f0bd5302dd
Import xz-embedded from git. This is from commit hash '6a8a2364434763a033781f6b2a605ace9a021013'. This makes it possible to use CRC64 but for now it's intentionally not added to build.
164 lines
6.9 KiB
Plaintext
164 lines
6.9 KiB
Plaintext
|
|
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. See userspace/xzminidec.c for an example program.
|
|
|
|
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.
|
|
|
|
Integrity check support
|
|
|
|
XZ Embedded always supports the integrity check types None and
|
|
CRC32. Support for CRC64 is optional. SHA-256 is currently not
|
|
supported in XZ Embedded although the .xz format does support it.
|
|
The xz tool from XZ Utils uses CRC64 by default, but CRC32 is usually
|
|
enough in embedded systems to keep the code size smaller.
|
|
|
|
If you want support for CRC64, you need to copy linux/lib/xz/xz_crc64.c
|
|
into your application, and #define XZ_USE_CRC64 in xz_config.h or in
|
|
compiler flags.
|
|
|
|
When using the internal CRC32 or CRC64, their lookup tables need to be
|
|
initialized with xz_crc32_init() and xz_crc64_init(), respectively.
|
|
See xz.h for details.
|
|
|
|
To use external CRC32 or CRC64 code instead of the code from
|
|
xz_crc32.c or xz_crc64.c, the following #defines may be used
|
|
in xz_config.h or in compiler flags:
|
|
|
|
#define XZ_INTERNAL_CRC32 0
|
|
#define XZ_INTERNAL_CRC64 0
|
|
|
|
Then it is up to you to provide compatible xz_crc32() or xz_crc64()
|
|
functions.
|
|
|
|
If the .xz file being decompressed uses an integrity check type that
|
|
isn't supported by XZ Embedded, it is treated as an error and the
|
|
file cannot be decompressed. For multi-call mode, this can be modified
|
|
by #defining XZ_DEC_ANY_CHECK. Then xz_dec_run() will return
|
|
XZ_UNSUPPORTED_CHECK when unsupported check type is detected. After
|
|
that decompression can be continued normally except that the
|
|
integrity check won't be verified. In single-call mode there's
|
|
no way to continue decoding, so XZ_DEC_ANY_CHECK is almost useless
|
|
in single-call mode.
|
|
|
|
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.
|
|
|