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-   -   Bug#571776: document symbols (http://www.linux-archive.org/debian-dpkg/616278-bug-571776-document-symbols.html)

Russ Allbery 01-02-2012 08:51 PM

Bug#571776: document symbols
 
Hello folks,

I took some time today and wrote a first draft of a new section of Policy
documenting symbols files, and the revisions to shlibs for their
interaction. Please review. There's quite a lot of material here,
including details from dpkg-shlibdeps, dpkg-gensymbols, and deb-symbols
documentation as well as additional requirements and recommendations
around how to maintain the minimal-version field.

I tried sending a unified diff, but the new sections are largely
unreadable since they're intermixed with the old sections being removed.
Hence, for review purposes, here are the symbols and shlibs sections in
their entirety, followed by a diff for the changes elsewhere in Policy.
You can also refer to branch bug571776-rra in the Policy repository.

<sect id="sharedlibs-symbols">
<heading>Dependencies between the library and other packages -
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. 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>
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>

<p>
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>

<sect1 id="symbols-paths">
<heading>The <file>symbols</file> files present on the
system</heading>

<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>
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>

<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>

<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>

<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>

<item>
<p><file>symbols</file> control files for packages
installed on the system</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>
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 id="dpkg-shlibdeps">
<heading>How to use <prgn>dpkg-shlibdeps</prgn> and the
<tt>symbols</tt> files</heading>

<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>
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 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>
For more details on <prgn>dpkg-shlibdeps</prgn>,
see <manref name="dpkg-shlibdeps" section="1">.
</p>
</sect1>

<sect1 id="symbols">
<heading>The <file>symbols</file> File Format</heading>

<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>

<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>
<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>
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>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>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>
In our example, the first line of
the <tt>zlib1g</tt> <file>symbols</file> file would be:
<example compact="compact">
libz.so.1 zlib1g #MINVER#
</example>
</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>
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>
<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>
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 id="shlibs-paths">
<heading>The <file>shlibs</file> 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 <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/<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>
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>


diff --git a/policy.sgml b/policy.sgml
index 79281e9..cca4b6d 100644
--- a/policy.sgml
+++ b/policy.sgml
@@ -840,10 +840,11 @@
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>

@@ -5521,9 +5522,9 @@ Replaces: mail-transport-agent
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>
@@ -7702,8 +8153,9 @@ INSTALL = install -s # (or use strip on the files in debian/tmp)
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,
@@ -10481,89 +10933,6 @@ END-INFO-DIR-ENTRY
<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


--
Russ Allbery (rra@debian.org) <http://www.eyrie.org/~eagle/>


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Jakub Wilk 01-03-2012 10:29 PM

Bug#571776: document symbols
 
* Russ Allbery <rra@debian.org>, 2012-01-02, 13:51:

<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>


Hmm. It was my understanding that one of the purposes of
Build-Depends-Package is to avoid bumping symbol versions in situations
like this.


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Russ Allbery 01-03-2012 10:41 PM

Bug#571776: document symbols
 
Jakub Wilk <jwilk@debian.org> writes:
> * Russ Allbery <rra@debian.org>, 2012-01-02, 13:51:

>> <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>

> Hmm. It was my understanding that one of the purposes of
> Build-Depends-Package is to avoid bumping symbol versions in situations
> like this.

That moves the onus from the library maintainer to the client package
maintainer, who then has to know whether the code is sensitive to this
sort of change and be constantly tightening the Build-Depends. That
sounds wrong; determining whether a particular library client cares about
a behavior change can be quite difficult, particularly compared to just
bumping the symbol revision if the implementation has changed.

Hm, I suppose that if the client upstream knows about this sort of thing,
they may document it somewhere, which would make it easier. But I'm
thinking about a library client that, say, probes for the version of the
package in configure or via a version provided by the library and
selectively enables behavior based on those results without otherwise
saying anything about it. That sort of thing is pretty common and
sometimes hard to notice.

Also, historically, this sort of version bump was required for shlibs, so
this is just moving the requirement along to symbols.

--
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Raphael Hertzog 01-12-2012 06:52 AM

Bug#571776: document symbols
 
Hi,

On Mon, 02 Jan 2012, Russ Allbery wrote:
> <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. 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

s/linnked/linked/

[...]
> <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>

In practice I don't think that we have any package providing a symbols
files without a shlibs file.

[...]

> <sect1 id="dpkg-shlibdeps">
> <heading>How to use <prgn>dpkg-shlibdeps</prgn> and the
> <tt>symbols</tt> files</heading>
>
> <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>
> but normally finding all of the binaries is more
> complex.

I would drop the part above (up to the 4 dashes that I added). This
example will only mislead people IMO because debian/tmp/ is far from being
the norm. debian/<pkg> is much more common for single binary packages. And
as you said, it doesn't cover all cases.

> <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 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>

I would indicate in the footnote that dh_shlibdeps/dh_gencontrol use an
alternate substvars file by default (debian/<pkg>.substvars).

> <sect1 id="symbols">
> <heading>The <file>symbols</file> File Format</heading>
[...]
> 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.)

What leading space are you referring to ?

[...]
> <sect1 id="shlibs-paths">
> <heading>The <file>shlibs</file> files present on the
> system</heading>
[...]
> <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>

debian/shlibs is (no longer) a standard file... debhelper doesn't install
such files, it generates shlibs files on the fly and I don't believe that
any modern package still has debian/shlibs.

So I would rewrite this paragraph to just say that DEBIAN/shlibs is the
shlibs file produced by the current package build.

[...]
> <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/<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>

I would shorten the explanation here and drop the example of how to
install a manually crafted shlibs file. This is far from being the norm
and should not be difficult to find out alone if one really needs it.

----
Besides those details, everything was excellent and I'm happy to second
this (with or without any of the suggested fixes above).

Thanks for the great work!
--
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liberate it: http://debian-handbook.info/liberation/


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Russ Allbery 01-13-2012 05:02 PM

Bug#571776: document symbols
 
Raphael Hertzog <hertzog@debian.org> writes:
> On Mon, 02 Jan 2012, Russ Allbery wrote:

> [...]
>> <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>

> In practice I don't think that we have any package providing a symbols
> files without a shlibs file.

Yes, but there was some discussion in the Policy bug asking why shlibs
files were required when they're not used if a symbols file is present,
and while I originally argued that keeping them both made sense, I came
around to that position after reviewing the bug discussion. It doesn't
hurt anything, but there doesn't really seem to be any point in providing
shlibs if symbols is present.

> ----
>> 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>
>> but normally finding all of the binaries is more
>> complex.

> I would drop the part above (up to the 4 dashes that I added). This
> example will only mislead people IMO because debian/tmp/ is far from
> being the norm. debian/<pkg> is much more common for single binary
> packages. And as you said, it doesn't cover all cases.

Yeah, good point. This was retained from the old shlibs documentation,
but at this point I don't think anyone really looks here to see how to do
this. Dropped.

>> 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>

> I would indicate in the footnote that dh_shlibdeps/dh_gencontrol use an
> alternate substvars file by default (debian/<pkg>.substvars).

I now have:

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>, including generating
separate <file>substvars</file> files for each binary
package and calling <prgn>dpkg-gencontrol</prgn> with the
appropriate flags.
</footnote>

>> <sect1 id="symbols">
>> <heading>The <file>symbols</file> File Format</heading>
> [...]
>> 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.)

> What leading space are you referring to ?

I now have:

(Don't forget the space before the <tt>*</tt> so that it will
be parsed as part of the entry for that library.)

Due to the way that the formatting of Policy works, it's very hard to tell
that there's a space there, and unlike with symbols where the indentation
is fairly obvious, it's not completely obvious that it's required.

> [...]
>> <sect1 id="shlibs-paths">
>> <heading>The <file>shlibs</file> files present on the
>> system</heading>
> [...]
>> <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>

> debian/shlibs is (no longer) a standard file... debhelper doesn't install
> such files, it generates shlibs files on the fly and I don't believe that
> any modern package still has debian/shlibs.

> So I would rewrite this paragraph to just say that DEBIAN/shlibs is the
> shlibs file produced by the current package build.

I now have:

<p>
These files are generated as part of the package build
process and staged for inclusion as control files in the
binary packages being built. They provide details of
any shared libraries included in the same package.
</p>

> I would shorten the explanation here and drop the example of how to
> install a manually crafted shlibs file. This is far from being the norm
> and should not be difficult to find out alone if one really needs it.

I've replaced this section with just:

<sect1>
<heading>Providing a <file>shlibs</file> file</heading>

<p>
To provide a <file>shlibs</file> file for a shared library
binary package, create a <file>shlibs</file> file following
the format described above and place it in
the <file>DEBIAN</file> directory for that package during the
build. It will then be included as a control file for that
package<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>.
</p>

<p>
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>

Thanks for the review!

--
Russ Allbery (rra@debian.org) <http://www.eyrie.org/~eagle/>


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Archive: 87ehv3a3ak.fsf@windlord.stanford.edu">http://lists.debian.org/87ehv3a3ak.fsf@windlord.stanford.edu

Russ Allbery 01-13-2012 05:08 PM

Bug#571776: document symbols
 
Russ Allbery <rra@debian.org> writes:

> I tried sending a unified diff, but the new sections are largely
> unreadable since they're intermixed with the old sections being removed.
> Hence, for review purposes, here are the symbols and shlibs sections in
> their entirety, followed by a diff for the changes elsewhere in Policy.
> You can also refer to branch bug571776-rra in the Policy repository.

Here is an updated diff with the changes from Raphael's review. git diff
--patience actually generates a decent diff (I learn something new every
day!), so I didn't have to separate out the new sections.

diff --git a/policy.sgml b/policy.sgml
index 23c1913..b57dd76 100644
--- a/policy.sgml
+++ b/policy.sgml
@@ -840,10 +840,11 @@
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>

@@ -5521,9 +5522,9 @@ Replaces: mail-transport-agent
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>
@@ -5792,361 +5793,789 @@ Replaces: mail-transport-agent
</p>
</sect>

+ <sect id="sharedlibs-symbols">
+ <heading>Dependencies between the library and other packages -
+ 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. 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 linked
+ 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>
+ 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>
+
+ <p>
+ 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>
+
+ <sect1 id="symbols-paths">
+ <heading>The <file>symbols</file> files present on the
+ system</heading>
+
+ <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>
+ 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>
+
+ <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>
+
+ <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>
+
+ <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>
+
+ <item>
+ <p><file>symbols</file> control files for packages
+ installed on the system</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>
+ 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 id="dpkg-shlibdeps">
+ <heading>How to use <prgn>dpkg-shlibdeps</prgn> and the
+ <tt>symbols</tt> files</heading>
+
+ <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.<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 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>, including generating
+ separate <file>substvars</file> files for each binary
+ package and calling <prgn>dpkg-gencontrol</prgn> with the
+ appropriate flags.
+ </footnote>
+ </p>
+
+ <p>
+ For more details on <prgn>dpkg-shlibdeps</prgn>,
+ see <manref name="dpkg-shlibdeps" section="1">.
+ </p>
+ </sect1>
+
+ <sect1 id="symbols">
+ <heading>The <file>symbols</file> File Format</heading>
+
+ <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>
+
+ <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>
+ <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>
+ 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>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>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>
+ In our example, the first line of
+ the <tt>zlib1g</tt> <file>symbols</file> file would be:
+ <example compact="compact">
+libz.so.1 zlib1g #MINVER#
+ </example>
+ </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 space before the <tt>*</tt> so that it will
+ be parsed as part of the entry for that library.)
+ </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>
- 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.
+ 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>
- 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>
- </footnote>
+ <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>
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.
+ 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>
- <heading>The <tt>shlibs</tt> files present on the system</heading>
+ <sect1 id="shlibs-paths">
+ <heading>The <file>shlibs</file> 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.)
- </p>
+ <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>
- <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>

- <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>

- <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>

- <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>

- <item>
- <p><file>DEBIAN/shlibs</file> files in the "build directory"</p>
+ <p>
+ These files are generated as part of the package build
+ process and staged for inclusion as control files in the
+ binary packages being built. They provide details of
+ any shared libraries included in the same package.
+ </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>shlibs</file> control files for packages
+ installed on the system</p>

- <item>
- <p><file>/var/lib/dpkg/info/*.shlibs</file></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>

- <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>/etc/dpkg/shlibs.default</file></p>

- <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>
- 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>
+ 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
+ <sect1>
+ <heading>How to use <prgn>dpkg-shlibdeps</prgn> and the
<file>shlibs</file> 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">
-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>
+ <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>
- 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>
+ 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>

- <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>
+ <sect1 id="shlibs">
+ <heading>The <file>shlibs</file> File Format</heading>

- <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>
-
- <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>
-
- <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">
+ <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>
+ </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>
+ 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>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>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 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
- <example compact="compact">
-objdump -p /usr/lib/libz.so.1.1.3 | grep SONAME
- </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>
+ <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>
+ <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 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.
- </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 (>= 1:1.1.3)
- </example>
- </p>
- </sect1>
+ <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>
+ <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/shlibs.<var>package</var></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>
+ <p>
+ To provide a <file>shlibs</file> file for a shared library
+ binary package, create a <file>shlibs</file> file following
+ the format described above and place it in
+ the <file>DEBIAN</file> directory for that package during the
+ build. It will then be included as a control file for that
+ package<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>.
+ </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>
+ <p>
+ 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>

@@ -7743,8 +8172,9 @@ INSTALL = install -s # (or use strip on the files in debian/tmp)
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,
@@ -10522,89 +10952,6 @@ END-INFO-DIR-ENTRY
<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

--
Russ Allbery (rra@debian.org) <http://www.eyrie.org/~eagle/>


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Raphael Hertzog 01-13-2012 06:38 PM

Bug#571776: document symbols
 
On Fri, 13 Jan 2012, Russ Allbery wrote:
> >> 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.)
>
> > What leading space are you referring to ?
>
> I now have:
>
> (Don't forget the space before the <tt>*</tt> so that it will
> be parsed as part of the entry for that library.)
>
> Due to the way that the formatting of Policy works, it's very hard to tell
> that there's a space there, and unlike with symbols where the indentation
> is fairly obvious, it's not completely obvious that it's required.

There is no leading space before the "*". Just like "|" it must be
on the first column to differentiate with symbol definitions which do have
a leading space on their lines.

> Thanks for the review!

All the other corrections you made are fine. Thanks!

Cheers,
--
Raphaël Hertzog ◈ Debian Developer

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Raphael Hertzog 01-13-2012 06:55 PM

Bug#571776: document symbols
 
On Fri, 13 Jan 2012, Russ Allbery wrote:
> + <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>

I think this description adapted from the deb-symbols(5) manual page
mislead you into thinking that there were leading spaces before | or *
when in fact there are none.

I have updated the manual page to make it look like this now:

library-soname main-dependency-template
[| alternative-dependency-template]
[...]
[* field-name: field-value]
[...]
symbol minimal-version [id-of-dependency-template]

> + <example>
> +libGL.so.1 libgl1
> + | libgl1-mesa-glx #MINVER#

Drop the leading space on that last line.

> + publicGlSymbol@Base 6.3-1
> + [...]
> + implementationSpecificSymbol@Base 6.5.2-7 1
> + [...]

> + For our example, the <tt>zlib1g</tt> <file>symbols</file> file
> + would contain:
> + <example compact="compact">
> + * Build-Depends-Package: zlib1g-dev

And here too.

> + </example>
> + (Don't forget the space before the <tt>*</tt> so that it will
> + be parsed as part of the entry for that library.)

And that sentence is then useless (or needs to be reworded).

Cheers,
--
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Russ Allbery 01-13-2012 07:45 PM

Bug#571776: document symbols
 
Raphael Hertzog <hertzog@debian.org> writes:

> There is no leading space before the "*". Just like "|" it must be on
> the first column to differentiate with symbol definitions which do have
> a leading space on their lines.

Oh, then deb-symbols(5) is wrong for both * and |... oh, I see, I was
misreading how the syntax definition worked and the spaces around []
weren't literal. Aie.

I'll fix.

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Russ Allbery 01-13-2012 10:12 PM

Bug#571776: document symbols
 
Raphael Hertzog <hertzog@debian.org> writes:

> I think this description adapted from the deb-symbols(5) manual page
> mislead you into thinking that there were leading spaces before | or *
> when in fact there are none.

> I have updated the manual page to make it look like this now:

> library-soname main-dependency-template
> [| alternative-dependency-template]
> [...]
> [* field-name: field-value]
> [...]
> symbol minimal-version [id-of-dependency-template]

Thanks, I've now fixed my draft text as well.

>> + <example>
>> +libGL.so.1 libgl1
>> + | libgl1-mesa-glx #MINVER#

> Drop the leading space on that last line.

Done.

>> + For our example, the <tt>zlib1g</tt> <file>symbols</file> file
>> + would contain:
>> + <example compact="compact">
>> + * Build-Depends-Package: zlib1g-dev

> And here too.

Done.

>> + </example>
>> + (Don't forget the space before the <tt>*</tt> so that it will
>> + be parsed as part of the entry for that library.)

> And that sentence is then useless (or needs to be reworded).

Dropped.

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