# Advanced packaging

Here are some hints and pointers for advanced packaging topics that you are most likely to deal with. You are strongly advised to read all the references suggested here.

You may need to manually edit the packaging template files generated by the `dh_make` command to address topics covered in this chapter. The newer `debmake` command should address these topics better.

## Shared libraries

Before packaging shared libraries, you should read the following primary references in detail:

- Debian Policy Manual, 8 "Shared libraries"

- Debian Policy Manual, 9.1.1 "File System Structure"

- Debian Policy Manual, 10.2 "Libraries"

Here are some oversimplified hints for you to get started:

- Shared libraries are ELF object files containing compiled code.

- Shared libraries are distributed as `*.so` files. (Neither `*.a` files nor `*.la` files)

- Shared libraries are mainly used to share common codes among multiple executables with the `ld` mechanism.

- Shared libraries are sometimes used to provide multiple plugins to an executable with the `dlopen` mechanism.

- Shared libraries export symbols, which represent compiled objects such as variables, functions, and classes; and enable access to them from the linked executables.

- The SONAME of a shared library `lib`foo`.so`.`1`: `objdump -p lib`foo`.so.`1` | grep SONAME`

  Alternatively: `readelf -d lib`foo`.so.`1` | grep SONAME`

- The SONAME of a shared library usually matches the library file name (but not always).

- The SONAME of shared libraries linked to ``/usr/bin/foo``: `objdump -p `/usr/bin/foo` | grep NEEDED`

  Alternatively: `readelf -d lib`foo`.so.`1` | grep NEEDED`

- `lib`foo``1``: the library package for the shared library `lib`foo`.so.`1`` with the SONAME ABI version `1`.

  See Debian Policy Manual, 8.1 "Run-time shared libraries".

- The package maintainer scripts of the library package must call `ldconfig` under the specific circumstances to create the necessary symbolic links for the SONAME.

  See Debian Policy Manual, 8.1.1 "ldconfig".

- `lib`foo``1`-dbg`: the debugging symbols package that contains the debugging symbols for the shared library package `lib`foo``1``.

- `lib`foo`-dev`: the development package that contains the header files etc. for the shared library `lib`foo`.so.`1``.

  See Debian Policy Manual, 8.3 "Static libraries" and Debian Policy Manual, 8.4 "Development files".

- Debian packages should not contain `*.la` Libtool archive files in general.

  See Debian wiki ReleaseGoals/LAFileRemoval.

- Debian packages should not use RPATH in general.

  See Debian wiki RpathIssue.

- Although it is somewhat outdated and is only a secondary reference, Debian Library Packaging Guide may still be useful.

## Managing `debian/`package`.symbols`

When you package a shared library, you should create a `debian/`package`.symbols` file to manage the minimal version associated with each symbol for backward-compatible ABI changes under the same SONAME of the library for the same shared library package name.

Backward-incompatible ABI changes normally require you to update the SONAME of the library and the shared library package name to new ones.

You should read the following primary references in detail:

- Debian Policy Manual, 8.6.3 "The symbols system"

  For C++ libraries and other cases where tracking individual symbols is too difficult, follow Debian Policy Manual, 8.6.4 "The shlibs system", instead.

- dh_makeshlibs

  1

- dpkg-gensymbols

  1

- dpkg-shlibdeps

  1

- deb-symbols

  5

Here is a rough example of how to create the `libfoo1` package from the upstream version `1.3` with the proper `debian/libfoo1.symbols` file:

- Prepare the skeleton debianized source tree using the upstream `libfoo-1.3.tar.gz` file.

  - If this is the first packaging of the `libfoo1` package, create the `debian/libfoo1.symbols` file with empty content.

  - If the previous upstream version `1.2` was packaged as the `libfoo1` package with the proper `debian/libfoo1.symbols` in its source package, use it again.

  - If the previous upstream version `1.2` was not packaged with `debian/libfoo1.symbols`, create it as the `symbols` file from all available binary packages of the same shared library package name containing the same SONAME of the library, for example, versions `1.1-1` and `1.2-1`.

    All previous versions of Debian packages are available at http://snapshot.debian.org/. The Debian revision is dropped from the version to make it easier to backport the package: `1.1` << `1.1-1~bpo70+1` << `1.1-1` and `1.2` << `1.2-1~bpo70+1` << `1.2-1`

        $ dpkg-deb -x libfoo1_1.1-1.deb libfoo1_1.1-1
        $ dpkg-deb -x libfoo1_1.2-1.deb libfoo1_1.2-1
        $ : > symbols
        $ dpkg-gensymbols -v1.1 -plibfoo1 -Plibfoo1_1.1-1 -Osymbols
        $ dpkg-gensymbols -v1.2 -plibfoo1 -Plibfoo1_1.2-1 -Osymbols

- Make trial builds of the source tree with tools such as `debuild` and `pdebuild`. (If this fails due to missing symbols etc., there were some backward-incompatible ABI changes that require you to bump the shared library package name to something like `libfoo1a` and you should start over again.)

      $ cd libfoo-1.3
      $ debuild
      ...
      dpkg-gensymbols: warning: some new symbols appeared in the symbols file: ...
       see diff output below
      --- debian/libfoo1.symbols (libfoo1_1.3-1_amd64)
      +++ dpkg-gensymbolsFE5gzx        2012-11-11 02:24:53.609667389 +0900
      @@ -127,6 +127,7 @@
        foo_get_name@Base 1.1
        foo_get_longname@Base 1.2
        foo_get_type@Base 1.1
      + foo_get_longtype@Base 1.3-1
        foo_get_symbol@Base 1.1
        foo_get_rank@Base 1.1
        foo_new@Base 1.1
      ...

- If you see the diff printed by the `dpkg-gensymbols` as above, extract the proper updated `symbols` file from the generated binary package of the shared library.

  The Debian revision is dropped from the version to make it easier to backport the package: `1.3` << `1.3-1~bpo70+1` << `1.3-1`

      $ cd ..
      $ dpkg-deb -R  libfoo1_1.3_amd64.deb libfoo1-tmp
      $ sed -e 's/1\.3-1/1\.3/' libfoo1-tmp/DEBIAN/symbols \
              >libfoo-1.3/debian/libfoo1.symbols

- Build release packages with tools such as `debuild` and `pdebuild`.

      $ cd libfoo-1.3
      $ debuild clean
      $ debuild
      ...

In addition to the above examples, we need to check the ABI compatibility further and bump versions for some symbols manually as needed.

See Debian Policy Manual, 8.6.2 "Shared library ABI changes".

Although it is only a secondary reference, Debian wiki UsingSymbolsFiles and its linked web pages may be useful.

## Multiarch

The multiarch feature introduced to Debian wheezy integrates support for cross-architecture installation of binary packages (particularly `i386`<->`amd64`, but also other combinations) in `dpkg` and `apt`. You should read the following references in detail:

- Ubuntu wiki MultiarchSpec (upstream)

- Debian wiki Multiarch/Implementation (Debian situation)

It uses the triplet such as `i386-linux-gnu` and `x86_64-linux-gnu` for the install path of shared libraries. The actual triplet path is dynamically set into the `$(DEB_HOST_MULTIARCH)` variable using the

dpkg-architecture

1 command for each binary package build. For example, the path to install multiarch libraries are changed as follows:

Old special purpose library paths such as `/lib32/` and `/lib64/` are not used anymore.

Old path | i386 multiarch path | amd64 multiarch path
`/lib/` | `/lib/i386-linux-gnu/` | `/lib/x86_64-linux-gnu/`
`/usr/lib/` | `/usr/lib/i386-linux-gnu/` | `/usr/lib/x86_64-linux-gnu/`

Here are some typical multiarch package split scenario examples for the following:

- a library source `lib`foo`-1.tar.gz`

- a tool source ``bar`-1.tar.gz` written in a compiled language

- a tool source ``baz`-1.tar.gz` written in an interpreted language

Package | Architecture: | Multi-Arch: | Package content
`lib`foo``1`` | any | same | the shared library, co-installable
`lib`foo``1`-dbg` | any | same | the shared library debug symbols, co-installable
`lib`foo`-dev` | any | same | the shared library header files etc., co-installable
`lib`foo`-tools` | any | foreign | the run-time support programs, not co-installable
`lib`foo`-doc` | all | foreign | the shared library documentation files
``bar`` | any | foreign | the compiled program files, not co-installable
``bar`-doc` | all | foreign | the documentation files for the program
``baz`` | all | foreign | the interpreted program files

Please note that the development package should contain a symlink for the associated shared library without a version number. E.g.: `/usr/lib/x86_64-linux-gnu/libfoo.so` -> `libfoo.so.1`

## Building a shared library package

You can build a Debian library package enabling multiarch support using

dh

1 as follows:

- Update `debian/control`.

  - Add `Build-Depends: debhelper (>=10)` for the source package section.

  - Add `Pre-Depends: ${misc:Pre-Depends}` for each shared library binary package.

  - Add `Multi-Arch:` stanza for each binary package section.

- Set `debian/compat` to "10".

- Adjust the path from the normal `/usr/lib/` to the multiarch `/usr/lib/$(DEB_HOST_MULTIARCH)/` for all packaging scripts.

  - Call `DEB_HOST_MULTIARCH ?= $(shell dpkg-architecture -qDEB_HOST_MULTIARCH)` in `debian/rules` to set the `DEB_HOST_MULTIARCH` variable first.

  - Replace `/usr/lib/` with `/usr/lib/$(DEB_HOST_MULTIARCH)/` in `debian/rules`.

  - If `./configure` is used in part of the `override_dh_auto_configure` target in `debian/rules`, make sure to replace it with `dh_auto_configure --` .

    Alternatively, you can add `--libdir=\$${prefix}/lib/$(DEB_HOST_MULTIARCH)` and `--libexecdir=\$${prefix}/lib/$(DEB_HOST_MULTIARCH)` arguments to `./configure`. Please note that `--libexecdir` specifies the default path to install executable programs run by other programs rather than by users. Its Autotools default is `/usr/libexec/` but its Debian default is `/usr/lib/`.

  - Replace all occurrences of `/usr/lib/` with `/usr/lib/*/` in `debian/`foo`.install` files.

  - Generate files like `debian/`foo`.links` from `debian/`foo`.links.in` dynamically by adding a script to the `override_dh_auto_configure` target in `debian/rules`.

        override_dh_auto_configure:
                dh_auto_configure
                sed 's/@DEB_HOST_MULTIARCH@/$(DEB_HOST_MULTIARCH)/g' \
                        debian/foo.links.in > debian/foo.links

Please make sure to verify that the shared library package contains only the expected files, and that your -dev package still works.

All files installed simultaneously as the multiarch package to the same file path should have exactly the same file content. You must be careful of differences generated by the data byte order and by the compression algorithm.

## Native Debian package

If a package is maintained only for Debian or possibly only for local use, its source may contain all the `debian/*` files in it. There are 2 ways to package it.

You can make the upstream tarball by excluding the `debian/*` files and package it as a non-native Debian package as in workflow. This is the normal way, which some people encourage using.

The alternative is the workflow of the native Debian package.

- Create a native Debian source package in the `3.0 (native)` format using a single compressed tar file in which all files are included.

  - ``package`_`version`.tar.gz`
  - ``package`_`version`.dsc`

- Build Debian binary packages from the native Debian source package.

  - ``package`_`version`_`arch`.deb`

For example, if you have source files in `~/mypackage-1.0` without the `debian/*` files, you can create a native Debian package by issuing the `dh_make` command as follows:

    $ cd ~/mypackage-1.0
    $ dh_make --native

Then the `debian` directory and its contents are created just like in non-native-dh-make. This does not create a tarball, since this is a native Debian package. But that is the only difference. The rest of the packaging activities are practically the same.

After execution of the `dpkg-buildpackage` command, you will see the following files in the parent directory:

- `mypackage_1.0.tar.gz`

  This is the source code tarball created from the `mypackage-1.0` directory by the `dpkg-source` command. (Its suffix is not `orig.tar.gz`.)

- `mypackage_1.0.dsc`

  This is a summary of the contents of the source code, as in the non-native Debian package. (There is no Debian revision.)

- `mypackage_1.0_i386.deb`

  This is your completed binary package, as in the non-native Debian package. (There is no Debian revision.)

- `mypackage_1.0_i386.changes`

  This file describes all the changes made in the current package version as in the non-native Debian package. (There is no Debian revision.)