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NAME upx - compress or expand executable files SYNOPSIS upx [ *command* ] [ *options* ] *filename*... ABSTRACT The Ultimate Packer for eXecutables Copyright (c) 1996-2000 Markus Oberhumer & Laszlo Molnar http://wildsau.idv.uni-linz.ac.at/mfx/upx.html http://www.nexus.hu/upx 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/i386 * 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 --stdout: writes all output to stdout [ ...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 -7. * 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 very long time. Note that compression level -9 can be quite slow for some large files, but you definitely should use it when releasing a final version of your program. (E.g. it took about 20 minutes to compress the almost 5 MB MAME 0.34 with -9 on my Pentium 133, but the resulting executable was still ~65 kB smaller than when using -7.) 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 several hours 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 limitiation. On Vax/VMS, the name of the environment variable is UPX_OPT, to avoid a conflict with the symbol set for invocation of the program. 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, 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/i386 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@jk.uni-linz.ac.at> http://wildsau.idv.uni-linz.ac.at/mfx/upx.html Laszlo Molnar <ml1050@cdata.tvnet.hu> http://www.nexus.hu/upx COPYRIGHT Copyright (C) 1996-2000 Markus Franz Xaver Johannes Oberhumer Copyright (C) 1996-2000 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.