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diff --git a/pod/perlhack.pod b/pod/perlhack.pod index 4c645a6c41..a676f46afb 100644 --- a/pod/perlhack.pod +++ b/pod/perlhack.pod @@ -1041,6 +1041,55 @@ is broken (for example, the utf8 length cache on long utf8 strings). Add a test that will take a fraction of a second normally, and minutes otherwise, causing the test file to time out on failure. +=head2 Building perl at older commits + +In the course of hacking on the Perl core distribution, you may have occasion +to configure, build and test perl at an old commit. Sometimes C<make> will +fail during this process. If that happens, you may be able to salvage the +situation by using the Devel::PatchPerl library from CPAN (not included in the +core) to bring the source code at that commit to a buildable state. + +Here's a real world example, taken from work done to resolve +L<perl #72414|https://rt.perl.org/Ticket/Display.html?id=72414>. +Use of F<Porting/bisect.pl> had identified commit +C<ba77e4cc9d1ceebf472c9c5c18b2377ee47062e6> as the commit in which a bug was +corrected. To confirm, a P5P developer wanted to configure and build perl at +commit C<ba77e4c^> (presumably "bad") and then at C<ba77e4c> (presumably +"good"). Normal configuration and build was attempted: + + $ sh ./Configure -des -Dusedevel + $ make test_prep + +C<make>, however, failed with output (excerpted) like this: + + cc -fstack-protector -L/usr/local/lib -o miniperl \ + gv.o toke.o perly.o pad.o regcomp.o dump.o util.o \ + mg.o reentr.o mro.o hv.o av.o run.o pp_hot.o sv.o \ + pp.o scope.o pp_ctl.o pp_sys.o doop.o doio.o regexec.o \ + utf8.o taint.o deb.o universal.o globals.o perlio.o \ + perlapi.o numeric.o mathoms.o locale.o pp_pack.o pp_sort.o \ + miniperlmain.o opmini.o perlmini.o + pp.o: In function `Perl_pp_pow': + pp.c:(.text+0x2db9): undefined reference to `pow' + ... + collect2: error: ld returned 1 exit status + makefile:348: recipe for target 'miniperl' failed + make: *** [miniperl] Error 1 + +Another P5P contributor recommended installation and use of Devel::PatchPerl +for this situation, first to determine the version of perl at the commit in +question, then to patch the source code at that point to facilitate a build. + + $ perl -MDevel::PatchPerl -e \ + 'print Devel::PatchPerl->determine_version("/path/to/sourcecode"), "\n";' + 5.11.1 + $ perl -MDevel::PatchPerl -e \ + 'Devel::PatchPerl->patch_source("5.11.1", "/path/to/sourcecode");' + +Once the source was patched, C<./Configure> and C<make test_prep> were called +and completed successfully, enabling confirmation of the findings in RT +#72414. + =head1 MORE READING FOR GUTS HACKERS To hack on the Perl guts, you'll need to read the following things: |