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Kernel Support for miscellaneous (your favourite) Binary Formats v1.1
====================================================================
This Kernel feature allows to invoke almost (for restrictions see below) every
program by simply typing it's name in the shell.
This includes for example compiled Java(TM), Python or Emacs programs.
To achieve this you must tell binfmt_misc which interpreter has to be invoked with
which binary. Binfmt_misc recognises the binary-type by matching some bytes at the
beginning of the file with a magic byte sequence (masking out specified bits) you
have supplied. Binfmt_misc can also recognise a filename extension (aka .com) and
optionally strip it off.
To actually register a new binary type, you have to set up a string looking like
:name:type:offset:magic:mask:interpreter: (where you can choose the ':' upon your
needs) and echo it to /proc/sys/fs/binfmt_misc/register.
Here is what the fields mean:
- 'name' is an identifier string. A new /proc file will be created with this
this name below /proc/sys/fs/binfmt_misc
- 'type' is the type of recognition. Give 'M' for magic and 'E' for extension.
Give the corresponding lowercase letter to let binfmt_misc strip of the
filename extension.
- 'offset' is the offset of the magic/mask in the file counted in bytes. This
defaults to 0 if you omit it (i.e. you write ':name:type::magic...')
- 'magic' is the byte sequence binfmt_misc is matching for. The magic string
may contain hex-encoded characters like \x0a or \xA4. In a shell environment
you will have to write \\x0a to prevent the shell from eating your \.
If you chose filename extension matching, this is the extension to be
recognised (the \x0a specials are not allowed). Extension matching is case
sensitive!
- 'mask' is an (optional, defaults to all 0xff) mask. You can mask out some bits
from matching by supplying a string like magic and as long as magic. The
mask is anded with the byte sequence of the file.
- 'interpreter' is the program that should be invoked with the binary as first
argument (specify the full path)
There are some restrictions:
- the whole register string may not exceed 255 characters
- the magic must resist in the first 128 bytes of the file, i.e. offset+size(magic)
has to be less than 128
- the interpreter string may not exceed 127 characters
You may want to add the binary formats in one of your /etc/rc scripts during boot-up.
Read the manual of your init program to figure out how to do this right.
A few examples (assumed you are in /proc/sys/fs/binfmt_misc):
- enable Java(TM)-support (like binfmt_java):
echo ":Java:M::\xca\xfe\xba\xbe::/usr/local/bin/java:" > register
echo :Applet:M::\<\!--applet::/usr/local/bin/appletviewer: > register
- enable support for em86 (like binfmt_em86, for Alpha AXP only):
echo ":i386:M::\x7fELF\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x03:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfb\xff\xff:/bin/em86:" > register
echo ":i486:M::\x7fELF\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x06:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfb\xff\xff:/bin/em86:" > register
- enable support for packed DOS applications (pre-configured dosemu hdimages):
echo ":DEXE:M::\x0eDEX::/usr/bin/dosexec:" > register
- enable support for DOS/Windows executables (using mzloader and dosemu/wine):
echo ":DOSWin:M::MZ::/usr/sbin/mzloader:" > register
echo ":DOS:E::com::/usr/sbin/mzloader:" > register
You can enable/disable binfmt_misc or one binary type by echoing 0 (to disable)
or 1 (to enable) to /proc/sys/fs/binfmt_misc/status or /proc/.../the_name.
Catting the file tells you the current status of binfmt_misc/the entry.
You can remove one entry or all entries by echoing -1 to /proc/.../the_name
or /proc/sys/fs/binfmt_misc/status.
HINTS:
======
If your interpreter does not look at the PATH to determine the full name of the
program, you need to invoke a wrapper-script (like the following for java) first:
#!/bin/sh
FOO=`which $1` || exit 1
shift
/usr/local/bin/java $FOO ${1+$@}
There is a web page about binfmt_misc at
http://www.anatom.uni-tuebingen.de/~richi/linux/binfmt_misc.html
Richard Günther, richard.guenther@student.uni-tuebingen.de
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