1dpkg-gensymbols(1)                dpkg suite                dpkg-gensymbols(1)
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NAME

6       dpkg-gensymbols - generate symbols files (shared library dependency
7       information)
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SYNOPSIS

10       dpkg-gensymbols [option...]
11

DESCRIPTION

13       dpkg-gensymbols scans a temporary build tree (debian/tmp by default)
14       looking for libraries and generates a symbols file describing them.
15       This file, if non-empty, is then installed in the DEBIAN subdirectory
16       of the build tree so that it ends up included in the control
17       information of the package.
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19       When generating those files, it uses as input some symbols files
20       provided by the maintainer. It looks for the following files (and uses
21       the first that is found):
22
23       •   debian/package.symbols.arch
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25       •   debian/symbols.arch
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27       •   debian/package.symbols
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29       •   debian/symbols
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31       The main interest of those files is to provide the minimal version
32       associated to each symbol provided by the libraries. Usually it
33       corresponds to the first version of that package that provided the
34       symbol, but it can be manually incremented by the maintainer if the ABI
35       of the symbol is extended without breaking backwards compatibility.
36       It's the responsibility of the maintainer to keep those files up-to-
37       date and accurate, but dpkg-gensymbols helps with that.
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39       When the generated symbols files differ from the maintainer supplied
40       one, dpkg-gensymbols will print a diff between the two versions.
41       Furthermore if the difference is too significant, it will even fail
42       (you can customize how much difference you can tolerate, see the -c
43       option).
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MAINTAINING SYMBOLS FILES

46       The base interchange format of the symbols file is described in deb-
47       symbols(5), which is used by the symbols files included in binary
48       packages. These are generated from template symbols files with a format
49       based on the former, described in deb-src-symbols(5) and included in
50       source packages.
51
52       The symbols files are really useful only if they reflect the evolution
53       of the package through several releases. Thus the maintainer has to
54       update them every time that a new symbol is added so that its
55       associated minimal version matches reality.
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57       The diffs contained in the build logs can be used as a starting point,
58       but the maintainer, additionally, has to make sure that the behaviour
59       of those symbols has not changed in a way that would make anything
60       using those symbols and linking against the new version, stop working
61       with the old version.
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63       In most cases, the diff applies directly to the debian/package.symbols
64       file. That said, further tweaks are usually needed: it's recommended
65       for example to drop the Debian revision from the minimal version so
66       that backports with a lower version number but the same upstream
67       version still satisfy the generated dependencies.  If the Debian
68       revision can't be dropped because the symbol really got added by the
69       Debian specific change, then one should suffix the version with ‘~’.
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71       Before applying any patch to the symbols file, the maintainer should
72       double-check that it's sane. Public symbols are not supposed to
73       disappear, so the patch should ideally only add new lines.
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75       Note that you can put comments in symbols files.
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77       Do not forget to check if old symbol versions need to be increased.
78       There is no way dpkg-gensymbols can warn about this. Blindly applying
79       the diff or assuming there is nothing to change if there is no diff,
80       without checking for such changes, can lead to packages with loose
81       dependencies that claim they can work with older packages they cannot
82       work with. This will introduce hard to find bugs with (partial)
83       upgrades.
84
85   Good library management
86       A well-maintained library has the following features:
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88       •   its API is stable (public symbols are never dropped, only new
89           public symbols are added) and changes in incompatible ways only
90           when the SONAME changes;
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92       •   ideally, it uses symbol versioning to achieve ABI stability despite
93           internal changes and API extension;
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95       •   it doesn't export private symbols (such symbols can be tagged
96           optional as workaround).
97
98       While maintaining the symbols file, it's easy to notice appearance and
99       disappearance of symbols. But it's more difficult to catch incompatible
100       API and ABI change. Thus the maintainer should read thoroughly the
101       upstream changelog looking for cases where the rules of good library
102       management have been broken. If potential problems are discovered, the
103       upstream author should be notified as an upstream fix is always better
104       than a Debian specific work-around.
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OPTIONS

107       -Ppackage-build-dir
108           Scan package-build-dir instead of debian/tmp.
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110       -ppackage
111           Define the package name. Required if more than one binary package
112           is listed in debian/control (or if there's no debian/control file).
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114       -vversion
115           Define the package version. Defaults to the version extracted from
116           debian/changelog. Required if called outside of a source package
117           tree.
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119       -elibrary-file
120           Only analyze libraries explicitly listed instead of finding all
121           public libraries. You can use shell patterns used for pathname
122           expansions (see the File::Glob(3perl) manual page for details) in
123           library-file to match multiple libraries with a single argument
124           (otherwise you need multiple -e).
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126       -ldirectory
127           Prepend directory to the list of directories to search for private
128           shared libraries (since dpkg 1.19.1). This option can be used
129           multiple times.
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131           Note: Use this option instead of setting LD_LIBRARY_PATH, as that
132           environment variable is used to control the run-time linker and
133           abusing it to set the shared library paths at build-time can be
134           problematic when cross-compiling for example.
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136       -Ifilename
137           Use filename as reference file to generate the symbols file that is
138           integrated in the package itself.
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140       -O[filename]
141           Print the generated symbols file to standard output or to filename
142           if specified, rather than to debian/tmp/DEBIAN/symbols (or package-
143           build-dir/DEBIAN/symbols if -P was used). If filename is pre-
144           existing, its contents are used as basis for the generated symbols
145           file.  You can use this feature to update a symbols file so that it
146           matches a newer upstream version of your library.
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148       -t  Write the symbol file in template mode rather than the format
149           compatible with deb-symbols(5). The main difference is that in the
150           template mode symbol names and tags are written in their original
151           form contrary to the post-processed symbol names with tags stripped
152           in the compatibility mode.  Moreover, some symbols might be omitted
153           when writing a standard deb-symbols(5) file (according to the tag
154           processing rules) while all symbols are always written to the
155           symbol file template.
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157       -c[0-4]
158           Define the checks to do when comparing the generated symbols file
159           with the template file used as starting point. By default the level
160           is 1. Increasing levels do more checks and include all checks of
161           lower levels. Level 0 never fails. Level 1 fails if some symbols
162           have disappeared. Level 2 fails if some new symbols have been
163           introduced. Level 3 fails if some libraries have disappeared. Level
164           4 fails if some libraries have been introduced.
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166           This value can be overridden by the environment variable
167           DPKG_GENSYMBOLS_CHECK_LEVEL.
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169       -q  Keep quiet and never generate a diff between generated symbols file
170           and the template file used as starting point or show any warnings
171           about new/lost libraries or new/lost symbols. This option only
172           disables informational output but not the checks themselves (see -c
173           option).
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175       -aarch
176           Assume arch as host architecture when processing symbol files. Use
177           this option to generate a symbol file or diff for any architecture
178           provided its binaries are already available.
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180       -d  Enable debug mode. Numerous messages are displayed to explain what
181           dpkg-gensymbols does.
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183       -V  Enable verbose mode. The generated symbols file contains deprecated
184           symbols as comments. Furthermore in template mode, pattern symbols
185           are followed by comments listing real symbols that have matched the
186           pattern.
187
188       -?, --help
189           Show the usage message and exit.
190
191       --version
192           Show the version and exit.
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ENVIRONMENT

195       DPKG_GENSYMBOLS_CHECK_LEVEL
196           Overrides the command check level, even if the -c command-line
197           argument was given (note that this goes against the common
198           convention of command-line arguments having precedence over
199           environment variables).
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201       DPKG_COLORS
202           Sets the color mode (since dpkg 1.18.5).  The currently accepted
203           values are: auto (default), always and never.
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205       DPKG_NLS
206           If set, it will be used to decide whether to activate Native
207           Language Support, also known as internationalization (or i18n)
208           support (since dpkg 1.19.0).  The accepted values are: 0 and 1
209           (default).
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SEE ALSO

212       <https://people.redhat.com/drepper/symbol-versioning>,
213       <https://people.redhat.com/drepper/goodpractice.pdf>,
214       <https://people.redhat.com/drepper/dsohowto.pdf>, deb-src-symbol(5),
215       deb-symbols(5), dpkg-shlibdeps(1).
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2191.20.9                            2021-04-13                dpkg-gensymbols(1)
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