*FH{IO} and $. scoping ickiness #1420

p5pRT · 2000-03-22T02:25:26Z

Migrated from rt.perl.org#2566 (status was 'open')

Searchable as RT2566$

p5pRT · 2000-03-22T02:25:26Z

From @simoncozens

othersideofthe:simon ~ % perl -wle 'my $a;
my $f=do { local *FH; open(FH,"/etc/passwd"); *FH; };
0 while <$f>; print $.'
48

othersideofthe:simon ~ % perl -wle 'my $a;
my $f=do { local *FH; open(FH,"/etc/passwd"); *FH{IO}; };
0 while <$f>; print $.'
Use of uninitialized value in print at -e line 1.

othersideofthe:simon ~ % perl -wle 'my $a;
my $f=do { local *FH; open(FH,"/etc/passwd"); *FH{IO}; };
$a=$. while <$f>; print $.'
48

Perl Info


Flags:
    category=core
    severity=low

Site configuration information for perl v5.6.0:

Configured by simon at Wed Mar 22 01:37:29 JST 2000.

Summary of my perl5 (revision 5.0 version 6 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.2.14, archname=i686-linux
    uname='linux othersideofthe.earth.li 2.2.14 #3 smp mon mar 13 02:10:19 jst 2000 i686 unknown '
    config_args='-d'
    hint=previous, useposix=true, d_sigaction=define
    usethreads=undef use5005threads=undef useithreads=undef usemultiplicity=undef
    useperlio=undef d_sfio=undef uselargefiles=define 
    use64bitint=undef use64bitall=undef uselongdouble=undef usesocks=undef
  Compiler:
    cc='cc', optimize='-g', gccversion=2.95.2 20000220 (Debian GNU/Linux)
    cppflags='-fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
    ccflags ='-fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
    stdchar='char', d_stdstdio=define, usevfork=false
    intsize=4, longsize=4, ptrsize=4, doublesize=8
    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, usemymalloc=n, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lnsl -lndbm -lgdbm -ldb -ldl -lm -lc -lposix -lcrypt
    libc=/lib/libc-2.1.3.so, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
    cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:
    v5.6.0-RC3


@INC for perl v5.6.0:
    /usr/local/lib/perl5/5.6.0/i686-linux
    /usr/local/lib/perl5/5.6.0
    /usr/local/lib/perl5/site_perl/5.6.0/i686-linux
    /usr/local/lib/perl5/site_perl/5.6.0
    /usr/local/lib/perl5/site_perl/5.5.670
    /usr/local/lib/perl5/site_perl
    .


Environment for perl v5.6.0:
    HOME=/home/simon
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/simon/bin:/bin:/usr/bin:/usr/X11R6/bin:/usr/rhs/bin:/usr/local/bin:/usr/local/sbin:/usr/sbin:/sbin:/opt/kde/bin:/home/simon/bin
    PERL_BADLANG (unset)
    SHELL=/bin/zsh

p5pRT · 2004-12-13T23:37:55Z

From @schwern

This appears to have gotten worse.

> othersideofthe:simon ~ % perl -wle 'my $a;
> my $f=do { local *FH; open(FH,"/etc/passwd"); *FH; };
> 0 while <$f>; print $.'
> 48

[~] perl5.6.2 -wle 'my $a;
my $f=do { local *FH; open(FH,"/etc/passwd"); *FH; };
0 while <$f>; print $.'
28
[~] perl5.8.6 -wle 'my $a;
my $f=do { local *FH; open(FH,"/etc/passwd"); *FH; };
0 while <$f>; print $.'
readline() on unopened filehandle FH at -e line 3.
0


> othersideofthe:simon ~ % perl -wle 'my $a;
> my $f=do { local *FH; open(FH,"/etc/passwd"); *FH{IO}; };
> 0 while <$f>; print $.'
> Use of uninitialized value in print at -e line 1.

[~] perl5.6.2 -wle 'my $a;
my $f=do { local *FH; open(FH,"/etc/passwd"); *FH{IO}; };
0 while <$f>; print $.'
Use of uninitialized value in print at -e line 3.

[~] perl5.8.6 -wle 'my $a;
my $f=do { local *FH; open(FH,"/etc/passwd"); *FH{IO}; };
0 while <$f>; print $.'
Use of uninitialized value in print at -e line 3.


> othersideofthe:simon ~ % perl -wle 'my $a;
> my $f=do { local *FH; open(FH,"/etc/passwd"); *FH{IO}; };
> $a=$. while <$f>; print $.'
> 48

[~] perl5.6.2 -wle 'my $a;
my $f=do { local *FH; open(FH,"/etc/passwd"); *FH{IO}; };
$a=$. while <$f>; print $.'
28
[~] perl5.8.6 -wle 'my $a;
my $f=do { local *FH; open(FH,"/etc/passwd"); *FH{IO}; };
$a=$. while <$f>; print $.'
28

p5pRT · 2020-01-17T23:34:16Z

@simoncozens, thank you for reporting Perl RT 2566. Your ticket has been moved to #1420

toddr · 2020-02-03T02:31:16Z

This appears to still be an issue on perl 5.30. $. is not set if you do <$f> where $f was assigned from *FH{IO}

Leont · 2020-02-03T14:49:59Z

This appears to still be an issue on perl 5.30. $. is not set if you do <$f> where $f was assigned from *FH{IO}

This can also be formulated as «$^LAST_FH is not set if you do <$f> where $f was an IO reference instead of a glob reference»

tonycoz · 2020-12-10T05:41:44Z

This appears to still be an issue on perl 5.30. $. is not set if you do <$f> where $f was assigned from *FH{IO}

This can also be formulated as $^LAST_FH is not set if you do <$f> where $f was an IO reference instead of a glob reference

It's not so much that it's not set, it's that it's set and then immediately cleared.

Each of the I/O ops either has a rv2gv generated for it (most) or calls rv2gv itself (readline), which for an IO ref create a mortal GV which is then assigned to PL_last_in_gv, on the next FREETMPS that's released and PL_last_in_gv is cleared (in Perl_sv_clear()).

It's always been possible to extract a reference to the IO SV from a glob, and use that for I/O, but such use would set PL_last_in_gv to a temporary GV which would almost immediately be released, clearing PL_last_in_gv. This would result in reads from $. returning its most recently read value (even from another handle) and modification being ignored, while ${^LAST_FH} would return undef, even though the file handle is still open. To fix this, store the underlying IO object as well as the GV. Retaining the GV lets errors continue to report the GV name where possible, while the IO object means $. and ${^LAST_FH} can still work if the IO object still exists. This does not try to fix the problem where localization can leave PL_last_in_gv (and now PL_last_in_io) pointing at a SV that has been destroyed, the original changes that introduced PL_last_in_gv didn't keep a reference count for the GV, since this would prevent the file being close automatically when the reference to to the glob went out of scope. Fixes Perl#1420

p5pRT added Severity Low distro-Linux needsTest type-core labels Oct 18, 2019

p5pRT mentioned this issue Oct 19, 2019

Program terminated with signal 11, Segmentation fault. #12469

Closed

tonycoz mentioned this issue Sep 14, 2021

perl: mg.c:1046: Perl_magic_get: Assertion `isGV_with_GP(PL_last_in_gv)' failed. #19124

Open

tonycoz linked a pull request Sep 14, 2021 that will close this issue

retain the last file handle even if it's an IO reference #19125

Draft

xenu removed affects-5.6 labels Nov 19, 2021

xenu removed the Severity Low label Dec 29, 2021

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*FH{IO} and $. scoping ickiness #1420

*FH{IO} and $. scoping ickiness #1420

p5pRT commented Mar 22, 2000

p5pRT commented Mar 22, 2000 •

edited by toddr

p5pRT commented Dec 13, 2004 •

edited by toddr

p5pRT commented Jan 17, 2020

toddr commented Feb 3, 2020

Leont commented Feb 3, 2020 •

edited

tonycoz commented Dec 10, 2020

*FH{IO} and $. scoping ickiness #1420

*FH{IO} and $. scoping ickiness #1420

Comments

p5pRT commented Mar 22, 2000

p5pRT commented Mar 22, 2000 • edited by toddr

From @simoncozens

p5pRT commented Dec 13, 2004 • edited by toddr

From @schwern

p5pRT commented Jan 17, 2020

toddr commented Feb 3, 2020

Leont commented Feb 3, 2020 • edited

tonycoz commented Dec 10, 2020

p5pRT commented Mar 22, 2000 •

edited by toddr

p5pRT commented Dec 13, 2004 •

edited by toddr

Leont commented Feb 3, 2020 •

edited