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 98 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 98 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 98 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:
35 =head2 Fully automatic API checks
37 Knowing which parts of the API are not backwards compatible and
38 probably need C<Devel::PPPort> support is another problem that's
39 not easy to deal with manually. If you run
41 perl Makefile.PL --with-apicheck
43 a C file is generated by F<parts/apicheck.pl> that is compiled
44 and linked with C<Devel::PPPort>. This C file has the purpose of
45 using each of the public API functions/macros once.
47 The required information is derived from C<parts/embed.fnc> (just
48 a copy of bleadperl's C<embed.fnc>) and C<parts/apidoc.fnc> (which
49 is generated by F<devel/mkapidoc.sh> and simply collects the rest
50 of the apidoc entries spread over the Perl source code).
51 The generated C file C<apicheck.c> is currently about 500k in size
52 and takes quite a while to compile.
54 Usually, C<apicheck.c> won't compile with older perls. And even if
55 it compiles, there's still a good chance of the dynamic linker
56 failing at C<make test> time. But that's on purpose!
58 We can use these failures to find changes in the API automatically.
59 The two Perl scripts F<devel/mktodo> and F<devel/mktodo.pl>
60 repeatedly run C<Devel::PPPort> with the apicheck code through
61 all different versions of perl. Scanning the output of the compiler
62 and the dynamic linker for errors, the files in F<parts/todo/> are
63 generated. These files list all parts of the public API that don't
64 work with less than a certain version of Perl.
66 This information is in turn used by F<parts/apicheck.pl> to mask
67 API calls in the generated C file for these versions, so the
68 process can be stopped by the time F<apicheck.c> compiles cleanly
69 and the dynamic linker is happy. (Actually, this process generates
70 false positives, so each API call is checked once more afterwards.)
72 Running C<devel/mktodo> takes a couple of hours.
74 When running C<devel/mktodo> with the C<--base> option, it will
75 generate the I<baseline> todo files by disabling all functionality
76 provided by C<Devel::PPPort>. These are required for implementing
77 the C<--compat-version> option of the C<ppport.h> script. The
78 baseline todo files hold the information about which version of
79 Perl lacks a certain part of the API.
81 However, only the documented public API can be checked this way.
82 And since C<Devel::PPPort> provides more macros, these would not be
83 affected by C<--compat-version>. It's the job of F<devel/scanprov>
84 to figure out the baseline information for all remaining provided
85 macros by scanning the include files in the F<CORE> directory of
86 various Perl versions.
88 It's not very often that one has to regenerate the baseline and
89 todo files, and the process hasn't been automated yet, but it's
90 basically only the following steps:
96 You need a whole bunch of different Perls. The more, the better.
97 You can use F<devel/buildperl.pl> to build them. I keep my perls
98 in F</tmp/perl>, so most of the tools take this as a default.
102 Remove all existing todo files in the F<parts/base> and
103 F<parts/todo> directories.
107 Update the API information. Copy the latest F<embed.fnc> file from
108 bleadperl to the F<parts> directory and run F<devel/mkapidoc.sh> to
109 collect the remaining information in F<parts/apidoc.fnc>.
113 Build the new baseline by running
115 perl devel/mktodo --base
117 in the root directory of the distribution. When it's finished,
118 move all files from the F<parts/todo> directory to F<parts/base>.
122 Build the new todo files by running
126 in the root directory of the distribution.
130 Finally, add the remaining baseline information by running
132 perl Makefile.PL && make
133 perl devel/scanprov write
137 =head2 Implementation
139 Residing in F<parts/inc/> is the "heart" of C<Devel::PPPort>. Each
140 of the files implements a part of the supported API, along with
141 hints, dependency information, XS code and tests.
142 The files are in a POD-like format that is parsed using the
143 functions in F<parts/ppptools.pl>.
145 The scripts F<PPPort_pm.PL>, F<PPPort_xs.PL> and F<mktests.PL> all
146 use the information in F<parts/inc/> to generate the main module
147 F<PPPort.pm>, the XS code in F<PPPort.xs> and various test files
150 All of these files could be generated on the fly while building
151 C<Devel::PPPort>, but not having the tests in C<t/> and not having
152 F<PPPort.xs> will confuse Configure and TEST/harness in the core.
153 Not having F<PPPort.pm> will be bad for viewing the docs on
154 C<search.cpan.org>. So unfortunately, it's unavoidable to put
155 some redundancy into the package.
157 =head2 Adding stuff to Devel::PPPort
159 First, check if the code you plan to add fits into one of the
160 existing files in F<parts/inc/>. If not, just start a new one and
161 remember to include it from within F<PPPort_pm.PL>.
163 Each file holds all relevant data for implementing a certain part
170 A list of the provided API in the C<=provides> section.
174 The implementation to add to F<ppport.h> in the C<=implementation>
179 The code required to add to PPPort.xs for testing the implementation.
180 This code goes into the C<=xshead>, C<=xsinit>, C<=xsmisc>, C<=xsboot>
181 and C<=xsubs> section. Have a look at the template at the bottom
182 of F<PPPort_xs.PL> to see where the code ends up.
186 The tests in the C<=tests> section. Remember not to use any fancy
187 modules or syntax elements, as the test code should be able to run
188 with Perl 5.003, which, for example, doesn't support C<my> in
191 for my $x (1, 2, 3) { } # won't work with 5.003
193 You can use C<ok()> to report success or failure:
198 Regular expressions are not supported as the second argument to C<ok>,
199 because older perls do not support the C<qr> operator.
203 It's usually the best approach to just copy an existing file and
204 use it as a template.
206 =head2 Implementation Hints
208 In the C<=implementation> section, you can use
210 __UNDEFINED__ macro some definition
215 # define macro some definition
218 The macro can have optional arguments and the definition can even
219 span multiple lines, like in
221 __UNDEFINED__ SvMAGIC_set(sv, val) \
222 STMT_START { assert(SvTYPE(sv) >= SVt_PVMG); \
223 (((XPVMG*) SvANY(sv))->xmg_magic = (val)); } STMT_END
225 This usually makes the code more compact and readable. And you
226 only have to add C<__UNDEFINED__> to the C<=provided> section.
228 Version checking can be tricky if you want to do it correct.
231 #if { VERSION < 5.9.3 }
235 #if ((PERL_VERSION < 9) || (PERL_VERSION == 9 && PERL_SUBVERSION < 3))
237 The version number can be either of the new form C<5.x.x> or of the older
238 form C<5.00x_yy>. Both are translated into the correct preprocessor
239 statements. It is also possible to combine this with other statements:
241 #if { VERSION >= 5.004 } && !defined(sv_vcatpvf)
243 #elif { VERSION < 5.004_63 } && { VERSION != 5.004_05 }
247 This not only works in the C<=implementation> section, but also in
248 the C<=xsubs>, C<=xsinit>, C<=xsmisc>, C<=xshead> and C<=xsboot> sections.
252 To automatically test C<Devel::PPPort> with lots of different Perl
253 versions, you can use the F<soak> script. Just pass it a list of
254 all Perl binaries you want to test.
256 =head2 Special Makefile targets
262 to regenerate all of the autogenerated files. To get rid of all
263 generated files (except for F<parts/todo/*> and F<parts/base/*>),
270 =head2 Submitting Patches
272 If you've added some functionality to C<Devel::PPPort>, please
273 consider submitting a patch with your work to either the author
274 (E<lt>mhx@cpan.orgE<gt>) or to the CPAN Request Tracker at
275 L<http://rt.cpan.org>.
277 When submitting patches, please only add the relevant changes
278 and don't include the differences of the generated files. You
279 can use the C<purge_all> target to delete all autogenerated
284 Version 3.x, Copyright (C) 2004-2006, Marcus Holland-Moritz.
286 Version 2.x, Copyright (C) 2001, Paul Marquess.
288 Version 1.x, Copyright (C) 1999, Kenneth Albanowski.
290 This program is free software; you can redistribute it and/or
291 modify it under the same terms as Perl itself.