Among those files are the package maintainer scripts
and <file>control</file>, the <qref id="binarycontrolfiles">binary
package control file</qref> that contains the control fields for
- the package. Other control information files
- include <qref id="sharedlibs-shlibdeps">the <file>shlibs</file>
- file</qref> used to store shared library dependency information
- and the <file>conffiles</file> file that lists the package's
+ the package. Other control information files include
+ the <qref id="sharedlibs-symbols"><file>symbols</file> file</qref>
+ or <qref id="sharedlibs-shlibdeps"><file>shlibs</file> file</qref>
+ used to store shared library dependency information and
+ the <file>conffiles</file> file that lists the package's
configuration files (described in <ref id="config-files">).
</p>
linked against the old shared library. Correct versioning of
dependencies on the newer shared library by binaries that use
the new interfaces is handled via
- the <qref id="sharedlibs-shlibdeps"><tt>shlibs</tt>
- system</qref> or via symbols files (see
- <manref name="deb-symbols" section="5">).
+ the <qref id="sharedlibs-symbols"><tt>symbols</tt> system</qref>
+ or the <qref id="sharedlibs-shlibdeps"><tt>shlibs</tt>
+ system</qref>.
</p>
<p>
</p>
</sect>
- <sect id="sharedlibs-shlibdeps">
+ <sect id="sharedlibs-symbols">
<heading>Dependencies between the library and other packages -
- the <tt>shlibs</tt> system</heading>
+ the <tt>symbols</tt> system</heading>
<p>
If a package contains a binary or library which links to a
- shared library, we must ensure that when the package is
- installed on the system, all of the libraries needed are
- also installed. This requirement led to the creation of the
- <tt>shlibs</tt> system, which is very simple in its design:
- any package which <em>provides</em> a shared library also
- provides information on the package dependencies required to
- ensure the presence of this library, and any package which
- <em>uses</em> a shared library uses this information to
- determine the dependencies it requires. The files which
- contain the mapping from shared libraries to the necessary
- dependency information are called <file>shlibs</file> files.
- </p>
-
- <p>
- When a package is built which contains any shared libraries, it
- must provide a <file>shlibs</file> file for other packages to
- use. When a package is built which contains any shared
- libraries or compiled binaries, it must run
- <qref id="pkg-dpkg-shlibdeps"><prgn>dpkg-shlibdeps</prgn></qref>
- on these to determine the libraries used and hence the
- dependencies needed by this package.<footnote>
- <p>
- <prgn>dpkg-shlibdeps</prgn> will use a program
- like <prgn>objdump</prgn> or <prgn>readelf</prgn> to find
- the libraries directly needed by the binaries or shared
- libraries in the package.
- </p>
-
- <p>
- We say that a binary <tt>foo</tt> <em>directly</em> uses
- a library <tt>libbar</tt> if it is explicitly linked
- with that library (that is, the library is listed in the ELF
- <tt>NEEDED</tt> attribute, caused by adding <tt>-lbar</tt>
- to the link line when the binary is created). Other
- libraries that are needed by <tt>libbar</tt> are linked
- <em>indirectly</em> to <tt>foo</tt>, and the dynamic
- linker will load them automatically when it loads
- <tt>libbar</tt>. A package should depend on the libraries
- it directly uses, but not the libraries it indirectly uses.
- The dependencies for those libraries will automatically pull
- in the other libraries.
- </p>
-
- <p>
- A good example of where this helps is the following. We
- could update <tt>libimlib</tt> with a new version that
- supports a new graphics format called dgf (but retaining the
- same major version number) and depends on <tt>libdgf</tt>.
- If we used <prgn>ldd</prgn> to add dependencies for every
- library directly or indirectly linked with a binary, every
- package that uses <tt>libimlib</tt> would need to be
- recompiled so it would also depend on <tt>libdgf</tt> or it
- wouldn't run due to missing symbols. Since dependencies are
- only added based on ELF <tt>NEEDED</tt> attribute, packages
- using <tt>libimlib</tt> can rely on <tt>libimlib</tt> itself
- having the dependency on <tt>libdgf</tt> and so they would
- not need rebuilding.
- </p>
+ shared library, we must ensure that, when the package is
+ installed on the system, all of the libraries needed are also
+ installed. These dependencies must be added to the binary
+ package when it is built, since they may change based on which
+ version of a shared library the binary or library was linnked
+ with. To allow these dependencies to be constructed, shared
+ libraries must provide either a <file>symbols</file> file or
+ a <file>shlibs</file> file, which provide information on the
+ package dependencies required to ensure the presence of this
+ library. Any package which uses a shared library must use these
+ files to determine the required dependencies when it is built.
+ </p>
+
+ <p>
+ <file>shlibs</file> files were the original mechanism for
+ handling library dependencies. They are documented
+ in <ref id="sharedlibs-shlibdeps">. <file>symbols</file> files,
+ documented in this section, are recommended for most packages,
+ since they provide dependency information for each exported
+ symbol and therefore generate more accurate dependencies for
+ binaries that do not use symbols from newer versions of the
+ shared library. However, <file>shlibs</file> files must be used
+ for udebs. Packages which provide a <file>symbols</file> file
+ are not required to provide a <file>shlibs</file> file.
+ </p>
+
+ <p>
+ When a package that contains any shared libraries or compiled
+ binaries is built, it must run <prgn>dpkg-shlibdeps</prgn> on
+ each shared library and compiled binary to determine the
+ libraries used and hence the dependencies needed by the
+ package.<footnote>
+ <prgn>dpkg-shlibdeps</prgn> will use a program
+ like <prgn>objdump</prgn> or <prgn>readelf</prgn> to find the
+ libraries and the symbols in those libraries directly needed
+ by the binaries or shared libraries in the package.
</footnote>
</p>
<p>
- In the following sections, we will first describe where the
- various <tt>shlibs</tt> files are to be found, then how to
- use <prgn>dpkg-shlibdeps</prgn>, and finally the <tt>shlibs</tt>
- file format and how to create them if your package contains a
- shared library.
+ We say that a binary <tt>foo</tt> <em>directly</em> uses a
+ library <tt>libbar</tt> if it is explicitly linked with that
+ library (that is, the library is listed in the
+ ELF <tt>NEEDED</tt> attribute, caused by adding <tt>-lbar</tt>
+ to the link line when the binary is created). Other libraries
+ that are needed by <tt>libbar</tt> are
+ linked <em>indirectly</em> to <tt>foo</tt>, and the dynamic
+ linker will load them automatically when it
+ loads <tt>libbar</tt>. A package should depend on the libraries
+ it directly uses, but not the libraries it indirectly uses. The
+ dependencies for those libraries will automatically pull in the
+ other libraries. <prgn>dpkg-shlibdeps</prgn> will handle this
+ logic automatically, but package maintainers need to be aware of
+ this distinction between directly and indirectly using a library
+ if they have to override its results for some reason.
+ <footnote>
+ A good example of where this helps is the following. We could
+ update <tt>libimlib</tt> with a new version that supports a
+ new graphics format called dgf (but retaining the same major
+ version number) and depends on <tt>libdgf</tt>. If we
+ used <prgn>ldd</prgn> to add dependencies for every library
+ directly or indirectly linked with a binary, every package
+ that uses <tt>libimlib</tt> would need to be recompiled so it
+ would also depend on <tt>libdgf</tt> or it wouldn't run due to
+ missing symbols. Since dependencies are only added based on
+ ELF <tt>NEEDED</tt> attribute, packages
+ using <tt>libimlib</tt> can rely on <tt>libimlib</tt> itself
+ having the dependency on <tt>libdgf</tt> and so they would not
+ need rebuilding.
+ </footnote>
</p>
- <sect1>
- <heading>The <tt>shlibs</tt> files present on the system</heading>
-
<p>
- There are several places where <tt>shlibs</tt> files are
- found. The following list gives them in the order in which
- they are read by
- <qref id="pkg-dpkg-shlibdeps"><prgn>dpkg-shlibdeps</prgn></qref>.
- (The first one which gives the required information is used.)
+ In the following sections, we will first describe where the
+ various <file>symbols</file> files are to be found, then how to
+ use <prgn>dpkg-shlibdeps</prgn>, and finally
+ the <file>symbols</file> file format and how to create them if
+ your package contains a shared library.
</p>
- <p>
- <list>
- <item>
- <p><file>debian/shlibs.local</file></p>
-
- <p>
- This lists overrides for this package. This file should
- normally not be used, but may be needed temporarily in
- unusual situations to work around bugs in other packages,
- or in unusual cases where the normally declared dependency
- information in the installed <file>shlibs</file> file for
- a library cannot be used. This file overrides information
- obtained from any other source.
- </p>
- </item>
+ <sect1 id="symbols-paths">
+ <heading>The <file>symbols</file> files present on the
+ system</heading>
- <item>
- <p><file>/etc/dpkg/shlibs.override</file></p>
+ <p>
+ <file>symbols</file> files for a shared library are normally
+ provided by the shared library package, but there are several
+ override paths that are checked first in case that information
+ is wrong or missing. The following list gives them in the
+ order in which they are read by <prgn>dpkg-shlibdeps</prgn>
+ The first one that contains the required information is used.
+ <list>
+ <item>
+ <p><file>debian/*/DEBIAN/symbols</file></p>
- <p>
- This lists global overrides. This list is normally
- empty. It is maintained by the local system
- administrator.
- </p>
- </item>
+ <p>
+ During the package build, if the package itself contains
+ shared libraries with <file>symbols</file> files, they
+ will be generated in these staging directories
+ by <prgn>dpkg-gensymbols</prgn>. <file>symbols</file>
+ files found in the build tree take precedence
+ over <file>symbols</file> files from other binary
+ packages.
+ </p>
- <item>
- <p><file>DEBIAN/shlibs</file> files in the "build directory"</p>
+ <p>
+ These files must exist
+ before <prgn>dpkg-shlibdeps</prgn> is run or the
+ dependencies of binaries and libraries from a source
+ package on other libraries from that same source package
+ will not be correct. In practice, this means
+ that <prgn>dpkg-gensymbols</prgn> must be run
+ before <prgn>dpkg-shlibdeps</prgn> during the package
+ build.<footnote>
+ An example may clarify. Suppose the source
+ package <tt>foo</tt> generates two binary
+ packages, <tt>libfoo2</tt> and <tt>foo-runtime</tt>.
+ When building the binary packages, the contents of the
+ packages are staged in the
+ directories <file>debian/libfoo2</file>
+ and <file>debian/foo-runtime</file> respectively.
+ (<file>debian/tmp</file> could be used instead of one
+ of these.) Since <tt>libfoo2</tt> provides
+ the <tt>libfoo</tt> shared library, it will contain
+ a <tt>symbols</tt> file, which will be installed
+ in <file>debian/libfoo2/DEBIAN/symbols</file>,
+ eventually to be included as a control file in that
+ package. When <prgn>dpkg-shlibdeps</prgn> is run on
+ the
+ executable <file>debian/foo-runtime/usr/bin/foo-prog</file>,
+ it will examine
+ the <file>debian/libfoo2/DEBIAN/symbols</file> file to
+ determine whether <tt>foo-prog</tt>'s library
+ dependencies are satisfied by any of the libraries
+ provided by <tt>libfoo2</tt>. Since those binaries
+ were linked against the just-built shared library as
+ part of the build process, the <file>symbols</file>
+ file for the newly-built <tt>libfoo2</tt> must take
+ precedence over a <file>symbols</file> file for any
+ other <tt>libfoo2</tt> package already installed on
+ the system.
+ </footnote>
+ </p>
+ </item>
- <p>
- When packages are being built,
- any <file>debian/shlibs</file> files are copied into the
- control information file area of the temporary build
- directory and given the name <file>shlibs</file>. These
- files give details of any shared libraries included in the
- same package.<footnote>
- An example may help here. Let us say that the source
- package <tt>foo</tt> generates two binary
- packages, <tt>libfoo2</tt> and <tt>foo-runtime</tt>.
- When building the binary packages, the two packages are
- created in the directories <file>debian/libfoo2</file>
- and <file>debian/foo-runtime</file> respectively.
- (<file>debian/tmp</file> could be used instead of one of
- these.) Since <tt>libfoo2</tt> provides the
- <tt>libfoo</tt> shared library, it will require a
- <tt>shlibs</tt> file, which will be installed in
- <file>debian/libfoo2/DEBIAN/shlibs</file>, eventually to
- become <file>/var/lib/dpkg/info/libfoo2.shlibs</file>.
- When <prgn>dpkg-shlibdeps</prgn> is run on the
- executable <file>debian/foo-runtime/usr/bin/foo-prog</file>,
- it will examine
- the <file>debian/libfoo2/DEBIAN/shlibs</file> file to
- determine whether <tt>foo-prog</tt>'s library
- dependencies are satisfied by any of the libraries
- provided by <tt>libfoo2</tt>. For this reason,
- <prgn>dpkg-shlibdeps</prgn> must only be run once all of
- the individual binary packages' <tt>shlibs</tt> files
- have been installed into the build directory.
- </footnote>
- </p>
- </item>
+ <item>
+ <p>
+ <file>/etc/dpkg/symbols/<var>package</var>.symbols.<var>arch</var></file>
+ and <file>/etc/dpkg/symbols/<var>package</var>.symbols</file>
+ </p>
- <item>
- <p><file>/var/lib/dpkg/info/*.shlibs</file></p>
+ <p>
+ Per-system overrides of shared library dependencies.
+ These files normally do not exist. They are maintained
+ by the local system administrator and must not be
+ created by any Debian package.
+ </p>
+ </item>
- <p>
- These are the <file>shlibs</file> files corresponding to
- all of the packages installed on the system, and are
- maintained by the relevant package maintainers.
- </p>
- </item>
+ <item>
+ <p><file>symbols</file> control files for packages
+ installed on the system</p>
- <item>
- <p><file>/etc/dpkg/shlibs.default</file></p>
+ <p>
+ The <file>symbols</file> control files for all the
+ packages currently installed on the system are searched
+ last. This will be the most common source of shared
+ library dependency information. These are normally
+ found in <file>/var/lib/dpkg/info/*.symbols</file>, but
+ packages should not rely on this and instead should
+ use <tt>dpkg-query --control-path <var>package</var>
+ symbols</tt> if for some reason these files need to be
+ examined.
+ </p>
+ </item>
+ </list>
+ </p>
- <p>
- This file lists any shared libraries whose packages
- have failed to provide correct <file>shlibs</file> files.
- It was used when the <file>shlibs</file> setup was first
- introduced, but it is now normally empty. It is
- maintained by the <tt>dpkg</tt> maintainer.
- </p>
- </item>
- </list>
- </p>
- </sect1>
+ <p>
+ Be aware that if a <file>debian/shlibs.local</file> exists in
+ the source package, it will override any <file>symbols</file>
+ files. This is the only case where a <file>shlibs</file> is
+ used despite <file>symbols</file> files being present. See
+ <ref id="shlibs-paths"> and <ref id="sharedlibs-shlibdeps">
+ for more information.
+ </p>
+ </sect1>
- <sect1>
- <heading>How to use <prgn>dpkg-shlibdeps</prgn> and the
- <file>shlibs</file> files</heading>
+ <sect1 id="dpkg-shlibdeps">
+
<heading>How to use <prgn>dpkg-shlibdeps</prgn> and the
+ <tt>symbols</tt> files</heading>
- <p>
- Put a call to
- <qref id="pkg-dpkg-shlibdeps"><prgn>dpkg-shlibdeps</prgn></qref>
- into your <file>debian/rules</file> file. If your package
- contains only compiled binaries and libraries (but no scripts),
- you can use a command such as:
- <example compact="compact">
+ <p>
+ If your package contains any compiled binaries or shared
+ libraries, put a call to <prgn>dpkg-shlibdeps</prgn> into
+ your <file>debian/rules</file> file in the source package.
+ List all of the compiled binaries, libraries, or loadable
+ modules in your package. If your source package builds only a
+ single binary package that contains only compiled binaries and
+ libraries (but no scripts) and is not multiarch, you can use a
+ command such as:
+ <example compact="compact">
dpkg-shlibdeps debian/tmp/usr/bin/* debian/tmp/usr/sbin/* \
debian/tmp/usr/lib/*
- </example>
- Otherwise, you will need to explicitly list the compiled
- binaries and libraries.<footnote>
- If you are using <tt>debhelper</tt>, the
- <prgn>dh_shlibdeps</prgn> program will do this work for you.
- It will also correctly handle multi-binary packages.
- </footnote>
- </p>
+ </example>
+ but normally finding all of the binaries is more
+ complex.<footnote>
+ The easiest way to do this is to use a package helper
+ framework such as <tt>debhelper</tt>. If you are
+ using <tt>debhelper</tt>, the <prgn>dh_shlibdeps</prgn>
+ program will do this work for you. It will also correctly
+ handle multi-binary packages.
+ </footnote>
+ </p>
- <p>
- This command puts the dependency information into the
- <file>debian/substvars</file> file, which is then used by
- <prgn>dpkg-gencontrol</prgn>. You will need to place a
- <tt>${shlibs:Depends}</tt> variable in the <tt>Depends</tt>
- field in the control file for this to work.
- </p>
+ <p>
+ This command puts the dependency information into
+ the <file>debian/substvars</file> file, which is then used
+ by <prgn>dpkg-gencontrol</prgn>. You will need to place
+ a <tt>${shlibs:Depends}</tt> variable in the <tt>Depends</tt>
+ field in the control file of every binary package built by
+ this source package that contains compiled binaries,
+ libraries, or loadable modules. If you have multiple binary
+ packages, you will need to call <prgn>dpkg-shlibdeps</prgn> on
+ each one which contains compiled libraries or binaries, using
+ the <tt>-T</tt> option to the <tt>dpkg</tt> utilities to
+ specify a different <file>substvars</file> file for each
+ binary package.<footnote>
+ Again, <prgn>dh_shlibdeps</prgn>
+ and <prgn>dh_gencontrol</prgn> will handle all of this for
+ you if you're using <tt>debhelper</tt>.
+ </footnote>
+ </p>
- <p>
- If you have multiple binary packages, you will need to call
- <prgn>dpkg-shlibdeps</prgn> on each one which contains
- compiled libraries or binaries. In such a case, you will
- need to use the <tt>-T</tt> option to the <tt>dpkg</tt>
- utilities to specify a different <file>substvars</file> file.
- </p>
+ <p>
+ For more details on <prgn>dpkg-shlibdeps</prgn>,
+ see <manref name="dpkg-shlibdeps" section="1">.
+ </p>
+ </sect1>
- <p>
- If you are creating a udeb for use in the Debian Installer,
- you will need to specify that <prgn>dpkg-shlibdeps</prgn>
- should use the dependency line of type <tt>udeb</tt> by
- adding the <tt>-tudeb</tt> option<footnote>
- <prgn>dh_shlibdeps</prgn> from the <tt>debhelper</tt> suite
- will automatically add this option if it knows it is
- processing a udeb.
- </footnote>. If there is no dependency line of
- type <tt>udeb</tt> in the <file>shlibs</file>
- file, <prgn>dpkg-shlibdeps</prgn> will fall back to the regular
- dependency line.
- </p>
+ <sect1 id="symbols">
+ <heading>The <file>symbols</file> File Format</heading>
- <p>
- For more details on <prgn>dpkg-shlibdeps</prgn>, please see
- <ref id="pkg-dpkg-shlibdeps"> and
- <manref name="dpkg-shlibdeps" section="1">.
- </p>
- </sect1>
+ <p>
+ The following documents the format of the <file>symbols</file>
+ control file as included in binary packages. These files are
+ built from template <file>symbols</file> files in the source
+ package by <prgn>dpkg-gensymbols</prgn>. The template files
+ support a richer syntax that
+ allows <prgn>dpkg-gensymbols</prgn> to do some of the tedious
+ work involved in maintaining <file>symbols</file> files, such
+ as handling C++ symbols or optional symbols that may not exist
+ on particular architectures. When
+ writing <file>symbols</file> files for a shared library
+ package, refer to <manref name="dpkg-gensymbols" section="1">
+ for the richer syntax.
+ </p>
- <sect1 id="shlibs">
- <heading>The <file>shlibs</file> File Format</heading>
+ <p>
+ A <file>symbols</file> may contain one or more entries, one
+ for each shared library contained in the package corresponding
+ to that <file>symbols</file>. Each entry has the following
+ format:
+ </p>
- <p>
- Each <file>shlibs</file> file has the same format. Lines
- beginning with <tt>#</tt> are considered to be comments and
- are ignored. Each line is of the form:
- <example compact="compact">
-[<var>type</var>: ]<var>library-name</var> <var>soname-version</var> <var>dependencies ...</var>
- </example>
- </p>
+ <p>
+ <example>
+<var>library-soname</var> <var>main-dependency-template</var>
+[ | <var>alternative-dependency-template</var> ]
+[ ... ]
+[ * <var>field-name</var>: <var>field-value</var> ]
+[ ... ]
+ <var>symbol</var> <var>minimal-version</var>[ <var>id-of-dependency-template</var> ]
+ </example>
+ </p>
- <p>
- We will explain this by reference to the example of the
- <tt>zlib1g</tt> package, which (at the time of writing)
- installs the shared library <file>/usr/lib/libz.so.1.1.3</file>.
- </p>
+ <p>
+ To explain this format, we'll use the the <tt>zlib1g</tt>
+ package as an example, which (at the time of writing) installs
+ the shared library <file>/usr/lib/libz.so.1.2.3.4</file>.
+ Mandatory lines will be described first, followed by optional
+ lines.
+ </p>
- <p>
- <var>type</var> is an optional element that indicates the type
- of package for which the line is valid. The only type currently
- in use is <tt>udeb</tt>. The colon and space after the type are
- required.
- </p>
+ <p>
+ <var>library-soname</var> must contain exactly the value of
+ the ELF <tt>SONAME</tt> attribute of the shared library. In
+ our example, this is <tt>libz.so.1</tt>.<footnote>
+ This can be determined by using the command
+ <example compact="compact">
+readelf -d /usr/lib/libz.so.1.2.3.4 | grep SONAME
+ </example>
+ </footnote>
+ </p>
- <p>
- <var>library-name</var> is the name of the shared library,
- in this case <tt>libz</tt>. (This must match the name part
- of the soname, see below.)
- </p>
+ <p>
+ <var>main-dependency-template</var> has the same syntax as a
+ dependency field in a binary package control file, except that
+ the string <tt>#MINVER#</tt> is replaced by a version
+ restriction like <tt>(>= <var>version</var>)</tt> or by
+ nothing if an unversioned dependency is deemed sufficient.
+ The version restriction will be based on which symbols from
+ the shared library are referenced and the version at which
+ they were introduced (see below). In nearly all
+ cases, <var>main-dependency-template</var> will
+ be <tt><var>package</var> #MINVER#</tt>,
+ where <var>package</var> is the name of the binary package
+ containing the shared library. This adds a simple,
+ possibly-versioned dependency on the shared library package.
+ In some rare cases, such as when multiple packages provide the
+ same shared library ABI, the dependency template may need to
+ be more complex.
+ </p>
- <p>
- <var>soname-version</var> is the version part of the soname of
- the library. The soname is the thing that must exactly match
- for the library to be recognized by the dynamic linker, and is
- usually of the form
- <tt><var>name</var>.so.<var>major-version</var></tt>, in our
- example, <tt>libz.so.1</tt>.<footnote>
- This can be determined using the command
+ <p>
+ In our example, the first line of
+ the <tt>zlib1g</tt> <file>symbols</file> file would be:
<example compact="compact">
-objdump -p /usr/lib/libz.so.1.1.3 | grep SONAME
+libz.so.1 zlib1g #MINVER#
</example>
- </footnote>
- The version part is the part which comes after
- <tt>.so.</tt>, so in our case, it is <tt>1</tt>. The soname may
- instead be of the form
- <tt><var>name</var>-<var>major-version</var>.so</tt>, such
- as <tt>libdb-4.8.so</tt>, in which case the name would
- be <tt>libdb</tt> and the version would be <tt>4.8</tt>.
- </p>
+ </p>
+
+ <p>
+ Each public symbol exported by the shared library must have a
+ corresponding symbol line, indented by one
+ space. <var>symbol</var> is the exported symbol (which, for
+ C++, means the mangled symbol) followed by <tt>@</tt> and the
+ symbol version, or the string <tt>Base</tt> if there is no
+ symbol version. <var>minimal-version</var> is the most recent
+ version of the shared library that changed the behavior of
+ that symbol, whether by adding it, changing its function
+ signature (the parameters, their types, or the return type),
+ or its behavior in a way that is visible to a
+ caller. <var>id-of-dependency-template</var> is an optional
+ field that references
+ an <var>alternative-dependency-template</var>; see below for a
+ full description.
+ </p>
+
+ <p>
+ For example, <tt>libz.so.1</tt> contains the
+ symbols <tt>compress</tt>
+ and <tt>compressBound</tt>. <tt>compress</tt> has no symbol
+ version and last changed its behavior in upstream
+ version <tt>1:1.1.4</tt>. <tt>compressBound</tt> has the
+ symbol version <tt>ZLIB_1.2.0</tt>, was introduced in upstream
+ version <tt>1:1.2.0</tt>, and has not changed its behavior.
+ Its <file>symbols</file> file therefore contains the lines:
+ <example compact="compact">
+ compress@Base 1:1.1.4
+ compressBound@ZLIB_1.2.0 1:1.2.0
+ </example>
+ Packages using only <tt>compress</tt> would then get a
+ dependency of <tt>zlib1g (>= 1:1.1.4)</tt>, but packages
+ using <tt>compressBound</tt> would get a dependency
+ of <tt>zlib1g (>= 1:1.2.0)</tt>.
+ </p>
+
+ <p>
+ One or more <var>alternative-dependency-template</var> lines
+ may be provided. These are used in cases where some symbols
+ in the shared library should use one dependency template while
+ others should use a different template. The alternative
+ dependency templates are used only if a symbol line contains
+ the <var>id-of-dependency-template</var> field. The first
+ alternative dependency template is numbered 1, the second 2,
+ and so forth.<footnote>
+ An example of where this may be needed is with a library
+ that implements the libGL interface. All GL implementations
+ provide the same set of base interfaces, and then may
+ provide some additional interfaces only used by programs
+ that require that specific GL implementation. So, for
+ example, libgl1-mesa-glx may use the
+ following <file>symbols</file> file:
+ <example>
+libGL.so.1 libgl1
+| libgl1-mesa-glx #MINVER#
+ publicGlSymbol@Base 6.3-1
+ [...]
+ implementationSpecificSymbol@Base 6.5.2-7 1
+ [...]
+ </example>
+ Binaries or shared libraries using
+ only <tt>publicGlSymbol</tt> would depend only
+ on <tt>libgl1</tt> (which may be provided by multiple
+ packages), but ones
+ using <tt>implementationSpecificSymbol</tt> would get a
+ dependency on <tt>libgl1-mesa-glx (>= 6.5.2-7)</tt>
+ </footnote>
+ </p>
+
+ <p>
+ Finally, the entry for the library may contain one or more
+ metadata fields. Currently, the only
+ supported <var>field-name</var>
+ is <tt>Build-Depends-Package</tt>, whose value lists
+ the <qref id="sharedlibs-dev">library development
+ package</qref> on which packages using this shared library
+ declare a build dependency. If this field is
+ present, <prgn>dpkg-shlibdeps</prgn> uses it to ensure that
+ the resulting binary package dependency on the shared library
+ is at least as strict as the source package dependency on the
+ shared library development package.<footnote>
+ This field should normally not be necessary, since if the
+ behavior of any symbol has changed, the corresponding
+ symbol <var>minimal-version</var> should have been
+ increased. But including it makes the <tt>symbols</tt>
+ system more robust by tightening the dependency in cases
+ where the package using the shared library specifically
+ requires at least a particular version of the shared library
+ development package for some reason.
+ </footnote>
+ For our example, the <tt>zlib1g</tt> <file>symbols</file> file
+ would contain:
+ <example compact="compact">
+ * Build-Depends-Package: zlib1g-dev
+ </example>
+ (Don't forget the leading space.)
+ </p>
+
+ <p>
+ Also see <manref name="deb-symbols" section="5">.
+ </p>
+ </sect1>
+
+ <sect1 id="providing-symbols">
+ <heading>Providing a <file>symbols</file> file</heading>
+
+ <p>
+ If your package provides a shared library, you should arrange
+ to include a <file>symbols</file> control file following the
+ format described above in that package. You must include
+ either a <file>symbols</file> control file or
+ a <file>shlibs</file> control file.
+ </p>
+
+ <p>
+ Normally, this is done by creating a <file>symbols</file> in
+ the source package
+ named <file>debian/<var>package</var>.symbols</file>
+ or <file>debian/symbols</file>, possibly
+ with <file>.<var>arch</var></file> appended if the symbols
+ information varies by architecture. This file may use the
+ extended syntax documented
+ in <manref name="dpkg-gensymbols" section="1">. Then,
+ call <prgn>dpkg-gensymbols</prgn> as part of the package build
+ process. It will create <file>symbols</file> files in the
+ package staging area based on the binaries and libraries in
+ the package staging area and the <file>symbols</file> files in
+ the source package.<footnote>
+ If you are
+ using <tt>debhelper</tt>, <prgn>dh_makeshlibs</prgn> will
+ take care of calling either <prgn>dpkg-gensymbols</prgn>
+ or generating a <file>shlibs</file> file as appropriate.
+ </footnote>
+ </p>
+
+ <p>
+ Packages that provide <file>symbols</file> files must keep
+ them up-to-date to ensure correct dependencies in packages
+ that use the shared libraries. This means updating
+ the <file>symbols</file> file whenever a new public symbol is
+ added, changing the <var>minimal-version</var> field whenever
+ a symbol changes behavior or signature, and changing
+ the <var>library-soname</var>
+ and <var>main-dependency-template</var>, and probably all of
+ the <var>minimal-version</var> fields, when the library
+ changes <tt>SONAME</tt>. Removing a public symbol from
+ the <file>symbols</file> file because it's no longer provided
+ by the library normally requires changing the <tt>SONAME</tt>
+ of the library. See <ref id="sharedlibs-runtime">.
+ </p>
+
+ <p>
+ Special care should be taken in updating
+ the <var>minimal-version</var> field when the behavior of a
+ public symbol changes. This is easy to neglect, since there
+ is no automated method of determining such changes, but
+ failing to update <var>minimal-version</var> in this case may
+ result in binary packages with too-weak dependencies that will
+ fail at runtime, possibly in ways that can cause security
+ vulnerabilities. If the package maintainer believes that a
+ symbol behavior change may have occurred but isn't sure, it's
+ safer to update the <var>minimal-version</var> of all possibly
+ affected symbols to the current upstream version rather than
+ leave them unmodified. This may result in unnecessarily
+ strict dependencies, but it ensures that packages whose
+ dependencies are satisfied will work properly.
+ </p>
+
+ <p>
+ A common example of when a change
+ to <var>minimal-version</var> is required is a function that
+ takes an enum or struct argument that controls what the
+ function does. For example:
+ <example>
+enum library_op { OP_FOO, OP_BAR };
+int library_do_operation(enum library_op);
+ </example>
+ If a new operation, <tt>OP_BAZ</tt>, is added,
+ the <var>minimal-version</var>
+ of <tt>library_do_operation</tt> must be increased to the
+ version at which <tt>OP_BAZ</tt> was introduced. Otherwise, a
+ binary built against the new version of the library (having
+ detected at compile-time that the library
+ supports <tt>OP_BAZ</tt>) may be installed with a shared
+ library that doesn't support <tt>OP_BAZ</tt> and will fail at
+ runtime when it tries to pass <tt>OP_BAZ</tt> into this
+ function.
+ </p>
+
+ <p>
+ The <var>minimal-version</var> field normally should not
+ contain the Debian revision of the package, since the library
+ behavior is normally fixed for a particular upstream version
+ and any Debian packaging of that upstream version will have
+ the same behavior. In the rare case that the library behavior
+ was changed in a particular Debian revision,
+ appending <tt>~</tt> to the end of
+ the <var>minimal-version</var> that includes the Debian
+ revision is recommended, since this allows backports of the
+ shared library package using the normal backport versioning
+ convention to satisfy the dependency.
+ </p>
+ </sect1>
+ </sect>
+
+ <sect id="sharedlibs-shlibdeps">
+ <heading>Dependencies between the library and other packages -
+ the <tt>shlibs</tt> system</heading>
<p>
- <var>dependencies</var> has the same syntax as a dependency
- field in a binary package control file. It should give
- details of which packages are required to satisfy a binary
- built against the version of the library contained in the
- package. See <ref id="depsyntax"> for details.
+ The <tt>shlibs</tt> system is an alternative to
+ the <tt>symbols</tt> system for declaring dependencies for
+ shared libraries. It predated the <tt>symbols</tt> system and
+ is therefore frequently seen in older packages. It is also
+ required for udebs, which do not support <tt>symbols</tt>.
</p>
<p>
- In our example, if the first version of the <tt>zlib1g</tt>
- package which contained a minor number of at least
- <tt>1.3</tt> was <var>1:1.1.3-1</var>, then the
- <tt>shlibs</tt> entry for this library could say:
- <example compact="compact">
-libz 1 zlib1g (>= 1:1.1.3)
- </example>
- The version-specific dependency is to avoid warnings from
- the dynamic linker about using older shared libraries with
- newer binaries.
+ <file>shlibs</file> files do not provide as detailed of
+ information as <file>symbols</file> files. They only provide
+ information about the library as a whole, not individual
+ symbols, and therefore have to force tighter dependencies since
+ they have no way of relaxing dependencies for binaries and
+ libraries that only use symbols whose behavior has not changed.
+ Because of this, and because of some problems with
+ how <file>shlibs</file> files represent the
+ library <tt>SONAME</tt>, <file>symbols</file> files are
+ recommended instead for any shared library package that isn't a
+ udeb.
</p>
<p>
- As zlib1g also provides a udeb containing the shared library,
- there would also be a second line:
- <example compact="compact">
-udeb: libz 1 zlib1g-udeb (>= 1:1.1.3)
- </example>
+ In the following sections, we will first describe where the
+ various <file>shlibs</file> files are to be found, then how to
+ use <prgn>dpkg-shlibdeps</prgn>, and finally
+ the <file>shlibs</file> file format and how to create them if
+ your package contains a shared library. Much of the information
+ about <file>shlibs</file> files is the same as
+ for <file>symbols</file> files, so only the differences will be
+ mentioned.
</p>
- </sect1>
- <sect1>
- <heading>Providing a <file>shlibs</file> file</heading>
+ <sect1 id="shlibs-paths">
+ <heading>The <file>shlibs</file> files present on the
+ system</heading>
- <p>
- If your package provides a shared library, you need to create
- a <file>shlibs</file> file following the format described above.
- It is usual to call this file <file>debian/shlibs</file> (but if
- you have multiple binary packages, you might want to call it
- <file>debian/shlibs.<var>package</var></file> instead). Then
- let <file>debian/rules</file> install it in the control
- information file area:
- <example compact="compact">
+ <p>
+ There are several places where <tt>shlibs</tt> files are
+ found. The following list gives them in the order in which
+ they are read by <prgn>dpkg-shlibdeps</prgn>. (The first one
+ which gives the required information is used.)
+ <list>
+ <item>
+ <p><file>debian/shlibs.local</file></p>
+
+ <p>
+ This lists overrides for this package. This file should
+ normally not be used, but may be needed temporarily in
+ unusual situations to work around bugs in other
+ packages, or in unusual cases where the normally
+ declared dependency information in the
+ installed <file>shlibs</file> file for a library cannot
+ be used. This file overrides information obtained from
+ any other source.
+ </p>
+ </item>
+
+ <item>
+ <p><file>/etc/dpkg/shlibs.override</file></p>
+
+ <p>
+ This lists global overrides. This list is normally
+ empty. It is maintained by the local system
+ administrator.
+ </p>
+ </item>
+
+ <item>
+ <p><file>DEBIAN/shlibs</file> files in the "build
+ directory"</p>
+
+ <p>
+ When packages are being built,
+ any <file>debian/shlibs</file> files are copied into the
+ control information file area of the temporary build
+ directory and given the name <file>shlibs</file>. These
+ files give details of any shared libraries included in
+ the same package.
+ </p>
+ </item>
+
+ <item>
+ <p><file>shlibs</file> control files for packages
+ installed on the system</p>
+
+ <p>
+ The <file>shlibs</file> control files for all the
+ packages currently installed on the system. These are
+ normally found
+ in <file>/var/lib/dpkg/info/*.symbols</file>, but
+ packages should not rely on this and instead should
+ use <tt>dpkg-query --control-path <var>package</var>
+ shlibs</tt> if for some reason these files need to be
+ examined.
+ </p>
+ </item>
+
+ <item>
+ <p><file>/etc/dpkg/shlibs.default</file></p>
+
+ <p>
+ This file lists any shared libraries whose packages have
+ failed to provide correct <file>shlibs</file> files. It
+ was used when the <file>shlibs</file> setup was first
+ introduced, but it is now normally empty. It is
+ maintained by the <tt>dpkg</tt> maintainer.
+ </p>
+ </item>
+ </list>
+ </p>
+
+ <p>
+ If a <file>symbols</file> file for a shared library package
+ is available, <prgn>dpkg-shlibdeps</prgn> will always use it
+ in preference to a <file>shlibs</file>, with the exception
+ of <file>debian/shlibs.local</file>. The latter overrides any
+ other <file>shlibs</file> or <file>symbols</file> files.
+ </p>
+ </sect1>
+
+ <sect1>
+ <heading>How to use <prgn>dpkg-shlibdeps</prgn> and the
+ <file>shlibs</file> files</heading>
+
+ <p>
+ Use of <prgn>dpkg-shlibdeps</prgn> with <file>shlibs</file>
+ files is generally the same as with <file>symbols</file>
+ files. See <ref id="dpkg-shlibdeps">.
+ </p>
+
+ <p>
+ If you are creating a udeb for use in the Debian Installer,
+ you will need to specify that <prgn>dpkg-shlibdeps</prgn>
+ should use the dependency line of type <tt>udeb</tt> by
+ adding the <tt>-tudeb</tt> option<footnote>
+ <prgn>dh_shlibdeps</prgn> from the <tt>debhelper</tt> suite
+ will automatically add this option if it knows it is
+ processing a udeb.
+ </footnote>. If there is no dependency line of
+ type <tt>udeb</tt> in the <file>shlibs</file>
+ file, <prgn>dpkg-shlibdeps</prgn> will fall back to the
+ regular dependency line.
+ </p>
+ </sect1>
+
+ <sect1 id="shlibs">
+ <heading>The <file>shlibs</file> File Format</heading>
+
+ <p>
+ Each <file>shlibs</file> file has the same format. Lines
+ beginning with <tt>#</tt> are considered to be comments and
+ are ignored. Each line is of the form:
+ <example compact="compact">
+[<var>type</var>: ]<var>library-name</var> <var>soname-version</var> <var>dependencies ...</var>
+ </example>
+ </p>
+
+ <p>
+ We will explain this by reference to the example of the
+ <tt>zlib1g</tt> package, which (at the time of writing)
+ installs the shared
+ library <file>/usr/lib/libz.so.1.2.3.4</file>.
+ </p>
+
+ <p>
+ <var>type</var> is an optional element that indicates the type
+ of package for which the line is valid. The only type
+ currently in use is <tt>udeb</tt>. The colon and space after
+ the type are required.
+ </p>
+
+ <p>
+ <var>library-name</var> is the name of the shared library, in
+ this case <tt>libz</tt>. (This must match the name part of
+ the soname, see below.)
+ </p>
+
+ <p>
+ <var>soname-version</var> is the version part of the
+ ELF <tt>SONAME</tt> attribute of the library.
+ The <tt>SONAME</tt> is the thing that must exactly match for
+ the library to be recognized by the dynamic linker, and is
+ usually of the
+ form <tt><var>name</var>.so.<var>major-version</var></tt>, in
+ our example, <tt>libz.so.1</tt>.
+ The version part is the part which comes after
+ <tt>.so.</tt>, so in our case, it is <tt>1</tt>. The soname
+ may instead be of the
+ form <tt><var>name</var>-<var>major-version</var>.so</tt>,
+ such as <tt>libdb-5.1.so</tt>, in which case the name would
+ be <tt>libdb</tt> and the version would be <tt>5.1</tt>.
+ </p>
+
+ <p>
+ <var>dependencies</var> has the same syntax as a dependency
+ field in a binary package control file. It should give
+ details of which packages are required to satisfy a binary
+ built against the version of the library contained in the
+ package. See <ref id="depsyntax"> for details.
+ </p>
+
+ <p>
+ In our example, if the last change to the <tt>zlib1g</tt>
+ package that could change behavior for a client of that
+ library was in version <tt>1:1.2.3.3.dfsg-1</tt>, then
+ the <tt>shlibs</tt> entry for this library could say:
+ <example compact="compact">
+libz 1 zlib1g (>= 1:1.2.3.3.dfsg-1)
+ </example>
+ This version restriction must be new enough that any binary
+ built against the current version of the library will work
+ with any version of the shared library that satisfies that
+ dependency.
+ </p>
+
+ <p>
+ As zlib1g also provides a udeb containing the shared library,
+ there would also be a second line:
+ <example compact="compact">
+udeb: libz 1 zlib1g-udeb (>= 1:1.2.3.3.dfsg-1)
+ </example>
+ </p>
+ </sect1>
+
+ <sect1>
+ <heading>Providing a <file>shlibs</file> file</heading>
+
+ <p>
+ If your package provides a shared library, you need to create
+ a <file>shlibs</file> file following the format described
+ above. It is usual to call this
+ file <file>debian/shlibs</file> (but if you have multiple
+ binary packages, you might want to call
+ it <file>debian/<var>package</var>.shlibs</file> instead).
+ Then let <file>debian/rules</file> install it in the control
+ information file area:
+ <example compact="compact">
install -m644 debian/shlibs debian/tmp/DEBIAN
- </example>
- or, in the case of a multi-binary package:
- <example compact="compact">
-install -m644 debian/shlibs.<var>package</var> debian/<var>package</var>/DEBIAN/shlibs
- </example>
- An alternative way of doing this is to create the
- <file>shlibs</file> file in the control information file area
- directly from <file>debian/rules</file> without using
- a <file>debian/shlibs</file> file at all,<footnote>
- This is what <prgn>dh_makeshlibs</prgn> in
- the <package>debhelper</package> suite does. If your package
- also has a udeb that provides a shared
- library, <prgn>dh_makeshlibs</prgn> can automatically generate
- the <tt>udeb:</tt> lines if you specify the name of the udeb
- with the <tt>--add-udeb</tt> option.
- </footnote>
- since the <file>debian/shlibs</file> file itself is ignored by
- <prgn>dpkg-shlibdeps</prgn>.
- </p>
+ </example>
+ or, in the case of a multi-binary package:
+ <example compact="compact">
+install -m644 debian/<var>package</var>.shlibs debian/<var>package</var>/DEBIAN/shlibs
+ </example>
+ An alternative way of doing this is to create
+ the <file>shlibs</file> file in the control information file
+ area directly from <file>debian/rules</file> without using
+ a <file>debian/shlibs</file> file at all,<footnote>
+
This is what <prgn>dh_makeshlibs</prgn> in
+
the <package>debhelper</package> suite does. If your package
+ also has a udeb that provides a shared
+ library, <prgn>dh_makeshlibs</prgn> can automatically
+ generate the <tt>udeb:</tt> lines if you specify the name of
+ the udeb with the <tt>--add-udeb</tt> option.
+ </footnote>
+ since the <file>debian/shlibs</file> file itself is ignored by
+
<prgn>dpkg-shlibdeps</prgn>.
+ </p>
- <p>
- As <prgn>dpkg-shlibdeps</prgn> reads the
- <file>DEBIAN/shlibs</file> files in all of the binary packages
- being built from this source package, all of the
- <file>DEBIAN/shlibs</file> files should be installed before
- <prgn>dpkg-shlibdeps</prgn> is called on any of the binary
- packages.
- </p>
- </sect1>
+ Since <prgn>dpkg-shlibdeps</prgn> reads
+ the <file>DEBIAN/shlibs</file> files in all of the binary
+ packages being built from this source package, all of
+ the <file>DEBIAN/shlibs</file> files should be installed
+ before <prgn>dpkg-shlibdeps</prgn> is called on any of the
+ binary packages.
+ </p>
+ </sect1>
</sect>
</chapt>
Although not enforced by the build tools, shared libraries
must be linked against all libraries that they use symbols from
in the same way that binaries are. This ensures the correct
- functioning of the <qref id="sharedlibs-shlibdeps">shlibs</qref>
- system and guarantees that all libraries can be safely opened
+ functioning of the <qref id="sharedlibs-symbols">symbols</qref>
+ and <qref id="sharedlibs-shlibdeps">shlibs</qref>
+ systems and guarantees that all libraries can be safely opened
with <tt>dlopen()</tt>. Packagers may wish to use the gcc
option <tt>-Wl,-z,defs</tt> when building a shared library.
Since this option enforces symbol resolution at build time,
<prgn>dpkg-genchanges</prgn>.</p>
</sect1>
- <sect1 id="pkg-dpkg-shlibdeps">
- <heading>
- <prgn>dpkg-shlibdeps</prgn> - calculates shared library
- dependencies
- </heading>
-
- <p>
- This program is usually called from <file>debian/rules</file>
- just before <prgn>dpkg-gencontrol</prgn> (see <ref
- id="pkg-sourcetree">), in the top level of the source tree.
- </p>
-
- <p>
- Its arguments are executables and shared libraries
- <footnote>
- <p>
- They may be specified either in the locations in the
- source tree where they are created or in the locations
- in the temporary build tree where they are installed
- prior to binary package creation.
- </p>
- </footnote> for which shared library dependencies should
- be included in the binary package's control file.
- </p>
-
- <p>
- If some of the found shared libraries should only
- warrant a <tt>Recommends</tt> or <tt>Suggests</tt>, or if
- some warrant a <tt>Pre-Depends</tt>, this can be achieved
- by using the <tt>-d<var>dependency-field</var></tt> option
- before those executable(s). (Each <tt>-d</tt> option
- takes effect until the next <tt>-d</tt>.)
- </p>
-
- <p>
- <prgn>dpkg-shlibdeps</prgn> does not directly cause the
- output control file to be modified. Instead by default it
- adds to the <file>debian/substvars</file> file variable
- settings like <tt>shlibs:Depends</tt>. These variable
- settings must be referenced in dependency fields in the
- appropriate per-binary-package sections of the source
- control file.
- </p>
-
- <p>
- For example, a package that generates an essential part
- which requires dependencies, and optional parts that
- which only require a recommendation, would separate those
- two sets of dependencies into two different fields.<footnote>
- At the time of writing, an example for this was the
- <package/xmms/ package, with Depends used for the xmms
- executable, Recommends for the plug-ins and Suggests for
- even more optional features provided by unzip.
- </footnote>
- It can say in its <file>debian/rules</file>:
- <example>
- dpkg-shlibdeps -dDepends <var>program anotherprogram ...</var> \
- -dRecommends <var>optionalpart anotheroptionalpart</var>
- </example>
- and then in its main control file <file>debian/control</file>:
- <example>
- <var>...</var>
- Depends: ${shlibs:Depends}
- Recommends: ${shlibs:Recommends}
- <var>...</var>
- </example>
- </p>
-
- <p>
- Sources which produce several binary packages with
- different shared library dependency requirements can use
- the <tt>-p<var>varnameprefix</var></tt> option to override
- the default <tt>shlibs:</tt> prefix (one invocation of
- <prgn>dpkg-shlibdeps</prgn> per setting of this option).
- They can thus produce several sets of dependency
- variables, each of the form
- <tt><var>varnameprefix</var>:<var>dependencyfield</var></tt>,
- which can be referred to in the appropriate parts of the
- binary package control files.
- </p>
- </sect1>
-
-
<sect1 id="pkg-dpkg-distaddfile">
<heading>
<prgn>dpkg-distaddfile</prgn> - adds a file to
projects / debian / debian-policy.git / commitdiff