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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 | |
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36 | in what does and does not change in the Perl language. Various |
37 | releases of Perl are shepherded by a ``pumpking'', a porter | |
38 | responsible for gathering patches, deciding on a patch-by-patch | |
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 |
ecd89ac3 NC |
41 | Perl, and Jarkko Hietaniemi was the pumpking for the 5.8 release, and |
42 | Hugo van der Sanden and Rafael Garcia-Suarez share the pumpking for | |
43 | the 5.10 release. | |
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44 | |
45 | In addition, various people are pumpkings for different things. For | |
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46 | instance, Andy Dougherty and Jarkko Hietaniemi did a grand job as the |
47 | I<Configure> pumpkin up till the 5.8 release. For the 5.10 release | |
48 | H.Merijn Brand took over. | |
e8cd7eae GS |
49 | |
50 | Larry sees Perl development along the lines of the US government: | |
51 | there's the Legislature (the porters), the Executive branch (the | |
52 | pumpkings), and the Supreme Court (Larry). The legislature can | |
53 | discuss and submit patches to the executive branch all they like, but | |
54 | the executive branch is free to veto them. Rarely, the Supreme Court | |
55 | will side with the executive branch over the legislature, or the | |
56 | legislature over the executive branch. Mostly, however, the | |
57 | legislature and the executive branch are supposed to get along and | |
58 | work out their differences without impeachment or court cases. | |
59 | ||
60 | You might sometimes see reference to Rule 1 and Rule 2. Larry's power | |
61 | as Supreme Court is expressed in The Rules: | |
62 | ||
63 | =over 4 | |
64 | ||
65 | =item 1 | |
66 | ||
67 | Larry is always by definition right about how Perl should behave. | |
68 | This means he has final veto power on the core functionality. | |
69 | ||
70 | =item 2 | |
71 | ||
72 | Larry is allowed to change his mind about any matter at a later date, | |
73 | regardless of whether he previously invoked Rule 1. | |
74 | ||
75 | =back | |
76 | ||
77 | Got that? Larry is always right, even when he was wrong. It's rare | |
78 | to see either Rule exercised, but they are often alluded to. | |
79 | ||
80 | New features and extensions to the language are contentious, because | |
81 | the criteria used by the pumpkings, Larry, and other porters to decide | |
82 | which features should be implemented and incorporated are not codified | |
83 | in a few small design goals as with some other languages. Instead, | |
84 | the heuristics are flexible and often difficult to fathom. Here is | |
85 | one person's list, roughly in decreasing order of importance, of | |
86 | heuristics that new features have to be weighed against: | |
87 | ||
88 | =over 4 | |
89 | ||
90 | =item Does concept match the general goals of Perl? | |
91 | ||
92 | These haven't been written anywhere in stone, but one approximation | |
93 | is: | |
94 | ||
95 | 1. Keep it fast, simple, and useful. | |
96 | 2. Keep features/concepts as orthogonal as possible. | |
97 | 3. No arbitrary limits (platforms, data sizes, cultures). | |
98 | 4. Keep it open and exciting to use/patch/advocate Perl everywhere. | |
99 | 5. Either assimilate new technologies, or build bridges to them. | |
100 | ||
101 | =item Where is the implementation? | |
102 | ||
103 | All the talk in the world is useless without an implementation. In | |
104 | almost every case, the person or people who argue for a new feature | |
105 | will be expected to be the ones who implement it. Porters capable | |
106 | of coding new features have their own agendas, and are not available | |
107 | to implement your (possibly good) idea. | |
108 | ||
109 | =item Backwards compatibility | |
110 | ||
111 | It's a cardinal sin to break existing Perl programs. New warnings are | |
112 | contentious--some say that a program that emits warnings is not | |
113 | broken, while others say it is. Adding keywords has the potential to | |
114 | break programs, changing the meaning of existing token sequences or | |
115 | functions might break programs. | |
116 | ||
117 | =item Could it be a module instead? | |
118 | ||
119 | Perl 5 has extension mechanisms, modules and XS, specifically to avoid | |
120 | the need to keep changing the Perl interpreter. You can write modules | |
121 | that export functions, you can give those functions prototypes so they | |
122 | can be called like built-in functions, you can even write XS code to | |
123 | mess with the runtime data structures of the Perl interpreter if you | |
124 | want to implement really complicated things. If it can be done in a | |
125 | module instead of in the core, it's highly unlikely to be added. | |
126 | ||
127 | =item Is the feature generic enough? | |
128 | ||
129 | Is this something that only the submitter wants added to the language, | |
130 | or would it be broadly useful? Sometimes, instead of adding a feature | |
131 | with a tight focus, the porters might decide to wait until someone | |
132 | implements the more generalized feature. For instance, instead of | |
133 | implementing a ``delayed evaluation'' feature, the porters are waiting | |
134 | for a macro system that would permit delayed evaluation and much more. | |
135 | ||
136 | =item Does it potentially introduce new bugs? | |
137 | ||
138 | Radical rewrites of large chunks of the Perl interpreter have the | |
139 | potential to introduce new bugs. The smaller and more localized the | |
140 | change, the better. | |
141 | ||
142 | =item Does it preclude other desirable features? | |
143 | ||
144 | A patch is likely to be rejected if it closes off future avenues of | |
145 | development. For instance, a patch that placed a true and final | |
146 | interpretation on prototypes is likely to be rejected because there | |
147 | are still options for the future of prototypes that haven't been | |
148 | addressed. | |
149 | ||
150 | =item Is the implementation robust? | |
151 | ||
152 | Good patches (tight code, complete, correct) stand more chance of | |
153 | going in. Sloppy or incorrect patches might be placed on the back | |
154 | burner until the pumpking has time to fix, or might be discarded | |
155 | altogether without further notice. | |
156 | ||
157 | =item Is the implementation generic enough to be portable? | |
158 | ||
159 | The worst patches make use of a system-specific features. It's highly | |
160 | unlikely that nonportable additions to the Perl language will be | |
161 | accepted. | |
162 | ||
a936dd3c NC |
163 | =item Is the implementation tested? |
164 | ||
165 | Patches which change behaviour (fixing bugs or introducing new features) | |
166 | must include regression tests to verify that everything works as expected. | |
167 | Without tests provided by the original author, how can anyone else changing | |
168 | perl in the future be sure that they haven't unwittingly broken the behaviour | |
169 | the patch implements? And without tests, how can the patch's author be | |
9d077eaa | 170 | confident that his/her hard work put into the patch won't be accidentally |
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171 | thrown away by someone in the future? |
172 | ||
e8cd7eae GS |
173 | =item Is there enough documentation? |
174 | ||
175 | Patches without documentation are probably ill-thought out or | |
176 | incomplete. Nothing can be added without documentation, so submitting | |
177 | a patch for the appropriate manpages as well as the source code is | |
a936dd3c | 178 | always a good idea. |
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179 | |
180 | =item Is there another way to do it? | |
181 | ||
182 | Larry said ``Although the Perl Slogan is I<There's More Than One Way | |
183 | to Do It>, I hesitate to make 10 ways to do something''. This is a | |
184 | tricky heuristic to navigate, though--one man's essential addition is | |
185 | another man's pointless cruft. | |
186 | ||
187 | =item Does it create too much work? | |
188 | ||
189 | Work for the pumpking, work for Perl programmers, work for module | |
190 | authors, ... Perl is supposed to be easy. | |
191 | ||
f6c51b38 GS |
192 | =item Patches speak louder than words |
193 | ||
194 | Working code is always preferred to pie-in-the-sky ideas. A patch to | |
195 | add a feature stands a much higher chance of making it to the language | |
196 | than does a random feature request, no matter how fervently argued the | |
197 | request might be. This ties into ``Will it be useful?'', as the fact | |
198 | that someone took the time to make the patch demonstrates a strong | |
199 | desire for the feature. | |
200 | ||
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201 | =back |
202 | ||
203 | If you're on the list, you might hear the word ``core'' bandied | |
204 | around. It refers to the standard distribution. ``Hacking on the | |
205 | core'' means you're changing the C source code to the Perl | |
206 | interpreter. ``A core module'' is one that ships with Perl. | |
207 | ||
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208 | =head2 Keeping in sync |
209 | ||
e8cd7eae | 210 | The source code to the Perl interpreter, in its different versions, is |
f224927c JH |
211 | kept in a repository managed by a revision control system ( which is |
212 | currently the Perforce program, see http://perforce.com/ ). The | |
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213 | pumpkings and a few others have access to the repository to check in |
214 | changes. Periodically the pumpking for the development version of Perl | |
215 | will release a new version, so the rest of the porters can see what's | |
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216 | changed. The current state of the main trunk of repository, and patches |
217 | that describe the individual changes that have happened since the last | |
218 | public release are available at this location: | |
219 | ||
0cfb3454 | 220 | http://public.activestate.com/gsar/APC/ |
2be4c08b GS |
221 | ftp://ftp.linux.activestate.com/pub/staff/gsar/APC/ |
222 | ||
0cfb3454 GS |
223 | If you're looking for a particular change, or a change that affected |
224 | a particular set of files, you may find the B<Perl Repository Browser> | |
225 | useful: | |
226 | ||
227 | http://public.activestate.com/cgi-bin/perlbrowse | |
228 | ||
229 | You may also want to subscribe to the perl5-changes mailing list to | |
230 | receive a copy of each patch that gets submitted to the maintenance | |
231 | and development "branches" of the perl repository. See | |
232 | http://lists.perl.org/ for subscription information. | |
233 | ||
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234 | If you are a member of the perl5-porters mailing list, it is a good |
235 | thing to keep in touch with the most recent changes. If not only to | |
236 | verify if what you would have posted as a bug report isn't already | |
237 | solved in the most recent available perl development branch, also | |
238 | known as perl-current, bleading edge perl, bleedperl or bleadperl. | |
2be4c08b GS |
239 | |
240 | Needless to say, the source code in perl-current is usually in a perpetual | |
241 | state of evolution. You should expect it to be very buggy. Do B<not> use | |
242 | it for any purpose other than testing and development. | |
e8cd7eae | 243 | |
3e148164 JH |
244 | Keeping in sync with the most recent branch can be done in several ways, |
245 | but the most convenient and reliable way is using B<rsync>, available at | |
246 | ftp://rsync.samba.org/pub/rsync/ . (You can also get the most recent | |
247 | branch by FTP.) | |
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248 | |
249 | If you choose to keep in sync using rsync, there are two approaches | |
3e148164 | 250 | to doing so: |
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251 | |
252 | =over 4 | |
253 | ||
254 | =item rsync'ing the source tree | |
255 | ||
3e148164 | 256 | Presuming you are in the directory where your perl source resides |
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257 | and you have rsync installed and available, you can `upgrade' to |
258 | the bleadperl using: | |
259 | ||
260 | # rsync -avz rsync://ftp.linux.activestate.com/perl-current/ . | |
261 | ||
262 | This takes care of updating every single item in the source tree to | |
263 | the latest applied patch level, creating files that are new (to your | |
264 | distribution) and setting date/time stamps of existing files to | |
265 | reflect the bleadperl status. | |
266 | ||
c6d0653e LC |
267 | Note that this will not delete any files that were in '.' before |
268 | the rsync. Once you are sure that the rsync is running correctly, | |
269 | run it with the --delete and the --dry-run options like this: | |
270 | ||
271 | # rsync -avz --delete --dry-run rsync://ftp.linux.activestate.com/perl-current/ . | |
272 | ||
273 | This will I<simulate> an rsync run that also deletes files not | |
274 | present in the bleadperl master copy. Observe the results from | |
275 | this run closely. If you are sure that the actual run would delete | |
276 | no files precious to you, you could remove the '--dry-run' option. | |
277 | ||
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278 | You can than check what patch was the latest that was applied by |
279 | looking in the file B<.patch>, which will show the number of the | |
280 | latest patch. | |
281 | ||
282 | If you have more than one machine to keep in sync, and not all of | |
283 | them have access to the WAN (so you are not able to rsync all the | |
284 | source trees to the real source), there are some ways to get around | |
285 | this problem. | |
286 | ||
287 | =over 4 | |
288 | ||
289 | =item Using rsync over the LAN | |
290 | ||
291 | Set up a local rsync server which makes the rsynced source tree | |
3e148164 | 292 | available to the LAN and sync the other machines against this |
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293 | directory. |
294 | ||
1577cd80 | 295 | From http://rsync.samba.org/README.html : |
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296 | |
297 | "Rsync uses rsh or ssh for communication. It does not need to be | |
298 | setuid and requires no special privileges for installation. It | |
3958b146 | 299 | does not require an inetd entry or a daemon. You must, however, |
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300 | have a working rsh or ssh system. Using ssh is recommended for |
301 | its security features." | |
302 | ||
303 | =item Using pushing over the NFS | |
304 | ||
305 | Having the other systems mounted over the NFS, you can take an | |
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306 | active pushing approach by checking the just updated tree against |
307 | the other not-yet synced trees. An example would be | |
308 | ||
309 | #!/usr/bin/perl -w | |
310 | ||
311 | use strict; | |
312 | use File::Copy; | |
313 | ||
314 | my %MF = map { | |
315 | m/(\S+)/; | |
316 | $1 => [ (stat $1)[2, 7, 9] ]; # mode, size, mtime | |
317 | } `cat MANIFEST`; | |
318 | ||
319 | my %remote = map { $_ => "/$_/pro/3gl/CPAN/perl-5.7.1" } qw(host1 host2); | |
320 | ||
321 | foreach my $host (keys %remote) { | |
322 | unless (-d $remote{$host}) { | |
323 | print STDERR "Cannot Xsync for host $host\n"; | |
324 | next; | |
325 | } | |
326 | foreach my $file (keys %MF) { | |
327 | my $rfile = "$remote{$host}/$file"; | |
328 | my ($mode, $size, $mtime) = (stat $rfile)[2, 7, 9]; | |
329 | defined $size or ($mode, $size, $mtime) = (0, 0, 0); | |
330 | $size == $MF{$file}[1] && $mtime == $MF{$file}[2] and next; | |
331 | printf "%4s %-34s %8d %9d %8d %9d\n", | |
332 | $host, $file, $MF{$file}[1], $MF{$file}[2], $size, $mtime; | |
333 | unlink $rfile; | |
334 | copy ($file, $rfile); | |
335 | utime time, $MF{$file}[2], $rfile; | |
336 | chmod $MF{$file}[0], $rfile; | |
337 | } | |
338 | } | |
339 | ||
340 | though this is not perfect. It could be improved with checking | |
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341 | file checksums before updating. Not all NFS systems support |
342 | reliable utime support (when used over the NFS). | |
343 | ||
344 | =back | |
345 | ||
346 | =item rsync'ing the patches | |
347 | ||
348 | The source tree is maintained by the pumpking who applies patches to | |
349 | the files in the tree. These patches are either created by the | |
350 | pumpking himself using C<diff -c> after updating the file manually or | |
351 | by applying patches sent in by posters on the perl5-porters list. | |
352 | These patches are also saved and rsync'able, so you can apply them | |
353 | yourself to the source files. | |
354 | ||
355 | Presuming you are in a directory where your patches reside, you can | |
3e148164 | 356 | get them in sync with |
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357 | |
358 | # rsync -avz rsync://ftp.linux.activestate.com/perl-current-diffs/ . | |
359 | ||
360 | This makes sure the latest available patch is downloaded to your | |
361 | patch directory. | |
362 | ||
3e148164 | 363 | It's then up to you to apply these patches, using something like |
a1f349fd | 364 | |
df3477ff | 365 | # last=`ls -t *.gz | sed q` |
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366 | # rsync -avz rsync://ftp.linux.activestate.com/perl-current-diffs/ . |
367 | # find . -name '*.gz' -newer $last -exec gzcat {} \; >blead.patch | |
368 | # cd ../perl-current | |
369 | # patch -p1 -N <../perl-current-diffs/blead.patch | |
370 | ||
371 | or, since this is only a hint towards how it works, use CPAN-patchaperl | |
372 | from Andreas König to have better control over the patching process. | |
373 | ||
374 | =back | |
375 | ||
f7e1e956 | 376 | =head2 Why rsync the source tree |
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377 | |
378 | =over 4 | |
379 | ||
10f58044 | 380 | =item It's easier to rsync the source tree |
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381 | |
382 | Since you don't have to apply the patches yourself, you are sure all | |
383 | files in the source tree are in the right state. | |
384 | ||
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385 | =item It's more reliable |
386 | ||
0cfb3454 GS |
387 | While both the rsync-able source and patch areas are automatically |
388 | updated every few minutes, keep in mind that applying patches may | |
389 | sometimes mean careful hand-holding, especially if your version of | |
390 | the C<patch> program does not understand how to deal with new files, | |
391 | files with 8-bit characters, or files without trailing newlines. | |
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392 | |
393 | =back | |
394 | ||
f7e1e956 | 395 | =head2 Why rsync the patches |
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396 | |
397 | =over 4 | |
398 | ||
10f58044 | 399 | =item It's easier to rsync the patches |
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400 | |
401 | If you have more than one machine that you want to keep in track with | |
3e148164 | 402 | bleadperl, it's easier to rsync the patches only once and then apply |
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403 | them to all the source trees on the different machines. |
404 | ||
405 | In case you try to keep in pace on 5 different machines, for which | |
406 | only one of them has access to the WAN, rsync'ing all the source | |
3e148164 | 407 | trees should than be done 5 times over the NFS. Having |
a1f349fd | 408 | rsync'ed the patches only once, I can apply them to all the source |
3e148164 | 409 | trees automatically. Need you say more ;-) |
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410 | |
411 | =item It's a good reference | |
412 | ||
413 | If you do not only like to have the most recent development branch, | |
414 | but also like to B<fix> bugs, or extend features, you want to dive | |
415 | into the sources. If you are a seasoned perl core diver, you don't | |
416 | need no manuals, tips, roadmaps, perlguts.pod or other aids to find | |
417 | your way around. But if you are a starter, the patches may help you | |
418 | in finding where you should start and how to change the bits that | |
419 | bug you. | |
420 | ||
421 | The file B<Changes> is updated on occasions the pumpking sees as his | |
422 | own little sync points. On those occasions, he releases a tar-ball of | |
423 | the current source tree (i.e. perl@7582.tar.gz), which will be an | |
424 | excellent point to start with when choosing to use the 'rsync the | |
425 | patches' scheme. Starting with perl@7582, which means a set of source | |
426 | files on which the latest applied patch is number 7582, you apply all | |
f18956b7 | 427 | succeeding patches available from then on (7583, 7584, ...). |
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428 | |
429 | You can use the patches later as a kind of search archive. | |
430 | ||
431 | =over 4 | |
432 | ||
433 | =item Finding a start point | |
434 | ||
435 | If you want to fix/change the behaviour of function/feature Foo, just | |
436 | scan the patches for patches that mention Foo either in the subject, | |
3e148164 | 437 | the comments, or the body of the fix. A good chance the patch shows |
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438 | you the files that are affected by that patch which are very likely |
439 | to be the starting point of your journey into the guts of perl. | |
440 | ||
441 | =item Finding how to fix a bug | |
442 | ||
443 | If you've found I<where> the function/feature Foo misbehaves, but you | |
444 | don't know how to fix it (but you do know the change you want to | |
445 | make), you can, again, peruse the patches for similar changes and | |
446 | look how others apply the fix. | |
447 | ||
448 | =item Finding the source of misbehaviour | |
449 | ||
450 | When you keep in sync with bleadperl, the pumpking would love to | |
3958b146 | 451 | I<see> that the community efforts really work. So after each of his |
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452 | sync points, you are to 'make test' to check if everything is still |
453 | in working order. If it is, you do 'make ok', which will send an OK | |
454 | report to perlbug@perl.org. (If you do not have access to a mailer | |
3e148164 | 455 | from the system you just finished successfully 'make test', you can |
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456 | do 'make okfile', which creates the file C<perl.ok>, which you can |
457 | than take to your favourite mailer and mail yourself). | |
458 | ||
3958b146 | 459 | But of course, as always, things will not always lead to a success |
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460 | path, and one or more test do not pass the 'make test'. Before |
461 | sending in a bug report (using 'make nok' or 'make nokfile'), check | |
462 | the mailing list if someone else has reported the bug already and if | |
463 | so, confirm it by replying to that message. If not, you might want to | |
464 | trace the source of that misbehaviour B<before> sending in the bug, | |
465 | which will help all the other porters in finding the solution. | |
466 | ||
3e148164 JH |
467 | Here the saved patches come in very handy. You can check the list of |
468 | patches to see which patch changed what file and what change caused | |
469 | the misbehaviour. If you note that in the bug report, it saves the | |
470 | one trying to solve it, looking for that point. | |
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471 | |
472 | =back | |
473 | ||
474 | If searching the patches is too bothersome, you might consider using | |
475 | perl's bugtron to find more information about discussions and | |
476 | ramblings on posted bugs. | |
477 | ||
3e148164 JH |
478 | If you want to get the best of both worlds, rsync both the source |
479 | tree for convenience, reliability and ease and rsync the patches | |
480 | for reference. | |
481 | ||
52315700 RF |
482 | =back |
483 | ||
611e9550 NC |
484 | =head2 Working with the source |
485 | ||
486 | Because you cannot use the Perforce client, you cannot easily generate | |
487 | diffs against the repository, nor will merges occur when you update | |
488 | via rsync. If you edit a file locally and then rsync against the | |
489 | latest source, changes made in the remote copy will I<overwrite> your | |
490 | local versions! | |
491 | ||
492 | The best way to deal with this is to maintain a tree of symlinks to | |
493 | the rsync'd source. Then, when you want to edit a file, you remove | |
494 | the symlink, copy the real file into the other tree, and edit it. You | |
495 | can then diff your edited file against the original to generate a | |
496 | patch, and you can safely update the original tree. | |
497 | ||
498 | Perl's F<Configure> script can generate this tree of symlinks for you. | |
499 | The following example assumes that you have used rsync to pull a copy | |
500 | of the Perl source into the F<perl-rsync> directory. In the directory | |
501 | above that one, you can execute the following commands: | |
502 | ||
503 | mkdir perl-dev | |
504 | cd perl-dev | |
505 | ../perl-rsync/Configure -Dmksymlinks -Dusedevel -D"optimize=-g" | |
506 | ||
507 | This will start the Perl configuration process. After a few prompts, | |
508 | you should see something like this: | |
509 | ||
510 | Symbolic links are supported. | |
511 | ||
512 | Checking how to test for symbolic links... | |
513 | Your builtin 'test -h' may be broken. | |
514 | Trying external '/usr/bin/test -h'. | |
515 | You can test for symbolic links with '/usr/bin/test -h'. | |
516 | ||
517 | Creating the symbolic links... | |
518 | (First creating the subdirectories...) | |
519 | (Then creating the symlinks...) | |
520 | ||
521 | The specifics may vary based on your operating system, of course. | |
522 | After you see this, you can abort the F<Configure> script, and you | |
523 | will see that the directory you are in has a tree of symlinks to the | |
524 | F<perl-rsync> directories and files. | |
525 | ||
526 | If you plan to do a lot of work with the Perl source, here are some | |
527 | Bourne shell script functions that can make your life easier: | |
528 | ||
529 | function edit { | |
530 | if [ -L $1 ]; then | |
531 | mv $1 $1.orig | |
532 | cp $1.orig $1 | |
533 | vi $1 | |
534 | else | |
535 | /bin/vi $1 | |
536 | fi | |
537 | } | |
538 | ||
539 | function unedit { | |
540 | if [ -L $1.orig ]; then | |
541 | rm $1 | |
542 | mv $1.orig $1 | |
543 | fi | |
544 | } | |
545 | ||
546 | Replace "vi" with your favorite flavor of editor. | |
547 | ||
548 | Here is another function which will quickly generate a patch for the | |
549 | files which have been edited in your symlink tree: | |
550 | ||
551 | mkpatchorig() { | |
552 | local diffopts | |
553 | for f in `find . -name '*.orig' | sed s,^\./,,` | |
554 | do | |
555 | case `echo $f | sed 's,.orig$,,;s,.*\.,,'` in | |
556 | c) diffopts=-p ;; | |
557 | pod) diffopts='-F^=' ;; | |
558 | *) diffopts= ;; | |
559 | esac | |
560 | diff -du $diffopts $f `echo $f | sed 's,.orig$,,'` | |
561 | done | |
562 | } | |
563 | ||
564 | This function produces patches which include enough context to make | |
565 | your changes obvious. This makes it easier for the Perl pumpking(s) | |
566 | to review them when you send them to the perl5-porters list, and that | |
567 | means they're more likely to get applied. | |
568 | ||
569 | This function assumed a GNU diff, and may require some tweaking for | |
570 | other diff variants. | |
52315700 | 571 | |
123f35db | 572 | =head2 Perlbug administration |
52315700 | 573 | |
123f35db JH |
574 | There is a single remote administrative interface for modifying bug status, |
575 | category, open issues etc. using the B<RT> I<bugtracker> system, maintained | |
576 | by I<Robert Spier>. Become an administrator, and close any bugs you can get | |
577 | your sticky mitts on: | |
52315700 | 578 | |
123f35db | 579 | http://rt.perl.org |
52315700 | 580 | |
123f35db | 581 | The bugtracker mechanism for B<perl5> bugs in particular is at: |
52315700 | 582 | |
123f35db | 583 | http://bugs6.perl.org/perlbug |
52315700 | 584 | |
123f35db | 585 | To email the bug system administrators: |
52315700 | 586 | |
123f35db | 587 | "perlbug-admin" <perlbug-admin@perl.org> |
52315700 | 588 | |
52315700 | 589 | |
a1f349fd MB |
590 | =head2 Submitting patches |
591 | ||
f7e1e956 MS |
592 | Always submit patches to I<perl5-porters@perl.org>. If you're |
593 | patching a core module and there's an author listed, send the author a | |
594 | copy (see L<Patching a core module>). This lets other porters review | |
595 | your patch, which catches a surprising number of errors in patches. | |
596 | Either use the diff program (available in source code form from | |
f224927c | 597 | ftp://ftp.gnu.org/pub/gnu/ , or use Johan Vromans' I<makepatch> |
f7e1e956 MS |
598 | (available from I<CPAN/authors/id/JV/>). Unified diffs are preferred, |
599 | but context diffs are accepted. Do not send RCS-style diffs or diffs | |
600 | without context lines. More information is given in the | |
601 | I<Porting/patching.pod> file in the Perl source distribution. Please | |
602 | patch against the latest B<development> version (e.g., if you're | |
603 | fixing a bug in the 5.005 track, patch against the latest 5.005_5x | |
604 | version). Only patches that survive the heat of the development | |
605 | branch get applied to maintenance versions. | |
606 | ||
607 | Your patch should update the documentation and test suite. See | |
608 | L<Writing a test>. | |
e8cd7eae GS |
609 | |
610 | To report a bug in Perl, use the program I<perlbug> which comes with | |
611 | Perl (if you can't get Perl to work, send mail to the address | |
f18956b7 | 612 | I<perlbug@perl.org> or I<perlbug@perl.com>). Reporting bugs through |
e8cd7eae | 613 | I<perlbug> feeds into the automated bug-tracking system, access to |
f224927c | 614 | which is provided through the web at http://bugs.perl.org/ . It |
e8cd7eae GS |
615 | often pays to check the archives of the perl5-porters mailing list to |
616 | see whether the bug you're reporting has been reported before, and if | |
617 | so whether it was considered a bug. See above for the location of | |
618 | the searchable archives. | |
619 | ||
f224927c | 620 | The CPAN testers ( http://testers.cpan.org/ ) are a group of |
ba139f7d JH |
621 | volunteers who test CPAN modules on a variety of platforms. Perl |
622 | Smokers ( http://archives.develooper.com/daily-build@perl.org/ ) | |
623 | automatically tests Perl source releases on platforms with various | |
624 | configurations. Both efforts welcome volunteers. | |
e8cd7eae | 625 | |
e8cd7eae GS |
626 | It's a good idea to read and lurk for a while before chipping in. |
627 | That way you'll get to see the dynamic of the conversations, learn the | |
628 | personalities of the players, and hopefully be better prepared to make | |
629 | a useful contribution when do you speak up. | |
630 | ||
631 | If after all this you still think you want to join the perl5-porters | |
f6c51b38 GS |
632 | mailing list, send mail to I<perl5-porters-subscribe@perl.org>. To |
633 | unsubscribe, send mail to I<perl5-porters-unsubscribe@perl.org>. | |
e8cd7eae | 634 | |
a422fd2d SC |
635 | To hack on the Perl guts, you'll need to read the following things: |
636 | ||
637 | =over 3 | |
638 | ||
639 | =item L<perlguts> | |
640 | ||
641 | This is of paramount importance, since it's the documentation of what | |
642 | goes where in the Perl source. Read it over a couple of times and it | |
643 | might start to make sense - don't worry if it doesn't yet, because the | |
644 | best way to study it is to read it in conjunction with poking at Perl | |
645 | source, and we'll do that later on. | |
646 | ||
647 | You might also want to look at Gisle Aas's illustrated perlguts - | |
648 | there's no guarantee that this will be absolutely up-to-date with the | |
649 | latest documentation in the Perl core, but the fundamentals will be | |
1577cd80 | 650 | right. ( http://gisle.aas.no/perl/illguts/ ) |
a422fd2d SC |
651 | |
652 | =item L<perlxstut> and L<perlxs> | |
653 | ||
654 | A working knowledge of XSUB programming is incredibly useful for core | |
655 | hacking; XSUBs use techniques drawn from the PP code, the portion of the | |
656 | guts that actually executes a Perl program. It's a lot gentler to learn | |
657 | those techniques from simple examples and explanation than from the core | |
658 | itself. | |
659 | ||
660 | =item L<perlapi> | |
661 | ||
662 | The documentation for the Perl API explains what some of the internal | |
663 | functions do, as well as the many macros used in the source. | |
664 | ||
665 | =item F<Porting/pumpkin.pod> | |
666 | ||
667 | This is a collection of words of wisdom for a Perl porter; some of it is | |
668 | only useful to the pumpkin holder, but most of it applies to anyone | |
669 | wanting to go about Perl development. | |
670 | ||
671 | =item The perl5-porters FAQ | |
672 | ||
7d7d5695 RGS |
673 | This should be available from http://simon-cozens.org/writings/p5p-faq ; |
674 | alternatively, you can get the FAQ emailed to you by sending mail to | |
675 | C<perl5-porters-faq@perl.org>. It contains hints on reading perl5-porters, | |
676 | information on how perl5-porters works and how Perl development in general | |
677 | works. | |
a422fd2d SC |
678 | |
679 | =back | |
680 | ||
681 | =head2 Finding Your Way Around | |
682 | ||
683 | Perl maintenance can be split into a number of areas, and certain people | |
684 | (pumpkins) will have responsibility for each area. These areas sometimes | |
685 | correspond to files or directories in the source kit. Among the areas are: | |
686 | ||
687 | =over 3 | |
688 | ||
689 | =item Core modules | |
690 | ||
691 | Modules shipped as part of the Perl core live in the F<lib/> and F<ext/> | |
692 | subdirectories: F<lib/> is for the pure-Perl modules, and F<ext/> | |
693 | contains the core XS modules. | |
694 | ||
f7e1e956 MS |
695 | =item Tests |
696 | ||
697 | There are tests for nearly all the modules, built-ins and major bits | |
698 | of functionality. Test files all have a .t suffix. Module tests live | |
699 | in the F<lib/> and F<ext/> directories next to the module being | |
700 | tested. Others live in F<t/>. See L<Writing a test> | |
701 | ||
a422fd2d SC |
702 | =item Documentation |
703 | ||
704 | Documentation maintenance includes looking after everything in the | |
705 | F<pod/> directory, (as well as contributing new documentation) and | |
706 | the documentation to the modules in core. | |
707 | ||
708 | =item Configure | |
709 | ||
710 | The configure process is the way we make Perl portable across the | |
711 | myriad of operating systems it supports. Responsibility for the | |
712 | configure, build and installation process, as well as the overall | |
713 | portability of the core code rests with the configure pumpkin - others | |
714 | help out with individual operating systems. | |
715 | ||
716 | The files involved are the operating system directories, (F<win32/>, | |
717 | F<os2/>, F<vms/> and so on) the shell scripts which generate F<config.h> | |
718 | and F<Makefile>, as well as the metaconfig files which generate | |
719 | F<Configure>. (metaconfig isn't included in the core distribution.) | |
720 | ||
721 | =item Interpreter | |
722 | ||
723 | And of course, there's the core of the Perl interpreter itself. Let's | |
724 | have a look at that in a little more detail. | |
725 | ||
726 | =back | |
727 | ||
728 | Before we leave looking at the layout, though, don't forget that | |
729 | F<MANIFEST> contains not only the file names in the Perl distribution, | |
730 | but short descriptions of what's in them, too. For an overview of the | |
731 | important files, try this: | |
732 | ||
733 | perl -lne 'print if /^[^\/]+\.[ch]\s+/' MANIFEST | |
734 | ||
735 | =head2 Elements of the interpreter | |
736 | ||
737 | The work of the interpreter has two main stages: compiling the code | |
738 | into the internal representation, or bytecode, and then executing it. | |
739 | L<perlguts/Compiled code> explains exactly how the compilation stage | |
740 | happens. | |
741 | ||
742 | Here is a short breakdown of perl's operation: | |
743 | ||
744 | =over 3 | |
745 | ||
746 | =item Startup | |
747 | ||
748 | The action begins in F<perlmain.c>. (or F<miniperlmain.c> for miniperl) | |
749 | This is very high-level code, enough to fit on a single screen, and it | |
750 | resembles the code found in L<perlembed>; most of the real action takes | |
751 | place in F<perl.c> | |
752 | ||
753 | First, F<perlmain.c> allocates some memory and constructs a Perl | |
754 | interpreter: | |
755 | ||
756 | 1 PERL_SYS_INIT3(&argc,&argv,&env); | |
757 | 2 | |
758 | 3 if (!PL_do_undump) { | |
759 | 4 my_perl = perl_alloc(); | |
760 | 5 if (!my_perl) | |
761 | 6 exit(1); | |
762 | 7 perl_construct(my_perl); | |
763 | 8 PL_perl_destruct_level = 0; | |
764 | 9 } | |
765 | ||
766 | Line 1 is a macro, and its definition is dependent on your operating | |
767 | system. Line 3 references C<PL_do_undump>, a global variable - all | |
768 | global variables in Perl start with C<PL_>. This tells you whether the | |
769 | current running program was created with the C<-u> flag to perl and then | |
770 | F<undump>, which means it's going to be false in any sane context. | |
771 | ||
772 | Line 4 calls a function in F<perl.c> to allocate memory for a Perl | |
773 | interpreter. It's quite a simple function, and the guts of it looks like | |
774 | this: | |
775 | ||
776 | my_perl = (PerlInterpreter*)PerlMem_malloc(sizeof(PerlInterpreter)); | |
777 | ||
778 | Here you see an example of Perl's system abstraction, which we'll see | |
779 | later: C<PerlMem_malloc> is either your system's C<malloc>, or Perl's | |
780 | own C<malloc> as defined in F<malloc.c> if you selected that option at | |
781 | configure time. | |
782 | ||
783 | Next, in line 7, we construct the interpreter; this sets up all the | |
784 | special variables that Perl needs, the stacks, and so on. | |
785 | ||
786 | Now we pass Perl the command line options, and tell it to go: | |
787 | ||
788 | exitstatus = perl_parse(my_perl, xs_init, argc, argv, (char **)NULL); | |
789 | if (!exitstatus) { | |
790 | exitstatus = perl_run(my_perl); | |
791 | } | |
792 | ||
793 | ||
794 | C<perl_parse> is actually a wrapper around C<S_parse_body>, as defined | |
795 | in F<perl.c>, which processes the command line options, sets up any | |
796 | statically linked XS modules, opens the program and calls C<yyparse> to | |
797 | parse it. | |
798 | ||
799 | =item Parsing | |
800 | ||
801 | The aim of this stage is to take the Perl source, and turn it into an op | |
802 | tree. We'll see what one of those looks like later. Strictly speaking, | |
803 | there's three things going on here. | |
804 | ||
805 | C<yyparse>, the parser, lives in F<perly.c>, although you're better off | |
806 | reading the original YACC input in F<perly.y>. (Yes, Virginia, there | |
807 | B<is> a YACC grammar for Perl!) The job of the parser is to take your | |
808 | code and `understand' it, splitting it into sentences, deciding which | |
809 | operands go with which operators and so on. | |
810 | ||
811 | The parser is nobly assisted by the lexer, which chunks up your input | |
812 | into tokens, and decides what type of thing each token is: a variable | |
813 | name, an operator, a bareword, a subroutine, a core function, and so on. | |
814 | The main point of entry to the lexer is C<yylex>, and that and its | |
815 | associated routines can be found in F<toke.c>. Perl isn't much like | |
816 | other computer languages; it's highly context sensitive at times, it can | |
817 | be tricky to work out what sort of token something is, or where a token | |
818 | ends. As such, there's a lot of interplay between the tokeniser and the | |
819 | parser, which can get pretty frightening if you're not used to it. | |
820 | ||
821 | As the parser understands a Perl program, it builds up a tree of | |
822 | operations for the interpreter to perform during execution. The routines | |
823 | which construct and link together the various operations are to be found | |
824 | in F<op.c>, and will be examined later. | |
825 | ||
826 | =item Optimization | |
827 | ||
828 | Now the parsing stage is complete, and the finished tree represents | |
829 | the operations that the Perl interpreter needs to perform to execute our | |
830 | program. Next, Perl does a dry run over the tree looking for | |
831 | optimisations: constant expressions such as C<3 + 4> will be computed | |
832 | now, and the optimizer will also see if any multiple operations can be | |
833 | replaced with a single one. For instance, to fetch the variable C<$foo>, | |
834 | instead of grabbing the glob C<*foo> and looking at the scalar | |
835 | component, the optimizer fiddles the op tree to use a function which | |
836 | directly looks up the scalar in question. The main optimizer is C<peep> | |
837 | in F<op.c>, and many ops have their own optimizing functions. | |
838 | ||
839 | =item Running | |
840 | ||
841 | Now we're finally ready to go: we have compiled Perl byte code, and all | |
842 | that's left to do is run it. The actual execution is done by the | |
843 | C<runops_standard> function in F<run.c>; more specifically, it's done by | |
844 | these three innocent looking lines: | |
845 | ||
846 | while ((PL_op = CALL_FPTR(PL_op->op_ppaddr)(aTHX))) { | |
847 | PERL_ASYNC_CHECK(); | |
848 | } | |
849 | ||
850 | You may be more comfortable with the Perl version of that: | |
851 | ||
852 | PERL_ASYNC_CHECK() while $Perl::op = &{$Perl::op->{function}}; | |
853 | ||
854 | Well, maybe not. Anyway, each op contains a function pointer, which | |
855 | stipulates the function which will actually carry out the operation. | |
856 | This function will return the next op in the sequence - this allows for | |
857 | things like C<if> which choose the next op dynamically at run time. | |
858 | The C<PERL_ASYNC_CHECK> makes sure that things like signals interrupt | |
859 | execution if required. | |
860 | ||
861 | The actual functions called are known as PP code, and they're spread | |
862 | between four files: F<pp_hot.c> contains the `hot' code, which is most | |
863 | often used and highly optimized, F<pp_sys.c> contains all the | |
864 | system-specific functions, F<pp_ctl.c> contains the functions which | |
865 | implement control structures (C<if>, C<while> and the like) and F<pp.c> | |
866 | contains everything else. These are, if you like, the C code for Perl's | |
867 | built-in functions and operators. | |
868 | ||
8298e346 NC |
869 | Note that each C<pp_> function is expected to return a pointer to the next |
870 | op. Calls to perl subs (and eval blocks) are handled within the same | |
871 | runops loop, and do not consume extra space on the C stack. For example, | |
872 | C<pp_entersub> and C<pp_entertry> just push a C<CxSUB> or C<CxEVAL> block | |
873 | struct onto the context stack which contain the address of the op | |
874 | following the sub call or eval. They then return the first op of that sub | |
875 | or eval block, and so execution continues of that sub or block. Later, a | |
876 | C<pp_leavesub> or C<pp_leavetry> op pops the C<CxSUB> or C<CxEVAL>, | |
877 | retrieves the return op from it, and returns it. | |
878 | ||
879 | =item Exception handing | |
880 | ||
881 | Perl's exception handing (ie C<die> etc) is built on top of the low-level | |
882 | C<setjmp()>/C<longjmp()> C-library functions. These basically provide a | |
883 | way to capture the current PC and SP registers and later restore them; ie | |
884 | a C<longjmp()> continues at the point in code where a previous C<setjmp()> | |
885 | was done, with anything further up on the C stack being lost. This is why | |
886 | code should always save values using C<SAVE_FOO> rather than in auto | |
887 | variables. | |
888 | ||
889 | The perl core wraps C<setjmp()> etc in the macros C<JMPENV_PUSH> and | |
890 | C<JMPENV_JUMP>. The basic rule of perl exceptions is that C<exit>, and | |
891 | C<die> (in the absence of C<eval>) perform a C<JMPENV_JUMP(2)>, while | |
892 | C<die> within C<eval> does a C<JMPENV_JUMP(3)>. | |
893 | ||
894 | At entry points to perl, such as C<perl_parse()>, C<perl_run()> and | |
895 | C<call_sv(cv, G_EVAL)> each does a C<JMPENV_PUSH>, then enter a runops | |
896 | loop or whatever, and handle possible exception returns. For a 2 return, | |
897 | final cleanup is performed, such as popping stacks and calling C<CHECK> or | |
898 | C<END> blocks. Amongst other things, this is how scope cleanup still | |
899 | occurs during an C<exit>. | |
900 | ||
901 | If a C<die> can find a C<CxEVAL> block on the context stack, then the | |
902 | stack is popped to that level and the return op in that block is assigned | |
903 | to C<PL_restartop>; then a C<JMPENV_JUMP(3)> is performed. This normally | |
904 | passes control back to the guard. In the case of C<perl_run> and | |
905 | C<call_sv>, a non-null C<PL_restartop> triggers re-entry to the runops | |
906 | loop. The is the normal way that C<die> or C<croak> is handled within an | |
907 | C<eval>. | |
908 | ||
909 | Sometimes ops are executed within an inner runops loop, such as tie, sort | |
910 | or overload code. In this case, something like | |
911 | ||
912 | sub FETCH { eval { die } } | |
913 | ||
914 | would cause a longjmp right back to the guard in C<perl_run>, popping both | |
915 | runops loops, which is clearly incorrect. One way to avoid this is for the | |
916 | tie code to do a C<JMPENV_PUSH> before executing C<FETCH> in the inner | |
917 | runops loop, but for efficiency reasons, perl in fact just sets a flag, | |
918 | using C<CATCH_SET(TRUE)>. The C<pp_require>, C<pp_entereval> and | |
919 | C<pp_entertry> ops check this flag, and if true, they call C<docatch>, | |
920 | which does a C<JMPENV_PUSH> and starts a new runops level to execute the | |
921 | code, rather than doing it on the current loop. | |
922 | ||
923 | As a further optimisation, on exit from the eval block in the C<FETCH>, | |
924 | execution of the code following the block is still carried on in the inner | |
925 | loop. When an exception is raised, C<docatch> compares the C<JMPENV> | |
926 | level of the C<CxEVAL> with C<PL_top_env> and if they differ, just | |
927 | re-throws the exception. In this way any inner loops get popped. | |
928 | ||
929 | Here's an example. | |
930 | ||
931 | 1: eval { tie @a, 'A' }; | |
932 | 2: sub A::TIEARRAY { | |
933 | 3: eval { die }; | |
934 | 4: die; | |
935 | 5: } | |
936 | ||
937 | To run this code, C<perl_run> is called, which does a C<JMPENV_PUSH> then | |
938 | enters a runops loop. This loop executes the eval and tie ops on line 1, | |
939 | with the eval pushing a C<CxEVAL> onto the context stack. | |
940 | ||
941 | The C<pp_tie> does a C<CATCH_SET(TRUE)>, then starts a second runops loop | |
942 | to execute the body of C<TIEARRAY>. When it executes the entertry op on | |
943 | line 3, C<CATCH_GET> is true, so C<pp_entertry> calls C<docatch> which | |
944 | does a C<JMPENV_PUSH> and starts a third runops loop, which then executes | |
945 | the die op. At this point the C call stack looks like this: | |
946 | ||
947 | Perl_pp_die | |
948 | Perl_runops # third loop | |
949 | S_docatch_body | |
950 | S_docatch | |
951 | Perl_pp_entertry | |
952 | Perl_runops # second loop | |
953 | S_call_body | |
954 | Perl_call_sv | |
955 | Perl_pp_tie | |
956 | Perl_runops # first loop | |
957 | S_run_body | |
958 | perl_run | |
959 | main | |
960 | ||
961 | and the context and data stacks, as shown by C<-Dstv>, look like: | |
962 | ||
963 | STACK 0: MAIN | |
964 | CX 0: BLOCK => | |
965 | CX 1: EVAL => AV() PV("A"\0) | |
966 | retop=leave | |
967 | STACK 1: MAGIC | |
968 | CX 0: SUB => | |
969 | retop=(null) | |
970 | CX 1: EVAL => * | |
971 | retop=nextstate | |
972 | ||
973 | The die pops the first C<CxEVAL> off the context stack, sets | |
974 | C<PL_restartop> from it, does a C<JMPENV_JUMP(3)>, and control returns to | |
975 | the top C<docatch>. This then starts another third-level runops level, | |
976 | which executes the nextstate, pushmark and die ops on line 4. At the point | |
977 | that the second C<pp_die> is called, the C call stack looks exactly like | |
978 | that above, even though we are no longer within an inner eval; this is | |
979 | because of the optimization mentioned earlier. However, the context stack | |
980 | now looks like this, ie with the top CxEVAL popped: | |
981 | ||
982 | STACK 0: MAIN | |
983 | CX 0: BLOCK => | |
984 | CX 1: EVAL => AV() PV("A"\0) | |
985 | retop=leave | |
986 | STACK 1: MAGIC | |
987 | CX 0: SUB => | |
988 | retop=(null) | |
989 | ||
990 | The die on line 4 pops the context stack back down to the CxEVAL, leaving | |
991 | it as: | |
992 | ||
993 | STACK 0: MAIN | |
994 | CX 0: BLOCK => | |
995 | ||
996 | As usual, C<PL_restartop> is extracted from the C<CxEVAL>, and a | |
997 | C<JMPENV_JUMP(3)> done, which pops the C stack back to the docatch: | |
998 | ||
999 | S_docatch | |
1000 | Perl_pp_entertry | |
1001 | Perl_runops # second loop | |
1002 | S_call_body | |
1003 | Perl_call_sv | |
1004 | Perl_pp_tie | |
1005 | Perl_runops # first loop | |
1006 | S_run_body | |
1007 | perl_run | |
1008 | main | |
1009 | ||
1010 | In this case, because the C<JMPENV> level recorded in the C<CxEVAL> | |
1011 | differs from the current one, C<docatch> just does a C<JMPENV_JUMP(3)> | |
1012 | and the C stack unwinds to: | |
1013 | ||
1014 | perl_run | |
1015 | main | |
1016 | ||
1017 | Because C<PL_restartop> is non-null, C<run_body> starts a new runops loop | |
1018 | and execution continues. | |
1019 | ||
a422fd2d SC |
1020 | =back |
1021 | ||
1022 | =head2 Internal Variable Types | |
1023 | ||
1024 | You should by now have had a look at L<perlguts>, which tells you about | |
1025 | Perl's internal variable types: SVs, HVs, AVs and the rest. If not, do | |
1026 | that now. | |
1027 | ||
1028 | These variables are used not only to represent Perl-space variables, but | |
1029 | also any constants in the code, as well as some structures completely | |
1030 | internal to Perl. The symbol table, for instance, is an ordinary Perl | |
1031 | hash. Your code is represented by an SV as it's read into the parser; | |
1032 | any program files you call are opened via ordinary Perl filehandles, and | |
1033 | so on. | |
1034 | ||
1035 | The core L<Devel::Peek|Devel::Peek> module lets us examine SVs from a | |
1036 | Perl program. Let's see, for instance, how Perl treats the constant | |
1037 | C<"hello">. | |
1038 | ||
1039 | % perl -MDevel::Peek -e 'Dump("hello")' | |
1040 | 1 SV = PV(0xa041450) at 0xa04ecbc | |
1041 | 2 REFCNT = 1 | |
1042 | 3 FLAGS = (POK,READONLY,pPOK) | |
1043 | 4 PV = 0xa0484e0 "hello"\0 | |
1044 | 5 CUR = 5 | |
1045 | 6 LEN = 6 | |
1046 | ||
1047 | Reading C<Devel::Peek> output takes a bit of practise, so let's go | |
1048 | through it line by line. | |
1049 | ||
1050 | Line 1 tells us we're looking at an SV which lives at C<0xa04ecbc> in | |
1051 | memory. SVs themselves are very simple structures, but they contain a | |
1052 | pointer to a more complex structure. In this case, it's a PV, a | |
1053 | structure which holds a string value, at location C<0xa041450>. Line 2 | |
1054 | is the reference count; there are no other references to this data, so | |
1055 | it's 1. | |
1056 | ||
1057 | Line 3 are the flags for this SV - it's OK to use it as a PV, it's a | |
1058 | read-only SV (because it's a constant) and the data is a PV internally. | |
1059 | Next we've got the contents of the string, starting at location | |
1060 | C<0xa0484e0>. | |
1061 | ||
1062 | Line 5 gives us the current length of the string - note that this does | |
1063 | B<not> include the null terminator. Line 6 is not the length of the | |
1064 | string, but the length of the currently allocated buffer; as the string | |
1065 | grows, Perl automatically extends the available storage via a routine | |
1066 | called C<SvGROW>. | |
1067 | ||
1068 | You can get at any of these quantities from C very easily; just add | |
1069 | C<Sv> to the name of the field shown in the snippet, and you've got a | |
1070 | macro which will return the value: C<SvCUR(sv)> returns the current | |
1071 | length of the string, C<SvREFCOUNT(sv)> returns the reference count, | |
1072 | C<SvPV(sv, len)> returns the string itself with its length, and so on. | |
1073 | More macros to manipulate these properties can be found in L<perlguts>. | |
1074 | ||
1075 | Let's take an example of manipulating a PV, from C<sv_catpvn>, in F<sv.c> | |
1076 | ||
1077 | 1 void | |
1078 | 2 Perl_sv_catpvn(pTHX_ register SV *sv, register const char *ptr, register STRLEN len) | |
1079 | 3 { | |
1080 | 4 STRLEN tlen; | |
1081 | 5 char *junk; | |
1082 | ||
1083 | 6 junk = SvPV_force(sv, tlen); | |
1084 | 7 SvGROW(sv, tlen + len + 1); | |
1085 | 8 if (ptr == junk) | |
1086 | 9 ptr = SvPVX(sv); | |
1087 | 10 Move(ptr,SvPVX(sv)+tlen,len,char); | |
1088 | 11 SvCUR(sv) += len; | |
1089 | 12 *SvEND(sv) = '\0'; | |
1090 | 13 (void)SvPOK_only_UTF8(sv); /* validate pointer */ | |
1091 | 14 SvTAINT(sv); | |
1092 | 15 } | |
1093 | ||
1094 | This is a function which adds a string, C<ptr>, of length C<len> onto | |
1095 | the end of the PV stored in C<sv>. The first thing we do in line 6 is | |
1096 | make sure that the SV B<has> a valid PV, by calling the C<SvPV_force> | |
1097 | macro to force a PV. As a side effect, C<tlen> gets set to the current | |
1098 | value of the PV, and the PV itself is returned to C<junk>. | |
1099 | ||
b1866b2d | 1100 | In line 7, we make sure that the SV will have enough room to accommodate |
a422fd2d SC |
1101 | the old string, the new string and the null terminator. If C<LEN> isn't |
1102 | big enough, C<SvGROW> will reallocate space for us. | |
1103 | ||
1104 | Now, if C<junk> is the same as the string we're trying to add, we can | |
1105 | grab the string directly from the SV; C<SvPVX> is the address of the PV | |
1106 | in the SV. | |
1107 | ||
1108 | Line 10 does the actual catenation: the C<Move> macro moves a chunk of | |
1109 | memory around: we move the string C<ptr> to the end of the PV - that's | |
1110 | the start of the PV plus its current length. We're moving C<len> bytes | |
1111 | of type C<char>. After doing so, we need to tell Perl we've extended the | |
1112 | string, by altering C<CUR> to reflect the new length. C<SvEND> is a | |
1113 | macro which gives us the end of the string, so that needs to be a | |
1114 | C<"\0">. | |
1115 | ||
1116 | Line 13 manipulates the flags; since we've changed the PV, any IV or NV | |
1117 | values will no longer be valid: if we have C<$a=10; $a.="6";> we don't | |
cd458e05 | 1118 | want to use the old IV of 10. C<SvPOK_only_utf8> is a special UTF-8-aware |
a422fd2d SC |
1119 | version of C<SvPOK_only>, a macro which turns off the IOK and NOK flags |
1120 | and turns on POK. The final C<SvTAINT> is a macro which launders tainted | |
1121 | data if taint mode is turned on. | |
1122 | ||
1123 | AVs and HVs are more complicated, but SVs are by far the most common | |
1124 | variable type being thrown around. Having seen something of how we | |
1125 | manipulate these, let's go on and look at how the op tree is | |
1126 | constructed. | |
1127 | ||
1128 | =head2 Op Trees | |
1129 | ||
1130 | First, what is the op tree, anyway? The op tree is the parsed | |
1131 | representation of your program, as we saw in our section on parsing, and | |
1132 | it's the sequence of operations that Perl goes through to execute your | |
1133 | program, as we saw in L</Running>. | |
1134 | ||
1135 | An op is a fundamental operation that Perl can perform: all the built-in | |
1136 | functions and operators are ops, and there are a series of ops which | |
1137 | deal with concepts the interpreter needs internally - entering and | |
1138 | leaving a block, ending a statement, fetching a variable, and so on. | |
1139 | ||
1140 | The op tree is connected in two ways: you can imagine that there are two | |
1141 | "routes" through it, two orders in which you can traverse the tree. | |
1142 | First, parse order reflects how the parser understood the code, and | |
1143 | secondly, execution order tells perl what order to perform the | |
1144 | operations in. | |
1145 | ||
1146 | The easiest way to examine the op tree is to stop Perl after it has | |
1147 | finished parsing, and get it to dump out the tree. This is exactly what | |
7d7d5695 RGS |
1148 | the compiler backends L<B::Terse|B::Terse>, L<B::Concise|B::Concise> |
1149 | and L<B::Debug|B::Debug> do. | |
a422fd2d SC |
1150 | |
1151 | Let's have a look at how Perl sees C<$a = $b + $c>: | |
1152 | ||
1153 | % perl -MO=Terse -e '$a=$b+$c' | |
1154 | 1 LISTOP (0x8179888) leave | |
1155 | 2 OP (0x81798b0) enter | |
1156 | 3 COP (0x8179850) nextstate | |
1157 | 4 BINOP (0x8179828) sassign | |
1158 | 5 BINOP (0x8179800) add [1] | |
1159 | 6 UNOP (0x81796e0) null [15] | |
1160 | 7 SVOP (0x80fafe0) gvsv GV (0x80fa4cc) *b | |
1161 | 8 UNOP (0x81797e0) null [15] | |
1162 | 9 SVOP (0x8179700) gvsv GV (0x80efeb0) *c | |
1163 | 10 UNOP (0x816b4f0) null [15] | |
1164 | 11 SVOP (0x816dcf0) gvsv GV (0x80fa460) *a | |
1165 | ||
1166 | Let's start in the middle, at line 4. This is a BINOP, a binary | |
1167 | operator, which is at location C<0x8179828>. The specific operator in | |
1168 | question is C<sassign> - scalar assignment - and you can find the code | |
1169 | which implements it in the function C<pp_sassign> in F<pp_hot.c>. As a | |
1170 | binary operator, it has two children: the add operator, providing the | |
1171 | result of C<$b+$c>, is uppermost on line 5, and the left hand side is on | |
1172 | line 10. | |
1173 | ||
1174 | Line 10 is the null op: this does exactly nothing. What is that doing | |
1175 | there? If you see the null op, it's a sign that something has been | |
1176 | optimized away after parsing. As we mentioned in L</Optimization>, | |
1177 | the optimization stage sometimes converts two operations into one, for | |
1178 | example when fetching a scalar variable. When this happens, instead of | |
1179 | rewriting the op tree and cleaning up the dangling pointers, it's easier | |
1180 | just to replace the redundant operation with the null op. Originally, | |
1181 | the tree would have looked like this: | |
1182 | ||
1183 | 10 SVOP (0x816b4f0) rv2sv [15] | |
1184 | 11 SVOP (0x816dcf0) gv GV (0x80fa460) *a | |
1185 | ||
1186 | That is, fetch the C<a> entry from the main symbol table, and then look | |
1187 | at the scalar component of it: C<gvsv> (C<pp_gvsv> into F<pp_hot.c>) | |
1188 | happens to do both these things. | |
1189 | ||
1190 | The right hand side, starting at line 5 is similar to what we've just | |
1191 | seen: we have the C<add> op (C<pp_add> also in F<pp_hot.c>) add together | |
1192 | two C<gvsv>s. | |
1193 | ||
1194 | Now, what's this about? | |
1195 | ||
1196 | 1 LISTOP (0x8179888) leave | |
1197 | 2 OP (0x81798b0) enter | |
1198 | 3 COP (0x8179850) nextstate | |
1199 | ||
1200 | C<enter> and C<leave> are scoping ops, and their job is to perform any | |
1201 | housekeeping every time you enter and leave a block: lexical variables | |
1202 | are tidied up, unreferenced variables are destroyed, and so on. Every | |
1203 | program will have those first three lines: C<leave> is a list, and its | |
1204 | children are all the statements in the block. Statements are delimited | |
1205 | by C<nextstate>, so a block is a collection of C<nextstate> ops, with | |
1206 | the ops to be performed for each statement being the children of | |
1207 | C<nextstate>. C<enter> is a single op which functions as a marker. | |
1208 | ||
1209 | That's how Perl parsed the program, from top to bottom: | |
1210 | ||
1211 | Program | |
1212 | | | |
1213 | Statement | |
1214 | | | |
1215 | = | |
1216 | / \ | |
1217 | / \ | |
1218 | $a + | |
1219 | / \ | |
1220 | $b $c | |
1221 | ||
1222 | However, it's impossible to B<perform> the operations in this order: | |
1223 | you have to find the values of C<$b> and C<$c> before you add them | |
1224 | together, for instance. So, the other thread that runs through the op | |
1225 | tree is the execution order: each op has a field C<op_next> which points | |
1226 | to the next op to be run, so following these pointers tells us how perl | |
1227 | executes the code. We can traverse the tree in this order using | |
1228 | the C<exec> option to C<B::Terse>: | |
1229 | ||
1230 | % perl -MO=Terse,exec -e '$a=$b+$c' | |
1231 | 1 OP (0x8179928) enter | |
1232 | 2 COP (0x81798c8) nextstate | |
1233 | 3 SVOP (0x81796c8) gvsv GV (0x80fa4d4) *b | |
1234 | 4 SVOP (0x8179798) gvsv GV (0x80efeb0) *c | |
1235 | 5 BINOP (0x8179878) add [1] | |
1236 | 6 SVOP (0x816dd38) gvsv GV (0x80fa468) *a | |
1237 | 7 BINOP (0x81798a0) sassign | |
1238 | 8 LISTOP (0x8179900) leave | |
1239 | ||
1240 | This probably makes more sense for a human: enter a block, start a | |
1241 | statement. Get the values of C<$b> and C<$c>, and add them together. | |
1242 | Find C<$a>, and assign one to the other. Then leave. | |
1243 | ||
1244 | The way Perl builds up these op trees in the parsing process can be | |
1245 | unravelled by examining F<perly.y>, the YACC grammar. Let's take the | |
1246 | piece we need to construct the tree for C<$a = $b + $c> | |
1247 | ||
1248 | 1 term : term ASSIGNOP term | |
1249 | 2 { $$ = newASSIGNOP(OPf_STACKED, $1, $2, $3); } | |
1250 | 3 | term ADDOP term | |
1251 | 4 { $$ = newBINOP($2, 0, scalar($1), scalar($3)); } | |
1252 | ||
1253 | If you're not used to reading BNF grammars, this is how it works: You're | |
1254 | fed certain things by the tokeniser, which generally end up in upper | |
1255 | case. Here, C<ADDOP>, is provided when the tokeniser sees C<+> in your | |
1256 | code. C<ASSIGNOP> is provided when C<=> is used for assigning. These are | |
1257 | `terminal symbols', because you can't get any simpler than them. | |
1258 | ||
1259 | The grammar, lines one and three of the snippet above, tells you how to | |
1260 | build up more complex forms. These complex forms, `non-terminal symbols' | |
1261 | are generally placed in lower case. C<term> here is a non-terminal | |
1262 | symbol, representing a single expression. | |
1263 | ||
1264 | The grammar gives you the following rule: you can make the thing on the | |
1265 | left of the colon if you see all the things on the right in sequence. | |
1266 | This is called a "reduction", and the aim of parsing is to completely | |
1267 | reduce the input. There are several different ways you can perform a | |
1268 | reduction, separated by vertical bars: so, C<term> followed by C<=> | |
1269 | followed by C<term> makes a C<term>, and C<term> followed by C<+> | |
1270 | followed by C<term> can also make a C<term>. | |
1271 | ||
1272 | So, if you see two terms with an C<=> or C<+>, between them, you can | |
1273 | turn them into a single expression. When you do this, you execute the | |
1274 | code in the block on the next line: if you see C<=>, you'll do the code | |
1275 | in line 2. If you see C<+>, you'll do the code in line 4. It's this code | |
1276 | which contributes to the op tree. | |
1277 | ||
1278 | | term ADDOP term | |
1279 | { $$ = newBINOP($2, 0, scalar($1), scalar($3)); } | |
1280 | ||
1281 | What this does is creates a new binary op, and feeds it a number of | |
1282 | variables. The variables refer to the tokens: C<$1> is the first token in | |
1283 | the input, C<$2> the second, and so on - think regular expression | |
1284 | backreferences. C<$$> is the op returned from this reduction. So, we | |
1285 | call C<newBINOP> to create a new binary operator. The first parameter to | |
1286 | C<newBINOP>, a function in F<op.c>, is the op type. It's an addition | |
1287 | operator, so we want the type to be C<ADDOP>. We could specify this | |
1288 | directly, but it's right there as the second token in the input, so we | |
1289 | use C<$2>. The second parameter is the op's flags: 0 means `nothing | |
1290 | special'. Then the things to add: the left and right hand side of our | |
1291 | expression, in scalar context. | |
1292 | ||
1293 | =head2 Stacks | |
1294 | ||
1295 | When perl executes something like C<addop>, how does it pass on its | |
1296 | results to the next op? The answer is, through the use of stacks. Perl | |
1297 | has a number of stacks to store things it's currently working on, and | |
1298 | we'll look at the three most important ones here. | |
1299 | ||
1300 | =over 3 | |
1301 | ||
1302 | =item Argument stack | |
1303 | ||
1304 | Arguments are passed to PP code and returned from PP code using the | |
1305 | argument stack, C<ST>. The typical way to handle arguments is to pop | |
1306 | them off the stack, deal with them how you wish, and then push the result | |
1307 | back onto the stack. This is how, for instance, the cosine operator | |
1308 | works: | |
1309 | ||
1310 | NV value; | |
1311 | value = POPn; | |
1312 | value = Perl_cos(value); | |
1313 | XPUSHn(value); | |
1314 | ||
1315 | We'll see a more tricky example of this when we consider Perl's macros | |
1316 | below. C<POPn> gives you the NV (floating point value) of the top SV on | |
1317 | the stack: the C<$x> in C<cos($x)>. Then we compute the cosine, and push | |
1318 | the result back as an NV. The C<X> in C<XPUSHn> means that the stack | |
1319 | should be extended if necessary - it can't be necessary here, because we | |
1320 | know there's room for one more item on the stack, since we've just | |
1321 | removed one! The C<XPUSH*> macros at least guarantee safety. | |
1322 | ||
1323 | Alternatively, you can fiddle with the stack directly: C<SP> gives you | |
1324 | the first element in your portion of the stack, and C<TOP*> gives you | |
1325 | the top SV/IV/NV/etc. on the stack. So, for instance, to do unary | |
1326 | negation of an integer: | |
1327 | ||
1328 | SETi(-TOPi); | |
1329 | ||
1330 | Just set the integer value of the top stack entry to its negation. | |
1331 | ||
1332 | Argument stack manipulation in the core is exactly the same as it is in | |
1333 | XSUBs - see L<perlxstut>, L<perlxs> and L<perlguts> for a longer | |
1334 | description of the macros used in stack manipulation. | |
1335 | ||
1336 | =item Mark stack | |
1337 | ||
1338 | I say `your portion of the stack' above because PP code doesn't | |
1339 | necessarily get the whole stack to itself: if your function calls | |
1340 | another function, you'll only want to expose the arguments aimed for the | |
1341 | called function, and not (necessarily) let it get at your own data. The | |
1342 | way we do this is to have a `virtual' bottom-of-stack, exposed to each | |
1343 | function. The mark stack keeps bookmarks to locations in the argument | |
1344 | stack usable by each function. For instance, when dealing with a tied | |
1345 | variable, (internally, something with `P' magic) Perl has to call | |
1346 | methods for accesses to the tied variables. However, we need to separate | |
1347 | the arguments exposed to the method to the argument exposed to the | |
1348 | original function - the store or fetch or whatever it may be. Here's how | |
1349 | the tied C<push> is implemented; see C<av_push> in F<av.c>: | |
1350 | ||
1351 | 1 PUSHMARK(SP); | |
1352 | 2 EXTEND(SP,2); | |
1353 | 3 PUSHs(SvTIED_obj((SV*)av, mg)); | |
1354 | 4 PUSHs(val); | |
1355 | 5 PUTBACK; | |
1356 | 6 ENTER; | |
1357 | 7 call_method("PUSH", G_SCALAR|G_DISCARD); | |
1358 | 8 LEAVE; | |
1359 | 9 POPSTACK; | |
13a2d996 | 1360 | |
a422fd2d SC |
1361 | The lines which concern the mark stack are the first, fifth and last |
1362 | lines: they save away, restore and remove the current position of the | |
1363 | argument stack. | |
1364 | ||
1365 | Let's examine the whole implementation, for practice: | |
1366 | ||
1367 | 1 PUSHMARK(SP); | |
1368 | ||
1369 | Push the current state of the stack pointer onto the mark stack. This is | |
1370 | so that when we've finished adding items to the argument stack, Perl | |
1371 | knows how many things we've added recently. | |
1372 | ||
1373 | 2 EXTEND(SP,2); | |
1374 | 3 PUSHs(SvTIED_obj((SV*)av, mg)); | |
1375 | 4 PUSHs(val); | |
1376 | ||
1377 | We're going to add two more items onto the argument stack: when you have | |
1378 | a tied array, the C<PUSH> subroutine receives the object and the value | |
1379 | to be pushed, and that's exactly what we have here - the tied object, | |
1380 | retrieved with C<SvTIED_obj>, and the value, the SV C<val>. | |
1381 | ||
1382 | 5 PUTBACK; | |
1383 | ||
1384 | Next we tell Perl to make the change to the global stack pointer: C<dSP> | |
1385 | only gave us a local copy, not a reference to the global. | |
1386 | ||
1387 | 6 ENTER; | |
1388 | 7 call_method("PUSH", G_SCALAR|G_DISCARD); | |
1389 | 8 LEAVE; | |
1390 | ||
1391 | C<ENTER> and C<LEAVE> localise a block of code - they make sure that all | |
1392 | variables are tidied up, everything that has been localised gets | |
1393 | its previous value returned, and so on. Think of them as the C<{> and | |
1394 | C<}> of a Perl block. | |
1395 | ||
1396 | To actually do the magic method call, we have to call a subroutine in | |
1397 | Perl space: C<call_method> takes care of that, and it's described in | |
1398 | L<perlcall>. We call the C<PUSH> method in scalar context, and we're | |
1399 | going to discard its return value. | |
1400 | ||
1401 | 9 POPSTACK; | |
1402 | ||
1403 | Finally, we remove the value we placed on the mark stack, since we | |
1404 | don't need it any more. | |
1405 | ||
1406 | =item Save stack | |
1407 | ||
1408 | C doesn't have a concept of local scope, so perl provides one. We've | |
1409 | seen that C<ENTER> and C<LEAVE> are used as scoping braces; the save | |
1410 | stack implements the C equivalent of, for example: | |
1411 | ||
1412 | { | |
1413 | local $foo = 42; | |
1414 | ... | |
1415 | } | |
1416 | ||
1417 | See L<perlguts/Localising Changes> for how to use the save stack. | |
1418 | ||
1419 | =back | |
1420 | ||
1421 | =head2 Millions of Macros | |
1422 | ||
1423 | One thing you'll notice about the Perl source is that it's full of | |
1424 | macros. Some have called the pervasive use of macros the hardest thing | |
1425 | to understand, others find it adds to clarity. Let's take an example, | |
1426 | the code which implements the addition operator: | |
1427 | ||
1428 | 1 PP(pp_add) | |
1429 | 2 { | |
39644a26 | 1430 | 3 dSP; dATARGET; tryAMAGICbin(add,opASSIGN); |
a422fd2d SC |
1431 | 4 { |
1432 | 5 dPOPTOPnnrl_ul; | |
1433 | 6 SETn( left + right ); | |
1434 | 7 RETURN; | |
1435 | 8 } | |
1436 | 9 } | |
1437 | ||
1438 | Every line here (apart from the braces, of course) contains a macro. The | |
1439 | first line sets up the function declaration as Perl expects for PP code; | |
1440 | line 3 sets up variable declarations for the argument stack and the | |
1441 | target, the return value of the operation. Finally, it tries to see if | |
1442 | the addition operation is overloaded; if so, the appropriate subroutine | |
1443 | is called. | |
1444 | ||
1445 | Line 5 is another variable declaration - all variable declarations start | |
1446 | with C<d> - which pops from the top of the argument stack two NVs (hence | |
1447 | C<nn>) and puts them into the variables C<right> and C<left>, hence the | |
1448 | C<rl>. These are the two operands to the addition operator. Next, we | |
1449 | call C<SETn> to set the NV of the return value to the result of adding | |
1450 | the two values. This done, we return - the C<RETURN> macro makes sure | |
1451 | that our return value is properly handled, and we pass the next operator | |
1452 | to run back to the main run loop. | |
1453 | ||
1454 | Most of these macros are explained in L<perlapi>, and some of the more | |
1455 | important ones are explained in L<perlxs> as well. Pay special attention | |
1456 | to L<perlguts/Background and PERL_IMPLICIT_CONTEXT> for information on | |
1457 | the C<[pad]THX_?> macros. | |
1458 | ||
1aa6899f JH |
1459 | =head2 The .i Targets |
1460 | ||
1461 | You can expand the macros in a F<foo.c> file by saying | |
1462 | ||
1463 | make foo.i | |
1464 | ||
1465 | which will expand the macros using cpp. Don't be scared by the results. | |
1466 | ||
a422fd2d SC |
1467 | =head2 Poking at Perl |
1468 | ||
1469 | To really poke around with Perl, you'll probably want to build Perl for | |
1470 | debugging, like this: | |
1471 | ||
1472 | ./Configure -d -D optimize=-g | |
1473 | make | |
1474 | ||
1475 | C<-g> is a flag to the C compiler to have it produce debugging | |
1476 | information which will allow us to step through a running program. | |
1477 | F<Configure> will also turn on the C<DEBUGGING> compilation symbol which | |
1478 | enables all the internal debugging code in Perl. There are a whole bunch | |
1479 | of things you can debug with this: L<perlrun> lists them all, and the | |
1480 | best way to find out about them is to play about with them. The most | |
1481 | useful options are probably | |
1482 | ||
1483 | l Context (loop) stack processing | |
1484 | t Trace execution | |
1485 | o Method and overloading resolution | |
1486 | c String/numeric conversions | |
1487 | ||
1488 | Some of the functionality of the debugging code can be achieved using XS | |
1489 | modules. | |
13a2d996 | 1490 | |
a422fd2d SC |
1491 | -Dr => use re 'debug' |
1492 | -Dx => use O 'Debug' | |
1493 | ||
1494 | =head2 Using a source-level debugger | |
1495 | ||
1496 | If the debugging output of C<-D> doesn't help you, it's time to step | |
1497 | through perl's execution with a source-level debugger. | |
1498 | ||
1499 | =over 3 | |
1500 | ||
1501 | =item * | |
1502 | ||
1503 | We'll use C<gdb> for our examples here; the principles will apply to any | |
1504 | debugger, but check the manual of the one you're using. | |
1505 | ||
1506 | =back | |
1507 | ||
1508 | To fire up the debugger, type | |
1509 | ||
1510 | gdb ./perl | |
1511 | ||
1512 | You'll want to do that in your Perl source tree so the debugger can read | |
1513 | the source code. You should see the copyright message, followed by the | |
1514 | prompt. | |
1515 | ||
1516 | (gdb) | |
1517 | ||
1518 | C<help> will get you into the documentation, but here are the most | |
1519 | useful commands: | |
1520 | ||
1521 | =over 3 | |
1522 | ||
1523 | =item run [args] | |
1524 | ||
1525 | Run the program with the given arguments. | |
1526 | ||
1527 | =item break function_name | |
1528 | ||
1529 | =item break source.c:xxx | |
1530 | ||
1531 | Tells the debugger that we'll want to pause execution when we reach | |
cea6626f | 1532 | either the named function (but see L<perlguts/Internal Functions>!) or the given |
a422fd2d SC |
1533 | line in the named source file. |
1534 | ||
1535 | =item step | |
1536 | ||
1537 | Steps through the program a line at a time. | |
1538 | ||
1539 | =item next | |
1540 | ||
1541 | Steps through the program a line at a time, without descending into | |
1542 | functions. | |
1543 | ||
1544 | =item continue | |
1545 | ||
1546 | Run until the next breakpoint. | |
1547 | ||
1548 | =item finish | |
1549 | ||
1550 | Run until the end of the current function, then stop again. | |
1551 | ||
13a2d996 | 1552 | =item 'enter' |
a422fd2d SC |
1553 | |
1554 | Just pressing Enter will do the most recent operation again - it's a | |
1555 | blessing when stepping through miles of source code. | |
1556 | ||
1557 | =item print | |
1558 | ||
1559 | Execute the given C code and print its results. B<WARNING>: Perl makes | |
1aa6899f JH |
1560 | heavy use of macros, and F<gdb> does not necessarily support macros |
1561 | (see later L</"gdb macro support">). You'll have to substitute them | |
1562 | yourself, or to invoke cpp on the source code files | |
1563 | (see L</"The .i Targets">) | |
1564 | So, for instance, you can't say | |
a422fd2d SC |
1565 | |
1566 | print SvPV_nolen(sv) | |
1567 | ||
1568 | but you have to say | |
1569 | ||
1570 | print Perl_sv_2pv_nolen(sv) | |
1571 | ||
8f34e12f JH |
1572 | =back |
1573 | ||
a422fd2d SC |
1574 | You may find it helpful to have a "macro dictionary", which you can |
1575 | produce by saying C<cpp -dM perl.c | sort>. Even then, F<cpp> won't | |
1aa6899f JH |
1576 | recursively apply those macros for you. |
1577 | ||
1578 | =head2 gdb macro support | |
1579 | ||
1580 | Recent versions of F<gdb> have fairly good macro support, but | |
1581 | in order to use it you'll need to compile perl with macro definitions | |
1582 | included in the debugging information. Using F<gcc> version 3.1, this | |
1583 | means configuring with C<-Doptimize=-g3>. Other compilers might use a | |
1584 | different switch (if they support debugging macros at all). | |
a422fd2d | 1585 | |
a422fd2d SC |
1586 | =head2 Dumping Perl Data Structures |
1587 | ||
1588 | One way to get around this macro hell is to use the dumping functions in | |
1589 | F<dump.c>; these work a little like an internal | |
1590 | L<Devel::Peek|Devel::Peek>, but they also cover OPs and other structures | |
1591 | that you can't get at from Perl. Let's take an example. We'll use the | |
1592 | C<$a = $b + $c> we used before, but give it a bit of context: | |
1593 | C<$b = "6XXXX"; $c = 2.3;>. Where's a good place to stop and poke around? | |
1594 | ||
1595 | What about C<pp_add>, the function we examined earlier to implement the | |
1596 | C<+> operator: | |
1597 | ||
1598 | (gdb) break Perl_pp_add | |
1599 | Breakpoint 1 at 0x46249f: file pp_hot.c, line 309. | |
1600 | ||
cea6626f | 1601 | Notice we use C<Perl_pp_add> and not C<pp_add> - see L<perlguts/Internal Functions>. |
a422fd2d SC |
1602 | With the breakpoint in place, we can run our program: |
1603 | ||
1604 | (gdb) run -e '$b = "6XXXX"; $c = 2.3; $a = $b + $c' | |
1605 | ||
1606 | Lots of junk will go past as gdb reads in the relevant source files and | |
1607 | libraries, and then: | |
1608 | ||
1609 | Breakpoint 1, Perl_pp_add () at pp_hot.c:309 | |
39644a26 | 1610 | 309 dSP; dATARGET; tryAMAGICbin(add,opASSIGN); |
a422fd2d SC |
1611 | (gdb) step |
1612 | 311 dPOPTOPnnrl_ul; | |
1613 | (gdb) | |
1614 | ||
1615 | We looked at this bit of code before, and we said that C<dPOPTOPnnrl_ul> | |
1616 | arranges for two C<NV>s to be placed into C<left> and C<right> - let's | |
1617 | slightly expand it: | |
1618 | ||
1619 | #define dPOPTOPnnrl_ul NV right = POPn; \ | |
1620 | SV *leftsv = TOPs; \ | |
1621 | NV left = USE_LEFT(leftsv) ? SvNV(leftsv) : 0.0 | |
1622 | ||
1623 | C<POPn> takes the SV from the top of the stack and obtains its NV either | |
1624 | directly (if C<SvNOK> is set) or by calling the C<sv_2nv> function. | |
1625 | C<TOPs> takes the next SV from the top of the stack - yes, C<POPn> uses | |
1626 | C<TOPs> - but doesn't remove it. We then use C<SvNV> to get the NV from | |
1627 | C<leftsv> in the same way as before - yes, C<POPn> uses C<SvNV>. | |
1628 | ||
1629 | Since we don't have an NV for C<$b>, we'll have to use C<sv_2nv> to | |
1630 | convert it. If we step again, we'll find ourselves there: | |
1631 | ||
1632 | Perl_sv_2nv (sv=0xa0675d0) at sv.c:1669 | |
1633 | 1669 if (!sv) | |
1634 | (gdb) | |
1635 | ||
1636 | We can now use C<Perl_sv_dump> to investigate the SV: | |
1637 | ||
1638 | SV = PV(0xa057cc0) at 0xa0675d0 | |
1639 | REFCNT = 1 | |
1640 | FLAGS = (POK,pPOK) | |
1641 | PV = 0xa06a510 "6XXXX"\0 | |
1642 | CUR = 5 | |
1643 | LEN = 6 | |
1644 | $1 = void | |
1645 | ||
1646 | We know we're going to get C<6> from this, so let's finish the | |
1647 | subroutine: | |
1648 | ||
1649 | (gdb) finish | |
1650 | Run till exit from #0 Perl_sv_2nv (sv=0xa0675d0) at sv.c:1671 | |
1651 | 0x462669 in Perl_pp_add () at pp_hot.c:311 | |
1652 | 311 dPOPTOPnnrl_ul; | |
1653 | ||
1654 | We can also dump out this op: the current op is always stored in | |
1655 | C<PL_op>, and we can dump it with C<Perl_op_dump>. This'll give us | |
1656 | similar output to L<B::Debug|B::Debug>. | |
1657 | ||
1658 | { | |
1659 | 13 TYPE = add ===> 14 | |
1660 | TARG = 1 | |
1661 | FLAGS = (SCALAR,KIDS) | |
1662 | { | |
1663 | TYPE = null ===> (12) | |
1664 | (was rv2sv) | |
1665 | FLAGS = (SCALAR,KIDS) | |
1666 | { | |
1667 | 11 TYPE = gvsv ===> 12 | |
1668 | FLAGS = (SCALAR) | |
1669 | GV = main::b | |
1670 | } | |
1671 | } | |
1672 | ||
10f58044 | 1673 | # finish this later # |
a422fd2d SC |
1674 | |
1675 | =head2 Patching | |
1676 | ||
1677 | All right, we've now had a look at how to navigate the Perl sources and | |
1678 | some things you'll need to know when fiddling with them. Let's now get | |
1679 | on and create a simple patch. Here's something Larry suggested: if a | |
1680 | C<U> is the first active format during a C<pack>, (for example, | |
1681 | C<pack "U3C8", @stuff>) then the resulting string should be treated as | |
cd458e05 | 1682 | UTF-8 encoded. |
a422fd2d SC |
1683 | |
1684 | How do we prepare to fix this up? First we locate the code in question - | |
1685 | the C<pack> happens at runtime, so it's going to be in one of the F<pp> | |
1686 | files. Sure enough, C<pp_pack> is in F<pp.c>. Since we're going to be | |
1687 | altering this file, let's copy it to F<pp.c~>. | |
1688 | ||
a6ec74c1 JH |
1689 | [Well, it was in F<pp.c> when this tutorial was written. It has now been |
1690 | split off with C<pp_unpack> to its own file, F<pp_pack.c>] | |
1691 | ||
a422fd2d SC |
1692 | Now let's look over C<pp_pack>: we take a pattern into C<pat>, and then |
1693 | loop over the pattern, taking each format character in turn into | |
1694 | C<datum_type>. Then for each possible format character, we swallow up | |
1695 | the other arguments in the pattern (a field width, an asterisk, and so | |
1696 | on) and convert the next chunk input into the specified format, adding | |
1697 | it onto the output SV C<cat>. | |
1698 | ||
1699 | How do we know if the C<U> is the first format in the C<pat>? Well, if | |
1700 | we have a pointer to the start of C<pat> then, if we see a C<U> we can | |
1701 | test whether we're still at the start of the string. So, here's where | |
1702 | C<pat> is set up: | |
1703 | ||
1704 | STRLEN fromlen; | |
1705 | register char *pat = SvPVx(*++MARK, fromlen); | |
1706 | register char *patend = pat + fromlen; | |
1707 | register I32 len; | |
1708 | I32 datumtype; | |
1709 | SV *fromstr; | |
1710 | ||
1711 | We'll have another string pointer in there: | |
1712 | ||
1713 | STRLEN fromlen; | |
1714 | register char *pat = SvPVx(*++MARK, fromlen); | |
1715 | register char *patend = pat + fromlen; | |
1716 | + char *patcopy; | |
1717 | register I32 len; | |
1718 | I32 datumtype; | |
1719 | SV *fromstr; | |
1720 | ||
1721 | And just before we start the loop, we'll set C<patcopy> to be the start | |
1722 | of C<pat>: | |
1723 | ||
1724 | items = SP - MARK; | |
1725 | MARK++; | |
1726 | sv_setpvn(cat, "", 0); | |
1727 | + patcopy = pat; | |
1728 | while (pat < patend) { | |
1729 | ||
1730 | Now if we see a C<U> which was at the start of the string, we turn on | |
cd458e05 | 1731 | the C<UTF8> flag for the output SV, C<cat>: |
a422fd2d SC |
1732 | |
1733 | + if (datumtype == 'U' && pat==patcopy+1) | |
1734 | + SvUTF8_on(cat); | |
1735 | if (datumtype == '#') { | |
1736 | while (pat < patend && *pat != '\n') | |
1737 | pat++; | |
1738 | ||
1739 | Remember that it has to be C<patcopy+1> because the first character of | |
1740 | the string is the C<U> which has been swallowed into C<datumtype!> | |
1741 | ||
1742 | Oops, we forgot one thing: what if there are spaces at the start of the | |
1743 | pattern? C<pack(" U*", @stuff)> will have C<U> as the first active | |
1744 | character, even though it's not the first thing in the pattern. In this | |
1745 | case, we have to advance C<patcopy> along with C<pat> when we see spaces: | |
1746 | ||
1747 | if (isSPACE(datumtype)) | |
1748 | continue; | |
1749 | ||
1750 | needs to become | |
1751 | ||
1752 | if (isSPACE(datumtype)) { | |
1753 | patcopy++; | |
1754 | continue; | |
1755 | } | |
1756 | ||
1757 | OK. That's the C part done. Now we must do two additional things before | |
1758 | this patch is ready to go: we've changed the behaviour of Perl, and so | |
1759 | we must document that change. We must also provide some more regression | |
1760 | tests to make sure our patch works and doesn't create a bug somewhere | |
1761 | else along the line. | |
1762 | ||
b23b8711 MS |
1763 | The regression tests for each operator live in F<t/op/>, and so we |
1764 | make a copy of F<t/op/pack.t> to F<t/op/pack.t~>. Now we can add our | |
1765 | tests to the end. First, we'll test that the C<U> does indeed create | |
1766 | Unicode strings. | |
1767 | ||
1768 | t/op/pack.t has a sensible ok() function, but if it didn't we could | |
35c336e6 | 1769 | use the one from t/test.pl. |
b23b8711 | 1770 | |
35c336e6 MS |
1771 | require './test.pl'; |
1772 | plan( tests => 159 ); | |
b23b8711 MS |
1773 | |
1774 | so instead of this: | |
a422fd2d SC |
1775 | |
1776 | print 'not ' unless "1.20.300.4000" eq sprintf "%vd", pack("U*",1,20,300,4000); | |
1777 | print "ok $test\n"; $test++; | |
1778 | ||
35c336e6 MS |
1779 | we can write the more sensible (see L<Test::More> for a full |
1780 | explanation of is() and other testing functions). | |
b23b8711 | 1781 | |
35c336e6 | 1782 | is( "1.20.300.4000", sprintf "%vd", pack("U*",1,20,300,4000), |
812f5127 | 1783 | "U* produces unicode" ); |
b23b8711 | 1784 | |
a422fd2d SC |
1785 | Now we'll test that we got that space-at-the-beginning business right: |
1786 | ||
35c336e6 | 1787 | is( "1.20.300.4000", sprintf "%vd", pack(" U*",1,20,300,4000), |
812f5127 | 1788 | " with spaces at the beginning" ); |
a422fd2d SC |
1789 | |
1790 | And finally we'll test that we don't make Unicode strings if C<U> is B<not> | |
1791 | the first active format: | |
1792 | ||
35c336e6 | 1793 | isnt( v1.20.300.4000, sprintf "%vd", pack("C0U*",1,20,300,4000), |
812f5127 | 1794 | "U* not first isn't unicode" ); |
a422fd2d | 1795 | |
35c336e6 MS |
1796 | Mustn't forget to change the number of tests which appears at the top, |
1797 | or else the automated tester will get confused. This will either look | |
1798 | like this: | |
a422fd2d | 1799 | |
35c336e6 MS |
1800 | print "1..156\n"; |
1801 | ||
1802 | or this: | |
1803 | ||
1804 | plan( tests => 156 ); | |
a422fd2d SC |
1805 | |
1806 | We now compile up Perl, and run it through the test suite. Our new | |
1807 | tests pass, hooray! | |
1808 | ||
1809 | Finally, the documentation. The job is never done until the paperwork is | |
1810 | over, so let's describe the change we've just made. The relevant place | |
1811 | is F<pod/perlfunc.pod>; again, we make a copy, and then we'll insert | |
1812 | this text in the description of C<pack>: | |
1813 | ||
1814 | =item * | |
1815 | ||
1816 | If the pattern begins with a C<U>, the resulting string will be treated | |
cd458e05 JH |
1817 | as UTF-8-encoded Unicode. You can force UTF-8 encoding on in a string |
1818 | with an initial C<U0>, and the bytes that follow will be interpreted as | |
1819 | Unicode characters. If you don't want this to happen, you can begin your | |
1820 | pattern with C<C0> (or anything else) to force Perl not to UTF-8 encode your | |
a422fd2d SC |
1821 | string, and then follow this with a C<U*> somewhere in your pattern. |
1822 | ||
1823 | All done. Now let's create the patch. F<Porting/patching.pod> tells us | |
1824 | that if we're making major changes, we should copy the entire directory | |
1825 | to somewhere safe before we begin fiddling, and then do | |
13a2d996 | 1826 | |
a422fd2d SC |
1827 | diff -ruN old new > patch |
1828 | ||
1829 | However, we know which files we've changed, and we can simply do this: | |
1830 | ||
1831 | diff -u pp.c~ pp.c > patch | |
1832 | diff -u t/op/pack.t~ t/op/pack.t >> patch | |
1833 | diff -u pod/perlfunc.pod~ pod/perlfunc.pod >> patch | |
1834 | ||
1835 | We end up with a patch looking a little like this: | |
1836 | ||
1837 | --- pp.c~ Fri Jun 02 04:34:10 2000 | |
1838 | +++ pp.c Fri Jun 16 11:37:25 2000 | |
1839 | @@ -4375,6 +4375,7 @@ | |
1840 | register I32 items; | |
1841 | STRLEN fromlen; | |
1842 | register char *pat = SvPVx(*++MARK, fromlen); | |
1843 | + char *patcopy; | |
1844 | register char *patend = pat + fromlen; | |
1845 | register I32 len; | |
1846 | I32 datumtype; | |
1847 | @@ -4405,6 +4406,7 @@ | |
1848 | ... | |
1849 | ||
1850 | And finally, we submit it, with our rationale, to perl5-porters. Job | |
1851 | done! | |
1852 | ||
f7e1e956 MS |
1853 | =head2 Patching a core module |
1854 | ||
1855 | This works just like patching anything else, with an extra | |
1856 | consideration. Many core modules also live on CPAN. If this is so, | |
1857 | patch the CPAN version instead of the core and send the patch off to | |
1858 | the module maintainer (with a copy to p5p). This will help the module | |
1859 | maintainer keep the CPAN version in sync with the core version without | |
1860 | constantly scanning p5p. | |
1861 | ||
acbe17fc JP |
1862 | =head2 Adding a new function to the core |
1863 | ||
1864 | If, as part of a patch to fix a bug, or just because you have an | |
1865 | especially good idea, you decide to add a new function to the core, | |
1866 | discuss your ideas on p5p well before you start work. It may be that | |
1867 | someone else has already attempted to do what you are considering and | |
1868 | can give lots of good advice or even provide you with bits of code | |
1869 | that they already started (but never finished). | |
1870 | ||
1871 | You have to follow all of the advice given above for patching. It is | |
1872 | extremely important to test any addition thoroughly and add new tests | |
1873 | to explore all boundary conditions that your new function is expected | |
1874 | to handle. If your new function is used only by one module (e.g. toke), | |
1875 | then it should probably be named S_your_function (for static); on the | |
210b36aa | 1876 | other hand, if you expect it to accessible from other functions in |
acbe17fc JP |
1877 | Perl, you should name it Perl_your_function. See L<perlguts/Internal Functions> |
1878 | for more details. | |
1879 | ||
1880 | The location of any new code is also an important consideration. Don't | |
1881 | just create a new top level .c file and put your code there; you would | |
1882 | have to make changes to Configure (so the Makefile is created properly), | |
1883 | as well as possibly lots of include files. This is strictly pumpking | |
1884 | business. | |
1885 | ||
1886 | It is better to add your function to one of the existing top level | |
1887 | source code files, but your choice is complicated by the nature of | |
1888 | the Perl distribution. Only the files that are marked as compiled | |
1889 | static are located in the perl executable. Everything else is located | |
1890 | in the shared library (or DLL if you are running under WIN32). So, | |
1891 | for example, if a function was only used by functions located in | |
1892 | toke.c, then your code can go in toke.c. If, however, you want to call | |
1893 | the function from universal.c, then you should put your code in another | |
1894 | location, for example util.c. | |
1895 | ||
1896 | In addition to writing your c-code, you will need to create an | |
1897 | appropriate entry in embed.pl describing your function, then run | |
1898 | 'make regen_headers' to create the entries in the numerous header | |
1899 | files that perl needs to compile correctly. See L<perlguts/Internal Functions> | |
1900 | for information on the various options that you can set in embed.pl. | |
1901 | You will forget to do this a few (or many) times and you will get | |
1902 | warnings during the compilation phase. Make sure that you mention | |
1903 | this when you post your patch to P5P; the pumpking needs to know this. | |
1904 | ||
1905 | When you write your new code, please be conscious of existing code | |
884bad00 | 1906 | conventions used in the perl source files. See L<perlstyle> for |
acbe17fc JP |
1907 | details. Although most of the guidelines discussed seem to focus on |
1908 | Perl code, rather than c, they all apply (except when they don't ;). | |
1909 | See also I<Porting/patching.pod> file in the Perl source distribution | |
1910 | for lots of details about both formatting and submitting patches of | |
1911 | your changes. | |
1912 | ||
1913 | Lastly, TEST TEST TEST TEST TEST any code before posting to p5p. | |
1914 | Test on as many platforms as you can find. Test as many perl | |
1915 | Configure options as you can (e.g. MULTIPLICITY). If you have | |
1916 | profiling or memory tools, see L<EXTERNAL TOOLS FOR DEBUGGING PERL> | |
210b36aa | 1917 | below for how to use them to further test your code. Remember that |
acbe17fc JP |
1918 | most of the people on P5P are doing this on their own time and |
1919 | don't have the time to debug your code. | |
f7e1e956 MS |
1920 | |
1921 | =head2 Writing a test | |
1922 | ||
1923 | Every module and built-in function has an associated test file (or | |
1924 | should...). If you add or change functionality, you have to write a | |
1925 | test. If you fix a bug, you have to write a test so that bug never | |
1926 | comes back. If you alter the docs, it would be nice to test what the | |
1927 | new documentation says. | |
1928 | ||
1929 | In short, if you submit a patch you probably also have to patch the | |
1930 | tests. | |
1931 | ||
1932 | For modules, the test file is right next to the module itself. | |
1933 | F<lib/strict.t> tests F<lib/strict.pm>. This is a recent innovation, | |
1934 | so there are some snags (and it would be wonderful for you to brush | |
1935 | them out), but it basically works that way. Everything else lives in | |
1936 | F<t/>. | |
1937 | ||
1938 | =over 3 | |
1939 | ||
1940 | =item F<t/base/> | |
1941 | ||
1942 | Testing of the absolute basic functionality of Perl. Things like | |
1943 | C<if>, basic file reads and writes, simple regexes, etc. These are | |
1944 | run first in the test suite and if any of them fail, something is | |
1945 | I<really> broken. | |
1946 | ||
1947 | =item F<t/cmd/> | |
1948 | ||
1949 | These test the basic control structures, C<if/else>, C<while>, | |
35c336e6 | 1950 | subroutines, etc. |
f7e1e956 MS |
1951 | |
1952 | =item F<t/comp/> | |
1953 | ||
1954 | Tests basic issues of how Perl parses and compiles itself. | |
1955 | ||
1956 | =item F<t/io/> | |
1957 | ||
1958 | Tests for built-in IO functions, including command line arguments. | |
1959 | ||
1960 | =item F<t/lib/> | |
1961 | ||
1962 | The old home for the module tests, you shouldn't put anything new in | |
1963 | here. There are still some bits and pieces hanging around in here | |
1964 | that need to be moved. Perhaps you could move them? Thanks! | |
1965 | ||
1966 | =item F<t/op/> | |
1967 | ||
1968 | Tests for perl's built in functions that don't fit into any of the | |
1969 | other directories. | |
1970 | ||
1971 | =item F<t/pod/> | |
1972 | ||
1973 | Tests for POD directives. There are still some tests for the Pod | |
1974 | modules hanging around in here that need to be moved out into F<lib/>. | |
1975 | ||
1976 | =item F<t/run/> | |
1977 | ||
1978 | Testing features of how perl actually runs, including exit codes and | |
1979 | handling of PERL* environment variables. | |
1980 | ||
efb84706 JH |
1981 | =item F<t/uni/> |
1982 | ||
1983 | Tests for the core support of Unicode. | |
1984 | ||
1985 | =item F<t/win32/> | |
1986 | ||
1987 | Windows-specific tests. | |
1988 | ||
1989 | =item F<t/x2p> | |
1990 | ||
1991 | A test suite for the s2p converter. | |
1992 | ||
f7e1e956 MS |
1993 | =back |
1994 | ||
1995 | The core uses the same testing style as the rest of Perl, a simple | |
1996 | "ok/not ok" run through Test::Harness, but there are a few special | |
1997 | considerations. | |
1998 | ||
35c336e6 MS |
1999 | There are three ways to write a test in the core. Test::More, |
2000 | t/test.pl and ad hoc C<print $test ? "ok 42\n" : "not ok 42\n">. The | |
2001 | decision of which to use depends on what part of the test suite you're | |
2002 | working on. This is a measure to prevent a high-level failure (such | |
2003 | as Config.pm breaking) from causing basic functionality tests to fail. | |
2004 | ||
2005 | =over 4 | |
2006 | ||
2007 | =item t/base t/comp | |
2008 | ||
2009 | Since we don't know if require works, or even subroutines, use ad hoc | |
2010 | tests for these two. Step carefully to avoid using the feature being | |
2011 | tested. | |
2012 | ||
2013 | =item t/cmd t/run t/io t/op | |
2014 | ||
2015 | Now that basic require() and subroutines are tested, you can use the | |
2016 | t/test.pl library which emulates the important features of Test::More | |
2017 | while using a minimum of core features. | |
2018 | ||
2019 | You can also conditionally use certain libraries like Config, but be | |
2020 | sure to skip the test gracefully if it's not there. | |
2021 | ||
2022 | =item t/lib ext lib | |
2023 | ||
2024 | Now that the core of Perl is tested, Test::More can be used. You can | |
2025 | also use the full suite of core modules in the tests. | |
2026 | ||
2027 | =back | |
f7e1e956 MS |
2028 | |
2029 | When you say "make test" Perl uses the F<t/TEST> program to run the | |
c3f7b6fd NC |
2030 | test suite (except under Win32 where it uses F<t/harness> instead.) |
2031 | All tests are run from the F<t/> directory, B<not> the directory | |
2032 | which contains the test. This causes some problems with the tests | |
2033 | in F<lib/>, so here's some opportunity for some patching. | |
f7e1e956 MS |
2034 | |
2035 | You must be triply conscious of cross-platform concerns. This usually | |
2036 | boils down to using File::Spec and avoiding things like C<fork()> and | |
2037 | C<system()> unless absolutely necessary. | |
2038 | ||
e018f8be JH |
2039 | =head2 Special Make Test Targets |
2040 | ||
2041 | There are various special make targets that can be used to test Perl | |
2042 | slightly differently than the standard "test" target. Not all them | |
2043 | are expected to give a 100% success rate. Many of them have several | |
c3f7b6fd NC |
2044 | aliases, and many of them are not available on certain operating |
2045 | systems. | |
e018f8be JH |
2046 | |
2047 | =over 4 | |
2048 | ||
2049 | =item coretest | |
2050 | ||
7d7d5695 | 2051 | Run F<perl> on all core tests (F<t/*> and F<lib/[a-z]*> pragma tests). |
e018f8be | 2052 | |
c3f7b6fd NC |
2053 | (Not available on Win32) |
2054 | ||
e018f8be JH |
2055 | =item test.deparse |
2056 | ||
323661d1 NC |
2057 | Run all the tests through B::Deparse. Not all tests will succeed. |
2058 | ||
c3f7b6fd NC |
2059 | (Not available on Win32) |
2060 | ||
323661d1 NC |
2061 | =item test.taintwarn |
2062 | ||
2063 | Run all tests with the B<-t> command-line switch. Not all tests | |
2064 | are expected to succeed (until they're specifically fixed, of course). | |
e018f8be | 2065 | |
c3f7b6fd NC |
2066 | (Not available on Win32) |
2067 | ||
e018f8be JH |
2068 | =item minitest |
2069 | ||
2070 | Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>, | |
2071 | F<t/op>, and F<t/uni> tests. | |
2072 | ||
f846bd0a JH |
2073 | =item test.valgrind check.valgrind utest.valgrind ucheck.valgrind |
2074 | ||
2075 | (Only in Linux) Run all the tests using the memory leak + naughty | |
2076 | memory access tool "valgrind". The log files will be named | |
2077 | F<testname.valgrind>. | |
2078 | ||
e018f8be JH |
2079 | =item test.third check.third utest.third ucheck.third |
2080 | ||
2081 | (Only in Tru64) Run all the tests using the memory leak + naughty | |
2082 | memory access tool "Third Degree". The log files will be named | |
2083 | F<perl3.log.testname>. | |
2084 | ||
2085 | =item test.torture torturetest | |
2086 | ||
2087 | Run all the usual tests and some extra tests. As of Perl 5.8.0 the | |
efb84706 | 2088 | only extra tests are Abigail's JAPHs, F<t/japh/abigail.t>. |
e018f8be JH |
2089 | |
2090 | You can also run the torture test with F<t/harness> by giving | |
2091 | C<-torture> argument to F<t/harness>. | |
2092 | ||
2093 | =item utest ucheck test.utf8 check.utf8 | |
2094 | ||
2095 | Run all the tests with -Mutf8. Not all tests will succeed. | |
2096 | ||
c3f7b6fd NC |
2097 | (Not available on Win32) |
2098 | ||
6dc97886 NC |
2099 | =item minitest.utf16 test.utf16 |
2100 | ||
2101 | Runs the tests with UTF-16 encoded scripts, encoded with different | |
2102 | versions of this encoding. | |
2103 | ||
2104 | C<make utest.utf16> runs the test suite with a combination of C<-utf8> and | |
2105 | C<-utf16> arguments to F<t/TEST>. | |
2106 | ||
c3f7b6fd NC |
2107 | (Not available on Win32) |
2108 | ||
efb84706 JH |
2109 | =item test_harness |
2110 | ||
2111 | Run the test suite with the F<t/harness> controlling program, instead of | |
2112 | F<t/TEST>. F<t/harness> is more sophisticated, and uses the | |
2113 | L<Test::Harness> module, thus using this test target supposes that perl | |
2114 | mostly works. The main advantage for our purposes is that it prints a | |
2115 | detailed summary of failed tests at the end. Also, unlike F<t/TEST>, it | |
2116 | doesn't redirect stderr to stdout. | |
2117 | ||
c3f7b6fd NC |
2118 | Note that under Win32 F<t/harness> is always used instead of F<t/TEST>, so |
2119 | there is no special "test_harness" target. | |
2120 | ||
2121 | Under Win32's "test" target you may use the TEST_SWITCHES and TEST_FILES | |
2122 | environment variables to control the behaviour of F<t/harness>. This means | |
2123 | you can say | |
2124 | ||
2125 | nmake test TEST_FILES="op/*.t" | |
2126 | nmake test TEST_SWITCHES="-torture" TEST_FILES="op/*.t" | |
2127 | ||
2128 | =item test-notty test_notty | |
2129 | ||
2130 | Sets PERL_SKIP_TTY_TEST to true before running normal test. | |
2131 | ||
efb84706 JH |
2132 | =back |
2133 | ||
2134 | =head2 Running tests by hand | |
2135 | ||
2136 | You can run part of the test suite by hand by using one the following | |
2137 | commands from the F<t/> directory : | |
2138 | ||
2139 | ./perl -I../lib TEST list-of-.t-files | |
2140 | ||
2141 | or | |
2142 | ||
2143 | ./perl -I../lib harness list-of-.t-files | |
2144 | ||
2145 | (if you don't specify test scripts, the whole test suite will be run.) | |
2146 | ||
c3f7b6fd NC |
2147 | =head3 Using t/harness for testing |
2148 | ||
2149 | If you use C<harness> for testing you have several command line options | |
2150 | available to you. The arguments are as follows, and are in the order | |
2151 | that they must appear if used together. | |
2152 | ||
2153 | harness -v -torture -re=pattern LIST OF FILES TO TEST | |
2154 | harness -v -torture -re LIST OF PATTERNS TO MATCH | |
2155 | ||
2156 | If C<LIST OF FILES TO TEST> is omitted the file list is obtained from | |
2157 | the manifest. The file list may include shell wildcards which will be | |
2158 | expanded out. | |
2159 | ||
2160 | =over 4 | |
2161 | ||
2162 | =item -v | |
2163 | ||
2164 | Run the tests under verbose mode so you can see what tests were run, | |
2165 | and debug outbut. | |
2166 | ||
2167 | =item -torture | |
2168 | ||
2169 | Run the torture tests as well as the normal set. | |
2170 | ||
2171 | =item -re=PATTERN | |
2172 | ||
2173 | Filter the file list so that all the test files run match PATTERN. | |
2174 | Note that this form is distinct from the B<-re LIST OF PATTERNS> form below | |
2175 | in that it allows the file list to be provided as well. | |
2176 | ||
2177 | =item -re LIST OF PATTERNS | |
2178 | ||
2179 | Filter the file list so that all the test files run match | |
2180 | /(LIST|OF|PATTERNS)/. Note that with this form the patterns | |
2181 | are joined by '|' and you cannot supply a list of files, instead | |
2182 | the test files are obtained from the MANIFEST. | |
2183 | ||
2184 | =back | |
2185 | ||
efb84706 JH |
2186 | You can run an individual test by a command similar to |
2187 | ||
2188 | ./perl -I../lib patho/to/foo.t | |
2189 | ||
2190 | except that the harnesses set up some environment variables that may | |
2191 | affect the execution of the test : | |
2192 | ||
2193 | =over 4 | |
2194 | ||
2195 | =item PERL_CORE=1 | |
2196 | ||
2197 | indicates that we're running this test part of the perl core test suite. | |
2198 | This is useful for modules that have a dual life on CPAN. | |
2199 | ||
2200 | =item PERL_DESTRUCT_LEVEL=2 | |
2201 | ||
2202 | is set to 2 if it isn't set already (see L</PERL_DESTRUCT_LEVEL>) | |
2203 | ||
2204 | =item PERL | |
2205 | ||
2206 | (used only by F<t/TEST>) if set, overrides the path to the perl executable | |
2207 | that should be used to run the tests (the default being F<./perl>). | |
2208 | ||
2209 | =item PERL_SKIP_TTY_TEST | |
2210 | ||
2211 | if set, tells to skip the tests that need a terminal. It's actually set | |
2212 | automatically by the Makefile, but can also be forced artificially by | |
2213 | running 'make test_notty'. | |
2214 | ||
e018f8be | 2215 | =back |
f7e1e956 | 2216 | |
902b9dbf MLF |
2217 | =head1 EXTERNAL TOOLS FOR DEBUGGING PERL |
2218 | ||
2219 | Sometimes it helps to use external tools while debugging and | |
2220 | testing Perl. This section tries to guide you through using | |
2221 | some common testing and debugging tools with Perl. This is | |
2222 | meant as a guide to interfacing these tools with Perl, not | |
2223 | as any kind of guide to the use of the tools themselves. | |
2224 | ||
6a8f7120 JH |
2225 | B<NOTE 1>: Running under memory debuggers such as Purify, valgrind, or |
2226 | Third Degree greatly slows down the execution: seconds become minutes, | |
2227 | minutes become hours. For example as of Perl 5.8.1, the | |
2228 | ext/Encode/t/Unicode.t takes extraordinarily long to complete under | |
2229 | e.g. Purify, Third Degree, and valgrind. Under valgrind it takes more | |
2230 | than six hours, even on a snappy computer-- the said test must be | |
2231 | doing something that is quite unfriendly for memory debuggers. If you | |
2232 | don't feel like waiting, that you can simply kill away the perl | |
2233 | process. | |
2234 | ||
2235 | B<NOTE 2>: To minimize the number of memory leak false alarms (see | |
2236 | L</PERL_DESTRUCT_LEVEL> for more information), you have to have | |
2237 | environment variable PERL_DESTRUCT_LEVEL set to 2. The F<TEST> | |
2238 | and harness scripts do that automatically. But if you are running | |
2239 | some of the tests manually-- for csh-like shells: | |
2240 | ||
2241 | setenv PERL_DESTRUCT_LEVEL 2 | |
2242 | ||
2243 | and for Bourne-type shells: | |
2244 | ||
2245 | PERL_DESTRUCT_LEVEL=2 | |
2246 | export PERL_DESTRUCT_LEVEL | |
2247 | ||
2248 | or in UNIXy environments you can also use the C<env> command: | |
2249 | ||
2250 | env PERL_DESTRUCT_LEVEL=2 valgrind ./perl -Ilib ... | |
2251 | ||
2252 | B<NOTE 3>: There are known memory leaks when there are compile-time | |
2253 | errors within eval or require, seeing C<S_doeval> in the call stack | |
2254 | is a good sign of these. Fixing these leaks is non-trivial, | |
2255 | unfortunately, but they must be fixed eventually. | |
84c414ed | 2256 | |
902b9dbf MLF |
2257 | =head2 Rational Software's Purify |
2258 | ||
2259 | Purify is a commercial tool that is helpful in identifying | |
2260 | memory overruns, wild pointers, memory leaks and other such | |
2261 | badness. Perl must be compiled in a specific way for | |
2262 | optimal testing with Purify. Purify is available under | |
2263 | Windows NT, Solaris, HP-UX, SGI, and Siemens Unix. | |
2264 | ||
902b9dbf MLF |
2265 | =head2 Purify on Unix |
2266 | ||
2267 | On Unix, Purify creates a new Perl binary. To get the most | |
2268 | benefit out of Purify, you should create the perl to Purify | |
2269 | using: | |
2270 | ||
2271 | sh Configure -Accflags=-DPURIFY -Doptimize='-g' \ | |
2272 | -Uusemymalloc -Dusemultiplicity | |
2273 | ||
2274 | where these arguments mean: | |
2275 | ||
2276 | =over 4 | |
2277 | ||
2278 | =item -Accflags=-DPURIFY | |
2279 | ||
2280 | Disables Perl's arena memory allocation functions, as well as | |
2281 | forcing use of memory allocation functions derived from the | |
2282 | system malloc. | |
2283 | ||
2284 | =item -Doptimize='-g' | |
2285 | ||
2286 | Adds debugging information so that you see the exact source | |
2287 | statements where the problem occurs. Without this flag, all | |
2288 | you will see is the source filename of where the error occurred. | |
2289 | ||
2290 | =item -Uusemymalloc | |
2291 | ||
2292 | Disable Perl's malloc so that Purify can more closely monitor | |
2293 | allocations and leaks. Using Perl's malloc will make Purify | |
2294 | report most leaks in the "potential" leaks category. | |
2295 | ||
2296 | =item -Dusemultiplicity | |
2297 | ||
2298 | Enabling the multiplicity option allows perl to clean up | |
2299 | thoroughly when the interpreter shuts down, which reduces the | |
2300 | number of bogus leak reports from Purify. | |
2301 | ||
2302 | =back | |
2303 | ||
2304 | Once you've compiled a perl suitable for Purify'ing, then you | |
2305 | can just: | |
2306 | ||
2307 | make pureperl | |
2308 | ||
2309 | which creates a binary named 'pureperl' that has been Purify'ed. | |
2310 | This binary is used in place of the standard 'perl' binary | |
2311 | when you want to debug Perl memory problems. | |
2312 | ||
2313 | As an example, to show any memory leaks produced during the | |
2314 | standard Perl testset you would create and run the Purify'ed | |
2315 | perl as: | |
2316 | ||
2317 | make pureperl | |
2318 | cd t | |
2319 | ../pureperl -I../lib harness | |
2320 | ||
2321 | which would run Perl on test.pl and report any memory problems. | |
2322 | ||
2323 | Purify outputs messages in "Viewer" windows by default. If | |
2324 | you don't have a windowing environment or if you simply | |
2325 | want the Purify output to unobtrusively go to a log file | |
2326 | instead of to the interactive window, use these following | |
2327 | options to output to the log file "perl.log": | |
2328 | ||
2329 | setenv PURIFYOPTIONS "-chain-length=25 -windows=no \ | |
2330 | -log-file=perl.log -append-logfile=yes" | |
2331 | ||
2332 | If you plan to use the "Viewer" windows, then you only need this option: | |
2333 | ||
2334 | setenv PURIFYOPTIONS "-chain-length=25" | |
2335 | ||
c406981e JH |
2336 | In Bourne-type shells: |
2337 | ||
98631ff8 JL |
2338 | PURIFYOPTIONS="..." |
2339 | export PURIFYOPTIONS | |
c406981e JH |
2340 | |
2341 | or if you have the "env" utility: | |
2342 | ||
98631ff8 | 2343 | env PURIFYOPTIONS="..." ../pureperl ... |
c406981e | 2344 | |
902b9dbf MLF |
2345 | =head2 Purify on NT |
2346 | ||
2347 | Purify on Windows NT instruments the Perl binary 'perl.exe' | |
2348 | on the fly. There are several options in the makefile you | |
2349 | should change to get the most use out of Purify: | |
2350 | ||
2351 | =over 4 | |
2352 | ||
2353 | =item DEFINES | |
2354 | ||
2355 | You should add -DPURIFY to the DEFINES line so the DEFINES | |
2356 | line looks something like: | |
2357 | ||
2358 | DEFINES = -DWIN32 -D_CONSOLE -DNO_STRICT $(CRYPT_FLAG) -DPURIFY=1 | |
2359 | ||
2360 | to disable Perl's arena memory allocation functions, as | |
2361 | well as to force use of memory allocation functions derived | |
2362 | from the system malloc. | |
2363 | ||
2364 | =item USE_MULTI = define | |
2365 | ||
2366 | Enabling the multiplicity option allows perl to clean up | |
2367 | thoroughly when the interpreter shuts down, which reduces the | |
2368 | number of bogus leak reports from Purify. | |
2369 | ||
2370 | =item #PERL_MALLOC = define | |
2371 | ||
2372 | Disable Perl's malloc so that Purify can more closely monitor | |
2373 | allocations and leaks. Using Perl's malloc will make Purify | |
2374 | report most leaks in the "potential" leaks category. | |
2375 | ||
2376 | =item CFG = Debug | |
2377 | ||
2378 | Adds debugging information so that you see the exact source | |
2379 | statements where the problem occurs. Without this flag, all | |
2380 | you will see is the source filename of where the error occurred. | |
2381 | ||
2382 | =back | |
2383 | ||
2384 | As an example, to show any memory leaks produced during the | |
2385 | standard Perl testset you would create and run Purify as: | |
2386 | ||
2387 | cd win32 | |
2388 | make | |
2389 | cd ../t | |
2390 | purify ../perl -I../lib harness | |
2391 | ||
2392 | which would instrument Perl in memory, run Perl on test.pl, | |
2393 | then finally report any memory problems. | |
2394 | ||
f846bd0a JH |
2395 | =head2 valgrind |
2396 | ||
2397 | The excellent valgrind tool can be used to find out both memory leaks | |
2398 | and illegal memory accesses. As of August 2003 it unfortunately works | |
2399 | only on x86 (ELF) Linux. The special "test.valgrind" target can be used | |
6a8f7120 JH |
2400 | to run the tests under valgrind. Found errors and memory leaks are |
2401 | logged in files named F<test.valgrind>. | |
2402 | ||
2403 | As system libraries (most notably glibc) are also triggering errors, | |
2404 | valgrind allows to suppress such errors using suppression files. The | |
2405 | default suppression file that comes with valgrind already catches a lot | |
2406 | of them. Some additional suppressions are defined in F<t/perl.supp>. | |
f846bd0a JH |
2407 | |
2408 | To get valgrind and for more information see | |
2409 | ||
2410 | http://developer.kde.org/~sewardj/ | |
2411 | ||
f134cc4e | 2412 | =head2 Compaq's/Digital's/HP's Third Degree |
09187cb1 JH |
2413 | |
2414 | Third Degree is a tool for memory leak detection and memory access checks. | |
2415 | It is one of the many tools in the ATOM toolkit. The toolkit is only | |
2416 | available on Tru64 (formerly known as Digital UNIX formerly known as | |
2417 | DEC OSF/1). | |
2418 | ||
2419 | When building Perl, you must first run Configure with -Doptimize=-g | |
2420 | and -Uusemymalloc flags, after that you can use the make targets | |
51a35ef1 JH |
2421 | "perl.third" and "test.third". (What is required is that Perl must be |
2422 | compiled using the C<-g> flag, you may need to re-Configure.) | |
09187cb1 | 2423 | |
64cea5fd | 2424 | The short story is that with "atom" you can instrument the Perl |
83f0ef60 | 2425 | executable to create a new executable called F<perl.third>. When the |
4ae3d70a | 2426 | instrumented executable is run, it creates a log of dubious memory |
83f0ef60 | 2427 | traffic in file called F<perl.3log>. See the manual pages of atom and |
4ae3d70a JH |
2428 | third for more information. The most extensive Third Degree |
2429 | documentation is available in the Compaq "Tru64 UNIX Programmer's | |
2430 | Guide", chapter "Debugging Programs with Third Degree". | |
64cea5fd | 2431 | |
9c54ecba | 2432 | The "test.third" leaves a lot of files named F<foo_bar.3log> in the t/ |
64cea5fd JH |
2433 | subdirectory. There is a problem with these files: Third Degree is so |
2434 | effective that it finds problems also in the system libraries. | |
9c54ecba JH |
2435 | Therefore you should used the Porting/thirdclean script to cleanup |
2436 | the F<*.3log> files. | |
64cea5fd JH |
2437 | |
2438 | There are also leaks that for given certain definition of a leak, | |
2439 | aren't. See L</PERL_DESTRUCT_LEVEL> for more information. | |
2440 | ||
2441 | =head2 PERL_DESTRUCT_LEVEL | |
2442 | ||
6a8f7120 JH |
2443 | If you want to run any of the tests yourself manually using e.g. |
2444 | valgrind, or the pureperl or perl.third executables, please note that | |
2445 | by default perl B<does not> explicitly cleanup all the memory it has | |
2446 | allocated (such as global memory arenas) but instead lets the exit() | |
2447 | of the whole program "take care" of such allocations, also known as | |
2448 | "global destruction of objects". | |
64cea5fd JH |
2449 | |
2450 | There is a way to tell perl to do complete cleanup: set the | |
2451 | environment variable PERL_DESTRUCT_LEVEL to a non-zero value. | |
2452 | The t/TEST wrapper does set this to 2, and this is what you | |
2453 | need to do too, if you don't want to see the "global leaks": | |
1f56d61a | 2454 | For example, for "third-degreed" Perl: |
64cea5fd | 2455 | |
1f56d61a | 2456 | env PERL_DESTRUCT_LEVEL=2 ./perl.third -Ilib t/foo/bar.t |
09187cb1 | 2457 | |
414f2397 RGS |
2458 | (Note: the mod_perl apache module uses also this environment variable |
2459 | for its own purposes and extended its semantics. Refer to the mod_perl | |
c240c76d JH |
2460 | documentation for more information. Also, spawned threads do the |
2461 | equivalent of setting this variable to the value 1.) | |
2462 | ||
2463 | If, at the end of a run you get the message I<N scalars leaked>, you can | |
2464 | recompile with C<-DDEBUG_LEAKING_SCALARS>, which will cause | |
2465 | the addresses of all those leaked SVs to be dumped; it also converts | |
2466 | C<new_SV()> from a macro into a real function, so you can use your | |
2467 | favourite debugger to discover where those pesky SVs were allocated. | |
414f2397 | 2468 | |
51a35ef1 JH |
2469 | =head2 Profiling |
2470 | ||
2471 | Depending on your platform there are various of profiling Perl. | |
2472 | ||
2473 | There are two commonly used techniques of profiling executables: | |
10f58044 | 2474 | I<statistical time-sampling> and I<basic-block counting>. |
51a35ef1 JH |
2475 | |
2476 | The first method takes periodically samples of the CPU program | |
2477 | counter, and since the program counter can be correlated with the code | |
2478 | generated for functions, we get a statistical view of in which | |
2479 | functions the program is spending its time. The caveats are that very | |
2480 | small/fast functions have lower probability of showing up in the | |
2481 | profile, and that periodically interrupting the program (this is | |
2482 | usually done rather frequently, in the scale of milliseconds) imposes | |
2483 | an additional overhead that may skew the results. The first problem | |
2484 | can be alleviated by running the code for longer (in general this is a | |
2485 | good idea for profiling), the second problem is usually kept in guard | |
2486 | by the profiling tools themselves. | |
2487 | ||
10f58044 | 2488 | The second method divides up the generated code into I<basic blocks>. |
51a35ef1 JH |
2489 | Basic blocks are sections of code that are entered only in the |
2490 | beginning and exited only at the end. For example, a conditional jump | |
2491 | starts a basic block. Basic block profiling usually works by | |
10f58044 | 2492 | I<instrumenting> the code by adding I<enter basic block #nnnn> |
51a35ef1 JH |
2493 | book-keeping code to the generated code. During the execution of the |
2494 | code the basic block counters are then updated appropriately. The | |
2495 | caveat is that the added extra code can skew the results: again, the | |
2496 | profiling tools usually try to factor their own effects out of the | |
2497 | results. | |
2498 | ||
83f0ef60 JH |
2499 | =head2 Gprof Profiling |
2500 | ||
51a35ef1 JH |
2501 | gprof is a profiling tool available in many UNIX platforms, |
2502 | it uses F<statistical time-sampling>. | |
83f0ef60 JH |
2503 | |
2504 | You can build a profiled version of perl called "perl.gprof" by | |
51a35ef1 JH |
2505 | invoking the make target "perl.gprof" (What is required is that Perl |
2506 | must be compiled using the C<-pg> flag, you may need to re-Configure). | |
2507 | Running the profiled version of Perl will create an output file called | |
2508 | F<gmon.out> is created which contains the profiling data collected | |
2509 | during the execution. | |
83f0ef60 JH |
2510 | |
2511 | The gprof tool can then display the collected data in various ways. | |
2512 | Usually gprof understands the following options: | |
2513 | ||
2514 | =over 4 | |
2515 | ||
2516 | =item -a | |
2517 | ||
2518 | Suppress statically defined functions from the profile. | |
2519 | ||
2520 | =item -b | |
2521 | ||
2522 | Suppress the verbose descriptions in the profile. | |
2523 | ||
2524 | =item -e routine | |
2525 | ||
2526 | Exclude the given routine and its descendants from the profile. | |
2527 | ||
2528 | =item -f routine | |
2529 | ||
2530 | Display only the given routine and its descendants in the profile. | |
2531 | ||
2532 | =item -s | |
2533 | ||
2534 | Generate a summary file called F<gmon.sum> which then may be given | |
2535 | to subsequent gprof runs to accumulate data over several runs. | |
2536 | ||
2537 | =item -z | |
2538 | ||
2539 | Display routines that have zero usage. | |
2540 | ||
2541 | =back | |
2542 | ||
2543 | For more detailed explanation of the available commands and output | |
2544 | formats, see your own local documentation of gprof. | |
2545 | ||
51a35ef1 JH |
2546 | =head2 GCC gcov Profiling |
2547 | ||
10f58044 | 2548 | Starting from GCC 3.0 I<basic block profiling> is officially available |
51a35ef1 JH |
2549 | for the GNU CC. |
2550 | ||
2551 | You can build a profiled version of perl called F<perl.gcov> by | |
2552 | invoking the make target "perl.gcov" (what is required that Perl must | |
2553 | be compiled using gcc with the flags C<-fprofile-arcs | |
2554 | -ftest-coverage>, you may need to re-Configure). | |
2555 | ||
2556 | Running the profiled version of Perl will cause profile output to be | |
2557 | generated. For each source file an accompanying ".da" file will be | |
2558 | created. | |
2559 | ||
2560 | To display the results you use the "gcov" utility (which should | |
2561 | be installed if you have gcc 3.0 or newer installed). F<gcov> is | |
2562 | run on source code files, like this | |
2563 | ||
2564 | gcov sv.c | |
2565 | ||
2566 | which will cause F<sv.c.gcov> to be created. The F<.gcov> files | |
2567 | contain the source code annotated with relative frequencies of | |
2568 | execution indicated by "#" markers. | |
2569 | ||
2570 | Useful options of F<gcov> include C<-b> which will summarise the | |
2571 | basic block, branch, and function call coverage, and C<-c> which | |
2572 | instead of relative frequencies will use the actual counts. For | |
2573 | more information on the use of F<gcov> and basic block profiling | |
2574 | with gcc, see the latest GNU CC manual, as of GCC 3.0 see | |
2575 | ||
2576 | http://gcc.gnu.org/onlinedocs/gcc-3.0/gcc.html | |
2577 | ||
2578 | and its section titled "8. gcov: a Test Coverage Program" | |
2579 | ||
2580 | http://gcc.gnu.org/onlinedocs/gcc-3.0/gcc_8.html#SEC132 | |
2581 | ||
4ae3d70a JH |
2582 | =head2 Pixie Profiling |
2583 | ||
51a35ef1 JH |
2584 | Pixie is a profiling tool available on IRIX and Tru64 (aka Digital |
2585 | UNIX aka DEC OSF/1) platforms. Pixie does its profiling using | |
10f58044 | 2586 | I<basic-block counting>. |
4ae3d70a | 2587 | |
83f0ef60 | 2588 | You can build a profiled version of perl called F<perl.pixie> by |
51a35ef1 JH |
2589 | invoking the make target "perl.pixie" (what is required is that Perl |
2590 | must be compiled using the C<-g> flag, you may need to re-Configure). | |
2591 | ||
2592 | In Tru64 a file called F<perl.Addrs> will also be silently created, | |
2593 | this file contains the addresses of the basic blocks. Running the | |
2594 | profiled version of Perl will create a new file called "perl.Counts" | |
2595 | which contains the counts for the basic block for that particular | |
2596 | program execution. | |
4ae3d70a | 2597 | |
51a35ef1 | 2598 | To display the results you use the F<prof> utility. The exact |
4ae3d70a JH |
2599 | incantation depends on your operating system, "prof perl.Counts" in |
2600 | IRIX, and "prof -pixie -all -L. perl" in Tru64. | |
2601 | ||
6c41479b JH |
2602 | In IRIX the following prof options are available: |
2603 | ||
2604 | =over 4 | |
2605 | ||
2606 | =item -h | |
2607 | ||
2608 | Reports the most heavily used lines in descending order of use. | |
6e36760b | 2609 | Useful for finding the hotspot lines. |
6c41479b JH |
2610 | |
2611 | =item -l | |
2612 | ||
2613 | Groups lines by procedure, with procedures sorted in descending order of use. | |
2614 | Within a procedure, lines are listed in source order. | |
6e36760b | 2615 | Useful for finding the hotspots of procedures. |
6c41479b JH |
2616 | |
2617 | =back | |
2618 | ||
2619 | In Tru64 the following options are available: | |
2620 | ||
2621 | =over 4 | |
2622 | ||
3958b146 | 2623 | =item -p[rocedures] |
6c41479b | 2624 | |
3958b146 | 2625 | Procedures sorted in descending order by the number of cycles executed |
6e36760b | 2626 | in each procedure. Useful for finding the hotspot procedures. |
6c41479b JH |
2627 | (This is the default option.) |
2628 | ||
24000d2f | 2629 | =item -h[eavy] |
6c41479b | 2630 | |
6e36760b JH |
2631 | Lines sorted in descending order by the number of cycles executed in |
2632 | each line. Useful for finding the hotspot lines. | |
6c41479b | 2633 | |
24000d2f | 2634 | =item -i[nvocations] |
6c41479b | 2635 | |
6e36760b JH |
2636 | The called procedures are sorted in descending order by number of calls |
2637 | made to the procedures. Useful for finding the most used procedures. | |
6c41479b | 2638 | |
24000d2f | 2639 | =item -l[ines] |
6c41479b JH |
2640 | |
2641 | Grouped by procedure, sorted by cycles executed per procedure. | |
6e36760b | 2642 | Useful for finding the hotspots of procedures. |
6c41479b JH |
2643 | |
2644 | =item -testcoverage | |
2645 | ||
2646 | The compiler emitted code for these lines, but the code was unexecuted. | |
2647 | ||
24000d2f | 2648 | =item -z[ero] |
6c41479b JH |
2649 | |
2650 | Unexecuted procedures. | |
2651 | ||
aa500c9e | 2652 | =back |
6c41479b JH |
2653 | |
2654 | For further information, see your system's manual pages for pixie and prof. | |
4ae3d70a | 2655 | |
b8ddf6b3 SB |
2656 | =head2 Miscellaneous tricks |
2657 | ||
2658 | =over 4 | |
2659 | ||
2660 | =item * | |
2661 | ||
cc177e1a | 2662 | Those debugging perl with the DDD frontend over gdb may find the |
b8ddf6b3 SB |
2663 | following useful: |
2664 | ||
2665 | You can extend the data conversion shortcuts menu, so for example you | |
2666 | can display an SV's IV value with one click, without doing any typing. | |
2667 | To do that simply edit ~/.ddd/init file and add after: | |
2668 | ||
2669 | ! Display shortcuts. | |
2670 | Ddd*gdbDisplayShortcuts: \ | |
2671 | /t () // Convert to Bin\n\ | |
2672 | /d () // Convert to Dec\n\ | |
2673 | /x () // Convert to Hex\n\ | |
2674 | /o () // Convert to Oct(\n\ | |
2675 | ||
2676 | the following two lines: | |
2677 | ||
2678 | ((XPV*) (())->sv_any )->xpv_pv // 2pvx\n\ | |
2679 | ((XPVIV*) (())->sv_any )->xiv_iv // 2ivx | |
2680 | ||
2681 | so now you can do ivx and pvx lookups or you can plug there the | |
2682 | sv_peek "conversion": | |
2683 | ||
2684 | Perl_sv_peek(my_perl, (SV*)()) // sv_peek | |
2685 | ||
2686 | (The my_perl is for threaded builds.) | |
2687 | Just remember that every line, but the last one, should end with \n\ | |
2688 | ||
2689 | Alternatively edit the init file interactively via: | |
2690 | 3rd mouse button -> New Display -> Edit Menu | |
2691 | ||
2692 | Note: you can define up to 20 conversion shortcuts in the gdb | |
2693 | section. | |
2694 | ||
9965345d JH |
2695 | =item * |
2696 | ||
2697 | If you see in a debugger a memory area mysteriously full of 0xabababab, | |
2698 | you may be seeing the effect of the Poison() macro, see L<perlclib>. | |
2699 | ||
b8ddf6b3 SB |
2700 | =back |
2701 | ||
a422fd2d SC |
2702 | =head2 CONCLUSION |
2703 | ||
2704 | We've had a brief look around the Perl source, an overview of the stages | |
2705 | F<perl> goes through when it's running your code, and how to use a | |
902b9dbf MLF |
2706 | debugger to poke at the Perl guts. We took a very simple problem and |
2707 | demonstrated how to solve it fully - with documentation, regression | |
2708 | tests, and finally a patch for submission to p5p. Finally, we talked | |
2709 | about how to use external tools to debug and test Perl. | |
a422fd2d SC |
2710 | |
2711 | I'd now suggest you read over those references again, and then, as soon | |
2712 | as possible, get your hands dirty. The best way to learn is by doing, | |
2713 | so: | |
2714 | ||
2715 | =over 3 | |
2716 | ||
2717 | =item * | |
2718 | ||
2719 | Subscribe to perl5-porters, follow the patches and try and understand | |
2720 | them; don't be afraid to ask if there's a portion you're not clear on - | |
2721 | who knows, you may unearth a bug in the patch... | |
2722 | ||
2723 | =item * | |
2724 | ||
2725 | Keep up to date with the bleeding edge Perl distributions and get | |
2726 | familiar with the changes. Try and get an idea of what areas people are | |
2727 | working on and the changes they're making. | |
2728 | ||
2729 | =item * | |
2730 | ||
3e148164 | 2731 | Do read the README associated with your operating system, e.g. README.aix |
a1f349fd MB |
2732 | on the IBM AIX OS. Don't hesitate to supply patches to that README if |
2733 | you find anything missing or changed over a new OS release. | |
2734 | ||
2735 | =item * | |
2736 | ||
a422fd2d SC |
2737 | Find an area of Perl that seems interesting to you, and see if you can |
2738 | work out how it works. Scan through the source, and step over it in the | |
2739 | debugger. Play, poke, investigate, fiddle! You'll probably get to | |
2740 | understand not just your chosen area but a much wider range of F<perl>'s | |
2741 | activity as well, and probably sooner than you'd think. | |
2742 | ||
2743 | =back | |
2744 | ||
2745 | =over 3 | |
2746 | ||
2747 | =item I<The Road goes ever on and on, down from the door where it began.> | |
2748 | ||
2749 | =back | |
2750 | ||
2751 | If you can do these things, you've started on the long road to Perl porting. | |
2752 | Thanks for wanting to help make Perl better - and happy hacking! | |
2753 | ||
e8cd7eae GS |
2754 | =head1 AUTHOR |
2755 | ||
2756 | This document was written by Nathan Torkington, and is maintained by | |
2757 | the perl5-porters mailing list. | |
2758 |