dpkg-gensymbols - generate symbols files (shared library dependency information)
dpkg-gensymbols [
option...]
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).
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.
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.
-
-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.
- 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).
<
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).