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unpacking a 4-byte long on a 32-bit system causes segfault #9739

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p5pRT opened this issue May 20, 2009 · 6 comments
Closed

unpacking a 4-byte long on a 32-bit system causes segfault #9739

p5pRT opened this issue May 20, 2009 · 6 comments
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type-portability wontfix

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@p5pRT
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p5pRT commented May 20, 2009

Migrated from rt.perl.org#65862 (status was 'rejected')

Searchable as RT65862$
@p5pRT
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p5pRT commented May 20, 2009

From cjac@colliertech.org

Created by cjac@colliertech.org

08​:05 < dngor> Here's an example of Perl, pointer arithmetic, and
segfaulting​: perl -wle
  'print unpack("P4",pack("L",~0));'
08​:08 <%cj> $ perl -wle 'print unpack("P4",pack("L",~0));' && echo $?
08​:08 <%cj> 0
08​:08 <%cj> but on solaris​:
08​:09 <%cj> $ perl -wle 'print unpack("P4",pack("L",~0));' && echo $?
08​:09 <%cj> Segmentation Fault
08​:11 < dnm> $ uname -srm ; perl -wle 'print $];print
unpack("P4",pack("L",~0));'
08​:11 < dnm> Linux 2.6.29.3 i686
08​:11 < dnm> 5.010000
08​:11 < dnm> Segmentation fault
08​:22 <%cj> dnm​: ah, i686

(turns out the one which worked [the system details below] is 'Linux
2.6.28-11-generic x86_64' and the solaris is 'SunOS 5.9 sun4u')

Perl Info 

Flags:
    category=core
    severity=medium

Site configuration information for perl 5.10.0:

Configured by Debian Project at Mon Jan  5 22:36:05 UTC 2009.

Summary of my perl5 (revision 5 version 10 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.6.24-16-server,
archname=x86_64-linux-gnu-thread-multi
    uname='linux yellow 2.6.24-16-server #1 smp thu apr 10 13:15:38 utc
2008 x86_64 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN
-Dcccdlflags=-fPIC -Darchname=x86_64-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/5.10.0
-Dsitearch=/usr/local/lib/perl/5.10.0 -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.5.10.0 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN
-fno-strict-aliasing -pipe -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 -I/usr/local/include'
    ccversion='', gccversion='4.3.3 20081217 (prerelease)',
gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t',
lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib /lib64 /usr/lib64
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.9.so, so=so, useshrplib=true,
libperl=libperl.so.5.10.0
    gnulibc_version='2.9'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -L/usr/local/lib'

Locally applied patches:
    


@INC for perl 5.10.0:
    /etc/perl
    /usr/local/lib/perl/5.10.0
    /usr/local/share/perl/5.10.0
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.10
    /usr/share/perl/5.10
    /usr/local/lib/site_perl
    .


Environment for perl 5.10.0:
    HOME=/home/cjac
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)

PATH=/home/cjac/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/bash

@p5pRT
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p5pRT commented May 22, 2009

From @iabyn

On Wed, May 20, 2009 at 08​:57​:26AM -0700, C.J. Adams-Collier (via RT) wrote​:

08​:09 <%cj> $ perl -wle 'print unpack("P4",pack("L",~0));' && echo $?
08​:09 <%cj> Segmentation Fault

So, you are creating a pointer whose value is 0xffffffff (or longer for
64-bit), then trying to access a 4-character string at that address, which
gives a SEGV. What behaviour were you expecting?

--
"Emacs isn't a bad OS once you get used to it.
It just lacks a decent editor."

@p5pRT
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p5pRT commented May 22, 2009

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

@p5pRT
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p5pRT commented May 22, 2009

From cjac@colliertech.org

a handoff to die() or some other friendly-like, non-broken failure

On Fri, May 22, 2009 at 8​:33 AM, Dave Mitchell <davem@​iabyn.com> wrote​:

On Wed, May 20, 2009 at 08​:57​:26AM -0700, C.J. Adams-Collier (via RT)
wrote​:

08​:09 <%cj> $ perl -wle 'print unpack("P4",pack("L",~0));' && echo $?
08​:09 <%cj> Segmentation Fault

So, you are creating a pointer whose value is 0xffffffff (or longer for
64-bit), then trying to access a 4-character string at that address, which
gives a SEGV. What behaviour were you expecting?

--
"Emacs isn't a bad OS once you get used to it.
It just lacks a decent editor."

@p5pRT
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p5pRT commented May 22, 2009

From @iabyn

On Fri, May 22, 2009 at 10​:07​:10AM -0400, C.J. Adams-Collier wrote​:

a handoff to die() or some other friendly-like, non-broken failure

Which is essentially impossible to do portably.

On Fri, May 22, 2009 at 8​:33 AM, Dave Mitchell <davem@​iabyn.com> wrote​:

On Wed, May 20, 2009 at 08​:57​:26AM -0700, C.J. Adams-Collier (via RT)
wrote​:

08​:09 <%cj> $ perl -wle 'print unpack("P4",pack("L",~0));' && echo $?
08​:09 <%cj> Segmentation Fault

So, you are creating a pointer whose value is 0xffffffff (or longer for
64-bit), then trying to access a 4-character string at that address, which
gives a SEGV. What behaviour were you expecting?

--
"Emacs isn't a bad OS once you get used to it.
It just lacks a decent editor."

--
This is a great day for France!
  -- Nixon at Charles De Gaulle's funeral

@p5pRT
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p5pRT commented Nov 20, 2011

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

@p5pRT p5pRT closed this as completed Nov 20, 2011
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