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Another self-modifyingloop bug #6533

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p5pRT opened this issue May 24, 2003 · 5 comments
Open

Another self-modifyingloop bug #6533

p5pRT opened this issue May 24, 2003 · 5 comments
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distro-All leak/refcount/malloc type-core

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@p5pRT
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p5pRT commented May 24, 2003

Migrated from rt.perl.org#22312 (status was 'open')

Searchable as RT22312$
@p5pRT
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p5pRT commented May 24, 2003

From perl-5.8.0@ton.iguana.be

Created by perl-5.8.0@ton.iguana.be

perl -e 'map{@​a=($_+=0)x$_}@​a=/\B./g for 1100..2000'
Segmentation fault (core dumped)

A bit different from the normal ones which mostly involve
modifying a "for" loop variable. "map" usually can take
these abuses.

Perl Info 

Flags:
    category=core
    severity=low

Site configuration information for perl v5.8.0:

Configured by ton at Tue Nov 12 01:56:18 CET 2002.

Summary of my perl5 (revision 5.0 version 8 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.4.19, archname=i686-linux-thread-multi-64int-ld
    uname='linux quasar 2.4.19 #5 wed oct 2 02:34:25 cest 2002 i686 unknown '
    config_args=''
    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=define use64bitall=undef uselongdouble=define
    usemymalloc=y, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2 -fomit-frame-pointer',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -I/usr/local/include'
    ccversion='', gccversion='2.95.3 20010315 (release)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long long', ivsize=8, nvtype='long double', nvsize=12, 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=-lnsl -lndbm -ldb -ldl -lm -lpthread -lc -lposix -lcrypt -lutil
    perllibs=-lnsl -ldl -lm -lpthread -lc -lposix -lcrypt -lutil
    libc=/lib/libc-2.2.4.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.2.4'
  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:
    /usr/lib/perl5/5.8.0/i686-linux-thread-multi-64int-ld
    /usr/lib/perl5/5.8.0
    /usr/lib/perl5/site_perl/5.8.0/i686-linux-thread-multi-64int-ld
    /usr/lib/perl5/site_perl/5.8.0
    /usr/lib/perl5/site_perl
    .


Environment for perl v5.8.0:
    HOME=/home/ton
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/ton/bin.Linux:/home/ton/bin:/home/ton/bin.SampleSetup:/usr/local/bin:/usr/local/sbin:/usr/local/jre/bin:/home/oracle/product/9.0.1/bin:/usr/local/ar/bin:/usr/games/bin:/usr/X11R6/bin:/usr/share/bin:/usr/bin:/usr/sbin:/bin:/sbin:.
    PERL_BADLANG (unset)
    SHELL=/bin/bash

@p5pRT
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p5pRT commented Jul 17, 2005

From @schwern

[perl-5.8.0@​ton.iguana.be - Sat May 24 14​:07​:05 2003]​:

perl -e 'map{@​a=($_+=0)x$_}@​a=/\B./g for 1100..2000'
Segmentation fault (core dumped)

A bit different from the normal ones which mostly involve
modifying a "for" loop variable. "map" usually can take
these abuses.

Confirmed segfaulting in 5.8.6 and bleadperl@​25156. 5.6.2, 5.5.4 and
5.4.5 don't segfault.

@p5pRT
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p5pRT commented Jul 17, 2005

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

@p5pRT
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p5pRT commented Jul 18, 2005

From @iabyn

On Sun, Jul 17, 2005 at 03​:55​:28PM -0700, Michael G Schwern via RT wrote​:

[perl-5.8.0@​ton.iguana.be - Sat May 24 14​:07​:05 2003]​:

perl -e 'map{@​a=($_+=0)x$_}@​a=/\B./g for 1100..2000'
Segmentation fault (core dumped)

A bit different from the normal ones which mostly involve
modifying a "for" loop variable. "map" usually can take
these abuses.

Confirmed segfaulting in 5.8.6 and bleadperl@​25156. 5.6.2, 5.5.4 and
5.4.5 don't segfault.

Not a lot we an do about this except to possibly do for 'map'/'grep' what
I did with 'for'; and that is to put a test in for a freed value, and if
so, bail out. It's not perfect, but it's usually better than an segfault​:

  $ ./perl -we '@​a=1..9; @​a = () for @​a,1'
  Use of freed value in iteration at -e line 1.
  $

The only question is whether it's worth the small slowdown of testing the
refcnt of $_ at each iteration?

--
You live and learn (although usually you just live).

@p5pRT
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p5pRT commented Jul 18, 2005

From @schwern

On Mon, Jul 18, 2005 at 08​:37​:14PM +0100, Dave Mitchell wrote​:

The only question is whether it's worth the small slowdown of testing the
refcnt of $_ at each iteration?

A good rule of thumb is "Perl should never kill perl" and any marginal
slow down is worth hanging onto that.

--
Michael G Schwern schwern@​pobox.com http​://www.pobox.com/~schwern
ROCKS FALL! EVERYONE DIES!
  http​://www.somethingpositive.net/sp05032002.shtml

@xenu xenu removed the Severity Low label Dec 29, 2021
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