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Loading Data::Dumper corrupts PL_sv_yes, or changes semantics of !0 at the least #12397

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p5pRT opened this issue Sep 11, 2012 · 7 comments
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@p5pRT
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@p5pRT p5pRT commented Sep 11, 2012

Migrated from rt.perl.org#114838 (status was 'resolved')

Searchable as RT114838$

@p5pRT
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@p5pRT p5pRT commented Sep 11, 2012

From @demerphq

Created by @demerphq

This is a bug report for perl from demerphq@​gmail.com,
generated with the help of perlbug 1.39 running under perl 5.17.4.

-----------------------------------------------------------------
Loading Data​::Dumper on thread enabled perls seems to change the meaning
of !0, possibly indicating that it corrupts PL_sv_yes.

The aritificially high REFCNT demonstrates that we get PL_sv_yes and
PL_sv_no as expected​:

$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -le'Dump(sub{ \@​_ }->(!1,
!0))' 2>&1 | grep "REFCNT"
  REFCNT = 1
  REFCNT = 1
  REFCNT = 2147483648
  REFCNT = 2147483645

Now we load Data​::Dumper first, and we see that the !0 case magically changes​:

$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -MData​::Dumper
-le'Dump(sub{ \@​_ }->(!1, !0))' 2>&1 | grep "REFCNT"
  REFCNT = 1
  REFCNT = 1
  REFCNT = 2147483648
  REFCNT = 2

A closer inspection of both​:
  REFCNT = 2147483645
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
vs
  REFCNT = 2
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)

Shows that other than the refcount and the fact that it is no longer
PL_sv_yes the
returned value is as expected. See
Sereal/Sereal@21a209e
for the test fail fix in Sereal which lead to this, inside Sereal we test for

sv == &PL_sv_yes

which stops happening if DD is loaded early.

Full Devel​::Peek output is here​:

$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -le'Dump(sub{ \@​_ }->(!1, !0))'
SV = IV(0x1126e80) at 0x1126e90
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x1146ce8
  SV = PVAV(0x1128c58) at 0x1146ce8
  REFCNT = 1
  FLAGS = ()
  ARRAY = 0x113ebc8
  FILL = 1
  MAX = 1
  ARYLEN = 0x0
  FLAGS = (REAL)
  Elt No. 0
  SV = PVNV(0x1125cb8) at 0x1124830
  REFCNT = 2147483648
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
  IV = 0
  NV = 0
  PV = 0x7f4105 ""
  CUR = 0
  LEN = 0
  Elt No. 1
  SV = PVNV(0x1125cd8) at 0x1124848
  REFCNT = 2147483645
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
  IV = 1
  NV = 1
  PV = 0x7f4103 "1"
  CUR = 1
  LEN = 0
$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -MData​::Dumper
-le'Dump(sub{ \@​_ }->(!1, !0))'
SV = IV(0x17d1e98) at 0x17d1ea8
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x17d1da0
  SV = PVAV(0x17d3c58) at 0x17d1da0
  REFCNT = 1
  FLAGS = ()
  ARRAY = 0x17e9c08
  FILL = 1
  MAX = 1
  ARYLEN = 0x0
  FLAGS = (REAL)
  Elt No. 0
  SV = PVNV(0x17d0cb8) at 0x17cf830
  REFCNT = 2147483648
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
  IV = 0
  NV = 0
  PV = 0x7f4105 ""
  CUR = 0
  LEN = 0
  Elt No. 1
  SV = PVNV(0x1a42478) at 0x17fff00
  REFCNT = 2
  FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
  IV = 1
  NV = 1
  PV = 0x19f3bc8 "1"\0
  CUR = 1
  LEN = 16

Perl Info

Flags:
    category=core
    severity=medium

Site configuration information for perl 5.17.4:

Configured by yorton at Tue Sep 11 10:59:05 CEST 2012.

Summary of my perl5 (revision 5 version 17 subversion 4) configuration:
  Commit id: 3eebda9adef018d9dd8bb23c07514da7a3e65b97
  Platform:
    osname=linux, osvers=3.0.0-12-generic, archname=x86_64-linux-thread-multi
    uname='linux yam 3.0.0-12-generic #20-ubuntu smp fri oct 7
14:56:25 utc 2011 x86_64 x86_64 x86_64 gnulinux '
    config_args='-Doptimize=-g -d -Dusedevel -Dusethreads
-Dprefix=~/bleadperl -Dcc=ccache gcc -Dld=gcc -DDEBUGGING'
    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='ccache gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBUGGING
-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include
-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-g',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBUGGING
-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.6.1', 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='gcc', ldflags =' -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /lib/x86_64-linux-gnu /lib/../lib
/usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib /usr/lib
    libs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.13'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -g -L/usr/local/lib
-fstack-protector'

Locally applied patches:



@INC for perl 5.17.4:
    /home/yorton/bleadperl/lib/site_perl/5.17.4/x86_64-linux-thread-multi
    /home/yorton/bleadperl/lib/site_perl/5.17.4
    /home/yorton/bleadperl/lib/5.17.4/x86_64-linux-thread-multi
    /home/yorton/bleadperl/lib/5.17.4
    .


Environment for perl 5.17.4:
    HOME=/home/yorton
    LANG=en_US.UTF-8
    LANGUAGE=en
    LC_COLLATE=en_US.UTF-8
    LC_CTYPE=en_US.UTF-8
    LC_MESSAGES=en_US.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/yorton/bin:/usr/lib/lightdm/lightdm:/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 p5pRT commented Sep 11, 2012

From @demerphq

On 11 September 2012 12​:09, yves orton <perlbug-followup@​perl.org> wrote​:

# New Ticket Created by yves orton
# Please include the string​: [perl #114838]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=114838 >

This is a bug report for perl from demerphq@​gmail.com,
generated with the help of perlbug 1.39 running under perl 5.17.4.

-----------------------------------------------------------------
Loading Data​::Dumper on thread enabled perls seems to change the meaning
of !0, possibly indicating that it corrupts PL_sv_yes.

The aritificially high REFCNT demonstrates that we get PL_sv_yes and
PL_sv_no as expected​:

$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -le'Dump(sub{ \@​_ }->(!1,
!0))' 2>&1 | grep "REFCNT"
REFCNT = 1
REFCNT = 1
REFCNT = 2147483648
REFCNT = 2147483645

Now we load Data​::Dumper first, and we see that the !0 case magically changes​:

$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -MData​::Dumper
-le'Dump(sub{ \@​_ }->(!1, !0))' 2>&1 | grep "REFCNT"
REFCNT = 1
REFCNT = 1
REFCNT = 2147483648
REFCNT = 2

A closer inspection of both​:
REFCNT = 2147483645
FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
vs
REFCNT = 2
FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)

Shows that other than the refcount and the fact that it is no longer
PL_sv_yes the
returned value is as expected. See
Sereal/Sereal@21a209e
for the test fail fix in Sereal which lead to this, inside Sereal we test for

sv == &PL_sv_yes

which stops happening if DD is loaded early.

Full Devel​::Peek output is here​:

$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -le'Dump(sub{ \@​_ }->(!1, !0))'
SV = IV(0x1126e80) at 0x1126e90
REFCNT = 1
FLAGS = (TEMP,ROK)
RV = 0x1146ce8
SV = PVAV(0x1128c58) at 0x1146ce8
REFCNT = 1
FLAGS = ()
ARRAY = 0x113ebc8
FILL = 1
MAX = 1
ARYLEN = 0x0
FLAGS = (REAL)
Elt No. 0
SV = PVNV(0x1125cb8) at 0x1124830
REFCNT = 2147483648
FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
IV = 0
NV = 0
PV = 0x7f4105 ""
CUR = 0
LEN = 0
Elt No. 1
SV = PVNV(0x1125cd8) at 0x1124848
REFCNT = 2147483645
FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
IV = 1
NV = 1
PV = 0x7f4103 "1"
CUR = 1
LEN = 0
$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -MData​::Dumper
-le'Dump(sub{ \@​_ }->(!1, !0))'
SV = IV(0x17d1e98) at 0x17d1ea8
REFCNT = 1
FLAGS = (TEMP,ROK)
RV = 0x17d1da0
SV = PVAV(0x17d3c58) at 0x17d1da0
REFCNT = 1
FLAGS = ()
ARRAY = 0x17e9c08
FILL = 1
MAX = 1
ARYLEN = 0x0
FLAGS = (REAL)
Elt No. 0
SV = PVNV(0x17d0cb8) at 0x17cf830
REFCNT = 2147483648
FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
IV = 0
NV = 0
PV = 0x7f4105 ""
CUR = 0
LEN = 0
Elt No. 1
SV = PVNV(0x1a42478) at 0x17fff00
REFCNT = 2
FLAGS = (PADTMP,IOK,NOK,POK,READONLY,pIOK,pNOK,pPOK)
IV = 1
NV = 1
PV = 0x19f3bc8 "1"\0
CUR = 1
LEN = 16

I can reduce this down further and eliminate Data​::Dumper​:

$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -le'BEGIN { Dump(sub{ \@​_
}->(!1, !0));} Dump(sub{ \@​_ }->(!1, !0));' 2>&1 | grep "REFCNT\|0x"
SV = IV(0x2870f10) at 0x2870f20
  REFCNT = 1
  RV = 0x2870080
  SV = PVAV(0x2844d20) at 0x2870080
  REFCNT = 1
  ARRAY = 0x288c068
  ARYLEN = 0x0
  SV = PVNV(0x2841cb8) at 0x2840830
  REFCNT = 2147483648
  PV = 0x7f4105 ""
  SV = PVNV(0x2841cd8) at 0x2840848
  REFCNT = 2147483645
  PV = 0x7f4103 "1"
SV = IV(0x2842e80) at 0x2842e90
  REFCNT = 1
  RV = 0x2870038
  SV = PVAV(0x2845810) at 0x2870038
  REFCNT = 1
  ARRAY = 0x285abf8
  ARYLEN = 0x0
  SV = PVNV(0x2842218) at 0x2862cb8
  REFCNT = 2
  PV = 0x2878e58 ""\0
  SV = PVNV(0x2842238) at 0x2842da0
  REFCNT = 2
  PV = 0x28779d8 "1"\0

I have no idea what is going on. This only happens under threads.

Cheers,
Yves

--
perl -Mre=debug -e "/just|another|perl|hacker/"

@p5pRT
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@p5pRT p5pRT commented Oct 9, 2012

From @cpansprout

On Tue Sep 11 03​:25​:41 2012, demerphq wrote​:

I can reduce this down further and eliminate Data​::Dumper​:

$ ~/bleadperl/bin/perl5.17.4 -MDevel​::Peek -le'BEGIN { Dump(sub{ \@​_
}->(!1, !0));} Dump(sub{ \@​_ }->(!1, !0));' 2>&1 | grep "REFCNT\|0x"
SV = IV(0x2870f10) at 0x2870f20
REFCNT = 1
RV = 0x2870080
SV = PVAV(0x2844d20) at 0x2870080
REFCNT = 1
ARRAY = 0x288c068
ARYLEN = 0x0
SV = PVNV(0x2841cb8) at 0x2840830
REFCNT = 2147483648
PV = 0x7f4105 ""
SV = PVNV(0x2841cd8) at 0x2840848
REFCNT = 2147483645
PV = 0x7f4103 "1"
SV = IV(0x2842e80) at 0x2842e90
REFCNT = 1
RV = 0x2870038
SV = PVAV(0x2845810) at 0x2870038
REFCNT = 1
ARRAY = 0x285abf8
ARYLEN = 0x0
SV = PVNV(0x2842218) at 0x2862cb8
REFCNT = 2
PV = 0x2878e58 ""\0
SV = PVNV(0x2842238) at 0x2842da0
REFCNT = 2
PV = 0x28779d8 "1"\0

I have no idea what is going on. This only happens under threads.

If you show the full Devel​::Peek output, you will see that the immortals
have the PADTMP flag set.

There is this awful piece of code in op.c​:S_finalize_op​:

  case OP_CONST​:
  if (cSVOPo->op_private & OPpCONST_STRICT)
  no_bareword_allowed(o);
  /* FALLTHROUGH */
#ifdef USE_ITHREADS
  case OP_HINTSEVAL​:
  case OP_METHOD_NAMED​:
  /* Relocate sv to the pad for thread safety.
  * Despite being a "constant", the SV is written to,
  * for reference counts, sv_upgrade() etc. */
  if (cSVOPo->op_sv) {
  const PADOFFSET ix = pad_alloc(OP_CONST, SVs_PADTMP);
  if (o->op_type != OP_METHOD_NAMED &&
  (SvPADTMP(cSVOPo->op_sv) || SvPADMY(cSVOPo->op_sv)))
  {
  /* If op_sv is already a PADTMP/MY then it is being used by
  * some pad, so make a copy. */
  sv_setsv(PAD_SVl(ix),cSVOPo->op_sv);
  SvREADONLY_on(PAD_SVl(ix));
  SvREFCNT_dec(cSVOPo->op_sv);
  }

See also
<https://rt-archive.perl.org/perl5/Ticket/Display.html?id=105906#txn-1048294>.
It’s basically the same bug.

--

Father Chrysostomos

@p5pRT
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@p5pRT p5pRT commented Oct 9, 2012

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

@p5pRT
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@p5pRT p5pRT commented Jul 26, 2013

From @cpansprout

Fixed in 82b84d0.

--

Father Chrysostomos

@p5pRT
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@p5pRT p5pRT commented Jul 26, 2013

From [Unknown Contact. See original ticket]

Fixed in 82b84d0.

--

Father Chrysostomos

@p5pRT
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@p5pRT p5pRT commented Jul 26, 2013

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

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