Contents of /trunk/mkinitrd-magellan/busybox/archival/libunarchive/unxz/README
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Wed Aug 18 21:56:57 2010 UTC (13 years, 9 months ago) by niro
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Wed Aug 18 21:56:57 2010 UTC (13 years, 9 months ago) by niro
File size: 5836 byte(s)
-updated to busybox-1.17.1
1 | |
2 | XZ 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. |
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 | |
18 | Compiling 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 | |
49 | Compiler 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, |
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 | |
62 | Embedding 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 | |
87 | BCJ 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 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 | |
113 | Notes 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 | |
128 | Specifying 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. |
136 |