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panic: attempt to copy freed scalar #15086

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p5pRT opened this issue Dec 10, 2015 · 6 comments
Closed

panic: attempt to copy freed scalar #15086

p5pRT opened this issue Dec 10, 2015 · 6 comments
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distro-Linux type-core

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@p5pRT
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p5pRT commented Dec 10, 2015

Migrated from rt.perl.org#126872 (status was 'rejected')

Searchable as RT126872$
@p5pRT
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p5pRT commented Dec 10, 2015

From @KES777

Created by @KES777

$ perl -d​:KillPrint -e 0
panic​: attempt to copy freed scalar 2175990 to 2175600 at /home/kes/work/projects/perl_libs/Devel/DebugHooks.pm line 17.
BEGIN failed--compilation aborted.

$cat Devel/KillPrint.pm
package Devel​::KillPrint;

our $VERSION = '0.01';

sub import {
}

use Devel​::DebugHooks;

1;

$cat Devel/DebugHooks.pm
package Devel​::DebugHooks;

our $VERSION = '0.01';

sub import {
}

package # hide the package from the PAUSE indexer
  DB;

sub frames {
  my $level = shift;
  return ( [ @​DB​::args ], caller( $level +1 ) ) if defined $level;
}

sub DB {
}

sub trace_subs {
  my $level = 0;

  my( $args, @​frame ) = DB​::frames( $level );
}

sub sub {
  trace_subs;
  return &$DB​::sub;
};

1;

PS. This were another tuturial question.

Perl Info 

Flags:
    category=core
    severity=low

Site configuration information for perl 5.22.0:

Configured by kes at Tue Sep 29 16:12:55 EEST 2015.

Summary of my perl5 (revision 5 version 22 subversion 0) configuration:
   
  Platform:
    osname=linux, osvers=3.13.0-37-generic, archname=x86_64-linux
    uname='linux keswork 3.13.0-37-generic #64-ubuntu smp mon sep 22 21:28:38 utc 2014 x86_64 x86_64 x86_64 gnulinux '
    config_args='-des -Dprefix=/home/kes/perl'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.8.4', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678, doublekind=3
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16, longdblkind=3
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.8/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
    libs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.19.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.19'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector'



@INC for perl 5.22.0:
    /home/kes/work/projects/perl_libs
    /home/kes/perl5/lib/perl5/x86_64-linux
    /home/kes/perl5/lib/perl5
    /home/kes/perl/lib/site_perl/5.22.0/x86_64-linux
    /home/kes/perl/lib/site_perl/5.22.0
    /home/kes/perl/lib/5.22.0/x86_64-linux
    /home/kes/perl/lib/5.22.0
    .


Environment for perl 5.22.0:
    HOME=/home/kes
    LANG=ru_UA.UTF-8
    LANGUAGE=en
    LC_MESSAGES=en_US.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/kes/perl/bin:/home/kes/perl/bin:/home/kes/perl5/bin:/home/kes/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
    PERL5DB=BEGIN { require "Devel/KillPrint.pm" }
    PERL5LIB=/home/kes/work/projects/perl_libs:/home/kes/perl5/lib/perl5
    PERLDB_OPTS=RemotePort=keswork:9001
    PERL_BADLANG (unset)
    PERL_MB_OPT=--install_base "/home/kes/perl5"
    PERL_MM_OPT=INSTALL_BASE=/home/kes/perl5
    SHELL=/bin/bash

@p5pRT
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p5pRT commented Dec 10, 2015

From @KES777

if in sub frames I add line​:

sub frames {
  my $level = shift;
+my @​frame = caller( $level +1 );
  return ( [ @​DB​::args ], caller( $level +1 ) ) if defined $level;
}

In this case I do not get panic

@p5pRT
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p5pRT commented Dec 10, 2015

From [Unknown Contact. See original ticket]

if in sub frames I add line​:

sub frames {
  my $level = shift;
+my @​frame = caller( $level +1 );
  return ( [ @​DB​::args ], caller( $level +1 ) ) if defined $level;
}

In this case I do not get panic

@p5pRT
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p5pRT commented Dec 15, 2015

From @tonycoz

On Thu Dec 10 09​:24​:41 2015, kes-kes@​yandex.ua wrote​:

[Please describe your issue here]

$ perl -d​:KillPrint -e 0
panic​: attempt to copy freed scalar 2175990 to 2175600 at
/home/kes/work/projects/perl_libs/Devel/DebugHooks.pm line 17.
BEGIN failed--compilation aborted.

@​DB​::args is a very low-level copy of the subroutine arguments, it doesn't keep reference counts to those arguments, so if you use @​DB​::args when the sub call that was used to populate it has returned, its values are invalid.

Your code is attemptting to use values in @​DB​::args from the *previous* call to caller(), for which the subroutine has returned.

If you ensure caller() is called before you use @​DB​::args​:

sub frames {
  my $level = shift;
  my @​c = caller($level+1);
  return ( [ @​DB​::args ], @​c ) if defined $level;
}

there's no crash.

Tony

@p5pRT
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p5pRT commented Dec 15, 2015

The RT System itself - Status changed from 'new' to 'open'

@p5pRT
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p5pRT commented Dec 17, 2015

@tonycoz - Status changed from 'open' to 'rejected'

@p5pRT p5pRT closed this as completed Dec 17, 2015
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