dpkg-gensymbols

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

NAME
       dpkg-gensymbols - generate symbols files (shared library dependency
       information)

SYNOPSIS
       dpkg-gensymbols [option...]

DESCRIPTION
       dpkg-gensymbols scans a temporary build tree (debian/tmp by default)
       looking for libraries and generates a 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):

       o   debian/package.symbols.arch

       o   debian/symbols.arch

       o   debian/package.symbols

       o   debian/symbols

       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 dpkg-gensymbols helps with that.

       When the generated symbols files differ from the maintainer supplied
       one, 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 -c
       option).

MAINTAINING SYMBOLS FILES
       The base interchange format of the symbols file is described in 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 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/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 '~'.

       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 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.

   Good library management
       A well-maintained library has the following features:

       o   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;

       o   ideally, it uses symbol versioning to achieve ABI stability despite
           internal changes and API extension;

       o   it doesn't export private symbols (such symbols can be tagged
           optional as workaround).

       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.

OPTIONS
       -Ppackage-build-dir
           Scan package-build-dir instead of debian/tmp.

       -ppackage
           Define the package name. Required if more than one binary package
           is listed in debian/control (or if there's no debian/control file).

       -vversion
           Define the package version. Defaults to the version extracted from
           debian/changelog. Required if called outside of a source package
           tree.

       -elibrary-file
           Only analyze libraries explicitly listed instead of finding all
           public libraries. You can use shell patterns used for pathname
           expansions (see the File::Glob(3perl) manual page for details) in
           library-file to match multiple libraries with a single argument
           (otherwise you need multiple -e).

       -ldirectory
           Prepend directory to the list of directories to search for private
           shared libraries (since dpkg 1.19.1). This option can be used
           multiple times.

           Note: Use this option instead of setting 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.

       -Ifilename
           Use filename as reference file to generate the symbols file that is
           integrated in the package itself.

       -O[filename]
           Print the generated symbols file to standard output or to filename
           if specified, rather than to debian/tmp/DEBIAN/symbols (or package-
           build-dir/DEBIAN/symbols if -P was used). If 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.

       -t  Write the symbol file in template mode rather than the format
           compatible with 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 deb-symbols(5) file (according to the tag
           processing rules) while all symbols are always written to the
           symbol file template.

       -c[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.

           Level 0
               Never fails.

           Level 1
               Fails if some symbols have disappeared.

           Level 2
               Fails if some new symbols have been introduced.

           Level 3
               Fails if some libraries have disappeared.

           Level 4
               Fails if some libraries have been introduced.

           This value can be overridden by the environment variable
           DPKG_GENSYMBOLS_CHECK_LEVEL.

       -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 -c
           option).

       -aarch
           Assume 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.

       -d  Enable debug mode. Numerous messages are displayed to explain what
           dpkg-gensymbols does.

       -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.

       -?, --help
           Show the usage message and exit.

       --version
           Show the version and exit.

ENVIRONMENT
       DPKG_GENSYMBOLS_CHECK_LEVEL
           Overrides the command check level, even if the -c command-line
           argument was given (note that this goes against the common
           convention of command-line arguments having precedence over
           environment variables).

       DPKG_COLORS
           Sets the color mode (since dpkg 1.18.5).  The currently accepted
           values are: auto (default), always and never.

       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: 0 and 1
           (default).

SEE ALSO
       <https://people.redhat.com/drepper/symbol-versioning>,
       <https://people.redhat.com/drepper/goodpractice.pdf>,
       <https://people.redhat.com/drepper/dsohowto.pdf>, deb-src-symbol(5),
       deb-symbols(5), dpkg-shlibdeps(1).

1.21.1                            2024-02-23                dpkg-gensymbols(1)