3 HACKERS - Devel::PPPort internals for hackers
7 So you probably want to hack C<Devel::PPPort>?
9 Well, here's some information to get you started with what's
10 lying around in this distribution.
14 =head2 How to build 114 versions of Perl
16 C<Devel::PPPort> supports Perl versions between 5.003 and bleadperl.
17 To guarantee this support, I need some of these versions on my
18 machine. I currently have 114 different Perl version/configuration
19 combinations installed on my laptop.
21 As many of the old Perl distributions need patching to compile
22 cleanly on newer systems (and because building 114 Perls by hand
23 just isn't fun), I wrote a tool to build all the different
24 versions and configurations. You can find it in F<devel/buildperl.pl>.
25 It can currently build the following Perl releases:
36 =head2 Fully automatic API checks
38 Knowing which parts of the API are not backwards compatible and
39 probably need C<Devel::PPPort> support is another problem that's
40 not easy to deal with manually. If you run
42 perl Makefile.PL --with-apicheck
44 a C file is generated by F<parts/apicheck.pl> that is compiled
45 and linked with C<Devel::PPPort>. This C file has the purpose of
46 using each of the public API functions/macros once.
48 The required information is derived from C<parts/embed.fnc> (just
49 a copy of bleadperl's C<embed.fnc>), C<parts/apidoc.fnc> (which
50 is generated by F<devel/mkapidoc.sh> and simply collects the rest
51 of the apidoc entries spread over the Perl source code) and
52 C<parts/ppport.fnc> (which lists all API provided purely by
54 The generated C file C<apicheck.c> is currently about 500k in size
55 and takes quite a while to compile.
57 Usually, C<apicheck.c> won't compile with older perls. And even if
58 it compiles, there's still a good chance of the dynamic linker
59 failing at C<make test> time. But that's on purpose!
61 We can use these failures to find changes in the API automatically.
62 The two Perl scripts F<devel/mktodo> and F<devel/mktodo.pl>
63 repeatedly run C<Devel::PPPort> with the apicheck code through
64 all different versions of perl. Scanning the output of the compiler
65 and the dynamic linker for errors, the files in F<parts/todo/> are
66 generated. These files list all parts of the public API that don't
67 work with less than a certain version of Perl.
69 This information is in turn used by F<parts/apicheck.pl> to mask
70 API calls in the generated C file for these versions, so the
71 process can be stopped by the time F<apicheck.c> compiles cleanly
72 and the dynamic linker is happy. (Actually, this process may generate
73 false positives, so by default each API call is checked once more
76 Running C<devel/mktodo> takes about an hour, depending of course
77 on the machine you're running it on. If you run it with
78 the C<--nocheck> option, it won't recheck the API calls that failed
79 in the compilation stage and it'll take significantly less time.
80 Running with C<--nocheck> should usually be safe.
82 When running C<devel/mktodo> with the C<--base> option, it will
83 generate the I<baseline> todo files by disabling all functionality
84 provided by C<Devel::PPPort>. These are required for implementing
85 the C<--compat-version> option of the C<ppport.h> script. The
86 baseline todo files hold the information about which version of
87 Perl lacks a certain part of the API.
89 However, only the documented public API can be checked this way.
90 And since C<Devel::PPPort> provides more macros, these would not be
91 affected by C<--compat-version>. It's the job of F<devel/scanprov>
92 to figure out the baseline information for all remaining provided
93 macros by scanning the include files in the F<CORE> directory of
94 various Perl versions.
96 The whole process isn't platform independent. It has currently been
97 tested only under Linux, and it definitely requires at least C<gcc> and
100 It's not very often that one has to regenerate the baseline and todo
101 files. If you have to, you can either run F<devel/regenerate> or just
102 execute the following steps by hand:
108 You need a whole bunch of different Perls. The more, the better.
109 You can use F<devel/buildperl.pl> to build them. I keep my perls
110 in F</tmp/perl>, so most of the tools take this as a default.
114 You also need a freshly built bleadperl that is in the path under
115 exactly this name. (The name of the executable is currently hardcoded
116 in F<devel/mktodo> and F<devel/scanprov>.)
120 Remove all existing todo files in the F<parts/base> and
121 F<parts/todo> directories.
125 Update the API information. Copy the latest F<embed.fnc> file from
126 bleadperl to the F<parts> directory and run F<devel/mkapidoc.sh> to
127 collect the remaining information in F<parts/apidoc.fnc>.
131 Build the new baseline by running
133 perl devel/mktodo --base
135 in the root directory of the distribution. When it's finished,
136 move all files from the F<parts/todo> directory to F<parts/base>.
140 Build the new todo files by running
144 in the root directory of the distribution.
148 Finally, add the remaining baseline information by running
150 perl Makefile.PL && make
151 perl devel/scanprov write
155 =head2 Implementation
157 Residing in F<parts/inc/> is the "heart" of C<Devel::PPPort>. Each
158 of the files implements a part of the supported API, along with
159 hints, dependency information, XS code and tests.
160 The files are in a POD-like format that is parsed using the
161 functions in F<parts/ppptools.pl>.
163 The scripts F<PPPort_pm.PL>, F<PPPort_xs.PL> and F<mktests.PL> all
164 use the information in F<parts/inc/> to generate the main module
165 F<PPPort.pm>, the XS code in F<RealPPPort.xs> and various test files
168 All of these files could be generated on the fly while building
169 C<Devel::PPPort>, but not having the tests in C<t/> will confuse
170 TEST/harness in the core. Not having F<PPPort.pm> will be bad for
171 viewing the docs on C<search.cpan.org>. So unfortunately, it's
172 unavoidable to put some redundancy into the package.
174 =head2 Adding stuff to Devel::PPPort
176 First, check if the code you plan to add fits into one of the
177 existing files in F<parts/inc/>. If not, just start a new one and
178 remember to include it from within F<PPPort_pm.PL>.
180 Each file holds all relevant data for implementing a certain part
187 A list of the provided API in the C<=provides> section.
191 The implementation to add to F<ppport.h> in the C<=implementation>
196 The code required to add to PPPort.xs for testing the implementation.
197 This code goes into the C<=xshead>, C<=xsinit>, C<=xsmisc>, C<=xsboot>
198 and C<=xsubs> section. Have a look at the template at the bottom
199 of F<PPPort_xs.PL> to see where the code ends up.
203 The tests in the C<=tests> section. Remember not to use any fancy
204 modules or syntax elements, as the test code should be able to run
205 with Perl 5.003, which, for example, doesn't support C<my> in
208 for my $x (1, 2, 3) { } # won't work with 5.003
210 You can use C<ok()> to report success or failure:
215 Regular expressions are not supported as the second argument to C<ok>,
216 because older perls do not support the C<qr> operator.
220 It's usually the best approach to just copy an existing file and
221 use it as a template.
223 =head2 Implementation Hints
225 In the C<=implementation> section, you can use
227 __UNDEFINED__ macro some definition
232 # define macro some definition
235 The macro can have optional arguments and the definition can even
236 span multiple lines, like in
238 __UNDEFINED__ SvMAGIC_set(sv, val) \
239 STMT_START { assert(SvTYPE(sv) >= SVt_PVMG); \
240 (((XPVMG*) SvANY(sv))->xmg_magic = (val)); } STMT_END
242 This usually makes the code more compact and readable. And you
243 only have to add C<__UNDEFINED__> to the C<=provided> section.
245 Version checking can be tricky if you want to do it correct.
248 #if { VERSION < 5.9.3 }
252 #if ((PERL_VERSION < 9) || (PERL_VERSION == 9 && PERL_SUBVERSION < 3))
254 The version number can be either of the new form C<5.x.x> or of the older
255 form C<5.00x_yy>. Both are translated into the correct preprocessor
256 statements. It is also possible to combine this with other statements:
258 #if { VERSION >= 5.004 } && !defined(sv_vcatpvf)
260 #elif { VERSION < 5.004_63 } && { VERSION != 5.004_05 }
264 This not only works in the C<=implementation> section, but also in
265 the C<=xsubs>, C<=xsinit>, C<=xsmisc>, C<=xshead> and C<=xsboot> sections.
269 To automatically test C<Devel::PPPort> with lots of different Perl
270 versions, you can use the F<soak> script. Just pass it a list of
271 all Perl binaries you want to test.
273 =head2 Special Makefile targets
279 to regenerate all of the autogenerated files. To get rid of all
280 generated files (except for F<parts/todo/*> and F<parts/base/*>),
287 =head2 Submitting Patches
289 If you've added some functionality to C<Devel::PPPort>, please
290 consider submitting a patch with your work to either the author
291 (E<lt>mhx@cpan.orgE<gt>) or to the CPAN Request Tracker at
292 L<http://rt.cpan.org>.
294 When submitting patches, please only add the relevant changes
295 and don't include the differences of the generated files. You
296 can use the C<purge_all> target to delete all autogenerated
299 =head2 Integrating into the Perl core
301 When integrating this module into the Perl core, be sure to
302 remove the following files from the distribution. They are
303 either not needed or generated on the fly when building this
312 Version 3.x, Copyright (C) 2004-2009, Marcus Holland-Moritz.
314 Version 2.x, Copyright (C) 2001, Paul Marquess.
316 Version 1.x, Copyright (C) 1999, Kenneth Albanowski.
318 This program is free software; you can redistribute it and/or
319 modify it under the same terms as Perl itself.
323 See L<ppport.h> and L<devel/regenerate>.