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XZ Embedded =========== XZ Embedded is a relatively small, limited implementation of the .xz file format. Currently only decoding is implemented. XZ Embedded was written for use in the Linux kernel, but the code can be easily used in other environments too, including regular userspace applications. This README contains information that is useful only when the copy of XZ Embedded isn't part of the Linux kernel tree. You should also read linux/Documentation/xz.txt even if you aren't using XZ Embedded as part of Linux; information in that file is not repeated in this README. Compiling the Linux kernel module The xz_dec module depends on crc32 module, so make sure that you have it enabled (CONFIG_CRC32). Building the xz_dec and xz_dec_test modules without support for BCJ filters: cd linux/lib/xz make -C /path/to/kernel/source \ KCPPFLAGS=-I"$(pwd)/../../include" M="$(pwd)" \ CONFIG_XZ_DEC=m CONFIG_XZ_DEC_TEST=m Building the xz_dec and xz_dec_test modules with support for BCJ filters: cd linux/lib/xz make -C /path/to/kernel/source \ KCPPFLAGS=-I"$(pwd)/../../include" M="$(pwd)" \ CONFIG_XZ_DEC=m CONFIG_XZ_DEC_TEST=m CONFIG_XZ_DEC_BCJ=y \ CONFIG_XZ_DEC_X86=y CONFIG_XZ_DEC_POWERPC=y \ CONFIG_XZ_DEC_IA64=y CONFIG_XZ_DEC_ARM=y \ CONFIG_XZ_DEC_ARMTHUMB=y CONFIG_XZ_DEC_SPARC=y If you want only one or a few of the BCJ filters, omit the appropriate variables. CONFIG_XZ_DEC_BCJ=y is always required to build the support code shared between all BCJ filters. Most people don't need the xz_dec_test module. You can skip building it by omitting CONFIG_XZ_DEC_TEST=m from the make command line. Compiler requirements XZ Embedded should compile as either GNU-C89 (used in the Linux kernel) or with any C99 compiler. Getting the code to compile with non-GNU C89 compiler or a C++ compiler should be quite easy as long as there is a data type for unsigned 64-bit integer (or the code is modified not to support large files, which needs some more care than just using 32-bit integer instead of 64-bit). If you use GCC, try to use a recent version. For example, on x86-32, xz_dec_lzma2.c compiled with GCC 3.3.6 is 15-25 % slower than when compiled with GCC 4.3.3. Embedding into userspace applications To embed the XZ decoder, copy the following files into a single directory in your source code tree: linux/include/linux/xz.h linux/lib/xz/xz_crc32.c linux/lib/xz/xz_dec_lzma2.c linux/lib/xz/xz_dec_stream.c linux/lib/xz/xz_lzma2.h linux/lib/xz/xz_private.h linux/lib/xz/xz_stream.h userspace/xz_config.h Alternatively, xz.h may be placed into a different directory but then that directory must be in the compiler include path when compiling the .c files. Your code should use only the functions declared in xz.h. The rest of the .h files are meant only for internal use in XZ Embedded. You may want to modify xz_config.h to be more suitable for your build environment. Probably you should at least skim through it even if the default file works as is. BCJ filter support If you want support for one or more BCJ filters, you need to copy also linux/lib/xz/xz_dec_bcj.c into your application, and use appropriate #defines in xz_config.h or in compiler flags. You don't need these #defines in the code that just uses XZ Embedded via xz.h, but having them always #defined doesn't hurt either. #define Instruction set BCJ filter endianness XZ_DEC_X86 x86-32 or x86-64 Little endian only XZ_DEC_POWERPC PowerPC Big endian only XZ_DEC_IA64 Itanium (IA-64) Big or little endian XZ_DEC_ARM ARM Little endian only XZ_DEC_ARMTHUMB ARM-Thumb Little endian only XZ_DEC_SPARC SPARC Big or little endian While some architectures are (partially) bi-endian, the endianness setting doesn't change the endianness of the instructions on all architectures. That's why Itanium and SPARC filters work for both big and little endian executables (Itanium has little endian instructions and SPARC has big endian instructions). There currently is no filter for little endian PowerPC or big endian ARM or ARM-Thumb. Implementing filters for them can be considered if there is a need for such filters in real-world applications. Notes about shared libraries If you are including XZ Embedded into a shared library, you very probably should rename the xz_* functions to prevent symbol conflicts in case your library is linked against some other library or application that also has XZ Embedded in it (which may even be a different version of XZ Embedded). TODO: Provide an easy way to do this. Please don't create a shared library of XZ Embedded itself unless it is fine to rebuild everything depending on that shared library everytime you upgrade to a newer version of XZ Embedded. There are no API or ABI stability guarantees between different versions of XZ Embedded.