source: MondoRescue/branches/3.3/mindi-busybox/archival/libarchive/unxz/README@ 3621

Last change on this file since 3621 was 3621, checked in by Bruno Cornec, 7 years ago

New 3?3 banch for incorporation of latest busybox 1.25. Changing minor version to handle potential incompatibilities.
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1
2XZ Embedded
3===========
4
5 XZ Embedded is a relatively small, limited implementation of the .xz
6 file format. Currently only decoding is implemented.
7
8 XZ Embedded was written for use in the Linux kernel, but the code can
9 be easily used in other environments too, including regular userspace
10 applications. See userspace/xzminidec.c for an example program.
11
12 This README contains information that is useful only when the copy
13 of XZ Embedded isn't part of the Linux kernel tree. You should also
14 read linux/Documentation/xz.txt even if you aren't using XZ Embedded
15 as part of Linux; information in that file is not repeated in this
16 README.
17
18Compiling the Linux kernel module
19
20 The xz_dec module depends on crc32 module, so make sure that you have
21 it enabled (CONFIG_CRC32).
22
23 Building the xz_dec and xz_dec_test modules without support for BCJ
24 filters:
25
26 cd linux/lib/xz
27 make -C /path/to/kernel/source \
28 KCPPFLAGS=-I"$(pwd)/../../include" M="$(pwd)" \
29 CONFIG_XZ_DEC=m CONFIG_XZ_DEC_TEST=m
30
31 Building the xz_dec and xz_dec_test modules with support for BCJ
32 filters:
33
34 cd linux/lib/xz
35 make -C /path/to/kernel/source \
36 KCPPFLAGS=-I"$(pwd)/../../include" M="$(pwd)" \
37 CONFIG_XZ_DEC=m CONFIG_XZ_DEC_TEST=m CONFIG_XZ_DEC_BCJ=y \
38 CONFIG_XZ_DEC_X86=y CONFIG_XZ_DEC_POWERPC=y \
39 CONFIG_XZ_DEC_IA64=y CONFIG_XZ_DEC_ARM=y \
40 CONFIG_XZ_DEC_ARMTHUMB=y CONFIG_XZ_DEC_SPARC=y
41
42 If you want only one or a few of the BCJ filters, omit the appropriate
43 variables. CONFIG_XZ_DEC_BCJ=y is always required to build the support
44 code shared between all BCJ filters.
45
46 Most people don't need the xz_dec_test module. You can skip building
47 it by omitting CONFIG_XZ_DEC_TEST=m from the make command line.
48
49Compiler requirements
50
51 XZ Embedded should compile as either GNU-C89 (used in the Linux
52 kernel) or with any C99 compiler. Getting the code to compile with
53 non-GNU C89 compiler or a C++ compiler should be quite easy as
54 long as there is a data type for unsigned 64-bit integer (or the
55 code is modified not to support large files, which needs some more
56 care than just using 32-bit integer instead of 64-bit).
57
58 If you use GCC, try to use a recent version. For example, on x86-32,
59 xz_dec_lzma2.c compiled with GCC 3.3.6 is 15-25 % slower than when
60 compiled with GCC 4.3.3.
61
62Embedding into userspace applications
63
64 To embed the XZ decoder, copy the following files into a single
65 directory in your source code tree:
66
67 linux/include/linux/xz.h
68 linux/lib/xz/xz_crc32.c
69 linux/lib/xz/xz_dec_lzma2.c
70 linux/lib/xz/xz_dec_stream.c
71 linux/lib/xz/xz_lzma2.h
72 linux/lib/xz/xz_private.h
73 linux/lib/xz/xz_stream.h
74 userspace/xz_config.h
75
76 Alternatively, xz.h may be placed into a different directory but then
77 that directory must be in the compiler include path when compiling
78 the .c files.
79
80 Your code should use only the functions declared in xz.h. The rest of
81 the .h files are meant only for internal use in XZ Embedded.
82
83 You may want to modify xz_config.h to be more suitable for your build
84 environment. Probably you should at least skim through it even if the
85 default file works as is.
86
87BCJ filter support
88
89 If you want support for one or more BCJ filters, you need to copy also
90 linux/lib/xz/xz_dec_bcj.c into your application, and use appropriate
91 #defines in xz_config.h or in compiler flags. You don't need these
92 #defines in the code that just uses XZ Embedded via xz.h, but having
93 them always #defined doesn't hurt either.
94
95 #define Instruction set BCJ filter endianness
96 XZ_DEC_X86 x86-32 or x86-64 Little endian only
97 XZ_DEC_POWERPC PowerPC Big endian only
98 XZ_DEC_IA64 Itanium (IA-64) Big or little endian
99 XZ_DEC_ARM ARM Little endian only
100 XZ_DEC_ARMTHUMB ARM-Thumb Little endian only
101 XZ_DEC_SPARC SPARC Big or little endian
102
103 While some architectures are (partially) bi-endian, the endianness
104 setting doesn't change the endianness of the instructions on all
105 architectures. That's why Itanium and SPARC filters work for both big
106 and little endian executables (Itanium has little endian instructions
107 and SPARC has big endian instructions).
108
109 There currently is no filter for little endian PowerPC or big endian
110 ARM or ARM-Thumb. Implementing filters for them can be considered if
111 there is a need for such filters in real-world applications.
112
113Notes about shared libraries
114
115 If you are including XZ Embedded into a shared library, you very
116 probably should rename the xz_* functions to prevent symbol
117 conflicts in case your library is linked against some other library
118 or application that also has XZ Embedded in it (which may even be
119 a different version of XZ Embedded). TODO: Provide an easy way
120 to do this.
121
122 Please don't create a shared library of XZ Embedded itself unless
123 it is fine to rebuild everything depending on that shared library
124 everytime you upgrade to a newer version of XZ Embedded. There are
125 no API or ABI stability guarantees between different versions of
126 XZ Embedded.
127
128Specifying the calling convention
129
130 XZ_FUNC macro was included to support declaring functions with __init
131 in Linux. Outside Linux, it can be used to specify the calling
132 convention on systems that support multiple calling conventions.
133 For example, on Windows, you may make all functions use the stdcall
134 calling convention by defining XZ_FUNC=__stdcall when building and
135 using the functions from XZ Embedded.
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