bug in fh pointers w/perlio on dup() #7017

p5pRT · 2004-01-05T23:15:43Z

Migrated from rt.perl.org#24818 (status was 'open')

Searchable as RT24818$

p5pRT · 2004-01-05T23:15:57Z

From stas@stason.org

Created by stas@stason.org

Consider the following short program:

# using Symbol to support older perls
use Symbol;
for (1..2) {
my $dup = Symbol::gensym();
open $dup, "<&DATA" or die "Can't dup DATA: $!";
print "DATA: " . tell(DATA) . "\n";
print "dup : " . tell($dup) . "\n";
#seek $dup, tell(DATA), 0; # rewind to the beginning
<$dup>;
}

__DATA__
foo
bar

w/o perlio we get:

DATA: 309
dup : 309
DATA: 318
dup : 318

the DATA fh pointer is correctly moved along with 'dup'
as per dup(2).

w/ perlio we get:

DATA: 309
dup : 309
DATA: 309
dup : 313

the DATA fh pointer is frozen and doesn't get moved to
the same pointer as the 'dup' fh.

as rgs quoted on irc:

<rgs> that's what my dup(2) manpage says
<rgs> "After successful return of dup or dup2, the old
and new descriptors may be used interchangeably."

and Nicolas has followed up:

<Nicholas> problem (presumably) is that duping by file
number means that the original file handle has buffered
data, while the new one does not. so underlying Unix fh
is not at the same file offset as the return from ftell
might lead you to think

This is observed with any perl 5.8.x

Perl Info


Flags:
     category=core
     severity=medium

Site configuration information for perl v5.8.1:

Configured by gb at Mon Sep  1 17:25:48 CEST 2003.

Summary of my perl5 (revision 5.0 version 8 subversion 1) configuration:
   Platform:
     osname=linux, osvers=2.4.18-23mdksmp, archname=i386-linux-thread-multi
     uname='linux hp6.mandrakesoft.com 2.4.18-23mdksmp #1 smp fri aug 2 
12:31:40 cest 2002 i686 unknown unknown gnulinux '
     config_args='-des -Dinc_version_list=5.8.0/i386-linux-thread-multi 5.8.0 
5.6.1 5.6.0 -Darchname=i386-linux -Dcc=gcc -Doptimize=-O2 -fomit-frame-pointer 
-pipe -march=i586 -mcpu=pentiumpro  -Dprefix=/usr -Dvendorprefix=/usr 
-Dsiteprefix=/usr -Dman3ext=3pm -Dcf_by=MandrakeSoft -Dmyhostname=localhost 
-Dperladmin=root@localhost -Dd_dosuid -Ud_csh -Duseshrplib -Dusethreads'
     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='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS 
-fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE 
-D_FILE_OFFSET_BITS=64 -I/usr/include/gdbm',
     optimize='-O2 -fomit-frame-pointer -pipe -march=i586 -mcpu=pentiumpro ',
     cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS 
-fno-strict-aliasing -I/usr/local/include -I/usr/include/gdbm'
     ccversion='', gccversion='3.3.1 (Mandrake Linux 9.2 3.3.1-1mdk)', 
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='gcc', ldflags =' -L/usr/local/lib'
     libpth=/usr/local/lib /lib /usr/lib
     libs=-lnsl -lndbm -lgdbm -ldl -lm -lcrypt -lutil -lpthread -lc
     perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
     libc=/lib/libc-2.3.2.so, so=so, useshrplib=true, libperl=libperl.so
     gnulibc_version='2.3.2'
   Dynamic Linking:
     dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic 
-Wl,-rpath,/usr/lib/perl5/5.8.1/i386-linux-thread-multi/CORE'
     cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:
     RC4


@INC for perl v5.8.1:
     /usr/lib/perl5/5.8.1/i386-linux-thread-multi
     /usr/lib/perl5/5.8.1
     /usr/lib/perl5/site_perl/5.8.1/i386-linux-thread-multi
     /usr/lib/perl5/site_perl/5.8.1
     /usr/lib/perl5/site_perl/5.8.0/i386-linux-thread-multi
     /usr/lib/perl5/site_perl/5.8.0
     /usr/lib/perl5/site_perl
     /usr/lib/perl5/vendor_perl/5.8.1/i386-linux-thread-multi
     /usr/lib/perl5/vendor_perl/5.8.1
     /usr/lib/perl5/vendor_perl/5.8.0/i386-linux-thread-multi
     /usr/lib/perl5/vendor_perl/5.8.0
     /usr/lib/perl5/vendor_perl
     .


Environment for perl v5.8.1:
     HOME=/home/stas
     LANG=en_GB
     LANGUAGE=en_GB:en
     LC_ADDRESS=en_CA
     LC_COLLATE=en_GB
     LC_CTYPE=en_GB
     LC_IDENTIFICATION=en_CA
     LC_MEASUREMENT=en_CA
     LC_MESSAGES=en_GB
     LC_MONETARY=en_CA
     LC_NAME=en_CA
     LC_NUMERIC=en_CA
     LC_PAPER=en_CA
     LC_TELEPHONE=en_CA
     LC_TIME=en_GB
     LD_LIBRARY_PATH (unset)
     LOGDIR (unset)
 
PATH=/usr//bin:/bin:/usr/bin:.:/usr/local/bin:/usr/X11R6/bin:/usr/games:/home/stas/bin:/home/stas/bin:/usr/local/bin:/usr/X11R6/bin:/usr/java/j2re1.4.0/bin/
     PERLDOC_PAGER=less -R
     PERL_BADLANG (unset)
     SHELL=/bin/tcsh

__________________________________________________________________
Stas Bekman            JAm_pH ------> Just Another mod_perl Hacker
http://stason.org/     mod_perl Guide ---> http://perl.apache.org
mailto:stas@stason.org http://use.perl.org http://apacheweek.com
http://modperlbook.org http://apache.org   http://ticketmaster.com

p5pRT · 2005-04-08T17:35:18Z

From @smpeters

[stas - Mon Jan 05 15:15:57 2004]:

This is a bug report for perl from stas@stason.org,
generated with the help of perlbug 1.34 running under perl v5.8.1.

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

Consider the following short program:

# using Symbol to support older perls
use Symbol;
for (1..2) {
my $dup = Symbol::gensym();
open $dup, "<&DATA" or die "Can't dup DATA: $!";
print "DATA: " . tell(DATA) . "\n";
print "dup : " . tell($dup) . "\n";
#seek $dup, tell(DATA), 0; # rewind to the beginning
<$dup>;
}

__DATA__
foo
bar

w/o perlio we get:

DATA: 309
dup : 309
DATA: 318
dup : 318

the DATA fh pointer is correctly moved along with 'dup'
as per dup(2).

w/ perlio we get:

DATA: 309
dup : 309
DATA: 309
dup : 313

the DATA fh pointer is frozen and doesn't get moved to
the same pointer as the 'dup' fh.

as rgs quoted on irc:

<rgs> that's what my dup(2) manpage says
<rgs> "After successful return of dup or dup2, the old
and new descriptors may be used interchangeably."

and Nicolas has followed up:

<Nicholas> problem (presumably) is that duping by file
number means that the original file handle has buffered
data, while the new one does not. so underlying Unix fh
is not at the same file offset as the return from ftell
might lead you to think

This is observed with any perl 5.8.x

I wondering if either case you have above is correct. On Linux, I see
the following...

steve@kirk:~$ PERLIO=:stdio perl rt_24818.pl
DATA: 279
dup : 287
DATA: 279
dup : 287
steve@kirk:~$ PERLIO=:perlio perl rt_24818.pl
DATA: 279
dup : 279
DATA: 279
dup : 283

According to dup(2), each file descriptor should be unique, so the
handling by :stdio seems to be fine.

Looking at the PERLIO_DEBUG output, one thing sticks out, but I don't
know if it is incorrect. It appears that the :unix layer is sending the
wrong parameters to PerlIOBase_dup.

For example, with :stdio
PerlIOBase_dup stdio f=3c00e214 o=3c00e210 param=0

with :perlio
PerlIOBase_dup perlio f=3c00e214 o=3c00e210 param=0

with :mmap
PerlIOBase_dup mmap f=3c00e214 o=3c00e210 param=0

with :unix
PerlIOBase_dup unix f=3c00e214 o=3c00c980 param=0

On :unix, the address of the original filehandle is not getting sent in.
Maybe this is a bug, maybe not. It is something to look into further
though.

p5pRT · 2005-04-08T17:35:20Z

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

p5pRT · 2005-04-08T17:45:12Z

From stas@stason.org

Steve Peters via RT wrote:

[stas - Mon Jan 05 15:15:57 2004]:

This is a bug report for perl from stas@stason.org,
generated with the help of perlbug 1.34 running under perl v5.8.1.

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

Consider the following short program:

# using Symbol to support older perls
use Symbol;
for (1..2) {
my $dup = Symbol::gensym();
open $dup, "<&DATA" or die "Can't dup DATA: $!";
print "DATA: " . tell(DATA) . "\n";
print "dup : " . tell($dup) . "\n";
#seek $dup, tell(DATA), 0; # rewind to the beginning
<$dup>;
}

__DATA__
foo
bar

w/o perlio we get:

DATA: 309
dup : 309
DATA: 318
dup : 318

the DATA fh pointer is correctly moved along with 'dup'
as per dup(2).

w/ perlio we get:

DATA: 309
dup : 309
DATA: 309
dup : 313

the DATA fh pointer is frozen and doesn't get moved to
the same pointer as the 'dup' fh.

as rgs quoted on irc:

<rgs> that's what my dup(2) manpage says
<rgs> "After successful return of dup or dup2, the old
and new descriptors may be used interchangeably."

and Nicolas has followed up:

<Nicholas> problem (presumably) is that duping by file
number means that the original file handle has buffered
data, while the new one does not. so underlying Unix fh
is not at the same file offset as the return from ftell
might lead you to think

This is observed with any perl 5.8.x

I wondering if either case you have above is correct. On Linux, I see
the following...

steve@kirk:~$ PERLIO=:stdio perl rt_24818.pl
DATA: 279
dup : 287
DATA: 279
dup : 287

I get the same with PERLIO=:stdio as you do, Steve. The w/o perlio test was with perl that had no perlio enabed. Here it is again:

/tmp> env PERLIO=:perlio perl-5.8.6-ithread xxx
DATA: 277
dup : 277
DATA: 277
dup : 281
/tmp> env PERLIO=:stdio perl-5.8.6-ithread xxx
DATA: 277
dup : 285
DATA: 277
dup : 285
/tmp> perl-5.8.6-nouseperlio xxx
DATA: 277
dup : 277
DATA: 285
dup : 285

--
__________________________________________________________________
Stas Bekman JAm_pH ------> Just Another mod_perl Hacker
http://stason.org/ mod_perl Guide ---> http://perl.apache.org
mailto:stas@stason.org http://use.perl.org http://apacheweek.com
http://modperlbook.org http://apache.org http://ticketmaster.com

p5pRT added Severity Medium distro-Linux type-PerlIO type-core labels Oct 18, 2019

xenu removed the affects-5.8 label Nov 19, 2021

xenu removed the Severity Medium label Dec 15, 2021

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bug in fh pointers w/perlio on dup() #7017

bug in fh pointers w/perlio on dup() #7017

p5pRT commented Jan 5, 2004

p5pRT commented Jan 5, 2004

p5pRT commented Apr 8, 2005

p5pRT commented Apr 8, 2005

p5pRT commented Apr 8, 2005

bug in fh pointers w/perlio on dup() #7017

bug in fh pointers w/perlio on dup() #7017

Comments

p5pRT commented Jan 5, 2004

p5pRT commented Jan 5, 2004

From stas@stason.org

Created by stas@stason.org

p5pRT commented Apr 8, 2005

From @smpeters

p5pRT commented Apr 8, 2005

p5pRT commented Apr 8, 2005

From stas@stason.org