Data::Dumper segfaults on very large recursive structures

[p5pRT]

Migrated from rt.perl.org#24013 (status was 'open')

Searchable as RT24013$

[p5pRT]

From DavidBuckley@bigfoot.com

Created by DavidBuckley@bigfoot.com

Data​::Dumper's XS code segfaults when dealing with exceptionally
deep structures. Example​:

[19​:09​:46] bucko(tank) ~$ perl -MData​::Dumper -e '$a = {}; $b = $a; for (1..3500) { $b->{a} = {}; $b = $b->{a} } Dumper($a);'
Segmentation fault

This originally turned up in my threads bug [perl #23965], where
simple recursive structures become infinitely deep non-recursive
structures.

Perl Info

Flags:
    category=core
    severity=medium

This perlbug was built using Perl v5.8.0 - Sun Jun 16 02:13:30 BST 2002
It is being executed now by  Perl v5.8.0 - Thu Sep 11 20:57:21 EST 2003.

Site configuration information for perl v5.8.0:

Configured by Debian Project at Thu Sep 11 20:57:21 EST 2003.

Summary of my perl5 (revision 5.0 version 8 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.4.21-xfs+ti1211, archname=i386-linux-thread-multi
    uname='linux kosh 2.4.21-xfs+ti1211 #1 sat jul 12 10:35:04 est 2003 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dcccdlflags=-fPIC -Darchname=i386-linux -Dprefix=/usr -Dprivlib=/usr/share/perl/5.8.0 -Darchlib=/usr/lib/perl/5.8.0 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.8.0 -Dsitearch=/usr/local/lib/perl/5.8.0 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dlibperl=libperl.so.5.8.0 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef 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 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O3',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fno-strict-aliasing'
    ccversion='', gccversion='3.3.2 20030908 (Debian 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 =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lgdbm -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.3.2.so, so=so, useshrplib=true, libperl=libperl.so.5.8.0
    gnulibc_version='2.3.2'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:
    


@INC for perl v5.8.0:
    /etc/perl
    /usr/local/lib/perl/5.8.0
    /usr/local/share/perl/5.8.0
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.8.0
    /usr/share/perl/5.8.0
    /usr/local/lib/site_perl
    .


Environment for perl v5.8.0:
    HOME=/home/bucko
    LANG=C
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/bucko/bin:/usr/local/jdk1.2.2/bin:/usr/local/bin:/usr/bin:/bin:/usr/bin/X11:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/bash

[p5pRT]

From @smpeters

[DavidBuckley@​bigfoot.com - Tue Sep 23 11​:15​:56 2003]​:

This is a bug report for perl from DavidBuckley@​bigfoot.com,
generated with the help of perlbug 1.33 running under perl v5.8.0.

-----------------------------------------------------------------
[Please enter your report here]

Data​::Dumper's XS code segfaults when dealing with exceptionally
deep structures. Example​:

[19​:09​:46] bucko(tank) ~$ perl -MData​::Dumper -e '$a = {}; $b = $a;
for (1..3500) { $b->{a} = {}; $b = $b->{a} } Dumper($a);'
Segmentation fault

This originally turned up in my threads bug [perl #23965], where
simple recursive structures become infinitely deep non-recursive
structures.

I was unable to duplicate the SEGV on any of my machines, although I did
get an "Out of Memory!" error on one server. That said, the problem
with the SEGV seems to be taken care of.

[p5pRT]

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

[p5pRT]

@smpeters - Status changed from 'open' to 'resolved'

[p5pRT]

From @iabyn

Just re-opening this, as the bug *isn't* fixed. It's the classic C stack
echaustion. On a machine with enought RAM, the stack fills before memory
is exhausted, so you still get a segfault.

Can only be fixed my making Data​::Dumper non-recusive, which woudn't be
easy.

[p5pRT]

@iabyn - Status changed from 'resolved' to 'open'

[jkeenan]

From @iabyn

Just re-opening this, as the bug isn't fixed. It's the classic C stack exhaustion. On a machine with enough RAM, the stack fills before memory is exhausted, so you still get a segfault.

Can only be fixed my making Data​::Dumper non-recursive, which wouldn't be easy.

Unintentionally closed in RT-to-GH transition in October 2019; re-opening.