a much easier
time
debugging your code independently than
when
it is a
part of perl.
=item *
Here is an implementation of the POSIX
truncate
function
for
an operating
system
(VOS) that does not supply one, but which does supply the ftruncate()
function.
/* Beginning of modification history */
/* Written 02-01-02 by Nick Ing-Simmons (nick
@ing
-simmons.net) */
/* End of modification history */
/* VOS doesn't supply a
truncate
function, so we build one up
from the available POSIX functions. */
int
truncate
(const char
*path
, off_t len)
{
int
fd =
open
(path,O_WRONLY);
int
code = -1;
if
(fd >= 0) {
code = ftruncate(fd,len);
close
(fd);
}
return
code;
}
Place this file into a subdirectory that
has
the same name as the operating
system
. This file is named perl/vos/vos.c
=item *
If your operating
system
has
a hints file (in perl/hints/XXX.sh
for
an
operating
system
named XXX), then start
with
it. If your operating
system
has
no
hints file, then create one. You can
use
a hints file
for
a similar
operating
system
,
if
one
exists
, as a template.
=item *
Add lines like the following to your hints file. The first line
(d_truncate=
"define"
) instructs Configure that the
truncate
() function
exists
. The second line (archobjs=
"vos.o"
) instructs the makefiles that the
perl executable depends on the existence of a file named
"vos.o"
. (Make
will automatically look
for
"vos.c"
and compile it
with
the same options as
the perl source code). The final line (
"test -h..."
) adds a symbolic
link
to the top-level directory so that make can find vos.c. Of course, you
should
use
your own operating
system
name
for
the source file of extensions,
not
"vos.c"
.
d_truncate=
"define"
archobjs=
"vos.o"
test -h vos.c || ln -s vos/vos.c vos.c
The hints file is a series of shell commands that are run in the top-level
directory (the
"perl"
directory). Thus, these commands are simply executed
by Configure at an appropriate place during its execution.
=item *
At this point, you can run the Configure script and rebuild perl. Carefully
test the newly-built perl to ensure that normal paths, and error paths,
behave as you expect.
=back
=head2 Good ideas waiting
for
round tuits
=over 4
=item Configure -Dsrc=/blah/blah
We should be able to emulate B<configure --srcdir>. Tom Tromey
tromey
@creche
.cygnus.com
has
submitted some patches to
the dist-users mailing list along these lines. They have been folded
back into the main distribution, but various parts of the perl
Configure/build/install process still assume src=
'.'
.
=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<make clean> isn't all that useful, though
B<make realclean> and B<make distclean> 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 gconvert replacement
Maybe include a replacement function that doesn't lose data in rare
cases of coercion between string and numerical
values
.
=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<make> command will
try
to
use
before
it uses
F<Makefile>. Such may not be the case
for
all B<make> 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<Makefile.SH>
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. See
$d_fcntl_can_lock
in recent config.sh files though.
=back
=head2 Copyright Issues
The following is based on the consensus of a couple of IPR lawyers,
but it is of course not a legally binding statement, just a common
sense summary.
=over 4
=item *
Tacking on copyright statements is unnecessary to begin
with
because
of the Berne convention. But assuming you want to go ahead...
=item *
The right form of a copyright statement is
Copyright (C) Year, Year, ... by Someone
The (C) is not required everywhere but it doesn't hurt and in certain
jurisdictions it is required, so let
's leave it in. (Yes, it'
s true
that in some jurisdictions the
"(C)"
is not legally binding, one should
use
the true ringed-C. But we don't have that character available
for
Perl's source code.)
The years must be listed out separately. Year-Year is not correct.
Only the years
when
the piece
has
changed
'significantly'
may be added.
=item *
One cannot give away one
's copyright trivially. One can give one'
s
copyright away by using public domain, but even that requires a little
bit more than just saying
'this is in public domain'
. (What it
exactly requires depends on your jurisdiction.) But barring public
domain, one cannot
"transfer"
one's copyright to another person or
entity. In the context of software, it means that contributors cannot
give away their copyright or
"transfer"
it to the
"owner"
of the software.
Also remember that in many cases
if
you are employed by someone,
your work may be copyrighted to your employer, even
when
you are
contributing on your own
time
(this all depends on too many things
to list here). But the bottom line is that you definitely can't give
away a copyright you may not even have.
What is possible, however, is that the software can simply state
Copyright (C) Year, Year, ... by Someone and others
and then list the
"others"
somewhere in the distribution.
And this is exactly what Perl does. (The
"somewhere"
is
AUTHORS and the Changes* files.)
=item *
Split files, merged files, and generated files are problematic.
The rule of thumb: in
split
files, copy the copyright years of
the original file to all the new files; in merged files make
an union of the copyright years of all the old files; in generated
files propagate the copyright years of the generating file(s).
=item *
The files of Perl source code distribution
do
carry a lot of
copyrights, by various people. (There are many copyrights embedded in
perl.c,
for
example.) The most straightforward thing
for
pumpkings to
do
is to simply update Larry's copyrights at the beginning of the
*.[hcy], x2p/*.[hcy], *.pl, and README files, and leave all other
copyrights alone. Doing more than that requires quite a bit of tracking.
=back
=head1 AUTHORS
Original author: Andy Dougherty doughera
@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 authorZ<>(s).
=head1 LAST MODIFIED
2009-07-08-01 Jesse Vincent