Unexpected: Use of freed value in iteration at ...

[p5pRT]

Migrated from rt.perl.org#128634 (status was 'open')

Searchable as RT128634$

[p5pRT]

From @KES777

Created by @KES777

$ cat example.pl
my $hash = { a => {}, b => {} };
for my $value ( values %$hash ) {
  delete $hash->{ b };
  print $value; #<<<<< Use of freed value in iteration at ...
}

$ perl example.pl
Use of freed value in iteration at iter_free line 4.
HASH(0x1590178)
$ perl example.pl
HASH(0x17e6d38)HASH(0x17d1178)

That is not expected to get different behavior for two runs

Maybe related to​:
https://rt.perl.org/Public/Bug/Display.html?id=85026 which was closed as of 5.14.1
https://metacpan.org/pod/distribution/perl/pod/perl5141delta.pod#Bug-Fixes
* A bug has been fixed that would cause a "Use of freed value in iteration"
  error if the next two hash elements that would be iterated over are deleted. [perl #85026]

https://rt.perl.org/Public/Bug/Display.html?id=89548
https://rt.perl.org/Public/Bug/Display.html?id=77706

Perl Info

Flags:
    category=core
    severity=low

Site configuration information for perl 5.25.1:

Configured by kes at Sun Jun  5 17:16:28 EEST 2016.

Summary of my perl5 (revision 5 version 25 subversion 1) configuration:
   
  Platform:
    osname=linux, osvers=3.13.0-37-generic, archname=x86_64-linux
    uname='linux keswork 3.13.0-37-generic #64-ubuntu smp mon sep 22 21:28:38 utc 2014 x86_64 x86_64 x86_64 gnulinux '
    config_args='-de -Dprefix=/home/kes/perl5/perlbrew/perls/perl-5.25.1 -Dusedevel -Aeval:scriptdir=/home/kes/perl5/perlbrew/perls/perl-5.25.1/bin'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.8.4', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678, doublekind=3
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16, longdblkind=3
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.8/include-fixed /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
    libs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.19.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.19'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector'

Locally applied patches:
    Devel::PatchPerl 1.38


@INC for perl 5.25.1:
    /home/kes/perl5/perlbrew/perls/perl-5.25.1/lib/site_perl/5.25.1/x86_64-linux
    /home/kes/perl5/perlbrew/perls/perl-5.25.1/lib/site_perl/5.25.1
    /home/kes/perl5/perlbrew/perls/perl-5.25.1/lib/5.25.1/x86_64-linux
    /home/kes/perl5/perlbrew/perls/perl-5.25.1/lib/5.25.1
    .


Environment for perl 5.25.1:
    HOME=/home/kes
    LANG=ru_UA.UTF-8
    LANGUAGE=en
    LC_MESSAGES=en_US.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/kes/perl5/perlbrew/bin:/home/kes/perl5/perlbrew/perls/perl-5.25.1/bin:/home/kes/perl5/bin:/home/kes/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
    PERLBREW=command perlbrew
    PERLBREW_BASHRC_VERSION=0.75
    PERLBREW_HOME=/home/kes/.perlbrew
    PERLBREW_MANPATH=/home/kes/perl5/perlbrew/perls/perl-5.25.1/man
    PERLBREW_PATH=/home/kes/perl5/perlbrew/bin:/home/kes/perl5/perlbrew/perls/perl-5.25.1/bin
    PERLBREW_PERL=perl-5.25.1
    PERLBREW_ROOT=/home/kes/perl5/perlbrew
    PERLBREW_VERSION=0.75
    PERL_BADLANG (unset)
    SHELL=/bin/bash

[p5pRT]

From @cpansprout

On Sat Jul 16 10​:00​:14 2016, kes-kes@​yandex.ru wrote​:

$ cat example.pl
my $hash = { a => {}, b => {} };
for my $value ( values %$hash ) {
delete $hash->{ b };
print $value; #<<<<< Use of freed value in iteration at ...
}

$ perl example.pl
Use of freed value in iteration at iter_free line 4.
HASH(0x1590178)
$ perl example.pl
HASH(0x17e6d38)HASH(0x17d1178)

That is not expected to get different behavior for two runs

Maybe related to​:
https://rt.perl.org/Public/Bug/Display.html?id=85026 which was closed
as of 5.14.1
https://metacpan.org/pod/distribution/perl/pod/perl5141delta.pod#Bug-
Fixes
* A bug has been fixed that would cause a "Use of freed value in
iteration"
error if the next two hash elements that would be iterated over are
deleted. [perl #85026]

No, it’s not related to that.

https://rt.perl.org/Public/Bug/Display.html?id=89548
https://rt.perl.org/Public/Bug/Display.html?id=77706

That’s exactly it. The stack holds no reference counts and ‘delete $hash->{b}’ frees one of the return values of ‘values’ which is on the stack on items that ‘for’ is iterating through.

--

Father Chrysostomos

[p5pRT]

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