Tiny 7z archive extractors and SFX for Linux and Windows

This blog post contains links to the tiniest programs that can extract 7z (7-Zip) archives on Linux and Windows i386. These programs can also be used as SFX (self-extract archives) by appending a .7z file to them.

Please see my previous post about self-extracting 7z archives. In that post the smallest Linux extractor is of 118 kB, and the smallest Windows console extractor (the official one) is of 149 kB. The Linux extractor is based on the p7zip C++ sources, statically linked against uClibc and compiled with some GCC flags optimized for small binary size.

The smallest known Windows SFX extractor, 7zS2Con.sfx can be found in 7z922_extra.7z. It's of 27648 bytes (27 kB). It's based on the official ANSI C 7-Zip extractor sources, i.e. the C subdirectory in 7z922.tar.bz2. The fundamental difference between this smallest SFX and the normal Windows SFX is the implementation language (C vs C++) and the feature set (e.g. larger memory requirements, not all algorithms supported, encryption not supported, see the Limitations section below). See also this original forum topic for a discussion about features and limitations.

I've compiled the ANSI C 7-Zip extractor using uClibc and the size-optimized GCC flags, fixed some bugs, added some features (e.g. mtime, permissions, symlink, SFX mode), and compressed the binary using UPX. The result is the smallest known extractor (and SFX extractor) for Linux: 7z9.22LinuxI386ConTiny.sfx, 24116 bytes (24 kB, smaller than the Windows extractor, linked using diet libc). The sources are available as a GIT repostitory. The sources are optimized for Linux (they work on both i386 and amd64), but they should compile and work other Unix systems as well.

Features of the tiny Linux extractor

  • Small (the Linux statically linked binary is less than 40 kB).
  • Can be used to create a SFX (self-extract) binary by prepending to a 7z archive. (Same as the `7z -sfx' flag.)
  • It supports file and directory attributes (i.e. it calls chmod(2)).
  • It sets the mtime (i.e. it calls utimes(2)).
  • It can extract symlinks.
  • Has a command-line syntax compatible with the regular console SFX binaries.

Limitations of the tiny extractors (Windows and Linux)

  • It supports only: LZMA, LZMA2, BCJ, BCJ2, COPY.
  • It keeps an uncompressed version of each file in RAM.
  • It decompresses solid 7z blocks (it can be whole 7z archive) to RAM. So user that calls SFX installer must have free RAM of size of largest solid 7z block (size of 7z archive at simplest case).
  • The Windows extractor overwrites files without asking.
  • It always extracts to the current directory.
  • It does not support (and may misbehave for) encryption in archives.

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