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 105 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 105 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 105 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 may generate
70 false positives, so by default each API call is checked once more
73 Running C<devel/mktodo> takes about an hour, depending of course
74 on the machine you're running it on. If you run it with
75 the C<--nocheck> option, it won't recheck the API calls that failed
76 in the compilation stage and it'll take significantly less time.
77 Running with C<--nocheck> should usually be safe.
79 When running C<devel/mktodo> with the C<--base> option, it will
80 generate the I<baseline> todo files by disabling all functionality
81 provided by C<Devel::PPPort>. These are required for implementing
82 the C<--compat-version> option of the C<ppport.h> script. The
83 baseline todo files hold the information about which version of
84 Perl lacks a certain part of the API.
86 However, only the documented public API can be checked this way.
87 And since C<Devel::PPPort> provides more macros, these would not be
88 affected by C<--compat-version>. It's the job of F<devel/scanprov>
89 to figure out the baseline information for all remaining provided
90 macros by scanning the include files in the F<CORE> directory of
91 various Perl versions.
93 The whole process isn't platform independent. It has currently been
94 tested only under Linux, and it definitely requires at least C<gcc> and
97 It's not very often that one has to regenerate the baseline and todo
98 files. If you have to, you can either run F<devel/regenerate> or just
99 execute the following steps by hand:
105 You need a whole bunch of different Perls. The more, the better.
106 You can use F<devel/buildperl.pl> to build them. I keep my perls
107 in F</tmp/perl>, so most of the tools take this as a default.
111 Remove all existing todo files in the F<parts/base> and
112 F<parts/todo> directories.
116 Update the API information. Copy the latest F<embed.fnc> file from
117 bleadperl to the F<parts> directory and run F<devel/mkapidoc.sh> to
118 collect the remaining information in F<parts/apidoc.fnc>.
122 Build the new baseline by running
124 perl devel/mktodo --base
126 in the root directory of the distribution. When it's finished,
127 move all files from the F<parts/todo> directory to F<parts/base>.
131 Build the new todo files by running
135 in the root directory of the distribution.
139 Finally, add the remaining baseline information by running
141 perl Makefile.PL && make
142 perl devel/scanprov write
146 =head2 Implementation
148 Residing in F<parts/inc/> is the "heart" of C<Devel::PPPort>. Each
149 of the files implements a part of the supported API, along with
150 hints, dependency information, XS code and tests.
151 The files are in a POD-like format that is parsed using the
152 functions in F<parts/ppptools.pl>.
154 The scripts F<PPPort_pm.PL>, F<PPPort_xs.PL> and F<mktests.PL> all
155 use the information in F<parts/inc/> to generate the main module
156 F<PPPort.pm>, the XS code in F<PPPort.xs> and various test files
159 All of these files could be generated on the fly while building
160 C<Devel::PPPort>, but not having the tests in C<t/> and not having
161 F<PPPort.xs> will confuse Configure and TEST/harness in the core.
162 Not having F<PPPort.pm> will be bad for viewing the docs on
163 C<search.cpan.org>. So unfortunately, it's unavoidable to put
164 some redundancy into the package.
166 =head2 Adding stuff to Devel::PPPort
168 First, check if the code you plan to add fits into one of the
169 existing files in F<parts/inc/>. If not, just start a new one and
170 remember to include it from within F<PPPort_pm.PL>.
172 Each file holds all relevant data for implementing a certain part
179 A list of the provided API in the C<=provides> section.
183 The implementation to add to F<ppport.h> in the C<=implementation>
188 The code required to add to PPPort.xs for testing the implementation.
189 This code goes into the C<=xshead>, C<=xsinit>, C<=xsmisc>, C<=xsboot>
190 and C<=xsubs> section. Have a look at the template at the bottom
191 of F<PPPort_xs.PL> to see where the code ends up.
195 The tests in the C<=tests> section. Remember not to use any fancy
196 modules or syntax elements, as the test code should be able to run
197 with Perl 5.003, which, for example, doesn't support C<my> in
200 for my $x (1, 2, 3) { } # won't work with 5.003
202 You can use C<ok()> to report success or failure:
207 Regular expressions are not supported as the second argument to C<ok>,
208 because older perls do not support the C<qr> operator.
212 It's usually the best approach to just copy an existing file and
213 use it as a template.
215 =head2 Implementation Hints
217 In the C<=implementation> section, you can use
219 __UNDEFINED__ macro some definition
224 # define macro some definition
227 The macro can have optional arguments and the definition can even
228 span multiple lines, like in
230 __UNDEFINED__ SvMAGIC_set(sv, val) \
231 STMT_START { assert(SvTYPE(sv) >= SVt_PVMG); \
232 (((XPVMG*) SvANY(sv))->xmg_magic = (val)); } STMT_END
234 This usually makes the code more compact and readable. And you
235 only have to add C<__UNDEFINED__> to the C<=provided> section.
237 Version checking can be tricky if you want to do it correct.
240 #if { VERSION < 5.9.3 }
244 #if ((PERL_VERSION < 9) || (PERL_VERSION == 9 && PERL_SUBVERSION < 3))
246 The version number can be either of the new form C<5.x.x> or of the older
247 form C<5.00x_yy>. Both are translated into the correct preprocessor
248 statements. It is also possible to combine this with other statements:
250 #if { VERSION >= 5.004 } && !defined(sv_vcatpvf)
252 #elif { VERSION < 5.004_63 } && { VERSION != 5.004_05 }
256 This not only works in the C<=implementation> section, but also in
257 the C<=xsubs>, C<=xsinit>, C<=xsmisc>, C<=xshead> and C<=xsboot> sections.
261 To automatically test C<Devel::PPPort> with lots of different Perl
262 versions, you can use the F<soak> script. Just pass it a list of
263 all Perl binaries you want to test.
265 =head2 Special Makefile targets
271 to regenerate all of the autogenerated files. To get rid of all
272 generated files (except for F<parts/todo/*> and F<parts/base/*>),
279 =head2 Submitting Patches
281 If you've added some functionality to C<Devel::PPPort>, please
282 consider submitting a patch with your work to either the author
283 (E<lt>mhx@cpan.orgE<gt>) or to the CPAN Request Tracker at
284 L<http://rt.cpan.org>.
286 When submitting patches, please only add the relevant changes
287 and don't include the differences of the generated files. You
288 can use the C<purge_all> target to delete all autogenerated
293 Version 3.x, Copyright (C) 2004-2006, Marcus Holland-Moritz.
295 Version 2.x, Copyright (C) 2001, Paul Marquess.
297 Version 1.x, Copyright (C) 1999, Kenneth Albanowski.
299 This program is free software; you can redistribute it and/or
300 modify it under the same terms as Perl itself.
304 See L<ppport.h> and L<devel/regenerate>.