Undocumented unaligned pointer error messages #16154

p5pRT · 2017-09-17T16:46:56Z

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

Searchable as RT132112$

p5pRT · 2017-09-17T16:46:56Z

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 · 2017-09-17T16:46:56Z

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 · 2017-11-08T02:17:34Z

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 · 2017-11-08T02:17:34Z

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

p5pRT · 2017-11-08T03:40:05Z

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 · 2017-11-08T12:28:20Z

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 · 2017-11-08T12:28:20Z

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 · 2020-01-31T02:53:41Z

@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

p5pRT added the Severity Low label Oct 19, 2019

jkeenan added the hasPatch label Jan 31, 2020

xenu removed the Severity Low label Dec 29, 2021

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Undocumented unaligned pointer error messages #16154

Undocumented unaligned pointer error messages #16154

p5pRT commented Sep 17, 2017

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p5pRT commented Sep 17, 2017

p5pRT commented Nov 8, 2017

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p5pRT commented Nov 8, 2017

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jkeenan commented Jan 31, 2020

Undocumented unaligned pointer error messages #16154

Undocumented unaligned pointer error messages #16154

Comments

p5pRT commented Sep 17, 2017

p5pRT commented Sep 17, 2017

From @jkeenan

p5pRT commented Sep 17, 2017

From @jkeenan

p5pRT commented Nov 8, 2017

From @jkeenan

p5pRT commented Nov 8, 2017

p5pRT commented Nov 8, 2017

From @tonycoz

p5pRT commented Nov 8, 2017

From @jkeenan

p5pRT commented Nov 8, 2017

From @jkeenan

jkeenan commented Jan 31, 2020