Undocumented unaligned pointer error messages

[p5pRT]

Migrated from rt.perl.org#132112 (status was 'open')

Searchable as RT132112$

[p5pRT]

From @jkeenan

At lines 1313 and 1320 of malloc.c, there appear error messages which
are neither documented in pod/perldiag.pod nor (AFAICT) exercised in the
test suite.

  "Unaligned pointer in the free chain 0x%" UVxf "\n"

  "Unaligned \"next\" pointer in the free "
  "chain 0x%" UVxf " at 0x%" UVxf "\n",

#####
Malloc_t
Perl_malloc(size_t nbytes)
{
...
  /* remove from linked list */
#ifdef DEBUGGING
  if ( (PTR2UV(p) & (MEM_ALIGNBYTES - 1))
  /* Can't get this low */
  || (p && PTR2UV(p) < (1<<LOG_OF_MIN_ARENA)) ) {
  dTHX;
  PerlIO_printf(PerlIO_stderr(),
  "Unaligned pointer in the free chain 0x%" UVxf "\n",
  PTR2UV(p));
  }
  if ( (PTR2UV(p->ov_next) & (MEM_ALIGNBYTES - 1))
  || (p->ov_next && PTR2UV(p->ov_next) < (1<<LOG_OF_MIN_ARENA)) ) {
  dTHX;
  PerlIO_printf(PerlIO_stderr(),
  "Unaligned \"next\" pointer in the free "
  "chain 0x%" UVxf " at 0x%" UVxf "\n",
  PTR2UV(p->ov_next), PTR2UV(p));
  }
#endif
#####

How should they be documented?

Can they be exercised in the test suite?

Thank you very much.
Jim Keenan

[p5pRT]

From @jkeenan

Summary of my perl5 (revision 5 version 27 subversion 4) configuration​:
  Commit id​: e271727
  Platform​:
  osname=linux
  osvers=4.4.0-93-generic
  archname=x86_64-linux
  uname='linux zareason 4.4.0-93-generic #116-ubuntu smp fri aug 11 21​:17​:51 utc 2017 x86_64 x86_64 x86_64 gnulinux '
  config_args='-des -Dusedevel'
  hint=recommended
  useposix=true
  d_sigaction=define
  useithreads=undef
  usemultiplicity=undef
  use64bitint=define
  use64bitall=define
  uselongdouble=undef
  usemymalloc=n
  default_inc_excludes_dot=define
  bincompat5005=undef
  Compiler​:
  cc='cc'
  ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
  optimize='-O2'
  cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
  ccversion=''
  gccversion='5.4.0 20160609'
  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-strong -L/usr/local/lib'
  libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/5/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 /lib64 /usr/lib64
  libs=-lpthread -lnsl -ldb -ldl -lm -lcrypt -lutil -lc
  perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
  libc=libc-2.23.so
  so=so
  useshrplib=false
  libperl=libperl.a
  gnulibc_version='2.23'
  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-strong'

Characteristics of this binary (from libperl)​:
  Compile-time options​:
  HAS_TIMES
  PERLIO_LAYERS
  PERL_COPY_ON_WRITE
  PERL_DONT_CREATE_GVSV
  PERL_MALLOC_WRAP
  PERL_OP_PARENT
  PERL_PRESERVE_IVUV
  PERL_USE_DEVEL
  USE_64_BIT_ALL
  USE_64_BIT_INT
  USE_LARGE_FILES
  USE_LOCALE
  USE_LOCALE_COLLATE
  USE_LOCALE_CTYPE
  USE_LOCALE_NUMERIC
  USE_LOCALE_TIME
  USE_PERLIO
  USE_PERL_ATOF
  Built under linux
  Compiled at Sep 16 2017 10​:17​:33
  %ENV​:
  PERLBREW_BASHRC_VERSION="0.78"
  PERLBREW_HOME="/home/jkeenan/.perlbrew"
  PERLBREW_MANPATH="/home/jkeenan/perl5/perlbrew/perls/perl-5.26.0/man"
  PERLBREW_PATH="/home/jkeenan/perl5/perlbrew/bin​:/home/jkeenan/perl5/perlbrew/perls/perl-5.26.0/bin"
  PERLBREW_PERL="perl-5.26.0"
  PERLBREW_ROOT="/home/jkeenan/perl5/perlbrew"
  PERLBREW_VERSION="0.78"
  PERL_WORKDIR="/home/jkeenan/gitwork/perl"
  @​INC​:
  lib
  /usr/local/lib/perl5/site_perl/5.27.4/x86_64-linux
  /usr/local/lib/perl5/site_perl/5.27.4
  /usr/local/lib/perl5/5.27.4/x86_64-linux
  /usr/local/lib/perl5/5.27.4

[p5pRT]

From @jkeenan

On Sun, 17 Sep 2017 16​:46​:56 GMT, jkeenan@​pobox.com wrote​:

At lines 1313 and 1320 of malloc.c, there appear error messages which
are neither documented in pod/perldiag.pod nor (AFAICT) exercised in the
test suite.

           "Unaligned pointer in the free chain 0x%" UVxf "\\n"

           "Unaligned \\"next\\" pointer in the free "
           "chain 0x%" UVxf " at 0x%" UVxf "\\n"\,

#####
Malloc_t
Perl_malloc(size_t nbytes)
{
...
/* remove from linked list */
#ifdef DEBUGGING
if ( (PTR2UV(p) & (MEM_ALIGNBYTES - 1))
/* Can't get this low */
|| (p && PTR2UV(p) < (1<<LOG_OF_MIN_ARENA)) ) {
dTHX;
PerlIO_printf(PerlIO_stderr(),
"Unaligned pointer in the free chain 0x%" UVxf "\n",
PTR2UV(p));
}
if ( (PTR2UV(p->ov_next) & (MEM_ALIGNBYTES - 1))
|| (p->ov_next && PTR2UV(p->ov_next) < (1<<LOG_OF_MIN_ARENA)) ) {
dTHX;
PerlIO_printf(PerlIO_stderr(),
"Unaligned \"next\" pointer in the free "
"chain 0x%" UVxf " at 0x%" UVxf "\n",
PTR2UV(p->ov_next), PTR2UV(p));
}
#endif
#####

How should they be documented?

Can they be exercised in the test suite?

Can anyone comment on the questions above?

Thank you very much.

--
James E Keenan (jkeenan@​cpan.org)

[p5pRT]

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

[p5pRT]

From @tonycoz

On Sun, Sep 17, 2017 at 09​:46​:56AM -0700, James E Keenan wrote​:

# New Ticket Created by James E Keenan
# Please include the string​: [perl #132112]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=132112 >

At lines 1313 and 1320 of malloc.c, there appear error messages which
are neither documented in pod/perldiag.pod nor (AFAICT) exercised in the
test suite.

           "Unaligned pointer in the free chain 0x%" UVxf "\\n"

           "Unaligned \\"next\\" pointer in the free "
           "chain 0x%" UVxf " at 0x%" UVxf "\\n"\,

#####
Malloc_t
Perl_malloc(size_t nbytes)
{
...
/* remove from linked list */
#ifdef DEBUGGING
if ( (PTR2UV(p) & (MEM_ALIGNBYTES - 1))
/* Can't get this low */
|| (p && PTR2UV(p) < (1<<LOG_OF_MIN_ARENA)) ) {
dTHX;
PerlIO_printf(PerlIO_stderr(),
"Unaligned pointer in the free chain 0x%" UVxf "\n",
PTR2UV(p));
}
if ( (PTR2UV(p->ov_next) & (MEM_ALIGNBYTES - 1))
|| (p->ov_next && PTR2UV(p->ov_next) < (1<<LOG_OF_MIN_ARENA)) ) {
dTHX;
PerlIO_printf(PerlIO_stderr(),
"Unaligned \"next\" pointer in the free "
"chain 0x%" UVxf " at 0x%" UVxf "\n",
PTR2UV(p->ov_next), PTR2UV(p));
}
#endif
#####

How should they be documented?

We could add them to perldiag.

Can they be exercised in the test suite?

No. They depend on building with -Dusemymalloc *and* on the arena
being corrupted.

The first is unlikely, I don't know of any platform where we build
with -Dusemymalloc by default. The second indicates some other bug is
present.

Tony

[p5pRT]

From @jkeenan

On Wed, 08 Nov 2017 03​:40​:05 GMT, tonyc wrote​:

On Sun, Sep 17, 2017 at 09​:46​:56AM -0700, James E Keenan wrote​:

# New Ticket Created by James E Keenan
# Please include the string​: [perl #132112]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=132112 >

At lines 1313 and 1320 of malloc.c, there appear error messages which
are neither documented in pod/perldiag.pod nor (AFAICT) exercised in
the
test suite.

"Unaligned pointer in the free chain 0x%" UVxf "\n"

"Unaligned \"next\" pointer in the free "
"chain 0x%" UVxf " at 0x%" UVxf "\n",

#####
Malloc_t
Perl_malloc(size_t nbytes)
{
...
/* remove from linked list */
#ifdef DEBUGGING
if ( (PTR2UV(p) & (MEM_ALIGNBYTES - 1))
/* Can't get this low */
|| (p && PTR2UV(p) < (1<<LOG_OF_MIN_ARENA)) ) {
dTHX;
PerlIO_printf(PerlIO_stderr(),
"Unaligned pointer in the free chain 0x%" UVxf "\n",
PTR2UV(p));
}
if ( (PTR2UV(p->ov_next) & (MEM_ALIGNBYTES - 1))
|| (p->ov_next && PTR2UV(p->ov_next) <
(1<<LOG_OF_MIN_ARENA)) ) {
dTHX;
PerlIO_printf(PerlIO_stderr(),
"Unaligned \"next\" pointer in the free "
"chain 0x%" UVxf " at 0x%" UVxf "\n",
PTR2UV(p->ov_next), PTR2UV(p));
}
#endif
#####

How should they be documented?

We could add them to perldiag.

Can they be exercised in the test suite?

No. They depend on building with -Dusemymalloc *and* on the arena
being corrupted.

The first is unlikely, I don't know of any platform where we build
with -Dusemymalloc by default. The second indicates some other bug is
present.

Tony

Attached is a patch which passes 'make test_porting' but whose content needs improvement. Please review.

Thank you very much.

--
James E Keenan (jkeenan@​cpan.org)

[p5pRT]

From @jkeenan

132112-0001-Document-two-warnings-in-Perl_malloc.patch

From 5eb2b382fcac28cb8e656bba882bdae75f865955 Mon Sep 17 00:00:00 2001
From: James E Keenan <jkeenan@cpan.org>
Date: Wed, 8 Nov 2017 07:23:40 -0500
Subject: [PATCH] Document two warnings in Perl_malloc.

For: RT #132112
---
 pod/perldiag.pod | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 2cf2040..2eddf4c 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -6230,6 +6230,16 @@ certain type.  Arrays must be @NAME or C<@{EXPR}>.  Hashes must be
 (F) Your machine doesn't implement the umask function and you tried to
 use it to restrict permissions for yourself (EXPR & 0700).
 
+=item Unaligned "next" pointer in the free chain 0x% at 0x%
+
+(W malloc) In a perl built with C<-Dusemymalloc>, there was a problem when
+removing an item from a linked list.
+
+=item Unaligned pointer in the free chain 0x%
+
+(W malloc) In a perl built with C<-Dusemymalloc>, there was a problem when
+removing an item from a linked list.
+
 =item Unbalanced context: %d more PUSHes than POPs
 
 (S internal) The exit code detected an internal inconsistency in how
-- 
2.7.4

[jkeenan]

@iabyn @tonycoz Could you review the patch to pod/perldiag.pod I submitted for this ticket back in 2017?

Thank you very much.
Jim Keenan