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Bug 563794 - dev-util/valgrind - sem_open uninitialized padding field: Syscall param write(buf) points to uninitialised byte
Summary: dev-util/valgrind - sem_open uninitialized padding field: Syscall param write...
Status: UNCONFIRMED
Alias: None
Product: Gentoo Linux
Classification: Unclassified
Component: [OLD] Development (show other bugs)
Hardware: AMD64 Linux
: Normal normal (vote)
Assignee: Anthony Basile
URL:
Whiteboard:
Keywords:
Depends on:
Blocks:
 
Reported: 2015-10-22 13:53 UTC by Török Edwin
Modified: 2015-10-23 15:17 UTC (History)
0 users

See Also:
Package list:
Runtime testing required: ---


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Description Török Edwin 2015-10-22 13:53:52 UTC
valgrind-3.11.0 with glibc 2.22-r1 shows a warning about uninitialized bytes when calling sem_open if the semaphore doesn't exist yet.

Reproducible: Always

Steps to Reproduce:
$ cat >x.c <<EOF
#include <fcntl.h>
#include <sys/stat.h>
#include <semaphore.h>
int main()
{
    sem_unlink("/test");
    sem_t *sem = sem_open("/test", O_CREAT, 0600, 1);
    if (!sem) {
        perror("sem_open");
        return 1;
    }
    sem_close(sem);
    return 0;
}
EOF
$ gcc x.c -o xtest -pthread
$ valgrind ./xtest
Actual Results:  
==7687== Syscall param write(buf) points to uninitialised byte(s)
==7687==    at 0x4E45F90: __write_nocancel (syscall-template.S:84)
==7687==    by 0x4E44F0C: sem_open (sem_open.c:255)
==7687==    by 0x400735: main (in /home/edwin/xtest)
==7687==  Address 0xfff0001fc is on thread 1's stack
==7687==  in frame #1, created by sem_open (sem_open.c:141)


Expected Results:  
No warnings

I have read sem_open.c source from glibc 2.22 (which is different from 2.19), and found that the 'pad' field in 'struct new_sem' is not initialized.
valgrind is right, but since it is a padding field this is probably harmless,
so by default this should probably be supressed:

From sem_open.c:
#if __HAVE_64B_ATOMICS
      sem.newsem.data = value;
#else
      sem.newsem.value = value << SEM_VALUE_SHIFT;
      sem.newsem.nwaiters = 0;
#endif
      /* This always is a shared semaphore.  */
      sem.newsem.private = FUTEX_SHARED;

      /* Initialize the remaining bytes as well.  */
      memset ((char *) &sem.initsem + sizeof (struct new_sem), '\0',
              sizeof (sem_t) - sizeof (struct new_sem));

Where:

struct new_sem
{
#if __HAVE_64B_ATOMICS
  /* The data field holds both value (in the least-significant 32 bytes) and
     nwaiters.  */
# if __BYTE_ORDER == __LITTLE_ENDIAN
#  define SEM_VALUE_OFFSET 0
# elif __BYTE_ORDER == __BIG_ENDIAN
#  define SEM_VALUE_OFFSET 1
# else
# error Unsupported byte order.
# endif
# define SEM_NWAITERS_SHIFT 32
# define SEM_VALUE_MASK (~(unsigned int)0)
  uint64_t data;
  int private;
  int pad;
#else
# define SEM_VALUE_SHIFT 1
# define SEM_NWAITERS_MASK ((unsigned int)1)
  unsigned int value;
  int private;
  int pad;
  unsigned int nwaiters;
#endif
};

emerge --info
Portage 2.2.23 (python 3.4.3-final-0, default/linux/amd64/13.0, gcc-4.9.3, glibc-2.22-r1, 4.0.5-gentoo x86_64)
=================================================================
System uname: Linux-4.0.5-gentoo-x86_64-AMD_Opteron_63xx_class_CPU-with-gentoo-2.2
KiB Mem:     5970092 total,   2510128 free
KiB Swap:     524284 total,    524284 free
Timestamp of repository gentoo: Thu, 22 Oct 2015 13:30:01 +0000
sh bash 4.3_p42
ld GNU ld (Gentoo 2.25.1 p1.1) 2.25.1
app-shells/bash:          4.3_p42::gentoo
dev-lang/perl:            5.22.0::gentoo
dev-lang/python:          2.7.10::gentoo, 3.4.3::gentoo
dev-util/cmake:           3.3.2-r1::gentoo
dev-util/pkgconfig:       0.29::gentoo
sys-apps/baselayout:      2.2::gentoo
sys-apps/openrc:          0.18.3::gentoo
sys-apps/sandbox:         2.9::gentoo
sys-devel/autoconf:       2.69-r1::gentoo
sys-devel/automake:       1.13.4::gentoo, 1.14.1::gentoo, 1.15::gentoo
sys-devel/binutils:       2.25.1-r1::gentoo
sys-devel/gcc:            4.9.3::gentoo
sys-devel/gcc-config:     1.8::gentoo
sys-devel/libtool:        2.4.6-r1::gentoo
sys-devel/make:           4.1-r1::gentoo
sys-kernel/linux-headers: 4.2::gentoo (virtual/os-headers)
sys-libs/glibc:           2.22-r1::gentoo
Repositories:

gentoo
    location: /usr/portage
    sync-type: rsync
    sync-uri: rsync://rsync.gentoo.org/gentoo-portage
    priority: -1000

ACCEPT_KEYWORDS="amd64 ~x86"
ACCEPT_LICENSE="* -@EULA"
CBUILD="x86_64-pc-linux-gnu"
CFLAGS="-O2 -pipe -ggdb -mno-bmi"
CHOST="x86_64-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/share/gnupg/qualified.txt"
CONFIG_PROTECT_MASK="/etc/ca-certificates.conf /etc/env.d /etc/gconf /etc/gentoo-release /etc/revdep-rebuild /etc/sandbox.d /etc/terminfo"
CXXFLAGS="-O2 -pipe -ggdb -mno-bmi"
DISTDIR="/usr/portage/distfiles"
FCFLAGS="-O2 -pipe"
FEATURES="assume-digests binpkg-logs config-protect-if-modified distlocks ebuild-locks fixlafiles merge-sync news parallel-fetch preserve-libs protect-owned sandbox sfperms splitdebug strict unknown-features-warn unmerge-logs unmerge-orphans userfetch userpriv usersandbox usersync xattr"
FFLAGS="-O2 -pipe"
GENTOO_MIRRORS="http://distfiles.gentoo.org"
LANG="en_US.utf8"
LDFLAGS="-Wl,-O1 -Wl,--as-needed"
MAKEOPTS="-j7"
PKGDIR="/usr/portage/packages"
PORTAGE_CONFIGROOT="/"
PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --omit-dir-times --compress --force --whole-file --delete --stats --human-readable --timeout=180 --exclude=/distfiles --exclude=/local --exclude=/packages"
PORTAGE_TMPDIR="/var/tmp"
USE="acl amd64 berkdb bindist bzip2 cli cracklib crypt cxx dri fortran gdbm iconv ipv6 mmx mmxext modules multilib ncurses nls nptl openmp pam pcre readline seccomp session sse sse2 ssl tcpd unicode xattr zlib" ABI_X86="64" ALSA_CARDS="ali5451 als4000 atiixp atiixp-modem bt87x ca0106 cmipci emu10k1x ens1370 ens1371 es1938 es1968 fm801 hda-intel intel8x0 intel8x0m maestro3 trident usb-audio via82xx via82xx-modem ymfpci" APACHE2_MODULES="authn_core authz_core socache_shmcb unixd actions alias auth_basic authn_alias authn_anon authn_dbm authn_default authn_file authz_dbm authz_default authz_groupfile authz_host authz_owner authz_user autoindex cache cgi cgid dav dav_fs dav_lock deflate dir disk_cache env expires ext_filter file_cache filter headers include info log_config logio mem_cache mime mime_magic negotiation rewrite setenvif speling status unique_id userdir usertrack vhost_alias" CALLIGRA_FEATURES="kexi words flow plan sheets stage tables krita karbon braindump author" CAMERAS="ptp2" COLLECTD_PLUGINS="df interface irq load memory rrdtool swap syslog" CPU_FLAGS_X86="aes mmx mmxext popcnt sse sse2 sse3 sse4_1 sse4_2 ssse3" ELIBC="glibc" GPSD_PROTOCOLS="ashtech aivdm earthmate evermore fv18 garmin garmintxt gpsclock itrax mtk3301 nmea ntrip navcom oceanserver oldstyle oncore rtcm104v2 rtcm104v3 sirf superstar2 timing tsip tripmate tnt ublox ubx" INPUT_DEVICES="keyboard mouse evdev" KERNEL="linux" LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb ncurses text" LIBREOFFICE_EXTENSIONS="presenter-console presenter-minimizer" OFFICE_IMPLEMENTATION="libreoffice" PHP_TARGETS="php5-5" PYTHON_SINGLE_TARGET="python2_7" PYTHON_TARGETS="python2_7 python3_4" RUBY_TARGETS="ruby20 ruby21" USERLAND="GNU" VIDEO_CARDS="fbdev glint intel mach64 mga nouveau nv r128 radeon savage sis tdfx trident vesa via vmware dummy v4l" XTABLES_ADDONS="quota2 psd pknock lscan length2 ipv4options ipset ipp2p iface geoip fuzzy condition tee tarpit sysrq steal rawnat logmark ipmark dhcpmac delude chaos account"
Unset:  CC, CPPFLAGS, CTARGET, CXX, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LC_ALL, PORTAGE_BUNZIP2_COMMAND, PORTAGE_COMPRESS, PORTAGE_COMPRESS_FLAGS, PORTAGE_RSYNC_EXTRA_OPTS, USE_PYTHON