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[perl #77816] provide originating context of subroutine definitions

From:
jawnsy @ cpan . org
Date:
September 12, 2010 23:32
Subject:
[perl #77816] provide originating context of subroutine definitions
Message ID:
rt-3.6.HEAD-5116-1284342753-1272.77816-75-0@perl.org
# New Ticket Created by  jawnsy@cpan.org 
# Please include the string:  [perl #77816]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=77816 >



This is a bug report for perl from jawnsy@cpan.org,
generated with the help of perlbug 1.39 running under perl 5.10.1.


-----------------------------------------------------------------
[Please describe your issue here]

I noticed that subroutine redefinition messages from perl are not as helpful as they could be.

If we redefine something in perl, we get:

$ perl -we 'sub blah { 1; }; sub blah { 2; }'
Subroutine blah redefined at -e line 1.

Compiling a C program (using gcc) with redefinitions results in:

$ cc -std=c99 -pedantic -Wall -g -O0 -DDEBUG -I. -fPIC -c display.c -o display.o
display.c:20: error: conflicting types for ‘usage’
display.c:5: note: previous declaration of ‘usage’ was here

In a brief chat with the #toolchain folks, at first glance, it might be possible to add this feature (though it could be non-trivial to handle some of the obscure cases)

  <jawnsy> question: why isn't perl's message -- Subroutine blah redefined at -e line 1. -- more informative, like gcc's? (gcc shows the origin of the first definition)
  <jawnsy> is it something that's not possible based on how perl parses Perl, or is it just something nobody's ever thought about doing?
  <xdg> jawnsy, my guess is no one ever really considered it
  <xdg> Or maybe it's hard to find where a sub came from once it's been compiled?
  <jawnsy> xdg: I guess at this point it's not really worth adding... maybe I should add it as a wishlist thing in perl's RT, in case anyone is so inclined
  <xdg> jawnsy, sure.  I'm glancing at the core code right now in case it's trivial.
  <rafl> there is some cases where there isn't more information available
  <rafl> but most of the time it could be much more informative, yes
  <xdg> rafl, looks like every CV has ->FILE so that could help locate the original.  But without line number, it might be more annoying than helpful.
  <rafl> yeah, but the line is also around somewhere. in the COPs, i guess
  <rafl> except for xsubs and such
  <xdg> right.  I just don't know if there's a backreference to it.
  <rafl> but that's all just where it was compiled
  <rafl> not where it was added to the symbol table
  <xdg> jawnsy, it's probably possible.  open up an RT wishlist for it and maybe someone will get to it
  <rafl> that's the same most of the time, but doesn't have to be
  <rafl> it would be fixable with line debugging enabled tho
  <rafl> because that's what %DB::sub is intended for
  <rafl> we'd just need to update that on sub assignments to globs
  <jawnsy> not a big deal, of course. I was just trying to write similar type output for something I'm working on, and looked at gcc and perl
  <rafl> as for the place it's compiled at: perl -MO=Concise,foo -e'sub foo { 42 }'
  <rafl> <;> nextstate(main 1 -e:1) v ->2
  <rafl> so it's *somewhere* in the optree :)
  <xdg> Ah.  CV->START->line perhaps
  <rafl> something like that, yes
  <rafl> but still.. that isn't necessarily the right answer to "where was that sub previously defined", only very often :)
  <xdg> true, but it's a pointer to what subroutine is being replaced
  <rafl> that's not too useful, i'd think
  <xdg> you'd really need to know where the symbol was assigned to
  <xdg> I'm not sure anything actually does that kind of bookkeeping

In case this actually isn't possible, then I apologize for the noise. I just thought it'd be a nice feature, and could help to make perl (the binary) more friendly for new users.

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=wishlist
---
Site configuration information for perl 5.10.1:

Configured by Debian Project at Fri Aug  6 10:46:59 UTC 2010.

Summary of my perl5 (revision 5 version 10 subversion 1) configuration:
   
  Platform:
    osname=linux, osvers=2.6.32.17-dsa-ia32, archname=i486-linux-gnu-thread-multi
    uname='linux murphy 2.6.32.17-dsa-ia32 #1 smp tue aug 3 15:32:33 cest 2010 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i486-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.10 -Darchlib=/usr/lib/perl/5.10 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.10.1 -Dsitearch=/usr/local/lib/perl/5.10.1 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.10.1 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=undef, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2 -g',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.4.5 20100728 (prerelease)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib /usr/lib64
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.11.2.so, so=so, useshrplib=true, libperl=libperl.so.5.10.1
    gnulibc_version='2.11.2'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib -fstack-protector'

Locally applied patches:
    DEBPKG:debian/arm_thread_stress_timeout - http://bugs.debian.org/501970 Raise the timeout of ext/threads/shared/t/stress.t to accommodate slower build hosts
    DEBPKG:debian/cpan_config_path - Set location of CPAN::Config to /etc/perl as /usr may not be writable.
    DEBPKG:debian/cpan_definstalldirs - Provide a sensible INSTALLDIRS default for modules installed from CPAN.
    DEBPKG:debian/db_file_ver - http://bugs.debian.org/340047 Remove overly restrictive DB_File version check.
    DEBPKG:debian/doc_info - Replace generic man(1) instructions with Debian-specific information.
    DEBPKG:debian/enc2xs_inc - http://bugs.debian.org/290336 Tweak enc2xs to follow symlinks and ignore missing @INC directories.
    DEBPKG:debian/errno_ver - http://bugs.debian.org/343351 Remove Errno version check due to upgrade problems with long-running processes.
    DEBPKG:debian/extutils_hacks - Various debian-specific ExtUtils changes
    DEBPKG:debian/fakeroot - Postpone LD_LIBRARY_PATH evaluation to the binary targets.
    DEBPKG:debian/instmodsh_doc - Debian policy doesn't install .packlist files for core or vendor.
    DEBPKG:debian/ld_run_path - Remove standard libs from LD_RUN_PATH as per Debian policy.
    DEBPKG:debian/libnet_config_path - Set location of libnet.cfg to /etc/perl/Net as /usr may not be writable.
    DEBPKG:debian/m68k_thread_stress - http://bugs.debian.org/495826 Disable some threads tests on m68k for now due to missing TLS.
    DEBPKG:debian/mod_paths - Tweak @INC ordering for Debian
    DEBPKG:debian/module_build_man_extensions - http://bugs.debian.org/479460 Adjust Module::Build manual page extensions for the Debian Perl policy
    DEBPKG:debian/perl_synopsis - http://bugs.debian.org/278323 Rearrange perl.pod
    DEBPKG:debian/prune_libs - http://bugs.debian.org/128355 Prune the list of libraries wanted to what we actually need.
    DEBPKG:debian/use_gdbm - Explicitly link against -lgdbm_compat in ODBM_File/NDBM_File. 
    DEBPKG:fixes/assorted_docs - http://bugs.debian.org/443733 [384f06a] Math::BigInt::CalcEmu documentation grammar fix
    DEBPKG:fixes/net_smtp_docs - http://bugs.debian.org/100195 [rt.cpan.org #36038] Document the Net::SMTP 'Port' option
    DEBPKG:fixes/processPL - http://bugs.debian.org/357264 [rt.cpan.org #17224] Always use PERLRUNINST when building perl modules.
    DEBPKG:debian/perlivp - http://bugs.debian.org/510895 Make perlivp skip include directories in /usr/local
    DEBPKG:fixes/pod2man-index-backslash - http://bugs.debian.org/521256 Escape backslashes in .IX entries
    DEBPKG:debian/disable-zlib-bundling - Disable zlib bundling in Compress::Raw::Zlib
    DEBPKG:fixes/kfreebsd_cppsymbols - http://bugs.debian.org/533098 [3b910a0] Add gcc predefined macros to $Config{cppsymbols} on GNU/kFreeBSD.
    DEBPKG:debian/cpanplus_definstalldirs - http://bugs.debian.org/533707 Configure CPANPLUS to use the site directories by default.
    DEBPKG:debian/cpanplus_config_path - Save local versions of CPANPLUS::Config::System into /etc/perl.
    DEBPKG:fixes/kfreebsd-filecopy-pipes - http://bugs.debian.org/537555 [16f708c] Fix File::Copy::copy with pipes on GNU/kFreeBSD
    DEBPKG:fixes/anon-tmpfile-dir - http://bugs.debian.org/528544 [perl #66452] Honor TMPDIR when open()ing an anonymous temporary file
    DEBPKG:fixes/abstract-sockets - http://bugs.debian.org/329291 [89904c0] Add support for Abstract namespace sockets.
    DEBPKG:fixes/hurd_cppsymbols - http://bugs.debian.org/544307 [eeb92b7] Add gcc predefined macros to $Config{cppsymbols} on GNU/Hurd.
    DEBPKG:fixes/autodie-flock - http://bugs.debian.org/543731 Allow for flock returning EAGAIN instead of EWOULDBLOCK on linux/parisc
    DEBPKG:fixes/archive-tar-instance-error - http://bugs.debian.org/539355 [rt.cpan.org #48879] Separate Archive::Tar instance error strings from each other
    DEBPKG:fixes/positive-gpos - http://bugs.debian.org/545234 [perl #69056] [c584a96] Fix \\G crash on first match
    DEBPKG:debian/devel-ppport-ia64-optim - http://bugs.debian.org/548943 Work around an ICE on ia64
    DEBPKG:fixes/trie-logic-match - http://bugs.debian.org/552291 [perl #69973] [0abd0d7] Fix a DoS in Unicode processing [CVE-2009-3626]
    DEBPKG:fixes/hppa-thread-eagain - http://bugs.debian.org/554218 make the threads-shared test suite more robust, fixing failures on hppa
    DEBPKG:fixes/crash-on-undefined-destroy - http://bugs.debian.org/564074 [perl #71952] [1f15e67] Fix a NULL pointer dereference when looking for a DESTROY method
    DEBPKG:fixes/tainted-errno - http://bugs.debian.org/574129 [perl #61976] [be1cf43] fix an errno stringification bug in taint mode
    DEBPKG:fixes/safe-upgrade - http://bugs.debian.org/582978 Upgrade Safe.pm to 2.25, fixing CVE-2010-1974
    DEBPKG:fixes/tell-crash - http://bugs.debian.org/578577 [f4817f3] Fix a tell() crash on bad arguments.
    DEBPKG:fixes/format-write-crash - http://bugs.debian.org/579537 [perl #22977] [421f30e] Fix a crash in format/write
    DEBPKG:fixes/arm-alignment - http://bugs.debian.org/289884 [f1c7503] Prevent gcc from optimizing the alignment test away on armel
    DEBPKG:fixes/fcgi-test - Fix a failure in CGI/t/fast.t when FCGI is installed
    DEBPKG:fixes/hurd-ccflags - http://bugs.debian.org/587901 Make hints/gnu.sh append to $ccflags rather than overriding them
    DEBPKG:patchlevel - http://bugs.debian.org/567489 List packaged patches for 5.10.1-14 in patchlevel.h

---
@INC for perl 5.10.1:
    /etc/perl
    /usr/local/lib/perl/5.10.1
    /usr/local/share/perl/5.10.1
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.10
    /usr/share/perl/5.10
    /usr/local/lib/site_perl
    .

---
Environment for perl 5.10.1:
    HOME=/home/jon
    LANG=en_CA.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=~/.bin:/usr/local/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/sbin:/bin
    PERL_BADLANG (unset)
    SHELL=/bin/bash

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