Ubuntu Manpage: dpkg-gensymbols - generate symbols files (shared library dependency information)

Provided by: dpkg-dev_1.22.11ubuntu1_all

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):

• debian/package.symbols.arch

• debian/symbols.arch

• debian/package.symbols

• 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).

This program was introduced in dpkg 1.14.8.

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:

       •   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;

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

       •   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 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