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1 | =head1 NAME |
2 | ||
3 | perlhack - How to hack at the Perl internals | |
4 | ||
5 | =head1 DESCRIPTION | |
6 | ||
7 | This document attempts to explain how Perl development takes place, | |
8 | and ends with some suggestions for people wanting to become bona fide | |
9 | porters. | |
10 | ||
11 | The perl5-porters mailing list is where the Perl standard distribution | |
12 | is maintained and developed. The list can get anywhere from 10 to 150 | |
13 | messages a day, depending on the heatedness of the debate. Most days | |
14 | there are two or three patches, extensions, features, or bugs being | |
15 | discussed at a time. | |
16 | ||
f8e3975a | 17 | A searchable archive of the list is at either: |
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18 | |
19 | http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ | |
20 | ||
f8e3975a IP |
21 | or |
22 | ||
23 | http://archive.develooper.com/perl5-porters@perl.org/ | |
24 | ||
e8cd7eae GS |
25 | List subscribers (the porters themselves) come in several flavours. |
26 | Some are quiet curious lurkers, who rarely pitch in and instead watch | |
27 | the ongoing development to ensure they're forewarned of new changes or | |
28 | features in Perl. Some are representatives of vendors, who are there | |
29 | to make sure that Perl continues to compile and work on their | |
30 | platforms. Some patch any reported bug that they know how to fix, | |
31 | some are actively patching their pet area (threads, Win32, the regexp | |
32 | engine), while others seem to do nothing but complain. In other | |
33 | words, it's your usual mix of technical people. | |
34 | ||
35 | Over this group of porters presides Larry Wall. He has the final word | |
f6c51b38 | 36 | in what does and does not change in the Perl language. Various |
b432a672 AL |
37 | releases of Perl are shepherded by a "pumpking", a porter |
38 | responsible for gathering patches, deciding on a patch-by-patch, | |
f6c51b38 | 39 | feature-by-feature basis what will and will not go into the release. |
caf100c0 | 40 | For instance, Gurusamy Sarathy was the pumpking for the 5.6 release of |
961f29c6 | 41 | Perl, and Jarkko Hietaniemi was the pumpking for the 5.8 release, and |
1a88dbf8 | 42 | Rafael Garcia-Suarez holds the pumpking crown for the 5.10 release. |
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43 | |
44 | In addition, various people are pumpkings for different things. For | |
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45 | instance, Andy Dougherty and Jarkko Hietaniemi did a grand job as the |
46 | I<Configure> pumpkin up till the 5.8 release. For the 5.10 release | |
47 | H.Merijn Brand took over. | |
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48 | |
49 | Larry sees Perl development along the lines of the US government: | |
50 | there's the Legislature (the porters), the Executive branch (the | |
51 | pumpkings), and the Supreme Court (Larry). The legislature can | |
52 | discuss and submit patches to the executive branch all they like, but | |
53 | the executive branch is free to veto them. Rarely, the Supreme Court | |
54 | will side with the executive branch over the legislature, or the | |
55 | legislature over the executive branch. Mostly, however, the | |
56 | legislature and the executive branch are supposed to get along and | |
57 | work out their differences without impeachment or court cases. | |
58 | ||
59 | You might sometimes see reference to Rule 1 and Rule 2. Larry's power | |
60 | as Supreme Court is expressed in The Rules: | |
61 | ||
62 | =over 4 | |
63 | ||
64 | =item 1 | |
65 | ||
66 | Larry is always by definition right about how Perl should behave. | |
67 | This means he has final veto power on the core functionality. | |
68 | ||
69 | =item 2 | |
70 | ||
71 | Larry is allowed to change his mind about any matter at a later date, | |
72 | regardless of whether he previously invoked Rule 1. | |
73 | ||
74 | =back | |
75 | ||
76 | Got that? Larry is always right, even when he was wrong. It's rare | |
77 | to see either Rule exercised, but they are often alluded to. | |
78 | ||
79 | New features and extensions to the language are contentious, because | |
80 | the criteria used by the pumpkings, Larry, and other porters to decide | |
81 | which features should be implemented and incorporated are not codified | |
82 | in a few small design goals as with some other languages. Instead, | |
83 | the heuristics are flexible and often difficult to fathom. Here is | |
84 | one person's list, roughly in decreasing order of importance, of | |
85 | heuristics that new features have to be weighed against: | |
86 | ||
87 | =over 4 | |
88 | ||
89 | =item Does concept match the general goals of Perl? | |
90 | ||
91 | These haven't been written anywhere in stone, but one approximation | |
92 | is: | |
93 | ||
94 | 1. Keep it fast, simple, and useful. | |
95 | 2. Keep features/concepts as orthogonal as possible. | |
96 | 3. No arbitrary limits (platforms, data sizes, cultures). | |
97 | 4. Keep it open and exciting to use/patch/advocate Perl everywhere. | |
98 | 5. Either assimilate new technologies, or build bridges to them. | |
99 | ||
100 | =item Where is the implementation? | |
101 | ||
102 | All the talk in the world is useless without an implementation. In | |
103 | almost every case, the person or people who argue for a new feature | |
104 | will be expected to be the ones who implement it. Porters capable | |
105 | of coding new features have their own agendas, and are not available | |
106 | to implement your (possibly good) idea. | |
107 | ||
108 | =item Backwards compatibility | |
109 | ||
110 | It's a cardinal sin to break existing Perl programs. New warnings are | |
111 | contentious--some say that a program that emits warnings is not | |
112 | broken, while others say it is. Adding keywords has the potential to | |
113 | break programs, changing the meaning of existing token sequences or | |
114 | functions might break programs. | |
115 | ||
116 | =item Could it be a module instead? | |
117 | ||
118 | Perl 5 has extension mechanisms, modules and XS, specifically to avoid | |
119 | the need to keep changing the Perl interpreter. You can write modules | |
120 | that export functions, you can give those functions prototypes so they | |
121 | can be called like built-in functions, you can even write XS code to | |
122 | mess with the runtime data structures of the Perl interpreter if you | |
123 | want to implement really complicated things. If it can be done in a | |
124 | module instead of in the core, it's highly unlikely to be added. | |
125 | ||
126 | =item Is the feature generic enough? | |
127 | ||
128 | Is this something that only the submitter wants added to the language, | |
129 | or would it be broadly useful? Sometimes, instead of adding a feature | |
130 | with a tight focus, the porters might decide to wait until someone | |
131 | implements the more generalized feature. For instance, instead of | |
b432a672 | 132 | implementing a "delayed evaluation" feature, the porters are waiting |
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133 | for a macro system that would permit delayed evaluation and much more. |
134 | ||
135 | =item Does it potentially introduce new bugs? | |
136 | ||
137 | Radical rewrites of large chunks of the Perl interpreter have the | |
138 | potential to introduce new bugs. The smaller and more localized the | |
139 | change, the better. | |
140 | ||
141 | =item Does it preclude other desirable features? | |
142 | ||
143 | A patch is likely to be rejected if it closes off future avenues of | |
144 | development. For instance, a patch that placed a true and final | |
145 | interpretation on prototypes is likely to be rejected because there | |
146 | are still options for the future of prototypes that haven't been | |
147 | addressed. | |
148 | ||
149 | =item Is the implementation robust? | |
150 | ||
151 | Good patches (tight code, complete, correct) stand more chance of | |
152 | going in. Sloppy or incorrect patches might be placed on the back | |
153 | burner until the pumpking has time to fix, or might be discarded | |
154 | altogether without further notice. | |
155 | ||
156 | =item Is the implementation generic enough to be portable? | |
157 | ||
158 | The worst patches make use of a system-specific features. It's highly | |
353c6505 | 159 | unlikely that non-portable additions to the Perl language will be |
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160 | accepted. |
161 | ||
a936dd3c NC |
162 | =item Is the implementation tested? |
163 | ||
164 | Patches which change behaviour (fixing bugs or introducing new features) | |
165 | must include regression tests to verify that everything works as expected. | |
166 | Without tests provided by the original author, how can anyone else changing | |
167 | perl in the future be sure that they haven't unwittingly broken the behaviour | |
168 | the patch implements? And without tests, how can the patch's author be | |
9d077eaa | 169 | confident that his/her hard work put into the patch won't be accidentally |
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170 | thrown away by someone in the future? |
171 | ||
e8cd7eae GS |
172 | =item Is there enough documentation? |
173 | ||
174 | Patches without documentation are probably ill-thought out or | |
175 | incomplete. Nothing can be added without documentation, so submitting | |
176 | a patch for the appropriate manpages as well as the source code is | |
a936dd3c | 177 | always a good idea. |
e8cd7eae GS |
178 | |
179 | =item Is there another way to do it? | |
180 | ||
b432a672 AL |
181 | Larry said "Although the Perl Slogan is I<There's More Than One Way |
182 | to Do It>, I hesitate to make 10 ways to do something". This is a | |
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183 | tricky heuristic to navigate, though--one man's essential addition is |
184 | another man's pointless cruft. | |
185 | ||
186 | =item Does it create too much work? | |
187 | ||
188 | Work for the pumpking, work for Perl programmers, work for module | |
189 | authors, ... Perl is supposed to be easy. | |
190 | ||
f6c51b38 GS |
191 | =item Patches speak louder than words |
192 | ||
193 | Working code is always preferred to pie-in-the-sky ideas. A patch to | |
194 | add a feature stands a much higher chance of making it to the language | |
195 | than does a random feature request, no matter how fervently argued the | |
b432a672 | 196 | request might be. This ties into "Will it be useful?", as the fact |
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197 | that someone took the time to make the patch demonstrates a strong |
198 | desire for the feature. | |
199 | ||
e8cd7eae GS |
200 | =back |
201 | ||
b432a672 AL |
202 | If you're on the list, you might hear the word "core" bandied |
203 | around. It refers to the standard distribution. "Hacking on the | |
204 | core" means you're changing the C source code to the Perl | |
205 | interpreter. "A core module" is one that ships with Perl. | |
e8cd7eae | 206 | |
a1f349fd MB |
207 | =head2 Keeping in sync |
208 | ||
e8cd7eae | 209 | The source code to the Perl interpreter, in its different versions, is |
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210 | kept in a repository managed by the git revision control system. The |
211 | pumpkings and a few others have write access to the repository to check in | |
212 | changes. | |
2be4c08b | 213 | |
b16c2e4a | 214 | How to clone and use the git perl repository is described in L<perlrepository>. |
2be4c08b | 215 | |
b16c2e4a | 216 | You can also choose to use rsync to get a copy of the current source tree |
a77cd7b8 | 217 | for the bleadperl branch and all maintenance branches: |
0cfb3454 | 218 | |
a77cd7b8 MB |
219 | $ rsync -avz rsync://perl5.git.perl.org/perl-current . |
220 | $ rsync -avz rsync://perl5.git.perl.org/perl-5.12.x . | |
221 | $ rsync -avz rsync://perl5.git.perl.org/perl-5.10.x . | |
222 | $ rsync -avz rsync://perl5.git.perl.org/perl-5.8.x . | |
223 | $ rsync -avz rsync://perl5.git.perl.org/perl-5.6.x . | |
224 | $ rsync -avz rsync://perl5.git.perl.org/perl-5.005xx . | |
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225 | |
226 | (Add the C<--delete> option to remove leftover files) | |
0cfb3454 | 227 | |
a77cd7b8 MB |
228 | To get a full list of the available sync points: |
229 | ||
230 | $ rsync perl5.git.perl.org:: | |
231 | ||
0cfb3454 GS |
232 | You may also want to subscribe to the perl5-changes mailing list to |
233 | receive a copy of each patch that gets submitted to the maintenance | |
234 | and development "branches" of the perl repository. See | |
235 | http://lists.perl.org/ for subscription information. | |
236 | ||
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237 | If you are a member of the perl5-porters mailing list, it is a good |
238 | thing to keep in touch with the most recent changes. If not only to | |
239 | verify if what you would have posted as a bug report isn't already | |
240 | solved in the most recent available perl development branch, also | |
241 | known as perl-current, bleading edge perl, bleedperl or bleadperl. | |
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242 | |
243 | Needless to say, the source code in perl-current is usually in a perpetual | |
244 | state of evolution. You should expect it to be very buggy. Do B<not> use | |
245 | it for any purpose other than testing and development. | |
e8cd7eae | 246 | |
3fd28c4e | 247 | =head2 Perlbug administration |
52315700 | 248 | |
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249 | There is a single remote administrative interface for modifying bug status, |
250 | category, open issues etc. using the B<RT> bugtracker system, maintained | |
251 | by Robert Spier. Become an administrator, and close any bugs you can get | |
3fd28c4e | 252 | your sticky mitts on: |
52315700 | 253 | |
39417508 | 254 | http://bugs.perl.org/ |
52315700 | 255 | |
3fd28c4e | 256 | To email the bug system administrators: |
52315700 | 257 | |
3fd28c4e | 258 | "perlbug-admin" <perlbug-admin@perl.org> |
52315700 | 259 | |
a1f349fd MB |
260 | =head2 Submitting patches |
261 | ||
f7e1e956 MS |
262 | Always submit patches to I<perl5-porters@perl.org>. If you're |
263 | patching a core module and there's an author listed, send the author a | |
264 | copy (see L<Patching a core module>). This lets other porters review | |
265 | your patch, which catches a surprising number of errors in patches. | |
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266 | Please patch against the latest B<development> version. (e.g., even if |
267 | you're fixing a bug in the 5.8 track, patch against the C<blead> branch in | |
268 | the git repository.) | |
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269 | |
270 | If changes are accepted, they are applied to the development branch. Then | |
fe749c9a | 271 | the maintenance pumpking decides which of those patches is to be |
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272 | backported to the maint branch. Only patches that survive the heat of the |
273 | development branch get applied to maintenance versions. | |
f7e1e956 | 274 | |
2c8694a7 JH |
275 | Your patch should update the documentation and test suite. See |
276 | L<Writing a test>. If you have added or removed files in the distribution, | |
277 | edit the MANIFEST file accordingly, sort the MANIFEST file using | |
278 | C<make manisort>, and include those changes as part of your patch. | |
e8cd7eae | 279 | |
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280 | Patching documentation also follows the same order: if accepted, a patch |
281 | is first applied to B<development>, and if relevant then it's backported | |
282 | to B<maintenance>. (With an exception for some patches that document | |
283 | behaviour that only appears in the maintenance branch, but which has | |
284 | changed in the development version.) | |
285 | ||
e8cd7eae GS |
286 | To report a bug in Perl, use the program I<perlbug> which comes with |
287 | Perl (if you can't get Perl to work, send mail to the address | |
f18956b7 | 288 | I<perlbug@perl.org> or I<perlbug@perl.com>). Reporting bugs through |
e8cd7eae | 289 | I<perlbug> feeds into the automated bug-tracking system, access to |
902821cc | 290 | which is provided through the web at http://rt.perl.org/rt3/ . It |
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291 | often pays to check the archives of the perl5-porters mailing list to |
292 | see whether the bug you're reporting has been reported before, and if | |
293 | so whether it was considered a bug. See above for the location of | |
294 | the searchable archives. | |
295 | ||
f224927c | 296 | The CPAN testers ( http://testers.cpan.org/ ) are a group of |
ba139f7d | 297 | volunteers who test CPAN modules on a variety of platforms. Perl |
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298 | Smokers ( http://www.nntp.perl.org/group/perl.daily-build and |
299 | http://www.nntp.perl.org/group/perl.daily-build.reports/ ) | |
902821cc | 300 | automatically test Perl source releases on platforms with various |
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301 | configurations. Both efforts welcome volunteers. In order to get |
302 | involved in smoke testing of the perl itself visit | |
303 | L<http://search.cpan.org/dist/Test-Smoke>. In order to start smoke | |
68cbce50 CBW |
304 | testing CPAN modules visit L<http://search.cpan.org/dist/CPANPLUS-YACSmoke/> |
305 | or L<http://search.cpan.org/dist/minismokebox/> or | |
d3e8af89 | 306 | L<http://search.cpan.org/dist/CPAN-Reporter/>. |
e8cd7eae | 307 | |
e8cd7eae GS |
308 | It's a good idea to read and lurk for a while before chipping in. |
309 | That way you'll get to see the dynamic of the conversations, learn the | |
310 | personalities of the players, and hopefully be better prepared to make | |
311 | a useful contribution when do you speak up. | |
312 | ||
313 | If after all this you still think you want to join the perl5-porters | |
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314 | mailing list, send mail to I<perl5-porters-subscribe@perl.org>. To |
315 | unsubscribe, send mail to I<perl5-porters-unsubscribe@perl.org>. | |
e8cd7eae | 316 | |
a422fd2d SC |
317 | To hack on the Perl guts, you'll need to read the following things: |
318 | ||
319 | =over 3 | |
320 | ||
321 | =item L<perlguts> | |
322 | ||
323 | This is of paramount importance, since it's the documentation of what | |
324 | goes where in the Perl source. Read it over a couple of times and it | |
325 | might start to make sense - don't worry if it doesn't yet, because the | |
326 | best way to study it is to read it in conjunction with poking at Perl | |
327 | source, and we'll do that later on. | |
328 | ||
0aa6d4a5 RU |
329 | Gisle Aas's "illustrated perlguts", also known as I<illguts>, has very |
330 | helpful pictures: | |
de10be12 | 331 | |
0aa6d4a5 | 332 | L<http://search.cpan.org/dist/illguts/> |
a422fd2d SC |
333 | |
334 | =item L<perlxstut> and L<perlxs> | |
335 | ||
336 | A working knowledge of XSUB programming is incredibly useful for core | |
337 | hacking; XSUBs use techniques drawn from the PP code, the portion of the | |
338 | guts that actually executes a Perl program. It's a lot gentler to learn | |
339 | those techniques from simple examples and explanation than from the core | |
340 | itself. | |
341 | ||
342 | =item L<perlapi> | |
343 | ||
344 | The documentation for the Perl API explains what some of the internal | |
345 | functions do, as well as the many macros used in the source. | |
346 | ||
347 | =item F<Porting/pumpkin.pod> | |
348 | ||
349 | This is a collection of words of wisdom for a Perl porter; some of it is | |
350 | only useful to the pumpkin holder, but most of it applies to anyone | |
351 | wanting to go about Perl development. | |
352 | ||
353 | =item The perl5-porters FAQ | |
354 | ||
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355 | This should be available from http://dev.perl.org/perl5/docs/p5p-faq.html . |
356 | It contains hints on reading perl5-porters, information on how | |
357 | perl5-porters works and how Perl development in general works. | |
a422fd2d SC |
358 | |
359 | =back | |
360 | ||
361 | =head2 Finding Your Way Around | |
362 | ||
363 | Perl maintenance can be split into a number of areas, and certain people | |
364 | (pumpkins) will have responsibility for each area. These areas sometimes | |
365 | correspond to files or directories in the source kit. Among the areas are: | |
366 | ||
367 | =over 3 | |
368 | ||
369 | =item Core modules | |
370 | ||
c53fdc5e RF |
371 | Modules shipped as part of the Perl core live in various subdirectories, where |
372 | two are dedicated to core-only modules, and two are for the dual-life modules | |
373 | which live on CPAN and may be maintained separately with respect to the Perl | |
374 | core: | |
375 | ||
376 | lib/ is for pure-Perl modules, which exist in the core only. | |
377 | ||
195c30ce KW |
378 | ext/ is for XS extensions, and modules with special Makefile.PL |
379 | requirements, which exist in the core only. | |
c53fdc5e | 380 | |
195c30ce KW |
381 | cpan/ is for dual-life modules, where the CPAN module is |
382 | canonical (should be patched first). | |
c53fdc5e | 383 | |
195c30ce KW |
384 | dist/ is for dual-life modules, where the blead source is |
385 | canonical. | |
a422fd2d | 386 | |
6bdc4f2c FR |
387 | For some dual-life modules it has not been discussed if the CPAN version or the |
388 | blead source is canonical. Until that is done, those modules should be in | |
389 | F<cpan/>. | |
390 | ||
f7e1e956 MS |
391 | =item Tests |
392 | ||
393 | There are tests for nearly all the modules, built-ins and major bits | |
394 | of functionality. Test files all have a .t suffix. Module tests live | |
395 | in the F<lib/> and F<ext/> directories next to the module being | |
396 | tested. Others live in F<t/>. See L<Writing a test> | |
397 | ||
a422fd2d SC |
398 | =item Documentation |
399 | ||
400 | Documentation maintenance includes looking after everything in the | |
401 | F<pod/> directory, (as well as contributing new documentation) and | |
402 | the documentation to the modules in core. | |
403 | ||
404 | =item Configure | |
405 | ||
99c47ece | 406 | The Configure process is the way we make Perl portable across the |
a422fd2d | 407 | myriad of operating systems it supports. Responsibility for the |
99c47ece MB |
408 | Configure, build and installation process, as well as the overall |
409 | portability of the core code rests with the Configure pumpkin - | |
410 | others help out with individual operating systems. | |
411 | ||
e1020413 | 412 | The three files that fall under his/her responsibility are Configure, |
99c47ece MB |
413 | config_h.SH, and Porting/Glossary (and a whole bunch of small related |
414 | files that are less important here). The Configure pumpkin decides how | |
415 | patches to these are dealt with. Currently, the Configure pumpkin will | |
416 | accept patches in most common formats, even directly to these files. | |
417 | Other committers are allowed to commit to these files under the strict | |
418 | condition that they will inform the Configure pumpkin, either on IRC | |
419 | (if he/she happens to be around) or through (personal) e-mail. | |
a422fd2d SC |
420 | |
421 | The files involved are the operating system directories, (F<win32/>, | |
422 | F<os2/>, F<vms/> and so on) the shell scripts which generate F<config.h> | |
423 | and F<Makefile>, as well as the metaconfig files which generate | |
424 | F<Configure>. (metaconfig isn't included in the core distribution.) | |
425 | ||
99c47ece MB |
426 | See http://perl5.git.perl.org/metaconfig.git/blob/HEAD:/README for a |
427 | description of the full process involved. | |
428 | ||
a422fd2d SC |
429 | =item Interpreter |
430 | ||
431 | And of course, there's the core of the Perl interpreter itself. Let's | |
432 | have a look at that in a little more detail. | |
433 | ||
434 | =back | |
435 | ||
436 | Before we leave looking at the layout, though, don't forget that | |
437 | F<MANIFEST> contains not only the file names in the Perl distribution, | |
438 | but short descriptions of what's in them, too. For an overview of the | |
439 | important files, try this: | |
440 | ||
441 | perl -lne 'print if /^[^\/]+\.[ch]\s+/' MANIFEST | |
442 | ||
443 | =head2 Elements of the interpreter | |
444 | ||
445 | The work of the interpreter has two main stages: compiling the code | |
446 | into the internal representation, or bytecode, and then executing it. | |
447 | L<perlguts/Compiled code> explains exactly how the compilation stage | |
448 | happens. | |
449 | ||
450 | Here is a short breakdown of perl's operation: | |
451 | ||
452 | =over 3 | |
453 | ||
454 | =item Startup | |
455 | ||
456 | The action begins in F<perlmain.c>. (or F<miniperlmain.c> for miniperl) | |
457 | This is very high-level code, enough to fit on a single screen, and it | |
458 | resembles the code found in L<perlembed>; most of the real action takes | |
459 | place in F<perl.c> | |
460 | ||
9df8f87f LB |
461 | F<perlmain.c> is generated by L<writemain> from F<miniperlmain.c> at |
462 | make time, so you should make perl to follow this along. | |
463 | ||
a422fd2d | 464 | First, F<perlmain.c> allocates some memory and constructs a Perl |
9df8f87f | 465 | interpreter, along these lines: |
a422fd2d SC |
466 | |
467 | 1 PERL_SYS_INIT3(&argc,&argv,&env); | |
468 | 2 | |
469 | 3 if (!PL_do_undump) { | |
470 | 4 my_perl = perl_alloc(); | |
471 | 5 if (!my_perl) | |
472 | 6 exit(1); | |
473 | 7 perl_construct(my_perl); | |
474 | 8 PL_perl_destruct_level = 0; | |
475 | 9 } | |
476 | ||
477 | Line 1 is a macro, and its definition is dependent on your operating | |
478 | system. Line 3 references C<PL_do_undump>, a global variable - all | |
479 | global variables in Perl start with C<PL_>. This tells you whether the | |
480 | current running program was created with the C<-u> flag to perl and then | |
481 | F<undump>, which means it's going to be false in any sane context. | |
482 | ||
483 | Line 4 calls a function in F<perl.c> to allocate memory for a Perl | |
484 | interpreter. It's quite a simple function, and the guts of it looks like | |
485 | this: | |
486 | ||
195c30ce | 487 | my_perl = (PerlInterpreter*)PerlMem_malloc(sizeof(PerlInterpreter)); |
a422fd2d SC |
488 | |
489 | Here you see an example of Perl's system abstraction, which we'll see | |
490 | later: C<PerlMem_malloc> is either your system's C<malloc>, or Perl's | |
491 | own C<malloc> as defined in F<malloc.c> if you selected that option at | |
492 | configure time. | |
493 | ||
9df8f87f LB |
494 | Next, in line 7, we construct the interpreter using perl_construct, |
495 | also in F<perl.c>; this sets up all the special variables that Perl | |
496 | needs, the stacks, and so on. | |
a422fd2d SC |
497 | |
498 | Now we pass Perl the command line options, and tell it to go: | |
499 | ||
195c30ce KW |
500 | exitstatus = perl_parse(my_perl, xs_init, argc, argv, (char **)NULL); |
501 | if (!exitstatus) | |
502 | perl_run(my_perl); | |
9df8f87f | 503 | |
195c30ce | 504 | exitstatus = perl_destruct(my_perl); |
a422fd2d | 505 | |
195c30ce | 506 | perl_free(my_perl); |
a422fd2d SC |
507 | |
508 | C<perl_parse> is actually a wrapper around C<S_parse_body>, as defined | |
509 | in F<perl.c>, which processes the command line options, sets up any | |
510 | statically linked XS modules, opens the program and calls C<yyparse> to | |
511 | parse it. | |
512 | ||
513 | =item Parsing | |
514 | ||
515 | The aim of this stage is to take the Perl source, and turn it into an op | |
516 | tree. We'll see what one of those looks like later. Strictly speaking, | |
517 | there's three things going on here. | |
518 | ||
519 | C<yyparse>, the parser, lives in F<perly.c>, although you're better off | |
520 | reading the original YACC input in F<perly.y>. (Yes, Virginia, there | |
521 | B<is> a YACC grammar for Perl!) The job of the parser is to take your | |
b432a672 | 522 | code and "understand" it, splitting it into sentences, deciding which |
a422fd2d SC |
523 | operands go with which operators and so on. |
524 | ||
525 | The parser is nobly assisted by the lexer, which chunks up your input | |
526 | into tokens, and decides what type of thing each token is: a variable | |
527 | name, an operator, a bareword, a subroutine, a core function, and so on. | |
528 | The main point of entry to the lexer is C<yylex>, and that and its | |
529 | associated routines can be found in F<toke.c>. Perl isn't much like | |
530 | other computer languages; it's highly context sensitive at times, it can | |
531 | be tricky to work out what sort of token something is, or where a token | |
532 | ends. As such, there's a lot of interplay between the tokeniser and the | |
533 | parser, which can get pretty frightening if you're not used to it. | |
534 | ||
535 | As the parser understands a Perl program, it builds up a tree of | |
536 | operations for the interpreter to perform during execution. The routines | |
537 | which construct and link together the various operations are to be found | |
538 | in F<op.c>, and will be examined later. | |
539 | ||
540 | =item Optimization | |
541 | ||
542 | Now the parsing stage is complete, and the finished tree represents | |
543 | the operations that the Perl interpreter needs to perform to execute our | |
544 | program. Next, Perl does a dry run over the tree looking for | |
545 | optimisations: constant expressions such as C<3 + 4> will be computed | |
546 | now, and the optimizer will also see if any multiple operations can be | |
547 | replaced with a single one. For instance, to fetch the variable C<$foo>, | |
548 | instead of grabbing the glob C<*foo> and looking at the scalar | |
549 | component, the optimizer fiddles the op tree to use a function which | |
550 | directly looks up the scalar in question. The main optimizer is C<peep> | |
551 | in F<op.c>, and many ops have their own optimizing functions. | |
552 | ||
553 | =item Running | |
554 | ||
555 | Now we're finally ready to go: we have compiled Perl byte code, and all | |
556 | that's left to do is run it. The actual execution is done by the | |
557 | C<runops_standard> function in F<run.c>; more specifically, it's done by | |
558 | these three innocent looking lines: | |
559 | ||
16c91539 | 560 | while ((PL_op = PL_op->op_ppaddr(aTHX))) { |
a422fd2d SC |
561 | PERL_ASYNC_CHECK(); |
562 | } | |
563 | ||
564 | You may be more comfortable with the Perl version of that: | |
565 | ||
566 | PERL_ASYNC_CHECK() while $Perl::op = &{$Perl::op->{function}}; | |
567 | ||
568 | Well, maybe not. Anyway, each op contains a function pointer, which | |
569 | stipulates the function which will actually carry out the operation. | |
570 | This function will return the next op in the sequence - this allows for | |
571 | things like C<if> which choose the next op dynamically at run time. | |
572 | The C<PERL_ASYNC_CHECK> makes sure that things like signals interrupt | |
573 | execution if required. | |
574 | ||
575 | The actual functions called are known as PP code, and they're spread | |
b432a672 | 576 | between four files: F<pp_hot.c> contains the "hot" code, which is most |
a422fd2d SC |
577 | often used and highly optimized, F<pp_sys.c> contains all the |
578 | system-specific functions, F<pp_ctl.c> contains the functions which | |
579 | implement control structures (C<if>, C<while> and the like) and F<pp.c> | |
580 | contains everything else. These are, if you like, the C code for Perl's | |
581 | built-in functions and operators. | |
582 | ||
dfc98234 DM |
583 | Note that each C<pp_> function is expected to return a pointer to the next |
584 | op. Calls to perl subs (and eval blocks) are handled within the same | |
585 | runops loop, and do not consume extra space on the C stack. For example, | |
586 | C<pp_entersub> and C<pp_entertry> just push a C<CxSUB> or C<CxEVAL> block | |
587 | struct onto the context stack which contain the address of the op | |
588 | following the sub call or eval. They then return the first op of that sub | |
589 | or eval block, and so execution continues of that sub or block. Later, a | |
590 | C<pp_leavesub> or C<pp_leavetry> op pops the C<CxSUB> or C<CxEVAL>, | |
591 | retrieves the return op from it, and returns it. | |
592 | ||
593 | =item Exception handing | |
594 | ||
0503309d | 595 | Perl's exception handing (i.e. C<die> etc.) is built on top of the low-level |
dfc98234 | 596 | C<setjmp()>/C<longjmp()> C-library functions. These basically provide a |
28a5cf3b | 597 | way to capture the current PC and SP registers and later restore them; i.e. |
dfc98234 DM |
598 | a C<longjmp()> continues at the point in code where a previous C<setjmp()> |
599 | was done, with anything further up on the C stack being lost. This is why | |
600 | code should always save values using C<SAVE_FOO> rather than in auto | |
601 | variables. | |
602 | ||
603 | The perl core wraps C<setjmp()> etc in the macros C<JMPENV_PUSH> and | |
604 | C<JMPENV_JUMP>. The basic rule of perl exceptions is that C<exit>, and | |
605 | C<die> (in the absence of C<eval>) perform a C<JMPENV_JUMP(2)>, while | |
606 | C<die> within C<eval> does a C<JMPENV_JUMP(3)>. | |
607 | ||
608 | At entry points to perl, such as C<perl_parse()>, C<perl_run()> and | |
609 | C<call_sv(cv, G_EVAL)> each does a C<JMPENV_PUSH>, then enter a runops | |
610 | loop or whatever, and handle possible exception returns. For a 2 return, | |
611 | final cleanup is performed, such as popping stacks and calling C<CHECK> or | |
612 | C<END> blocks. Amongst other things, this is how scope cleanup still | |
613 | occurs during an C<exit>. | |
614 | ||
615 | If a C<die> can find a C<CxEVAL> block on the context stack, then the | |
616 | stack is popped to that level and the return op in that block is assigned | |
617 | to C<PL_restartop>; then a C<JMPENV_JUMP(3)> is performed. This normally | |
618 | passes control back to the guard. In the case of C<perl_run> and | |
619 | C<call_sv>, a non-null C<PL_restartop> triggers re-entry to the runops | |
620 | loop. The is the normal way that C<die> or C<croak> is handled within an | |
621 | C<eval>. | |
622 | ||
623 | Sometimes ops are executed within an inner runops loop, such as tie, sort | |
624 | or overload code. In this case, something like | |
625 | ||
626 | sub FETCH { eval { die } } | |
627 | ||
628 | would cause a longjmp right back to the guard in C<perl_run>, popping both | |
629 | runops loops, which is clearly incorrect. One way to avoid this is for the | |
630 | tie code to do a C<JMPENV_PUSH> before executing C<FETCH> in the inner | |
631 | runops loop, but for efficiency reasons, perl in fact just sets a flag, | |
632 | using C<CATCH_SET(TRUE)>. The C<pp_require>, C<pp_entereval> and | |
633 | C<pp_entertry> ops check this flag, and if true, they call C<docatch>, | |
634 | which does a C<JMPENV_PUSH> and starts a new runops level to execute the | |
635 | code, rather than doing it on the current loop. | |
636 | ||
637 | As a further optimisation, on exit from the eval block in the C<FETCH>, | |
638 | execution of the code following the block is still carried on in the inner | |
639 | loop. When an exception is raised, C<docatch> compares the C<JMPENV> | |
640 | level of the C<CxEVAL> with C<PL_top_env> and if they differ, just | |
641 | re-throws the exception. In this way any inner loops get popped. | |
642 | ||
643 | Here's an example. | |
644 | ||
645 | 1: eval { tie @a, 'A' }; | |
646 | 2: sub A::TIEARRAY { | |
647 | 3: eval { die }; | |
648 | 4: die; | |
649 | 5: } | |
650 | ||
651 | To run this code, C<perl_run> is called, which does a C<JMPENV_PUSH> then | |
652 | enters a runops loop. This loop executes the eval and tie ops on line 1, | |
653 | with the eval pushing a C<CxEVAL> onto the context stack. | |
654 | ||
655 | The C<pp_tie> does a C<CATCH_SET(TRUE)>, then starts a second runops loop | |
656 | to execute the body of C<TIEARRAY>. When it executes the entertry op on | |
657 | line 3, C<CATCH_GET> is true, so C<pp_entertry> calls C<docatch> which | |
658 | does a C<JMPENV_PUSH> and starts a third runops loop, which then executes | |
659 | the die op. At this point the C call stack looks like this: | |
660 | ||
661 | Perl_pp_die | |
662 | Perl_runops # third loop | |
663 | S_docatch_body | |
664 | S_docatch | |
665 | Perl_pp_entertry | |
666 | Perl_runops # second loop | |
667 | S_call_body | |
668 | Perl_call_sv | |
669 | Perl_pp_tie | |
670 | Perl_runops # first loop | |
671 | S_run_body | |
672 | perl_run | |
673 | main | |
674 | ||
675 | and the context and data stacks, as shown by C<-Dstv>, look like: | |
676 | ||
677 | STACK 0: MAIN | |
678 | CX 0: BLOCK => | |
679 | CX 1: EVAL => AV() PV("A"\0) | |
680 | retop=leave | |
681 | STACK 1: MAGIC | |
682 | CX 0: SUB => | |
683 | retop=(null) | |
684 | CX 1: EVAL => * | |
685 | retop=nextstate | |
686 | ||
687 | The die pops the first C<CxEVAL> off the context stack, sets | |
688 | C<PL_restartop> from it, does a C<JMPENV_JUMP(3)>, and control returns to | |
689 | the top C<docatch>. This then starts another third-level runops level, | |
690 | which executes the nextstate, pushmark and die ops on line 4. At the point | |
691 | that the second C<pp_die> is called, the C call stack looks exactly like | |
692 | that above, even though we are no longer within an inner eval; this is | |
693 | because of the optimization mentioned earlier. However, the context stack | |
694 | now looks like this, ie with the top CxEVAL popped: | |
695 | ||
696 | STACK 0: MAIN | |
697 | CX 0: BLOCK => | |
698 | CX 1: EVAL => AV() PV("A"\0) | |
699 | retop=leave | |
700 | STACK 1: MAGIC | |
701 | CX 0: SUB => | |
702 | retop=(null) | |
703 | ||
704 | The die on line 4 pops the context stack back down to the CxEVAL, leaving | |
705 | it as: | |
706 | ||
707 | STACK 0: MAIN | |
708 | CX 0: BLOCK => | |
709 | ||
710 | As usual, C<PL_restartop> is extracted from the C<CxEVAL>, and a | |
711 | C<JMPENV_JUMP(3)> done, which pops the C stack back to the docatch: | |
712 | ||
713 | S_docatch | |
714 | Perl_pp_entertry | |
715 | Perl_runops # second loop | |
716 | S_call_body | |
717 | Perl_call_sv | |
718 | Perl_pp_tie | |
719 | Perl_runops # first loop | |
720 | S_run_body | |
721 | perl_run | |
722 | main | |
723 | ||
724 | In this case, because the C<JMPENV> level recorded in the C<CxEVAL> | |
725 | differs from the current one, C<docatch> just does a C<JMPENV_JUMP(3)> | |
726 | and the C stack unwinds to: | |
727 | ||
728 | perl_run | |
729 | main | |
730 | ||
731 | Because C<PL_restartop> is non-null, C<run_body> starts a new runops loop | |
732 | and execution continues. | |
733 | ||
a422fd2d SC |
734 | =back |
735 | ||
736 | =head2 Internal Variable Types | |
737 | ||
738 | You should by now have had a look at L<perlguts>, which tells you about | |
739 | Perl's internal variable types: SVs, HVs, AVs and the rest. If not, do | |
740 | that now. | |
741 | ||
742 | These variables are used not only to represent Perl-space variables, but | |
743 | also any constants in the code, as well as some structures completely | |
744 | internal to Perl. The symbol table, for instance, is an ordinary Perl | |
745 | hash. Your code is represented by an SV as it's read into the parser; | |
746 | any program files you call are opened via ordinary Perl filehandles, and | |
747 | so on. | |
748 | ||
749 | The core L<Devel::Peek|Devel::Peek> module lets us examine SVs from a | |
750 | Perl program. Let's see, for instance, how Perl treats the constant | |
751 | C<"hello">. | |
752 | ||
753 | % perl -MDevel::Peek -e 'Dump("hello")' | |
754 | 1 SV = PV(0xa041450) at 0xa04ecbc | |
755 | 2 REFCNT = 1 | |
756 | 3 FLAGS = (POK,READONLY,pPOK) | |
757 | 4 PV = 0xa0484e0 "hello"\0 | |
758 | 5 CUR = 5 | |
759 | 6 LEN = 6 | |
760 | ||
761 | Reading C<Devel::Peek> output takes a bit of practise, so let's go | |
762 | through it line by line. | |
763 | ||
764 | Line 1 tells us we're looking at an SV which lives at C<0xa04ecbc> in | |
765 | memory. SVs themselves are very simple structures, but they contain a | |
766 | pointer to a more complex structure. In this case, it's a PV, a | |
767 | structure which holds a string value, at location C<0xa041450>. Line 2 | |
768 | is the reference count; there are no other references to this data, so | |
769 | it's 1. | |
770 | ||
771 | Line 3 are the flags for this SV - it's OK to use it as a PV, it's a | |
772 | read-only SV (because it's a constant) and the data is a PV internally. | |
773 | Next we've got the contents of the string, starting at location | |
774 | C<0xa0484e0>. | |
775 | ||
776 | Line 5 gives us the current length of the string - note that this does | |
777 | B<not> include the null terminator. Line 6 is not the length of the | |
778 | string, but the length of the currently allocated buffer; as the string | |
779 | grows, Perl automatically extends the available storage via a routine | |
780 | called C<SvGROW>. | |
781 | ||
782 | You can get at any of these quantities from C very easily; just add | |
783 | C<Sv> to the name of the field shown in the snippet, and you've got a | |
784 | macro which will return the value: C<SvCUR(sv)> returns the current | |
785 | length of the string, C<SvREFCOUNT(sv)> returns the reference count, | |
786 | C<SvPV(sv, len)> returns the string itself with its length, and so on. | |
787 | More macros to manipulate these properties can be found in L<perlguts>. | |
788 | ||
789 | Let's take an example of manipulating a PV, from C<sv_catpvn>, in F<sv.c> | |
790 | ||
791 | 1 void | |
792 | 2 Perl_sv_catpvn(pTHX_ register SV *sv, register const char *ptr, register STRLEN len) | |
793 | 3 { | |
794 | 4 STRLEN tlen; | |
795 | 5 char *junk; | |
796 | ||
797 | 6 junk = SvPV_force(sv, tlen); | |
798 | 7 SvGROW(sv, tlen + len + 1); | |
799 | 8 if (ptr == junk) | |
800 | 9 ptr = SvPVX(sv); | |
801 | 10 Move(ptr,SvPVX(sv)+tlen,len,char); | |
802 | 11 SvCUR(sv) += len; | |
803 | 12 *SvEND(sv) = '\0'; | |
804 | 13 (void)SvPOK_only_UTF8(sv); /* validate pointer */ | |
805 | 14 SvTAINT(sv); | |
806 | 15 } | |
807 | ||
808 | This is a function which adds a string, C<ptr>, of length C<len> onto | |
809 | the end of the PV stored in C<sv>. The first thing we do in line 6 is | |
810 | make sure that the SV B<has> a valid PV, by calling the C<SvPV_force> | |
811 | macro to force a PV. As a side effect, C<tlen> gets set to the current | |
812 | value of the PV, and the PV itself is returned to C<junk>. | |
813 | ||
b1866b2d | 814 | In line 7, we make sure that the SV will have enough room to accommodate |
a422fd2d SC |
815 | the old string, the new string and the null terminator. If C<LEN> isn't |
816 | big enough, C<SvGROW> will reallocate space for us. | |
817 | ||
818 | Now, if C<junk> is the same as the string we're trying to add, we can | |
819 | grab the string directly from the SV; C<SvPVX> is the address of the PV | |
820 | in the SV. | |
821 | ||
822 | Line 10 does the actual catenation: the C<Move> macro moves a chunk of | |
823 | memory around: we move the string C<ptr> to the end of the PV - that's | |
824 | the start of the PV plus its current length. We're moving C<len> bytes | |
825 | of type C<char>. After doing so, we need to tell Perl we've extended the | |
826 | string, by altering C<CUR> to reflect the new length. C<SvEND> is a | |
827 | macro which gives us the end of the string, so that needs to be a | |
828 | C<"\0">. | |
829 | ||
830 | Line 13 manipulates the flags; since we've changed the PV, any IV or NV | |
831 | values will no longer be valid: if we have C<$a=10; $a.="6";> we don't | |
1e54db1a | 832 | want to use the old IV of 10. C<SvPOK_only_utf8> is a special UTF-8-aware |
a422fd2d SC |
833 | version of C<SvPOK_only>, a macro which turns off the IOK and NOK flags |
834 | and turns on POK. The final C<SvTAINT> is a macro which launders tainted | |
835 | data if taint mode is turned on. | |
836 | ||
837 | AVs and HVs are more complicated, but SVs are by far the most common | |
838 | variable type being thrown around. Having seen something of how we | |
839 | manipulate these, let's go on and look at how the op tree is | |
840 | constructed. | |
841 | ||
842 | =head2 Op Trees | |
843 | ||
844 | First, what is the op tree, anyway? The op tree is the parsed | |
845 | representation of your program, as we saw in our section on parsing, and | |
846 | it's the sequence of operations that Perl goes through to execute your | |
847 | program, as we saw in L</Running>. | |
848 | ||
849 | An op is a fundamental operation that Perl can perform: all the built-in | |
850 | functions and operators are ops, and there are a series of ops which | |
851 | deal with concepts the interpreter needs internally - entering and | |
852 | leaving a block, ending a statement, fetching a variable, and so on. | |
853 | ||
854 | The op tree is connected in two ways: you can imagine that there are two | |
855 | "routes" through it, two orders in which you can traverse the tree. | |
856 | First, parse order reflects how the parser understood the code, and | |
857 | secondly, execution order tells perl what order to perform the | |
858 | operations in. | |
859 | ||
860 | The easiest way to examine the op tree is to stop Perl after it has | |
861 | finished parsing, and get it to dump out the tree. This is exactly what | |
7d7d5695 RGS |
862 | the compiler backends L<B::Terse|B::Terse>, L<B::Concise|B::Concise> |
863 | and L<B::Debug|B::Debug> do. | |
a422fd2d SC |
864 | |
865 | Let's have a look at how Perl sees C<$a = $b + $c>: | |
866 | ||
867 | % perl -MO=Terse -e '$a=$b+$c' | |
868 | 1 LISTOP (0x8179888) leave | |
869 | 2 OP (0x81798b0) enter | |
870 | 3 COP (0x8179850) nextstate | |
871 | 4 BINOP (0x8179828) sassign | |
872 | 5 BINOP (0x8179800) add [1] | |
873 | 6 UNOP (0x81796e0) null [15] | |
874 | 7 SVOP (0x80fafe0) gvsv GV (0x80fa4cc) *b | |
875 | 8 UNOP (0x81797e0) null [15] | |
876 | 9 SVOP (0x8179700) gvsv GV (0x80efeb0) *c | |
877 | 10 UNOP (0x816b4f0) null [15] | |
878 | 11 SVOP (0x816dcf0) gvsv GV (0x80fa460) *a | |
879 | ||
880 | Let's start in the middle, at line 4. This is a BINOP, a binary | |
881 | operator, which is at location C<0x8179828>. The specific operator in | |
882 | question is C<sassign> - scalar assignment - and you can find the code | |
883 | which implements it in the function C<pp_sassign> in F<pp_hot.c>. As a | |
884 | binary operator, it has two children: the add operator, providing the | |
885 | result of C<$b+$c>, is uppermost on line 5, and the left hand side is on | |
886 | line 10. | |
887 | ||
888 | Line 10 is the null op: this does exactly nothing. What is that doing | |
889 | there? If you see the null op, it's a sign that something has been | |
890 | optimized away after parsing. As we mentioned in L</Optimization>, | |
891 | the optimization stage sometimes converts two operations into one, for | |
892 | example when fetching a scalar variable. When this happens, instead of | |
893 | rewriting the op tree and cleaning up the dangling pointers, it's easier | |
894 | just to replace the redundant operation with the null op. Originally, | |
895 | the tree would have looked like this: | |
896 | ||
897 | 10 SVOP (0x816b4f0) rv2sv [15] | |
898 | 11 SVOP (0x816dcf0) gv GV (0x80fa460) *a | |
899 | ||
900 | That is, fetch the C<a> entry from the main symbol table, and then look | |
901 | at the scalar component of it: C<gvsv> (C<pp_gvsv> into F<pp_hot.c>) | |
902 | happens to do both these things. | |
903 | ||
904 | The right hand side, starting at line 5 is similar to what we've just | |
905 | seen: we have the C<add> op (C<pp_add> also in F<pp_hot.c>) add together | |
906 | two C<gvsv>s. | |
907 | ||
908 | Now, what's this about? | |
909 | ||
910 | 1 LISTOP (0x8179888) leave | |
911 | 2 OP (0x81798b0) enter | |
912 | 3 COP (0x8179850) nextstate | |
913 | ||
914 | C<enter> and C<leave> are scoping ops, and their job is to perform any | |
915 | housekeeping every time you enter and leave a block: lexical variables | |
916 | are tidied up, unreferenced variables are destroyed, and so on. Every | |
917 | program will have those first three lines: C<leave> is a list, and its | |
918 | children are all the statements in the block. Statements are delimited | |
919 | by C<nextstate>, so a block is a collection of C<nextstate> ops, with | |
920 | the ops to be performed for each statement being the children of | |
921 | C<nextstate>. C<enter> is a single op which functions as a marker. | |
922 | ||
923 | That's how Perl parsed the program, from top to bottom: | |
924 | ||
925 | Program | |
926 | | | |
927 | Statement | |
928 | | | |
929 | = | |
930 | / \ | |
931 | / \ | |
932 | $a + | |
933 | / \ | |
934 | $b $c | |
935 | ||
936 | However, it's impossible to B<perform> the operations in this order: | |
937 | you have to find the values of C<$b> and C<$c> before you add them | |
938 | together, for instance. So, the other thread that runs through the op | |
939 | tree is the execution order: each op has a field C<op_next> which points | |
940 | to the next op to be run, so following these pointers tells us how perl | |
941 | executes the code. We can traverse the tree in this order using | |
942 | the C<exec> option to C<B::Terse>: | |
943 | ||
944 | % perl -MO=Terse,exec -e '$a=$b+$c' | |
945 | 1 OP (0x8179928) enter | |
946 | 2 COP (0x81798c8) nextstate | |
947 | 3 SVOP (0x81796c8) gvsv GV (0x80fa4d4) *b | |
948 | 4 SVOP (0x8179798) gvsv GV (0x80efeb0) *c | |
949 | 5 BINOP (0x8179878) add [1] | |
950 | 6 SVOP (0x816dd38) gvsv GV (0x80fa468) *a | |
951 | 7 BINOP (0x81798a0) sassign | |
952 | 8 LISTOP (0x8179900) leave | |
953 | ||
954 | This probably makes more sense for a human: enter a block, start a | |
955 | statement. Get the values of C<$b> and C<$c>, and add them together. | |
956 | Find C<$a>, and assign one to the other. Then leave. | |
957 | ||
958 | The way Perl builds up these op trees in the parsing process can be | |
959 | unravelled by examining F<perly.y>, the YACC grammar. Let's take the | |
960 | piece we need to construct the tree for C<$a = $b + $c> | |
961 | ||
962 | 1 term : term ASSIGNOP term | |
963 | 2 { $$ = newASSIGNOP(OPf_STACKED, $1, $2, $3); } | |
964 | 3 | term ADDOP term | |
965 | 4 { $$ = newBINOP($2, 0, scalar($1), scalar($3)); } | |
966 | ||
967 | If you're not used to reading BNF grammars, this is how it works: You're | |
968 | fed certain things by the tokeniser, which generally end up in upper | |
969 | case. Here, C<ADDOP>, is provided when the tokeniser sees C<+> in your | |
970 | code. C<ASSIGNOP> is provided when C<=> is used for assigning. These are | |
b432a672 | 971 | "terminal symbols", because you can't get any simpler than them. |
a422fd2d SC |
972 | |
973 | The grammar, lines one and three of the snippet above, tells you how to | |
b432a672 | 974 | build up more complex forms. These complex forms, "non-terminal symbols" |
a422fd2d SC |
975 | are generally placed in lower case. C<term> here is a non-terminal |
976 | symbol, representing a single expression. | |
977 | ||
978 | The grammar gives you the following rule: you can make the thing on the | |
979 | left of the colon if you see all the things on the right in sequence. | |
980 | This is called a "reduction", and the aim of parsing is to completely | |
981 | reduce the input. There are several different ways you can perform a | |
982 | reduction, separated by vertical bars: so, C<term> followed by C<=> | |
983 | followed by C<term> makes a C<term>, and C<term> followed by C<+> | |
984 | followed by C<term> can also make a C<term>. | |
985 | ||
986 | So, if you see two terms with an C<=> or C<+>, between them, you can | |
987 | turn them into a single expression. When you do this, you execute the | |
988 | code in the block on the next line: if you see C<=>, you'll do the code | |
989 | in line 2. If you see C<+>, you'll do the code in line 4. It's this code | |
990 | which contributes to the op tree. | |
991 | ||
992 | | term ADDOP term | |
993 | { $$ = newBINOP($2, 0, scalar($1), scalar($3)); } | |
994 | ||
995 | What this does is creates a new binary op, and feeds it a number of | |
996 | variables. The variables refer to the tokens: C<$1> is the first token in | |
997 | the input, C<$2> the second, and so on - think regular expression | |
998 | backreferences. C<$$> is the op returned from this reduction. So, we | |
999 | call C<newBINOP> to create a new binary operator. The first parameter to | |
1000 | C<newBINOP>, a function in F<op.c>, is the op type. It's an addition | |
1001 | operator, so we want the type to be C<ADDOP>. We could specify this | |
1002 | directly, but it's right there as the second token in the input, so we | |
b432a672 AL |
1003 | use C<$2>. The second parameter is the op's flags: 0 means "nothing |
1004 | special". Then the things to add: the left and right hand side of our | |
a422fd2d SC |
1005 | expression, in scalar context. |
1006 | ||
1007 | =head2 Stacks | |
1008 | ||
1009 | When perl executes something like C<addop>, how does it pass on its | |
1010 | results to the next op? The answer is, through the use of stacks. Perl | |
1011 | has a number of stacks to store things it's currently working on, and | |
1012 | we'll look at the three most important ones here. | |
1013 | ||
1014 | =over 3 | |
1015 | ||
1016 | =item Argument stack | |
1017 | ||
1018 | Arguments are passed to PP code and returned from PP code using the | |
1019 | argument stack, C<ST>. The typical way to handle arguments is to pop | |
1020 | them off the stack, deal with them how you wish, and then push the result | |
1021 | back onto the stack. This is how, for instance, the cosine operator | |
1022 | works: | |
1023 | ||
1024 | NV value; | |
1025 | value = POPn; | |
1026 | value = Perl_cos(value); | |
1027 | XPUSHn(value); | |
1028 | ||
1029 | We'll see a more tricky example of this when we consider Perl's macros | |
1030 | below. C<POPn> gives you the NV (floating point value) of the top SV on | |
1031 | the stack: the C<$x> in C<cos($x)>. Then we compute the cosine, and push | |
1032 | the result back as an NV. The C<X> in C<XPUSHn> means that the stack | |
1033 | should be extended if necessary - it can't be necessary here, because we | |
1034 | know there's room for one more item on the stack, since we've just | |
1035 | removed one! The C<XPUSH*> macros at least guarantee safety. | |
1036 | ||
1037 | Alternatively, you can fiddle with the stack directly: C<SP> gives you | |
1038 | the first element in your portion of the stack, and C<TOP*> gives you | |
1039 | the top SV/IV/NV/etc. on the stack. So, for instance, to do unary | |
1040 | negation of an integer: | |
1041 | ||
1042 | SETi(-TOPi); | |
1043 | ||
1044 | Just set the integer value of the top stack entry to its negation. | |
1045 | ||
1046 | Argument stack manipulation in the core is exactly the same as it is in | |
1047 | XSUBs - see L<perlxstut>, L<perlxs> and L<perlguts> for a longer | |
1048 | description of the macros used in stack manipulation. | |
1049 | ||
1050 | =item Mark stack | |
1051 | ||
b432a672 | 1052 | I say "your portion of the stack" above because PP code doesn't |
a422fd2d SC |
1053 | necessarily get the whole stack to itself: if your function calls |
1054 | another function, you'll only want to expose the arguments aimed for the | |
1055 | called function, and not (necessarily) let it get at your own data. The | |
b432a672 | 1056 | way we do this is to have a "virtual" bottom-of-stack, exposed to each |
a422fd2d SC |
1057 | function. The mark stack keeps bookmarks to locations in the argument |
1058 | stack usable by each function. For instance, when dealing with a tied | |
b432a672 | 1059 | variable, (internally, something with "P" magic) Perl has to call |
a422fd2d SC |
1060 | methods for accesses to the tied variables. However, we need to separate |
1061 | the arguments exposed to the method to the argument exposed to the | |
ed233832 DM |
1062 | original function - the store or fetch or whatever it may be. Here's |
1063 | roughly how the tied C<push> is implemented; see C<av_push> in F<av.c>: | |
a422fd2d SC |
1064 | |
1065 | 1 PUSHMARK(SP); | |
1066 | 2 EXTEND(SP,2); | |
1067 | 3 PUSHs(SvTIED_obj((SV*)av, mg)); | |
1068 | 4 PUSHs(val); | |
1069 | 5 PUTBACK; | |
1070 | 6 ENTER; | |
1071 | 7 call_method("PUSH", G_SCALAR|G_DISCARD); | |
1072 | 8 LEAVE; | |
13a2d996 | 1073 | |
a422fd2d SC |
1074 | Let's examine the whole implementation, for practice: |
1075 | ||
1076 | 1 PUSHMARK(SP); | |
1077 | ||
1078 | Push the current state of the stack pointer onto the mark stack. This is | |
1079 | so that when we've finished adding items to the argument stack, Perl | |
1080 | knows how many things we've added recently. | |
1081 | ||
1082 | 2 EXTEND(SP,2); | |
1083 | 3 PUSHs(SvTIED_obj((SV*)av, mg)); | |
1084 | 4 PUSHs(val); | |
1085 | ||
1086 | We're going to add two more items onto the argument stack: when you have | |
1087 | a tied array, the C<PUSH> subroutine receives the object and the value | |
1088 | to be pushed, and that's exactly what we have here - the tied object, | |
1089 | retrieved with C<SvTIED_obj>, and the value, the SV C<val>. | |
1090 | ||
1091 | 5 PUTBACK; | |
1092 | ||
e89a6d4e JD |
1093 | Next we tell Perl to update the global stack pointer from our internal |
1094 | variable: C<dSP> only gave us a local copy, not a reference to the global. | |
a422fd2d SC |
1095 | |
1096 | 6 ENTER; | |
1097 | 7 call_method("PUSH", G_SCALAR|G_DISCARD); | |
1098 | 8 LEAVE; | |
1099 | ||
1100 | C<ENTER> and C<LEAVE> localise a block of code - they make sure that all | |
1101 | variables are tidied up, everything that has been localised gets | |
1102 | its previous value returned, and so on. Think of them as the C<{> and | |
1103 | C<}> of a Perl block. | |
1104 | ||
1105 | To actually do the magic method call, we have to call a subroutine in | |
1106 | Perl space: C<call_method> takes care of that, and it's described in | |
1107 | L<perlcall>. We call the C<PUSH> method in scalar context, and we're | |
e89a6d4e JD |
1108 | going to discard its return value. The call_method() function |
1109 | removes the top element of the mark stack, so there is nothing for | |
1110 | the caller to clean up. | |
a422fd2d | 1111 | |
a422fd2d SC |
1112 | =item Save stack |
1113 | ||
1114 | C doesn't have a concept of local scope, so perl provides one. We've | |
1115 | seen that C<ENTER> and C<LEAVE> are used as scoping braces; the save | |
1116 | stack implements the C equivalent of, for example: | |
1117 | ||
1118 | { | |
1119 | local $foo = 42; | |
1120 | ... | |
1121 | } | |
1122 | ||
1123 | See L<perlguts/Localising Changes> for how to use the save stack. | |
1124 | ||
1125 | =back | |
1126 | ||
1127 | =head2 Millions of Macros | |
1128 | ||
1129 | One thing you'll notice about the Perl source is that it's full of | |
1130 | macros. Some have called the pervasive use of macros the hardest thing | |
1131 | to understand, others find it adds to clarity. Let's take an example, | |
1132 | the code which implements the addition operator: | |
1133 | ||
1134 | 1 PP(pp_add) | |
1135 | 2 { | |
39644a26 | 1136 | 3 dSP; dATARGET; tryAMAGICbin(add,opASSIGN); |
a422fd2d SC |
1137 | 4 { |
1138 | 5 dPOPTOPnnrl_ul; | |
1139 | 6 SETn( left + right ); | |
1140 | 7 RETURN; | |
1141 | 8 } | |
1142 | 9 } | |
1143 | ||
1144 | Every line here (apart from the braces, of course) contains a macro. The | |
1145 | first line sets up the function declaration as Perl expects for PP code; | |
1146 | line 3 sets up variable declarations for the argument stack and the | |
1147 | target, the return value of the operation. Finally, it tries to see if | |
1148 | the addition operation is overloaded; if so, the appropriate subroutine | |
1149 | is called. | |
1150 | ||
1151 | Line 5 is another variable declaration - all variable declarations start | |
1152 | with C<d> - which pops from the top of the argument stack two NVs (hence | |
1153 | C<nn>) and puts them into the variables C<right> and C<left>, hence the | |
1154 | C<rl>. These are the two operands to the addition operator. Next, we | |
1155 | call C<SETn> to set the NV of the return value to the result of adding | |
1156 | the two values. This done, we return - the C<RETURN> macro makes sure | |
1157 | that our return value is properly handled, and we pass the next operator | |
1158 | to run back to the main run loop. | |
1159 | ||
1160 | Most of these macros are explained in L<perlapi>, and some of the more | |
1161 | important ones are explained in L<perlxs> as well. Pay special attention | |
1162 | to L<perlguts/Background and PERL_IMPLICIT_CONTEXT> for information on | |
1163 | the C<[pad]THX_?> macros. | |
1164 | ||
52d59bef JH |
1165 | =head2 The .i Targets |
1166 | ||
1167 | You can expand the macros in a F<foo.c> file by saying | |
1168 | ||
1169 | make foo.i | |
1170 | ||
1171 | which will expand the macros using cpp. Don't be scared by the results. | |
1172 | ||
955fec6b JH |
1173 | =head1 SOURCE CODE STATIC ANALYSIS |
1174 | ||
1175 | Various tools exist for analysing C source code B<statically>, as | |
1176 | opposed to B<dynamically>, that is, without executing the code. | |
1177 | It is possible to detect resource leaks, undefined behaviour, type | |
1178 | mismatches, portability problems, code paths that would cause illegal | |
1179 | memory accesses, and other similar problems by just parsing the C code | |
1180 | and looking at the resulting graph, what does it tell about the | |
1181 | execution and data flows. As a matter of fact, this is exactly | |
1182 | how C compilers know to give warnings about dubious code. | |
1183 | ||
1184 | =head2 lint, splint | |
1185 | ||
1186 | The good old C code quality inspector, C<lint>, is available in | |
1187 | several platforms, but please be aware that there are several | |
1188 | different implementations of it by different vendors, which means that | |
1189 | the flags are not identical across different platforms. | |
1190 | ||
1191 | There is a lint variant called C<splint> (Secure Programming Lint) | |
1192 | available from http://www.splint.org/ that should compile on any | |
1193 | Unix-like platform. | |
1194 | ||
1195 | There are C<lint> and <splint> targets in Makefile, but you may have | |
1196 | to diddle with the flags (see above). | |
1197 | ||
1198 | =head2 Coverity | |
1199 | ||
1200 | Coverity (http://www.coverity.com/) is a product similar to lint and | |
1201 | as a testbed for their product they periodically check several open | |
1202 | source projects, and they give out accounts to open source developers | |
1203 | to the defect databases. | |
1204 | ||
1205 | =head2 cpd (cut-and-paste detector) | |
1206 | ||
1207 | The cpd tool detects cut-and-paste coding. If one instance of the | |
1208 | cut-and-pasted code changes, all the other spots should probably be | |
1209 | changed, too. Therefore such code should probably be turned into a | |
1210 | subroutine or a macro. | |
1211 | ||
1212 | cpd (http://pmd.sourceforge.net/cpd.html) is part of the pmd project | |
1213 | (http://pmd.sourceforge.net/). pmd was originally written for static | |
1214 | analysis of Java code, but later the cpd part of it was extended to | |
1215 | parse also C and C++. | |
1216 | ||
a52aaefa RGS |
1217 | Download the pmd-bin-X.Y.zip () from the SourceForge site, extract the |
1218 | pmd-X.Y.jar from it, and then run that on source code thusly: | |
955fec6b JH |
1219 | |
1220 | java -cp pmd-X.Y.jar net.sourceforge.pmd.cpd.CPD --minimum-tokens 100 --files /some/where/src --language c > cpd.txt | |
1221 | ||
1222 | You may run into memory limits, in which case you should use the -Xmx option: | |
1223 | ||
1224 | java -Xmx512M ... | |
1225 | ||
1226 | =head2 gcc warnings | |
1227 | ||
1228 | Though much can be written about the inconsistency and coverage | |
1229 | problems of gcc warnings (like C<-Wall> not meaning "all the | |
1230 | warnings", or some common portability problems not being covered by | |
1231 | C<-Wall>, or C<-ansi> and C<-pedantic> both being a poorly defined | |
1232 | collection of warnings, and so forth), gcc is still a useful tool in | |
1233 | keeping our coding nose clean. | |
1234 | ||
1235 | The C<-Wall> is by default on. | |
1236 | ||
a8e98a71 JH |
1237 | The C<-ansi> (and its sidekick, C<-pedantic>) would be nice to be on |
1238 | always, but unfortunately they are not safe on all platforms, they can | |
1239 | for example cause fatal conflicts with the system headers (Solaris | |
1240 | being a prime example). If Configure C<-Dgccansipedantic> is used, | |
1241 | the C<cflags> frontend selects C<-ansi -pedantic> for the platforms | |
1242 | where they are known to be safe. | |
955fec6b JH |
1243 | |
1244 | Starting from Perl 5.9.4 the following extra flags are added: | |
1245 | ||
1246 | =over 4 | |
1247 | ||
1248 | =item * | |
1249 | ||
1250 | C<-Wendif-labels> | |
1251 | ||
1252 | =item * | |
1253 | ||
1254 | C<-Wextra> | |
1255 | ||
1256 | =item * | |
1257 | ||
1258 | C<-Wdeclaration-after-statement> | |
1259 | ||
1260 | =back | |
1261 | ||
1262 | The following flags would be nice to have but they would first need | |
0503309d | 1263 | their own Augean stablemaster: |
955fec6b JH |
1264 | |
1265 | =over 4 | |
1266 | ||
1267 | =item * | |
1268 | ||
1269 | C<-Wpointer-arith> | |
1270 | ||
1271 | =item * | |
1272 | ||
1273 | C<-Wshadow> | |
1274 | ||
1275 | =item * | |
1276 | ||
1277 | C<-Wstrict-prototypes> | |
1278 | ||
955fec6b JH |
1279 | =back |
1280 | ||
1281 | The C<-Wtraditional> is another example of the annoying tendency of | |
ac036724 | 1282 | gcc to bundle a lot of warnings under one switch (it would be |
1283 | impossible to deploy in practice because it would complain a lot) but | |
955fec6b JH |
1284 | it does contain some warnings that would be beneficial to have available |
1285 | on their own, such as the warning about string constants inside macros | |
1286 | containing the macro arguments: this behaved differently pre-ANSI | |
1287 | than it does in ANSI, and some C compilers are still in transition, | |
1288 | AIX being an example. | |
1289 | ||
1290 | =head2 Warnings of other C compilers | |
1291 | ||
1292 | Other C compilers (yes, there B<are> other C compilers than gcc) often | |
1293 | have their "strict ANSI" or "strict ANSI with some portability extensions" | |
1294 | modes on, like for example the Sun Workshop has its C<-Xa> mode on | |
1295 | (though implicitly), or the DEC (these days, HP...) has its C<-std1> | |
1296 | mode on. | |
1297 | ||
1298 | =head2 DEBUGGING | |
1299 | ||
1300 | You can compile a special debugging version of Perl, which allows you | |
1301 | to use the C<-D> option of Perl to tell more about what Perl is doing. | |
1302 | But sometimes there is no alternative than to dive in with a debugger, | |
1303 | either to see the stack trace of a core dump (very useful in a bug | |
1304 | report), or trying to figure out what went wrong before the core dump | |
1305 | happened, or how did we end up having wrong or unexpected results. | |
1306 | ||
a422fd2d SC |
1307 | =head2 Poking at Perl |
1308 | ||
1309 | To really poke around with Perl, you'll probably want to build Perl for | |
1310 | debugging, like this: | |
1311 | ||
1312 | ./Configure -d -D optimize=-g | |
1313 | make | |
1314 | ||
1315 | C<-g> is a flag to the C compiler to have it produce debugging | |
955fec6b JH |
1316 | information which will allow us to step through a running program, |
1317 | and to see in which C function we are at (without the debugging | |
1318 | information we might see only the numerical addresses of the functions, | |
1319 | which is not very helpful). | |
1320 | ||
a422fd2d SC |
1321 | F<Configure> will also turn on the C<DEBUGGING> compilation symbol which |
1322 | enables all the internal debugging code in Perl. There are a whole bunch | |
1323 | of things you can debug with this: L<perlrun> lists them all, and the | |
1324 | best way to find out about them is to play about with them. The most | |
1325 | useful options are probably | |
1326 | ||
1327 | l Context (loop) stack processing | |
1328 | t Trace execution | |
1329 | o Method and overloading resolution | |
1330 | c String/numeric conversions | |
1331 | ||
1332 | Some of the functionality of the debugging code can be achieved using XS | |
1333 | modules. | |
13a2d996 | 1334 | |
a422fd2d SC |
1335 | -Dr => use re 'debug' |
1336 | -Dx => use O 'Debug' | |
1337 | ||
1338 | =head2 Using a source-level debugger | |
1339 | ||
1340 | If the debugging output of C<-D> doesn't help you, it's time to step | |
1341 | through perl's execution with a source-level debugger. | |
1342 | ||
1343 | =over 3 | |
1344 | ||
1345 | =item * | |
1346 | ||
955fec6b JH |
1347 | We'll use C<gdb> for our examples here; the principles will apply to |
1348 | any debugger (many vendors call their debugger C<dbx>), but check the | |
1349 | manual of the one you're using. | |
a422fd2d SC |
1350 | |
1351 | =back | |
1352 | ||
1353 | To fire up the debugger, type | |
1354 | ||
1355 | gdb ./perl | |
1356 | ||
955fec6b JH |
1357 | Or if you have a core dump: |
1358 | ||
1359 | gdb ./perl core | |
1360 | ||
a422fd2d SC |
1361 | You'll want to do that in your Perl source tree so the debugger can read |
1362 | the source code. You should see the copyright message, followed by the | |
1363 | prompt. | |
1364 | ||
1365 | (gdb) | |
1366 | ||
1367 | C<help> will get you into the documentation, but here are the most | |
1368 | useful commands: | |
1369 | ||
1370 | =over 3 | |
1371 | ||
1372 | =item run [args] | |
1373 | ||
1374 | Run the program with the given arguments. | |
1375 | ||
1376 | =item break function_name | |
1377 | ||
1378 | =item break source.c:xxx | |
1379 | ||
1380 | Tells the debugger that we'll want to pause execution when we reach | |
cea6626f | 1381 | either the named function (but see L<perlguts/Internal Functions>!) or the given |
a422fd2d SC |
1382 | line in the named source file. |
1383 | ||
1384 | =item step | |
1385 | ||
1386 | Steps through the program a line at a time. | |
1387 | ||
1388 | =item next | |
1389 | ||
1390 | Steps through the program a line at a time, without descending into | |
1391 | functions. | |
1392 | ||
1393 | =item continue | |
1394 | ||
1395 | Run until the next breakpoint. | |
1396 | ||
1397 | =item finish | |
1398 | ||
1399 | Run until the end of the current function, then stop again. | |
1400 | ||
13a2d996 | 1401 | =item 'enter' |
a422fd2d SC |
1402 | |
1403 | Just pressing Enter will do the most recent operation again - it's a | |
1404 | blessing when stepping through miles of source code. | |
1405 | ||
1406 | =item print | |
1407 | ||
1408 | Execute the given C code and print its results. B<WARNING>: Perl makes | |
52d59bef JH |
1409 | heavy use of macros, and F<gdb> does not necessarily support macros |
1410 | (see later L</"gdb macro support">). You'll have to substitute them | |
1411 | yourself, or to invoke cpp on the source code files | |
1412 | (see L</"The .i Targets">) | |
1413 | So, for instance, you can't say | |
a422fd2d SC |
1414 | |
1415 | print SvPV_nolen(sv) | |
1416 | ||
1417 | but you have to say | |
1418 | ||
1419 | print Perl_sv_2pv_nolen(sv) | |
1420 | ||
ffc145e8 RK |
1421 | =back |
1422 | ||
a422fd2d SC |
1423 | You may find it helpful to have a "macro dictionary", which you can |
1424 | produce by saying C<cpp -dM perl.c | sort>. Even then, F<cpp> won't | |
07aa3531 | 1425 | recursively apply those macros for you. |
52d59bef JH |
1426 | |
1427 | =head2 gdb macro support | |
a422fd2d | 1428 | |
52d59bef | 1429 | Recent versions of F<gdb> have fairly good macro support, but |
ea031e66 RGS |
1430 | in order to use it you'll need to compile perl with macro definitions |
1431 | included in the debugging information. Using F<gcc> version 3.1, this | |
1432 | means configuring with C<-Doptimize=-g3>. Other compilers might use a | |
1433 | different switch (if they support debugging macros at all). | |
1434 | ||
a422fd2d SC |
1435 | =head2 Dumping Perl Data Structures |
1436 | ||
1437 | One way to get around this macro hell is to use the dumping functions in | |
1438 | F<dump.c>; these work a little like an internal | |
1439 | L<Devel::Peek|Devel::Peek>, but they also cover OPs and other structures | |
1440 | that you can't get at from Perl. Let's take an example. We'll use the | |
07aa3531 | 1441 | C<$a = $b + $c> we used before, but give it a bit of context: |
a422fd2d SC |
1442 | C<$b = "6XXXX"; $c = 2.3;>. Where's a good place to stop and poke around? |
1443 | ||
1444 | What about C<pp_add>, the function we examined earlier to implement the | |
1445 | C<+> operator: | |
1446 | ||
1447 | (gdb) break Perl_pp_add | |
1448 | Breakpoint 1 at 0x46249f: file pp_hot.c, line 309. | |
1449 | ||
cea6626f | 1450 | Notice we use C<Perl_pp_add> and not C<pp_add> - see L<perlguts/Internal Functions>. |
a422fd2d SC |
1451 | With the breakpoint in place, we can run our program: |
1452 | ||
1453 | (gdb) run -e '$b = "6XXXX"; $c = 2.3; $a = $b + $c' | |
1454 | ||
1455 | Lots of junk will go past as gdb reads in the relevant source files and | |
1456 | libraries, and then: | |
1457 | ||
1458 | Breakpoint 1, Perl_pp_add () at pp_hot.c:309 | |
39644a26 | 1459 | 309 dSP; dATARGET; tryAMAGICbin(add,opASSIGN); |
a422fd2d SC |
1460 | (gdb) step |
1461 | 311 dPOPTOPnnrl_ul; | |
1462 | (gdb) | |
1463 | ||
1464 | We looked at this bit of code before, and we said that C<dPOPTOPnnrl_ul> | |
1465 | arranges for two C<NV>s to be placed into C<left> and C<right> - let's | |
1466 | slightly expand it: | |
1467 | ||
195c30ce KW |
1468 | #define dPOPTOPnnrl_ul NV right = POPn; \ |
1469 | SV *leftsv = TOPs; \ | |
1470 | NV left = USE_LEFT(leftsv) ? SvNV(leftsv) : 0.0 | |
a422fd2d SC |
1471 | |
1472 | C<POPn> takes the SV from the top of the stack and obtains its NV either | |
1473 | directly (if C<SvNOK> is set) or by calling the C<sv_2nv> function. | |
1474 | C<TOPs> takes the next SV from the top of the stack - yes, C<POPn> uses | |
1475 | C<TOPs> - but doesn't remove it. We then use C<SvNV> to get the NV from | |
07aa3531 | 1476 | C<leftsv> in the same way as before - yes, C<POPn> uses C<SvNV>. |
a422fd2d SC |
1477 | |
1478 | Since we don't have an NV for C<$b>, we'll have to use C<sv_2nv> to | |
1479 | convert it. If we step again, we'll find ourselves there: | |
1480 | ||
1481 | Perl_sv_2nv (sv=0xa0675d0) at sv.c:1669 | |
1482 | 1669 if (!sv) | |
1483 | (gdb) | |
1484 | ||
1485 | We can now use C<Perl_sv_dump> to investigate the SV: | |
1486 | ||
1487 | SV = PV(0xa057cc0) at 0xa0675d0 | |
1488 | REFCNT = 1 | |
1489 | FLAGS = (POK,pPOK) | |
1490 | PV = 0xa06a510 "6XXXX"\0 | |
1491 | CUR = 5 | |
1492 | LEN = 6 | |
1493 | $1 = void | |
1494 | ||
1495 | We know we're going to get C<6> from this, so let's finish the | |
1496 | subroutine: | |
1497 | ||
1498 | (gdb) finish | |
1499 | Run till exit from #0 Perl_sv_2nv (sv=0xa0675d0) at sv.c:1671 | |
1500 | 0x462669 in Perl_pp_add () at pp_hot.c:311 | |
1501 | 311 dPOPTOPnnrl_ul; | |
1502 | ||
1503 | We can also dump out this op: the current op is always stored in | |
1504 | C<PL_op>, and we can dump it with C<Perl_op_dump>. This'll give us | |
1505 | similar output to L<B::Debug|B::Debug>. | |
1506 | ||
1507 | { | |
1508 | 13 TYPE = add ===> 14 | |
1509 | TARG = 1 | |
1510 | FLAGS = (SCALAR,KIDS) | |
1511 | { | |
1512 | TYPE = null ===> (12) | |
1513 | (was rv2sv) | |
1514 | FLAGS = (SCALAR,KIDS) | |
1515 | { | |
1516 | 11 TYPE = gvsv ===> 12 | |
1517 | FLAGS = (SCALAR) | |
1518 | GV = main::b | |
1519 | } | |
1520 | } | |
1521 | ||
10f58044 | 1522 | # finish this later # |
a422fd2d SC |
1523 | |
1524 | =head2 Patching | |
1525 | ||
1526 | All right, we've now had a look at how to navigate the Perl sources and | |
1527 | some things you'll need to know when fiddling with them. Let's now get | |
1528 | on and create a simple patch. Here's something Larry suggested: if a | |
07aa3531 | 1529 | C<U> is the first active format during a C<pack>, (for example, |
a422fd2d | 1530 | C<pack "U3C8", @stuff>) then the resulting string should be treated as |
1e54db1a | 1531 | UTF-8 encoded. |
a422fd2d | 1532 | |
168a53cc DR |
1533 | If you are working with a git clone of the Perl repository, you will want to |
1534 | create a branch for your changes. This will make creating a proper patch much | |
1535 | simpler. See the L<perlrepository> for details on how to do this. | |
1536 | ||
a422fd2d SC |
1537 | How do we prepare to fix this up? First we locate the code in question - |
1538 | the C<pack> happens at runtime, so it's going to be in one of the F<pp> | |
1539 | files. Sure enough, C<pp_pack> is in F<pp.c>. Since we're going to be | |
1540 | altering this file, let's copy it to F<pp.c~>. | |
1541 | ||
a6ec74c1 JH |
1542 | [Well, it was in F<pp.c> when this tutorial was written. It has now been |
1543 | split off with C<pp_unpack> to its own file, F<pp_pack.c>] | |
1544 | ||
a422fd2d SC |
1545 | Now let's look over C<pp_pack>: we take a pattern into C<pat>, and then |
1546 | loop over the pattern, taking each format character in turn into | |
1547 | C<datum_type>. Then for each possible format character, we swallow up | |
1548 | the other arguments in the pattern (a field width, an asterisk, and so | |
1549 | on) and convert the next chunk input into the specified format, adding | |
1550 | it onto the output SV C<cat>. | |
1551 | ||
1552 | How do we know if the C<U> is the first format in the C<pat>? Well, if | |
1553 | we have a pointer to the start of C<pat> then, if we see a C<U> we can | |
1554 | test whether we're still at the start of the string. So, here's where | |
1555 | C<pat> is set up: | |
1556 | ||
1557 | STRLEN fromlen; | |
1558 | register char *pat = SvPVx(*++MARK, fromlen); | |
1559 | register char *patend = pat + fromlen; | |
1560 | register I32 len; | |
1561 | I32 datumtype; | |
1562 | SV *fromstr; | |
1563 | ||
1564 | We'll have another string pointer in there: | |
1565 | ||
1566 | STRLEN fromlen; | |
1567 | register char *pat = SvPVx(*++MARK, fromlen); | |
1568 | register char *patend = pat + fromlen; | |
1569 | + char *patcopy; | |
1570 | register I32 len; | |
1571 | I32 datumtype; | |
1572 | SV *fromstr; | |
1573 | ||
1574 | And just before we start the loop, we'll set C<patcopy> to be the start | |
1575 | of C<pat>: | |
1576 | ||
1577 | items = SP - MARK; | |
1578 | MARK++; | |
1579 | sv_setpvn(cat, "", 0); | |
1580 | + patcopy = pat; | |
1581 | while (pat < patend) { | |
1582 | ||
1583 | Now if we see a C<U> which was at the start of the string, we turn on | |
1e54db1a | 1584 | the C<UTF8> flag for the output SV, C<cat>: |
a422fd2d SC |
1585 | |
1586 | + if (datumtype == 'U' && pat==patcopy+1) | |
1587 | + SvUTF8_on(cat); | |
1588 | if (datumtype == '#') { | |
1589 | while (pat < patend && *pat != '\n') | |
1590 | pat++; | |
1591 | ||
1592 | Remember that it has to be C<patcopy+1> because the first character of | |
1593 | the string is the C<U> which has been swallowed into C<datumtype!> | |
1594 | ||
1595 | Oops, we forgot one thing: what if there are spaces at the start of the | |
1596 | pattern? C<pack(" U*", @stuff)> will have C<U> as the first active | |
1597 | character, even though it's not the first thing in the pattern. In this | |
1598 | case, we have to advance C<patcopy> along with C<pat> when we see spaces: | |
1599 | ||
1600 | if (isSPACE(datumtype)) | |
1601 | continue; | |
1602 | ||
1603 | needs to become | |
1604 | ||
1605 | if (isSPACE(datumtype)) { | |
1606 | patcopy++; | |
1607 | continue; | |
1608 | } | |
1609 | ||
1610 | OK. That's the C part done. Now we must do two additional things before | |
1611 | this patch is ready to go: we've changed the behaviour of Perl, and so | |
1612 | we must document that change. We must also provide some more regression | |
1613 | tests to make sure our patch works and doesn't create a bug somewhere | |
1614 | else along the line. | |
1615 | ||
b23b8711 MS |
1616 | The regression tests for each operator live in F<t/op/>, and so we |
1617 | make a copy of F<t/op/pack.t> to F<t/op/pack.t~>. Now we can add our | |
1618 | tests to the end. First, we'll test that the C<U> does indeed create | |
07aa3531 | 1619 | Unicode strings. |
b23b8711 MS |
1620 | |
1621 | t/op/pack.t has a sensible ok() function, but if it didn't we could | |
35c336e6 | 1622 | use the one from t/test.pl. |
b23b8711 | 1623 | |
35c336e6 MS |
1624 | require './test.pl'; |
1625 | plan( tests => 159 ); | |
b23b8711 MS |
1626 | |
1627 | so instead of this: | |
a422fd2d | 1628 | |
195c30ce KW |
1629 | print 'not ' unless "1.20.300.4000" eq sprintf "%vd", |
1630 | pack("U*",1,20,300,4000); | |
a422fd2d SC |
1631 | print "ok $test\n"; $test++; |
1632 | ||
35c336e6 MS |
1633 | we can write the more sensible (see L<Test::More> for a full |
1634 | explanation of is() and other testing functions). | |
b23b8711 | 1635 | |
07aa3531 | 1636 | is( "1.20.300.4000", sprintf "%vd", pack("U*",1,20,300,4000), |
38a44b82 | 1637 | "U* produces Unicode" ); |
b23b8711 | 1638 | |
a422fd2d SC |
1639 | Now we'll test that we got that space-at-the-beginning business right: |
1640 | ||
35c336e6 | 1641 | is( "1.20.300.4000", sprintf "%vd", pack(" U*",1,20,300,4000), |
195c30ce | 1642 | " with spaces at the beginning" ); |
a422fd2d SC |
1643 | |
1644 | And finally we'll test that we don't make Unicode strings if C<U> is B<not> | |
1645 | the first active format: | |
1646 | ||
35c336e6 | 1647 | isnt( v1.20.300.4000, sprintf "%vd", pack("C0U*",1,20,300,4000), |
38a44b82 | 1648 | "U* not first isn't Unicode" ); |
a422fd2d | 1649 | |
35c336e6 MS |
1650 | Mustn't forget to change the number of tests which appears at the top, |
1651 | or else the automated tester will get confused. This will either look | |
1652 | like this: | |
a422fd2d | 1653 | |
35c336e6 MS |
1654 | print "1..156\n"; |
1655 | ||
1656 | or this: | |
1657 | ||
1658 | plan( tests => 156 ); | |
a422fd2d SC |
1659 | |
1660 | We now compile up Perl, and run it through the test suite. Our new | |
1661 | tests pass, hooray! | |
1662 | ||
1663 | Finally, the documentation. The job is never done until the paperwork is | |
1664 | over, so let's describe the change we've just made. The relevant place | |
1665 | is F<pod/perlfunc.pod>; again, we make a copy, and then we'll insert | |
1666 | this text in the description of C<pack>: | |
1667 | ||
1668 | =item * | |
1669 | ||
1670 | If the pattern begins with a C<U>, the resulting string will be treated | |
1e54db1a JH |
1671 | as UTF-8-encoded Unicode. You can force UTF-8 encoding on in a string |
1672 | with an initial C<U0>, and the bytes that follow will be interpreted as | |
195c30ce KW |
1673 | Unicode characters. If you don't want this to happen, you can begin |
1674 | your pattern with C<C0> (or anything else) to force Perl not to UTF-8 | |
1675 | encode your string, and then follow this with a C<U*> somewhere in your | |
1676 | pattern. | |
a422fd2d | 1677 | |
f7e1e956 MS |
1678 | =head2 Patching a core module |
1679 | ||
1680 | This works just like patching anything else, with an extra | |
1681 | consideration. Many core modules also live on CPAN. If this is so, | |
1682 | patch the CPAN version instead of the core and send the patch off to | |
1683 | the module maintainer (with a copy to p5p). This will help the module | |
1684 | maintainer keep the CPAN version in sync with the core version without | |
1685 | constantly scanning p5p. | |
1686 | ||
db300100 RGS |
1687 | The list of maintainers of core modules is usefully documented in |
1688 | F<Porting/Maintainers.pl>. | |
1689 | ||
acbe17fc JP |
1690 | =head2 Adding a new function to the core |
1691 | ||
1692 | If, as part of a patch to fix a bug, or just because you have an | |
1693 | especially good idea, you decide to add a new function to the core, | |
1694 | discuss your ideas on p5p well before you start work. It may be that | |
1695 | someone else has already attempted to do what you are considering and | |
1696 | can give lots of good advice or even provide you with bits of code | |
1697 | that they already started (but never finished). | |
1698 | ||
1699 | You have to follow all of the advice given above for patching. It is | |
1700 | extremely important to test any addition thoroughly and add new tests | |
1701 | to explore all boundary conditions that your new function is expected | |
1702 | to handle. If your new function is used only by one module (e.g. toke), | |
1703 | then it should probably be named S_your_function (for static); on the | |
210b36aa | 1704 | other hand, if you expect it to accessible from other functions in |
acbe17fc JP |
1705 | Perl, you should name it Perl_your_function. See L<perlguts/Internal Functions> |
1706 | for more details. | |
1707 | ||
1708 | The location of any new code is also an important consideration. Don't | |
1709 | just create a new top level .c file and put your code there; you would | |
1710 | have to make changes to Configure (so the Makefile is created properly), | |
1711 | as well as possibly lots of include files. This is strictly pumpking | |
1712 | business. | |
1713 | ||
1714 | It is better to add your function to one of the existing top level | |
1715 | source code files, but your choice is complicated by the nature of | |
1716 | the Perl distribution. Only the files that are marked as compiled | |
1717 | static are located in the perl executable. Everything else is located | |
1718 | in the shared library (or DLL if you are running under WIN32). So, | |
1719 | for example, if a function was only used by functions located in | |
1720 | toke.c, then your code can go in toke.c. If, however, you want to call | |
1721 | the function from universal.c, then you should put your code in another | |
1722 | location, for example util.c. | |
1723 | ||
1724 | In addition to writing your c-code, you will need to create an | |
1725 | appropriate entry in embed.pl describing your function, then run | |
1726 | 'make regen_headers' to create the entries in the numerous header | |
1727 | files that perl needs to compile correctly. See L<perlguts/Internal Functions> | |
1728 | for information on the various options that you can set in embed.pl. | |
1729 | You will forget to do this a few (or many) times and you will get | |
1730 | warnings during the compilation phase. Make sure that you mention | |
1731 | this when you post your patch to P5P; the pumpking needs to know this. | |
1732 | ||
1733 | When you write your new code, please be conscious of existing code | |
884bad00 | 1734 | conventions used in the perl source files. See L<perlstyle> for |
acbe17fc JP |
1735 | details. Although most of the guidelines discussed seem to focus on |
1736 | Perl code, rather than c, they all apply (except when they don't ;). | |
195c30ce | 1737 | Also see L<perlrepository> for lots of details about both formatting and |
552d2b87 | 1738 | submitting patches of your changes. |
acbe17fc JP |
1739 | |
1740 | Lastly, TEST TEST TEST TEST TEST any code before posting to p5p. | |
1741 | Test on as many platforms as you can find. Test as many perl | |
1742 | Configure options as you can (e.g. MULTIPLICITY). If you have | |
1743 | profiling or memory tools, see L<EXTERNAL TOOLS FOR DEBUGGING PERL> | |
210b36aa | 1744 | below for how to use them to further test your code. Remember that |
acbe17fc JP |
1745 | most of the people on P5P are doing this on their own time and |
1746 | don't have the time to debug your code. | |
f7e1e956 MS |
1747 | |
1748 | =head2 Writing a test | |
1749 | ||
1750 | Every module and built-in function has an associated test file (or | |
1751 | should...). If you add or change functionality, you have to write a | |
1752 | test. If you fix a bug, you have to write a test so that bug never | |
1753 | comes back. If you alter the docs, it would be nice to test what the | |
1754 | new documentation says. | |
1755 | ||
1756 | In short, if you submit a patch you probably also have to patch the | |
1757 | tests. | |
1758 | ||
1759 | For modules, the test file is right next to the module itself. | |
1760 | F<lib/strict.t> tests F<lib/strict.pm>. This is a recent innovation, | |
1761 | so there are some snags (and it would be wonderful for you to brush | |
1762 | them out), but it basically works that way. Everything else lives in | |
1763 | F<t/>. | |
1764 | ||
628f0a0a KW |
1765 | Testing of warning messages is often separately done by using expect scripts in |
1766 | F<t/lib/warnings>. This is because much of the setup for them is already done | |
1767 | for you. | |
1768 | ||
d5f28025 JV |
1769 | If you add a new test directory under F<t/>, it is imperative that you |
1770 | add that directory to F<t/HARNESS> and F<t/TEST>. | |
1771 | ||
f7e1e956 MS |
1772 | =over 3 |
1773 | ||
1774 | =item F<t/base/> | |
1775 | ||
1776 | Testing of the absolute basic functionality of Perl. Things like | |
1777 | C<if>, basic file reads and writes, simple regexes, etc. These are | |
1778 | run first in the test suite and if any of them fail, something is | |
1779 | I<really> broken. | |
1780 | ||
1781 | =item F<t/cmd/> | |
1782 | ||
1783 | These test the basic control structures, C<if/else>, C<while>, | |
35c336e6 | 1784 | subroutines, etc. |
f7e1e956 MS |
1785 | |
1786 | =item F<t/comp/> | |
1787 | ||
1788 | Tests basic issues of how Perl parses and compiles itself. | |
1789 | ||
1790 | =item F<t/io/> | |
1791 | ||
1792 | Tests for built-in IO functions, including command line arguments. | |
1793 | ||
1794 | =item F<t/lib/> | |
1795 | ||
1796 | The old home for the module tests, you shouldn't put anything new in | |
1797 | here. There are still some bits and pieces hanging around in here | |
1798 | that need to be moved. Perhaps you could move them? Thanks! | |
1799 | ||
3c295041 RGS |
1800 | =item F<t/mro/> |
1801 | ||
0503309d | 1802 | Tests for perl's method resolution order implementations |
3c295041 RGS |
1803 | (see L<mro>). |
1804 | ||
f7e1e956 MS |
1805 | =item F<t/op/> |
1806 | ||
1807 | Tests for perl's built in functions that don't fit into any of the | |
1808 | other directories. | |
1809 | ||
a4499558 YO |
1810 | =item F<t/re/> |
1811 | ||
1812 | Tests for regex related functions or behaviour. (These used to live | |
1813 | in t/op). | |
1814 | ||
f7e1e956 MS |
1815 | =item F<t/run/> |
1816 | ||
1817 | Testing features of how perl actually runs, including exit codes and | |
1818 | handling of PERL* environment variables. | |
1819 | ||
244d9cb7 RGS |
1820 | =item F<t/uni/> |
1821 | ||
1822 | Tests for the core support of Unicode. | |
1823 | ||
1824 | =item F<t/win32/> | |
1825 | ||
1826 | Windows-specific tests. | |
1827 | ||
1828 | =item F<t/x2p> | |
1829 | ||
1830 | A test suite for the s2p converter. | |
1831 | ||
f7e1e956 MS |
1832 | =back |
1833 | ||
1834 | The core uses the same testing style as the rest of Perl, a simple | |
1835 | "ok/not ok" run through Test::Harness, but there are a few special | |
1836 | considerations. | |
1837 | ||
35c336e6 MS |
1838 | There are three ways to write a test in the core. Test::More, |
1839 | t/test.pl and ad hoc C<print $test ? "ok 42\n" : "not ok 42\n">. The | |
1840 | decision of which to use depends on what part of the test suite you're | |
1841 | working on. This is a measure to prevent a high-level failure (such | |
1842 | as Config.pm breaking) from causing basic functionality tests to fail. | |
b3fe9f3f | 1843 | If you write your own test, use the L<Test Anything Protocol|TAP>. |
35c336e6 | 1844 | |
07aa3531 | 1845 | =over 4 |
35c336e6 MS |
1846 | |
1847 | =item t/base t/comp | |
1848 | ||
1849 | Since we don't know if require works, or even subroutines, use ad hoc | |
1850 | tests for these two. Step carefully to avoid using the feature being | |
1851 | tested. | |
1852 | ||
1853 | =item t/cmd t/run t/io t/op | |
1854 | ||
1855 | Now that basic require() and subroutines are tested, you can use the | |
1856 | t/test.pl library which emulates the important features of Test::More | |
1857 | while using a minimum of core features. | |
1858 | ||
1859 | You can also conditionally use certain libraries like Config, but be | |
1860 | sure to skip the test gracefully if it's not there. | |
1861 | ||
1862 | =item t/lib ext lib | |
1863 | ||
1864 | Now that the core of Perl is tested, Test::More can be used. You can | |
1865 | also use the full suite of core modules in the tests. | |
1866 | ||
1867 | =back | |
f7e1e956 MS |
1868 | |
1869 | When you say "make test" Perl uses the F<t/TEST> program to run the | |
07aa3531 JC |
1870 | test suite (except under Win32 where it uses F<t/harness> instead.) |
1871 | All tests are run from the F<t/> directory, B<not> the directory | |
1872 | which contains the test. This causes some problems with the tests | |
7205a85d | 1873 | in F<lib/>, so here's some opportunity for some patching. |
f7e1e956 MS |
1874 | |
1875 | You must be triply conscious of cross-platform concerns. This usually | |
1876 | boils down to using File::Spec and avoiding things like C<fork()> and | |
1877 | C<system()> unless absolutely necessary. | |
1878 | ||
e018f8be JH |
1879 | =head2 Special Make Test Targets |
1880 | ||
1881 | There are various special make targets that can be used to test Perl | |
1882 | slightly differently than the standard "test" target. Not all them | |
1883 | are expected to give a 100% success rate. Many of them have several | |
7205a85d YO |
1884 | aliases, and many of them are not available on certain operating |
1885 | systems. | |
e018f8be JH |
1886 | |
1887 | =over 4 | |
1888 | ||
1889 | =item coretest | |
1890 | ||
7d7d5695 | 1891 | Run F<perl> on all core tests (F<t/*> and F<lib/[a-z]*> pragma tests). |
e018f8be | 1892 | |
7205a85d YO |
1893 | (Not available on Win32) |
1894 | ||
e018f8be JH |
1895 | =item test.deparse |
1896 | ||
b26492ee RGS |
1897 | Run all the tests through B::Deparse. Not all tests will succeed. |
1898 | ||
7205a85d YO |
1899 | (Not available on Win32) |
1900 | ||
b26492ee RGS |
1901 | =item test.taintwarn |
1902 | ||
1903 | Run all tests with the B<-t> command-line switch. Not all tests | |
1904 | are expected to succeed (until they're specifically fixed, of course). | |
e018f8be | 1905 | |
7205a85d YO |
1906 | (Not available on Win32) |
1907 | ||
e018f8be JH |
1908 | =item minitest |
1909 | ||
1910 | Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>, | |
8cebccf4 | 1911 | F<t/op>, F<t/uni> and F<t/mro> tests. |
e018f8be | 1912 | |
7a834142 JH |
1913 | =item test.valgrind check.valgrind utest.valgrind ucheck.valgrind |
1914 | ||
1915 | (Only in Linux) Run all the tests using the memory leak + naughty | |
1916 | memory access tool "valgrind". The log files will be named | |
1917 | F<testname.valgrind>. | |
1918 | ||
e018f8be JH |
1919 | =item test.third check.third utest.third ucheck.third |
1920 | ||
1921 | (Only in Tru64) Run all the tests using the memory leak + naughty | |
1922 | memory access tool "Third Degree". The log files will be named | |
60a57c1c | 1923 | F<perl.3log.testname>. |
e018f8be JH |
1924 | |
1925 | =item test.torture torturetest | |
1926 | ||
1927 | Run all the usual tests and some extra tests. As of Perl 5.8.0 the | |
244d9cb7 | 1928 | only extra tests are Abigail's JAPHs, F<t/japh/abigail.t>. |
e018f8be JH |
1929 | |
1930 | You can also run the torture test with F<t/harness> by giving | |
1931 | C<-torture> argument to F<t/harness>. | |
1932 | ||
1933 | =item utest ucheck test.utf8 check.utf8 | |
1934 | ||
1935 | Run all the tests with -Mutf8. Not all tests will succeed. | |
1936 | ||
7205a85d YO |
1937 | (Not available on Win32) |
1938 | ||
cc0710ff RGS |
1939 | =item minitest.utf16 test.utf16 |
1940 | ||
1941 | Runs the tests with UTF-16 encoded scripts, encoded with different | |
1942 | versions of this encoding. | |
1943 | ||
1944 | C<make utest.utf16> runs the test suite with a combination of C<-utf8> and | |
1945 | C<-utf16> arguments to F<t/TEST>. | |
1946 | ||
7205a85d YO |
1947 | (Not available on Win32) |
1948 | ||
244d9cb7 RGS |
1949 | =item test_harness |
1950 | ||
1951 | Run the test suite with the F<t/harness> controlling program, instead of | |
1952 | F<t/TEST>. F<t/harness> is more sophisticated, and uses the | |
1953 | L<Test::Harness> module, thus using this test target supposes that perl | |
1954 | mostly works. The main advantage for our purposes is that it prints a | |
00bf5cd9 RGS |
1955 | detailed summary of failed tests at the end. Also, unlike F<t/TEST>, it |
1956 | doesn't redirect stderr to stdout. | |
244d9cb7 | 1957 | |
7205a85d YO |
1958 | Note that under Win32 F<t/harness> is always used instead of F<t/TEST>, so |
1959 | there is no special "test_harness" target. | |
1960 | ||
1961 | Under Win32's "test" target you may use the TEST_SWITCHES and TEST_FILES | |
1962 | environment variables to control the behaviour of F<t/harness>. This means | |
1963 | you can say | |
1964 | ||
1965 | nmake test TEST_FILES="op/*.t" | |
1966 | nmake test TEST_SWITCHES="-torture" TEST_FILES="op/*.t" | |
1967 | ||
a75f557c JV |
1968 | =item Parallel tests |
1969 | ||
1970 | The core distribution can now run its regression tests in parallel on | |
1971 | Unix-like platforms. Instead of running C<make test>, set C<TEST_JOBS> in | |
1972 | your environment to the number of tests to run in parallel, and run | |
1973 | C<make test_harness>. On a Bourne-like shell, this can be done as | |
1974 | ||
1975 | TEST_JOBS=3 make test_harness # Run 3 tests in parallel | |
1976 | ||
1977 | An environment variable is used, rather than parallel make itself, because | |
1978 | L<TAP::Harness> needs to be able to schedule individual non-conflicting test | |
1979 | scripts itself, and there is no standard interface to C<make> utilities to | |
1980 | interact with their job schedulers. | |
1981 | ||
1982 | Note that currently some test scripts may fail when run in parallel (most | |
1983 | notably C<ext/IO/t/io_dir.t>). If necessary run just the failing scripts | |
1984 | again sequentially and see if the failures go away. | |
7205a85d YO |
1985 | =item test-notty test_notty |
1986 | ||
1987 | Sets PERL_SKIP_TTY_TEST to true before running normal test. | |
1988 | ||
244d9cb7 RGS |
1989 | =back |
1990 | ||
1991 | =head2 Running tests by hand | |
1992 | ||
1993 | You can run part of the test suite by hand by using one the following | |
1994 | commands from the F<t/> directory : | |
1995 | ||
1996 | ./perl -I../lib TEST list-of-.t-files | |
1997 | ||
1998 | or | |
1999 | ||
2000 | ./perl -I../lib harness list-of-.t-files | |
2001 | ||
2002 | (if you don't specify test scripts, the whole test suite will be run.) | |
2003 | ||
7205a85d YO |
2004 | =head3 Using t/harness for testing |
2005 | ||
2006 | If you use C<harness> for testing you have several command line options | |
2007 | available to you. The arguments are as follows, and are in the order | |
2008 | that they must appear if used together. | |
2009 | ||
2010 | harness -v -torture -re=pattern LIST OF FILES TO TEST | |
2011 | harness -v -torture -re LIST OF PATTERNS TO MATCH | |
2012 | ||
2013 | If C<LIST OF FILES TO TEST> is omitted the file list is obtained from | |
07aa3531 | 2014 | the manifest. The file list may include shell wildcards which will be |
7205a85d YO |
2015 | expanded out. |
2016 | ||
2017 | =over 4 | |
2018 | ||
2019 | =item -v | |
2020 | ||
07aa3531 | 2021 | Run the tests under verbose mode so you can see what tests were run, |
8550bf48 | 2022 | and debug output. |
7205a85d YO |
2023 | |
2024 | =item -torture | |
2025 | ||
2026 | Run the torture tests as well as the normal set. | |
2027 | ||
2028 | =item -re=PATTERN | |
2029 | ||
2030 | Filter the file list so that all the test files run match PATTERN. | |
2031 | Note that this form is distinct from the B<-re LIST OF PATTERNS> form below | |
2032 | in that it allows the file list to be provided as well. | |
2033 | ||
2034 | =item -re LIST OF PATTERNS | |
2035 | ||
07aa3531 | 2036 | Filter the file list so that all the test files run match |
7205a85d YO |
2037 | /(LIST|OF|PATTERNS)/. Note that with this form the patterns |
2038 | are joined by '|' and you cannot supply a list of files, instead | |
2039 | the test files are obtained from the MANIFEST. | |
2040 | ||
2041 | =back | |
2042 | ||
244d9cb7 RGS |
2043 | You can run an individual test by a command similar to |
2044 | ||
2045 | ./perl -I../lib patho/to/foo.t | |
2046 | ||
2047 | except that the harnesses set up some environment variables that may | |
2048 | affect the execution of the test : | |
2049 | ||
07aa3531 | 2050 | =over 4 |
244d9cb7 RGS |
2051 | |
2052 | =item PERL_CORE=1 | |
2053 | ||
2054 | indicates that we're running this test part of the perl core test suite. | |
2055 | This is useful for modules that have a dual life on CPAN. | |
2056 | ||
2057 | =item PERL_DESTRUCT_LEVEL=2 | |
2058 | ||
2059 | is set to 2 if it isn't set already (see L</PERL_DESTRUCT_LEVEL>) | |
2060 | ||
2061 | =item PERL | |
2062 | ||
2063 | (used only by F<t/TEST>) if set, overrides the path to the perl executable | |
2064 | that should be used to run the tests (the default being F<./perl>). | |
2065 | ||
2066 | =item PERL_SKIP_TTY_TEST | |
2067 | ||
2068 | if set, tells to skip the tests that need a terminal. It's actually set | |
2069 | automatically by the Makefile, but can also be forced artificially by | |
2070 | running 'make test_notty'. | |
2071 | ||
e018f8be | 2072 | =back |
f7e1e956 | 2073 | |
7cd58830 RGS |
2074 | =head3 Other environment variables that may influence tests |
2075 | ||
2076 | =over 4 | |
2077 | ||
2078 | =item PERL_TEST_Net_Ping | |
2079 | ||
2080 | Setting this variable runs all the Net::Ping modules tests, | |
2081 | otherwise some tests that interact with the outside world are skipped. | |
2082 | See L<perl58delta>. | |
2083 | ||
2084 | =item PERL_TEST_NOVREXX | |
2085 | ||
2086 | Setting this variable skips the vrexx.t tests for OS2::REXX. | |
2087 | ||
2088 | =item PERL_TEST_NUMCONVERTS | |
2089 | ||
2090 | This sets a variable in op/numconvert.t. | |
2091 | ||
2092 | =back | |
2093 | ||
2094 | See also the documentation for the Test and Test::Harness modules, | |
2095 | for more environment variables that affect testing. | |
2096 | ||
d7889f52 JH |
2097 | =head2 Common problems when patching Perl source code |
2098 | ||
2099 | Perl source plays by ANSI C89 rules: no C99 (or C++) extensions. In | |
2100 | some cases we have to take pre-ANSI requirements into consideration. | |
2101 | You don't care about some particular platform having broken Perl? | |
2102 | I hear there is still a strong demand for J2EE programmers. | |
2103 | ||
2104 | =head2 Perl environment problems | |
2105 | ||
2106 | =over 4 | |
2107 | ||
2108 | =item * | |
2109 | ||
2110 | Not compiling with threading | |
2111 | ||
2112 | Compiling with threading (-Duseithreads) completely rewrites | |
2113 | the function prototypes of Perl. You better try your changes | |
0bec6c03 | 2114 | with that. Related to this is the difference between "Perl_-less" |
d7889f52 JH |
2115 | and "Perl_-ly" APIs, for example: |
2116 | ||
2117 | Perl_sv_setiv(aTHX_ ...); | |
2118 | sv_setiv(...); | |
2119 | ||
ee9468a2 RGS |
2120 | The first one explicitly passes in the context, which is needed for e.g. |
2121 | threaded builds. The second one does that implicitly; do not get them | |
def4ed7d JH |
2122 | mixed. If you are not passing in a aTHX_, you will need to do a dTHX |
2123 | (or a dVAR) as the first thing in the function. | |
d7889f52 JH |
2124 | |
2125 | See L<perlguts/"How multiple interpreters and concurrency are supported"> | |
2126 | for further discussion about context. | |
2127 | ||
2128 | =item * | |
2129 | ||
2130 | Not compiling with -DDEBUGGING | |
2131 | ||
2132 | The DEBUGGING define exposes more code to the compiler, | |
0bec6c03 | 2133 | therefore more ways for things to go wrong. You should try it. |
d7889f52 JH |
2134 | |
2135 | =item * | |
2136 | ||
ee9468a2 RGS |
2137 | Introducing (non-read-only) globals |
2138 | ||
2139 | Do not introduce any modifiable globals, truly global or file static. | |
bc028b6b JH |
2140 | They are bad form and complicate multithreading and other forms of |
2141 | concurrency. The right way is to introduce them as new interpreter | |
2142 | variables, see F<intrpvar.h> (at the very end for binary compatibility). | |
ee9468a2 RGS |
2143 | |
2144 | Introducing read-only (const) globals is okay, as long as you verify | |
2145 | with e.g. C<nm libperl.a|egrep -v ' [TURtr] '> (if your C<nm> has | |
2146 | BSD-style output) that the data you added really is read-only. | |
2147 | (If it is, it shouldn't show up in the output of that command.) | |
2148 | ||
2149 | If you want to have static strings, make them constant: | |
2150 | ||
2151 | static const char etc[] = "..."; | |
2152 | ||
bc028b6b | 2153 | If you want to have arrays of constant strings, note carefully |
ee9468a2 RGS |
2154 | the right combination of C<const>s: |
2155 | ||
2156 | static const char * const yippee[] = | |
2157 | {"hi", "ho", "silver"}; | |
2158 | ||
bc028b6b JH |
2159 | There is a way to completely hide any modifiable globals (they are all |
2160 | moved to heap), the compilation setting C<-DPERL_GLOBAL_STRUCT_PRIVATE>. | |
2161 | It is not normally used, but can be used for testing, read more | |
def4ed7d | 2162 | about it in L<perlguts/"Background and PERL_IMPLICIT_CONTEXT">. |
bc028b6b | 2163 | |
ee9468a2 RGS |
2164 | =item * |
2165 | ||
d7889f52 JH |
2166 | Not exporting your new function |
2167 | ||
2168 | Some platforms (Win32, AIX, VMS, OS/2, to name a few) require any | |
2169 | function that is part of the public API (the shared Perl library) | |
2170 | to be explicitly marked as exported. See the discussion about | |
2171 | F<embed.pl> in L<perlguts>. | |
2172 | ||
2173 | =item * | |
2174 | ||
2175 | Exporting your new function | |
2176 | ||
2177 | The new shiny result of either genuine new functionality or your | |
2178 | arduous refactoring is now ready and correctly exported. So what | |
def4ed7d | 2179 | could possibly go wrong? |
d7889f52 JH |
2180 | |
2181 | Maybe simply that your function did not need to be exported in the | |
2182 | first place. Perl has a long and not so glorious history of exporting | |
2183 | functions that it should not have. | |
2184 | ||
2185 | If the function is used only inside one source code file, make it | |
2186 | static. See the discussion about F<embed.pl> in L<perlguts>. | |
2187 | ||
2188 | If the function is used across several files, but intended only for | |
2189 | Perl's internal use (and this should be the common case), do not | |
2190 | export it to the public API. See the discussion about F<embed.pl> | |
2191 | in L<perlguts>. | |
2192 | ||
2193 | =back | |
2194 | ||
5b38b9cd | 2195 | =head2 Portability problems |
d7889f52 JH |
2196 | |
2197 | The following are common causes of compilation and/or execution | |
2198 | failures, not common to Perl as such. The C FAQ is good bedtime | |
0bec6c03 | 2199 | reading. Please test your changes with as many C compilers and |
ac036724 | 2200 | platforms as possible; we will, anyway, and it's nice to save |
0bec6c03 JH |
2201 | oneself from public embarrassment. |
2202 | ||
9aaf14db RGS |
2203 | If using gcc, you can add the C<-std=c89> option which will hopefully |
2204 | catch most of these unportabilities. (However it might also catch | |
2205 | incompatibilities in your system's header files.) | |
d1307786 | 2206 | |
a8e98a71 JH |
2207 | Use the Configure C<-Dgccansipedantic> flag to enable the gcc |
2208 | C<-ansi -pedantic> flags which enforce stricter ANSI rules. | |
2209 | ||
def4ed7d JH |
2210 | If using the C<gcc -Wall> note that not all the possible warnings |
2211 | (like C<-Wunitialized>) are given unless you also compile with C<-O>. | |
2212 | ||
2213 | Note that if using gcc, starting from Perl 5.9.5 the Perl core source | |
2214 | code files (the ones at the top level of the source code distribution, | |
2215 | but not e.g. the extensions under ext/) are automatically compiled | |
2216 | with as many as possible of the C<-std=c89>, C<-ansi>, C<-pedantic>, | |
2217 | and a selection of C<-W> flags (see cflags.SH). | |
27565cb6 | 2218 | |
0bec6c03 | 2219 | Also study L<perlport> carefully to avoid any bad assumptions |
def4ed7d | 2220 | about the operating system, filesystems, and so forth. |
0bec6c03 | 2221 | |
606fd33d | 2222 | You may once in a while try a "make microperl" to see whether we |
63796a85 | 2223 | can still compile Perl with just the bare minimum of interfaces. |
606fd33d | 2224 | (See README.micro.) |
ee9468a2 | 2225 | |
0bec6c03 | 2226 | Do not assume an operating system indicates a certain compiler. |
d7889f52 JH |
2227 | |
2228 | =over 4 | |
2229 | ||
2230 | =item * | |
2231 | ||
2232 | Casting pointers to integers or casting integers to pointers | |
2233 | ||
2234 | void castaway(U8* p) | |
2235 | { | |
2236 | IV i = p; | |
2237 | ||
2238 | or | |
2239 | ||
2240 | void castaway(U8* p) | |
2241 | { | |
2242 | IV i = (IV)p; | |
2243 | ||
ee9468a2 | 2244 | Both are bad, and broken, and unportable. Use the PTR2IV() |
d7889f52 JH |
2245 | macro that does it right. (Likewise, there are PTR2UV(), PTR2NV(), |
2246 | INT2PTR(), and NUM2PTR().) | |
2247 | ||
2248 | =item * | |
2249 | ||
0bec6c03 JH |
2250 | Casting between data function pointers and data pointers |
2251 | ||
d7889f52 JH |
2252 | Technically speaking casting between function pointers and data |
2253 | pointers is unportable and undefined, but practically speaking | |
2254 | it seems to work, but you should use the FPTR2DPTR() and DPTR2FPTR() | |
0bec6c03 | 2255 | macros. Sometimes you can also play games with unions. |
d7889f52 JH |
2256 | |
2257 | =item * | |
2258 | ||
2259 | Assuming sizeof(int) == sizeof(long) | |
2260 | ||
2261 | There are platforms where longs are 64 bits, and platforms where ints | |
2262 | are 64 bits, and while we are out to shock you, even platforms where | |
2263 | shorts are 64 bits. This is all legal according to the C standard. | |
2264 | (In other words, "long long" is not a portable way to specify 64 bits, | |
2265 | and "long long" is not even guaranteed to be any wider than "long".) | |
63796a85 JH |
2266 | |
2267 | Instead, use the definitions IV, UV, IVSIZE, I32SIZE, and so forth. | |
2268 | Avoid things like I32 because they are B<not> guaranteed to be | |
2269 | I<exactly> 32 bits, they are I<at least> 32 bits, nor are they | |
2270 | guaranteed to be B<int> or B<long>. If you really explicitly need | |
2271 | 64-bit variables, use I64 and U64, but only if guarded by HAS_QUAD. | |
d7889f52 JH |
2272 | |
2273 | =item * | |
2274 | ||
2275 | Assuming one can dereference any type of pointer for any type of data | |
2276 | ||
2277 | char *p = ...; | |
def4ed7d | 2278 | long pony = *p; /* BAD */ |
d7889f52 JH |
2279 | |
2280 | Many platforms, quite rightly so, will give you a core dump instead | |
2281 | of a pony if the p happens not be correctly aligned. | |
2282 | ||
2283 | =item * | |
2284 | ||
2285 | Lvalue casts | |
2286 | ||
def4ed7d | 2287 | (int)*p = ...; /* BAD */ |
d7889f52 JH |
2288 | |
2289 | Simply not portable. Get your lvalue to be of the right type, | |
27565cb6 JH |
2290 | or maybe use temporary variables, or dirty tricks with unions. |
2291 | ||
2292 | =item * | |
2293 | ||
606fd33d JH |
2294 | Assume B<anything> about structs (especially the ones you |
2295 | don't control, like the ones coming from the system headers) | |
27565cb6 JH |
2296 | |
2297 | =over 8 | |
2298 | ||
2299 | =item * | |
2300 | ||
2301 | That a certain field exists in a struct | |
2302 | ||
2303 | =item * | |
2304 | ||
902821cc | 2305 | That no other fields exist besides the ones you know of |
27565cb6 JH |
2306 | |
2307 | =item * | |
2308 | ||
606fd33d | 2309 | That a field is of certain signedness, sizeof, or type |
27565cb6 JH |
2310 | |
2311 | =item * | |
2312 | ||
2313 | That the fields are in a certain order | |
2314 | ||
606fd33d JH |
2315 | =over 8 |
2316 | ||
27565cb6 JH |
2317 | =item * |
2318 | ||
606fd33d JH |
2319 | While C guarantees the ordering specified in the struct definition, |
2320 | between different platforms the definitions might differ | |
2321 | ||
2322 | =back | |
27565cb6 JH |
2323 | |
2324 | =item * | |
2325 | ||
606fd33d JH |
2326 | That the sizeof(struct) or the alignments are the same everywhere |
2327 | ||
2328 | =over 8 | |
27565cb6 JH |
2329 | |
2330 | =item * | |
2331 | ||
606fd33d JH |
2332 | There might be padding bytes between the fields to align the fields - |
2333 | the bytes can be anything | |
2334 | ||
2335 | =item * | |
2336 | ||
2337 | Structs are required to be aligned to the maximum alignment required | |
2338 | by the fields - which for native types is for usually equivalent to | |
2339 | sizeof() of the field | |
2340 | ||
2341 | =back | |
27565cb6 JH |
2342 | |
2343 | =back | |
d7889f52 JH |
2344 | |
2345 | =item * | |
2346 | ||
2bbc8d55 SP |
2347 | Assuming the character set is ASCIIish |
2348 | ||
2349 | Perl can compile and run under EBCDIC platforms. See L<perlebcdic>. | |
2350 | This is transparent for the most part, but because the character sets | |
2351 | differ, you shouldn't use numeric (decimal, octal, nor hex) constants | |
2352 | to refer to characters. You can safely say 'A', but not 0x41. | |
2353 | You can safely say '\n', but not \012. | |
2354 | If a character doesn't have a trivial input form, you can | |
2355 | create a #define for it in both C<utfebcdic.h> and C<utf8.h>, so that | |
2356 | it resolves to different values depending on the character set being used. | |
2357 | (There are three different EBCDIC character sets defined in C<utfebcdic.h>, | |
2358 | so it might be best to insert the #define three times in that file.) | |
2359 | ||
2360 | Also, the range 'A' - 'Z' in ASCII is an unbroken sequence of 26 upper case | |
2361 | alphabetic characters. That is not true in EBCDIC. Nor for 'a' to 'z'. | |
2362 | But '0' - '9' is an unbroken range in both systems. Don't assume anything | |
2363 | about other ranges. | |
2364 | ||
2365 | Many of the comments in the existing code ignore the possibility of EBCDIC, | |
2366 | and may be wrong therefore, even if the code works. | |
2367 | This is actually a tribute to the successful transparent insertion of being | |
fe749c9a | 2368 | able to handle EBCDIC without having to change pre-existing code. |
2bbc8d55 SP |
2369 | |
2370 | UTF-8 and UTF-EBCDIC are two different encodings used to represent Unicode | |
2371 | code points as sequences of bytes. Macros | |
2372 | with the same names (but different definitions) | |
2373 | in C<utf8.h> and C<utfebcdic.h> | |
fe749c9a KW |
2374 | are used to allow the calling code to think that there is only one such |
2375 | encoding. | |
2376 | This is almost always referred to as C<utf8>, but it means the EBCDIC version | |
2377 | as well. Again, comments in the code may well be wrong even if the code itself | |
2378 | is right. | |
2bbc8d55 SP |
2379 | For example, the concept of C<invariant characters> differs between ASCII and |
2380 | EBCDIC. | |
2381 | On ASCII platforms, only characters that do not have the high-order | |
2382 | bit set (i.e. whose ordinals are strict ASCII, 0 - 127) | |
2383 | are invariant, and the documentation and comments in the code | |
2384 | may assume that, | |
2385 | often referring to something like, say, C<hibit>. | |
2386 | The situation differs and is not so simple on EBCDIC machines, but as long as | |
2387 | the code itself uses the C<NATIVE_IS_INVARIANT()> macro appropriately, it | |
2388 | works, even if the comments are wrong. | |
2389 | ||
2390 | =item * | |
2391 | ||
2392 | Assuming the character set is just ASCII | |
2393 | ||
2394 | ASCII is a 7 bit encoding, but bytes have 8 bits in them. The 128 extra | |
2395 | characters have different meanings depending on the locale. Absent a locale, | |
2396 | currently these extra characters are generally considered to be unassigned, | |
2397 | and this has presented some problems. | |
e1b711da | 2398 | This is being changed starting in 5.12 so that these characters will |
2bbc8d55 SP |
2399 | be considered to be Latin-1 (ISO-8859-1). |
2400 | ||
2401 | =item * | |
2402 | ||
0bec6c03 JH |
2403 | Mixing #define and #ifdef |
2404 | ||
2405 | #define BURGLE(x) ... \ | |
def4ed7d | 2406 | #ifdef BURGLE_OLD_STYLE /* BAD */ |
0bec6c03 JH |
2407 | ... do it the old way ... \ |
2408 | #else | |
2409 | ... do it the new way ... \ | |
2410 | #endif | |
2411 | ||
ee9468a2 RGS |
2412 | You cannot portably "stack" cpp directives. For example in the above |
2413 | you need two separate BURGLE() #defines, one for each #ifdef branch. | |
2414 | ||
2415 | =item * | |
2416 | ||
2bbc8d55 | 2417 | Adding non-comment stuff after #endif or #else |
ee9468a2 RGS |
2418 | |
2419 | #ifdef SNOSH | |
2420 | ... | |
def4ed7d | 2421 | #else !SNOSH /* BAD */ |
ee9468a2 | 2422 | ... |
def4ed7d | 2423 | #endif SNOSH /* BAD */ |
ee9468a2 | 2424 | |
def4ed7d JH |
2425 | The #endif and #else cannot portably have anything non-comment after |
2426 | them. If you want to document what is going (which is a good idea | |
2427 | especially if the branches are long), use (C) comments: | |
ee9468a2 RGS |
2428 | |
2429 | #ifdef SNOSH | |
2430 | ... | |
2431 | #else /* !SNOSH */ | |
2432 | ... | |
2433 | #endif /* SNOSH */ | |
2434 | ||
2435 | The gcc option C<-Wendif-labels> warns about the bad variant | |
2436 | (by default on starting from Perl 5.9.4). | |
0bec6c03 JH |
2437 | |
2438 | =item * | |
2439 | ||
27565cb6 JH |
2440 | Having a comma after the last element of an enum list |
2441 | ||
2442 | enum color { | |
2443 | CERULEAN, | |
2444 | CHARTREUSE, | |
def4ed7d | 2445 | CINNABAR, /* BAD */ |
27565cb6 JH |
2446 | }; |
2447 | ||
2448 | is not portable. Leave out the last comma. | |
2449 | ||
2450 | Also note that whether enums are implicitly morphable to ints | |
2451 | varies between compilers, you might need to (int). | |
2452 | ||
2453 | =item * | |
2454 | ||
d7889f52 JH |
2455 | Using //-comments |
2456 | ||
def4ed7d | 2457 | // This function bamfoodles the zorklator. /* BAD */ |
d7889f52 JH |
2458 | |
2459 | That is C99 or C++. Perl is C89. Using the //-comments is silently | |
0bec6c03 JH |
2460 | allowed by many C compilers but cranking up the ANSI C89 strictness |
2461 | (which we like to do) causes the compilation to fail. | |
d7889f52 JH |
2462 | |
2463 | =item * | |
2464 | ||
2465 | Mixing declarations and code | |
2466 | ||
2467 | void zorklator() | |
2468 | { | |
2469 | int n = 3; | |
def4ed7d | 2470 | set_zorkmids(n); /* BAD */ |
d7889f52 JH |
2471 | int q = 4; |
2472 | ||
0bec6c03 JH |
2473 | That is C99 or C++. Some C compilers allow that, but you shouldn't. |
2474 | ||
63796a85 JH |
2475 | The gcc option C<-Wdeclaration-after-statements> scans for such problems |
2476 | (by default on starting from Perl 5.9.4). | |
2477 | ||
0bec6c03 JH |
2478 | =item * |
2479 | ||
2480 | Introducing variables inside for() | |
2481 | ||
def4ed7d | 2482 | for(int i = ...; ...; ...) { /* BAD */ |
0bec6c03 JH |
2483 | |
2484 | That is C99 or C++. While it would indeed be awfully nice to have that | |
2485 | also in C89, to limit the scope of the loop variable, alas, we cannot. | |
d7889f52 JH |
2486 | |
2487 | =item * | |
2488 | ||
2489 | Mixing signed char pointers with unsigned char pointers | |
2490 | ||
2491 | int foo(char *s) { ... } | |
2492 | ... | |
2493 | unsigned char *t = ...; /* Or U8* t = ... */ | |
def4ed7d | 2494 | foo(t); /* BAD */ |
d7889f52 JH |
2495 | |
2496 | While this is legal practice, it is certainly dubious, and downright | |
2497 | fatal in at least one platform: for example VMS cc considers this a | |
def4ed7d JH |
2498 | fatal error. One cause for people often making this mistake is that a |
2499 | "naked char" and therefore dereferencing a "naked char pointer" have | |
2500 | an undefined signedness: it depends on the compiler and the flags of | |
2501 | the compiler and the underlying platform whether the result is signed | |
2502 | or unsigned. For this very same reason using a 'char' as an array | |
2503 | index is bad. | |
d7889f52 JH |
2504 | |
2505 | =item * | |
2506 | ||
2507 | Macros that have string constants and their arguments as substrings of | |
2508 | the string constants | |
2509 | ||
def4ed7d | 2510 | #define FOO(n) printf("number = %d\n", n) /* BAD */ |
d7889f52 JH |
2511 | FOO(10); |
2512 | ||
2513 | Pre-ANSI semantics for that was equivalent to | |
2514 | ||
2515 | printf("10umber = %d\10"); | |
2516 | ||
0bec6c03 JH |
2517 | which is probably not what you were expecting. Unfortunately at least |
2518 | one reasonably common and modern C compiler does "real backward | |
63796a85 | 2519 | compatibility" here, in AIX that is what still happens even though the |
0bec6c03 JH |
2520 | rest of the AIX compiler is very happily C89. |
2521 | ||
2522 | =item * | |
2523 | ||
ee9468a2 RGS |
2524 | Using printf formats for non-basic C types |
2525 | ||
2526 | IV i = ...; | |
def4ed7d | 2527 | printf("i = %d\n", i); /* BAD */ |
ee9468a2 RGS |
2528 | |
2529 | While this might by accident work in some platform (where IV happens | |
2530 | to be an C<int>), in general it cannot. IV might be something larger. | |
2531 | Even worse the situation is with more specific types (defined by Perl's | |
2532 | configuration step in F<config.h>): | |
2533 | ||
2534 | Uid_t who = ...; | |
def4ed7d | 2535 | printf("who = %d\n", who); /* BAD */ |
ee9468a2 RGS |
2536 | |
2537 | The problem here is that Uid_t might be not only not C<int>-wide | |
2538 | but it might also be unsigned, in which case large uids would be | |
2539 | printed as negative values. | |
2540 | ||
2541 | There is no simple solution to this because of printf()'s limited | |
2542 | intelligence, but for many types the right format is available as | |
2543 | with either 'f' or '_f' suffix, for example: | |
2544 | ||
2545 | IVdf /* IV in decimal */ | |
2546 | UVxf /* UV is hexadecimal */ | |
2547 | ||
2548 | printf("i = %"IVdf"\n", i); /* The IVdf is a string constant. */ | |
2549 | ||
2550 | Uid_t_f /* Uid_t in decimal */ | |
2551 | ||
2552 | printf("who = %"Uid_t_f"\n", who); | |
2553 | ||
63796a85 JH |
2554 | Or you can try casting to a "wide enough" type: |
2555 | ||
2556 | printf("i = %"IVdf"\n", (IV)something_very_small_and_signed); | |
2557 | ||
2558 | Also remember that the C<%p> format really does require a void pointer: | |
2559 | ||
2560 | U8* p = ...; | |
2561 | printf("p = %p\n", (void*)p); | |
2562 | ||
ee9468a2 RGS |
2563 | The gcc option C<-Wformat> scans for such problems. |
2564 | ||
2565 | =item * | |
2566 | ||
0bec6c03 JH |
2567 | Blindly using variadic macros |
2568 | ||
63796a85 JH |
2569 | gcc has had them for a while with its own syntax, and C99 brought |
2570 | them with a standardized syntax. Don't use the former, and use | |
2571 | the latter only if the HAS_C99_VARIADIC_MACROS is defined. | |
0bec6c03 JH |
2572 | |
2573 | =item * | |
2574 | ||
2575 | Blindly passing va_list | |
2576 | ||
2577 | Not all platforms support passing va_list to further varargs (stdarg) | |
2578 | functions. The right thing to do is to copy the va_list using the | |
2579 | Perl_va_copy() if the NEED_VA_COPY is defined. | |
d7889f52 | 2580 | |
ee9468a2 RGS |
2581 | =item * |
2582 | ||
e5afc1ae | 2583 | Using gcc statement expressions |
63796a85 | 2584 | |
def4ed7d | 2585 | val = ({...;...;...}); /* BAD */ |
63796a85 | 2586 | |
def4ed7d JH |
2587 | While a nice extension, it's not portable. The Perl code does |
2588 | admittedly use them if available to gain some extra speed | |
2589 | (essentially as a funky form of inlining), but you shouldn't. | |
63796a85 JH |
2590 | |
2591 | =item * | |
2592 | ||
2bbc8d55 | 2593 | Binding together several statements in a macro |
63796a85 JH |
2594 | |
2595 | Use the macros STMT_START and STMT_END. | |
2596 | ||
2597 | STMT_START { | |
2598 | ... | |
2599 | } STMT_END | |
2600 | ||
2601 | =item * | |
2602 | ||
ee9468a2 RGS |
2603 | Testing for operating systems or versions when should be testing for features |
2604 | ||
def4ed7d | 2605 | #ifdef __FOONIX__ /* BAD */ |
ee9468a2 RGS |
2606 | foo = quux(); |
2607 | #endif | |
2608 | ||
2609 | Unless you know with 100% certainty that quux() is only ever available | |
2610 | for the "Foonix" operating system B<and> that is available B<and> | |
2611 | correctly working for B<all> past, present, B<and> future versions of | |
2612 | "Foonix", the above is very wrong. This is more correct (though still | |
2613 | not perfect, because the below is a compile-time check): | |
2614 | ||
2615 | #ifdef HAS_QUUX | |
2616 | foo = quux(); | |
2617 | #endif | |
2618 | ||
def4ed7d | 2619 | How does the HAS_QUUX become defined where it needs to be? Well, if |
e1020413 | 2620 | Foonix happens to be Unixy enough to be able to run the Configure |
ee9468a2 RGS |
2621 | script, and Configure has been taught about detecting and testing |
2622 | quux(), the HAS_QUUX will be correctly defined. In other platforms, | |
2623 | the corresponding configuration step will hopefully do the same. | |
2624 | ||
2625 | In a pinch, if you cannot wait for Configure to be educated, | |
2626 | or if you have a good hunch of where quux() might be available, | |
2627 | you can temporarily try the following: | |
2628 | ||
2629 | #if (defined(__FOONIX__) || defined(__BARNIX__)) | |
2630 | # define HAS_QUUX | |
2631 | #endif | |
2632 | ||
2633 | ... | |
2634 | ||
2635 | #ifdef HAS_QUUX | |
2636 | foo = quux(); | |
2637 | #endif | |
2638 | ||
2639 | But in any case, try to keep the features and operating systems separate. | |
2640 | ||
d7889f52 JH |
2641 | =back |
2642 | ||
ad7244db JH |
2643 | =head2 Problematic System Interfaces |
2644 | ||
2645 | =over 4 | |
2646 | ||
2647 | =item * | |
2648 | ||
353c6505 | 2649 | malloc(0), realloc(0), calloc(0, 0) are non-portable. To be portable |
ad7244db JH |
2650 | allocate at least one byte. (In general you should rarely need to |
2651 | work at this low level, but instead use the various malloc wrappers.) | |
2652 | ||
2653 | =item * | |
2654 | ||
2655 | snprintf() - the return type is unportable. Use my_snprintf() instead. | |
2656 | ||
2657 | =back | |
2658 | ||
d7889f52 JH |
2659 | =head2 Security problems |
2660 | ||
2661 | Last but not least, here are various tips for safer coding. | |
2662 | ||
2663 | =over 4 | |
2664 | ||
2665 | =item * | |
2666 | ||
2667 | Do not use gets() | |
2668 | ||
2669 | Or we will publicly ridicule you. Seriously. | |
2670 | ||
2671 | =item * | |
2672 | ||
d1307786 | 2673 | Do not use strcpy() or strcat() or strncpy() or strncat() |
d7889f52 | 2674 | |
d1307786 JH |
2675 | Use my_strlcpy() and my_strlcat() instead: they either use the native |
2676 | implementation, or Perl's own implementation (borrowed from the public | |
2677 | domain implementation of INN). | |
d7889f52 JH |
2678 | |
2679 | =item * | |
2680 | ||
2681 | Do not use sprintf() or vsprintf() | |
2682 | ||
0bec6c03 | 2683 | If you really want just plain byte strings, use my_snprintf() |
64d9b66b | 2684 | and my_vsnprintf() instead, which will try to use snprintf() and |
0bec6c03 JH |
2685 | vsnprintf() if those safer APIs are available. If you want something |
2686 | fancier than a plain byte string, use SVs and Perl_sv_catpvf(). | |
d7889f52 JH |
2687 | |
2688 | =back | |
2689 | ||
902b9dbf MLF |
2690 | =head1 EXTERNAL TOOLS FOR DEBUGGING PERL |
2691 | ||
2692 | Sometimes it helps to use external tools while debugging and | |
2693 | testing Perl. This section tries to guide you through using | |
2694 | some common testing and debugging tools with Perl. This is | |
2695 | meant as a guide to interfacing these tools with Perl, not | |
2696 | as any kind of guide to the use of the tools themselves. | |
2697 | ||
a958818a JH |
2698 | B<NOTE 1>: Running under memory debuggers such as Purify, valgrind, or |
2699 | Third Degree greatly slows down the execution: seconds become minutes, | |
2700 | minutes become hours. For example as of Perl 5.8.1, the | |
2701 | ext/Encode/t/Unicode.t takes extraordinarily long to complete under | |
2702 | e.g. Purify, Third Degree, and valgrind. Under valgrind it takes more | |
ac036724 | 2703 | than six hours, even on a snappy computer. The said test must be |
a958818a JH |
2704 | doing something that is quite unfriendly for memory debuggers. If you |
2705 | don't feel like waiting, that you can simply kill away the perl | |
2706 | process. | |
2707 | ||
2708 | B<NOTE 2>: To minimize the number of memory leak false alarms (see | |
ac036724 | 2709 | L</PERL_DESTRUCT_LEVEL> for more information), you have to set the |
2710 | environment variable PERL_DESTRUCT_LEVEL to 2. | |
2711 | ||
2712 | For csh-like shells: | |
a958818a JH |
2713 | |
2714 | setenv PERL_DESTRUCT_LEVEL 2 | |
2715 | ||
ac036724 | 2716 | For Bourne-type shells: |
a958818a JH |
2717 | |
2718 | PERL_DESTRUCT_LEVEL=2 | |
2719 | export PERL_DESTRUCT_LEVEL | |
2720 | ||
ac036724 | 2721 | In Unixy environments you can also use the C<env> command: |
a958818a JH |
2722 | |
2723 | env PERL_DESTRUCT_LEVEL=2 valgrind ./perl -Ilib ... | |
a1b65709 | 2724 | |
37c0adeb JH |
2725 | B<NOTE 3>: There are known memory leaks when there are compile-time |
2726 | errors within eval or require, seeing C<S_doeval> in the call stack | |
2727 | is a good sign of these. Fixing these leaks is non-trivial, | |
2728 | unfortunately, but they must be fixed eventually. | |
2729 | ||
f50e5b73 MH |
2730 | B<NOTE 4>: L<DynaLoader> will not clean up after itself completely |
2731 | unless Perl is built with the Configure option | |
2732 | C<-Accflags=-DDL_UNLOAD_ALL_AT_EXIT>. | |
2733 | ||
902b9dbf MLF |
2734 | =head2 Rational Software's Purify |
2735 | ||
2736 | Purify is a commercial tool that is helpful in identifying | |
2737 | memory overruns, wild pointers, memory leaks and other such | |
2738 | badness. Perl must be compiled in a specific way for | |
2739 | optimal testing with Purify. Purify is available under | |
2740 | Windows NT, Solaris, HP-UX, SGI, and Siemens Unix. | |
2741 | ||
902b9dbf MLF |
2742 | =head2 Purify on Unix |
2743 | ||
2744 | On Unix, Purify creates a new Perl binary. To get the most | |
2745 | benefit out of Purify, you should create the perl to Purify | |
2746 | using: | |
2747 | ||
2748 | sh Configure -Accflags=-DPURIFY -Doptimize='-g' \ | |
2749 | -Uusemymalloc -Dusemultiplicity | |
2750 | ||
2751 | where these arguments mean: | |
2752 | ||
2753 | =over 4 | |
2754 | ||
2755 | =item -Accflags=-DPURIFY | |
2756 | ||
2757 | Disables Perl's arena memory allocation functions, as well as | |
2758 | forcing use of memory allocation functions derived from the | |
2759 | system malloc. | |
2760 | ||
2761 | =item -Doptimize='-g' | |
2762 | ||
2763 | Adds debugging information so that you see the exact source | |
2764 | statements where the problem occurs. Without this flag, all | |
2765 | you will see is the source filename of where the error occurred. | |
2766 | ||
2767 | =item -Uusemymalloc | |
2768 | ||
2769 | Disable Perl's malloc so that Purify can more closely monitor | |
2770 | allocations and leaks. Using Perl's malloc will make Purify | |
2771 | report most leaks in the "potential" leaks category. | |
2772 | ||
2773 | =item -Dusemultiplicity | |
2774 | ||
2775 | Enabling the multiplicity option allows perl to clean up | |
2776 | thoroughly when the interpreter shuts down, which reduces the | |
2777 | number of bogus leak reports from Purify. | |
2778 | ||
2779 | =back | |
2780 | ||
2781 | Once you've compiled a perl suitable for Purify'ing, then you | |
2782 | can just: | |
2783 | ||
07aa3531 | 2784 | make pureperl |
902b9dbf MLF |
2785 | |
2786 | which creates a binary named 'pureperl' that has been Purify'ed. | |
2787 | This binary is used in place of the standard 'perl' binary | |
2788 | when you want to debug Perl memory problems. | |
2789 | ||
2790 | As an example, to show any memory leaks produced during the | |
2791 | standard Perl testset you would create and run the Purify'ed | |
2792 | perl as: | |
2793 | ||
2794 | make pureperl | |
2795 | cd t | |
07aa3531 | 2796 | ../pureperl -I../lib harness |
902b9dbf MLF |
2797 | |
2798 | which would run Perl on test.pl and report any memory problems. | |
2799 | ||
2800 | Purify outputs messages in "Viewer" windows by default. If | |
2801 | you don't have a windowing environment or if you simply | |
2802 | want the Purify output to unobtrusively go to a log file | |
2803 | instead of to the interactive window, use these following | |
2804 | options to output to the log file "perl.log": | |
2805 | ||
2806 | setenv PURIFYOPTIONS "-chain-length=25 -windows=no \ | |
2807 | -log-file=perl.log -append-logfile=yes" | |
2808 | ||
2809 | If you plan to use the "Viewer" windows, then you only need this option: | |
2810 | ||
2811 | setenv PURIFYOPTIONS "-chain-length=25" | |
2812 | ||
c406981e JH |
2813 | In Bourne-type shells: |
2814 | ||
98631ff8 JL |
2815 | PURIFYOPTIONS="..." |
2816 | export PURIFYOPTIONS | |
c406981e JH |
2817 | |
2818 | or if you have the "env" utility: | |
2819 | ||
98631ff8 | 2820 | env PURIFYOPTIONS="..." ../pureperl ... |
c406981e | 2821 | |
902b9dbf MLF |
2822 | =head2 Purify on NT |
2823 | ||
2824 | Purify on Windows NT instruments the Perl binary 'perl.exe' | |
2825 | on the fly. There are several options in the makefile you | |
2826 | should change to get the most use out of Purify: | |
2827 | ||
2828 | =over 4 | |
2829 | ||
2830 | =item DEFINES | |
2831 | ||
2832 | You should add -DPURIFY to the DEFINES line so the DEFINES | |
2833 | line looks something like: | |
2834 | ||
195c30ce | 2835 | DEFINES = -DWIN32 -D_CONSOLE -DNO_STRICT $(CRYPT_FLAG) -DPURIFY=1 |
902b9dbf MLF |
2836 | |
2837 | to disable Perl's arena memory allocation functions, as | |
2838 | well as to force use of memory allocation functions derived | |
2839 | from the system malloc. | |
2840 | ||
2841 | =item USE_MULTI = define | |
2842 | ||
2843 | Enabling the multiplicity option allows perl to clean up | |
2844 | thoroughly when the interpreter shuts down, which reduces the | |
2845 | number of bogus leak reports from Purify. | |
2846 | ||
2847 | =item #PERL_MALLOC = define | |
2848 | ||
2849 | Disable Perl's malloc so that Purify can more closely monitor | |
2850 | allocations and leaks. Using Perl's malloc will make Purify | |
2851 | report most leaks in the "potential" leaks category. | |
2852 | ||
2853 | =item CFG = Debug | |
2854 | ||
2855 | Adds debugging information so that you see the exact source | |
2856 | statements where the problem occurs. Without this flag, all | |
2857 | you will see is the source filename of where the error occurred. | |
2858 | ||
2859 | =back | |
2860 | ||
2861 | As an example, to show any memory leaks produced during the | |
2862 | standard Perl testset you would create and run Purify as: | |
2863 | ||
2864 | cd win32 | |
2865 | make | |
2866 | cd ../t | |
07aa3531 | 2867 | purify ../perl -I../lib harness |
902b9dbf MLF |
2868 | |
2869 | which would instrument Perl in memory, run Perl on test.pl, | |
2870 | then finally report any memory problems. | |
2871 | ||
7a834142 JH |
2872 | =head2 valgrind |
2873 | ||
2874 | The excellent valgrind tool can be used to find out both memory leaks | |
9df8f87f LB |
2875 | and illegal memory accesses. As of version 3.3.0, Valgrind only |
2876 | supports Linux on x86, x86-64 and PowerPC. The special "test.valgrind" | |
2877 | target can be used to run the tests under valgrind. Found errors | |
2878 | and memory leaks are logged in files named F<testfile.valgrind>. | |
07aa3531 JC |
2879 | |
2880 | Valgrind also provides a cachegrind tool, invoked on perl as: | |
2881 | ||
038c294a | 2882 | VG_OPTS=--tool=cachegrind make test.valgrind |
d44161bf MHM |
2883 | |
2884 | As system libraries (most notably glibc) are also triggering errors, | |
2885 | valgrind allows to suppress such errors using suppression files. The | |
2886 | default suppression file that comes with valgrind already catches a lot | |
2887 | of them. Some additional suppressions are defined in F<t/perl.supp>. | |
7a834142 JH |
2888 | |
2889 | To get valgrind and for more information see | |
2890 | ||
2891 | http://developer.kde.org/~sewardj/ | |
2892 | ||
f134cc4e | 2893 | =head2 Compaq's/Digital's/HP's Third Degree |
09187cb1 JH |
2894 | |
2895 | Third Degree is a tool for memory leak detection and memory access checks. | |
2896 | It is one of the many tools in the ATOM toolkit. The toolkit is only | |
2897 | available on Tru64 (formerly known as Digital UNIX formerly known as | |
2898 | DEC OSF/1). | |
2899 | ||
2900 | When building Perl, you must first run Configure with -Doptimize=-g | |
2901 | and -Uusemymalloc flags, after that you can use the make targets | |
51a35ef1 JH |
2902 | "perl.third" and "test.third". (What is required is that Perl must be |
2903 | compiled using the C<-g> flag, you may need to re-Configure.) | |
09187cb1 | 2904 | |
64cea5fd | 2905 | The short story is that with "atom" you can instrument the Perl |
83f0ef60 | 2906 | executable to create a new executable called F<perl.third>. When the |
4ae3d70a | 2907 | instrumented executable is run, it creates a log of dubious memory |
83f0ef60 | 2908 | traffic in file called F<perl.3log>. See the manual pages of atom and |
4ae3d70a JH |
2909 | third for more information. The most extensive Third Degree |
2910 | documentation is available in the Compaq "Tru64 UNIX Programmer's | |
2911 | Guide", chapter "Debugging Programs with Third Degree". | |
64cea5fd | 2912 | |
9c54ecba | 2913 | The "test.third" leaves a lot of files named F<foo_bar.3log> in the t/ |
64cea5fd JH |
2914 | subdirectory. There is a problem with these files: Third Degree is so |
2915 | effective that it finds problems also in the system libraries. | |
9c54ecba JH |
2916 | Therefore you should used the Porting/thirdclean script to cleanup |
2917 | the F<*.3log> files. | |
64cea5fd JH |
2918 | |
2919 | There are also leaks that for given certain definition of a leak, | |
2920 | aren't. See L</PERL_DESTRUCT_LEVEL> for more information. | |
2921 | ||
2922 | =head2 PERL_DESTRUCT_LEVEL | |
2923 | ||
a958818a JH |
2924 | If you want to run any of the tests yourself manually using e.g. |
2925 | valgrind, or the pureperl or perl.third executables, please note that | |
2926 | by default perl B<does not> explicitly cleanup all the memory it has | |
2927 | allocated (such as global memory arenas) but instead lets the exit() | |
2928 | of the whole program "take care" of such allocations, also known as | |
2929 | "global destruction of objects". | |
64cea5fd JH |
2930 | |
2931 | There is a way to tell perl to do complete cleanup: set the | |
2932 | environment variable PERL_DESTRUCT_LEVEL to a non-zero value. | |
2933 | The t/TEST wrapper does set this to 2, and this is what you | |
2934 | need to do too, if you don't want to see the "global leaks": | |
1f56d61a | 2935 | For example, for "third-degreed" Perl: |
64cea5fd | 2936 | |
1f56d61a | 2937 | env PERL_DESTRUCT_LEVEL=2 ./perl.third -Ilib t/foo/bar.t |
09187cb1 | 2938 | |
414f2397 RGS |
2939 | (Note: the mod_perl apache module uses also this environment variable |
2940 | for its own purposes and extended its semantics. Refer to the mod_perl | |
287a822c RGS |
2941 | documentation for more information. Also, spawned threads do the |
2942 | equivalent of setting this variable to the value 1.) | |
5a6c59ef DM |
2943 | |
2944 | If, at the end of a run you get the message I<N scalars leaked>, you can | |
fd0854ff DM |
2945 | recompile with C<-DDEBUG_LEAKING_SCALARS>, which will cause the addresses |
2946 | of all those leaked SVs to be dumped along with details as to where each | |
2947 | SV was originally allocated. This information is also displayed by | |
2948 | Devel::Peek. Note that the extra details recorded with each SV increases | |
2949 | memory usage, so it shouldn't be used in production environments. It also | |
2950 | converts C<new_SV()> from a macro into a real function, so you can use | |
2951 | your favourite debugger to discover where those pesky SVs were allocated. | |
414f2397 | 2952 | |
d7a2c63c MHM |
2953 | If you see that you're leaking memory at runtime, but neither valgrind |
2954 | nor C<-DDEBUG_LEAKING_SCALARS> will find anything, you're probably | |
2955 | leaking SVs that are still reachable and will be properly cleaned up | |
2956 | during destruction of the interpreter. In such cases, using the C<-Dm> | |
2957 | switch can point you to the source of the leak. If the executable was | |
2958 | built with C<-DDEBUG_LEAKING_SCALARS>, C<-Dm> will output SV allocations | |
2959 | in addition to memory allocations. Each SV allocation has a distinct | |
2960 | serial number that will be written on creation and destruction of the SV. | |
2961 | So if you're executing the leaking code in a loop, you need to look for | |
2962 | SVs that are created, but never destroyed between each cycle. If such an | |
2963 | SV is found, set a conditional breakpoint within C<new_SV()> and make it | |
2964 | break only when C<PL_sv_serial> is equal to the serial number of the | |
2965 | leaking SV. Then you will catch the interpreter in exactly the state | |
2966 | where the leaking SV is allocated, which is sufficient in many cases to | |
2967 | find the source of the leak. | |
2968 | ||
2969 | As C<-Dm> is using the PerlIO layer for output, it will by itself | |
2970 | allocate quite a bunch of SVs, which are hidden to avoid recursion. | |
2971 | You can bypass the PerlIO layer if you use the SV logging provided | |
2972 | by C<-DPERL_MEM_LOG> instead. | |
2973 | ||
46c6c7e2 JH |
2974 | =head2 PERL_MEM_LOG |
2975 | ||
10a879f5 JC |
2976 | If compiled with C<-DPERL_MEM_LOG>, both memory and SV allocations go |
2977 | through logging functions, which is handy for breakpoint setting. | |
2978 | ||
2979 | Unless C<-DPERL_MEM_LOG_NOIMPL> is also compiled, the logging | |
2e5b5004 | 2980 | functions read $ENV{PERL_MEM_LOG} to determine whether to log the |
10a879f5 JC |
2981 | event, and if so how: |
2982 | ||
2e5b5004 RGS |
2983 | $ENV{PERL_MEM_LOG} =~ /m/ Log all memory ops |
2984 | $ENV{PERL_MEM_LOG} =~ /s/ Log all SV ops | |
2985 | $ENV{PERL_MEM_LOG} =~ /t/ include timestamp in Log | |
2986 | $ENV{PERL_MEM_LOG} =~ /^(\d+)/ write to FD given (default is 2) | |
10a879f5 JC |
2987 | |
2988 | Memory logging is somewhat similar to C<-Dm> but is independent of | |
2989 | C<-DDEBUGGING>, and at a higher level; all uses of Newx(), Renew(), | |
2e5b5004 | 2990 | and Safefree() are logged with the caller's source code file and line |
10a879f5 JC |
2991 | number (and C function name, if supported by the C compiler). In |
2992 | contrast, C<-Dm> is directly at the point of C<malloc()>. SV logging | |
2993 | is similar. | |
2994 | ||
2995 | Since the logging doesn't use PerlIO, all SV allocations are logged | |
2996 | and no extra SV allocations are introduced by enabling the logging. | |
2997 | If compiled with C<-DDEBUG_LEAKING_SCALARS>, the serial number for | |
2998 | each SV allocation is also logged. | |
d7a2c63c | 2999 | |
51a35ef1 JH |
3000 | =head2 Profiling |
3001 | ||
3002 | Depending on your platform there are various of profiling Perl. | |
3003 | ||
3004 | There are two commonly used techniques of profiling executables: | |
10f58044 | 3005 | I<statistical time-sampling> and I<basic-block counting>. |
51a35ef1 JH |
3006 | |
3007 | The first method takes periodically samples of the CPU program | |
3008 | counter, and since the program counter can be correlated with the code | |
3009 | generated for functions, we get a statistical view of in which | |
3010 | functions the program is spending its time. The caveats are that very | |
3011 | small/fast functions have lower probability of showing up in the | |
3012 | profile, and that periodically interrupting the program (this is | |
3013 | usually done rather frequently, in the scale of milliseconds) imposes | |
3014 | an additional overhead that may skew the results. The first problem | |
3015 | can be alleviated by running the code for longer (in general this is a | |
3016 | good idea for profiling), the second problem is usually kept in guard | |
3017 | by the profiling tools themselves. | |
3018 | ||
10f58044 | 3019 | The second method divides up the generated code into I<basic blocks>. |
51a35ef1 JH |
3020 | Basic blocks are sections of code that are entered only in the |
3021 | beginning and exited only at the end. For example, a conditional jump | |
3022 | starts a basic block. Basic block profiling usually works by | |
10f58044 | 3023 | I<instrumenting> the code by adding I<enter basic block #nnnn> |
51a35ef1 JH |
3024 | book-keeping code to the generated code. During the execution of the |
3025 | code the basic block counters are then updated appropriately. The | |
3026 | caveat is that the added extra code can skew the results: again, the | |
3027 | profiling tools usually try to factor their own effects out of the | |
3028 | results. | |
3029 | ||
83f0ef60 JH |
3030 | =head2 Gprof Profiling |
3031 | ||
e1020413 | 3032 | gprof is a profiling tool available in many Unix platforms, |
51a35ef1 | 3033 | it uses F<statistical time-sampling>. |
83f0ef60 JH |
3034 | |
3035 | You can build a profiled version of perl called "perl.gprof" by | |
51a35ef1 JH |
3036 | invoking the make target "perl.gprof" (What is required is that Perl |
3037 | must be compiled using the C<-pg> flag, you may need to re-Configure). | |
3038 | Running the profiled version of Perl will create an output file called | |
3039 | F<gmon.out> is created which contains the profiling data collected | |
3040 | during the execution. | |
83f0ef60 JH |
3041 | |
3042 | The gprof tool can then display the collected data in various ways. | |
3043 | Usually gprof understands the following options: | |
3044 | ||
3045 | =over 4 | |
3046 | ||
3047 | =item -a | |
3048 | ||
3049 | Suppress statically defined functions from the profile. | |
3050 | ||
3051 | =item -b | |
3052 | ||
3053 | Suppress the verbose descriptions in the profile. | |
3054 | ||
3055 | =item -e routine | |
3056 | ||
3057 | Exclude the given routine and its descendants from the profile. | |
3058 | ||
3059 | =item -f routine | |
3060 | ||
3061 | Display only the given routine and its descendants in the profile. | |
3062 | ||
3063 | =item -s | |
3064 | ||
3065 | Generate a summary file called F<gmon.sum> which then may be given | |
3066 | to subsequent gprof runs to accumulate data over several runs. | |
3067 | ||
3068 | =item -z | |
3069 | ||
3070 | Display routines that have zero usage. | |
3071 | ||
3072 | =back | |
3073 | ||
3074 | For more detailed explanation of the available commands and output | |
3075 | formats, see your own local documentation of gprof. | |
3076 | ||
038c294a | 3077 | quick hint: |
07aa3531 | 3078 | |
289d61c2 JL |
3079 | $ sh Configure -des -Dusedevel -Doptimize='-pg' && make perl.gprof |
3080 | $ ./perl.gprof someprog # creates gmon.out in current directory | |
3081 | $ gprof ./perl.gprof > out | |
07aa3531 JC |
3082 | $ view out |
3083 | ||
51a35ef1 JH |
3084 | =head2 GCC gcov Profiling |
3085 | ||
10f58044 | 3086 | Starting from GCC 3.0 I<basic block profiling> is officially available |
51a35ef1 JH |
3087 | for the GNU CC. |
3088 | ||
3089 | You can build a profiled version of perl called F<perl.gcov> by | |
3090 | invoking the make target "perl.gcov" (what is required that Perl must | |
3091 | be compiled using gcc with the flags C<-fprofile-arcs | |
3092 | -ftest-coverage>, you may need to re-Configure). | |
3093 | ||
3094 | Running the profiled version of Perl will cause profile output to be | |
3095 | generated. For each source file an accompanying ".da" file will be | |
3096 | created. | |
3097 | ||
3098 | To display the results you use the "gcov" utility (which should | |
3099 | be installed if you have gcc 3.0 or newer installed). F<gcov> is | |
3100 | run on source code files, like this | |
3101 | ||
3102 | gcov sv.c | |
3103 | ||
3104 | which will cause F<sv.c.gcov> to be created. The F<.gcov> files | |
3105 | contain the source code annotated with relative frequencies of | |
3106 | execution indicated by "#" markers. | |
3107 | ||
3108 | Useful options of F<gcov> include C<-b> which will summarise the | |
3109 | basic block, branch, and function call coverage, and C<-c> which | |
3110 | instead of relative frequencies will use the actual counts. For | |
3111 | more information on the use of F<gcov> and basic block profiling | |
3112 | with gcc, see the latest GNU CC manual, as of GCC 3.0 see | |
3113 | ||
3114 | http://gcc.gnu.org/onlinedocs/gcc-3.0/gcc.html | |
3115 | ||
3116 | and its section titled "8. gcov: a Test Coverage Program" | |
3117 | ||
3118 | http://gcc.gnu.org/onlinedocs/gcc-3.0/gcc_8.html#SEC132 | |
3119 | ||
07aa3531 JC |
3120 | quick hint: |
3121 | ||
27837272 AB |
3122 | $ sh Configure -des -Dusedevel -Doptimize='-g' \ |
3123 | -Accflags='-fprofile-arcs -ftest-coverage' \ | |
07aa3531 JC |
3124 | -Aldflags='-fprofile-arcs -ftest-coverage' && make perl.gcov |
3125 | $ rm -f regexec.c.gcov regexec.gcda | |
3126 | $ ./perl.gcov | |
3127 | $ gcov regexec.c | |
3128 | $ view regexec.c.gcov | |
3129 | ||
4ae3d70a JH |
3130 | =head2 Pixie Profiling |
3131 | ||
51a35ef1 JH |
3132 | Pixie is a profiling tool available on IRIX and Tru64 (aka Digital |
3133 | UNIX aka DEC OSF/1) platforms. Pixie does its profiling using | |
10f58044 | 3134 | I<basic-block counting>. |
4ae3d70a | 3135 | |
83f0ef60 | 3136 | You can build a profiled version of perl called F<perl.pixie> by |
51a35ef1 JH |
3137 | invoking the make target "perl.pixie" (what is required is that Perl |
3138 | must be compiled using the C<-g> flag, you may need to re-Configure). | |
3139 | ||
3140 | In Tru64 a file called F<perl.Addrs> will also be silently created, | |
3141 | this file contains the addresses of the basic blocks. Running the | |
3142 | profiled version of Perl will create a new file called "perl.Counts" | |
3143 | which contains the counts for the basic block for that particular | |
3144 | program execution. | |
4ae3d70a | 3145 | |
51a35ef1 | 3146 | To display the results you use the F<prof> utility. The exact |
4ae3d70a JH |
3147 | incantation depends on your operating system, "prof perl.Counts" in |
3148 | IRIX, and "prof -pixie -all -L. perl" in Tru64. | |
3149 | ||
6c41479b JH |
3150 | In IRIX the following prof options are available: |
3151 | ||
3152 | =over 4 | |
3153 | ||
3154 | =item -h | |
3155 | ||
3156 | Reports the most heavily used lines in descending order of use. | |
6e36760b | 3157 | Useful for finding the hotspot lines. |
6c41479b JH |
3158 | |
3159 | =item -l | |
3160 | ||
3161 | Groups lines by procedure, with procedures sorted in descending order of use. | |
3162 | Within a procedure, lines are listed in source order. | |
6e36760b | 3163 | Useful for finding the hotspots of procedures. |
6c41479b JH |
3164 | |
3165 | =back | |
3166 | ||
3167 | In Tru64 the following options are available: | |
3168 | ||
3169 | =over 4 | |
3170 | ||
3958b146 | 3171 | =item -p[rocedures] |
6c41479b | 3172 | |
3958b146 | 3173 | Procedures sorted in descending order by the number of cycles executed |
6e36760b | 3174 | in each procedure. Useful for finding the hotspot procedures. |
6c41479b JH |
3175 | (This is the default option.) |
3176 | ||
24000d2f | 3177 | =item -h[eavy] |
6c41479b | 3178 | |
6e36760b JH |
3179 | Lines sorted in descending order by the number of cycles executed in |
3180 | each line. Useful for finding the hotspot lines. | |
6c41479b | 3181 | |
24000d2f | 3182 | =item -i[nvocations] |
6c41479b | 3183 | |
6e36760b JH |
3184 | The called procedures are sorted in descending order by number of calls |
3185 | made to the procedures. Useful for finding the most used procedures. | |
6c41479b | 3186 | |
24000d2f | 3187 | =item -l[ines] |
6c41479b JH |
3188 | |
3189 | Grouped by procedure, sorted by cycles executed per procedure. | |
6e36760b | 3190 | Useful for finding the hotspots of procedures. |
6c41479b JH |
3191 | |
3192 | =item -testcoverage | |
3193 | ||
3194 | The compiler emitted code for these lines, but the code was unexecuted. | |
3195 | ||
24000d2f | 3196 | =item -z[ero] |
6c41479b JH |
3197 | |
3198 | Unexecuted procedures. | |
3199 | ||
aa500c9e | 3200 | =back |
6c41479b JH |
3201 | |
3202 | For further information, see your system's manual pages for pixie and prof. | |
4ae3d70a | 3203 | |
b8ddf6b3 SB |
3204 | =head2 Miscellaneous tricks |
3205 | ||
3206 | =over 4 | |
3207 | ||
3208 | =item * | |
3209 | ||
cc177e1a | 3210 | Those debugging perl with the DDD frontend over gdb may find the |
b8ddf6b3 SB |
3211 | following useful: |
3212 | ||
3213 | You can extend the data conversion shortcuts menu, so for example you | |
3214 | can display an SV's IV value with one click, without doing any typing. | |
3215 | To do that simply edit ~/.ddd/init file and add after: | |
3216 | ||
3217 | ! Display shortcuts. | |
3218 | Ddd*gdbDisplayShortcuts: \ | |
3219 | /t () // Convert to Bin\n\ | |
3220 | /d () // Convert to Dec\n\ | |
3221 | /x () // Convert to Hex\n\ | |
3222 | /o () // Convert to Oct(\n\ | |
3223 | ||
3224 | the following two lines: | |
3225 | ||
3226 | ((XPV*) (())->sv_any )->xpv_pv // 2pvx\n\ | |
3227 | ((XPVIV*) (())->sv_any )->xiv_iv // 2ivx | |
3228 | ||
3229 | so now you can do ivx and pvx lookups or you can plug there the | |
3230 | sv_peek "conversion": | |
3231 | ||
3232 | Perl_sv_peek(my_perl, (SV*)()) // sv_peek | |
3233 | ||
3234 | (The my_perl is for threaded builds.) | |
3235 | Just remember that every line, but the last one, should end with \n\ | |
3236 | ||
3237 | Alternatively edit the init file interactively via: | |
3238 | 3rd mouse button -> New Display -> Edit Menu | |
3239 | ||
3240 | Note: you can define up to 20 conversion shortcuts in the gdb | |
3241 | section. | |
3242 | ||
9965345d JH |
3243 | =item * |
3244 | ||
7e337ee0 JH |
3245 | If you see in a debugger a memory area mysteriously full of 0xABABABAB |
3246 | or 0xEFEFEFEF, you may be seeing the effect of the Poison() macros, | |
3247 | see L<perlclib>. | |
9965345d | 3248 | |
f1fac472 NC |
3249 | =item * |
3250 | ||
3251 | Under ithreads the optree is read only. If you want to enforce this, to check | |
3252 | for write accesses from buggy code, compile with C<-DPL_OP_SLAB_ALLOC> to | |
3253 | enable the OP slab allocator and C<-DPERL_DEBUG_READONLY_OPS> to enable code | |
3254 | that allocates op memory via C<mmap>, and sets it read-only at run time. | |
3255 | Any write access to an op results in a C<SIGBUS> and abort. | |
3256 | ||
3257 | This code is intended for development only, and may not be portable even to | |
3258 | all Unix variants. Also, it is an 80% solution, in that it isn't able to make | |
3259 | all ops read only. Specifically it | |
3260 | ||
3261 | =over | |
3262 | ||
3263 | =item 1 | |
3264 | ||
3265 | Only sets read-only on all slabs of ops at C<CHECK> time, hence ops allocated | |
3266 | later via C<require> or C<eval> will be re-write | |
3267 | ||
3268 | =item 2 | |
3269 | ||
3270 | Turns an entire slab of ops read-write if the refcount of any op in the slab | |
3271 | needs to be decreased. | |
3272 | ||
3273 | =item 3 | |
3274 | ||
3275 | Turns an entire slab of ops read-write if any op from the slab is freed. | |
3276 | ||
b8ddf6b3 SB |
3277 | =back |
3278 | ||
f1fac472 NC |
3279 | It's not possible to turn the slabs to read-only after an action requiring |
3280 | read-write access, as either can happen during op tree building time, so | |
3281 | there may still be legitimate write access. | |
3282 | ||
3283 | However, as an 80% solution it is still effective, as currently it catches | |
3284 | a write access during the generation of F<Config.pm>, which means that we | |
3285 | can't yet build F<perl> with this enabled. | |
3286 | ||
3287 | =back | |
3288 | ||
3289 | ||
955fec6b | 3290 | =head1 CONCLUSION |
a422fd2d | 3291 | |
955fec6b JH |
3292 | We've had a brief look around the Perl source, how to maintain quality |
3293 | of the source code, an overview of the stages F<perl> goes through | |
3294 | when it's running your code, how to use debuggers to poke at the Perl | |
3295 | guts, and finally how to analyse the execution of Perl. We took a very | |
3296 | simple problem and demonstrated how to solve it fully - with | |
3297 | documentation, regression tests, and finally a patch for submission to | |
3298 | p5p. Finally, we talked about how to use external tools to debug and | |
3299 | test Perl. | |
a422fd2d SC |
3300 | |
3301 | I'd now suggest you read over those references again, and then, as soon | |
3302 | as possible, get your hands dirty. The best way to learn is by doing, | |
07aa3531 | 3303 | so: |
a422fd2d SC |
3304 | |
3305 | =over 3 | |
3306 | ||
3307 | =item * | |
3308 | ||
3309 | Subscribe to perl5-porters, follow the patches and try and understand | |
3310 | them; don't be afraid to ask if there's a portion you're not clear on - | |
3311 | who knows, you may unearth a bug in the patch... | |
3312 | ||
3313 | =item * | |
3314 | ||
3315 | Keep up to date with the bleeding edge Perl distributions and get | |
3316 | familiar with the changes. Try and get an idea of what areas people are | |
3317 | working on and the changes they're making. | |
3318 | ||
3319 | =item * | |
3320 | ||
3e148164 | 3321 | Do read the README associated with your operating system, e.g. README.aix |
a1f349fd MB |
3322 | on the IBM AIX OS. Don't hesitate to supply patches to that README if |
3323 | you find anything missing or changed over a new OS release. | |
3324 | ||
3325 | =item * | |
3326 | ||
a422fd2d SC |
3327 | Find an area of Perl that seems interesting to you, and see if you can |
3328 | work out how it works. Scan through the source, and step over it in the | |
3329 | debugger. Play, poke, investigate, fiddle! You'll probably get to | |
3330 | understand not just your chosen area but a much wider range of F<perl>'s | |
3331 | activity as well, and probably sooner than you'd think. | |
3332 | ||
3333 | =back | |
3334 | ||
3335 | =over 3 | |
3336 | ||
3337 | =item I<The Road goes ever on and on, down from the door where it began.> | |
3338 | ||
3339 | =back | |
3340 | ||
64d9b66b | 3341 | If you can do these things, you've started on the long road to Perl porting. |
a422fd2d SC |
3342 | Thanks for wanting to help make Perl better - and happy hacking! |
3343 | ||
4ac71550 TC |
3344 | =head2 Metaphoric Quotations |
3345 | ||
3346 | If you recognized the quote about the Road above, you're in luck. | |
3347 | ||
3348 | Most software projects begin each file with a literal description of each | |
3349 | file's purpose. Perl instead begins each with a literary allusion to that | |
3350 | file's purpose. | |
3351 | ||
3352 | Like chapters in many books, all top-level Perl source files (along with a | |
3353 | few others here and there) begin with an epigramic inscription that alludes, | |
3354 | indirectly and metaphorically, to the material you're about to read. | |
3355 | ||
3356 | Quotations are taken from writings of J.R.R Tolkien pertaining to his | |
3357 | Legendarium, almost always from I<The Lord of the Rings>. Chapters and | |
3358 | page numbers are given using the following editions: | |
3359 | ||
3360 | =over 4 | |
3361 | ||
3362 | =item * | |
3363 | ||
3364 | I<The Hobbit>, by J.R.R. Tolkien. The hardcover, 70th-anniversary | |
3365 | edition of 2007 was used, published in the UK by Harper Collins Publishers | |
3366 | and in the US by the Houghton Mifflin Company. | |
3367 | ||
3368 | =item * | |
3369 | ||
3370 | I<The Lord of the Rings>, by J.R.R. Tolkien. The hardcover, | |
3371 | 50th-anniversary edition of 2004 was used, published in the UK by Harper | |
3372 | Collins Publishers and in the US by the Houghton Mifflin Company. | |
3373 | ||
3374 | =item * | |
3375 | ||
3376 | I<The Lays of Beleriand>, by J.R.R. Tolkien and published posthumously by his | |
3377 | son and literary executor, C.J.R. Tolkien, being the 3rd of the 12 volumes | |
3378 | in Christopher's mammoth I<History of Middle Earth>. Page numbers derive | |
3379 | from the hardcover edition, first published in 1983 by George Allen & | |
3380 | Unwin; no page numbers changed for the special 3-volume omnibus edition of | |
3381 | 2002 or the various trade-paper editions, all again now by Harper Collins | |
3382 | or Houghton Mifflin. | |
3383 | ||
3384 | =back | |
3385 | ||
3386 | Other JRRT books fair game for quotes would thus include I<The Adventures of | |
3387 | Tom Bombadil>, I<The Silmarillion>, I<Unfinished Tales>, and I<The Tale of | |
3388 | the Children of Hurin>, all but the first posthumously assembled by CJRT. | |
3389 | But I<The Lord of the Rings> itself is perfectly fine and probably best to | |
3390 | quote from, provided you can find a suitable quote there. | |
3391 | ||
3392 | So if you were to supply a new, complete, top-level source file to add to | |
3393 | Perl, you should conform to this peculiar practice by yourself selecting an | |
3394 | appropriate quotation from Tolkien, retaining the original spelling and | |
3395 | punctuation and using the same format the rest of the quotes are in. | |
3396 | Indirect and oblique is just fine; remember, it's a metaphor, so being meta | |
3397 | is, after all, what it's for. | |
3398 | ||
e8cd7eae GS |
3399 | =head1 AUTHOR |
3400 | ||
3401 | This document was written by Nathan Torkington, and is maintained by | |
3402 | the perl5-porters mailing list. | |
4ac71550 | 3403 | |
b16c2e4a RGS |
3404 | =head1 SEE ALSO |
3405 | ||
3406 | L<perlrepository> |