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+# dpkg manual page - dpkg-gensymbols(1)
+#
+# Copyright © 2007-2011 Raphaël Hertzog <hertzog@debian.org>
+# Copyright © 2009-2010 Modestas Vainius <modestas@vainius.eu>
+# Copyright © 2012-2015 Guillem Jover <guillem@debian.org>
+#
+# This is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+=encoding utf8
+
+=head1 NAME
+
+dpkg-gensymbols - generate symbols files (shared library dependency information)
+
+=head1 SYNOPSIS
+
+B<dpkg-gensymbols>
+[I<option>...]
+
+=head1 DESCRIPTION
+
+B<dpkg-gensymbols>
+scans a temporary build tree (debian/tmp by default) looking for libraries
+and generates a I<symbols> file describing them.
+This file, if
+non-empty, is then installed in the DEBIAN subdirectory of the build tree
+so that it ends up included in the control information of the package.
+
+When generating those files, it uses as input some symbols files
+provided by the maintainer.
+It looks for the following files (and uses the
+first that is found):
+
+=over
+
+=item *
+
+debian/I<package>.symbols.I<arch>
+
+=item *
+
+debian/symbols.I<arch>
+
+=item *
+
+debian/I<package>.symbols
+
+=item *
+
+debian/symbols
+
+=back
+
+The main interest of those files is to provide the minimal version
+associated to each symbol provided by the libraries.
+Usually it
+corresponds to the first version of that package that provided the symbol,
+but it can be manually incremented by the maintainer if the ABI of the
+symbol is extended without breaking backwards compatibility.
+It's the
+responsibility of the maintainer to keep those files up-to-date and
+accurate, but B<dpkg-gensymbols> helps with that.
+
+When the generated symbols files differ from the maintainer supplied
+one, B<dpkg-gensymbols> will print a diff between the two versions.
+Furthermore if the difference is too significant, it will even fail (you
+can customize how much difference you can tolerate, see the B<-c>
+option).
+
+This program was introduced in dpkg 1.14.8.
+
+=head1 MAINTAINING SYMBOLS FILES
+
+The base interchange format of the symbols file is described in
+L<deb-symbols(5)>, which is used by the symbols files included in
+binary packages.
+These are generated from template symbols files
+with a format based on the former, described in L<deb-src-symbols(5)>
+and included in source packages.
+
+The symbols files are really useful only if they reflect the evolution of
+the package through several releases.
+Thus the maintainer has to update
+them every time that a new symbol is added so that its associated minimal
+version matches reality.
+
+The diffs contained in the build logs can be used as a starting point,
+but the maintainer, additionally, has to make sure that the behaviour
+of those symbols has not changed in a way that would make anything
+using those symbols and linking against the new version, stop working
+with the old version.
+
+In most cases, the diff applies directly to the
+debian/I<package>.symbols file.
+That said, further tweaks are usually
+needed: it's recommended for example to drop the Debian revision
+from the minimal version so that backports with a lower version number
+but the same upstream version still satisfy the generated dependencies.
+If the Debian revision can't be dropped because the symbol really got
+added by the Debian specific change, then one should suffix the version
+with ‘B<~>’.
+
+Before applying any patch to the symbols file, the maintainer should
+double-check that it's sane.
+Public symbols are not supposed to disappear,
+so the patch should ideally only add new lines.
+
+Note that you can put comments in symbols files.
+
+Do not forget to check if old symbol versions need to be increased.
+There is no way B<dpkg-gensymbols> can warn about this.
+Blindly
+applying the diff or assuming there is nothing to change if there is
+no diff, without checking for such changes, can lead to packages with
+loose dependencies that claim they can work with older packages they
+cannot work with.
+This will introduce hard to find bugs with (partial)
+upgrades.
+
+=head2 Good library management
+
+A well-maintained library has the following features:
+
+=over
+
+=item *
+
+its API is stable (public symbols are never dropped, only new public
+symbols are added) and changes in incompatible ways only when the SONAME
+changes;
+
+=item *
+
+ideally, it uses symbol versioning to achieve ABI stability despite
+internal changes and API extension;
+
+=item *
+
+it doesn't export private symbols (such symbols can be tagged optional as
+workaround).
+
+=back
+
+While maintaining the symbols file, it's easy to notice appearance and
+disappearance of symbols.
+But it's more difficult to catch incompatible API and ABI change.
+Thus the maintainer should read thoroughly the
+upstream changelog looking for cases where the rules of good library
+management have been broken.
+If potential problems are discovered,
+the upstream author should be notified as an upstream fix is always better
+than a Debian specific work-around.
+
+=head1 OPTIONS
+
+=over
+
+=item B<-P>I<package-build-dir>
+
+Scan I<package-build-dir> instead of debian/tmp.
+
+=item B<-p>I<package>
+
+Define the package name.
+Required if more than one binary package is listed in
+debian/control (or if there's no debian/control file).
+
+=item B<-v>I<version>
+
+Define the package version.
+Defaults to the version extracted from debian/changelog.
+Required if called outside of a source package tree.
+
+=item B<-e>I<library-file>
+
+Only analyze libraries explicitly listed instead of finding all public
+libraries.
+You can use shell patterns used for pathname expansions (see
+the L<File::Glob> manual page for details) in I<library-file>
+to match multiple libraries with a single argument (otherwise you need
+multiple B<-e>).
+
+=item B<-l>I<directory>
+
+Prepend
+I<directory>
+to the list of directories to search for private shared libraries
+(since dpkg 1.19.1).
+This option can be used multiple times.
+
+B<Note>: Use this option instead of setting B<LD_LIBRARY_PATH>,
+as that environment variable is used to control the run-time linker
+and abusing it to set the shared library paths at build-time can be
+problematic when cross-compiling for example.
+
+=item B<-I>I<filename>
+
+Use I<filename> as reference file to generate the symbols file
+that is integrated in the package itself.
+
+=item B<-O>[I<filename>]
+
+Print the generated symbols file to standard output or to I<filename>
+if specified, rather than to
+B<debian/tmp/DEBIAN/symbols>
+(or
+I<package-build-dir>B</DEBIAN/symbols>
+if
+B<-P>
+was used).
+If I<filename> is pre-existing, its contents are used as
+basis for the generated symbols file.
+You can use this feature to update a symbols file so that it matches a
+newer upstream version of your library.
+
+=item B<-t>
+
+Write the symbol file in template mode rather than the format compatible with
+L<deb-symbols(5)>.
+The main difference is that in the template mode symbol
+names and tags are written in their original form contrary to the
+post-processed symbol names with tags stripped in the compatibility mode.
+Moreover, some symbols might be omitted when writing a standard
+L<deb-symbols(5)> file (according to the tag processing rules) while all
+symbols are always written to the symbol file template.
+
+=item B<-c>I<[0-4]>
+
+Define the checks to do when comparing the generated symbols file with the
+template file used as starting point.
+By default the level is 1.
+Increasing
+levels do more checks and include all checks of lower levels.
+
+=over
+
+=item Level 0
+
+Never fails.
+
+=item Level 1
+
+Fails if some symbols have disappeared.
+
+=item Level 2
+
+Fails if some new symbols have been introduced.
+
+=item Level 3
+
+Fails if some libraries have disappeared.
+
+=item Level 4
+
+Fails if some libraries have been introduced.
+
+=back
+
+This value can be overridden by the environment variable
+B<DPKG_GENSYMBOLS_CHECK_LEVEL>.
+
+=item B<-q>
+
+Keep quiet and never generate a diff between generated symbols file and the
+template file used as starting point or show any warnings about new/lost
+libraries or new/lost symbols.
+This option only disables informational output
+but not the checks themselves (see B<-c> option).
+
+=item B<-a>I<arch>
+
+Assume I<arch> as host architecture when processing symbol files.
+Use this
+option to generate a symbol file or diff for any architecture provided its
+binaries are already available.
+
+=item B<-d>
+
+Enable debug mode.
+Numerous messages are displayed to explain what
+B<dpkg-gensymbols>
+does.
+
+=item B<-V>
+
+Enable verbose mode.
+The generated symbols file contains deprecated symbols as comments.
+Furthermore in template mode, pattern symbols
+are followed by comments listing real symbols that have matched the
+pattern.
+
+=item B<-?>, B<--help>
+
+Show the usage message and exit.
+
+=item B<--version>
+
+Show the version and exit.
+
+=back
+
+=head1 ENVIRONMENT
+
+=over
+
+=item B<DPKG_GENSYMBOLS_CHECK_LEVEL>
+
+Overrides the command check level, even if the B<-c> command-line
+argument was given (note that this goes against the common convention
+of command-line arguments having precedence over environment variables).
+
+=item B<DPKG_COLORS>
+
+Sets the color mode (since dpkg 1.18.5).
+The currently accepted values are: B<auto> (default), B<always> and
+B<never>.
+
+=item B<DPKG_NLS>
+
+If set, it will be used to decide whether to activate Native Language Support,
+also known as internationalization (or i18n) support (since dpkg 1.19.0).
+The accepted values are: B<0> and B<1> (default).
+
+=back
+
+=head1 SEE ALSO
+
+L<https://people.redhat.com/drepper/symbol-versioning>,
+L<https://people.redhat.com/drepper/goodpractice.pdf>,
+L<https://people.redhat.com/drepper/dsohowto.pdf>,
+L<deb-src-symbol(5)>,
+L<deb-symbols(5)>,
+L<dpkg-shlibdeps(1)>.