# NAME

upx - compress or expand executable files

# SYNOPSIS

upx [ command ] [ options ] filename...

# ABSTRACT

                The Ultimate Packer for eXecutables
      Copyright (c) 1996-2001 Markus Oberhumer & Laszlo Molnar
           http://wildsau.idv.uni-linz.ac.at/mfx/upx.html
                        http://upx.tsx.org

UPX is a portable, extendable, high-performance executable packer for several different executable formats. It achieves an excellent compression ratio and offers *very* fast decompression. Your executables suffer no memory overhead or other drawbacks for most of the formats supported.

While you may use UPX freely for both non-commercial and commercial executables (for details see the file LICENSE), we would highly appreciate if you credit UPX and ourselves in the documentation, possibly including a reference to the UPX home page. Thanks.

[ Using UPX in non-OpenSource applications without proper credits is considered not politically correct ;-) ]

# DISCLAIMER

UPX comes with ABSOLUTELY NO WARRANTY; for details see the file LICENSE.

Having said that, we think that UPX is quite stable now. Indeed we have compressed lots of files without any problems. Also, the current version has undergone several months of beta testing - actually it's almost 2 years since our first public beta.

This is the first production quality release, and we plan that future 1.xx releases will be backward compatible with this version.

Please report all problems or suggestions to the authors. Thanks.

# DESCRIPTION

UPX is a versatile executable packer with the following features:

      - excellent compression ratio: compresses better than zip/gzip,
          use UPX to decrease the size of your distribution !

      - very fast decompression: about 10 MB/sec even on my old Pentium 133

      - no memory overhead for your compressed executables for most of the
          supported formats

      - safe: you can list, test and unpack your executables
          Also, a checksum of both the compressed and uncompressed file is
          maintained internally.

      - universal: UPX can pack a number of executable formats:
          * dos/exe
          * dos/sys
          * dos/com
          * djgpp2/coff
          * watcom/le (supporting DOS4G, PMODE/W, DOS32a and CauseWay)
          * win32/pe
          * rtm32/pe
          * tmt/adam
          * linux/386
          * atari/tos

      - portable: UPX is written in portable endian-neutral C++

      - extendable: because of the class layout it's very easy to support
          new executable formats or add new compression algorithms

      - free: UPX can be distributed and used freely. And from version 0.99
          the full source code of UPX is released under the GNU General Public
          License (GPL) !

You probably understand now why we call UPX the ``ultimate'' executable packer.

# COMMANDS

## Compress

This is the default operation, eg. upx yourfile.exe will compress the file specified on the command line.

## Decompress

All UPX supported file formats can be unpacked using the -d switch, eg. upx -d yourfile.exe will uncompress the file you've just compressed.

## Test

The -t command tests the integrity of the compressed and uncompressed data, eg. upx -t yourfile.exe check whether your file can be safely decompressed. Note, that this command doesn't check the whole file, only the part that will be uncompressed during program execution. This means that you should not use this command instead of a virus checker.

## List

The -l command prints out some information about the compressed files specified on the command line as parameters, eg upx -l yourfile.exe shows the compressed / uncompressed size and the compression ratio of yourfile.exe.

# OPTIONS

-q: be quiet, suppress warnings

-q -q (or -qq): be very quiet, suppress errors

-q -q -q (or -qqq): produce no output at all

--help: prints the help

--version: print the version of UPX

[ ...to be written... - type `upx --help' for now ]

# COMPRESSION LEVELS & TUNING

UPX offers ten different compression levels from -1 to -9, and --best. The default compression level is -8 for files smaller than 512 kB, and -7 otherwise.

- Compression levels 1, 2 and 3 are pretty fast.

- Compression levels 4, 5 and 6 achieve a good time/ratio performance.

- Compression levels 7, 8 and 9 favor compression ratio over speed.

- Compression level --best may take a long time.

Note that compression level -9 can be somewaht slow for large files, but you definitely should use it when releasing a final version of your program.

Since UPX 0.70 there is also an extra compression level --best which squeezes out even some more compression ratio. While it is usually fine to use this option with your favorite .com file it may take a long time to compress a multi-megabyte program. You have been warned.

Tips for even better compression:

- Try if --overlay=strip works.

- For win32/pe programs there's --strip-relocs=0. See notes below.

# OVERLAY HANDLING OPTIONS

UPX handles overlays like many other executable packers do: it simply copies the overlay after the compressed image. This works with some files, but doesn't work with others.

Since version 0.90 UPX defaults to --overlay=copy for all executable formats.

      --overlay=copy    Copy any extra data attached to the file. [DEFAULT]

      --overlay=strip   Strip any overlay from the program instead of
                        copying it. Be warned, this may make the compressed
                        program crash or otherwise unusable.

      --overlay=skip    Refuse to compress any program which has an overlay.

# ENVIRONMENT

The environment variable UPX can hold a set of default options for UPX. These options are interpreted first and can be overwritten by explicit command line parameters. For example:

        for DOS/Windows:   set UPX=-9 --compress-icons#1
        for sh/ksh/zsh:    UPX="-9 --compress-icons=1"; export UPX
        for csh/tcsh:      setenv UPX "-9 --compress-icons=1"

Under DOS/Windows you must use '#' instead of '=' when setting the environment variable because of a COMMAND.COM limitation.

Not all of the options are valid in the environment variable - UPX will tell you.

You can use the --no-env option to turn this support off.

# NOTES FOR THE SUPPORTED EXECUTABLE FORMATS

## NOTES FOR ATARI/TOS

This is the executable format used by the Atari ST/TT, a 68000 based personal computer which was popular in the late '80s. Support of this format is only because of nostalgic feelings of one of the authors and serves no practical purpose :-).

Packed programs will be byte-identical to the original after uncompression. All debug information will be stripped, though.

Extra options available for this executable format:

      (none)

## NOTES FOR DOS/COM

Obviously UPX won't work with executables that want to read data from themselves (like some commandline utilities that ship with Win95/98).

Compressed programs only work on a 286+.

Packed programs will be byte-identical to the original after uncompression.

Maximum uncompressed size: ~65100 bytes.

Extra options available for this executable format:

      --8086              Create an executable that works on any 8086 CPU.

## NOTES FOR DOS/EXE

dos/exe stands for all ``normal'' 16-bit DOS executables.

Obviously UPX won't work with executables that want to read data from themselves (like some command line utilities that ship with Win95/98).

Compressed programs only work on a 286+.

Extra options available for this executable format:

      --8086              Create an executable that works on any 8086 CPU.

      --no-reloc          Use no relocation records in the exe header.

## NOTES FOR DOS/SYS

You can only compress plain sys files, sys/exe (two in one) combos are not supported.

Compressed programs only work on a 286+.

Packed programs will be byte-identical to the original after uncompression.

Maximum uncompressed size: ~65350 bytes.

Extra options available for this executable format:

      --8086              Create an executable that works on any 8086 CPU.

## NOTES FOR DJGPP2/COFF

First of all, it is recommended to use UPX *instead* of strip. strip has the very bad habit of replacing your stub with its own (outdated) version. Additionally UPX corrects a bug/feature in strip v2.8.x: it will fix the 4 KByte aligment of the stub.

UPX includes the full functionality of stubify. This means it will automatically stubify your COFF files. Use the option --coff to disable this behaviour (see below).

UPX automatically handles Allegro packfiles.

The DLM format (a rather exotic shared library extension) is not supported.

Packed programs will be byte-identical to the original after uncompression. All debug information and trailing garbage will be stripped, though.

BTW, UPX is the successor of the DJP executable packer.

Extra options available for this executable format:

      --coff              Produce COFF output instead of EXE. By default
                          UPX keeps your current stub.

## NOTES FOR LINUX/386

How it works:

      Because Linux is a real operating system, the in-place in-memory
      decompression scheme used in the other executable formats doesn't
      work here.

      Instead we must use temporary decompression to disk. Interestingly -
      because of the good memory management of the Linux kernel - this
      often does not introduce a noticable delay, and in fact there
      will be no disk access at all if you have enough free memory as
      the entire process takes places within the filesystem buffers.

      A compressed executable consists of the UPX stub and an overlay
      which contains the original program in a compressed form.

      The UPX stub is a statically linked ELF executable and does
      the following at program startup:

        1) decompress the overlay to a temporary location in /tmp
        2) open the temporary file for reading
        3) try to delete the temporary file and start (execve)
           the uncompressed program in /tmp using /proc/<pid>/fd/X as
           attained by step 2)
        4) if that fails, fork off a subprocess to clean up and
           start the program in /tmp in the meantime

      The UPX stub is about 1700 bytes long, partly written in assembler
      and only uses kernel syscalls. It is not linked against any libc.

Benefits:

      - UPX can compress all executables, be it AOUT, ELF, libc4, libc5,
        libc6, Shell/Perl/Python/... scripts, standalone Java .class
        binaries, or whatever...
        All scripts and programs will work just as before.

      - Compressed programs are completely self-contained. No need for
        any external program.

      - UPX keeps your original program untouched. This means that
        after decompression you will have a byte-identical version,
        and you can use UPX as a file compressor just like gzip.
        [ Note that UPX maintains a checksum of the file internally,
          so it is indeed a reliable alternative. ]

      - As the stub only uses syscalls and isn't linked against libc it
        should run under any Linux configuration that can run ELF
        binaries and has working /proc support.

      - For the same reason compressed executables should run under
        FreeBSD and other systems which can run Linux binaries.
        [ Please send feedback on this topic ]

Drawbacks:

      - You need additional free disk space for the uncompressed program
        in your /tmp directory. This program is deleted immediately after
        decompression, but you still need it for the full execution time
        of the program.

      - You must have /proc filesystem support as the stub wants to open
        /proc/<pid>/exe and needs /proc/<pid>/fd/X. This also means that you
        cannot compress programs that are used during the boot sequence
        before /proc is mounted.

      - `ldd' and `size' won't show anything useful because all they
        see is the statically linked stub (since version 0.82 the section
        headers are stripped from the UPX stub and `size' doesn't even
        recognize the file format any longer - looks like a binutils bug).

      - Utilities like `top' will display numerical values in the process
        name field. This is because Linux computes the process name from
        the first argument of the last execve syscall (which is typically
        something like /proc/<pid>/fd/3).

      - To reduce memory requirements during uncompression UPX splits the
        original file into blocks, so the compression ratio is a little bit
        worse than with the other executable formats (but still quite nice).
        [ Advise from kernel experts which can tell me more about the
          execve memory semantics is welcome. Maybe this shortcoming
          could be removed. ]

      - Because of temporary decompression to disk the decompression speed
        is not as fast as with the other executable formats. Still, I can see
        no noticable delay when starting programs like my ~3 MB emacs (which
        is less than 1 MB when compressed :-).

Notes:

      - As UPX leaves your original program untouched it is advantageous
        to strip it before compression.

      - It is not advisable to compress programs which usually have many
        instances running (like `make') because the common segments of
        compressed programs won't be shared any longer between different
        processes.

      - If you compress a script you will lose platform independence -
        this could be a problem if you are using NFS mounted disks.

      - Compression of suid, guid and sticky-bit programs is rejected
        because of possible security implications.

      - For the same reason there is no sense in making any compressed
        program suid.

      - Obviously UPX won't work with executables that want to read data
        from themselves. E.g., this might be a problem for Perl scripts
        which access their __DATA__ lines.

      - In case of internal errors the stub will abort with exitcode 127.
        Typical reasons for this to happen are that the program has somehow
        been modified after compression, you have run out of disk space
        or your /proc filesystem is not yet mounted.
        Running `strace -o strace.log compressed_exe' will tell you more.

Extra options available for this executable format:

      (none)

## NOTES FOR RTM32/PE

Same as win32/pe.

## NOTES FOR TMT/ADAM

This format is used by the TMT Pascal compiler - see http://www.tmt.com/ .

Extra options available for this executable format:

      (none)

## NOTES FOR WATCOM/LE

UPX has been successfully tested with the following extenders: DOS4G, DOS4GW, PMODE/W, DOS32a, CauseWay. The WDOS/X extender is partly supported (for details see the file bugs BUGS).

Yes, you can use your compressed executables with DOS4GW.

The LX format is not yet supported.

DLLs are not supported.

Extra options available for this executable format:

      --le                Produce an unbound LE output instead of
                          keeping the current stub.

## NOTES FOR WIN32/PE

The PE support in UPX is quite stable now, but definitely there are still some incompabilities with some files.

Because of the way UPX (and other packers for this format) works, you can see increased memory usage of your compressed files. If you start several instances of huge compressed programs you're wasting memory because the common segements of the program won't get shared across the instances. On the other hand if you're compressing only smaller programs, or running only one instance of larger programs, then this penalty is smaller, but it's still there.

If you're running executables from network, then compressed programs will load faster, and require less bandwidth during execution.

DLLs are supported.

Extra options available for this executable format:

     --compress-exports=0 Don't compress the export section.
                          Use this if you plan to run the compressed
                          program under Wine.
     --compress-exports=1 Compress the export section. [DEFAULT]
                          Compression of the export section can improve the
                          compression ratio quite a bit but may not work
                          with all programs (like winword.exe).
                          UPX never compresses the export section of a DLL
                          regardless of this option.

      --compress-icons=0  Don't compress any icons.
      --compress-icons=1  Compress all but the first icon.
      --compress-icons=2  Compress all icons which are not in the
                          first icon directory. [DEFAULT]

      --compress-resources=0  Don't compress any resources at all.

      --force             Force compression even when there is an
                          unexpected value in a header field.
                          Use with care.

      --strip-relocs=0    Don't strip relocation records.
      --strip-relocs=1    Strip relocation records. [DEFAULT]
                          This option only works on executables with base
                          address greater or equal to 0x400000. Usually the
                          compressed files becomes smaller, but some files
                          may become larger. Note that the resulting file will
                          not work under Win32s.
                          UPX never strips relocations from a DLL
                          regardless of this option.

# DIAGNOSTICS

Exit status is normally 0; if an error occurs, exit status is 1. If a warning occurs, exit status is 2.

UPX's diagnostics are intended to be self-explanatory.

# BUGS

Please report all bugs immediately to the authors.

# AUTHORS

     Markus F.X.J. Oberhumer <markus@oberhumer.com>
     http://www.oberhumer.com

     Laszlo Molnar <ml1050@cdata.tvnet.hu>

# COPYRIGHT

Copyright (C) 1996-2001 Markus Franz Xaver Johannes Oberhumer

Copyright (C) 1996-2001 Laszlo Molnar

This program may be used freely, and you are welcome to redistribute it under certain conditions.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the UPX License Agreement for more details.

You should have received a copy of the UPX License Agreement along with this program; see the file LICENSE. If not, visit the UPX home page.