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binfmt_misc

The term binfmt_misc describes a capability of the Linux kernel which allows arbitrary executable file formats to be recognized and passed to certain user space applications, such as emulators and virtual machines.

Explanation

The executable formats are registered through a special purpose file system interface (similar to /proc). Your kernel must be configured with “CONFIG_BINFMT_MISC” built-in or as a module.
The “register” file contains lines in a specific format:

:name:type:offset:magic:mask:interpreter:
  • name is the name of the binary format.
  • type is either E or M
    • If it is E, the executable file format is identified by its filename extension: magic is the file extension to be associated with the binary format; offset and mask are ignored.
    • If it is M, the format is identified by magic number at an absolute offset in the file and mask is a bitmask indicating which bits in the number are significant.
  • interpreter is a program that is to be run with the matching file as an argument.

Preparation

Before attempting to register a program emulator like wine or qemu with the kernel as an interpreter, you have to ensure that the binfmt_misc filesystem is mounted and ready.
Add the following line to “/etc/fstab” in order to mount the special filesystem:

none /proc/sys/fs/binfmt_misc binfmt_misc defaults 0 0

You may have to uncomment the line below in “/etc/rc.d/rc.modules”:

# /sbin/modprobe binfmt_misc

Then use lines like the one below to register a new binary file format. The examples here allow you to start MS Windows binaries more easily, but the interesting bit is the ARM binary file format. You should be able to use this setup to create a chroot installation of ARMedslack on a x86 or x86_64 host computer, and then run something like

chroot /path/to/arm_filesystem_root /bin/bash

to enter an emulated ARM filesystem without being bothered by qemu commandlines.

Typically, the following lines should be placed in the local boot initialization script “/etc/rc.d/rc.local” because the binary formats and their userspace interpreters have to be re-registered at every boot:

# Support for Windows binaries through Wine:
{ echo ':DOSWin:M::MZ::/usr/bin/wine:' > /proc/sys/fs/binfmt_misc/register; } 2>/dev/null

# Support for ARM binaries through Qemu:
{ echo ':arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/usr/bin/qemu-arm-static:' > /proc/sys/fs/binfmt_misc/register; } 2>/dev/null
{ echo ':armeb:M::\x7fELF\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff:/usr/bin/qemu-armeb-static:' > /proc/sys/fs/binfmt_misc/register; } 2>/dev/null

The case of qemu as interpreter of ARM binaries is a bit special. It requires that you use a statically compiled version of qemu's ARM userspace emulation. The qemu-arm executable must not depend on any dynamic linking of host libraries - when the kernel starts it, it will find itself in an environment of nothing but ARM binary code.

When registering a new binary format with the kernel, it will create a file in “/proc/sys/fs/binfmt_misc/” with human-readable details for the format you just registered.

Execution

Once a binary file format has been registered like this, you no longer have to start a program with this format by first starting its emulator. It can now be started directly. For example,

wine ~/.wine/dosdevices/c\:/windows/notepad.exe

is no longer required; it is enough to run

~/.wine/dosdevices/c\:/windows/notepad.exe

If you add the Wine directories to your $PATH then you could even suffice with typing “notepad.exe”.

Appendix

Here is a qemu.SlackBuild script which is able to build the static binary you need for ARM emulation through binfmt_misc.

#!/bin/sh
# $Id: qemu-static.SlackBuild,v 1.1 2012/02/20 16:28:29 root Exp root $
# Copyright 2007, 2008, 2009, 2010, 2012  Eric Hameleers, Eindhoven, Netherlands
# All rights reserved.
#
#   Permission to use, copy, modify, and distribute this software for
#   any purpose with or without fee is hereby granted, provided that
#   the above copyright notice and this permission notice appear in all
#   copies.
#
#   THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
#   WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
#   MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
#   IN NO EVENT SHALL THE AUTHORS AND COPYRIGHT HOLDERS AND THEIR
#   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
#   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
#   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
#   USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
#   ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
#   OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
#   OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
#   SUCH DAMAGE.
# -----------------------------------------------------------------------------
#
# Slackware SlackBuild script 
# ===========================
# By:        Eric Hameleers <alien@slackware.com>
# For:       qemu
# Descr:     a generic machine emulator and virtualizer
# URL:       http://qemu.org/
# Needs:     
# Changelog:
# 1.0.1-1:    18/feb/2012 by Eric Hameleers <alien@slackware.com>
#             * After another long hiatus, let's pick up this build...
#               once more. This time to complement my qemu-kvm package which
#               I limited to KVM supported architecture exclusively.
# 
# Run 'sh qemu.SlackBuild' to build a Slackware package.
# The package (.tgz) plus descriptive .txt file are created in /tmp .
# Install using 'installpkg'. 
#
# -----------------------------------------------------------------------------
 
# Set initial variables:
 
PRGNAM=qemu
PRGNAM2=qemu-static
VERSION=${VERSION:-"1.0.1"}
GLIB=${GLIB:-"2.28.8"}
BUILD=${BUILD:-1}
NUMJOBS=${NUMJOBS:" -j4 "}
TAG=${TAG:-alien}
 
# If you also want static binaries for user emulation, set BUILD_STATIC=YES
# This will create a second package "qemu-static" with user emulation binaries.
# NOTE:
# This fails with the glibc 1.13 of Slackware 13.37 !
# The static compilation pulls in the glib-2.0 libraries; since Slackware does
# not include static versions of these, we will have to build them now:
BUILD_STATIC=${BUILD_STATIC:-YES}
 
# The documentation:
DOCS="CODING_STYLE COPYING* Changelog LICENSE MAINTAINERS README* TODO VERSION"
 
# Where do we look for sources?
SRCDIR=$(cd $(dirname $0); pwd)
 
# Place to build (TMP) package (PKG) and output (OUTPUT) the program:
TMP=${TMP:-/tmp/build}
PKG=$TMP/package-$PRGNAM
PKG2=$TMP/package-${PRGNAM2}
PKGGLIB=$TMP/package-glib_static
OUTPUT=${OUTPUT:-/tmp}
 
SOURCE[0]="$SRCDIR/${PRGNAM}-${VERSION}.tar.gz"
SRCURL[0]="http://wiki.qemu.org/download/${PRGNAM}-${VERSION}.tar.gz"
USE[0]="YES"
 
SOURCE[1]="$SRCDIR/glib-${GLIB}.tar.xz"
SRCURL[1]="http://ftp.gnome.org/pub/GNOME/sources/glib/$(echo $GLIB |cut -d. -f1,2)/glib-${GLIB}.tar.xz"
USE[1]="$BUILD_STATIC"
 
##
## --- with a little luck, you won't have to edit below this point --- ##
##
 
# Automatically determine the architecture we're building on:
MARCH=$( uname -m )
if [ -z "$ARCH" ]; then
  case "$MARCH" in
    i?86)    export ARCH=i486 ;;
    armv7hl) export ARCH=$MARCH ;;
    arm*)    export ARCH=arm ;;
    # Unless $ARCH is already set, use uname -m for all other archs:
    *)       export ARCH=$MARCH ;;
  esac
fi
 
case "$ARCH" in
  i486)      SLKCFLAGS="-O2 -march=i486 -mtune=i686"
             SLKLDFLAGS=""; LIBDIRSUFFIX=""
             ;;
  x86_64)    SLKCFLAGS="-O2 -fPIC"
             SLKLDFLAGS="-L/usr/lib64"; LIBDIRSUFFIX="64"
             ;;
  armv7hl)   SLKCFLAGS="-O2 -march=armv7-a -mfpu=vfpv3-d16"
             SLKLDFLAGS=""; LIBDIRSUFFIX=""
             ;;
  *)         SLKCFLAGS="-O2"
             SLKLDFLAGS=""; LIBDIRSUFFIX=""
             ;;
esac
 
# Exit the script on errors:
set -e
trap 'echo "$0 FAILED at line $LINENO!" | tee $OUTPUT/error-${PRGNAM}.log' ERR
# Catch unitialized variables:
set -u
P1=${1:-1}
 
# Save old umask and set to 0022:
_UMASK_=$(umask)
umask 0022
 
# Create working directories:
mkdir -p $OUTPUT          # place for the package to be saved
mkdir -p $TMP/tmp-$PRGNAM # location to build the source
mkdir -p $PKG             # place for the package to be built
rm -rf $PKG/*             # always erase old package's contents
rm -rf $TMP/tmp-$PRGNAM/* # remove the remnants of previous build
rm -rf $OUTPUT/{configure,make,install,error,makepkg}-$PRGNAM.log
                          # remove old log files
 
# Source file availability:
for (( i = 0; i < ${#SOURCE[*]}; i++ )) ; do
  [ "${USE[$i]}" != "YES" ] && continue
  if ! [ -f ${SOURCE[$i]} ]; then
    echo "Source '$(basename ${SOURCE[$i]})' not available yet..."
    # Check if the $SRCDIR is writable at all - if not, download to $OUTPUT
    [ -w "$SRCDIR" ] || SOURCE[$i]="$OUTPUT/$(basename ${SOURCE[$i]})"
    if [ -f ${SOURCE[$i]} ]; then echo "Ah, found it!"; continue; fi
    if ! [ "x${SRCURL[$i]}" == "x" ]; then
      echo "Will download file to $(dirname $SOURCE[$i])"
      wget -nv -T 20 -O "${SOURCE[$i]}" "${SRCURL[$i]}" || true
      if [ $? -ne 0 -o ! -s "${SOURCE[$i]}" ]; then
        echo "Fail to download '$(basename ${SOURCE[$i]})'. Aborting the build."
        mv -f "${SOURCE[$i]}" "${SOURCE[$i]}".FAIL
        exit 1
      fi
    else
      echo "File '$(basename ${SOURCE[$i]})' not available. Aborting the build."
      exit 1
    fi
  fi
done
 
if [ "$P1" == "--download" ]; then
  echo "Download complete."
  exit 0
fi
 
# --- PACKAGE BUILDING ---
 
echo "++"
echo "|| $PRGNAM-$VERSION"
echo "++"
 
cd $TMP/tmp-$PRGNAM
echo "Extracting the source archive(s) for $PRGNAM..."
tar -xvf ${SOURCE[0]}
cd ${PRGNAM}-${VERSION}
chown -R root:root .
chmod -R u+w,go+r-w,a+X-s .
 
echo Building ...
 
# Compensate for users who forgot to run "su -":
if ! which texi2html 1>/dev/null 2>/dev/null ; then
  export PATH=$PATH:/usr/share/texmf/bin
fi
 
# The SlackBuild needs VDE, so abort if it was not installed:
if ! pkg-config --exists vdeplug ; then
  echo -e "**\n** VDE is not installed! Please install it first!\n**"
  exit 1
fi
 
function qemuconfigure () {
 
  # If you do not care for all the exotic target platforms, then you can add
  # a subset of targets to the 'configure' block below. For instance,
  # to only build x86_64 and arm targets, change this line:
  # --target-list="" \
  # to:
  # --target-list=x86_64-softmmu,x86_64-linux-user,arm-softmmu,arm-linux-user \
 
  ./configure \
    --prefix=/usr \
    --sysconfdir=/etc \
    --mandir=/usr/man \
    --datadir=/usr/share/$PRGNAM \
    --docdir=/usr/doc/$PRGNAM-$VERSION \
    --enable-linux-user \
    $*
}
 
# First configure the usual non-static build including ALSA and SDL support:
echo -e "**\n** making dynamic...\n**"
export LDFLAGS="$SLKLDFLAGS"
export CFLAGS="$SLKCFLAGS"
export CXXFLAGS="$SLKCFLAGS"
qemuconfigure \
  --enable-system \
  --target-list="" \
  --audio-drv-list=alsa,oss,sdl,esd \
  --audio-card-list=ac97,es1370,sb16,cs4231a,adlib,gus \
  --enable-mixemu \
  --enable-vde \
  2>&1 | tee $OUTPUT/configure-${PRGNAM}.log
 
# Compile and install into $PKG:
make $NUMJOBS OS_CFLAGS="$SLKCFLAGS" \
  2>&1 | tee $OUTPUT/make-${PRGNAM}.log
make OS_CFLAGS="$SLKCFLAGS" DESTDIR=$PKG install \
  2>&1 |tee $OUTPUT/install-${PRGNAM}.log
 
if [ "$BUILD_STATIC" = "YES" ]; then
 
  # Clean up for the next step:
  echo -e "**\n** making clean...\n**"
  make clean
 
  # Next, configure a static build - here we target non-PC architectures only.
  # The static binaries can be used in a chroot on the host system:
  echo -e "**\n** making static...\n**"
 
  ( # Build a static glib-2.0:
 
    # Remove the remnants of previous build:
    rm -rf $PKG2 $PKGGLIB 
    mkdir -p $PKG2 $PKGGLIB 
 
    cd $TMP/tmp-$PRGNAM
    echo "Extracting the source archive(s) for glib..."
    tar -xvf ${SOURCE[1]}
    cd glib-$GLIB
    chown -R root:root .
    chmod -R u+w,go+r-w,a+X-s .
    CFLAGS="$SLKCFLAGS" \
    ./configure \
      --prefix=/usr \
      --libdir=/usr/lib${LIBDIRSUFFIX} \
      --sysconfdir=/etc \
      --mandir=/usr/man \
      --disable-dynamic \
      --enable-static \
      --build=$ARCH-slackware-linux \
      2>&1 | tee $OUTPUT/configure_static-${PRGNAM}_glib.log
 
    # Compile glib and install the static library in a temporary location
    # where qemu can pick it up:
    make $NUMJOBS \
      2>&1 | tee $OUTPUT/make_static-${PRGNAM}_glib.log
    make install DESTDIR=$PKGGLIB \
      2>&1 | tee $OUTPUT/install_static-${PRGNAM}_glib.log
  )
 
  export CFLAGS="-I$PKGGLIB/usr/include $SLKCFLAGS"
  export CXXFLAGS="-I$PKGGLIB/usr/include $SLKCFLAGS"
  export LDFLAGS="-L$PKGGLIB/usr/lib${LIBDIRSUFFIX} $SLKLDFLAGS"
  export PKG_CONFIG_PATH="$PKGGLIB/usr/lib${LIBDIRSUFFIX}/pkgconfig"
 
  qemuconfigure \
    --disable-system \
    --disable-curses \
    --disable-sdl \
    --disable-bluez \
    --disable-docs \
    --disable-guest-agent \
    --disable-kvm \
    --disable-vde \
    --disable-smartcard \
    --disable-smartcard-nss \
    --disable-vnc \
    --static \
    2>&1 | tee $OUTPUT/configure_static-${PRGNAM}.log
 
  # Compile and install into $PKG2:
  make $NUMJOBS OS_CFLAGS="$SLKCFLAGS" \
    2>&1 | tee $OUTPUT/make_static-${PRGNAM}.log
  make OS_CFLAGS="$SLKCFLAGS" DESTDIR=$PKG2 install \
    2>&1 |tee $OUTPUT/install_static-${PRGNAM}.log
 
  # Rename the binaries so that they do not clash with the dynamic binaries:
  for FILE in $PKG2/usr/bin/* ; do
    mv $FILE ${FILE}-static
  done
 
  # The user mode emulators do no need these bios/keymap files:
  rm -rf $PKG2/usr/share/$PRGNAM
  rmdir $PKG2/usr/share 2>/dev/null || true
 
  # Add documentation:
  mkdir -p $PKG2/usr/doc/$PRGNAM2-$VERSION
  cp -a $DOCS $PKG2/usr/doc/$PRGNAM2-$VERSION || true
  cat $SRCDIR/$(basename $0) \
    > $PKG2/usr/doc/$PRGNAM2-$VERSION/$PRGNAM.SlackBuild
  chown -R root:root $PKG2/usr/doc/$PRGNAM2-$VERSION
  find $PKG2/usr/doc -type f -exec chmod 644 {} \;
 
  # Compress the man page(s):
  if [ -d $PKG2/usr/man ]; then
    find $PKG2/usr/man -type f -name "*.?" -exec gzip -9f {} \;
    for i in $(find $PKG2/usr/man -type l -name "*.?") ; do ln -s $( readlink $i ).gz $i.gz ; rm $i ; done
  fi
 
  # Add a package description:
  mkdir -p $PKG2/install
  cat $SRCDIR/${PRGNAM2}.slack-desc > $PKG2/install/slack-desc
 
  # Build the package:
  cd $PKG2
  makepkg --linkadd y --chown n $OUTPUT/${PRGNAM2}-${VERSION}-${ARCH}-${BUILD}${TAG}.tgz 2>&1 | tee $OUTPUT/makepkg-${PRGNAM2}.log
  cd $OUTPUT
  md5sum ${PRGNAM2}-${VERSION}-${ARCH}-${BUILD}${TAG}.tgz > ${PRGNAM2}-${VERSION}-${ARCH}-${BUILD}${TAG}.tgz.md5
  cd -
  cat $PKG2/install/slack-desc | grep "^${PRGNAM2}" > $OUTPUT/${PRGNAM2}-${VERSION}-${ARCH}-${BUILD}${TAG}.txt
 
fi # End [ "$BUILD_STATIC" = "YES" ]
 
# Continuing with the default dynamic build:
 
# Add documentation:
mkdir -p $PKG/usr/doc/$PRGNAM-$VERSION
cp -a $DOCS $PKG/usr/doc/$PRGNAM-$VERSION || true
cat $SRCDIR/$(basename $0) > $PKG/usr/doc/$PRGNAM-$VERSION/$PRGNAM.SlackBuild
chown -R root:root $PKG/usr/doc/$PRGNAM-$VERSION
find $PKG/usr/doc -type f -exec chmod 644 {} \;
 
# Compress the man page(s):
if [ -d $PKG/usr/man ]; then
  find $PKG/usr/man -type f -name "*.?" -exec gzip -9f {} \;
  for i in $(find $PKG/usr/man -type l -name "*.?") ; do ln -s $( readlink $i ).gz $i.gz ; rm $i ; done
fi
 
# Strip binaries:
find $PKG | xargs file | grep -e "executable" -e "shared object" \
  | grep ELF | cut -f 1 -d : | xargs strip --strip-unneeded 2> /dev/null || true
 
# Clean up:
find $PKG/usr/share -type f -size 0 -exec rm -f {} \; 2>/dev/null || true
 
# Add a package description:
mkdir -p $PKG/install
cat $SRCDIR/${PRGNAM}.slack-desc > $PKG/install/slack-desc
cat $SRCDIR/${PRGNAM}.slack-required > $PKG/install/slack-required
 
# Build the package:
cd $PKG
makepkg --linkadd y --chown n $OUTPUT/${PRGNAM}-${VERSION}-${ARCH}-${BUILD}${TAG}.tgz 2>&1 | tee $OUTPUT/makepkg-${PRGNAM}.log
cd $OUTPUT
md5sum ${PRGNAM}-${VERSION}-${ARCH}-${BUILD}${TAG}.tgz > ${PRGNAM}-${VERSION}-${ARCH}-${BUILD}${TAG}.tgz.md5
cd -
cat $PKG/install/slack-desc | grep "^${PRGNAM}" > $OUTPUT/${PRGNAM}-${VERSION}-${ARCH}-${BUILD}${TAG}.txt
cat $PKG/install/slack-required > $OUTPUT/${PRGNAM}-${VERSION}-${ARCH}-${BUILD}${TAG}.dep
 
# Restore the original umask:
umask ${_UMASK_}

You'll also need the qemu-static.slack-desc file:

# HOW TO EDIT THIS FILE:
# The "handy ruler" below makes it easier to edit a package description.  Line
# up the first '|' above the ':' following the base package name, and the '|'
# on the right side marks the last column you can put a character in.  You must
# make exactly 11 lines for the formatting to be correct.  It's also
# customary to leave one space after the ':'.

           |-----handy-ruler------------------------------------------------------|
qemu-static: qemu-static (a processor emulator)
qemu-static:
qemu-static: QEMU is a FAST! processor emulator using dynamic translation to
qemu-static: achieve good emulation speed. QEMU has two operating modes:
qemu-static: Full system emulation and User mode emulation.
qemu-static:
qemu-static: This package contains statically compiled binaries of only the
qemu-static: User mode emulators, for use inside chroot environments.
qemu-static:
qemu-static:
qemu-static: Home page at http://qemu.org/

Sources


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