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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 | |
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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 | |
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21 | or |
22 | |
23 | http://archive.develooper.com/perl5-porters@perl.org/ |
24 | |
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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. |
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40 | For instance, Gurusamy Sarathy was the pumpking for the 5.6 release of |
41 | Perl, and Jarkko Hietaniemi is the pumpking for the 5.8 release, and |
42 | Hugo van der Sanden will be the pumpking for the 5.10 release. |
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43 | |
44 | In addition, various people are pumpkings for different things. For |
45 | instance, Andy Dougherty and Jarkko Hietaniemi share the I<Configure> |
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46 | pumpkin. |
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47 | |
48 | Larry sees Perl development along the lines of the US government: |
49 | there's the Legislature (the porters), the Executive branch (the |
50 | pumpkings), and the Supreme Court (Larry). The legislature can |
51 | discuss and submit patches to the executive branch all they like, but |
52 | the executive branch is free to veto them. Rarely, the Supreme Court |
53 | will side with the executive branch over the legislature, or the |
54 | legislature over the executive branch. Mostly, however, the |
55 | legislature and the executive branch are supposed to get along and |
56 | work out their differences without impeachment or court cases. |
57 | |
58 | You might sometimes see reference to Rule 1 and Rule 2. Larry's power |
59 | as Supreme Court is expressed in The Rules: |
60 | |
61 | =over 4 |
62 | |
63 | =item 1 |
64 | |
65 | Larry is always by definition right about how Perl should behave. |
66 | This means he has final veto power on the core functionality. |
67 | |
68 | =item 2 |
69 | |
70 | Larry is allowed to change his mind about any matter at a later date, |
71 | regardless of whether he previously invoked Rule 1. |
72 | |
73 | =back |
74 | |
75 | Got that? Larry is always right, even when he was wrong. It's rare |
76 | to see either Rule exercised, but they are often alluded to. |
77 | |
78 | New features and extensions to the language are contentious, because |
79 | the criteria used by the pumpkings, Larry, and other porters to decide |
80 | which features should be implemented and incorporated are not codified |
81 | in a few small design goals as with some other languages. Instead, |
82 | the heuristics are flexible and often difficult to fathom. Here is |
83 | one person's list, roughly in decreasing order of importance, of |
84 | heuristics that new features have to be weighed against: |
85 | |
86 | =over 4 |
87 | |
88 | =item Does concept match the general goals of Perl? |
89 | |
90 | These haven't been written anywhere in stone, but one approximation |
91 | is: |
92 | |
93 | 1. Keep it fast, simple, and useful. |
94 | 2. Keep features/concepts as orthogonal as possible. |
95 | 3. No arbitrary limits (platforms, data sizes, cultures). |
96 | 4. Keep it open and exciting to use/patch/advocate Perl everywhere. |
97 | 5. Either assimilate new technologies, or build bridges to them. |
98 | |
99 | =item Where is the implementation? |
100 | |
101 | All the talk in the world is useless without an implementation. In |
102 | almost every case, the person or people who argue for a new feature |
103 | will be expected to be the ones who implement it. Porters capable |
104 | of coding new features have their own agendas, and are not available |
105 | to implement your (possibly good) idea. |
106 | |
107 | =item Backwards compatibility |
108 | |
109 | It's a cardinal sin to break existing Perl programs. New warnings are |
110 | contentious--some say that a program that emits warnings is not |
111 | broken, while others say it is. Adding keywords has the potential to |
112 | break programs, changing the meaning of existing token sequences or |
113 | functions might break programs. |
114 | |
115 | =item Could it be a module instead? |
116 | |
117 | Perl 5 has extension mechanisms, modules and XS, specifically to avoid |
118 | the need to keep changing the Perl interpreter. You can write modules |
119 | that export functions, you can give those functions prototypes so they |
120 | can be called like built-in functions, you can even write XS code to |
121 | mess with the runtime data structures of the Perl interpreter if you |
122 | want to implement really complicated things. If it can be done in a |
123 | module instead of in the core, it's highly unlikely to be added. |
124 | |
125 | =item Is the feature generic enough? |
126 | |
127 | Is this something that only the submitter wants added to the language, |
128 | or would it be broadly useful? Sometimes, instead of adding a feature |
129 | with a tight focus, the porters might decide to wait until someone |
130 | implements the more generalized feature. For instance, instead of |
131 | implementing a ``delayed evaluation'' feature, the porters are waiting |
132 | for a macro system that would permit delayed evaluation and much more. |
133 | |
134 | =item Does it potentially introduce new bugs? |
135 | |
136 | Radical rewrites of large chunks of the Perl interpreter have the |
137 | potential to introduce new bugs. The smaller and more localized the |
138 | change, the better. |
139 | |
140 | =item Does it preclude other desirable features? |
141 | |
142 | A patch is likely to be rejected if it closes off future avenues of |
143 | development. For instance, a patch that placed a true and final |
144 | interpretation on prototypes is likely to be rejected because there |
145 | are still options for the future of prototypes that haven't been |
146 | addressed. |
147 | |
148 | =item Is the implementation robust? |
149 | |
150 | Good patches (tight code, complete, correct) stand more chance of |
151 | going in. Sloppy or incorrect patches might be placed on the back |
152 | burner until the pumpking has time to fix, or might be discarded |
153 | altogether without further notice. |
154 | |
155 | =item Is the implementation generic enough to be portable? |
156 | |
157 | The worst patches make use of a system-specific features. It's highly |
158 | unlikely that nonportable additions to the Perl language will be |
159 | accepted. |
160 | |
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161 | =item Is the implementation tested? |
162 | |
163 | Patches which change behaviour (fixing bugs or introducing new features) |
164 | must include regression tests to verify that everything works as expected. |
165 | Without tests provided by the original author, how can anyone else changing |
166 | perl in the future be sure that they haven't unwittingly broken the behaviour |
167 | the patch implements? And without tests, how can the patch's author be |
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168 | confident that his/her hard work put into the patch won't be accidentally |
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169 | thrown away by someone in the future? |
170 | |
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171 | =item Is there enough documentation? |
172 | |
173 | Patches without documentation are probably ill-thought out or |
174 | incomplete. Nothing can be added without documentation, so submitting |
175 | a patch for the appropriate manpages as well as the source code is |
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176 | always a good idea. |
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177 | |
178 | =item Is there another way to do it? |
179 | |
180 | Larry said ``Although the Perl Slogan is I<There's More Than One Way |
181 | to Do It>, I hesitate to make 10 ways to do something''. This is a |
182 | tricky heuristic to navigate, though--one man's essential addition is |
183 | another man's pointless cruft. |
184 | |
185 | =item Does it create too much work? |
186 | |
187 | Work for the pumpking, work for Perl programmers, work for module |
188 | authors, ... Perl is supposed to be easy. |
189 | |
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190 | =item Patches speak louder than words |
191 | |
192 | Working code is always preferred to pie-in-the-sky ideas. A patch to |
193 | add a feature stands a much higher chance of making it to the language |
194 | than does a random feature request, no matter how fervently argued the |
195 | request might be. This ties into ``Will it be useful?'', as the fact |
196 | that someone took the time to make the patch demonstrates a strong |
197 | desire for the feature. |
198 | |
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199 | =back |
200 | |
201 | If you're on the list, you might hear the word ``core'' bandied |
202 | around. It refers to the standard distribution. ``Hacking on the |
203 | core'' means you're changing the C source code to the Perl |
204 | interpreter. ``A core module'' is one that ships with Perl. |
205 | |
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206 | =head2 Keeping in sync |
207 | |
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208 | The source code to the Perl interpreter, in its different versions, is |
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209 | kept in a repository managed by a revision control system ( which is |
210 | currently the Perforce program, see http://perforce.com/ ). The |
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211 | pumpkings and a few others have access to the repository to check in |
212 | changes. Periodically the pumpking for the development version of Perl |
213 | will release a new version, so the rest of the porters can see what's |
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214 | changed. The current state of the main trunk of repository, and patches |
215 | that describe the individual changes that have happened since the last |
216 | public release are available at this location: |
217 | |
218 | ftp://ftp.linux.activestate.com/pub/staff/gsar/APC/ |
219 | |
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220 | If you are a member of the perl5-porters mailing list, it is a good |
221 | thing to keep in touch with the most recent changes. If not only to |
222 | verify if what you would have posted as a bug report isn't already |
223 | solved in the most recent available perl development branch, also |
224 | known as perl-current, bleading edge perl, bleedperl or bleadperl. |
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225 | |
226 | Needless to say, the source code in perl-current is usually in a perpetual |
227 | state of evolution. You should expect it to be very buggy. Do B<not> use |
228 | it for any purpose other than testing and development. |
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229 | |
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230 | Keeping in sync with the most recent branch can be done in several ways, |
231 | but the most convenient and reliable way is using B<rsync>, available at |
232 | ftp://rsync.samba.org/pub/rsync/ . (You can also get the most recent |
233 | branch by FTP.) |
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234 | |
235 | If you choose to keep in sync using rsync, there are two approaches |
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236 | to doing so: |
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237 | |
238 | =over 4 |
239 | |
240 | =item rsync'ing the source tree |
241 | |
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242 | Presuming you are in the directory where your perl source resides |
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243 | and you have rsync installed and available, you can `upgrade' to |
244 | the bleadperl using: |
245 | |
246 | # rsync -avz rsync://ftp.linux.activestate.com/perl-current/ . |
247 | |
248 | This takes care of updating every single item in the source tree to |
249 | the latest applied patch level, creating files that are new (to your |
250 | distribution) and setting date/time stamps of existing files to |
251 | reflect the bleadperl status. |
252 | |
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253 | Note that this will not delete any files that were in '.' before |
254 | the rsync. Once you are sure that the rsync is running correctly, |
255 | run it with the --delete and the --dry-run options like this: |
256 | |
257 | # rsync -avz --delete --dry-run rsync://ftp.linux.activestate.com/perl-current/ . |
258 | |
259 | This will I<simulate> an rsync run that also deletes files not |
260 | present in the bleadperl master copy. Observe the results from |
261 | this run closely. If you are sure that the actual run would delete |
262 | no files precious to you, you could remove the '--dry-run' option. |
263 | |
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264 | You can than check what patch was the latest that was applied by |
265 | looking in the file B<.patch>, which will show the number of the |
266 | latest patch. |
267 | |
268 | If you have more than one machine to keep in sync, and not all of |
269 | them have access to the WAN (so you are not able to rsync all the |
270 | source trees to the real source), there are some ways to get around |
271 | this problem. |
272 | |
273 | =over 4 |
274 | |
275 | =item Using rsync over the LAN |
276 | |
277 | Set up a local rsync server which makes the rsynced source tree |
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278 | available to the LAN and sync the other machines against this |
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279 | directory. |
280 | |
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281 | From http://rsync.samba.org/README.html : |
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282 | |
283 | "Rsync uses rsh or ssh for communication. It does not need to be |
284 | setuid and requires no special privileges for installation. It |
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285 | does not require an inetd entry or a daemon. You must, however, |
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286 | have a working rsh or ssh system. Using ssh is recommended for |
287 | its security features." |
288 | |
289 | =item Using pushing over the NFS |
290 | |
291 | Having the other systems mounted over the NFS, you can take an |
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292 | active pushing approach by checking the just updated tree against |
293 | the other not-yet synced trees. An example would be |
294 | |
295 | #!/usr/bin/perl -w |
296 | |
297 | use strict; |
298 | use File::Copy; |
299 | |
300 | my %MF = map { |
301 | m/(\S+)/; |
302 | $1 => [ (stat $1)[2, 7, 9] ]; # mode, size, mtime |
303 | } `cat MANIFEST`; |
304 | |
305 | my %remote = map { $_ => "/$_/pro/3gl/CPAN/perl-5.7.1" } qw(host1 host2); |
306 | |
307 | foreach my $host (keys %remote) { |
308 | unless (-d $remote{$host}) { |
309 | print STDERR "Cannot Xsync for host $host\n"; |
310 | next; |
311 | } |
312 | foreach my $file (keys %MF) { |
313 | my $rfile = "$remote{$host}/$file"; |
314 | my ($mode, $size, $mtime) = (stat $rfile)[2, 7, 9]; |
315 | defined $size or ($mode, $size, $mtime) = (0, 0, 0); |
316 | $size == $MF{$file}[1] && $mtime == $MF{$file}[2] and next; |
317 | printf "%4s %-34s %8d %9d %8d %9d\n", |
318 | $host, $file, $MF{$file}[1], $MF{$file}[2], $size, $mtime; |
319 | unlink $rfile; |
320 | copy ($file, $rfile); |
321 | utime time, $MF{$file}[2], $rfile; |
322 | chmod $MF{$file}[0], $rfile; |
323 | } |
324 | } |
325 | |
326 | though this is not perfect. It could be improved with checking |
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327 | file checksums before updating. Not all NFS systems support |
328 | reliable utime support (when used over the NFS). |
329 | |
330 | =back |
331 | |
332 | =item rsync'ing the patches |
333 | |
334 | The source tree is maintained by the pumpking who applies patches to |
335 | the files in the tree. These patches are either created by the |
336 | pumpking himself using C<diff -c> after updating the file manually or |
337 | by applying patches sent in by posters on the perl5-porters list. |
338 | These patches are also saved and rsync'able, so you can apply them |
339 | yourself to the source files. |
340 | |
341 | Presuming you are in a directory where your patches reside, you can |
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342 | get them in sync with |
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343 | |
344 | # rsync -avz rsync://ftp.linux.activestate.com/perl-current-diffs/ . |
345 | |
346 | This makes sure the latest available patch is downloaded to your |
347 | patch directory. |
348 | |
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349 | It's then up to you to apply these patches, using something like |
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350 | |
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351 | # last=`ls -t *.gz | sed q` |
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352 | # rsync -avz rsync://ftp.linux.activestate.com/perl-current-diffs/ . |
353 | # find . -name '*.gz' -newer $last -exec gzcat {} \; >blead.patch |
354 | # cd ../perl-current |
355 | # patch -p1 -N <../perl-current-diffs/blead.patch |
356 | |
357 | or, since this is only a hint towards how it works, use CPAN-patchaperl |
358 | from Andreas König to have better control over the patching process. |
359 | |
360 | =back |
361 | |
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362 | =head2 Why rsync the source tree |
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363 | |
364 | =over 4 |
365 | |
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366 | =item It's easier to rsync the source tree |
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367 | |
368 | Since you don't have to apply the patches yourself, you are sure all |
369 | files in the source tree are in the right state. |
370 | |
371 | =item It's more recent |
372 | |
373 | According to Gurusamy Sarathy: |
374 | |
375 | "... The rsync mirror is automatic and syncs with the repository |
376 | every five minutes. |
377 | |
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378 | "Updating the patch area still requires manual intervention |
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379 | (with all the goofiness that implies, which you've noted) and |
380 | is typically on a daily cycle. Making this process automatic |
381 | is on my tuit list, but don't ask me when." |
382 | |
383 | =item It's more reliable |
384 | |
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385 | Well, since the patches are updated by hand, I don't have to say any |
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386 | more ... (see Sarathy's remark). |
387 | |
388 | =back |
389 | |
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390 | =head2 Why rsync the patches |
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391 | |
392 | =over 4 |
393 | |
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394 | =item It's easier to rsync the patches |
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395 | |
396 | If you have more than one machine that you want to keep in track with |
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397 | bleadperl, it's easier to rsync the patches only once and then apply |
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398 | them to all the source trees on the different machines. |
399 | |
400 | In case you try to keep in pace on 5 different machines, for which |
401 | only one of them has access to the WAN, rsync'ing all the source |
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402 | trees should than be done 5 times over the NFS. Having |
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403 | rsync'ed the patches only once, I can apply them to all the source |
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404 | trees automatically. Need you say more ;-) |
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405 | |
406 | =item It's a good reference |
407 | |
408 | If you do not only like to have the most recent development branch, |
409 | but also like to B<fix> bugs, or extend features, you want to dive |
410 | into the sources. If you are a seasoned perl core diver, you don't |
411 | need no manuals, tips, roadmaps, perlguts.pod or other aids to find |
412 | your way around. But if you are a starter, the patches may help you |
413 | in finding where you should start and how to change the bits that |
414 | bug you. |
415 | |
416 | The file B<Changes> is updated on occasions the pumpking sees as his |
417 | own little sync points. On those occasions, he releases a tar-ball of |
418 | the current source tree (i.e. perl@7582.tar.gz), which will be an |
419 | excellent point to start with when choosing to use the 'rsync the |
420 | patches' scheme. Starting with perl@7582, which means a set of source |
421 | files on which the latest applied patch is number 7582, you apply all |
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422 | succeeding patches available from then on (7583, 7584, ...). |
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423 | |
424 | You can use the patches later as a kind of search archive. |
425 | |
426 | =over 4 |
427 | |
428 | =item Finding a start point |
429 | |
430 | If you want to fix/change the behaviour of function/feature Foo, just |
431 | scan the patches for patches that mention Foo either in the subject, |
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432 | the comments, or the body of the fix. A good chance the patch shows |
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433 | you the files that are affected by that patch which are very likely |
434 | to be the starting point of your journey into the guts of perl. |
435 | |
436 | =item Finding how to fix a bug |
437 | |
438 | If you've found I<where> the function/feature Foo misbehaves, but you |
439 | don't know how to fix it (but you do know the change you want to |
440 | make), you can, again, peruse the patches for similar changes and |
441 | look how others apply the fix. |
442 | |
443 | =item Finding the source of misbehaviour |
444 | |
445 | When you keep in sync with bleadperl, the pumpking would love to |
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446 | I<see> that the community efforts really work. So after each of his |
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447 | sync points, you are to 'make test' to check if everything is still |
448 | in working order. If it is, you do 'make ok', which will send an OK |
449 | report to perlbug@perl.org. (If you do not have access to a mailer |
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450 | from the system you just finished successfully 'make test', you can |
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451 | do 'make okfile', which creates the file C<perl.ok>, which you can |
452 | than take to your favourite mailer and mail yourself). |
453 | |
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454 | But of course, as always, things will not always lead to a success |
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455 | path, and one or more test do not pass the 'make test'. Before |
456 | sending in a bug report (using 'make nok' or 'make nokfile'), check |
457 | the mailing list if someone else has reported the bug already and if |
458 | so, confirm it by replying to that message. If not, you might want to |
459 | trace the source of that misbehaviour B<before> sending in the bug, |
460 | which will help all the other porters in finding the solution. |
461 | |
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462 | Here the saved patches come in very handy. You can check the list of |
463 | patches to see which patch changed what file and what change caused |
464 | the misbehaviour. If you note that in the bug report, it saves the |
465 | one trying to solve it, looking for that point. |
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466 | |
467 | =back |
468 | |
469 | If searching the patches is too bothersome, you might consider using |
470 | perl's bugtron to find more information about discussions and |
471 | ramblings on posted bugs. |
472 | |
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473 | If you want to get the best of both worlds, rsync both the source |
474 | tree for convenience, reliability and ease and rsync the patches |
475 | for reference. |
476 | |
52315700 |
477 | =back |
478 | |
479 | |
480 | =head2 Perlbug remote interface |
481 | |
482 | =over 4 |
483 | |
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484 | There are three (3) remote administrative interfaces for modifying bug |
485 | status, category, etc. In all cases an admin must be first registered |
486 | with the Perlbug database by sending an email request to |
487 | richard@perl.org or bugmongers@perl.org. |
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488 | |
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489 | The main requirement is the willingness to classify, (with the |
490 | emphasis on closing where possible :), outstanding bugs. Further |
491 | explanation can be garnered from the web at http://bugs.perl.org/ , or |
492 | by asking on the admin mailing list at: bugmongers@perl.org |
52315700 |
493 | |
494 | For more info on the web see |
495 | |
496 | http://bugs.perl.org/perlbug.cgi?req=spec |
497 | |
498 | |
499 | B<The interfaces:> |
500 | |
501 | |
502 | =item 1 http://bugs.perl.org |
503 | |
504 | Login via the web, (remove B<admin/> if only browsing), where interested Cc's, tests, patches and change-ids, etc. may be assigned. |
505 | |
506 | http://bugs.perl.org/admin/index.html |
507 | |
508 | |
509 | =item 2 bugdb@perl.org |
510 | |
511 | Where the subject line is used for commands: |
512 | |
513 | To: bugdb@perl.org |
514 | Subject: -a close bugid1 bugid2 aix install |
515 | |
516 | To: bugdb@perl.org |
517 | Subject: -h |
518 | |
519 | |
520 | =item 3 commands_and_bugdids@bugs.perl.org |
521 | |
522 | Where the address itself is the source for the commands: |
523 | |
524 | To: close_bugid1_bugid2_aix@bugs.perl.org |
525 | |
526 | To: help@bugs.perl.org |
527 | |
528 | |
529 | =item notes, patches, tests |
530 | |
531 | For patches and tests, the message body is assigned to the appropriate bug/s and forwarded to p5p for their attention. |
532 | |
533 | To: test_<bugid1>_aix_close@bugs.perl.org |
534 | Subject: this is a test for the (now closed) aix bug |
535 | |
536 | Test is the body of the mail |
537 | |
538 | =back |
539 | |
a1f349fd |
540 | =head2 Submitting patches |
541 | |
f7e1e956 |
542 | Always submit patches to I<perl5-porters@perl.org>. If you're |
543 | patching a core module and there's an author listed, send the author a |
544 | copy (see L<Patching a core module>). This lets other porters review |
545 | your patch, which catches a surprising number of errors in patches. |
546 | Either use the diff program (available in source code form from |
f224927c |
547 | ftp://ftp.gnu.org/pub/gnu/ , or use Johan Vromans' I<makepatch> |
f7e1e956 |
548 | (available from I<CPAN/authors/id/JV/>). Unified diffs are preferred, |
549 | but context diffs are accepted. Do not send RCS-style diffs or diffs |
550 | without context lines. More information is given in the |
551 | I<Porting/patching.pod> file in the Perl source distribution. Please |
552 | patch against the latest B<development> version (e.g., if you're |
553 | fixing a bug in the 5.005 track, patch against the latest 5.005_5x |
554 | version). Only patches that survive the heat of the development |
555 | branch get applied to maintenance versions. |
556 | |
557 | Your patch should update the documentation and test suite. See |
558 | L<Writing a test>. |
e8cd7eae |
559 | |
560 | To report a bug in Perl, use the program I<perlbug> which comes with |
561 | Perl (if you can't get Perl to work, send mail to the address |
f18956b7 |
562 | I<perlbug@perl.org> or I<perlbug@perl.com>). Reporting bugs through |
e8cd7eae |
563 | I<perlbug> feeds into the automated bug-tracking system, access to |
f224927c |
564 | which is provided through the web at http://bugs.perl.org/ . It |
e8cd7eae |
565 | often pays to check the archives of the perl5-porters mailing list to |
566 | see whether the bug you're reporting has been reported before, and if |
567 | so whether it was considered a bug. See above for the location of |
568 | the searchable archives. |
569 | |
f224927c |
570 | The CPAN testers ( http://testers.cpan.org/ ) are a group of |
e8cd7eae |
571 | volunteers who test CPAN modules on a variety of platforms. Perl Labs |
f224927c |
572 | ( http://labs.perl.org/ ) automatically tests Perl source releases on |
f6c51b38 |
573 | platforms and gives feedback to the CPAN testers mailing list. Both |
574 | efforts welcome volunteers. |
e8cd7eae |
575 | |
e8cd7eae |
576 | It's a good idea to read and lurk for a while before chipping in. |
577 | That way you'll get to see the dynamic of the conversations, learn the |
578 | personalities of the players, and hopefully be better prepared to make |
579 | a useful contribution when do you speak up. |
580 | |
581 | If after all this you still think you want to join the perl5-porters |
f6c51b38 |
582 | mailing list, send mail to I<perl5-porters-subscribe@perl.org>. To |
583 | unsubscribe, send mail to I<perl5-porters-unsubscribe@perl.org>. |
e8cd7eae |
584 | |
a422fd2d |
585 | To hack on the Perl guts, you'll need to read the following things: |
586 | |
587 | =over 3 |
588 | |
589 | =item L<perlguts> |
590 | |
591 | This is of paramount importance, since it's the documentation of what |
592 | goes where in the Perl source. Read it over a couple of times and it |
593 | might start to make sense - don't worry if it doesn't yet, because the |
594 | best way to study it is to read it in conjunction with poking at Perl |
595 | source, and we'll do that later on. |
596 | |
597 | You might also want to look at Gisle Aas's illustrated perlguts - |
598 | there's no guarantee that this will be absolutely up-to-date with the |
599 | latest documentation in the Perl core, but the fundamentals will be |
1577cd80 |
600 | right. ( http://gisle.aas.no/perl/illguts/ ) |
a422fd2d |
601 | |
602 | =item L<perlxstut> and L<perlxs> |
603 | |
604 | A working knowledge of XSUB programming is incredibly useful for core |
605 | hacking; XSUBs use techniques drawn from the PP code, the portion of the |
606 | guts that actually executes a Perl program. It's a lot gentler to learn |
607 | those techniques from simple examples and explanation than from the core |
608 | itself. |
609 | |
610 | =item L<perlapi> |
611 | |
612 | The documentation for the Perl API explains what some of the internal |
613 | functions do, as well as the many macros used in the source. |
614 | |
615 | =item F<Porting/pumpkin.pod> |
616 | |
617 | This is a collection of words of wisdom for a Perl porter; some of it is |
618 | only useful to the pumpkin holder, but most of it applies to anyone |
619 | wanting to go about Perl development. |
620 | |
621 | =item The perl5-porters FAQ |
622 | |
623 | This is posted to perl5-porters at the beginning on every month, and |
f224927c |
624 | should be available from http://perlhacker.org/p5p-faq ; alternatively, |
a422fd2d |
625 | you can get the FAQ emailed to you by sending mail to |
626 | C<perl5-porters-faq@perl.org>. It contains hints on reading |
627 | perl5-porters, information on how perl5-porters works and how Perl |
628 | development in general works. |
629 | |
630 | =back |
631 | |
632 | =head2 Finding Your Way Around |
633 | |
634 | Perl maintenance can be split into a number of areas, and certain people |
635 | (pumpkins) will have responsibility for each area. These areas sometimes |
636 | correspond to files or directories in the source kit. Among the areas are: |
637 | |
638 | =over 3 |
639 | |
640 | =item Core modules |
641 | |
642 | Modules shipped as part of the Perl core live in the F<lib/> and F<ext/> |
643 | subdirectories: F<lib/> is for the pure-Perl modules, and F<ext/> |
644 | contains the core XS modules. |
645 | |
f7e1e956 |
646 | =item Tests |
647 | |
648 | There are tests for nearly all the modules, built-ins and major bits |
649 | of functionality. Test files all have a .t suffix. Module tests live |
650 | in the F<lib/> and F<ext/> directories next to the module being |
651 | tested. Others live in F<t/>. See L<Writing a test> |
652 | |
a422fd2d |
653 | =item Documentation |
654 | |
655 | Documentation maintenance includes looking after everything in the |
656 | F<pod/> directory, (as well as contributing new documentation) and |
657 | the documentation to the modules in core. |
658 | |
659 | =item Configure |
660 | |
661 | The configure process is the way we make Perl portable across the |
662 | myriad of operating systems it supports. Responsibility for the |
663 | configure, build and installation process, as well as the overall |
664 | portability of the core code rests with the configure pumpkin - others |
665 | help out with individual operating systems. |
666 | |
667 | The files involved are the operating system directories, (F<win32/>, |
668 | F<os2/>, F<vms/> and so on) the shell scripts which generate F<config.h> |
669 | and F<Makefile>, as well as the metaconfig files which generate |
670 | F<Configure>. (metaconfig isn't included in the core distribution.) |
671 | |
672 | =item Interpreter |
673 | |
674 | And of course, there's the core of the Perl interpreter itself. Let's |
675 | have a look at that in a little more detail. |
676 | |
677 | =back |
678 | |
679 | Before we leave looking at the layout, though, don't forget that |
680 | F<MANIFEST> contains not only the file names in the Perl distribution, |
681 | but short descriptions of what's in them, too. For an overview of the |
682 | important files, try this: |
683 | |
684 | perl -lne 'print if /^[^\/]+\.[ch]\s+/' MANIFEST |
685 | |
686 | =head2 Elements of the interpreter |
687 | |
688 | The work of the interpreter has two main stages: compiling the code |
689 | into the internal representation, or bytecode, and then executing it. |
690 | L<perlguts/Compiled code> explains exactly how the compilation stage |
691 | happens. |
692 | |
693 | Here is a short breakdown of perl's operation: |
694 | |
695 | =over 3 |
696 | |
697 | =item Startup |
698 | |
699 | The action begins in F<perlmain.c>. (or F<miniperlmain.c> for miniperl) |
700 | This is very high-level code, enough to fit on a single screen, and it |
701 | resembles the code found in L<perlembed>; most of the real action takes |
702 | place in F<perl.c> |
703 | |
704 | First, F<perlmain.c> allocates some memory and constructs a Perl |
705 | interpreter: |
706 | |
707 | 1 PERL_SYS_INIT3(&argc,&argv,&env); |
708 | 2 |
709 | 3 if (!PL_do_undump) { |
710 | 4 my_perl = perl_alloc(); |
711 | 5 if (!my_perl) |
712 | 6 exit(1); |
713 | 7 perl_construct(my_perl); |
714 | 8 PL_perl_destruct_level = 0; |
715 | 9 } |
716 | |
717 | Line 1 is a macro, and its definition is dependent on your operating |
718 | system. Line 3 references C<PL_do_undump>, a global variable - all |
719 | global variables in Perl start with C<PL_>. This tells you whether the |
720 | current running program was created with the C<-u> flag to perl and then |
721 | F<undump>, which means it's going to be false in any sane context. |
722 | |
723 | Line 4 calls a function in F<perl.c> to allocate memory for a Perl |
724 | interpreter. It's quite a simple function, and the guts of it looks like |
725 | this: |
726 | |
727 | my_perl = (PerlInterpreter*)PerlMem_malloc(sizeof(PerlInterpreter)); |
728 | |
729 | Here you see an example of Perl's system abstraction, which we'll see |
730 | later: C<PerlMem_malloc> is either your system's C<malloc>, or Perl's |
731 | own C<malloc> as defined in F<malloc.c> if you selected that option at |
732 | configure time. |
733 | |
734 | Next, in line 7, we construct the interpreter; this sets up all the |
735 | special variables that Perl needs, the stacks, and so on. |
736 | |
737 | Now we pass Perl the command line options, and tell it to go: |
738 | |
739 | exitstatus = perl_parse(my_perl, xs_init, argc, argv, (char **)NULL); |
740 | if (!exitstatus) { |
741 | exitstatus = perl_run(my_perl); |
742 | } |
743 | |
744 | |
745 | C<perl_parse> is actually a wrapper around C<S_parse_body>, as defined |
746 | in F<perl.c>, which processes the command line options, sets up any |
747 | statically linked XS modules, opens the program and calls C<yyparse> to |
748 | parse it. |
749 | |
750 | =item Parsing |
751 | |
752 | The aim of this stage is to take the Perl source, and turn it into an op |
753 | tree. We'll see what one of those looks like later. Strictly speaking, |
754 | there's three things going on here. |
755 | |
756 | C<yyparse>, the parser, lives in F<perly.c>, although you're better off |
757 | reading the original YACC input in F<perly.y>. (Yes, Virginia, there |
758 | B<is> a YACC grammar for Perl!) The job of the parser is to take your |
759 | code and `understand' it, splitting it into sentences, deciding which |
760 | operands go with which operators and so on. |
761 | |
762 | The parser is nobly assisted by the lexer, which chunks up your input |
763 | into tokens, and decides what type of thing each token is: a variable |
764 | name, an operator, a bareword, a subroutine, a core function, and so on. |
765 | The main point of entry to the lexer is C<yylex>, and that and its |
766 | associated routines can be found in F<toke.c>. Perl isn't much like |
767 | other computer languages; it's highly context sensitive at times, it can |
768 | be tricky to work out what sort of token something is, or where a token |
769 | ends. As such, there's a lot of interplay between the tokeniser and the |
770 | parser, which can get pretty frightening if you're not used to it. |
771 | |
772 | As the parser understands a Perl program, it builds up a tree of |
773 | operations for the interpreter to perform during execution. The routines |
774 | which construct and link together the various operations are to be found |
775 | in F<op.c>, and will be examined later. |
776 | |
777 | =item Optimization |
778 | |
779 | Now the parsing stage is complete, and the finished tree represents |
780 | the operations that the Perl interpreter needs to perform to execute our |
781 | program. Next, Perl does a dry run over the tree looking for |
782 | optimisations: constant expressions such as C<3 + 4> will be computed |
783 | now, and the optimizer will also see if any multiple operations can be |
784 | replaced with a single one. For instance, to fetch the variable C<$foo>, |
785 | instead of grabbing the glob C<*foo> and looking at the scalar |
786 | component, the optimizer fiddles the op tree to use a function which |
787 | directly looks up the scalar in question. The main optimizer is C<peep> |
788 | in F<op.c>, and many ops have their own optimizing functions. |
789 | |
790 | =item Running |
791 | |
792 | Now we're finally ready to go: we have compiled Perl byte code, and all |
793 | that's left to do is run it. The actual execution is done by the |
794 | C<runops_standard> function in F<run.c>; more specifically, it's done by |
795 | these three innocent looking lines: |
796 | |
797 | while ((PL_op = CALL_FPTR(PL_op->op_ppaddr)(aTHX))) { |
798 | PERL_ASYNC_CHECK(); |
799 | } |
800 | |
801 | You may be more comfortable with the Perl version of that: |
802 | |
803 | PERL_ASYNC_CHECK() while $Perl::op = &{$Perl::op->{function}}; |
804 | |
805 | Well, maybe not. Anyway, each op contains a function pointer, which |
806 | stipulates the function which will actually carry out the operation. |
807 | This function will return the next op in the sequence - this allows for |
808 | things like C<if> which choose the next op dynamically at run time. |
809 | The C<PERL_ASYNC_CHECK> makes sure that things like signals interrupt |
810 | execution if required. |
811 | |
812 | The actual functions called are known as PP code, and they're spread |
813 | between four files: F<pp_hot.c> contains the `hot' code, which is most |
814 | often used and highly optimized, F<pp_sys.c> contains all the |
815 | system-specific functions, F<pp_ctl.c> contains the functions which |
816 | implement control structures (C<if>, C<while> and the like) and F<pp.c> |
817 | contains everything else. These are, if you like, the C code for Perl's |
818 | built-in functions and operators. |
819 | |
820 | =back |
821 | |
822 | =head2 Internal Variable Types |
823 | |
824 | You should by now have had a look at L<perlguts>, which tells you about |
825 | Perl's internal variable types: SVs, HVs, AVs and the rest. If not, do |
826 | that now. |
827 | |
828 | These variables are used not only to represent Perl-space variables, but |
829 | also any constants in the code, as well as some structures completely |
830 | internal to Perl. The symbol table, for instance, is an ordinary Perl |
831 | hash. Your code is represented by an SV as it's read into the parser; |
832 | any program files you call are opened via ordinary Perl filehandles, and |
833 | so on. |
834 | |
835 | The core L<Devel::Peek|Devel::Peek> module lets us examine SVs from a |
836 | Perl program. Let's see, for instance, how Perl treats the constant |
837 | C<"hello">. |
838 | |
839 | % perl -MDevel::Peek -e 'Dump("hello")' |
840 | 1 SV = PV(0xa041450) at 0xa04ecbc |
841 | 2 REFCNT = 1 |
842 | 3 FLAGS = (POK,READONLY,pPOK) |
843 | 4 PV = 0xa0484e0 "hello"\0 |
844 | 5 CUR = 5 |
845 | 6 LEN = 6 |
846 | |
847 | Reading C<Devel::Peek> output takes a bit of practise, so let's go |
848 | through it line by line. |
849 | |
850 | Line 1 tells us we're looking at an SV which lives at C<0xa04ecbc> in |
851 | memory. SVs themselves are very simple structures, but they contain a |
852 | pointer to a more complex structure. In this case, it's a PV, a |
853 | structure which holds a string value, at location C<0xa041450>. Line 2 |
854 | is the reference count; there are no other references to this data, so |
855 | it's 1. |
856 | |
857 | Line 3 are the flags for this SV - it's OK to use it as a PV, it's a |
858 | read-only SV (because it's a constant) and the data is a PV internally. |
859 | Next we've got the contents of the string, starting at location |
860 | C<0xa0484e0>. |
861 | |
862 | Line 5 gives us the current length of the string - note that this does |
863 | B<not> include the null terminator. Line 6 is not the length of the |
864 | string, but the length of the currently allocated buffer; as the string |
865 | grows, Perl automatically extends the available storage via a routine |
866 | called C<SvGROW>. |
867 | |
868 | You can get at any of these quantities from C very easily; just add |
869 | C<Sv> to the name of the field shown in the snippet, and you've got a |
870 | macro which will return the value: C<SvCUR(sv)> returns the current |
871 | length of the string, C<SvREFCOUNT(sv)> returns the reference count, |
872 | C<SvPV(sv, len)> returns the string itself with its length, and so on. |
873 | More macros to manipulate these properties can be found in L<perlguts>. |
874 | |
875 | Let's take an example of manipulating a PV, from C<sv_catpvn>, in F<sv.c> |
876 | |
877 | 1 void |
878 | 2 Perl_sv_catpvn(pTHX_ register SV *sv, register const char *ptr, register STRLEN len) |
879 | 3 { |
880 | 4 STRLEN tlen; |
881 | 5 char *junk; |
882 | |
883 | 6 junk = SvPV_force(sv, tlen); |
884 | 7 SvGROW(sv, tlen + len + 1); |
885 | 8 if (ptr == junk) |
886 | 9 ptr = SvPVX(sv); |
887 | 10 Move(ptr,SvPVX(sv)+tlen,len,char); |
888 | 11 SvCUR(sv) += len; |
889 | 12 *SvEND(sv) = '\0'; |
890 | 13 (void)SvPOK_only_UTF8(sv); /* validate pointer */ |
891 | 14 SvTAINT(sv); |
892 | 15 } |
893 | |
894 | This is a function which adds a string, C<ptr>, of length C<len> onto |
895 | the end of the PV stored in C<sv>. The first thing we do in line 6 is |
896 | make sure that the SV B<has> a valid PV, by calling the C<SvPV_force> |
897 | macro to force a PV. As a side effect, C<tlen> gets set to the current |
898 | value of the PV, and the PV itself is returned to C<junk>. |
899 | |
b1866b2d |
900 | In line 7, we make sure that the SV will have enough room to accommodate |
a422fd2d |
901 | the old string, the new string and the null terminator. If C<LEN> isn't |
902 | big enough, C<SvGROW> will reallocate space for us. |
903 | |
904 | Now, if C<junk> is the same as the string we're trying to add, we can |
905 | grab the string directly from the SV; C<SvPVX> is the address of the PV |
906 | in the SV. |
907 | |
908 | Line 10 does the actual catenation: the C<Move> macro moves a chunk of |
909 | memory around: we move the string C<ptr> to the end of the PV - that's |
910 | the start of the PV plus its current length. We're moving C<len> bytes |
911 | of type C<char>. After doing so, we need to tell Perl we've extended the |
912 | string, by altering C<CUR> to reflect the new length. C<SvEND> is a |
913 | macro which gives us the end of the string, so that needs to be a |
914 | C<"\0">. |
915 | |
916 | Line 13 manipulates the flags; since we've changed the PV, any IV or NV |
917 | values will no longer be valid: if we have C<$a=10; $a.="6";> we don't |
918 | want to use the old IV of 10. C<SvPOK_only_utf8> is a special UTF8-aware |
919 | version of C<SvPOK_only>, a macro which turns off the IOK and NOK flags |
920 | and turns on POK. The final C<SvTAINT> is a macro which launders tainted |
921 | data if taint mode is turned on. |
922 | |
923 | AVs and HVs are more complicated, but SVs are by far the most common |
924 | variable type being thrown around. Having seen something of how we |
925 | manipulate these, let's go on and look at how the op tree is |
926 | constructed. |
927 | |
928 | =head2 Op Trees |
929 | |
930 | First, what is the op tree, anyway? The op tree is the parsed |
931 | representation of your program, as we saw in our section on parsing, and |
932 | it's the sequence of operations that Perl goes through to execute your |
933 | program, as we saw in L</Running>. |
934 | |
935 | An op is a fundamental operation that Perl can perform: all the built-in |
936 | functions and operators are ops, and there are a series of ops which |
937 | deal with concepts the interpreter needs internally - entering and |
938 | leaving a block, ending a statement, fetching a variable, and so on. |
939 | |
940 | The op tree is connected in two ways: you can imagine that there are two |
941 | "routes" through it, two orders in which you can traverse the tree. |
942 | First, parse order reflects how the parser understood the code, and |
943 | secondly, execution order tells perl what order to perform the |
944 | operations in. |
945 | |
946 | The easiest way to examine the op tree is to stop Perl after it has |
947 | finished parsing, and get it to dump out the tree. This is exactly what |
948 | the compiler backends L<B::Terse|B::Terse> and L<B::Debug|B::Debug> do. |
949 | |
950 | Let's have a look at how Perl sees C<$a = $b + $c>: |
951 | |
952 | % perl -MO=Terse -e '$a=$b+$c' |
953 | 1 LISTOP (0x8179888) leave |
954 | 2 OP (0x81798b0) enter |
955 | 3 COP (0x8179850) nextstate |
956 | 4 BINOP (0x8179828) sassign |
957 | 5 BINOP (0x8179800) add [1] |
958 | 6 UNOP (0x81796e0) null [15] |
959 | 7 SVOP (0x80fafe0) gvsv GV (0x80fa4cc) *b |
960 | 8 UNOP (0x81797e0) null [15] |
961 | 9 SVOP (0x8179700) gvsv GV (0x80efeb0) *c |
962 | 10 UNOP (0x816b4f0) null [15] |
963 | 11 SVOP (0x816dcf0) gvsv GV (0x80fa460) *a |
964 | |
965 | Let's start in the middle, at line 4. This is a BINOP, a binary |
966 | operator, which is at location C<0x8179828>. The specific operator in |
967 | question is C<sassign> - scalar assignment - and you can find the code |
968 | which implements it in the function C<pp_sassign> in F<pp_hot.c>. As a |
969 | binary operator, it has two children: the add operator, providing the |
970 | result of C<$b+$c>, is uppermost on line 5, and the left hand side is on |
971 | line 10. |
972 | |
973 | Line 10 is the null op: this does exactly nothing. What is that doing |
974 | there? If you see the null op, it's a sign that something has been |
975 | optimized away after parsing. As we mentioned in L</Optimization>, |
976 | the optimization stage sometimes converts two operations into one, for |
977 | example when fetching a scalar variable. When this happens, instead of |
978 | rewriting the op tree and cleaning up the dangling pointers, it's easier |
979 | just to replace the redundant operation with the null op. Originally, |
980 | the tree would have looked like this: |
981 | |
982 | 10 SVOP (0x816b4f0) rv2sv [15] |
983 | 11 SVOP (0x816dcf0) gv GV (0x80fa460) *a |
984 | |
985 | That is, fetch the C<a> entry from the main symbol table, and then look |
986 | at the scalar component of it: C<gvsv> (C<pp_gvsv> into F<pp_hot.c>) |
987 | happens to do both these things. |
988 | |
989 | The right hand side, starting at line 5 is similar to what we've just |
990 | seen: we have the C<add> op (C<pp_add> also in F<pp_hot.c>) add together |
991 | two C<gvsv>s. |
992 | |
993 | Now, what's this about? |
994 | |
995 | 1 LISTOP (0x8179888) leave |
996 | 2 OP (0x81798b0) enter |
997 | 3 COP (0x8179850) nextstate |
998 | |
999 | C<enter> and C<leave> are scoping ops, and their job is to perform any |
1000 | housekeeping every time you enter and leave a block: lexical variables |
1001 | are tidied up, unreferenced variables are destroyed, and so on. Every |
1002 | program will have those first three lines: C<leave> is a list, and its |
1003 | children are all the statements in the block. Statements are delimited |
1004 | by C<nextstate>, so a block is a collection of C<nextstate> ops, with |
1005 | the ops to be performed for each statement being the children of |
1006 | C<nextstate>. C<enter> is a single op which functions as a marker. |
1007 | |
1008 | That's how Perl parsed the program, from top to bottom: |
1009 | |
1010 | Program |
1011 | | |
1012 | Statement |
1013 | | |
1014 | = |
1015 | / \ |
1016 | / \ |
1017 | $a + |
1018 | / \ |
1019 | $b $c |
1020 | |
1021 | However, it's impossible to B<perform> the operations in this order: |
1022 | you have to find the values of C<$b> and C<$c> before you add them |
1023 | together, for instance. So, the other thread that runs through the op |
1024 | tree is the execution order: each op has a field C<op_next> which points |
1025 | to the next op to be run, so following these pointers tells us how perl |
1026 | executes the code. We can traverse the tree in this order using |
1027 | the C<exec> option to C<B::Terse>: |
1028 | |
1029 | % perl -MO=Terse,exec -e '$a=$b+$c' |
1030 | 1 OP (0x8179928) enter |
1031 | 2 COP (0x81798c8) nextstate |
1032 | 3 SVOP (0x81796c8) gvsv GV (0x80fa4d4) *b |
1033 | 4 SVOP (0x8179798) gvsv GV (0x80efeb0) *c |
1034 | 5 BINOP (0x8179878) add [1] |
1035 | 6 SVOP (0x816dd38) gvsv GV (0x80fa468) *a |
1036 | 7 BINOP (0x81798a0) sassign |
1037 | 8 LISTOP (0x8179900) leave |
1038 | |
1039 | This probably makes more sense for a human: enter a block, start a |
1040 | statement. Get the values of C<$b> and C<$c>, and add them together. |
1041 | Find C<$a>, and assign one to the other. Then leave. |
1042 | |
1043 | The way Perl builds up these op trees in the parsing process can be |
1044 | unravelled by examining F<perly.y>, the YACC grammar. Let's take the |
1045 | piece we need to construct the tree for C<$a = $b + $c> |
1046 | |
1047 | 1 term : term ASSIGNOP term |
1048 | 2 { $$ = newASSIGNOP(OPf_STACKED, $1, $2, $3); } |
1049 | 3 | term ADDOP term |
1050 | 4 { $$ = newBINOP($2, 0, scalar($1), scalar($3)); } |
1051 | |
1052 | If you're not used to reading BNF grammars, this is how it works: You're |
1053 | fed certain things by the tokeniser, which generally end up in upper |
1054 | case. Here, C<ADDOP>, is provided when the tokeniser sees C<+> in your |
1055 | code. C<ASSIGNOP> is provided when C<=> is used for assigning. These are |
1056 | `terminal symbols', because you can't get any simpler than them. |
1057 | |
1058 | The grammar, lines one and three of the snippet above, tells you how to |
1059 | build up more complex forms. These complex forms, `non-terminal symbols' |
1060 | are generally placed in lower case. C<term> here is a non-terminal |
1061 | symbol, representing a single expression. |
1062 | |
1063 | The grammar gives you the following rule: you can make the thing on the |
1064 | left of the colon if you see all the things on the right in sequence. |
1065 | This is called a "reduction", and the aim of parsing is to completely |
1066 | reduce the input. There are several different ways you can perform a |
1067 | reduction, separated by vertical bars: so, C<term> followed by C<=> |
1068 | followed by C<term> makes a C<term>, and C<term> followed by C<+> |
1069 | followed by C<term> can also make a C<term>. |
1070 | |
1071 | So, if you see two terms with an C<=> or C<+>, between them, you can |
1072 | turn them into a single expression. When you do this, you execute the |
1073 | code in the block on the next line: if you see C<=>, you'll do the code |
1074 | in line 2. If you see C<+>, you'll do the code in line 4. It's this code |
1075 | which contributes to the op tree. |
1076 | |
1077 | | term ADDOP term |
1078 | { $$ = newBINOP($2, 0, scalar($1), scalar($3)); } |
1079 | |
1080 | What this does is creates a new binary op, and feeds it a number of |
1081 | variables. The variables refer to the tokens: C<$1> is the first token in |
1082 | the input, C<$2> the second, and so on - think regular expression |
1083 | backreferences. C<$$> is the op returned from this reduction. So, we |
1084 | call C<newBINOP> to create a new binary operator. The first parameter to |
1085 | C<newBINOP>, a function in F<op.c>, is the op type. It's an addition |
1086 | operator, so we want the type to be C<ADDOP>. We could specify this |
1087 | directly, but it's right there as the second token in the input, so we |
1088 | use C<$2>. The second parameter is the op's flags: 0 means `nothing |
1089 | special'. Then the things to add: the left and right hand side of our |
1090 | expression, in scalar context. |
1091 | |
1092 | =head2 Stacks |
1093 | |
1094 | When perl executes something like C<addop>, how does it pass on its |
1095 | results to the next op? The answer is, through the use of stacks. Perl |
1096 | has a number of stacks to store things it's currently working on, and |
1097 | we'll look at the three most important ones here. |
1098 | |
1099 | =over 3 |
1100 | |
1101 | =item Argument stack |
1102 | |
1103 | Arguments are passed to PP code and returned from PP code using the |
1104 | argument stack, C<ST>. The typical way to handle arguments is to pop |
1105 | them off the stack, deal with them how you wish, and then push the result |
1106 | back onto the stack. This is how, for instance, the cosine operator |
1107 | works: |
1108 | |
1109 | NV value; |
1110 | value = POPn; |
1111 | value = Perl_cos(value); |
1112 | XPUSHn(value); |
1113 | |
1114 | We'll see a more tricky example of this when we consider Perl's macros |
1115 | below. C<POPn> gives you the NV (floating point value) of the top SV on |
1116 | the stack: the C<$x> in C<cos($x)>. Then we compute the cosine, and push |
1117 | the result back as an NV. The C<X> in C<XPUSHn> means that the stack |
1118 | should be extended if necessary - it can't be necessary here, because we |
1119 | know there's room for one more item on the stack, since we've just |
1120 | removed one! The C<XPUSH*> macros at least guarantee safety. |
1121 | |
1122 | Alternatively, you can fiddle with the stack directly: C<SP> gives you |
1123 | the first element in your portion of the stack, and C<TOP*> gives you |
1124 | the top SV/IV/NV/etc. on the stack. So, for instance, to do unary |
1125 | negation of an integer: |
1126 | |
1127 | SETi(-TOPi); |
1128 | |
1129 | Just set the integer value of the top stack entry to its negation. |
1130 | |
1131 | Argument stack manipulation in the core is exactly the same as it is in |
1132 | XSUBs - see L<perlxstut>, L<perlxs> and L<perlguts> for a longer |
1133 | description of the macros used in stack manipulation. |
1134 | |
1135 | =item Mark stack |
1136 | |
1137 | I say `your portion of the stack' above because PP code doesn't |
1138 | necessarily get the whole stack to itself: if your function calls |
1139 | another function, you'll only want to expose the arguments aimed for the |
1140 | called function, and not (necessarily) let it get at your own data. The |
1141 | way we do this is to have a `virtual' bottom-of-stack, exposed to each |
1142 | function. The mark stack keeps bookmarks to locations in the argument |
1143 | stack usable by each function. For instance, when dealing with a tied |
1144 | variable, (internally, something with `P' magic) Perl has to call |
1145 | methods for accesses to the tied variables. However, we need to separate |
1146 | the arguments exposed to the method to the argument exposed to the |
1147 | original function - the store or fetch or whatever it may be. Here's how |
1148 | the tied C<push> is implemented; see C<av_push> in F<av.c>: |
1149 | |
1150 | 1 PUSHMARK(SP); |
1151 | 2 EXTEND(SP,2); |
1152 | 3 PUSHs(SvTIED_obj((SV*)av, mg)); |
1153 | 4 PUSHs(val); |
1154 | 5 PUTBACK; |
1155 | 6 ENTER; |
1156 | 7 call_method("PUSH", G_SCALAR|G_DISCARD); |
1157 | 8 LEAVE; |
1158 | 9 POPSTACK; |
13a2d996 |
1159 | |
a422fd2d |
1160 | The lines which concern the mark stack are the first, fifth and last |
1161 | lines: they save away, restore and remove the current position of the |
1162 | argument stack. |
1163 | |
1164 | Let's examine the whole implementation, for practice: |
1165 | |
1166 | 1 PUSHMARK(SP); |
1167 | |
1168 | Push the current state of the stack pointer onto the mark stack. This is |
1169 | so that when we've finished adding items to the argument stack, Perl |
1170 | knows how many things we've added recently. |
1171 | |
1172 | 2 EXTEND(SP,2); |
1173 | 3 PUSHs(SvTIED_obj((SV*)av, mg)); |
1174 | 4 PUSHs(val); |
1175 | |
1176 | We're going to add two more items onto the argument stack: when you have |
1177 | a tied array, the C<PUSH> subroutine receives the object and the value |
1178 | to be pushed, and that's exactly what we have here - the tied object, |
1179 | retrieved with C<SvTIED_obj>, and the value, the SV C<val>. |
1180 | |
1181 | 5 PUTBACK; |
1182 | |
1183 | Next we tell Perl to make the change to the global stack pointer: C<dSP> |
1184 | only gave us a local copy, not a reference to the global. |
1185 | |
1186 | 6 ENTER; |
1187 | 7 call_method("PUSH", G_SCALAR|G_DISCARD); |
1188 | 8 LEAVE; |
1189 | |
1190 | C<ENTER> and C<LEAVE> localise a block of code - they make sure that all |
1191 | variables are tidied up, everything that has been localised gets |
1192 | its previous value returned, and so on. Think of them as the C<{> and |
1193 | C<}> of a Perl block. |
1194 | |
1195 | To actually do the magic method call, we have to call a subroutine in |
1196 | Perl space: C<call_method> takes care of that, and it's described in |
1197 | L<perlcall>. We call the C<PUSH> method in scalar context, and we're |
1198 | going to discard its return value. |
1199 | |
1200 | 9 POPSTACK; |
1201 | |
1202 | Finally, we remove the value we placed on the mark stack, since we |
1203 | don't need it any more. |
1204 | |
1205 | =item Save stack |
1206 | |
1207 | C doesn't have a concept of local scope, so perl provides one. We've |
1208 | seen that C<ENTER> and C<LEAVE> are used as scoping braces; the save |
1209 | stack implements the C equivalent of, for example: |
1210 | |
1211 | { |
1212 | local $foo = 42; |
1213 | ... |
1214 | } |
1215 | |
1216 | See L<perlguts/Localising Changes> for how to use the save stack. |
1217 | |
1218 | =back |
1219 | |
1220 | =head2 Millions of Macros |
1221 | |
1222 | One thing you'll notice about the Perl source is that it's full of |
1223 | macros. Some have called the pervasive use of macros the hardest thing |
1224 | to understand, others find it adds to clarity. Let's take an example, |
1225 | the code which implements the addition operator: |
1226 | |
1227 | 1 PP(pp_add) |
1228 | 2 { |
39644a26 |
1229 | 3 dSP; dATARGET; tryAMAGICbin(add,opASSIGN); |
a422fd2d |
1230 | 4 { |
1231 | 5 dPOPTOPnnrl_ul; |
1232 | 6 SETn( left + right ); |
1233 | 7 RETURN; |
1234 | 8 } |
1235 | 9 } |
1236 | |
1237 | Every line here (apart from the braces, of course) contains a macro. The |
1238 | first line sets up the function declaration as Perl expects for PP code; |
1239 | line 3 sets up variable declarations for the argument stack and the |
1240 | target, the return value of the operation. Finally, it tries to see if |
1241 | the addition operation is overloaded; if so, the appropriate subroutine |
1242 | is called. |
1243 | |
1244 | Line 5 is another variable declaration - all variable declarations start |
1245 | with C<d> - which pops from the top of the argument stack two NVs (hence |
1246 | C<nn>) and puts them into the variables C<right> and C<left>, hence the |
1247 | C<rl>. These are the two operands to the addition operator. Next, we |
1248 | call C<SETn> to set the NV of the return value to the result of adding |
1249 | the two values. This done, we return - the C<RETURN> macro makes sure |
1250 | that our return value is properly handled, and we pass the next operator |
1251 | to run back to the main run loop. |
1252 | |
1253 | Most of these macros are explained in L<perlapi>, and some of the more |
1254 | important ones are explained in L<perlxs> as well. Pay special attention |
1255 | to L<perlguts/Background and PERL_IMPLICIT_CONTEXT> for information on |
1256 | the C<[pad]THX_?> macros. |
1257 | |
a422fd2d |
1258 | =head2 Poking at Perl |
1259 | |
1260 | To really poke around with Perl, you'll probably want to build Perl for |
1261 | debugging, like this: |
1262 | |
1263 | ./Configure -d -D optimize=-g |
1264 | make |
1265 | |
1266 | C<-g> is a flag to the C compiler to have it produce debugging |
1267 | information which will allow us to step through a running program. |
1268 | F<Configure> will also turn on the C<DEBUGGING> compilation symbol which |
1269 | enables all the internal debugging code in Perl. There are a whole bunch |
1270 | of things you can debug with this: L<perlrun> lists them all, and the |
1271 | best way to find out about them is to play about with them. The most |
1272 | useful options are probably |
1273 | |
1274 | l Context (loop) stack processing |
1275 | t Trace execution |
1276 | o Method and overloading resolution |
1277 | c String/numeric conversions |
1278 | |
1279 | Some of the functionality of the debugging code can be achieved using XS |
1280 | modules. |
13a2d996 |
1281 | |
a422fd2d |
1282 | -Dr => use re 'debug' |
1283 | -Dx => use O 'Debug' |
1284 | |
1285 | =head2 Using a source-level debugger |
1286 | |
1287 | If the debugging output of C<-D> doesn't help you, it's time to step |
1288 | through perl's execution with a source-level debugger. |
1289 | |
1290 | =over 3 |
1291 | |
1292 | =item * |
1293 | |
1294 | We'll use C<gdb> for our examples here; the principles will apply to any |
1295 | debugger, but check the manual of the one you're using. |
1296 | |
1297 | =back |
1298 | |
1299 | To fire up the debugger, type |
1300 | |
1301 | gdb ./perl |
1302 | |
1303 | You'll want to do that in your Perl source tree so the debugger can read |
1304 | the source code. You should see the copyright message, followed by the |
1305 | prompt. |
1306 | |
1307 | (gdb) |
1308 | |
1309 | C<help> will get you into the documentation, but here are the most |
1310 | useful commands: |
1311 | |
1312 | =over 3 |
1313 | |
1314 | =item run [args] |
1315 | |
1316 | Run the program with the given arguments. |
1317 | |
1318 | =item break function_name |
1319 | |
1320 | =item break source.c:xxx |
1321 | |
1322 | Tells the debugger that we'll want to pause execution when we reach |
cea6626f |
1323 | either the named function (but see L<perlguts/Internal Functions>!) or the given |
a422fd2d |
1324 | line in the named source file. |
1325 | |
1326 | =item step |
1327 | |
1328 | Steps through the program a line at a time. |
1329 | |
1330 | =item next |
1331 | |
1332 | Steps through the program a line at a time, without descending into |
1333 | functions. |
1334 | |
1335 | =item continue |
1336 | |
1337 | Run until the next breakpoint. |
1338 | |
1339 | =item finish |
1340 | |
1341 | Run until the end of the current function, then stop again. |
1342 | |
13a2d996 |
1343 | =item 'enter' |
a422fd2d |
1344 | |
1345 | Just pressing Enter will do the most recent operation again - it's a |
1346 | blessing when stepping through miles of source code. |
1347 | |
1348 | =item print |
1349 | |
1350 | Execute the given C code and print its results. B<WARNING>: Perl makes |
1351 | heavy use of macros, and F<gdb> is not aware of macros. You'll have to |
1352 | substitute them yourself. So, for instance, you can't say |
1353 | |
1354 | print SvPV_nolen(sv) |
1355 | |
1356 | but you have to say |
1357 | |
1358 | print Perl_sv_2pv_nolen(sv) |
1359 | |
1360 | You may find it helpful to have a "macro dictionary", which you can |
1361 | produce by saying C<cpp -dM perl.c | sort>. Even then, F<cpp> won't |
1362 | recursively apply the macros for you. |
1363 | |
1364 | =back |
1365 | |
1366 | =head2 Dumping Perl Data Structures |
1367 | |
1368 | One way to get around this macro hell is to use the dumping functions in |
1369 | F<dump.c>; these work a little like an internal |
1370 | L<Devel::Peek|Devel::Peek>, but they also cover OPs and other structures |
1371 | that you can't get at from Perl. Let's take an example. We'll use the |
1372 | C<$a = $b + $c> we used before, but give it a bit of context: |
1373 | C<$b = "6XXXX"; $c = 2.3;>. Where's a good place to stop and poke around? |
1374 | |
1375 | What about C<pp_add>, the function we examined earlier to implement the |
1376 | C<+> operator: |
1377 | |
1378 | (gdb) break Perl_pp_add |
1379 | Breakpoint 1 at 0x46249f: file pp_hot.c, line 309. |
1380 | |
cea6626f |
1381 | Notice we use C<Perl_pp_add> and not C<pp_add> - see L<perlguts/Internal Functions>. |
a422fd2d |
1382 | With the breakpoint in place, we can run our program: |
1383 | |
1384 | (gdb) run -e '$b = "6XXXX"; $c = 2.3; $a = $b + $c' |
1385 | |
1386 | Lots of junk will go past as gdb reads in the relevant source files and |
1387 | libraries, and then: |
1388 | |
1389 | Breakpoint 1, Perl_pp_add () at pp_hot.c:309 |
39644a26 |
1390 | 309 dSP; dATARGET; tryAMAGICbin(add,opASSIGN); |
a422fd2d |
1391 | (gdb) step |
1392 | 311 dPOPTOPnnrl_ul; |
1393 | (gdb) |
1394 | |
1395 | We looked at this bit of code before, and we said that C<dPOPTOPnnrl_ul> |
1396 | arranges for two C<NV>s to be placed into C<left> and C<right> - let's |
1397 | slightly expand it: |
1398 | |
1399 | #define dPOPTOPnnrl_ul NV right = POPn; \ |
1400 | SV *leftsv = TOPs; \ |
1401 | NV left = USE_LEFT(leftsv) ? SvNV(leftsv) : 0.0 |
1402 | |
1403 | C<POPn> takes the SV from the top of the stack and obtains its NV either |
1404 | directly (if C<SvNOK> is set) or by calling the C<sv_2nv> function. |
1405 | C<TOPs> takes the next SV from the top of the stack - yes, C<POPn> uses |
1406 | C<TOPs> - but doesn't remove it. We then use C<SvNV> to get the NV from |
1407 | C<leftsv> in the same way as before - yes, C<POPn> uses C<SvNV>. |
1408 | |
1409 | Since we don't have an NV for C<$b>, we'll have to use C<sv_2nv> to |
1410 | convert it. If we step again, we'll find ourselves there: |
1411 | |
1412 | Perl_sv_2nv (sv=0xa0675d0) at sv.c:1669 |
1413 | 1669 if (!sv) |
1414 | (gdb) |
1415 | |
1416 | We can now use C<Perl_sv_dump> to investigate the SV: |
1417 | |
1418 | SV = PV(0xa057cc0) at 0xa0675d0 |
1419 | REFCNT = 1 |
1420 | FLAGS = (POK,pPOK) |
1421 | PV = 0xa06a510 "6XXXX"\0 |
1422 | CUR = 5 |
1423 | LEN = 6 |
1424 | $1 = void |
1425 | |
1426 | We know we're going to get C<6> from this, so let's finish the |
1427 | subroutine: |
1428 | |
1429 | (gdb) finish |
1430 | Run till exit from #0 Perl_sv_2nv (sv=0xa0675d0) at sv.c:1671 |
1431 | 0x462669 in Perl_pp_add () at pp_hot.c:311 |
1432 | 311 dPOPTOPnnrl_ul; |
1433 | |
1434 | We can also dump out this op: the current op is always stored in |
1435 | C<PL_op>, and we can dump it with C<Perl_op_dump>. This'll give us |
1436 | similar output to L<B::Debug|B::Debug>. |
1437 | |
1438 | { |
1439 | 13 TYPE = add ===> 14 |
1440 | TARG = 1 |
1441 | FLAGS = (SCALAR,KIDS) |
1442 | { |
1443 | TYPE = null ===> (12) |
1444 | (was rv2sv) |
1445 | FLAGS = (SCALAR,KIDS) |
1446 | { |
1447 | 11 TYPE = gvsv ===> 12 |
1448 | FLAGS = (SCALAR) |
1449 | GV = main::b |
1450 | } |
1451 | } |
1452 | |
10f58044 |
1453 | # finish this later # |
a422fd2d |
1454 | |
1455 | =head2 Patching |
1456 | |
1457 | All right, we've now had a look at how to navigate the Perl sources and |
1458 | some things you'll need to know when fiddling with them. Let's now get |
1459 | on and create a simple patch. Here's something Larry suggested: if a |
1460 | C<U> is the first active format during a C<pack>, (for example, |
1461 | C<pack "U3C8", @stuff>) then the resulting string should be treated as |
1462 | UTF8 encoded. |
1463 | |
1464 | How do we prepare to fix this up? First we locate the code in question - |
1465 | the C<pack> happens at runtime, so it's going to be in one of the F<pp> |
1466 | files. Sure enough, C<pp_pack> is in F<pp.c>. Since we're going to be |
1467 | altering this file, let's copy it to F<pp.c~>. |
1468 | |
a6ec74c1 |
1469 | [Well, it was in F<pp.c> when this tutorial was written. It has now been |
1470 | split off with C<pp_unpack> to its own file, F<pp_pack.c>] |
1471 | |
a422fd2d |
1472 | Now let's look over C<pp_pack>: we take a pattern into C<pat>, and then |
1473 | loop over the pattern, taking each format character in turn into |
1474 | C<datum_type>. Then for each possible format character, we swallow up |
1475 | the other arguments in the pattern (a field width, an asterisk, and so |
1476 | on) and convert the next chunk input into the specified format, adding |
1477 | it onto the output SV C<cat>. |
1478 | |
1479 | How do we know if the C<U> is the first format in the C<pat>? Well, if |
1480 | we have a pointer to the start of C<pat> then, if we see a C<U> we can |
1481 | test whether we're still at the start of the string. So, here's where |
1482 | C<pat> is set up: |
1483 | |
1484 | STRLEN fromlen; |
1485 | register char *pat = SvPVx(*++MARK, fromlen); |
1486 | register char *patend = pat + fromlen; |
1487 | register I32 len; |
1488 | I32 datumtype; |
1489 | SV *fromstr; |
1490 | |
1491 | We'll have another string pointer in there: |
1492 | |
1493 | STRLEN fromlen; |
1494 | register char *pat = SvPVx(*++MARK, fromlen); |
1495 | register char *patend = pat + fromlen; |
1496 | + char *patcopy; |
1497 | register I32 len; |
1498 | I32 datumtype; |
1499 | SV *fromstr; |
1500 | |
1501 | And just before we start the loop, we'll set C<patcopy> to be the start |
1502 | of C<pat>: |
1503 | |
1504 | items = SP - MARK; |
1505 | MARK++; |
1506 | sv_setpvn(cat, "", 0); |
1507 | + patcopy = pat; |
1508 | while (pat < patend) { |
1509 | |
1510 | Now if we see a C<U> which was at the start of the string, we turn on |
1511 | the UTF8 flag for the output SV, C<cat>: |
1512 | |
1513 | + if (datumtype == 'U' && pat==patcopy+1) |
1514 | + SvUTF8_on(cat); |
1515 | if (datumtype == '#') { |
1516 | while (pat < patend && *pat != '\n') |
1517 | pat++; |
1518 | |
1519 | Remember that it has to be C<patcopy+1> because the first character of |
1520 | the string is the C<U> which has been swallowed into C<datumtype!> |
1521 | |
1522 | Oops, we forgot one thing: what if there are spaces at the start of the |
1523 | pattern? C<pack(" U*", @stuff)> will have C<U> as the first active |
1524 | character, even though it's not the first thing in the pattern. In this |
1525 | case, we have to advance C<patcopy> along with C<pat> when we see spaces: |
1526 | |
1527 | if (isSPACE(datumtype)) |
1528 | continue; |
1529 | |
1530 | needs to become |
1531 | |
1532 | if (isSPACE(datumtype)) { |
1533 | patcopy++; |
1534 | continue; |
1535 | } |
1536 | |
1537 | OK. That's the C part done. Now we must do two additional things before |
1538 | this patch is ready to go: we've changed the behaviour of Perl, and so |
1539 | we must document that change. We must also provide some more regression |
1540 | tests to make sure our patch works and doesn't create a bug somewhere |
1541 | else along the line. |
1542 | |
b23b8711 |
1543 | The regression tests for each operator live in F<t/op/>, and so we |
1544 | make a copy of F<t/op/pack.t> to F<t/op/pack.t~>. Now we can add our |
1545 | tests to the end. First, we'll test that the C<U> does indeed create |
1546 | Unicode strings. |
1547 | |
1548 | t/op/pack.t has a sensible ok() function, but if it didn't we could |
35c336e6 |
1549 | use the one from t/test.pl. |
b23b8711 |
1550 | |
35c336e6 |
1551 | require './test.pl'; |
1552 | plan( tests => 159 ); |
b23b8711 |
1553 | |
1554 | so instead of this: |
a422fd2d |
1555 | |
1556 | print 'not ' unless "1.20.300.4000" eq sprintf "%vd", pack("U*",1,20,300,4000); |
1557 | print "ok $test\n"; $test++; |
1558 | |
35c336e6 |
1559 | we can write the more sensible (see L<Test::More> for a full |
1560 | explanation of is() and other testing functions). |
b23b8711 |
1561 | |
35c336e6 |
1562 | is( "1.20.300.4000", sprintf "%vd", pack("U*",1,20,300,4000), |
812f5127 |
1563 | "U* produces unicode" ); |
b23b8711 |
1564 | |
a422fd2d |
1565 | Now we'll test that we got that space-at-the-beginning business right: |
1566 | |
35c336e6 |
1567 | is( "1.20.300.4000", sprintf "%vd", pack(" U*",1,20,300,4000), |
812f5127 |
1568 | " with spaces at the beginning" ); |
a422fd2d |
1569 | |
1570 | And finally we'll test that we don't make Unicode strings if C<U> is B<not> |
1571 | the first active format: |
1572 | |
35c336e6 |
1573 | isnt( v1.20.300.4000, sprintf "%vd", pack("C0U*",1,20,300,4000), |
812f5127 |
1574 | "U* not first isn't unicode" ); |
a422fd2d |
1575 | |
35c336e6 |
1576 | Mustn't forget to change the number of tests which appears at the top, |
1577 | or else the automated tester will get confused. This will either look |
1578 | like this: |
a422fd2d |
1579 | |
35c336e6 |
1580 | print "1..156\n"; |
1581 | |
1582 | or this: |
1583 | |
1584 | plan( tests => 156 ); |
a422fd2d |
1585 | |
1586 | We now compile up Perl, and run it through the test suite. Our new |
1587 | tests pass, hooray! |
1588 | |
1589 | Finally, the documentation. The job is never done until the paperwork is |
1590 | over, so let's describe the change we've just made. The relevant place |
1591 | is F<pod/perlfunc.pod>; again, we make a copy, and then we'll insert |
1592 | this text in the description of C<pack>: |
1593 | |
1594 | =item * |
1595 | |
1596 | If the pattern begins with a C<U>, the resulting string will be treated |
1597 | as Unicode-encoded. You can force UTF8 encoding on in a string with an |
1598 | initial C<U0>, and the bytes that follow will be interpreted as Unicode |
1599 | characters. If you don't want this to happen, you can begin your pattern |
1600 | with C<C0> (or anything else) to force Perl not to UTF8 encode your |
1601 | string, and then follow this with a C<U*> somewhere in your pattern. |
1602 | |
1603 | All done. Now let's create the patch. F<Porting/patching.pod> tells us |
1604 | that if we're making major changes, we should copy the entire directory |
1605 | to somewhere safe before we begin fiddling, and then do |
13a2d996 |
1606 | |
a422fd2d |
1607 | diff -ruN old new > patch |
1608 | |
1609 | However, we know which files we've changed, and we can simply do this: |
1610 | |
1611 | diff -u pp.c~ pp.c > patch |
1612 | diff -u t/op/pack.t~ t/op/pack.t >> patch |
1613 | diff -u pod/perlfunc.pod~ pod/perlfunc.pod >> patch |
1614 | |
1615 | We end up with a patch looking a little like this: |
1616 | |
1617 | --- pp.c~ Fri Jun 02 04:34:10 2000 |
1618 | +++ pp.c Fri Jun 16 11:37:25 2000 |
1619 | @@ -4375,6 +4375,7 @@ |
1620 | register I32 items; |
1621 | STRLEN fromlen; |
1622 | register char *pat = SvPVx(*++MARK, fromlen); |
1623 | + char *patcopy; |
1624 | register char *patend = pat + fromlen; |
1625 | register I32 len; |
1626 | I32 datumtype; |
1627 | @@ -4405,6 +4406,7 @@ |
1628 | ... |
1629 | |
1630 | And finally, we submit it, with our rationale, to perl5-porters. Job |
1631 | done! |
1632 | |
f7e1e956 |
1633 | =head2 Patching a core module |
1634 | |
1635 | This works just like patching anything else, with an extra |
1636 | consideration. Many core modules also live on CPAN. If this is so, |
1637 | patch the CPAN version instead of the core and send the patch off to |
1638 | the module maintainer (with a copy to p5p). This will help the module |
1639 | maintainer keep the CPAN version in sync with the core version without |
1640 | constantly scanning p5p. |
1641 | |
acbe17fc |
1642 | =head2 Adding a new function to the core |
1643 | |
1644 | If, as part of a patch to fix a bug, or just because you have an |
1645 | especially good idea, you decide to add a new function to the core, |
1646 | discuss your ideas on p5p well before you start work. It may be that |
1647 | someone else has already attempted to do what you are considering and |
1648 | can give lots of good advice or even provide you with bits of code |
1649 | that they already started (but never finished). |
1650 | |
1651 | You have to follow all of the advice given above for patching. It is |
1652 | extremely important to test any addition thoroughly and add new tests |
1653 | to explore all boundary conditions that your new function is expected |
1654 | to handle. If your new function is used only by one module (e.g. toke), |
1655 | then it should probably be named S_your_function (for static); on the |
210b36aa |
1656 | other hand, if you expect it to accessible from other functions in |
acbe17fc |
1657 | Perl, you should name it Perl_your_function. See L<perlguts/Internal Functions> |
1658 | for more details. |
1659 | |
1660 | The location of any new code is also an important consideration. Don't |
1661 | just create a new top level .c file and put your code there; you would |
1662 | have to make changes to Configure (so the Makefile is created properly), |
1663 | as well as possibly lots of include files. This is strictly pumpking |
1664 | business. |
1665 | |
1666 | It is better to add your function to one of the existing top level |
1667 | source code files, but your choice is complicated by the nature of |
1668 | the Perl distribution. Only the files that are marked as compiled |
1669 | static are located in the perl executable. Everything else is located |
1670 | in the shared library (or DLL if you are running under WIN32). So, |
1671 | for example, if a function was only used by functions located in |
1672 | toke.c, then your code can go in toke.c. If, however, you want to call |
1673 | the function from universal.c, then you should put your code in another |
1674 | location, for example util.c. |
1675 | |
1676 | In addition to writing your c-code, you will need to create an |
1677 | appropriate entry in embed.pl describing your function, then run |
1678 | 'make regen_headers' to create the entries in the numerous header |
1679 | files that perl needs to compile correctly. See L<perlguts/Internal Functions> |
1680 | for information on the various options that you can set in embed.pl. |
1681 | You will forget to do this a few (or many) times and you will get |
1682 | warnings during the compilation phase. Make sure that you mention |
1683 | this when you post your patch to P5P; the pumpking needs to know this. |
1684 | |
1685 | When you write your new code, please be conscious of existing code |
884bad00 |
1686 | conventions used in the perl source files. See L<perlstyle> for |
acbe17fc |
1687 | details. Although most of the guidelines discussed seem to focus on |
1688 | Perl code, rather than c, they all apply (except when they don't ;). |
1689 | See also I<Porting/patching.pod> file in the Perl source distribution |
1690 | for lots of details about both formatting and submitting patches of |
1691 | your changes. |
1692 | |
1693 | Lastly, TEST TEST TEST TEST TEST any code before posting to p5p. |
1694 | Test on as many platforms as you can find. Test as many perl |
1695 | Configure options as you can (e.g. MULTIPLICITY). If you have |
1696 | profiling or memory tools, see L<EXTERNAL TOOLS FOR DEBUGGING PERL> |
210b36aa |
1697 | below for how to use them to further test your code. Remember that |
acbe17fc |
1698 | most of the people on P5P are doing this on their own time and |
1699 | don't have the time to debug your code. |
f7e1e956 |
1700 | |
1701 | =head2 Writing a test |
1702 | |
1703 | Every module and built-in function has an associated test file (or |
1704 | should...). If you add or change functionality, you have to write a |
1705 | test. If you fix a bug, you have to write a test so that bug never |
1706 | comes back. If you alter the docs, it would be nice to test what the |
1707 | new documentation says. |
1708 | |
1709 | In short, if you submit a patch you probably also have to patch the |
1710 | tests. |
1711 | |
1712 | For modules, the test file is right next to the module itself. |
1713 | F<lib/strict.t> tests F<lib/strict.pm>. This is a recent innovation, |
1714 | so there are some snags (and it would be wonderful for you to brush |
1715 | them out), but it basically works that way. Everything else lives in |
1716 | F<t/>. |
1717 | |
1718 | =over 3 |
1719 | |
1720 | =item F<t/base/> |
1721 | |
1722 | Testing of the absolute basic functionality of Perl. Things like |
1723 | C<if>, basic file reads and writes, simple regexes, etc. These are |
1724 | run first in the test suite and if any of them fail, something is |
1725 | I<really> broken. |
1726 | |
1727 | =item F<t/cmd/> |
1728 | |
1729 | These test the basic control structures, C<if/else>, C<while>, |
35c336e6 |
1730 | subroutines, etc. |
f7e1e956 |
1731 | |
1732 | =item F<t/comp/> |
1733 | |
1734 | Tests basic issues of how Perl parses and compiles itself. |
1735 | |
1736 | =item F<t/io/> |
1737 | |
1738 | Tests for built-in IO functions, including command line arguments. |
1739 | |
1740 | =item F<t/lib/> |
1741 | |
1742 | The old home for the module tests, you shouldn't put anything new in |
1743 | here. There are still some bits and pieces hanging around in here |
1744 | that need to be moved. Perhaps you could move them? Thanks! |
1745 | |
1746 | =item F<t/op/> |
1747 | |
1748 | Tests for perl's built in functions that don't fit into any of the |
1749 | other directories. |
1750 | |
1751 | =item F<t/pod/> |
1752 | |
1753 | Tests for POD directives. There are still some tests for the Pod |
1754 | modules hanging around in here that need to be moved out into F<lib/>. |
1755 | |
1756 | =item F<t/run/> |
1757 | |
1758 | Testing features of how perl actually runs, including exit codes and |
1759 | handling of PERL* environment variables. |
1760 | |
1761 | =back |
1762 | |
1763 | The core uses the same testing style as the rest of Perl, a simple |
1764 | "ok/not ok" run through Test::Harness, but there are a few special |
1765 | considerations. |
1766 | |
35c336e6 |
1767 | There are three ways to write a test in the core. Test::More, |
1768 | t/test.pl and ad hoc C<print $test ? "ok 42\n" : "not ok 42\n">. The |
1769 | decision of which to use depends on what part of the test suite you're |
1770 | working on. This is a measure to prevent a high-level failure (such |
1771 | as Config.pm breaking) from causing basic functionality tests to fail. |
1772 | |
1773 | =over 4 |
1774 | |
1775 | =item t/base t/comp |
1776 | |
1777 | Since we don't know if require works, or even subroutines, use ad hoc |
1778 | tests for these two. Step carefully to avoid using the feature being |
1779 | tested. |
1780 | |
1781 | =item t/cmd t/run t/io t/op |
1782 | |
1783 | Now that basic require() and subroutines are tested, you can use the |
1784 | t/test.pl library which emulates the important features of Test::More |
1785 | while using a minimum of core features. |
1786 | |
1787 | You can also conditionally use certain libraries like Config, but be |
1788 | sure to skip the test gracefully if it's not there. |
1789 | |
1790 | =item t/lib ext lib |
1791 | |
1792 | Now that the core of Perl is tested, Test::More can be used. You can |
1793 | also use the full suite of core modules in the tests. |
1794 | |
1795 | =back |
f7e1e956 |
1796 | |
1797 | When you say "make test" Perl uses the F<t/TEST> program to run the |
1798 | test suite. All tests are run from the F<t/> directory, B<not> the |
1799 | directory which contains the test. This causes some problems with the |
1800 | tests in F<lib/>, so here's some opportunity for some patching. |
1801 | |
1802 | You must be triply conscious of cross-platform concerns. This usually |
1803 | boils down to using File::Spec and avoiding things like C<fork()> and |
1804 | C<system()> unless absolutely necessary. |
1805 | |
e018f8be |
1806 | =head2 Special Make Test Targets |
1807 | |
1808 | There are various special make targets that can be used to test Perl |
1809 | slightly differently than the standard "test" target. Not all them |
1810 | are expected to give a 100% success rate. Many of them have several |
1811 | aliases. |
1812 | |
1813 | =over 4 |
1814 | |
1815 | =item coretest |
1816 | |
1817 | Run F<perl> on all but F<lib/*> tests. |
1818 | |
1819 | =item test.deparse |
1820 | |
1821 | Run all the tests through the B::Deparse. Not all tests will succeed. |
1822 | |
1823 | =item minitest |
1824 | |
1825 | Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>, |
1826 | F<t/op>, and F<t/uni> tests. |
1827 | |
1828 | =item test.third check.third utest.third ucheck.third |
1829 | |
1830 | (Only in Tru64) Run all the tests using the memory leak + naughty |
1831 | memory access tool "Third Degree". The log files will be named |
1832 | F<perl3.log.testname>. |
1833 | |
1834 | =item test.torture torturetest |
1835 | |
1836 | Run all the usual tests and some extra tests. As of Perl 5.8.0 the |
1837 | only extra tests are Abigail's JAPHs, t/japh/abigail.t. |
1838 | |
1839 | You can also run the torture test with F<t/harness> by giving |
1840 | C<-torture> argument to F<t/harness>. |
1841 | |
1842 | =item utest ucheck test.utf8 check.utf8 |
1843 | |
1844 | Run all the tests with -Mutf8. Not all tests will succeed. |
1845 | |
1846 | =back |
f7e1e956 |
1847 | |
902b9dbf |
1848 | =head1 EXTERNAL TOOLS FOR DEBUGGING PERL |
1849 | |
1850 | Sometimes it helps to use external tools while debugging and |
1851 | testing Perl. This section tries to guide you through using |
1852 | some common testing and debugging tools with Perl. This is |
1853 | meant as a guide to interfacing these tools with Perl, not |
1854 | as any kind of guide to the use of the tools themselves. |
1855 | |
1856 | =head2 Rational Software's Purify |
1857 | |
1858 | Purify is a commercial tool that is helpful in identifying |
1859 | memory overruns, wild pointers, memory leaks and other such |
1860 | badness. Perl must be compiled in a specific way for |
1861 | optimal testing with Purify. Purify is available under |
1862 | Windows NT, Solaris, HP-UX, SGI, and Siemens Unix. |
1863 | |
1864 | The only currently known leaks happen when there are |
1865 | compile-time errors within eval or require. (Fixing these |
1866 | is non-trivial, unfortunately, but they must be fixed |
1867 | eventually.) |
1868 | |
1869 | =head2 Purify on Unix |
1870 | |
1871 | On Unix, Purify creates a new Perl binary. To get the most |
1872 | benefit out of Purify, you should create the perl to Purify |
1873 | using: |
1874 | |
1875 | sh Configure -Accflags=-DPURIFY -Doptimize='-g' \ |
1876 | -Uusemymalloc -Dusemultiplicity |
1877 | |
1878 | where these arguments mean: |
1879 | |
1880 | =over 4 |
1881 | |
1882 | =item -Accflags=-DPURIFY |
1883 | |
1884 | Disables Perl's arena memory allocation functions, as well as |
1885 | forcing use of memory allocation functions derived from the |
1886 | system malloc. |
1887 | |
1888 | =item -Doptimize='-g' |
1889 | |
1890 | Adds debugging information so that you see the exact source |
1891 | statements where the problem occurs. Without this flag, all |
1892 | you will see is the source filename of where the error occurred. |
1893 | |
1894 | =item -Uusemymalloc |
1895 | |
1896 | Disable Perl's malloc so that Purify can more closely monitor |
1897 | allocations and leaks. Using Perl's malloc will make Purify |
1898 | report most leaks in the "potential" leaks category. |
1899 | |
1900 | =item -Dusemultiplicity |
1901 | |
1902 | Enabling the multiplicity option allows perl to clean up |
1903 | thoroughly when the interpreter shuts down, which reduces the |
1904 | number of bogus leak reports from Purify. |
1905 | |
1906 | =back |
1907 | |
1908 | Once you've compiled a perl suitable for Purify'ing, then you |
1909 | can just: |
1910 | |
1911 | make pureperl |
1912 | |
1913 | which creates a binary named 'pureperl' that has been Purify'ed. |
1914 | This binary is used in place of the standard 'perl' binary |
1915 | when you want to debug Perl memory problems. |
1916 | |
1f56d61a |
1917 | To minimize the number of memory leak false alarms |
1918 | (see L</PERL_DESTRUCT_LEVEL>), set environment variable |
1919 | PERL_DESTRUCT_LEVEL to 2. |
1920 | |
1921 | setenv PERL_DESTRUCT_LEVEL 2 |
1922 | |
1923 | In Bourne-type shells: |
1924 | |
1925 | PERL_DESTRUCT_LEVEL=2 |
1926 | export PERL_DESTRUCT_LEVEL |
1927 | |
902b9dbf |
1928 | As an example, to show any memory leaks produced during the |
1929 | standard Perl testset you would create and run the Purify'ed |
1930 | perl as: |
1931 | |
1932 | make pureperl |
1933 | cd t |
1934 | ../pureperl -I../lib harness |
1935 | |
1936 | which would run Perl on test.pl and report any memory problems. |
1937 | |
1938 | Purify outputs messages in "Viewer" windows by default. If |
1939 | you don't have a windowing environment or if you simply |
1940 | want the Purify output to unobtrusively go to a log file |
1941 | instead of to the interactive window, use these following |
1942 | options to output to the log file "perl.log": |
1943 | |
1944 | setenv PURIFYOPTIONS "-chain-length=25 -windows=no \ |
1945 | -log-file=perl.log -append-logfile=yes" |
1946 | |
1947 | If you plan to use the "Viewer" windows, then you only need this option: |
1948 | |
1949 | setenv PURIFYOPTIONS "-chain-length=25" |
1950 | |
c406981e |
1951 | In Bourne-type shells: |
1952 | |
98631ff8 |
1953 | PURIFYOPTIONS="..." |
1954 | export PURIFYOPTIONS |
c406981e |
1955 | |
1956 | or if you have the "env" utility: |
1957 | |
98631ff8 |
1958 | env PURIFYOPTIONS="..." ../pureperl ... |
c406981e |
1959 | |
902b9dbf |
1960 | =head2 Purify on NT |
1961 | |
1962 | Purify on Windows NT instruments the Perl binary 'perl.exe' |
1963 | on the fly. There are several options in the makefile you |
1964 | should change to get the most use out of Purify: |
1965 | |
1966 | =over 4 |
1967 | |
1968 | =item DEFINES |
1969 | |
1970 | You should add -DPURIFY to the DEFINES line so the DEFINES |
1971 | line looks something like: |
1972 | |
1973 | DEFINES = -DWIN32 -D_CONSOLE -DNO_STRICT $(CRYPT_FLAG) -DPURIFY=1 |
1974 | |
1975 | to disable Perl's arena memory allocation functions, as |
1976 | well as to force use of memory allocation functions derived |
1977 | from the system malloc. |
1978 | |
1979 | =item USE_MULTI = define |
1980 | |
1981 | Enabling the multiplicity option allows perl to clean up |
1982 | thoroughly when the interpreter shuts down, which reduces the |
1983 | number of bogus leak reports from Purify. |
1984 | |
1985 | =item #PERL_MALLOC = define |
1986 | |
1987 | Disable Perl's malloc so that Purify can more closely monitor |
1988 | allocations and leaks. Using Perl's malloc will make Purify |
1989 | report most leaks in the "potential" leaks category. |
1990 | |
1991 | =item CFG = Debug |
1992 | |
1993 | Adds debugging information so that you see the exact source |
1994 | statements where the problem occurs. Without this flag, all |
1995 | you will see is the source filename of where the error occurred. |
1996 | |
1997 | =back |
1998 | |
1999 | As an example, to show any memory leaks produced during the |
2000 | standard Perl testset you would create and run Purify as: |
2001 | |
2002 | cd win32 |
2003 | make |
2004 | cd ../t |
2005 | purify ../perl -I../lib harness |
2006 | |
2007 | which would instrument Perl in memory, run Perl on test.pl, |
2008 | then finally report any memory problems. |
2009 | |
f134cc4e |
2010 | B<NOTE>: as of Perl 5.8.0, the ext/Encode/t/Unicode.t takes |
2011 | extraordinarily long (hours?) to complete under Purify. It has been |
2012 | theorized that it would eventually finish, but nobody has so far been |
2013 | patient enough :-) (This same extreme slowdown has been seen also with |
2014 | the Third Degree tool, so the said test must be doing something that |
2015 | is quite unfriendly for memory debuggers.) It is suggested that you |
2016 | simply kill away that testing process. |
2017 | |
2018 | =head2 Compaq's/Digital's/HP's Third Degree |
09187cb1 |
2019 | |
2020 | Third Degree is a tool for memory leak detection and memory access checks. |
2021 | It is one of the many tools in the ATOM toolkit. The toolkit is only |
2022 | available on Tru64 (formerly known as Digital UNIX formerly known as |
2023 | DEC OSF/1). |
2024 | |
2025 | When building Perl, you must first run Configure with -Doptimize=-g |
2026 | and -Uusemymalloc flags, after that you can use the make targets |
51a35ef1 |
2027 | "perl.third" and "test.third". (What is required is that Perl must be |
2028 | compiled using the C<-g> flag, you may need to re-Configure.) |
09187cb1 |
2029 | |
64cea5fd |
2030 | The short story is that with "atom" you can instrument the Perl |
83f0ef60 |
2031 | executable to create a new executable called F<perl.third>. When the |
4ae3d70a |
2032 | instrumented executable is run, it creates a log of dubious memory |
83f0ef60 |
2033 | traffic in file called F<perl.3log>. See the manual pages of atom and |
4ae3d70a |
2034 | third for more information. The most extensive Third Degree |
2035 | documentation is available in the Compaq "Tru64 UNIX Programmer's |
2036 | Guide", chapter "Debugging Programs with Third Degree". |
64cea5fd |
2037 | |
9c54ecba |
2038 | The "test.third" leaves a lot of files named F<foo_bar.3log> in the t/ |
64cea5fd |
2039 | subdirectory. There is a problem with these files: Third Degree is so |
2040 | effective that it finds problems also in the system libraries. |
9c54ecba |
2041 | Therefore you should used the Porting/thirdclean script to cleanup |
2042 | the F<*.3log> files. |
64cea5fd |
2043 | |
2044 | There are also leaks that for given certain definition of a leak, |
2045 | aren't. See L</PERL_DESTRUCT_LEVEL> for more information. |
2046 | |
2047 | =head2 PERL_DESTRUCT_LEVEL |
2048 | |
2049 | If you want to run any of the tests yourself manually using the |
2050 | pureperl or perl.third executables, please note that by default |
2051 | perl B<does not> explicitly cleanup all the memory it has allocated |
2052 | (such as global memory arenas) but instead lets the exit() of |
2053 | the whole program "take care" of such allocations, also known |
2054 | as "global destruction of objects". |
2055 | |
2056 | There is a way to tell perl to do complete cleanup: set the |
2057 | environment variable PERL_DESTRUCT_LEVEL to a non-zero value. |
2058 | The t/TEST wrapper does set this to 2, and this is what you |
2059 | need to do too, if you don't want to see the "global leaks": |
1f56d61a |
2060 | For example, for "third-degreed" Perl: |
64cea5fd |
2061 | |
1f56d61a |
2062 | env PERL_DESTRUCT_LEVEL=2 ./perl.third -Ilib t/foo/bar.t |
09187cb1 |
2063 | |
414f2397 |
2064 | (Note: the mod_perl apache module uses also this environment variable |
2065 | for its own purposes and extended its semantics. Refer to the mod_perl |
2066 | documentation for more information.) |
2067 | |
51a35ef1 |
2068 | =head2 Profiling |
2069 | |
2070 | Depending on your platform there are various of profiling Perl. |
2071 | |
2072 | There are two commonly used techniques of profiling executables: |
10f58044 |
2073 | I<statistical time-sampling> and I<basic-block counting>. |
51a35ef1 |
2074 | |
2075 | The first method takes periodically samples of the CPU program |
2076 | counter, and since the program counter can be correlated with the code |
2077 | generated for functions, we get a statistical view of in which |
2078 | functions the program is spending its time. The caveats are that very |
2079 | small/fast functions have lower probability of showing up in the |
2080 | profile, and that periodically interrupting the program (this is |
2081 | usually done rather frequently, in the scale of milliseconds) imposes |
2082 | an additional overhead that may skew the results. The first problem |
2083 | can be alleviated by running the code for longer (in general this is a |
2084 | good idea for profiling), the second problem is usually kept in guard |
2085 | by the profiling tools themselves. |
2086 | |
10f58044 |
2087 | The second method divides up the generated code into I<basic blocks>. |
51a35ef1 |
2088 | Basic blocks are sections of code that are entered only in the |
2089 | beginning and exited only at the end. For example, a conditional jump |
2090 | starts a basic block. Basic block profiling usually works by |
10f58044 |
2091 | I<instrumenting> the code by adding I<enter basic block #nnnn> |
51a35ef1 |
2092 | book-keeping code to the generated code. During the execution of the |
2093 | code the basic block counters are then updated appropriately. The |
2094 | caveat is that the added extra code can skew the results: again, the |
2095 | profiling tools usually try to factor their own effects out of the |
2096 | results. |
2097 | |
83f0ef60 |
2098 | =head2 Gprof Profiling |
2099 | |
51a35ef1 |
2100 | gprof is a profiling tool available in many UNIX platforms, |
2101 | it uses F<statistical time-sampling>. |
83f0ef60 |
2102 | |
2103 | You can build a profiled version of perl called "perl.gprof" by |
51a35ef1 |
2104 | invoking the make target "perl.gprof" (What is required is that Perl |
2105 | must be compiled using the C<-pg> flag, you may need to re-Configure). |
2106 | Running the profiled version of Perl will create an output file called |
2107 | F<gmon.out> is created which contains the profiling data collected |
2108 | during the execution. |
83f0ef60 |
2109 | |
2110 | The gprof tool can then display the collected data in various ways. |
2111 | Usually gprof understands the following options: |
2112 | |
2113 | =over 4 |
2114 | |
2115 | =item -a |
2116 | |
2117 | Suppress statically defined functions from the profile. |
2118 | |
2119 | =item -b |
2120 | |
2121 | Suppress the verbose descriptions in the profile. |
2122 | |
2123 | =item -e routine |
2124 | |
2125 | Exclude the given routine and its descendants from the profile. |
2126 | |
2127 | =item -f routine |
2128 | |
2129 | Display only the given routine and its descendants in the profile. |
2130 | |
2131 | =item -s |
2132 | |
2133 | Generate a summary file called F<gmon.sum> which then may be given |
2134 | to subsequent gprof runs to accumulate data over several runs. |
2135 | |
2136 | =item -z |
2137 | |
2138 | Display routines that have zero usage. |
2139 | |
2140 | =back |
2141 | |
2142 | For more detailed explanation of the available commands and output |
2143 | formats, see your own local documentation of gprof. |
2144 | |
51a35ef1 |
2145 | =head2 GCC gcov Profiling |
2146 | |
10f58044 |
2147 | Starting from GCC 3.0 I<basic block profiling> is officially available |
51a35ef1 |
2148 | for the GNU CC. |
2149 | |
2150 | You can build a profiled version of perl called F<perl.gcov> by |
2151 | invoking the make target "perl.gcov" (what is required that Perl must |
2152 | be compiled using gcc with the flags C<-fprofile-arcs |
2153 | -ftest-coverage>, you may need to re-Configure). |
2154 | |
2155 | Running the profiled version of Perl will cause profile output to be |
2156 | generated. For each source file an accompanying ".da" file will be |
2157 | created. |
2158 | |
2159 | To display the results you use the "gcov" utility (which should |
2160 | be installed if you have gcc 3.0 or newer installed). F<gcov> is |
2161 | run on source code files, like this |
2162 | |
2163 | gcov sv.c |
2164 | |
2165 | which will cause F<sv.c.gcov> to be created. The F<.gcov> files |
2166 | contain the source code annotated with relative frequencies of |
2167 | execution indicated by "#" markers. |
2168 | |
2169 | Useful options of F<gcov> include C<-b> which will summarise the |
2170 | basic block, branch, and function call coverage, and C<-c> which |
2171 | instead of relative frequencies will use the actual counts. For |
2172 | more information on the use of F<gcov> and basic block profiling |
2173 | with gcc, see the latest GNU CC manual, as of GCC 3.0 see |
2174 | |
2175 | http://gcc.gnu.org/onlinedocs/gcc-3.0/gcc.html |
2176 | |
2177 | and its section titled "8. gcov: a Test Coverage Program" |
2178 | |
2179 | http://gcc.gnu.org/onlinedocs/gcc-3.0/gcc_8.html#SEC132 |
2180 | |
4ae3d70a |
2181 | =head2 Pixie Profiling |
2182 | |
51a35ef1 |
2183 | Pixie is a profiling tool available on IRIX and Tru64 (aka Digital |
2184 | UNIX aka DEC OSF/1) platforms. Pixie does its profiling using |
10f58044 |
2185 | I<basic-block counting>. |
4ae3d70a |
2186 | |
83f0ef60 |
2187 | You can build a profiled version of perl called F<perl.pixie> by |
51a35ef1 |
2188 | invoking the make target "perl.pixie" (what is required is that Perl |
2189 | must be compiled using the C<-g> flag, you may need to re-Configure). |
2190 | |
2191 | In Tru64 a file called F<perl.Addrs> will also be silently created, |
2192 | this file contains the addresses of the basic blocks. Running the |
2193 | profiled version of Perl will create a new file called "perl.Counts" |
2194 | which contains the counts for the basic block for that particular |
2195 | program execution. |
4ae3d70a |
2196 | |
51a35ef1 |
2197 | To display the results you use the F<prof> utility. The exact |
4ae3d70a |
2198 | incantation depends on your operating system, "prof perl.Counts" in |
2199 | IRIX, and "prof -pixie -all -L. perl" in Tru64. |
2200 | |
6c41479b |
2201 | In IRIX the following prof options are available: |
2202 | |
2203 | =over 4 |
2204 | |
2205 | =item -h |
2206 | |
2207 | Reports the most heavily used lines in descending order of use. |
6e36760b |
2208 | Useful for finding the hotspot lines. |
6c41479b |
2209 | |
2210 | =item -l |
2211 | |
2212 | Groups lines by procedure, with procedures sorted in descending order of use. |
2213 | Within a procedure, lines are listed in source order. |
6e36760b |
2214 | Useful for finding the hotspots of procedures. |
6c41479b |
2215 | |
2216 | =back |
2217 | |
2218 | In Tru64 the following options are available: |
2219 | |
2220 | =over 4 |
2221 | |
3958b146 |
2222 | =item -p[rocedures] |
6c41479b |
2223 | |
3958b146 |
2224 | Procedures sorted in descending order by the number of cycles executed |
6e36760b |
2225 | in each procedure. Useful for finding the hotspot procedures. |
6c41479b |
2226 | (This is the default option.) |
2227 | |
24000d2f |
2228 | =item -h[eavy] |
6c41479b |
2229 | |
6e36760b |
2230 | Lines sorted in descending order by the number of cycles executed in |
2231 | each line. Useful for finding the hotspot lines. |
6c41479b |
2232 | |
24000d2f |
2233 | =item -i[nvocations] |
6c41479b |
2234 | |
6e36760b |
2235 | The called procedures are sorted in descending order by number of calls |
2236 | made to the procedures. Useful for finding the most used procedures. |
6c41479b |
2237 | |
24000d2f |
2238 | =item -l[ines] |
6c41479b |
2239 | |
2240 | Grouped by procedure, sorted by cycles executed per procedure. |
6e36760b |
2241 | Useful for finding the hotspots of procedures. |
6c41479b |
2242 | |
2243 | =item -testcoverage |
2244 | |
2245 | The compiler emitted code for these lines, but the code was unexecuted. |
2246 | |
24000d2f |
2247 | =item -z[ero] |
6c41479b |
2248 | |
2249 | Unexecuted procedures. |
2250 | |
aa500c9e |
2251 | =back |
6c41479b |
2252 | |
2253 | For further information, see your system's manual pages for pixie and prof. |
4ae3d70a |
2254 | |
b8ddf6b3 |
2255 | =head2 Miscellaneous tricks |
2256 | |
2257 | =over 4 |
2258 | |
2259 | =item * |
2260 | |
cc177e1a |
2261 | Those debugging perl with the DDD frontend over gdb may find the |
b8ddf6b3 |
2262 | following useful: |
2263 | |
2264 | You can extend the data conversion shortcuts menu, so for example you |
2265 | can display an SV's IV value with one click, without doing any typing. |
2266 | To do that simply edit ~/.ddd/init file and add after: |
2267 | |
2268 | ! Display shortcuts. |
2269 | Ddd*gdbDisplayShortcuts: \ |
2270 | /t () // Convert to Bin\n\ |
2271 | /d () // Convert to Dec\n\ |
2272 | /x () // Convert to Hex\n\ |
2273 | /o () // Convert to Oct(\n\ |
2274 | |
2275 | the following two lines: |
2276 | |
2277 | ((XPV*) (())->sv_any )->xpv_pv // 2pvx\n\ |
2278 | ((XPVIV*) (())->sv_any )->xiv_iv // 2ivx |
2279 | |
2280 | so now you can do ivx and pvx lookups or you can plug there the |
2281 | sv_peek "conversion": |
2282 | |
2283 | Perl_sv_peek(my_perl, (SV*)()) // sv_peek |
2284 | |
2285 | (The my_perl is for threaded builds.) |
2286 | Just remember that every line, but the last one, should end with \n\ |
2287 | |
2288 | Alternatively edit the init file interactively via: |
2289 | 3rd mouse button -> New Display -> Edit Menu |
2290 | |
2291 | Note: you can define up to 20 conversion shortcuts in the gdb |
2292 | section. |
2293 | |
9965345d |
2294 | =item * |
2295 | |
2296 | If you see in a debugger a memory area mysteriously full of 0xabababab, |
2297 | you may be seeing the effect of the Poison() macro, see L<perlclib>. |
2298 | |
b8ddf6b3 |
2299 | =back |
2300 | |
a422fd2d |
2301 | =head2 CONCLUSION |
2302 | |
2303 | We've had a brief look around the Perl source, an overview of the stages |
2304 | F<perl> goes through when it's running your code, and how to use a |
902b9dbf |
2305 | debugger to poke at the Perl guts. We took a very simple problem and |
2306 | demonstrated how to solve it fully - with documentation, regression |
2307 | tests, and finally a patch for submission to p5p. Finally, we talked |
2308 | about how to use external tools to debug and test Perl. |
a422fd2d |
2309 | |
2310 | I'd now suggest you read over those references again, and then, as soon |
2311 | as possible, get your hands dirty. The best way to learn is by doing, |
2312 | so: |
2313 | |
2314 | =over 3 |
2315 | |
2316 | =item * |
2317 | |
2318 | Subscribe to perl5-porters, follow the patches and try and understand |
2319 | them; don't be afraid to ask if there's a portion you're not clear on - |
2320 | who knows, you may unearth a bug in the patch... |
2321 | |
2322 | =item * |
2323 | |
2324 | Keep up to date with the bleeding edge Perl distributions and get |
2325 | familiar with the changes. Try and get an idea of what areas people are |
2326 | working on and the changes they're making. |
2327 | |
2328 | =item * |
2329 | |
3e148164 |
2330 | Do read the README associated with your operating system, e.g. README.aix |
a1f349fd |
2331 | on the IBM AIX OS. Don't hesitate to supply patches to that README if |
2332 | you find anything missing or changed over a new OS release. |
2333 | |
2334 | =item * |
2335 | |
a422fd2d |
2336 | Find an area of Perl that seems interesting to you, and see if you can |
2337 | work out how it works. Scan through the source, and step over it in the |
2338 | debugger. Play, poke, investigate, fiddle! You'll probably get to |
2339 | understand not just your chosen area but a much wider range of F<perl>'s |
2340 | activity as well, and probably sooner than you'd think. |
2341 | |
2342 | =back |
2343 | |
2344 | =over 3 |
2345 | |
2346 | =item I<The Road goes ever on and on, down from the door where it began.> |
2347 | |
2348 | =back |
2349 | |
2350 | If you can do these things, you've started on the long road to Perl porting. |
2351 | Thanks for wanting to help make Perl better - and happy hacking! |
2352 | |
e8cd7eae |
2353 | =head1 AUTHOR |
2354 | |
2355 | This document was written by Nathan Torkington, and is maintained by |
2356 | the perl5-porters mailing list. |
2357 | |