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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 17 A searchable archive of the list is at either: 18 19 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/ 20 21 or 22 23 http://archive.develooper.com/perl5-porters@perl.org/ 24 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 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. 40 For instance, Gurusamy Sarathy was the pumpking for the 5.6 release of 41 Perl, and Jarkko Hietaniemi was the pumpking for the 5.8 release, and 42 Rafael Garcia-Suarez holds the pumpking crown for the 5.10 release. 43 44 In addition, various people are pumpkings for different things. For 45 instance, Andy Dougherty and Jarkko Hietaniemi did a grand job as the 46 I<Configure> pumpkin up till the 5.8 release. For the 5.10 release 47 H.Merijn Brand took over. 48 49 Larry sees Perl development along the lines of the US government: 50 there's the Legislature (the porters), the Executive branch (the 51 pumpkings), and the Supreme Court (Larry). The legislature can 52 discuss and submit patches to the executive branch all they like, but 53 the executive branch is free to veto them. Rarely, the Supreme Court 54 will side with the executive branch over the legislature, or the 55 legislature over the executive branch. Mostly, however, the 56 legislature and the executive branch are supposed to get along and 57 work out their differences without impeachment or court cases. 58 59 You might sometimes see reference to Rule 1 and Rule 2. Larry's power 60 as Supreme Court is expressed in The Rules: 61 62 =over 4 63 64 =item 1 65 66 Larry is always by definition right about how Perl should behave. 67 This means he has final veto power on the core functionality. 68 69 =item 2 70 71 Larry is allowed to change his mind about any matter at a later date, 72 regardless of whether he previously invoked Rule 1. 73 74 =back 75 76 Got that? Larry is always right, even when he was wrong. It's rare 77 to see either Rule exercised, but they are often alluded to. 78 79 New features and extensions to the language are contentious, because 80 the criteria used by the pumpkings, Larry, and other porters to decide 81 which features should be implemented and incorporated are not codified 82 in a few small design goals as with some other languages. Instead, 83 the heuristics are flexible and often difficult to fathom. Here is 84 one person's list, roughly in decreasing order of importance, of 85 heuristics that new features have to be weighed against: 86 87 =over 4 88 89 =item Does concept match the general goals of Perl? 90 91 These haven't been written anywhere in stone, but one approximation 92 is: 93 94 1. Keep it fast, simple, and useful. 95 2. Keep features/concepts as orthogonal as possible. 96 3. No arbitrary limits (platforms, data sizes, cultures). 97 4. Keep it open and exciting to use/patch/advocate Perl everywhere. 98 5. Either assimilate new technologies, or build bridges to them. 99 100 =item Where is the implementation? 101 102 All the talk in the world is useless without an implementation. In 103 almost every case, the person or people who argue for a new feature 104 will be expected to be the ones who implement it. Porters capable 105 of coding new features have their own agendas, and are not available 106 to implement your (possibly good) idea. 107 108 =item Backwards compatibility 109 110 It's a cardinal sin to break existing Perl programs. New warnings are 111 contentious--some say that a program that emits warnings is not 112 broken, while others say it is. Adding keywords has the potential to 113 break programs, changing the meaning of existing token sequences or 114 functions might break programs. 115 116 =item Could it be a module instead? 117 118 Perl 5 has extension mechanisms, modules and XS, specifically to avoid 119 the need to keep changing the Perl interpreter. You can write modules 120 that export functions, you can give those functions prototypes so they 121 can be called like built-in functions, you can even write XS code to 122 mess with the runtime data structures of the Perl interpreter if you 123 want to implement really complicated things. If it can be done in a 124 module instead of in the core, it's highly unlikely to be added. 125 126 =item Is the feature generic enough? 127 128 Is this something that only the submitter wants added to the language, 129 or would it be broadly useful? Sometimes, instead of adding a feature 130 with a tight focus, the porters might decide to wait until someone 131 implements the more generalized feature. For instance, instead of 132 implementing a "delayed evaluation" feature, the porters are waiting 133 for a macro system that would permit delayed evaluation and much more. 134 135 =item Does it potentially introduce new bugs? 136 137 Radical rewrites of large chunks of the Perl interpreter have the 138 potential to introduce new bugs. The smaller and more localized the 139 change, the better. 140 141 =item Does it preclude other desirable features? 142 143 A patch is likely to be rejected if it closes off future avenues of 144 development. For instance, a patch that placed a true and final 145 interpretation on prototypes is likely to be rejected because there 146 are still options for the future of prototypes that haven't been 147 addressed. 148 149 =item Is the implementation robust? 150 151 Good patches (tight code, complete, correct) stand more chance of 152 going in. Sloppy or incorrect patches might be placed on the back 153 burner until the pumpking has time to fix, or might be discarded 154 altogether without further notice. 155 156 =item Is the implementation generic enough to be portable? 157 158 The worst patches make use of a system-specific features. It's highly 159 unlikely that non-portable additions to the Perl language will be 160 accepted. 161 162 =item Is the implementation tested? 163 164 Patches which change behaviour (fixing bugs or introducing new features) 165 must include regression tests to verify that everything works as expected. 166 Without tests provided by the original author, how can anyone else changing 167 perl in the future be sure that they haven't unwittingly broken the behaviour 168 the patch implements? And without tests, how can the patch's author be 169 confident that his/her hard work put into the patch won't be accidentally 170 thrown away by someone in the future? 171 172 =item Is there enough documentation? 173 174 Patches without documentation are probably ill-thought out or 175 incomplete. Nothing can be added without documentation, so submitting 176 a patch for the appropriate manpages as well as the source code is 177 always a good idea. 178 179 =item Is there another way to do it? 180 181 Larry said "Although the Perl Slogan is I<There's More Than One Way 182 to Do It>, I hesitate to make 10 ways to do something". This is a 183 tricky heuristic to navigate, though--one man's essential addition is 184 another man's pointless cruft. 185 186 =item Does it create too much work? 187 188 Work for the pumpking, work for Perl programmers, work for module 189 authors, ... Perl is supposed to be easy. 190 191 =item Patches speak louder than words 192 193 Working code is always preferred to pie-in-the-sky ideas. A patch to 194 add a feature stands a much higher chance of making it to the language 195 than does a random feature request, no matter how fervently argued the 196 request might be. This ties into "Will it be useful?", as the fact 197 that someone took the time to make the patch demonstrates a strong 198 desire for the feature. 199 200 =back 201 202 If you're on the list, you might hear the word "core" bandied 203 around. It refers to the standard distribution. "Hacking on the 204 core" means you're changing the C source code to the Perl 205 interpreter. "A core module" is one that ships with Perl. 206 207 =head2 Keeping in sync 208 209 The source code to the Perl interpreter, in its different versions, is 210 kept in a repository managed by a revision control system ( which is 211 currently the Perforce program, see http://perforce.com/ ). The 212 pumpkings and a few others have access to the repository to check in 213 changes. Periodically the pumpking for the development version of Perl 214 will release a new version, so the rest of the porters can see what's 215 changed. The current state of the main trunk of repository, and patches 216 that describe the individual changes that have happened since the last 217 public release are available at this location: 218 219 http://public.activestate.com/pub/apc/ 220 ftp://public.activestate.com/pub/apc/ 221 222 If you're looking for a particular change, or a change that affected 223 a particular set of files, you may find the B<Perl Repository Browser> 224 useful: 225 226 http://public.activestate.com/cgi-bin/perlbrowse 227 228 You may also want to subscribe to the perl5-changes mailing list to 229 receive a copy of each patch that gets submitted to the maintenance 230 and development "branches" of the perl repository. See 231 http://lists.perl.org/ for subscription information. 232 233 If you are a member of the perl5-porters mailing list, it is a good 234 thing to keep in touch with the most recent changes. If not only to 235 verify if what you would have posted as a bug report isn't already 236 solved in the most recent available perl development branch, also 237 known as perl-current, bleading edge perl, bleedperl or bleadperl. 238 239 Needless to say, the source code in perl-current is usually in a perpetual 240 state of evolution. You should expect it to be very buggy. Do B<not> use 241 it for any purpose other than testing and development. 242 243 Keeping in sync with the most recent branch can be done in several ways, 244 but the most convenient and reliable way is using B<rsync>, available at 245 ftp://rsync.samba.org/pub/rsync/ . (You can also get the most recent 246 branch by FTP.) 247 248 If you choose to keep in sync using rsync, there are two approaches 249 to doing so: 250 251 =over 4 252 253 =item rsync'ing the source tree 254 255 Presuming you are in the directory where your perl source resides 256 and you have rsync installed and available, you can "upgrade" to 257 the bleadperl using: 258 259 # rsync -avz rsync://public.activestate.com/perl-current/ . 260 261 This takes care of updating every single item in the source tree to 262 the latest applied patch level, creating files that are new (to your 263 distribution) and setting date/time stamps of existing files to 264 reflect the bleadperl status. 265 266 Note that this will not delete any files that were in '.' before 267 the rsync. Once you are sure that the rsync is running correctly, 268 run it with the --delete and the --dry-run options like this: 269 270 # rsync -avz --delete --dry-run rsync://public.activestate.com/perl-current/ . 271 272 This will I<simulate> an rsync run that also deletes files not 273 present in the bleadperl master copy. Observe the results from 274 this run closely. If you are sure that the actual run would delete 275 no files precious to you, you could remove the '--dry-run' option. 276 277 You can than check what patch was the latest that was applied by 278 looking in the file B<.patch>, which will show the number of the 279 latest patch. 280 281 If you have more than one machine to keep in sync, and not all of 282 them have access to the WAN (so you are not able to rsync all the 283 source trees to the real source), there are some ways to get around 284 this problem. 285 286 =over 4 287 288 =item Using rsync over the LAN 289 290 Set up a local rsync server which makes the rsynced source tree 291 available to the LAN and sync the other machines against this 292 directory. 293 294 From http://rsync.samba.org/README.html : 295 296 "Rsync uses rsh or ssh for communication. It does not need to be 297 setuid and requires no special privileges for installation. It 298 does not require an inetd entry or a daemon. You must, however, 299 have a working rsh or ssh system. Using ssh is recommended for 300 its security features." 301 302 =item Using pushing over the NFS 303 304 Having the other systems mounted over the NFS, you can take an 305 active pushing approach by checking the just updated tree against 306 the other not-yet synced trees. An example would be 307 308 #!/usr/bin/perl -w 309 310 use strict; 311 use File::Copy; 312 313 my %MF = map { 314 m/(\S+)/; 315 $1 => [ (stat $1)[2, 7, 9] ]; # mode, size, mtime 316 } `cat MANIFEST`; 317 318 my %remote = map { $_ => "/$_/pro/3gl/CPAN/perl-5.7.1" } qw(host1 host2); 319 320 foreach my $host (keys %remote) { 321 unless (-d $remote{$host}) { 322 print STDERR "Cannot Xsync for host $host\n"; 323 next; 324 } 325 foreach my $file (keys %MF) { 326 my $rfile = "$remote{$host}/$file"; 327 my ($mode, $size, $mtime) = (stat $rfile)[2, 7, 9]; 328 defined $size or ($mode, $size, $mtime) = (0, 0, 0); 329 $size == $MF{$file}[1] && $mtime == $MF{$file}[2] and next; 330 printf "%4s %-34s %8d %9d %8d %9d\n", 331 $host, $file, $MF{$file}[1], $MF{$file}[2], $size, $mtime; 332 unlink $rfile; 333 copy ($file, $rfile); 334 utime time, $MF{$file}[2], $rfile; 335 chmod $MF{$file}[0], $rfile; 336 } 337 } 338 339 though this is not perfect. It could be improved with checking 340 file checksums before updating. Not all NFS systems support 341 reliable utime support (when used over the NFS). 342 343 =back 344 345 =item rsync'ing the patches 346 347 The source tree is maintained by the pumpking who applies patches to 348 the files in the tree. These patches are either created by the 349 pumpking himself using C<diff -c> after updating the file manually or 350 by applying patches sent in by posters on the perl5-porters list. 351 These patches are also saved and rsync'able, so you can apply them 352 yourself to the source files. 353 354 Presuming you are in a directory where your patches reside, you can 355 get them in sync with 356 357 # rsync -avz rsync://public.activestate.com/perl-current-diffs/ . 358 359 This makes sure the latest available patch is downloaded to your 360 patch directory. 361 362 It's then up to you to apply these patches, using something like 363 364 # last="`cat ../perl-current/.patch`.gz" 365 # rsync -avz rsync://public.activestate.com/perl-current-diffs/ . 366 # find . -name '*.gz' -newer $last -exec gzcat {} \; >blead.patch 367 # cd ../perl-current 368 # patch -p1 -N <../perl-current-diffs/blead.patch 369 370 or, since this is only a hint towards how it works, use CPAN-patchaperl 371 from Andreas König to have better control over the patching process. 372 373 =back 374 375 =head2 Why rsync the source tree 376 377 =over 4 378 379 =item It's easier to rsync the source tree 380 381 Since you don't have to apply the patches yourself, you are sure all 382 files in the source tree are in the right state. 383 384 =item It's more reliable 385 386 While both the rsync-able source and patch areas are automatically 387 updated every few minutes, keep in mind that applying patches may 388 sometimes mean careful hand-holding, especially if your version of 389 the C<patch> program does not understand how to deal with new files, 390 files with 8-bit characters, or files without trailing newlines. 391 392 =back 393 394 =head2 Why rsync the patches 395 396 =over 4 397 398 =item It's easier to rsync the patches 399 400 If you have more than one machine that you want to keep in track with 401 bleadperl, it's easier to rsync the patches only once and then apply 402 them to all the source trees on the different machines. 403 404 In case you try to keep in pace on 5 different machines, for which 405 only one of them has access to the WAN, rsync'ing all the source 406 trees should than be done 5 times over the NFS. Having 407 rsync'ed the patches only once, I can apply them to all the source 408 trees automatically. Need you say more ;-) 409 410 =item It's a good reference 411 412 If you do not only like to have the most recent development branch, 413 but also like to B<fix> bugs, or extend features, you want to dive 414 into the sources. If you are a seasoned perl core diver, you don't 415 need no manuals, tips, roadmaps, perlguts.pod or other aids to find 416 your way around. But if you are a starter, the patches may help you 417 in finding where you should start and how to change the bits that 418 bug you. 419 420 The file B<Changes> is updated on occasions the pumpking sees as his 421 own little sync points. On those occasions, he releases a tar-ball of 422 the current source tree (i.e. perl@7582.tar.gz), which will be an 423 excellent point to start with when choosing to use the 'rsync the 424 patches' scheme. Starting with perl@7582, which means a set of source 425 files on which the latest applied patch is number 7582, you apply all 426 succeeding patches available from then on (7583, 7584, ...). 427 428 You can use the patches later as a kind of search archive. 429 430 =over 4 431 432 =item Finding a start point 433 434 If you want to fix/change the behaviour of function/feature Foo, just 435 scan the patches for patches that mention Foo either in the subject, 436 the comments, or the body of the fix. A good chance the patch shows 437 you the files that are affected by that patch which are very likely 438 to be the starting point of your journey into the guts of perl. 439 440 =item Finding how to fix a bug 441 442 If you've found I<where> the function/feature Foo misbehaves, but you 443 don't know how to fix it (but you do know the change you want to 444 make), you can, again, peruse the patches for similar changes and 445 look how others apply the fix. 446 447 =item Finding the source of misbehaviour 448 449 When you keep in sync with bleadperl, the pumpking would love to 450 I<see> that the community efforts really work. So after each of his 451 sync points, you are to 'make test' to check if everything is still 452 in working order. If it is, you do 'make ok', which will send an OK 453 report to I<perlbug@perl.org>. (If you do not have access to a mailer 454 from the system you just finished successfully 'make test', you can 455 do 'make okfile', which creates the file C<perl.ok>, which you can 456 than take to your favourite mailer and mail yourself). 457 458 But of course, as always, things will not always lead to a success 459 path, and one or more test do not pass the 'make test'. Before 460 sending in a bug report (using 'make nok' or 'make nokfile'), check 461 the mailing list if someone else has reported the bug already and if 462 so, confirm it by replying to that message. If not, you might want to 463 trace the source of that misbehaviour B<before> sending in the bug, 464 which will help all the other porters in finding the solution. 465 466 Here the saved patches come in very handy. You can check the list of 467 patches to see which patch changed what file and what change caused 468 the misbehaviour. If you note that in the bug report, it saves the 469 one trying to solve it, looking for that point. 470 471 =back 472 473 If searching the patches is too bothersome, you might consider using 474 perl's bugtron to find more information about discussions and 475 ramblings on posted bugs. 476 477 If you want to get the best of both worlds, rsync both the source 478 tree for convenience, reliability and ease and rsync the patches 479 for reference. 480 481 =back 482 483 =head2 Working with the source 484 485 Because you cannot use the Perforce client, you cannot easily generate 486 diffs against the repository, nor will merges occur when you update 487 via rsync. If you edit a file locally and then rsync against the 488 latest source, changes made in the remote copy will I<overwrite> your 489 local versions! 490 491 The best way to deal with this is to maintain a tree of symlinks to 492 the rsync'd source. Then, when you want to edit a file, you remove 493 the symlink, copy the real file into the other tree, and edit it. You 494 can then diff your edited file against the original to generate a 495 patch, and you can safely update the original tree. 496 497 Perl's F<Configure> script can generate this tree of symlinks for you. 498 The following example assumes that you have used rsync to pull a copy 499 of the Perl source into the F<perl-rsync> directory. In the directory 500 above that one, you can execute the following commands: 501 502 mkdir perl-dev 503 cd perl-dev 504 ../perl-rsync/Configure -Dmksymlinks -Dusedevel -D"optimize=-g" 505 506 This will start the Perl configuration process. After a few prompts, 507 you should see something like this: 508 509 Symbolic links are supported. 510 511 Checking how to test for symbolic links... 512 Your builtin 'test -h' may be broken. 513 Trying external '/usr/bin/test -h'. 514 You can test for symbolic links with '/usr/bin/test -h'. 515 516 Creating the symbolic links... 517 (First creating the subdirectories...) 518 (Then creating the symlinks...) 519 520 The specifics may vary based on your operating system, of course. 521 After you see this, you can abort the F<Configure> script, and you 522 will see that the directory you are in has a tree of symlinks to the 523 F<perl-rsync> directories and files. 524 525 If you plan to do a lot of work with the Perl source, here are some 526 Bourne shell script functions that can make your life easier: 527 528 function edit { 529 if [ -L $1 ]; then 530 mv $1 $1.orig 531 cp $1.orig $1 532 vi $1 533 else 534 vi $1 535 fi 536 } 537 538 function unedit { 539 if [ -L $1.orig ]; then 540 rm $1 541 mv $1.orig $1 542 fi 543 } 544 545 Replace "vi" with your favorite flavor of editor. 546 547 Here is another function which will quickly generate a patch for the 548 files which have been edited in your symlink tree: 549 550 mkpatchorig() { 551 local diffopts 552 for f in `find . -name '*.orig' | sed s,^\./,,` 553 do 554 case `echo $f | sed 's,.orig$,,;s,.*\.,,'` in 555 c) diffopts=-p ;; 556 pod) diffopts='-F^=' ;; 557 *) diffopts= ;; 558 esac 559 diff -du $diffopts $f `echo $f | sed 's,.orig$,,'` 560 done 561 } 562 563 This function produces patches which include enough context to make 564 your changes obvious. This makes it easier for the Perl pumpking(s) 565 to review them when you send them to the perl5-porters list, and that 566 means they're more likely to get applied. 567 568 This function assumed a GNU diff, and may require some tweaking for 569 other diff variants. 570 571 =head2 Perlbug administration 572 573 There is a single remote administrative interface for modifying bug status, 574 category, open issues etc. using the B<RT> bugtracker system, maintained 575 by Robert Spier. Become an administrator, and close any bugs you can get 576 your sticky mitts on: 577 578 http://bugs.perl.org/ 579 580 To email the bug system administrators: 581 582 "perlbug-admin" <perlbug-admin@perl.org> 583 584 =head2 Submitting patches 585 586 Always submit patches to I<perl5-porters@perl.org>. If you're 587 patching a core module and there's an author listed, send the author a 588 copy (see L<Patching a core module>). This lets other porters review 589 your patch, which catches a surprising number of errors in patches. 590 Either use the diff program (available in source code form from 591 ftp://ftp.gnu.org/pub/gnu/ , or use Johan Vromans' I<makepatch> 592 (available from I<CPAN/authors/id/JV/>). Unified diffs are preferred, 593 but context diffs are accepted. Do not send RCS-style diffs or diffs 594 without context lines. More information is given in the 595 I<Porting/patching.pod> file in the Perl source distribution. Please 596 patch against the latest B<development> version. (e.g., even if you're 597 fixing a bug in the 5.8 track, patch against the latest B<development> 598 version rsynced from rsync://public.activestate.com/perl-current/ ) 599 600 If changes are accepted, they are applied to the development branch. Then 601 the 5.8 pumpking decides which of those patches is to be backported to the 602 maint branch. Only patches that survive the heat of the development 603 branch get applied to maintenance versions. 604 605 Your patch should update the documentation and test suite. See 606 L<Writing a test>. If you have added or removed files in the distribution, 607 edit the MANIFEST file accordingly, sort the MANIFEST file using 608 C<make manisort>, and include those changes as part of your patch. 609 610 Patching documentation also follows the same order: if accepted, a patch 611 is first applied to B<development>, and if relevant then it's backported 612 to B<maintenance>. (With an exception for some patches that document 613 behaviour that only appears in the maintenance branch, but which has 614 changed in the development version.) 615 616 To report a bug in Perl, use the program I<perlbug> which comes with 617 Perl (if you can't get Perl to work, send mail to the address 618 I<perlbug@perl.org> or I<perlbug@perl.com>). Reporting bugs through 619 I<perlbug> feeds into the automated bug-tracking system, access to 620 which is provided through the web at http://rt.perl.org/rt3/ . It 621 often pays to check the archives of the perl5-porters mailing list to 622 see whether the bug you're reporting has been reported before, and if 623 so whether it was considered a bug. See above for the location of 624 the searchable archives. 625 626 The CPAN testers ( http://testers.cpan.org/ ) are a group of 627 volunteers who test CPAN modules on a variety of platforms. Perl 628 Smokers ( http://www.nntp.perl.org/group/perl.daily-build and 629 http://www.nntp.perl.org/group/perl.daily-build.reports/ ) 630 automatically test Perl source releases on platforms with various 631 configurations. Both efforts welcome volunteers. In order to get 632 involved in smoke testing of the perl itself visit 633 L<http://search.cpan.org/dist/Test-Smoke>. In order to start smoke 634 testing CPAN modules visit L<http://search.cpan.org/dist/CPAN-YACSmoke/> 635 or L<http://search.cpan.org/dist/POE-Component-CPAN-YACSmoke/> or 636 L<http://search.cpan.org/dist/CPAN-Reporter/>. 637 638 It's a good idea to read and lurk for a while before chipping in. 639 That way you'll get to see the dynamic of the conversations, learn the 640 personalities of the players, and hopefully be better prepared to make 641 a useful contribution when do you speak up. 642 643 If after all this you still think you want to join the perl5-porters 644 mailing list, send mail to I<perl5-porters-subscribe@perl.org>. To 645 unsubscribe, send mail to I<perl5-porters-unsubscribe@perl.org>. 646 647 To hack on the Perl guts, you'll need to read the following things: 648 649 =over 3 650 651 =item L<perlguts> 652 653 This is of paramount importance, since it's the documentation of what 654 goes where in the Perl source. Read it over a couple of times and it 655 might start to make sense - don't worry if it doesn't yet, because the 656 best way to study it is to read it in conjunction with poking at Perl 657 source, and we'll do that later on. 658 659 You might also want to look at Gisle Aas's illustrated perlguts - 660 there's no guarantee that this will be absolutely up-to-date with the 661 latest documentation in the Perl core, but the fundamentals will be 662 right. ( http://gisle.aas.no/perl/illguts/ ) 663 664 =item L<perlxstut> and L<perlxs> 665 666 A working knowledge of XSUB programming is incredibly useful for core 667 hacking; XSUBs use techniques drawn from the PP code, the portion of the 668 guts that actually executes a Perl program. It's a lot gentler to learn 669 those techniques from simple examples and explanation than from the core 670 itself. 671 672 =item L<perlapi> 673 674 The documentation for the Perl API explains what some of the internal 675 functions do, as well as the many macros used in the source. 676 677 =item F<Porting/pumpkin.pod> 678 679 This is a collection of words of wisdom for a Perl porter; some of it is 680 only useful to the pumpkin holder, but most of it applies to anyone 681 wanting to go about Perl development. 682 683 =item The perl5-porters FAQ 684 685 This should be available from http://dev.perl.org/perl5/docs/p5p-faq.html . 686 It contains hints on reading perl5-porters, information on how 687 perl5-porters works and how Perl development in general works. 688 689 =back 690 691 =head2 Finding Your Way Around 692 693 Perl maintenance can be split into a number of areas, and certain people 694 (pumpkins) will have responsibility for each area. These areas sometimes 695 correspond to files or directories in the source kit. Among the areas are: 696 697 =over 3 698 699 =item Core modules 700 701 Modules shipped as part of the Perl core live in the F<lib/> and F<ext/> 702 subdirectories: F<lib/> is for the pure-Perl modules, and F<ext/> 703 contains the core XS modules. 704 705 =item Tests 706 707 There are tests for nearly all the modules, built-ins and major bits 708 of functionality. Test files all have a .t suffix. Module tests live 709 in the F<lib/> and F<ext/> directories next to the module being 710 tested. Others live in F<t/>. See L<Writing a test> 711 712 =item Documentation 713 714 Documentation maintenance includes looking after everything in the 715 F<pod/> directory, (as well as contributing new documentation) and 716 the documentation to the modules in core. 717 718 =item Configure 719 720 The configure process is the way we make Perl portable across the 721 myriad of operating systems it supports. Responsibility for the 722 configure, build and installation process, as well as the overall 723 portability of the core code rests with the configure pumpkin - others 724 help out with individual operating systems. 725 726 The files involved are the operating system directories, (F<win32/>, 727 F<os2/>, F<vms/> and so on) the shell scripts which generate F<config.h> 728 and F<Makefile>, as well as the metaconfig files which generate 729 F<Configure>. (metaconfig isn't included in the core distribution.) 730 731 =item Interpreter 732 733 And of course, there's the core of the Perl interpreter itself. Let's 734 have a look at that in a little more detail. 735 736 =back 737 738 Before we leave looking at the layout, though, don't forget that 739 F<MANIFEST> contains not only the file names in the Perl distribution, 740 but short descriptions of what's in them, too. For an overview of the 741 important files, try this: 742 743 perl -lne 'print if /^[^\/]+\.[ch]\s+/' MANIFEST 744 745 =head2 Elements of the interpreter 746 747 The work of the interpreter has two main stages: compiling the code 748 into the internal representation, or bytecode, and then executing it. 749 L<perlguts/Compiled code> explains exactly how the compilation stage 750 happens. 751 752 Here is a short breakdown of perl's operation: 753 754 =over 3 755 756 =item Startup 757 758 The action begins in F<perlmain.c>. (or F<miniperlmain.c> for miniperl) 759 This is very high-level code, enough to fit on a single screen, and it 760 resembles the code found in L<perlembed>; most of the real action takes 761 place in F<perl.c> 762 763 First, F<perlmain.c> allocates some memory and constructs a Perl 764 interpreter: 765 766 1 PERL_SYS_INIT3(&argc,&argv,&env); 767 2 768 3 if (!PL_do_undump) { 769 4 my_perl = perl_alloc(); 770 5 if (!my_perl) 771 6 exit(1); 772 7 perl_construct(my_perl); 773 8 PL_perl_destruct_level = 0; 774 9 } 775 776 Line 1 is a macro, and its definition is dependent on your operating 777 system. Line 3 references C<PL_do_undump>, a global variable - all 778 global variables in Perl start with C<PL_>. This tells you whether the 779 current running program was created with the C<-u> flag to perl and then 780 F<undump>, which means it's going to be false in any sane context. 781 782 Line 4 calls a function in F<perl.c> to allocate memory for a Perl 783 interpreter. It's quite a simple function, and the guts of it looks like 784 this: 785 786 my_perl = (PerlInterpreter*)PerlMem_malloc(sizeof(PerlInterpreter)); 787 788 Here you see an example of Perl's system abstraction, which we'll see 789 later: C<PerlMem_malloc> is either your system's C<malloc>, or Perl's 790 own C<malloc> as defined in F<malloc.c> if you selected that option at 791 configure time. 792 793 Next, in line 7, we construct the interpreter; this sets up all the 794 special variables that Perl needs, the stacks, and so on. 795 796 Now we pass Perl the command line options, and tell it to go: 797 798 exitstatus = perl_parse(my_perl, xs_init, argc, argv, (char **)NULL); 799 if (!exitstatus) { 800 exitstatus = perl_run(my_perl); 801 } 802 803 804 C<perl_parse> is actually a wrapper around C<S_parse_body>, as defined 805 in F<perl.c>, which processes the command line options, sets up any 806 statically linked XS modules, opens the program and calls C<yyparse> to 807 parse it. 808 809 =item Parsing 810 811 The aim of this stage is to take the Perl source, and turn it into an op 812 tree. We'll see what one of those looks like later. Strictly speaking, 813 there's three things going on here. 814 815 C<yyparse>, the parser, lives in F<perly.c>, although you're better off 816 reading the original YACC input in F<perly.y>. (Yes, Virginia, there 817 B<is> a YACC grammar for Perl!) The job of the parser is to take your 818 code and "understand" it, splitting it into sentences, deciding which 819 operands go with which operators and so on. 820 821 The parser is nobly assisted by the lexer, which chunks up your input 822 into tokens, and decides what type of thing each token is: a variable 823 name, an operator, a bareword, a subroutine, a core function, and so on. 824 The main point of entry to the lexer is C<yylex>, and that and its 825 associated routines can be found in F<toke.c>. Perl isn't much like 826 other computer languages; it's highly context sensitive at times, it can 827 be tricky to work out what sort of token something is, or where a token 828 ends. As such, there's a lot of interplay between the tokeniser and the 829 parser, which can get pretty frightening if you're not used to it. 830 831 As the parser understands a Perl program, it builds up a tree of 832 operations for the interpreter to perform during execution. The routines 833 which construct and link together the various operations are to be found 834 in F<op.c>, and will be examined later. 835 836 =item Optimization 837 838 Now the parsing stage is complete, and the finished tree represents 839 the operations that the Perl interpreter needs to perform to execute our 840 program. Next, Perl does a dry run over the tree looking for 841 optimisations: constant expressions such as C<3 + 4> will be computed 842 now, and the optimizer will also see if any multiple operations can be 843 replaced with a single one. For instance, to fetch the variable C<$foo>, 844 instead of grabbing the glob C<*foo> and looking at the scalar 845 component, the optimizer fiddles the op tree to use a function which 846 directly looks up the scalar in question. The main optimizer is C<peep> 847 in F<op.c>, and many ops have their own optimizing functions. 848 849 =item Running 850 851 Now we're finally ready to go: we have compiled Perl byte code, and all 852 that's left to do is run it. The actual execution is done by the 853 C<runops_standard> function in F<run.c>; more specifically, it's done by 854 these three innocent looking lines: 855 856 while ((PL_op = CALL_FPTR(PL_op->op_ppaddr)(aTHX))) { 857 PERL_ASYNC_CHECK(); 858 } 859 860 You may be more comfortable with the Perl version of that: 861 862 PERL_ASYNC_CHECK() while $Perl::op = &{$Perl::op->{function}}; 863 864 Well, maybe not. Anyway, each op contains a function pointer, which 865 stipulates the function which will actually carry out the operation. 866 This function will return the next op in the sequence - this allows for 867 things like C<if> which choose the next op dynamically at run time. 868 The C<PERL_ASYNC_CHECK> makes sure that things like signals interrupt 869 execution if required. 870 871 The actual functions called are known as PP code, and they're spread 872 between four files: F<pp_hot.c> contains the "hot" code, which is most 873 often used and highly optimized, F<pp_sys.c> contains all the 874 system-specific functions, F<pp_ctl.c> contains the functions which 875 implement control structures (C<if>, C<while> and the like) and F<pp.c> 876 contains everything else. These are, if you like, the C code for Perl's 877 built-in functions and operators. 878 879 Note that each C<pp_> function is expected to return a pointer to the next 880 op. Calls to perl subs (and eval blocks) are handled within the same 881 runops loop, and do not consume extra space on the C stack. For example, 882 C<pp_entersub> and C<pp_entertry> just push a C<CxSUB> or C<CxEVAL> block 883 struct onto the context stack which contain the address of the op 884 following the sub call or eval. They then return the first op of that sub 885 or eval block, and so execution continues of that sub or block. Later, a 886 C<pp_leavesub> or C<pp_leavetry> op pops the C<CxSUB> or C<CxEVAL>, 887 retrieves the return op from it, and returns it. 888 889 =item Exception handing 890 891 Perl's exception handing (i.e. C<die> etc.) is built on top of the low-level 892 C<setjmp()>/C<longjmp()> C-library functions. These basically provide a 893 way to capture the current PC and SP registers and later restore them; i.e. 894 a C<longjmp()> continues at the point in code where a previous C<setjmp()> 895 was done, with anything further up on the C stack being lost. This is why 896 code should always save values using C<SAVE_FOO> rather than in auto 897 variables. 898 899 The perl core wraps C<setjmp()> etc in the macros C<JMPENV_PUSH> and 900 C<JMPENV_JUMP>. The basic rule of perl exceptions is that C<exit>, and 901 C<die> (in the absence of C<eval>) perform a C<JMPENV_JUMP(2)>, while 902 C<die> within C<eval> does a C<JMPENV_JUMP(3)>. 903 904 At entry points to perl, such as C<perl_parse()>, C<perl_run()> and 905 C<call_sv(cv, G_EVAL)> each does a C<JMPENV_PUSH>, then enter a runops 906 loop or whatever, and handle possible exception returns. For a 2 return, 907 final cleanup is performed, such as popping stacks and calling C<CHECK> or 908 C<END> blocks. Amongst other things, this is how scope cleanup still 909 occurs during an C<exit>. 910 911 If a C<die> can find a C<CxEVAL> block on the context stack, then the 912 stack is popped to that level and the return op in that block is assigned 913 to C<PL_restartop>; then a C<JMPENV_JUMP(3)> is performed. This normally 914 passes control back to the guard. In the case of C<perl_run> and 915 C<call_sv>, a non-null C<PL_restartop> triggers re-entry to the runops 916 loop. The is the normal way that C<die> or C<croak> is handled within an 917 C<eval>. 918 919 Sometimes ops are executed within an inner runops loop, such as tie, sort 920 or overload code. In this case, something like 921 922 sub FETCH { eval { die } } 923 924 would cause a longjmp right back to the guard in C<perl_run>, popping both 925 runops loops, which is clearly incorrect. One way to avoid this is for the 926 tie code to do a C<JMPENV_PUSH> before executing C<FETCH> in the inner 927 runops loop, but for efficiency reasons, perl in fact just sets a flag, 928 using C<CATCH_SET(TRUE)>. The C<pp_require>, C<pp_entereval> and 929 C<pp_entertry> ops check this flag, and if true, they call C<docatch>, 930 which does a C<JMPENV_PUSH> and starts a new runops level to execute the 931 code, rather than doing it on the current loop. 932 933 As a further optimisation, on exit from the eval block in the C<FETCH>, 934 execution of the code following the block is still carried on in the inner 935 loop. When an exception is raised, C<docatch> compares the C<JMPENV> 936 level of the C<CxEVAL> with C<PL_top_env> and if they differ, just 937 re-throws the exception. In this way any inner loops get popped. 938 939 Here's an example. 940 941 1: eval { tie @a, 'A' }; 942 2: sub A::TIEARRAY { 943 3: eval { die }; 944 4: die; 945 5: } 946 947 To run this code, C<perl_run> is called, which does a C<JMPENV_PUSH> then 948 enters a runops loop. This loop executes the eval and tie ops on line 1, 949 with the eval pushing a C<CxEVAL> onto the context stack. 950 951 The C<pp_tie> does a C<CATCH_SET(TRUE)>, then starts a second runops loop 952 to execute the body of C<TIEARRAY>. When it executes the entertry op on 953 line 3, C<CATCH_GET> is true, so C<pp_entertry> calls C<docatch> which 954 does a C<JMPENV_PUSH> and starts a third runops loop, which then executes 955 the die op. At this point the C call stack looks like this: 956 957 Perl_pp_die 958 Perl_runops # third loop 959 S_docatch_body 960 S_docatch 961 Perl_pp_entertry 962 Perl_runops # second loop 963 S_call_body 964 Perl_call_sv 965 Perl_pp_tie 966 Perl_runops # first loop 967 S_run_body 968 perl_run 969 main 970 971 and the context and data stacks, as shown by C<-Dstv>, look like: 972 973 STACK 0: MAIN 974 CX 0: BLOCK => 975 CX 1: EVAL => AV() PV("A"\0) 976 retop=leave 977 STACK 1: MAGIC 978 CX 0: SUB => 979 retop=(null) 980 CX 1: EVAL => * 981 retop=nextstate 982 983 The die pops the first C<CxEVAL> off the context stack, sets 984 C<PL_restartop> from it, does a C<JMPENV_JUMP(3)>, and control returns to 985 the top C<docatch>. This then starts another third-level runops level, 986 which executes the nextstate, pushmark and die ops on line 4. At the point 987 that the second C<pp_die> is called, the C call stack looks exactly like 988 that above, even though we are no longer within an inner eval; this is 989 because of the optimization mentioned earlier. However, the context stack 990 now looks like this, ie with the top CxEVAL popped: 991 992 STACK 0: MAIN 993 CX 0: BLOCK => 994 CX 1: EVAL => AV() PV("A"\0) 995 retop=leave 996 STACK 1: MAGIC 997 CX 0: SUB => 998 retop=(null) 999 1000 The die on line 4 pops the context stack back down to the CxEVAL, leaving 1001 it as: 1002 1003 STACK 0: MAIN 1004 CX 0: BLOCK => 1005 1006 As usual, C<PL_restartop> is extracted from the C<CxEVAL>, and a 1007 C<JMPENV_JUMP(3)> done, which pops the C stack back to the docatch: 1008 1009 S_docatch 1010 Perl_pp_entertry 1011 Perl_runops # second loop 1012 S_call_body 1013 Perl_call_sv 1014 Perl_pp_tie 1015 Perl_runops # first loop 1016 S_run_body 1017 perl_run 1018 main 1019 1020 In this case, because the C<JMPENV> level recorded in the C<CxEVAL> 1021 differs from the current one, C<docatch> just does a C<JMPENV_JUMP(3)> 1022 and the C stack unwinds to: 1023 1024 perl_run 1025 main 1026 1027 Because C<PL_restartop> is non-null, C<run_body> starts a new runops loop 1028 and execution continues. 1029 1030 =back 1031 1032 =head2 Internal Variable Types 1033 1034 You should by now have had a look at L<perlguts>, which tells you about 1035 Perl's internal variable types: SVs, HVs, AVs and the rest. If not, do 1036 that now. 1037 1038 These variables are used not only to represent Perl-space variables, but 1039 also any constants in the code, as well as some structures completely 1040 internal to Perl. The symbol table, for instance, is an ordinary Perl 1041 hash. Your code is represented by an SV as it's read into the parser; 1042 any program files you call are opened via ordinary Perl filehandles, and 1043 so on. 1044 1045 The core L<Devel::Peek|Devel::Peek> module lets us examine SVs from a 1046 Perl program. Let's see, for instance, how Perl treats the constant 1047 C<"hello">. 1048 1049 % perl -MDevel::Peek -e 'Dump("hello")' 1050 1 SV = PV(0xa041450) at 0xa04ecbc 1051 2 REFCNT = 1 1052 3 FLAGS = (POK,READONLY,pPOK) 1053 4 PV = 0xa0484e0 "hello"\0 1054 5 CUR = 5 1055 6 LEN = 6 1056 1057 Reading C<Devel::Peek> output takes a bit of practise, so let's go 1058 through it line by line. 1059 1060 Line 1 tells us we're looking at an SV which lives at C<0xa04ecbc> in 1061 memory. SVs themselves are very simple structures, but they contain a 1062 pointer to a more complex structure. In this case, it's a PV, a 1063 structure which holds a string value, at location C<0xa041450>. Line 2 1064 is the reference count; there are no other references to this data, so 1065 it's 1. 1066 1067 Line 3 are the flags for this SV - it's OK to use it as a PV, it's a 1068 read-only SV (because it's a constant) and the data is a PV internally. 1069 Next we've got the contents of the string, starting at location 1070 C<0xa0484e0>. 1071 1072 Line 5 gives us the current length of the string - note that this does 1073 B<not> include the null terminator. Line 6 is not the length of the 1074 string, but the length of the currently allocated buffer; as the string 1075 grows, Perl automatically extends the available storage via a routine 1076 called C<SvGROW>. 1077 1078 You can get at any of these quantities from C very easily; just add 1079 C<Sv> to the name of the field shown in the snippet, and you've got a 1080 macro which will return the value: C<SvCUR(sv)> returns the current 1081 length of the string, C<SvREFCOUNT(sv)> returns the reference count, 1082 C<SvPV(sv, len)> returns the string itself with its length, and so on. 1083 More macros to manipulate these properties can be found in L<perlguts>. 1084 1085 Let's take an example of manipulating a PV, from C<sv_catpvn>, in F<sv.c> 1086 1087 1 void 1088 2 Perl_sv_catpvn(pTHX_ register SV *sv, register const char *ptr, register STRLEN len) 1089 3 { 1090 4 STRLEN tlen; 1091 5 char *junk; 1092 1093 6 junk = SvPV_force(sv, tlen); 1094 7 SvGROW(sv, tlen + len + 1); 1095 8 if (ptr == junk) 1096 9 ptr = SvPVX(sv); 1097 10 Move(ptr,SvPVX(sv)+tlen,len,char); 1098 11 SvCUR(sv) += len; 1099 12 *SvEND(sv) = '\0'; 1100 13 (void)SvPOK_only_UTF8(sv); /* validate pointer */ 1101 14 SvTAINT(sv); 1102 15 } 1103 1104 This is a function which adds a string, C<ptr>, of length C<len> onto 1105 the end of the PV stored in C<sv>. The first thing we do in line 6 is 1106 make sure that the SV B<has> a valid PV, by calling the C<SvPV_force> 1107 macro to force a PV. As a side effect, C<tlen> gets set to the current 1108 value of the PV, and the PV itself is returned to C<junk>. 1109 1110 In line 7, we make sure that the SV will have enough room to accommodate 1111 the old string, the new string and the null terminator. If C<LEN> isn't 1112 big enough, C<SvGROW> will reallocate space for us. 1113 1114 Now, if C<junk> is the same as the string we're trying to add, we can 1115 grab the string directly from the SV; C<SvPVX> is the address of the PV 1116 in the SV. 1117 1118 Line 10 does the actual catenation: the C<Move> macro moves a chunk of 1119 memory around: we move the string C<ptr> to the end of the PV - that's 1120 the start of the PV plus its current length. We're moving C<len> bytes 1121 of type C<char>. After doing so, we need to tell Perl we've extended the 1122 string, by altering C<CUR> to reflect the new length. C<SvEND> is a 1123 macro which gives us the end of the string, so that needs to be a 1124 C<"\0">. 1125 1126 Line 13 manipulates the flags; since we've changed the PV, any IV or NV 1127 values will no longer be valid: if we have C<$a=10; $a.="6";> we don't 1128 want to use the old IV of 10. C<SvPOK_only_utf8> is a special UTF-8-aware 1129 version of C<SvPOK_only>, a macro which turns off the IOK and NOK flags 1130 and turns on POK. The final C<SvTAINT> is a macro which launders tainted 1131 data if taint mode is turned on. 1132 1133 AVs and HVs are more complicated, but SVs are by far the most common 1134 variable type being thrown around. Having seen something of how we 1135 manipulate these, let's go on and look at how the op tree is 1136 constructed. 1137 1138 =head2 Op Trees 1139 1140 First, what is the op tree, anyway? The op tree is the parsed 1141 representation of your program, as we saw in our section on parsing, and 1142 it's the sequence of operations that Perl goes through to execute your 1143 program, as we saw in L</Running>. 1144 1145 An op is a fundamental operation that Perl can perform: all the built-in 1146 functions and operators are ops, and there are a series of ops which 1147 deal with concepts the interpreter needs internally - entering and 1148 leaving a block, ending a statement, fetching a variable, and so on. 1149 1150 The op tree is connected in two ways: you can imagine that there are two 1151 "routes" through it, two orders in which you can traverse the tree. 1152 First, parse order reflects how the parser understood the code, and 1153 secondly, execution order tells perl what order to perform the 1154 operations in. 1155 1156 The easiest way to examine the op tree is to stop Perl after it has 1157 finished parsing, and get it to dump out the tree. This is exactly what 1158 the compiler backends L<B::Terse|B::Terse>, L<B::Concise|B::Concise> 1159 and L<B::Debug|B::Debug> do. 1160 1161 Let's have a look at how Perl sees C<$a = $b + $c>: 1162 1163 % perl -MO=Terse -e '$a=$b+$c' 1164 1 LISTOP (0x8179888) leave 1165 2 OP (0x81798b0) enter 1166 3 COP (0x8179850) nextstate 1167 4 BINOP (0x8179828) sassign 1168 5 BINOP (0x8179800) add [1] 1169 6 UNOP (0x81796e0) null [15] 1170 7 SVOP (0x80fafe0) gvsv GV (0x80fa4cc) *b 1171 8 UNOP (0x81797e0) null [15] 1172 9 SVOP (0x8179700) gvsv GV (0x80efeb0) *c 1173 10 UNOP (0x816b4f0) null [15] 1174 11 SVOP (0x816dcf0) gvsv GV (0x80fa460) *a 1175 1176 Let's start in the middle, at line 4. This is a BINOP, a binary 1177 operator, which is at location C<0x8179828>. The specific operator in 1178 question is C<sassign> - scalar assignment - and you can find the code 1179 which implements it in the function C<pp_sassign> in F<pp_hot.c>. As a 1180 binary operator, it has two children: the add operator, providing the 1181 result of C<$b+$c>, is uppermost on line 5, and the left hand side is on 1182 line 10. 1183 1184 Line 10 is the null op: this does exactly nothing. What is that doing 1185 there? If you see the null op, it's a sign that something has been 1186 optimized away after parsing. As we mentioned in L</Optimization>, 1187 the optimization stage sometimes converts two operations into one, for 1188 example when fetching a scalar variable. When this happens, instead of 1189 rewriting the op tree and cleaning up the dangling pointers, it's easier 1190 just to replace the redundant operation with the null op. Originally, 1191 the tree would have looked like this: 1192 1193 10 SVOP (0x816b4f0) rv2sv [15] 1194 11 SVOP (0x816dcf0) gv GV (0x80fa460) *a 1195 1196 That is, fetch the C<a> entry from the main symbol table, and then look 1197 at the scalar component of it: C<gvsv> (C<pp_gvsv> into F<pp_hot.c>) 1198 happens to do both these things. 1199 1200 The right hand side, starting at line 5 is similar to what we've just 1201 seen: we have the C<add> op (C<pp_add> also in F<pp_hot.c>) add together 1202 two C<gvsv>s. 1203 1204 Now, what's this about? 1205 1206 1 LISTOP (0x8179888) leave 1207 2 OP (0x81798b0) enter 1208 3 COP (0x8179850) nextstate 1209 1210 C<enter> and C<leave> are scoping ops, and their job is to perform any 1211 housekeeping every time you enter and leave a block: lexical variables 1212 are tidied up, unreferenced variables are destroyed, and so on. Every 1213 program will have those first three lines: C<leave> is a list, and its 1214 children are all the statements in the block. Statements are delimited 1215 by C<nextstate>, so a block is a collection of C<nextstate> ops, with 1216 the ops to be performed for each statement being the children of 1217 C<nextstate>. C<enter> is a single op which functions as a marker. 1218 1219 That's how Perl parsed the program, from top to bottom: 1220 1221 Program 1222 | 1223 Statement 1224 | 1225 = 1226 / \ 1227 / \ 1228 $a + 1229 / \ 1230 $b $c 1231 1232 However, it's impossible to B<perform> the operations in this order: 1233 you have to find the values of C<$b> and C<$c> before you add them 1234 together, for instance. So, the other thread that runs through the op 1235 tree is the execution order: each op has a field C<op_next> which points 1236 to the next op to be run, so following these pointers tells us how perl 1237 executes the code. We can traverse the tree in this order using 1238 the C<exec> option to C<B::Terse>: 1239 1240 % perl -MO=Terse,exec -e '$a=$b+$c' 1241 1 OP (0x8179928) enter 1242 2 COP (0x81798c8) nextstate 1243 3 SVOP (0x81796c8) gvsv GV (0x80fa4d4) *b 1244 4 SVOP (0x8179798) gvsv GV (0x80efeb0) *c 1245 5 BINOP (0x8179878) add [1] 1246 6 SVOP (0x816dd38) gvsv GV (0x80fa468) *a 1247 7 BINOP (0x81798a0) sassign 1248 8 LISTOP (0x8179900) leave 1249 1250 This probably makes more sense for a human: enter a block, start a 1251 statement. Get the values of C<$b> and C<$c>, and add them together. 1252 Find C<$a>, and assign one to the other. Then leave. 1253 1254 The way Perl builds up these op trees in the parsing process can be 1255 unravelled by examining F<perly.y>, the YACC grammar. Let's take the 1256 piece we need to construct the tree for C<$a = $b + $c> 1257 1258 1 term : term ASSIGNOP term 1259 2 { $$ = newASSIGNOP(OPf_STACKED, $1, $2, $3); } 1260 3 | term ADDOP term 1261 4 { $$ = newBINOP($2, 0, scalar($1), scalar($3)); } 1262 1263 If you're not used to reading BNF grammars, this is how it works: You're 1264 fed certain things by the tokeniser, which generally end up in upper 1265 case. Here, C<ADDOP>, is provided when the tokeniser sees C<+> in your 1266 code. C<ASSIGNOP> is provided when C<=> is used for assigning. These are 1267 "terminal symbols", because you can't get any simpler than them. 1268 1269 The grammar, lines one and three of the snippet above, tells you how to 1270 build up more complex forms. These complex forms, "non-terminal symbols" 1271 are generally placed in lower case. C<term> here is a non-terminal 1272 symbol, representing a single expression. 1273 1274 The grammar gives you the following rule: you can make the thing on the 1275 left of the colon if you see all the things on the right in sequence. 1276 This is called a "reduction", and the aim of parsing is to completely 1277 reduce the input. There are several different ways you can perform a 1278 reduction, separated by vertical bars: so, C<term> followed by C<=> 1279 followed by C<term> makes a C<term>, and C<term> followed by C<+> 1280 followed by C<term> can also make a C<term>. 1281 1282 So, if you see two terms with an C<=> or C<+>, between them, you can 1283 turn them into a single expression. When you do this, you execute the 1284 code in the block on the next line: if you see C<=>, you'll do the code 1285 in line 2. If you see C<+>, you'll do the code in line 4. It's this code 1286 which contributes to the op tree. 1287 1288 | term ADDOP term 1289 { $$ = newBINOP($2, 0, scalar($1), scalar($3)); } 1290 1291 What this does is creates a new binary op, and feeds it a number of 1292 variables. The variables refer to the tokens: C<$1> is the first token in 1293 the input, C<$2> the second, and so on - think regular expression 1294 backreferences. C<$$> is the op returned from this reduction. So, we 1295 call C<newBINOP> to create a new binary operator. The first parameter to 1296 C<newBINOP>, a function in F<op.c>, is the op type. It's an addition 1297 operator, so we want the type to be C<ADDOP>. We could specify this 1298 directly, but it's right there as the second token in the input, so we 1299 use C<$2>. The second parameter is the op's flags: 0 means "nothing 1300 special". Then the things to add: the left and right hand side of our 1301 expression, in scalar context. 1302 1303 =head2 Stacks 1304 1305 When perl executes something like C<addop>, how does it pass on its 1306 results to the next op? The answer is, through the use of stacks. Perl 1307 has a number of stacks to store things it's currently working on, and 1308 we'll look at the three most important ones here. 1309 1310 =over 3 1311 1312 =item Argument stack 1313 1314 Arguments are passed to PP code and returned from PP code using the 1315 argument stack, C<ST>. The typical way to handle arguments is to pop 1316 them off the stack, deal with them how you wish, and then push the result 1317 back onto the stack. This is how, for instance, the cosine operator 1318 works: 1319 1320 NV value; 1321 value = POPn; 1322 value = Perl_cos(value); 1323 XPUSHn(value); 1324 1325 We'll see a more tricky example of this when we consider Perl's macros 1326 below. C<POPn> gives you the NV (floating point value) of the top SV on 1327 the stack: the C<$x> in C<cos($x)>. Then we compute the cosine, and push 1328 the result back as an NV. The C<X> in C<XPUSHn> means that the stack 1329 should be extended if necessary - it can't be necessary here, because we 1330 know there's room for one more item on the stack, since we've just 1331 removed one! The C<XPUSH*> macros at least guarantee safety. 1332 1333 Alternatively, you can fiddle with the stack directly: C<SP> gives you 1334 the first element in your portion of the stack, and C<TOP*> gives you 1335 the top SV/IV/NV/etc. on the stack. So, for instance, to do unary 1336 negation of an integer: 1337 1338 SETi(-TOPi); 1339 1340 Just set the integer value of the top stack entry to its negation. 1341 1342 Argument stack manipulation in the core is exactly the same as it is in 1343 XSUBs - see L<perlxstut>, L<perlxs> and L<perlguts> for a longer 1344 description of the macros used in stack manipulation. 1345 1346 =item Mark stack 1347 1348 I say "your portion of the stack" above because PP code doesn't 1349 necessarily get the whole stack to itself: if your function calls 1350 another function, you'll only want to expose the arguments aimed for the 1351 called function, and not (necessarily) let it get at your own data. The 1352 way we do this is to have a "virtual" bottom-of-stack, exposed to each 1353 function. The mark stack keeps bookmarks to locations in the argument 1354 stack usable by each function. For instance, when dealing with a tied 1355 variable, (internally, something with "P" magic) Perl has to call 1356 methods for accesses to the tied variables. However, we need to separate 1357 the arguments exposed to the method to the argument exposed to the 1358 original function - the store or fetch or whatever it may be. Here's 1359 roughly how the tied C<push> is implemented; see C<av_push> in F<av.c>: 1360 1361 1 PUSHMARK(SP); 1362 2 EXTEND(SP,2); 1363 3 PUSHs(SvTIED_obj((SV*)av, mg)); 1364 4 PUSHs(val); 1365 5 PUTBACK; 1366 6 ENTER; 1367 7 call_method("PUSH", G_SCALAR|G_DISCARD); 1368 8 LEAVE; 1369 1370 Let's examine the whole implementation, for practice: 1371 1372 1 PUSHMARK(SP); 1373 1374 Push the current state of the stack pointer onto the mark stack. This is 1375 so that when we've finished adding items to the argument stack, Perl 1376 knows how many things we've added recently. 1377 1378 2 EXTEND(SP,2); 1379 3 PUSHs(SvTIED_obj((SV*)av, mg)); 1380 4 PUSHs(val); 1381 1382 We're going to add two more items onto the argument stack: when you have 1383 a tied array, the C<PUSH> subroutine receives the object and the value 1384 to be pushed, and that's exactly what we have here - the tied object, 1385 retrieved with C<SvTIED_obj>, and the value, the SV C<val>. 1386 1387 5 PUTBACK; 1388 1389 Next we tell Perl to update the global stack pointer from our internal 1390 variable: C<dSP> only gave us a local copy, not a reference to the global. 1391 1392 6 ENTER; 1393 7 call_method("PUSH", G_SCALAR|G_DISCARD); 1394 8 LEAVE; 1395 1396 C<ENTER> and C<LEAVE> localise a block of code - they make sure that all 1397 variables are tidied up, everything that has been localised gets 1398 its previous value returned, and so on. Think of them as the C<{> and 1399 C<}> of a Perl block. 1400 1401 To actually do the magic method call, we have to call a subroutine in 1402 Perl space: C<call_method> takes care of that, and it's described in 1403 L<perlcall>. We call the C<PUSH> method in scalar context, and we're 1404 going to discard its return value. The call_method() function 1405 removes the top element of the mark stack, so there is nothing for 1406 the caller to clean up. 1407 1408 =item Save stack 1409 1410 C doesn't have a concept of local scope, so perl provides one. We've 1411 seen that C<ENTER> and C<LEAVE> are used as scoping braces; the save 1412 stack implements the C equivalent of, for example: 1413 1414 { 1415 local $foo = 42; 1416 ... 1417 } 1418 1419 See L<perlguts/Localising Changes> for how to use the save stack. 1420 1421 =back 1422 1423 =head2 Millions of Macros 1424 1425 One thing you'll notice about the Perl source is that it's full of 1426 macros. Some have called the pervasive use of macros the hardest thing 1427 to understand, others find it adds to clarity. Let's take an example, 1428 the code which implements the addition operator: 1429 1430 1 PP(pp_add) 1431 2 { 1432 3 dSP; dATARGET; tryAMAGICbin(add,opASSIGN); 1433 4 { 1434 5 dPOPTOPnnrl_ul; 1435 6 SETn( left + right ); 1436 7 RETURN; 1437 8 } 1438 9 } 1439 1440 Every line here (apart from the braces, of course) contains a macro. The 1441 first line sets up the function declaration as Perl expects for PP code; 1442 line 3 sets up variable declarations for the argument stack and the 1443 target, the return value of the operation. Finally, it tries to see if 1444 the addition operation is overloaded; if so, the appropriate subroutine 1445 is called. 1446 1447 Line 5 is another variable declaration - all variable declarations start 1448 with C<d> - which pops from the top of the argument stack two NVs (hence 1449 C<nn>) and puts them into the variables C<right> and C<left>, hence the 1450 C<rl>. These are the two operands to the addition operator. Next, we 1451 call C<SETn> to set the NV of the return value to the result of adding 1452 the two values. This done, we return - the C<RETURN> macro makes sure 1453 that our return value is properly handled, and we pass the next operator 1454 to run back to the main run loop. 1455 1456 Most of these macros are explained in L<perlapi>, and some of the more 1457 important ones are explained in L<perlxs> as well. Pay special attention 1458 to L<perlguts/Background and PERL_IMPLICIT_CONTEXT> for information on 1459 the C<[pad]THX_?> macros. 1460 1461 =head2 The .i Targets 1462 1463 You can expand the macros in a F<foo.c> file by saying 1464 1465 make foo.i 1466 1467 which will expand the macros using cpp. Don't be scared by the results. 1468 1469 =head1 SOURCE CODE STATIC ANALYSIS 1470 1471 Various tools exist for analysing C source code B<statically>, as 1472 opposed to B<dynamically>, that is, without executing the code. 1473 It is possible to detect resource leaks, undefined behaviour, type 1474 mismatches, portability problems, code paths that would cause illegal 1475 memory accesses, and other similar problems by just parsing the C code 1476 and looking at the resulting graph, what does it tell about the 1477 execution and data flows. As a matter of fact, this is exactly 1478 how C compilers know to give warnings about dubious code. 1479 1480 =head2 lint, splint 1481 1482 The good old C code quality inspector, C<lint>, is available in 1483 several platforms, but please be aware that there are several 1484 different implementations of it by different vendors, which means that 1485 the flags are not identical across different platforms. 1486 1487 There is a lint variant called C<splint> (Secure Programming Lint) 1488 available from http://www.splint.org/ that should compile on any 1489 Unix-like platform. 1490 1491 There are C<lint> and <splint> targets in Makefile, but you may have 1492 to diddle with the flags (see above). 1493 1494 =head2 Coverity 1495 1496 Coverity (http://www.coverity.com/) is a product similar to lint and 1497 as a testbed for their product they periodically check several open 1498 source projects, and they give out accounts to open source developers 1499 to the defect databases. 1500 1501 =head2 cpd (cut-and-paste detector) 1502 1503 The cpd tool detects cut-and-paste coding. If one instance of the 1504 cut-and-pasted code changes, all the other spots should probably be 1505 changed, too. Therefore such code should probably be turned into a 1506 subroutine or a macro. 1507 1508 cpd (http://pmd.sourceforge.net/cpd.html) is part of the pmd project 1509 (http://pmd.sourceforge.net/). pmd was originally written for static 1510 analysis of Java code, but later the cpd part of it was extended to 1511 parse also C and C++. 1512 1513 Download the pmd-bin-X.Y.zip () from the SourceForge site, extract the 1514 pmd-X.Y.jar from it, and then run that on source code thusly: 1515 1516 java -cp pmd-X.Y.jar net.sourceforge.pmd.cpd.CPD --minimum-tokens 100 --files /some/where/src --language c > cpd.txt 1517 1518 You may run into memory limits, in which case you should use the -Xmx option: 1519 1520 java -Xmx512M ... 1521 1522 =head2 gcc warnings 1523 1524 Though much can be written about the inconsistency and coverage 1525 problems of gcc warnings (like C<-Wall> not meaning "all the 1526 warnings", or some common portability problems not being covered by 1527 C<-Wall>, or C<-ansi> and C<-pedantic> both being a poorly defined 1528 collection of warnings, and so forth), gcc is still a useful tool in 1529 keeping our coding nose clean. 1530 1531 The C<-Wall> is by default on. 1532 1533 The C<-ansi> (and its sidekick, C<-pedantic>) would be nice to be on 1534 always, but unfortunately they are not safe on all platforms, they can 1535 for example cause fatal conflicts with the system headers (Solaris 1536 being a prime example). If Configure C<-Dgccansipedantic> is used, 1537 the C<cflags> frontend selects C<-ansi -pedantic> for the platforms 1538 where they are known to be safe. 1539 1540 Starting from Perl 5.9.4 the following extra flags are added: 1541 1542 =over 4 1543 1544 =item * 1545 1546 C<-Wendif-labels> 1547 1548 =item * 1549 1550 C<-Wextra> 1551 1552 =item * 1553 1554 C<-Wdeclaration-after-statement> 1555 1556 =back 1557 1558 The following flags would be nice to have but they would first need 1559 their own Augean stablemaster: 1560 1561 =over 4 1562 1563 =item * 1564 1565 C<-Wpointer-arith> 1566 1567 =item * 1568 1569 C<-Wshadow> 1570 1571 =item * 1572 1573 C<-Wstrict-prototypes> 1574 1575 =back 1576 1577 The C<-Wtraditional> is another example of the annoying tendency of 1578 gcc to bundle a lot of warnings under one switch -- it would be 1579 impossible to deploy in practice because it would complain a lot -- but 1580 it does contain some warnings that would be beneficial to have available 1581 on their own, such as the warning about string constants inside macros 1582 containing the macro arguments: this behaved differently pre-ANSI 1583 than it does in ANSI, and some C compilers are still in transition, 1584 AIX being an example. 1585 1586 =head2 Warnings of other C compilers 1587 1588 Other C compilers (yes, there B<are> other C compilers than gcc) often 1589 have their "strict ANSI" or "strict ANSI with some portability extensions" 1590 modes on, like for example the Sun Workshop has its C<-Xa> mode on 1591 (though implicitly), or the DEC (these days, HP...) has its C<-std1> 1592 mode on. 1593 1594 =head2 DEBUGGING 1595 1596 You can compile a special debugging version of Perl, which allows you 1597 to use the C<-D> option of Perl to tell more about what Perl is doing. 1598 But sometimes there is no alternative than to dive in with a debugger, 1599 either to see the stack trace of a core dump (very useful in a bug 1600 report), or trying to figure out what went wrong before the core dump 1601 happened, or how did we end up having wrong or unexpected results. 1602 1603 =head2 Poking at Perl 1604 1605 To really poke around with Perl, you'll probably want to build Perl for 1606 debugging, like this: 1607 1608 ./Configure -d -D optimize=-g 1609 make 1610 1611 C<-g> is a flag to the C compiler to have it produce debugging 1612 information which will allow us to step through a running program, 1613 and to see in which C function we are at (without the debugging 1614 information we might see only the numerical addresses of the functions, 1615 which is not very helpful). 1616 1617 F<Configure> will also turn on the C<DEBUGGING> compilation symbol which 1618 enables all the internal debugging code in Perl. There are a whole bunch 1619 of things you can debug with this: L<perlrun> lists them all, and the 1620 best way to find out about them is to play about with them. The most 1621 useful options are probably 1622 1623 l Context (loop) stack processing 1624 t Trace execution 1625 o Method and overloading resolution 1626 c String/numeric conversions 1627 1628 Some of the functionality of the debugging code can be achieved using XS 1629 modules. 1630 1631 -Dr => use re 'debug' 1632 -Dx => use O 'Debug' 1633 1634 =head2 Using a source-level debugger 1635 1636 If the debugging output of C<-D> doesn't help you, it's time to step 1637 through perl's execution with a source-level debugger. 1638 1639 =over 3 1640 1641 =item * 1642 1643 We'll use C<gdb> for our examples here; the principles will apply to 1644 any debugger (many vendors call their debugger C<dbx>), but check the 1645 manual of the one you're using. 1646 1647 =back 1648 1649 To fire up the debugger, type 1650 1651 gdb ./perl 1652 1653 Or if you have a core dump: 1654 1655 gdb ./perl core 1656 1657 You'll want to do that in your Perl source tree so the debugger can read 1658 the source code. You should see the copyright message, followed by the 1659 prompt. 1660 1661 (gdb) 1662 1663 C<help> will get you into the documentation, but here are the most 1664 useful commands: 1665 1666 =over 3 1667 1668 =item run [args] 1669 1670 Run the program with the given arguments. 1671 1672 =item break function_name 1673 1674 =item break source.c:xxx 1675 1676 Tells the debugger that we'll want to pause execution when we reach 1677 either the named function (but see L<perlguts/Internal Functions>!) or the given 1678 line in the named source file. 1679 1680 =item step 1681 1682 Steps through the program a line at a time. 1683 1684 =item next 1685 1686 Steps through the program a line at a time, without descending into 1687 functions. 1688 1689 =item continue 1690 1691 Run until the next breakpoint. 1692 1693 =item finish 1694 1695 Run until the end of the current function, then stop again. 1696 1697 =item 'enter' 1698 1699 Just pressing Enter will do the most recent operation again - it's a 1700 blessing when stepping through miles of source code. 1701 1702 =item print 1703 1704 Execute the given C code and print its results. B<WARNING>: Perl makes 1705 heavy use of macros, and F<gdb> does not necessarily support macros 1706 (see later L</"gdb macro support">). You'll have to substitute them 1707 yourself, or to invoke cpp on the source code files 1708 (see L</"The .i Targets">) 1709 So, for instance, you can't say 1710 1711 print SvPV_nolen(sv) 1712 1713 but you have to say 1714 1715 print Perl_sv_2pv_nolen(sv) 1716 1717 =back 1718 1719 You may find it helpful to have a "macro dictionary", which you can 1720 produce by saying C<cpp -dM perl.c | sort>. Even then, F<cpp> won't 1721 recursively apply those macros for you. 1722 1723 =head2 gdb macro support 1724 1725 Recent versions of F<gdb> have fairly good macro support, but 1726 in order to use it you'll need to compile perl with macro definitions 1727 included in the debugging information. Using F<gcc> version 3.1, this 1728 means configuring with C<-Doptimize=-g3>. Other compilers might use a 1729 different switch (if they support debugging macros at all). 1730 1731 =head2 Dumping Perl Data Structures 1732 1733 One way to get around this macro hell is to use the dumping functions in 1734 F<dump.c>; these work a little like an internal 1735 L<Devel::Peek|Devel::Peek>, but they also cover OPs and other structures 1736 that you can't get at from Perl. Let's take an example. We'll use the 1737 C<$a = $b + $c> we used before, but give it a bit of context: 1738 C<$b = "6XXXX"; $c = 2.3;>. Where's a good place to stop and poke around? 1739 1740 What about C<pp_add>, the function we examined earlier to implement the 1741 C<+> operator: 1742 1743 (gdb) break Perl_pp_add 1744 Breakpoint 1 at 0x46249f: file pp_hot.c, line 309. 1745 1746 Notice we use C<Perl_pp_add> and not C<pp_add> - see L<perlguts/Internal Functions>. 1747 With the breakpoint in place, we can run our program: 1748 1749 (gdb) run -e '$b = "6XXXX"; $c = 2.3; $a = $b + $c' 1750 1751 Lots of junk will go past as gdb reads in the relevant source files and 1752 libraries, and then: 1753 1754 Breakpoint 1, Perl_pp_add () at pp_hot.c:309 1755 309 dSP; dATARGET; tryAMAGICbin(add,opASSIGN); 1756 (gdb) step 1757 311 dPOPTOPnnrl_ul; 1758 (gdb) 1759 1760 We looked at this bit of code before, and we said that C<dPOPTOPnnrl_ul> 1761 arranges for two C<NV>s to be placed into C<left> and C<right> - let's 1762 slightly expand it: 1763 1764 #define dPOPTOPnnrl_ul NV right = POPn; \ 1765 SV *leftsv = TOPs; \ 1766 NV left = USE_LEFT(leftsv) ? SvNV(leftsv) : 0.0 1767 1768 C<POPn> takes the SV from the top of the stack and obtains its NV either 1769 directly (if C<SvNOK> is set) or by calling the C<sv_2nv> function. 1770 C<TOPs> takes the next SV from the top of the stack - yes, C<POPn> uses 1771 C<TOPs> - but doesn't remove it. We then use C<SvNV> to get the NV from 1772 C<leftsv> in the same way as before - yes, C<POPn> uses C<SvNV>. 1773 1774 Since we don't have an NV for C<$b>, we'll have to use C<sv_2nv> to 1775 convert it. If we step again, we'll find ourselves there: 1776 1777 Perl_sv_2nv (sv=0xa0675d0) at sv.c:1669 1778 1669 if (!sv) 1779 (gdb) 1780 1781 We can now use C<Perl_sv_dump> to investigate the SV: 1782 1783 SV = PV(0xa057cc0) at 0xa0675d0 1784 REFCNT = 1 1785 FLAGS = (POK,pPOK) 1786 PV = 0xa06a510 "6XXXX"\0 1787 CUR = 5 1788 LEN = 6 1789 $1 = void 1790 1791 We know we're going to get C<6> from this, so let's finish the 1792 subroutine: 1793 1794 (gdb) finish 1795 Run till exit from #0 Perl_sv_2nv (sv=0xa0675d0) at sv.c:1671 1796 0x462669 in Perl_pp_add () at pp_hot.c:311 1797 311 dPOPTOPnnrl_ul; 1798 1799 We can also dump out this op: the current op is always stored in 1800 C<PL_op>, and we can dump it with C<Perl_op_dump>. This'll give us 1801 similar output to L<B::Debug|B::Debug>. 1802 1803 { 1804 13 TYPE = add ===> 14 1805 TARG = 1 1806 FLAGS = (SCALAR,KIDS) 1807 { 1808 TYPE = null ===> (12) 1809 (was rv2sv) 1810 FLAGS = (SCALAR,KIDS) 1811 { 1812 11 TYPE = gvsv ===> 12 1813 FLAGS = (SCALAR) 1814 GV = main::b 1815 } 1816 } 1817 1818 # finish this later # 1819 1820 =head2 Patching 1821 1822 All right, we've now had a look at how to navigate the Perl sources and 1823 some things you'll need to know when fiddling with them. Let's now get 1824 on and create a simple patch. Here's something Larry suggested: if a 1825 C<U> is the first active format during a C<pack>, (for example, 1826 C<pack "U3C8", @stuff>) then the resulting string should be treated as 1827 UTF-8 encoded. 1828 1829 How do we prepare to fix this up? First we locate the code in question - 1830 the C<pack> happens at runtime, so it's going to be in one of the F<pp> 1831 files. Sure enough, C<pp_pack> is in F<pp.c>. Since we're going to be 1832 altering this file, let's copy it to F<pp.c~>. 1833 1834 [Well, it was in F<pp.c> when this tutorial was written. It has now been 1835 split off with C<pp_unpack> to its own file, F<pp_pack.c>] 1836 1837 Now let's look over C<pp_pack>: we take a pattern into C<pat>, and then 1838 loop over the pattern, taking each format character in turn into 1839 C<datum_type>. Then for each possible format character, we swallow up 1840 the other arguments in the pattern (a field width, an asterisk, and so 1841 on) and convert the next chunk input into the specified format, adding 1842 it onto the output SV C<cat>. 1843 1844 How do we know if the C<U> is the first format in the C<pat>? Well, if 1845 we have a pointer to the start of C<pat> then, if we see a C<U> we can 1846 test whether we're still at the start of the string. So, here's where 1847 C<pat> is set up: 1848 1849 STRLEN fromlen; 1850 register char *pat = SvPVx(*++MARK, fromlen); 1851 register char *patend = pat + fromlen; 1852 register I32 len; 1853 I32 datumtype; 1854 SV *fromstr; 1855 1856 We'll have another string pointer in there: 1857 1858 STRLEN fromlen; 1859 register char *pat = SvPVx(*++MARK, fromlen); 1860 register char *patend = pat + fromlen; 1861 + char *patcopy; 1862 register I32 len; 1863 I32 datumtype; 1864 SV *fromstr; 1865 1866 And just before we start the loop, we'll set C<patcopy> to be the start 1867 of C<pat>: 1868 1869 items = SP - MARK; 1870 MARK++; 1871 sv_setpvn(cat, "", 0); 1872 + patcopy = pat; 1873 while (pat < patend) { 1874 1875 Now if we see a C<U> which was at the start of the string, we turn on 1876 the C<UTF8> flag for the output SV, C<cat>: 1877 1878 + if (datumtype == 'U' && pat==patcopy+1) 1879 + SvUTF8_on(cat); 1880 if (datumtype == '#') { 1881 while (pat < patend && *pat != '\n') 1882 pat++; 1883 1884 Remember that it has to be C<patcopy+1> because the first character of 1885 the string is the C<U> which has been swallowed into C<datumtype!> 1886 1887 Oops, we forgot one thing: what if there are spaces at the start of the 1888 pattern? C<pack(" U*", @stuff)> will have C<U> as the first active 1889 character, even though it's not the first thing in the pattern. In this 1890 case, we have to advance C<patcopy> along with C<pat> when we see spaces: 1891 1892 if (isSPACE(datumtype)) 1893 continue; 1894 1895 needs to become 1896 1897 if (isSPACE(datumtype)) { 1898 patcopy++; 1899 continue; 1900 } 1901 1902 OK. That's the C part done. Now we must do two additional things before 1903 this patch is ready to go: we've changed the behaviour of Perl, and so 1904 we must document that change. We must also provide some more regression 1905 tests to make sure our patch works and doesn't create a bug somewhere 1906 else along the line. 1907 1908 The regression tests for each operator live in F<t/op/>, and so we 1909 make a copy of F<t/op/pack.t> to F<t/op/pack.t~>. Now we can add our 1910 tests to the end. First, we'll test that the C<U> does indeed create 1911 Unicode strings. 1912 1913 t/op/pack.t has a sensible ok() function, but if it didn't we could 1914 use the one from t/test.pl. 1915 1916 require './test.pl'; 1917 plan( tests => 159 ); 1918 1919 so instead of this: 1920 1921 print 'not ' unless "1.20.300.4000" eq sprintf "%vd", pack("U*",1,20,300,4000); 1922 print "ok $test\n"; $test++; 1923 1924 we can write the more sensible (see L<Test::More> for a full 1925 explanation of is() and other testing functions). 1926 1927 is( "1.20.300.4000", sprintf "%vd", pack("U*",1,20,300,4000), 1928 "U* produces Unicode" ); 1929 1930 Now we'll test that we got that space-at-the-beginning business right: 1931 1932 is( "1.20.300.4000", sprintf "%vd", pack(" U*",1,20,300,4000), 1933 " with spaces at the beginning" ); 1934 1935 And finally we'll test that we don't make Unicode strings if C<U> is B<not> 1936 the first active format: 1937 1938 isnt( v1.20.300.4000, sprintf "%vd", pack("C0U*",1,20,300,4000), 1939 "U* not first isn't Unicode" ); 1940 1941 Mustn't forget to change the number of tests which appears at the top, 1942 or else the automated tester will get confused. This will either look 1943 like this: 1944 1945 print "1..156\n"; 1946 1947 or this: 1948 1949 plan( tests => 156 ); 1950 1951 We now compile up Perl, and run it through the test suite. Our new 1952 tests pass, hooray! 1953 1954 Finally, the documentation. The job is never done until the paperwork is 1955 over, so let's describe the change we've just made. The relevant place 1956 is F<pod/perlfunc.pod>; again, we make a copy, and then we'll insert 1957 this text in the description of C<pack>: 1958 1959 =item * 1960 1961 If the pattern begins with a C<U>, the resulting string will be treated 1962 as UTF-8-encoded Unicode. You can force UTF-8 encoding on in a string 1963 with an initial C<U0>, and the bytes that follow will be interpreted as 1964 Unicode characters. If you don't want this to happen, you can begin your 1965 pattern with C<C0> (or anything else) to force Perl not to UTF-8 encode your 1966 string, and then follow this with a C<U*> somewhere in your pattern. 1967 1968 All done. Now let's create the patch. F<Porting/patching.pod> tells us 1969 that if we're making major changes, we should copy the entire directory 1970 to somewhere safe before we begin fiddling, and then do 1971 1972 diff -ruN old new > patch 1973 1974 However, we know which files we've changed, and we can simply do this: 1975 1976 diff -u pp.c~ pp.c > patch 1977 diff -u t/op/pack.t~ t/op/pack.t >> patch 1978 diff -u pod/perlfunc.pod~ pod/perlfunc.pod >> patch 1979 1980 We end up with a patch looking a little like this: 1981 1982 --- pp.c~ Fri Jun 02 04:34:10 2000 1983 +++ pp.c Fri Jun 16 11:37:25 2000 1984 @@ -4375,6 +4375,7 @@ 1985 register I32 items; 1986 STRLEN fromlen; 1987 register char *pat = SvPVx(*++MARK, fromlen); 1988 + char *patcopy; 1989 register char *patend = pat + fromlen; 1990 register I32 len; 1991 I32 datumtype; 1992 @@ -4405,6 +4406,7 @@ 1993 ... 1994 1995 And finally, we submit it, with our rationale, to perl5-porters. Job 1996 done! 1997 1998 =head2 Patching a core module 1999 2000 This works just like patching anything else, with an extra 2001 consideration. Many core modules also live on CPAN. If this is so, 2002 patch the CPAN version instead of the core and send the patch off to 2003 the module maintainer (with a copy to p5p). This will help the module 2004 maintainer keep the CPAN version in sync with the core version without 2005 constantly scanning p5p. 2006 2007 The list of maintainers of core modules is usefully documented in 2008 F<Porting/Maintainers.pl>. 2009 2010 =head2 Adding a new function to the core 2011 2012 If, as part of a patch to fix a bug, or just because you have an 2013 especially good idea, you decide to add a new function to the core, 2014 discuss your ideas on p5p well before you start work. It may be that 2015 someone else has already attempted to do what you are considering and 2016 can give lots of good advice or even provide you with bits of code 2017 that they already started (but never finished). 2018 2019 You have to follow all of the advice given above for patching. It is 2020 extremely important to test any addition thoroughly and add new tests 2021 to explore all boundary conditions that your new function is expected 2022 to handle. If your new function is used only by one module (e.g. toke), 2023 then it should probably be named S_your_function (for static); on the 2024 other hand, if you expect it to accessible from other functions in 2025 Perl, you should name it Perl_your_function. See L<perlguts/Internal Functions> 2026 for more details. 2027 2028 The location of any new code is also an important consideration. Don't 2029 just create a new top level .c file and put your code there; you would 2030 have to make changes to Configure (so the Makefile is created properly), 2031 as well as possibly lots of include files. This is strictly pumpking 2032 business. 2033 2034 It is better to add your function to one of the existing top level 2035 source code files, but your choice is complicated by the nature of 2036 the Perl distribution. Only the files that are marked as compiled 2037 static are located in the perl executable. Everything else is located 2038 in the shared library (or DLL if you are running under WIN32). So, 2039 for example, if a function was only used by functions located in 2040 toke.c, then your code can go in toke.c. If, however, you want to call 2041 the function from universal.c, then you should put your code in another 2042 location, for example util.c. 2043 2044 In addition to writing your c-code, you will need to create an 2045 appropriate entry in embed.pl describing your function, then run 2046 'make regen_headers' to create the entries in the numerous header 2047 files that perl needs to compile correctly. See L<perlguts/Internal Functions> 2048 for information on the various options that you can set in embed.pl. 2049 You will forget to do this a few (or many) times and you will get 2050 warnings during the compilation phase. Make sure that you mention 2051 this when you post your patch to P5P; the pumpking needs to know this. 2052 2053 When you write your new code, please be conscious of existing code 2054 conventions used in the perl source files. See L<perlstyle> for 2055 details. Although most of the guidelines discussed seem to focus on 2056 Perl code, rather than c, they all apply (except when they don't ;). 2057 See also I<Porting/patching.pod> file in the Perl source distribution 2058 for lots of details about both formatting and submitting patches of 2059 your changes. 2060 2061 Lastly, TEST TEST TEST TEST TEST any code before posting to p5p. 2062 Test on as many platforms as you can find. Test as many perl 2063 Configure options as you can (e.g. MULTIPLICITY). If you have 2064 profiling or memory tools, see L<EXTERNAL TOOLS FOR DEBUGGING PERL> 2065 below for how to use them to further test your code. Remember that 2066 most of the people on P5P are doing this on their own time and 2067 don't have the time to debug your code. 2068 2069 =head2 Writing a test 2070 2071 Every module and built-in function has an associated test file (or 2072 should...). If you add or change functionality, you have to write a 2073 test. If you fix a bug, you have to write a test so that bug never 2074 comes back. If you alter the docs, it would be nice to test what the 2075 new documentation says. 2076 2077 In short, if you submit a patch you probably also have to patch the 2078 tests. 2079 2080 For modules, the test file is right next to the module itself. 2081 F<lib/strict.t> tests F<lib/strict.pm>. This is a recent innovation, 2082 so there are some snags (and it would be wonderful for you to brush 2083 them out), but it basically works that way. Everything else lives in 2084 F<t/>. 2085 2086 =over 3 2087 2088 =item F<t/base/> 2089 2090 Testing of the absolute basic functionality of Perl. Things like 2091 C<if>, basic file reads and writes, simple regexes, etc. These are 2092 run first in the test suite and if any of them fail, something is 2093 I<really> broken. 2094 2095 =item F<t/cmd/> 2096 2097 These test the basic control structures, C<if/else>, C<while>, 2098 subroutines, etc. 2099 2100 =item F<t/comp/> 2101 2102 Tests basic issues of how Perl parses and compiles itself. 2103 2104 =item F<t/io/> 2105 2106 Tests for built-in IO functions, including command line arguments. 2107 2108 =item F<t/lib/> 2109 2110 The old home for the module tests, you shouldn't put anything new in 2111 here. There are still some bits and pieces hanging around in here 2112 that need to be moved. Perhaps you could move them? Thanks! 2113 2114 =item F<t/mro/> 2115 2116 Tests for perl's method resolution order implementations 2117 (see L<mro>). 2118 2119 =item F<t/op/> 2120 2121 Tests for perl's built in functions that don't fit into any of the 2122 other directories. 2123 2124 =item F<t/pod/> 2125 2126 Tests for POD directives. There are still some tests for the Pod 2127 modules hanging around in here that need to be moved out into F<lib/>. 2128 2129 =item F<t/run/> 2130 2131 Testing features of how perl actually runs, including exit codes and 2132 handling of PERL* environment variables. 2133 2134 =item F<t/uni/> 2135 2136 Tests for the core support of Unicode. 2137 2138 =item F<t/win32/> 2139 2140 Windows-specific tests. 2141 2142 =item F<t/x2p> 2143 2144 A test suite for the s2p converter. 2145 2146 =back 2147 2148 The core uses the same testing style as the rest of Perl, a simple 2149 "ok/not ok" run through Test::Harness, but there are a few special 2150 considerations. 2151 2152 There are three ways to write a test in the core. Test::More, 2153 t/test.pl and ad hoc C<print $test ? "ok 42\n" : "not ok 42\n">. The 2154 decision of which to use depends on what part of the test suite you're 2155 working on. This is a measure to prevent a high-level failure (such 2156 as Config.pm breaking) from causing basic functionality tests to fail. 2157 2158 =over 4 2159 2160 =item t/base t/comp 2161 2162 Since we don't know if require works, or even subroutines, use ad hoc 2163 tests for these two. Step carefully to avoid using the feature being 2164 tested. 2165 2166 =item t/cmd t/run t/io t/op 2167 2168 Now that basic require() and subroutines are tested, you can use the 2169 t/test.pl library which emulates the important features of Test::More 2170 while using a minimum of core features. 2171 2172 You can also conditionally use certain libraries like Config, but be 2173 sure to skip the test gracefully if it's not there. 2174 2175 =item t/lib ext lib 2176 2177 Now that the core of Perl is tested, Test::More can be used. You can 2178 also use the full suite of core modules in the tests. 2179 2180 =back 2181 2182 When you say "make test" Perl uses the F<t/TEST> program to run the 2183 test suite (except under Win32 where it uses F<t/harness> instead.) 2184 All tests are run from the F<t/> directory, B<not> the directory 2185 which contains the test. This causes some problems with the tests 2186 in F<lib/>, so here's some opportunity for some patching. 2187 2188 You must be triply conscious of cross-platform concerns. This usually 2189 boils down to using File::Spec and avoiding things like C<fork()> and 2190 C<system()> unless absolutely necessary. 2191 2192 =head2 Special Make Test Targets 2193 2194 There are various special make targets that can be used to test Perl 2195 slightly differently than the standard "test" target. Not all them 2196 are expected to give a 100% success rate. Many of them have several 2197 aliases, and many of them are not available on certain operating 2198 systems. 2199 2200 =over 4 2201 2202 =item coretest 2203 2204 Run F<perl> on all core tests (F<t/*> and F<lib/[a-z]*> pragma tests). 2205 2206 (Not available on Win32) 2207 2208 =item test.deparse 2209 2210 Run all the tests through B::Deparse. Not all tests will succeed. 2211 2212 (Not available on Win32) 2213 2214 =item test.taintwarn 2215 2216 Run all tests with the B<-t> command-line switch. Not all tests 2217 are expected to succeed (until they're specifically fixed, of course). 2218 2219 (Not available on Win32) 2220 2221 =item minitest 2222 2223 Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>, 2224 F<t/op>, F<t/uni> and F<t/mro> tests. 2225 2226 =item test.valgrind check.valgrind utest.valgrind ucheck.valgrind 2227 2228 (Only in Linux) Run all the tests using the memory leak + naughty 2229 memory access tool "valgrind". The log files will be named 2230 F<testname.valgrind>. 2231 2232 =item test.third check.third utest.third ucheck.third 2233 2234 (Only in Tru64) Run all the tests using the memory leak + naughty 2235 memory access tool "Third Degree". The log files will be named 2236 F<perl.3log.testname>. 2237 2238 =item test.torture torturetest 2239 2240 Run all the usual tests and some extra tests. As of Perl 5.8.0 the 2241 only extra tests are Abigail's JAPHs, F<t/japh/abigail.t>. 2242 2243 You can also run the torture test with F<t/harness> by giving 2244 C<-torture> argument to F<t/harness>. 2245 2246 =item utest ucheck test.utf8 check.utf8 2247 2248 Run all the tests with -Mutf8. Not all tests will succeed. 2249 2250 (Not available on Win32) 2251 2252 =item minitest.utf16 test.utf16 2253 2254 Runs the tests with UTF-16 encoded scripts, encoded with different 2255 versions of this encoding. 2256 2257 C<make utest.utf16> runs the test suite with a combination of C<-utf8> and 2258 C<-utf16> arguments to F<t/TEST>. 2259 2260 (Not available on Win32) 2261 2262 =item test_harness 2263 2264 Run the test suite with the F<t/harness> controlling program, instead of 2265 F<t/TEST>. F<t/harness> is more sophisticated, and uses the 2266 L<Test::Harness> module, thus using this test target supposes that perl 2267 mostly works. The main advantage for our purposes is that it prints a 2268 detailed summary of failed tests at the end. Also, unlike F<t/TEST>, it 2269 doesn't redirect stderr to stdout. 2270 2271 Note that under Win32 F<t/harness> is always used instead of F<t/TEST>, so 2272 there is no special "test_harness" target. 2273 2274 Under Win32's "test" target you may use the TEST_SWITCHES and TEST_FILES 2275 environment variables to control the behaviour of F<t/harness>. This means 2276 you can say 2277 2278 nmake test TEST_FILES="op/*.t" 2279 nmake test TEST_SWITCHES="-torture" TEST_FILES="op/*.t" 2280 2281 =item test-notty test_notty 2282 2283 Sets PERL_SKIP_TTY_TEST to true before running normal test. 2284 2285 =back 2286 2287 =head2 Running tests by hand 2288 2289 You can run part of the test suite by hand by using one the following 2290 commands from the F<t/> directory : 2291 2292 ./perl -I../lib TEST list-of-.t-files 2293 2294 or 2295 2296 ./perl -I../lib harness list-of-.t-files 2297 2298 (if you don't specify test scripts, the whole test suite will be run.) 2299 2300 =head3 Using t/harness for testing 2301 2302 If you use C<harness> for testing you have several command line options 2303 available to you. The arguments are as follows, and are in the order 2304 that they must appear if used together. 2305 2306 harness -v -torture -re=pattern LIST OF FILES TO TEST 2307 harness -v -torture -re LIST OF PATTERNS TO MATCH 2308 2309 If C<LIST OF FILES TO TEST> is omitted the file list is obtained from 2310 the manifest. The file list may include shell wildcards which will be 2311 expanded out. 2312 2313 =over 4 2314 2315 =item -v 2316 2317 Run the tests under verbose mode so you can see what tests were run, 2318 and debug outbut. 2319 2320 =item -torture 2321 2322 Run the torture tests as well as the normal set. 2323 2324 =item -re=PATTERN 2325 2326 Filter the file list so that all the test files run match PATTERN. 2327 Note that this form is distinct from the B<-re LIST OF PATTERNS> form below 2328 in that it allows the file list to be provided as well. 2329 2330 =item -re LIST OF PATTERNS 2331 2332 Filter the file list so that all the test files run match 2333 /(LIST|OF|PATTERNS)/. Note that with this form the patterns 2334 are joined by '|' and you cannot supply a list of files, instead 2335 the test files are obtained from the MANIFEST. 2336 2337 =back 2338 2339 You can run an individual test by a command similar to 2340 2341 ./perl -I../lib patho/to/foo.t 2342 2343 except that the harnesses set up some environment variables that may 2344 affect the execution of the test : 2345 2346 =over 4 2347 2348 =item PERL_CORE=1 2349 2350 indicates that we're running this test part of the perl core test suite. 2351 This is useful for modules that have a dual life on CPAN. 2352 2353 =item PERL_DESTRUCT_LEVEL=2 2354 2355 is set to 2 if it isn't set already (see L</PERL_DESTRUCT_LEVEL>) 2356 2357 =item PERL 2358 2359 (used only by F<t/TEST>) if set, overrides the path to the perl executable 2360 that should be used to run the tests (the default being F<./perl>). 2361 2362 =item PERL_SKIP_TTY_TEST 2363 2364 if set, tells to skip the tests that need a terminal. It's actually set 2365 automatically by the Makefile, but can also be forced artificially by 2366 running 'make test_notty'. 2367 2368 =back 2369 2370 =head3 Other environment variables that may influence tests 2371 2372 =over 4 2373 2374 =item PERL_TEST_Net_Ping 2375 2376 Setting this variable runs all the Net::Ping modules tests, 2377 otherwise some tests that interact with the outside world are skipped. 2378 See L<perl58delta>. 2379 2380 =item PERL_TEST_NOVREXX 2381 2382 Setting this variable skips the vrexx.t tests for OS2::REXX. 2383 2384 =item PERL_TEST_NUMCONVERTS 2385 2386 This sets a variable in op/numconvert.t. 2387 2388 =back 2389 2390 See also the documentation for the Test and Test::Harness modules, 2391 for more environment variables that affect testing. 2392 2393 =head2 Common problems when patching Perl source code 2394 2395 Perl source plays by ANSI C89 rules: no C99 (or C++) extensions. In 2396 some cases we have to take pre-ANSI requirements into consideration. 2397 You don't care about some particular platform having broken Perl? 2398 I hear there is still a strong demand for J2EE programmers. 2399 2400 =head2 Perl environment problems 2401 2402 =over 4 2403 2404 =item * 2405 2406 Not compiling with threading 2407 2408 Compiling with threading (-Duseithreads) completely rewrites 2409 the function prototypes of Perl. You better try your changes 2410 with that. Related to this is the difference between "Perl_-less" 2411 and "Perl_-ly" APIs, for example: 2412 2413 Perl_sv_setiv(aTHX_ ...); 2414 sv_setiv(...); 2415 2416 The first one explicitly passes in the context, which is needed for e.g. 2417 threaded builds. The second one does that implicitly; do not get them 2418 mixed. If you are not passing in a aTHX_, you will need to do a dTHX 2419 (or a dVAR) as the first thing in the function. 2420 2421 See L<perlguts/"How multiple interpreters and concurrency are supported"> 2422 for further discussion about context. 2423 2424 =item * 2425 2426 Not compiling with -DDEBUGGING 2427 2428 The DEBUGGING define exposes more code to the compiler, 2429 therefore more ways for things to go wrong. You should try it. 2430 2431 =item * 2432 2433 Introducing (non-read-only) globals 2434 2435 Do not introduce any modifiable globals, truly global or file static. 2436 They are bad form and complicate multithreading and other forms of 2437 concurrency. The right way is to introduce them as new interpreter 2438 variables, see F<intrpvar.h> (at the very end for binary compatibility). 2439 2440 Introducing read-only (const) globals is okay, as long as you verify 2441 with e.g. C<nm libperl.a|egrep -v ' [TURtr] '> (if your C<nm> has 2442 BSD-style output) that the data you added really is read-only. 2443 (If it is, it shouldn't show up in the output of that command.) 2444 2445 If you want to have static strings, make them constant: 2446 2447 static const char etc[] = "..."; 2448 2449 If you want to have arrays of constant strings, note carefully 2450 the right combination of C<const>s: 2451 2452 static const char * const yippee[] = 2453 {"hi", "ho", "silver"}; 2454 2455 There is a way to completely hide any modifiable globals (they are all 2456 moved to heap), the compilation setting C<-DPERL_GLOBAL_STRUCT_PRIVATE>. 2457 It is not normally used, but can be used for testing, read more 2458 about it in L<perlguts/"Background and PERL_IMPLICIT_CONTEXT">. 2459 2460 =item * 2461 2462 Not exporting your new function 2463 2464 Some platforms (Win32, AIX, VMS, OS/2, to name a few) require any 2465 function that is part of the public API (the shared Perl library) 2466 to be explicitly marked as exported. See the discussion about 2467 F<embed.pl> in L<perlguts>. 2468 2469 =item * 2470 2471 Exporting your new function 2472 2473 The new shiny result of either genuine new functionality or your 2474 arduous refactoring is now ready and correctly exported. So what 2475 could possibly go wrong? 2476 2477 Maybe simply that your function did not need to be exported in the 2478 first place. Perl has a long and not so glorious history of exporting 2479 functions that it should not have. 2480 2481 If the function is used only inside one source code file, make it 2482 static. See the discussion about F<embed.pl> in L<perlguts>. 2483 2484 If the function is used across several files, but intended only for 2485 Perl's internal use (and this should be the common case), do not 2486 export it to the public API. See the discussion about F<embed.pl> 2487 in L<perlguts>. 2488 2489 =back 2490 2491 =head2 Portability problems 2492 2493 The following are common causes of compilation and/or execution 2494 failures, not common to Perl as such. The C FAQ is good bedtime 2495 reading. Please test your changes with as many C compilers and 2496 platforms as possible -- we will, anyway, and it's nice to save 2497 oneself from public embarrassment. 2498 2499 If using gcc, you can add the C<-std=c89> option which will hopefully 2500 catch most of these unportabilities. (However it might also catch 2501 incompatibilities in your system's header files.) 2502 2503 Use the Configure C<-Dgccansipedantic> flag to enable the gcc 2504 C<-ansi -pedantic> flags which enforce stricter ANSI rules. 2505 2506 If using the C<gcc -Wall> note that not all the possible warnings 2507 (like C<-Wunitialized>) are given unless you also compile with C<-O>. 2508 2509 Note that if using gcc, starting from Perl 5.9.5 the Perl core source 2510 code files (the ones at the top level of the source code distribution, 2511 but not e.g. the extensions under ext/) are automatically compiled 2512 with as many as possible of the C<-std=c89>, C<-ansi>, C<-pedantic>, 2513 and a selection of C<-W> flags (see cflags.SH). 2514 2515 Also study L<perlport> carefully to avoid any bad assumptions 2516 about the operating system, filesystems, and so forth. 2517 2518 You may once in a while try a "make microperl" to see whether we 2519 can still compile Perl with just the bare minimum of interfaces. 2520 (See README.micro.) 2521 2522 Do not assume an operating system indicates a certain compiler. 2523 2524 =over 4 2525 2526 =item * 2527 2528 Casting pointers to integers or casting integers to pointers 2529 2530 void castaway(U8* p) 2531 { 2532 IV i = p; 2533 2534 or 2535 2536 void castaway(U8* p) 2537 { 2538 IV i = (IV)p; 2539 2540 Both are bad, and broken, and unportable. Use the PTR2IV() 2541 macro that does it right. (Likewise, there are PTR2UV(), PTR2NV(), 2542 INT2PTR(), and NUM2PTR().) 2543 2544 =item * 2545 2546 Casting between data function pointers and data pointers 2547 2548 Technically speaking casting between function pointers and data 2549 pointers is unportable and undefined, but practically speaking 2550 it seems to work, but you should use the FPTR2DPTR() and DPTR2FPTR() 2551 macros. Sometimes you can also play games with unions. 2552 2553 =item * 2554 2555 Assuming sizeof(int) == sizeof(long) 2556 2557 There are platforms where longs are 64 bits, and platforms where ints 2558 are 64 bits, and while we are out to shock you, even platforms where 2559 shorts are 64 bits. This is all legal according to the C standard. 2560 (In other words, "long long" is not a portable way to specify 64 bits, 2561 and "long long" is not even guaranteed to be any wider than "long".) 2562 2563 Instead, use the definitions IV, UV, IVSIZE, I32SIZE, and so forth. 2564 Avoid things like I32 because they are B<not> guaranteed to be 2565 I<exactly> 32 bits, they are I<at least> 32 bits, nor are they 2566 guaranteed to be B<int> or B<long>. If you really explicitly need 2567 64-bit variables, use I64 and U64, but only if guarded by HAS_QUAD. 2568 2569 =item * 2570 2571 Assuming one can dereference any type of pointer for any type of data 2572 2573 char *p = ...; 2574 long pony = *p; /* BAD */ 2575 2576 Many platforms, quite rightly so, will give you a core dump instead 2577 of a pony if the p happens not be correctly aligned. 2578 2579 =item * 2580 2581 Lvalue casts 2582 2583 (int)*p = ...; /* BAD */ 2584 2585 Simply not portable. Get your lvalue to be of the right type, 2586 or maybe use temporary variables, or dirty tricks with unions. 2587 2588 =item * 2589 2590 Assume B<anything> about structs (especially the ones you 2591 don't control, like the ones coming from the system headers) 2592 2593 =over 8 2594 2595 =item * 2596 2597 That a certain field exists in a struct 2598 2599 =item * 2600 2601 That no other fields exist besides the ones you know of 2602 2603 =item * 2604 2605 That a field is of certain signedness, sizeof, or type 2606 2607 =item * 2608 2609 That the fields are in a certain order 2610 2611 =over 8 2612 2613 =item * 2614 2615 While C guarantees the ordering specified in the struct definition, 2616 between different platforms the definitions might differ 2617 2618 =back 2619 2620 =item * 2621 2622 That the sizeof(struct) or the alignments are the same everywhere 2623 2624 =over 8 2625 2626 =item * 2627 2628 There might be padding bytes between the fields to align the fields - 2629 the bytes can be anything 2630 2631 =item * 2632 2633 Structs are required to be aligned to the maximum alignment required 2634 by the fields - which for native types is for usually equivalent to 2635 sizeof() of the field 2636 2637 =back 2638 2639 =back 2640 2641 =item * 2642 2643 Mixing #define and #ifdef 2644 2645 #define BURGLE(x) ... \ 2646 #ifdef BURGLE_OLD_STYLE /* BAD */ 2647 ... do it the old way ... \ 2648 #else 2649 ... do it the new way ... \ 2650 #endif 2651 2652 You cannot portably "stack" cpp directives. For example in the above 2653 you need two separate BURGLE() #defines, one for each #ifdef branch. 2654 2655 =item * 2656 2657 Adding stuff after #endif or #else 2658 2659 #ifdef SNOSH 2660 ... 2661 #else !SNOSH /* BAD */ 2662 ... 2663 #endif SNOSH /* BAD */ 2664 2665 The #endif and #else cannot portably have anything non-comment after 2666 them. If you want to document what is going (which is a good idea 2667 especially if the branches are long), use (C) comments: 2668 2669 #ifdef SNOSH 2670 ... 2671 #else /* !SNOSH */ 2672 ... 2673 #endif /* SNOSH */ 2674 2675 The gcc option C<-Wendif-labels> warns about the bad variant 2676 (by default on starting from Perl 5.9.4). 2677 2678 =item * 2679 2680 Having a comma after the last element of an enum list 2681 2682 enum color { 2683 CERULEAN, 2684 CHARTREUSE, 2685 CINNABAR, /* BAD */ 2686 }; 2687 2688 is not portable. Leave out the last comma. 2689 2690 Also note that whether enums are implicitly morphable to ints 2691 varies between compilers, you might need to (int). 2692 2693 =item * 2694 2695 Using //-comments 2696 2697 // This function bamfoodles the zorklator. /* BAD */ 2698 2699 That is C99 or C++. Perl is C89. Using the //-comments is silently 2700 allowed by many C compilers but cranking up the ANSI C89 strictness 2701 (which we like to do) causes the compilation to fail. 2702 2703 =item * 2704 2705 Mixing declarations and code 2706 2707 void zorklator() 2708 { 2709 int n = 3; 2710 set_zorkmids(n); /* BAD */ 2711 int q = 4; 2712 2713 That is C99 or C++. Some C compilers allow that, but you shouldn't. 2714 2715 The gcc option C<-Wdeclaration-after-statements> scans for such problems 2716 (by default on starting from Perl 5.9.4). 2717 2718 =item * 2719 2720 Introducing variables inside for() 2721 2722 for(int i = ...; ...; ...) { /* BAD */ 2723 2724 That is C99 or C++. While it would indeed be awfully nice to have that 2725 also in C89, to limit the scope of the loop variable, alas, we cannot. 2726 2727 =item * 2728 2729 Mixing signed char pointers with unsigned char pointers 2730 2731 int foo(char *s) { ... } 2732 ... 2733 unsigned char *t = ...; /* Or U8* t = ... */ 2734 foo(t); /* BAD */ 2735 2736 While this is legal practice, it is certainly dubious, and downright 2737 fatal in at least one platform: for example VMS cc considers this a 2738 fatal error. One cause for people often making this mistake is that a 2739 "naked char" and therefore dereferencing a "naked char pointer" have 2740 an undefined signedness: it depends on the compiler and the flags of 2741 the compiler and the underlying platform whether the result is signed 2742 or unsigned. For this very same reason using a 'char' as an array 2743 index is bad. 2744 2745 =item * 2746 2747 Macros that have string constants and their arguments as substrings of 2748 the string constants 2749 2750 #define FOO(n) printf("number = %d\n", n) /* BAD */ 2751 FOO(10); 2752 2753 Pre-ANSI semantics for that was equivalent to 2754 2755 printf("10umber = %d\10"); 2756 2757 which is probably not what you were expecting. Unfortunately at least 2758 one reasonably common and modern C compiler does "real backward 2759 compatibility" here, in AIX that is what still happens even though the 2760 rest of the AIX compiler is very happily C89. 2761 2762 =item * 2763 2764 Using printf formats for non-basic C types 2765 2766 IV i = ...; 2767 printf("i = %d\n", i); /* BAD */ 2768 2769 While this might by accident work in some platform (where IV happens 2770 to be an C<int>), in general it cannot. IV might be something larger. 2771 Even worse the situation is with more specific types (defined by Perl's 2772 configuration step in F<config.h>): 2773 2774 Uid_t who = ...; 2775 printf("who = %d\n", who); /* BAD */ 2776 2777 The problem here is that Uid_t might be not only not C<int>-wide 2778 but it might also be unsigned, in which case large uids would be 2779 printed as negative values. 2780 2781 There is no simple solution to this because of printf()'s limited 2782 intelligence, but for many types the right format is available as 2783 with either 'f' or '_f' suffix, for example: 2784 2785 IVdf /* IV in decimal */ 2786 UVxf /* UV is hexadecimal */ 2787 2788 printf("i = %"IVdf"\n", i); /* The IVdf is a string constant. */ 2789 2790 Uid_t_f /* Uid_t in decimal */ 2791 2792 printf("who = %"Uid_t_f"\n", who); 2793 2794 Or you can try casting to a "wide enough" type: 2795 2796 printf("i = %"IVdf"\n", (IV)something_very_small_and_signed); 2797 2798 Also remember that the C<%p> format really does require a void pointer: 2799 2800 U8* p = ...; 2801 printf("p = %p\n", (void*)p); 2802 2803 The gcc option C<-Wformat> scans for such problems. 2804 2805 =item * 2806 2807 Blindly using variadic macros 2808 2809 gcc has had them for a while with its own syntax, and C99 brought 2810 them with a standardized syntax. Don't use the former, and use 2811 the latter only if the HAS_C99_VARIADIC_MACROS is defined. 2812 2813 =item * 2814 2815 Blindly passing va_list 2816 2817 Not all platforms support passing va_list to further varargs (stdarg) 2818 functions. The right thing to do is to copy the va_list using the 2819 Perl_va_copy() if the NEED_VA_COPY is defined. 2820 2821 =item * 2822 2823 Using gcc statement expressions 2824 2825 val = ({...;...;...}); /* BAD */ 2826 2827 While a nice extension, it's not portable. The Perl code does 2828 admittedly use them if available to gain some extra speed 2829 (essentially as a funky form of inlining), but you shouldn't. 2830 2831 =item * 2832 2833 Binding together several statements 2834 2835 Use the macros STMT_START and STMT_END. 2836 2837 STMT_START { 2838 ... 2839 } STMT_END 2840 2841 =item * 2842 2843 Testing for operating systems or versions when should be testing for features 2844 2845 #ifdef __FOONIX__ /* BAD */ 2846 foo = quux(); 2847 #endif 2848 2849 Unless you know with 100% certainty that quux() is only ever available 2850 for the "Foonix" operating system B<and> that is available B<and> 2851 correctly working for B<all> past, present, B<and> future versions of 2852 "Foonix", the above is very wrong. This is more correct (though still 2853 not perfect, because the below is a compile-time check): 2854 2855 #ifdef HAS_QUUX 2856 foo = quux(); 2857 #endif 2858 2859 How does the HAS_QUUX become defined where it needs to be? Well, if 2860 Foonix happens to be UNIXy enough to be able to run the Configure 2861 script, and Configure has been taught about detecting and testing 2862 quux(), the HAS_QUUX will be correctly defined. In other platforms, 2863 the corresponding configuration step will hopefully do the same. 2864 2865 In a pinch, if you cannot wait for Configure to be educated, 2866 or if you have a good hunch of where quux() might be available, 2867 you can temporarily try the following: 2868 2869 #if (defined(__FOONIX__) || defined(__BARNIX__)) 2870 # define HAS_QUUX 2871 #endif 2872 2873 ... 2874 2875 #ifdef HAS_QUUX 2876 foo = quux(); 2877 #endif 2878 2879 But in any case, try to keep the features and operating systems separate. 2880 2881 =back 2882 2883 =head2 Problematic System Interfaces 2884 2885 =over 4 2886 2887 =item * 2888 2889 malloc(0), realloc(0), calloc(0, 0) are non-portable. To be portable 2890 allocate at least one byte. (In general you should rarely need to 2891 work at this low level, but instead use the various malloc wrappers.) 2892 2893 =item * 2894 2895 snprintf() - the return type is unportable. Use my_snprintf() instead. 2896 2897 =back 2898 2899 =head2 Security problems 2900 2901 Last but not least, here are various tips for safer coding. 2902 2903 =over 4 2904 2905 =item * 2906 2907 Do not use gets() 2908 2909 Or we will publicly ridicule you. Seriously. 2910 2911 =item * 2912 2913 Do not use strcpy() or strcat() or strncpy() or strncat() 2914 2915 Use my_strlcpy() and my_strlcat() instead: they either use the native 2916 implementation, or Perl's own implementation (borrowed from the public 2917 domain implementation of INN). 2918 2919 =item * 2920 2921 Do not use sprintf() or vsprintf() 2922 2923 If you really want just plain byte strings, use my_snprintf() 2924 and my_vsnprintf() instead, which will try to use snprintf() and 2925 vsnprintf() if those safer APIs are available. If you want something 2926 fancier than a plain byte string, use SVs and Perl_sv_catpvf(). 2927 2928 =back 2929 2930 =head1 EXTERNAL TOOLS FOR DEBUGGING PERL 2931 2932 Sometimes it helps to use external tools while debugging and 2933 testing Perl. This section tries to guide you through using 2934 some common testing and debugging tools with Perl. This is 2935 meant as a guide to interfacing these tools with Perl, not 2936 as any kind of guide to the use of the tools themselves. 2937 2938 B<NOTE 1>: Running under memory debuggers such as Purify, valgrind, or 2939 Third Degree greatly slows down the execution: seconds become minutes, 2940 minutes become hours. For example as of Perl 5.8.1, the 2941 ext/Encode/t/Unicode.t takes extraordinarily long to complete under 2942 e.g. Purify, Third Degree, and valgrind. Under valgrind it takes more 2943 than six hours, even on a snappy computer-- the said test must be 2944 doing something that is quite unfriendly for memory debuggers. If you 2945 don't feel like waiting, that you can simply kill away the perl 2946 process. 2947 2948 B<NOTE 2>: To minimize the number of memory leak false alarms (see 2949 L</PERL_DESTRUCT_LEVEL> for more information), you have to have 2950 environment variable PERL_DESTRUCT_LEVEL set to 2. The F<TEST> 2951 and harness scripts do that automatically. But if you are running 2952 some of the tests manually-- for csh-like shells: 2953 2954 setenv PERL_DESTRUCT_LEVEL 2 2955 2956 and for Bourne-type shells: 2957 2958 PERL_DESTRUCT_LEVEL=2 2959 export PERL_DESTRUCT_LEVEL 2960 2961 or in UNIXy environments you can also use the C<env> command: 2962 2963 env PERL_DESTRUCT_LEVEL=2 valgrind ./perl -Ilib ... 2964 2965 B<NOTE 3>: There are known memory leaks when there are compile-time 2966 errors within eval or require, seeing C<S_doeval> in the call stack 2967 is a good sign of these. Fixing these leaks is non-trivial, 2968 unfortunately, but they must be fixed eventually. 2969 2970 B<NOTE 4>: L<DynaLoader> will not clean up after itself completely 2971 unless Perl is built with the Configure option 2972 C<-Accflags=-DDL_UNLOAD_ALL_AT_EXIT>. 2973 2974 =head2 Rational Software's Purify 2975 2976 Purify is a commercial tool that is helpful in identifying 2977 memory overruns, wild pointers, memory leaks and other such 2978 badness. Perl must be compiled in a specific way for 2979 optimal testing with Purify. Purify is available under 2980 Windows NT, Solaris, HP-UX, SGI, and Siemens Unix. 2981 2982 =head2 Purify on Unix 2983 2984 On Unix, Purify creates a new Perl binary. To get the most 2985 benefit out of Purify, you should create the perl to Purify 2986 using: 2987 2988 sh Configure -Accflags=-DPURIFY -Doptimize='-g' \ 2989 -Uusemymalloc -Dusemultiplicity 2990 2991 where these arguments mean: 2992 2993 =over 4 2994 2995 =item -Accflags=-DPURIFY 2996 2997 Disables Perl's arena memory allocation functions, as well as 2998 forcing use of memory allocation functions derived from the 2999 system malloc. 3000 3001 =item -Doptimize='-g' 3002 3003 Adds debugging information so that you see the exact source 3004 statements where the problem occurs. Without this flag, all 3005 you will see is the source filename of where the error occurred. 3006 3007 =item -Uusemymalloc 3008 3009 Disable Perl's malloc so that Purify can more closely monitor 3010 allocations and leaks. Using Perl's malloc will make Purify 3011 report most leaks in the "potential" leaks category. 3012 3013 =item -Dusemultiplicity 3014 3015 Enabling the multiplicity option allows perl to clean up 3016 thoroughly when the interpreter shuts down, which reduces the 3017 number of bogus leak reports from Purify. 3018 3019 =back 3020 3021 Once you've compiled a perl suitable for Purify'ing, then you 3022 can just: 3023 3024 make pureperl 3025 3026 which creates a binary named 'pureperl' that has been Purify'ed. 3027 This binary is used in place of the standard 'perl' binary 3028 when you want to debug Perl memory problems. 3029 3030 As an example, to show any memory leaks produced during the 3031 standard Perl testset you would create and run the Purify'ed 3032 perl as: 3033 3034 make pureperl 3035 cd t 3036 ../pureperl -I../lib harness 3037 3038 which would run Perl on test.pl and report any memory problems. 3039 3040 Purify outputs messages in "Viewer" windows by default. If 3041 you don't have a windowing environment or if you simply 3042 want the Purify output to unobtrusively go to a log file 3043 instead of to the interactive window, use these following 3044 options to output to the log file "perl.log": 3045 3046 setenv PURIFYOPTIONS "-chain-length=25 -windows=no \ 3047 -log-file=perl.log -append-logfile=yes" 3048 3049 If you plan to use the "Viewer" windows, then you only need this option: 3050 3051 setenv PURIFYOPTIONS "-chain-length=25" 3052 3053 In Bourne-type shells: 3054 3055 PURIFYOPTIONS="..." 3056 export PURIFYOPTIONS 3057 3058 or if you have the "env" utility: 3059 3060 env PURIFYOPTIONS="..." ../pureperl ... 3061 3062 =head2 Purify on NT 3063 3064 Purify on Windows NT instruments the Perl binary 'perl.exe' 3065 on the fly. There are several options in the makefile you 3066 should change to get the most use out of Purify: 3067 3068 =over 4 3069 3070 =item DEFINES 3071 3072 You should add -DPURIFY to the DEFINES line so the DEFINES 3073 line looks something like: 3074 3075 DEFINES = -DWIN32 -D_CONSOLE -DNO_STRICT $(CRYPT_FLAG) -DPURIFY=1 3076 3077 to disable Perl's arena memory allocation functions, as 3078 well as to force use of memory allocation functions derived 3079 from the system malloc. 3080 3081 =item USE_MULTI = define 3082 3083 Enabling the multiplicity option allows perl to clean up 3084 thoroughly when the interpreter shuts down, which reduces the 3085 number of bogus leak reports from Purify. 3086 3087 =item #PERL_MALLOC = define 3088 3089 Disable Perl's malloc so that Purify can more closely monitor 3090 allocations and leaks. Using Perl's malloc will make Purify 3091 report most leaks in the "potential" leaks category. 3092 3093 =item CFG = Debug 3094 3095 Adds debugging information so that you see the exact source 3096 statements where the problem occurs. Without this flag, all 3097 you will see is the source filename of where the error occurred. 3098 3099 =back 3100 3101 As an example, to show any memory leaks produced during the 3102 standard Perl testset you would create and run Purify as: 3103 3104 cd win32 3105 make 3106 cd ../t 3107 purify ../perl -I../lib harness 3108 3109 which would instrument Perl in memory, run Perl on test.pl, 3110 then finally report any memory problems. 3111 3112 =head2 valgrind 3113 3114 The excellent valgrind tool can be used to find out both memory leaks 3115 and illegal memory accesses. As of August 2003 it unfortunately works 3116 only on x86 (ELF) Linux. The special "test.valgrind" target can be used 3117 to run the tests under valgrind. Found errors and memory leaks are 3118 logged in files named F<testfile.valgrind>. 3119 3120 Valgrind also provides a cachegrind tool, invoked on perl as: 3121 3122 VG_OPTS=--tool=cachegrind make test.valgrind 3123 3124 As system libraries (most notably glibc) are also triggering errors, 3125 valgrind allows to suppress such errors using suppression files. The 3126 default suppression file that comes with valgrind already catches a lot 3127 of them. Some additional suppressions are defined in F<t/perl.supp>. 3128 3129 To get valgrind and for more information see 3130 3131 http://developer.kde.org/~sewardj/ 3132 3133 =head2 Compaq's/Digital's/HP's Third Degree 3134 3135 Third Degree is a tool for memory leak detection and memory access checks. 3136 It is one of the many tools in the ATOM toolkit. The toolkit is only 3137 available on Tru64 (formerly known as Digital UNIX formerly known as 3138 DEC OSF/1). 3139 3140 When building Perl, you must first run Configure with -Doptimize=-g 3141 and -Uusemymalloc flags, after that you can use the make targets 3142 "perl.third" and "test.third". (What is required is that Perl must be 3143 compiled using the C<-g> flag, you may need to re-Configure.) 3144 3145 The short story is that with "atom" you can instrument the Perl 3146 executable to create a new executable called F<perl.third>. When the 3147 instrumented executable is run, it creates a log of dubious memory 3148 traffic in file called F<perl.3log>. See the manual pages of atom and 3149 third for more information. The most extensive Third Degree 3150 documentation is available in the Compaq "Tru64 UNIX Programmer's 3151 Guide", chapter "Debugging Programs with Third Degree". 3152 3153 The "test.third" leaves a lot of files named F<foo_bar.3log> in the t/ 3154 subdirectory. There is a problem with these files: Third Degree is so 3155 effective that it finds problems also in the system libraries. 3156 Therefore you should used the Porting/thirdclean script to cleanup 3157 the F<*.3log> files. 3158 3159 There are also leaks that for given certain definition of a leak, 3160 aren't. See L</PERL_DESTRUCT_LEVEL> for more information. 3161 3162 =head2 PERL_DESTRUCT_LEVEL 3163 3164 If you want to run any of the tests yourself manually using e.g. 3165 valgrind, or the pureperl or perl.third executables, please note that 3166 by default perl B<does not> explicitly cleanup all the memory it has 3167 allocated (such as global memory arenas) but instead lets the exit() 3168 of the whole program "take care" of such allocations, also known as 3169 "global destruction of objects". 3170 3171 There is a way to tell perl to do complete cleanup: set the 3172 environment variable PERL_DESTRUCT_LEVEL to a non-zero value. 3173 The t/TEST wrapper does set this to 2, and this is what you 3174 need to do too, if you don't want to see the "global leaks": 3175 For example, for "third-degreed" Perl: 3176 3177 env PERL_DESTRUCT_LEVEL=2 ./perl.third -Ilib t/foo/bar.t 3178 3179 (Note: the mod_perl apache module uses also this environment variable 3180 for its own purposes and extended its semantics. Refer to the mod_perl 3181 documentation for more information. Also, spawned threads do the 3182 equivalent of setting this variable to the value 1.) 3183 3184 If, at the end of a run you get the message I<N scalars leaked>, you can 3185 recompile with C<-DDEBUG_LEAKING_SCALARS>, which will cause the addresses 3186 of all those leaked SVs to be dumped along with details as to where each 3187 SV was originally allocated. This information is also displayed by 3188 Devel::Peek. Note that the extra details recorded with each SV increases 3189 memory usage, so it shouldn't be used in production environments. It also 3190 converts C<new_SV()> from a macro into a real function, so you can use 3191 your favourite debugger to discover where those pesky SVs were allocated. 3192 3193 =head2 PERL_MEM_LOG 3194 3195 If compiled with C<-DPERL_MEM_LOG>, all Newx() and Renew() allocations 3196 and Safefree() in the Perl core go through logging functions, which is 3197 handy for breakpoint setting. If also compiled with C<-DPERL_MEM_LOG_STDERR>, 3198 the allocations and frees are logged to STDERR (or more precisely, to the 3199 file descriptor 2) in these logging functions, with the calling source code 3200 file and line number (and C function name, if supported by the C compiler). 3201 3202 This logging is somewhat similar to C<-Dm> but independent of C<-DDEBUGGING>, 3203 and at a higher level (the C<-Dm> is directly at the point of C<malloc()>, 3204 while the C<PERL_MEM_LOG> is at the level of C<New()>). 3205 3206 =head2 Profiling 3207 3208 Depending on your platform there are various of profiling Perl. 3209 3210 There are two commonly used techniques of profiling executables: 3211 I<statistical time-sampling> and I<basic-block counting>. 3212 3213 The first method takes periodically samples of the CPU program 3214 counter, and since the program counter can be correlated with the code 3215 generated for functions, we get a statistical view of in which 3216 functions the program is spending its time. The caveats are that very 3217 small/fast functions have lower probability of showing up in the 3218 profile, and that periodically interrupting the program (this is 3219 usually done rather frequently, in the scale of milliseconds) imposes 3220 an additional overhead that may skew the results. The first problem 3221 can be alleviated by running the code for longer (in general this is a 3222 good idea for profiling), the second problem is usually kept in guard 3223 by the profiling tools themselves. 3224 3225 The second method divides up the generated code into I<basic blocks>. 3226 Basic blocks are sections of code that are entered only in the 3227 beginning and exited only at the end. For example, a conditional jump 3228 starts a basic block. Basic block profiling usually works by 3229 I<instrumenting> the code by adding I<enter basic block #nnnn> 3230 book-keeping code to the generated code. During the execution of the 3231 code the basic block counters are then updated appropriately. The 3232 caveat is that the added extra code can skew the results: again, the 3233 profiling tools usually try to factor their own effects out of the 3234 results. 3235 3236 =head2 Gprof Profiling 3237 3238 gprof is a profiling tool available in many UNIX platforms, 3239 it uses F<statistical time-sampling>. 3240 3241 You can build a profiled version of perl called "perl.gprof" by 3242 invoking the make target "perl.gprof" (What is required is that Perl 3243 must be compiled using the C<-pg> flag, you may need to re-Configure). 3244 Running the profiled version of Perl will create an output file called 3245 F<gmon.out> is created which contains the profiling data collected 3246 during the execution. 3247 3248 The gprof tool can then display the collected data in various ways. 3249 Usually gprof understands the following options: 3250 3251 =over 4 3252 3253 =item -a 3254 3255 Suppress statically defined functions from the profile. 3256 3257 =item -b 3258 3259 Suppress the verbose descriptions in the profile. 3260 3261 =item -e routine 3262 3263 Exclude the given routine and its descendants from the profile. 3264 3265 =item -f routine 3266 3267 Display only the given routine and its descendants in the profile. 3268 3269 =item -s 3270 3271 Generate a summary file called F<gmon.sum> which then may be given 3272 to subsequent gprof runs to accumulate data over several runs. 3273 3274 =item -z 3275 3276 Display routines that have zero usage. 3277 3278 =back 3279 3280 For more detailed explanation of the available commands and output 3281 formats, see your own local documentation of gprof. 3282 3283 quick hint: 3284 3285 $ sh Configure -des -Dusedevel -Doptimize='-g' -Accflags='-pg' -Aldflags='-pg' && make 3286 $ ./perl someprog # creates gmon.out in current directory 3287 $ gprof perl > out 3288 $ view out 3289 3290 =head2 GCC gcov Profiling 3291 3292 Starting from GCC 3.0 I<basic block profiling> is officially available 3293 for the GNU CC. 3294 3295 You can build a profiled version of perl called F<perl.gcov> by 3296 invoking the make target "perl.gcov" (what is required that Perl must 3297 be compiled using gcc with the flags C<-fprofile-arcs 3298 -ftest-coverage>, you may need to re-Configure). 3299 3300 Running the profiled version of Perl will cause profile output to be 3301 generated. For each source file an accompanying ".da" file will be 3302 created. 3303 3304 To display the results you use the "gcov" utility (which should 3305 be installed if you have gcc 3.0 or newer installed). F<gcov> is 3306 run on source code files, like this 3307 3308 gcov sv.c 3309 3310 which will cause F<sv.c.gcov> to be created. The F<.gcov> files 3311 contain the source code annotated with relative frequencies of 3312 execution indicated by "#" markers. 3313 3314 Useful options of F<gcov> include C<-b> which will summarise the 3315 basic block, branch, and function call coverage, and C<-c> which 3316 instead of relative frequencies will use the actual counts. For 3317 more information on the use of F<gcov> and basic block profiling 3318 with gcc, see the latest GNU CC manual, as of GCC 3.0 see 3319 3320 http://gcc.gnu.org/onlinedocs/gcc-3.0/gcc.html 3321 3322 and its section titled "8. gcov: a Test Coverage Program" 3323 3324 http://gcc.gnu.org/onlinedocs/gcc-3.0/gcc_8.html#SEC132 3325 3326 quick hint: 3327 3328 $ sh Configure -des -Doptimize='-g' -Accflags='-fprofile-arcs -ftest-coverage' \ 3329 -Aldflags='-fprofile-arcs -ftest-coverage' && make perl.gcov 3330 $ rm -f regexec.c.gcov regexec.gcda 3331 $ ./perl.gcov 3332 $ gcov regexec.c 3333 $ view regexec.c.gcov 3334 3335 =head2 Pixie Profiling 3336 3337 Pixie is a profiling tool available on IRIX and Tru64 (aka Digital 3338 UNIX aka DEC OSF/1) platforms. Pixie does its profiling using 3339 I<basic-block counting>. 3340 3341 You can build a profiled version of perl called F<perl.pixie> by 3342 invoking the make target "perl.pixie" (what is required is that Perl 3343 must be compiled using the C<-g> flag, you may need to re-Configure). 3344 3345 In Tru64 a file called F<perl.Addrs> will also be silently created, 3346 this file contains the addresses of the basic blocks. Running the 3347 profiled version of Perl will create a new file called "perl.Counts" 3348 which contains the counts for the basic block for that particular 3349 program execution. 3350 3351 To display the results you use the F<prof> utility. The exact 3352 incantation depends on your operating system, "prof perl.Counts" in 3353 IRIX, and "prof -pixie -all -L. perl" in Tru64. 3354 3355 In IRIX the following prof options are available: 3356 3357 =over 4 3358 3359 =item -h 3360 3361 Reports the most heavily used lines in descending order of use. 3362 Useful for finding the hotspot lines. 3363 3364 =item -l 3365 3366 Groups lines by procedure, with procedures sorted in descending order of use. 3367 Within a procedure, lines are listed in source order. 3368 Useful for finding the hotspots of procedures. 3369 3370 =back 3371 3372 In Tru64 the following options are available: 3373 3374 =over 4 3375 3376 =item -p[rocedures] 3377 3378 Procedures sorted in descending order by the number of cycles executed 3379 in each procedure. Useful for finding the hotspot procedures. 3380 (This is the default option.) 3381 3382 =item -h[eavy] 3383 3384 Lines sorted in descending order by the number of cycles executed in 3385 each line. Useful for finding the hotspot lines. 3386 3387 =item -i[nvocations] 3388 3389 The called procedures are sorted in descending order by number of calls 3390 made to the procedures. Useful for finding the most used procedures. 3391 3392 =item -l[ines] 3393 3394 Grouped by procedure, sorted by cycles executed per procedure. 3395 Useful for finding the hotspots of procedures. 3396 3397 =item -testcoverage 3398 3399 The compiler emitted code for these lines, but the code was unexecuted. 3400 3401 =item -z[ero] 3402 3403 Unexecuted procedures. 3404 3405 =back 3406 3407 For further information, see your system's manual pages for pixie and prof. 3408 3409 =head2 Miscellaneous tricks 3410 3411 =over 4 3412 3413 =item * 3414 3415 Those debugging perl with the DDD frontend over gdb may find the 3416 following useful: 3417 3418 You can extend the data conversion shortcuts menu, so for example you 3419 can display an SV's IV value with one click, without doing any typing. 3420 To do that simply edit ~/.ddd/init file and add after: 3421 3422 ! Display shortcuts. 3423 Ddd*gdbDisplayShortcuts: \ 3424 /t () // Convert to Bin\n\ 3425 /d () // Convert to Dec\n\ 3426 /x () // Convert to Hex\n\ 3427 /o () // Convert to Oct(\n\ 3428 3429 the following two lines: 3430 3431 ((XPV*) (())->sv_any )->xpv_pv // 2pvx\n\ 3432 ((XPVIV*) (())->sv_any )->xiv_iv // 2ivx 3433 3434 so now you can do ivx and pvx lookups or you can plug there the 3435 sv_peek "conversion": 3436 3437 Perl_sv_peek(my_perl, (SV*)()) // sv_peek 3438 3439 (The my_perl is for threaded builds.) 3440 Just remember that every line, but the last one, should end with \n\ 3441 3442 Alternatively edit the init file interactively via: 3443 3rd mouse button -> New Display -> Edit Menu 3444 3445 Note: you can define up to 20 conversion shortcuts in the gdb 3446 section. 3447 3448 =item * 3449 3450 If you see in a debugger a memory area mysteriously full of 0xABABABAB 3451 or 0xEFEFEFEF, you may be seeing the effect of the Poison() macros, 3452 see L<perlclib>. 3453 3454 =item * 3455 3456 Under ithreads the optree is read only. If you want to enforce this, to check 3457 for write accesses from buggy code, compile with C<-DPL_OP_SLAB_ALLOC> to 3458 enable the OP slab allocator and C<-DPERL_DEBUG_READONLY_OPS> to enable code 3459 that allocates op memory via C<mmap>, and sets it read-only at run time. 3460 Any write access to an op results in a C<SIGBUS> and abort. 3461 3462 This code is intended for development only, and may not be portable even to 3463 all Unix variants. Also, it is an 80% solution, in that it isn't able to make 3464 all ops read only. Specifically it 3465 3466 =over 3467 3468 =item 1 3469 3470 Only sets read-only on all slabs of ops at C<CHECK> time, hence ops allocated 3471 later via C<require> or C<eval> will be re-write 3472 3473 =item 2 3474 3475 Turns an entire slab of ops read-write if the refcount of any op in the slab 3476 needs to be decreased. 3477 3478 =item 3 3479 3480 Turns an entire slab of ops read-write if any op from the slab is freed. 3481 3482 =back 3483 3484 It's not possible to turn the slabs to read-only after an action requiring 3485 read-write access, as either can happen during op tree building time, so 3486 there may still be legitimate write access. 3487 3488 However, as an 80% solution it is still effective, as currently it catches 3489 a write access during the generation of F<Config.pm>, which means that we 3490 can't yet build F<perl> with this enabled. 3491 3492 =back 3493 3494 3495 =head1 CONCLUSION 3496 3497 We've had a brief look around the Perl source, how to maintain quality 3498 of the source code, an overview of the stages F<perl> goes through 3499 when it's running your code, how to use debuggers to poke at the Perl 3500 guts, and finally how to analyse the execution of Perl. We took a very 3501 simple problem and demonstrated how to solve it fully - with 3502 documentation, regression tests, and finally a patch for submission to 3503 p5p. Finally, we talked about how to use external tools to debug and 3504 test Perl. 3505 3506 I'd now suggest you read over those references again, and then, as soon 3507 as possible, get your hands dirty. The best way to learn is by doing, 3508 so: 3509 3510 =over 3 3511 3512 =item * 3513 3514 Subscribe to perl5-porters, follow the patches and try and understand 3515 them; don't be afraid to ask if there's a portion you're not clear on - 3516 who knows, you may unearth a bug in the patch... 3517 3518 =item * 3519 3520 Keep up to date with the bleeding edge Perl distributions and get 3521 familiar with the changes. Try and get an idea of what areas people are 3522 working on and the changes they're making. 3523 3524 =item * 3525 3526 Do read the README associated with your operating system, e.g. README.aix 3527 on the IBM AIX OS. Don't hesitate to supply patches to that README if 3528 you find anything missing or changed over a new OS release. 3529 3530 =item * 3531 3532 Find an area of Perl that seems interesting to you, and see if you can 3533 work out how it works. Scan through the source, and step over it in the 3534 debugger. Play, poke, investigate, fiddle! You'll probably get to 3535 understand not just your chosen area but a much wider range of F<perl>'s 3536 activity as well, and probably sooner than you'd think. 3537 3538 =back 3539 3540 =over 3 3541 3542 =item I<The Road goes ever on and on, down from the door where it began.> 3543 3544 =back 3545 3546 If you can do these things, you've started on the long road to Perl porting. 3547 Thanks for wanting to help make Perl better - and happy hacking! 3548 3549 =head1 AUTHOR 3550 3551 This document was written by Nathan Torkington, and is maintained by 3552 the perl5-porters mailing list.
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