doc: Move "System Configuration" higher.
* doc/guix.texi (GNU Distribution): Move "System Configuration" right after "System Installation".
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Ludovic Courtès
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935
doc/guix.texi
935
doc/guix.texi
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@ -2604,12 +2604,12 @@ For information on porting to other architectures or kernels,
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@menu
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* System Installation:: Installing the whole operating system.
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* System Configuration:: Configuring a GNU system.
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* Installing Debugging Files:: Feeding the debugger.
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* Package Modules:: Packages from the programmer's viewpoint.
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* Packaging Guidelines:: Growing the distribution.
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* Bootstrapping:: GNU/Linux built from scratch.
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* Porting:: Targeting another platform or kernel.
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* System Configuration:: Configuring a GNU system.
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@end menu
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Building this distribution is a cooperative effort, and you are invited
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@ -2781,473 +2781,6 @@ guix system disk-image --image-size=800MiB gnu/system/install.scm
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@file{gnu/system/install.scm} in the source tree for more information
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about the installation image.
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@node Installing Debugging Files
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@section Installing Debugging Files
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@cindex debugging files
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Program binaries, as produced by the GCC compilers for instance, are
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typically written in the ELF format, with a section containing
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@dfn{debugging information}. Debugging information is what allows the
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debugger, GDB, to map binary code to source code; it is required to
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debug a compiled program in good conditions.
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The problem with debugging information is that is takes up a fair amount
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of disk space. For example, debugging information for the GNU C Library
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weighs in at more than 60 MiB. Thus, as a user, keeping all the
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debugging info of all the installed programs is usually not an option.
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Yet, space savings should not come at the cost of an impediment to
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debugging---especially in the GNU system, which should make it easier
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for users to exert their computing freedom (@pxref{GNU Distribution}).
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Thankfully, the GNU Binary Utilities (Binutils) and GDB provide a
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mechanism that allows users to get the best of both worlds: debugging
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information can be stripped from the binaries and stored in separate
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files. GDB is then able to load debugging information from those files,
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when they are available (@pxref{Separate Debug Files,,, gdb, Debugging
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with GDB}).
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The GNU distribution takes advantage of this by storing debugging
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information in the @code{lib/debug} sub-directory of a separate package
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output unimaginatively called @code{debug} (@pxref{Packages with
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Multiple Outputs}). Users can choose to install the @code{debug} output
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of a package when they need it. For instance, the following command
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installs the debugging information for the GNU C Library and for GNU
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Guile:
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@example
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guix package -i glibc:debug guile:debug
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@end example
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GDB must then be told to look for debug files in the user's profile, by
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setting the @code{debug-file-directory} variable (consider setting it
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from the @file{~/.gdbinit} file, @pxref{Startup,,, gdb, Debugging with
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GDB}):
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@example
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(gdb) set debug-file-directory ~/.guix-profile/lib/debug
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@end example
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From there on, GDB will pick up debugging information from the
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@code{.debug} files under @file{~/.guix-profile/lib/debug}.
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In addition, you will most likely want GDB to be able to show the source
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code being debugged. To do that, you will have to unpack the source
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code of the package of interest (obtained with @code{guix build
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--source}, @pxref{Invoking guix build}), and to point GDB to that source
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directory using the @code{directory} command (@pxref{Source Path,
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@code{directory},, gdb, Debugging with GDB}).
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@c XXX: keep me up-to-date
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The @code{debug} output mechanism in Guix is implemented by the
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@code{gnu-build-system} (@pxref{Build Systems}). Currently, it is
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opt-in---debugging information is available only for those packages
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whose definition explicitly declares a @code{debug} output. This may be
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changed to opt-out in the future, if our build farm servers can handle
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the load. To check whether a package has a @code{debug} output, use
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@command{guix package --list-available} (@pxref{Invoking guix package}).
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@node Package Modules
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@section Package Modules
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From a programming viewpoint, the package definitions of the
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GNU distribution are provided by Guile modules in the @code{(gnu packages
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@dots{})} name space@footnote{Note that packages under the @code{(gnu
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packages @dots{})} module name space are not necessarily ``GNU
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packages''. This module naming scheme follows the usual Guile module
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naming convention: @code{gnu} means that these modules are distributed
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as part of the GNU system, and @code{packages} identifies modules that
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define packages.} (@pxref{Modules, Guile modules,, guile, GNU Guile
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Reference Manual}). For instance, the @code{(gnu packages emacs)}
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module exports a variable named @code{emacs}, which is bound to a
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@code{<package>} object (@pxref{Defining Packages}).
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The @code{(gnu packages @dots{})} module name space is special: it is
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automatically scanned for packages by the command-line tools. For
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instance, when running @code{guix package -i emacs}, all the @code{(gnu
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packages @dots{})} modules are scanned until one that exports a package
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object whose name is @code{emacs} is found. This package search
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facility is implemented in the @code{(gnu packages)} module.
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Users can store package definitions in modules with different
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names---e.g., @code{(my-packages emacs)}. In that case, commands such
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as @command{guix package} and @command{guix build} have to be used with
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the @code{-e} option so that they know where to find the package.
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The distribution is fully @dfn{bootstrapped} and @dfn{self-contained}:
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each package is built based solely on other packages in the
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distribution. The root of this dependency graph is a small set of
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@dfn{bootstrap binaries}, provided by the @code{(gnu packages
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bootstrap)} module. For more information on bootstrapping,
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@ref{Bootstrapping}.
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@node Packaging Guidelines
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@section Packaging Guidelines
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The GNU distribution is nascent and may well lack some of your favorite
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packages. This section describes how you can help make the distribution
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grow. @xref{Contributing}, for additional information on how you can
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help.
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Free software packages are usually distributed in the form of
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@dfn{source code tarballs}---typically @file{tar.gz} files that contain
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all the source files. Adding a package to the distribution means
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essentially two things: adding a @dfn{recipe} that describes how to
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build the package, including a list of other packages required to build
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it, and adding @dfn{package meta-data} along with that recipe, such as a
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description and licensing information.
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In Guix all this information is embodied in @dfn{package definitions}.
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Package definitions provide a high-level view of the package. They are
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written using the syntax of the Scheme programming language; in fact,
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for each package we define a variable bound to the package definition,
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and export that variable from a module (@pxref{Package Modules}).
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However, in-depth Scheme knowledge is @emph{not} a prerequisite for
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creating packages. For more information on package definitions,
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@ref{Defining Packages}.
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Once a package definition is in place, stored in a file in the Guix
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source tree, it can be tested using the @command{guix build} command
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(@pxref{Invoking guix build}). For example, assuming the new package is
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called @code{gnew}, you may run this command from the Guix build tree:
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@example
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./pre-inst-env guix build gnew --keep-failed
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@end example
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Using @code{--keep-failed} makes it easier to debug build failures since
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it provides access to the failed build tree. Another useful
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command-line option when debugging is @code{--log-file}, to access the
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build log.
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If the package is unknown to the @command{guix} command, it may be that
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the source file contains a syntax error, or lacks a @code{define-public}
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clause to export the package variable. To figure it out, you may load
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the module from Guile to get more information about the actual error:
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@example
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./pre-inst-env guile -c '(use-modules (gnu packages gnew))'
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@end example
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Once your package builds correctly, please send us a patch
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(@pxref{Contributing}). Well, if you need help, we will be happy to
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help you too. Once the patch is committed in the Guix repository, the
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new package automatically gets built on the supported platforms by
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@url{http://hydra.gnu.org/gnu/master, our continuous integration
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system}.
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@cindex substituter
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Users can obtain the new package definition simply by running
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@command{guix pull} (@pxref{Invoking guix pull}). When
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@code{hydra.gnu.org} is done building the package, installing the
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package automatically downloads binaries from there
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(@pxref{Substitutes}). The only place where human intervention is
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needed is to review and apply the patch.
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@menu
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* Software Freedom:: What may go into the distribution.
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* Package Naming:: What's in a name?
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* Version Numbers:: When the name is not enough.
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* Python Modules:: Taming the snake.
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* Perl Modules:: Little pearls.
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@end menu
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@node Software Freedom
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@subsection Software Freedom
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@c Adapted from http://www.gnu.org/philosophy/philosophy.html.
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The GNU operating system has been developed so that users can have
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freedom in their computing. GNU is @dfn{free software}, meaning that
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users have the @url{http://www.gnu.org/philosophy/free-sw.html,four
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essential freedoms}: to run the program, to study and change the program
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in source code form, to redistribute exact copies, and to distribute
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modified versions. Packages found in the GNU distribution provide only
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software that conveys these four freedoms.
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In addition, the GNU distribution follow the
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@url{http://www.gnu.org/distros/free-system-distribution-guidelines.html,free
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software distribution guidelines}. Among other things, these guidelines
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reject non-free firmware, recommendations of non-free software, and
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discuss ways to deal with trademarks and patents.
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Some packages contain a small and optional subset that violates the
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above guidelines, for instance because this subset is itself non-free
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code. When that happens, the offending items are removed with
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appropriate patches or code snippets in the package definition's
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@code{origin} form (@pxref{Defining Packages}). That way, @code{guix
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build --source} returns the ``freed'' source rather than the unmodified
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upstream source.
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@node Package Naming
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@subsection Package Naming
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A package has actually two names associated with it:
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First, there is the name of the @emph{Scheme variable}, the one following
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@code{define-public}. By this name, the package can be made known in the
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Scheme code, for instance as input to another package. Second, there is
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the string in the @code{name} field of a package definition. This name
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is used by package management commands such as
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@command{guix package} and @command{guix build}.
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Both are usually the same and correspond to the lowercase conversion of
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the project name chosen upstream, with underscores replaced with
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hyphens. For instance, GNUnet is available as @code{gnunet}, and
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SDL_net as @code{sdl-net}.
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We do not add @code{lib} prefixes for library packages, unless these are
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already part of the official project name. But see @pxref{Python
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Modules} and @ref{Perl Modules} for special rules concerning modules for
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the Python and Perl languages.
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@node Version Numbers
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@subsection Version Numbers
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We usually package only the latest version of a given free software
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project. But sometimes, for instance for incompatible library versions,
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two (or more) versions of the same package are needed. These require
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different Scheme variable names. We use the name as defined
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in @ref{Package Naming}
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for the most recent version; previous versions use the same name, suffixed
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by @code{-} and the smallest prefix of the version number that may
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distinguish the two versions.
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The name inside the package definition is the same for all versions of a
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package and does not contain any version number.
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For instance, the versions 2.24.20 and 3.9.12 of GTK+ may be packaged as follows:
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@example
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(define-public gtk+
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(package
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(name "gtk+")
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(version "3.9.12")
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...))
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(define-public gtk+-2
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(package
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(name "gtk+")
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(version "2.24.20")
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...))
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@end example
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If we also wanted GTK+ 3.8.2, this would be packaged as
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@example
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(define-public gtk+-3.8
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(package
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(name "gtk+")
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(version "3.8.2")
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...))
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@end example
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@node Python Modules
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@subsection Python Modules
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We currently package Python 2 and Python 3, under the Scheme variable names
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@code{python-2} and @code{python} as explained in @ref{Version Numbers}.
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To avoid confusion and naming clashes with other programming languages, it
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seems desirable that the name of a package for a Python module contains
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the word @code{python}.
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Some modules are compatible with only one version of Python, others with both.
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If the package Foo compiles only with Python 3, we name it
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@code{python-foo}; if it compiles only with Python 2, we name it
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@code{python2-foo}. If it is compatible with both versions, we create two
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packages with the corresponding names.
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If a project already contains the word @code{python}, we drop this;
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for instance, the module python-dateutil is packaged under the names
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@code{python-dateutil} and @code{python2-dateutil}.
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@node Perl Modules
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@subsection Perl Modules
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Perl programs standing for themselves are named as any other package,
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using the lowercase upstream name.
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For Perl packages containing a single class, we use the lowercase class name,
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replace all occurrences of @code{::} by dashes and prepend the prefix
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@code{perl-}.
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So the class @code{XML::Parser} becomes @code{perl-xml-parser}.
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Modules containing several classes keep their lowercase upstream name and
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are also prepended by @code{perl-}. Such modules tend to have the word
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@code{perl} somewhere in their name, which gets dropped in favor of the
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prefix. For instance, @code{libwww-perl} becomes @code{perl-libwww}.
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@node Bootstrapping
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@section Bootstrapping
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@c Adapted from the ELS 2013 paper.
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@cindex bootstrapping
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Bootstrapping in our context refers to how the distribution gets built
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``from nothing''. Remember that the build environment of a derivation
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contains nothing but its declared inputs (@pxref{Introduction}). So
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there's an obvious chicken-and-egg problem: how does the first package
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get built? How does the first compiler get compiled? Note that this is
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a question of interest only to the curious hacker, not to the regular
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user, so you can shamelessly skip this section if you consider yourself
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a ``regular user''.
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@cindex bootstrap binaries
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The GNU system is primarily made of C code, with libc at its core. The
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GNU build system itself assumes the availability of a Bourne shell and
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command-line tools provided by GNU Coreutils, Awk, Findutils, `sed', and
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`grep'. Furthermore, build programs---programs that run
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@code{./configure}, @code{make}, etc.---are written in Guile Scheme
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(@pxref{Derivations}). Consequently, to be able to build anything at
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all, from scratch, Guix relies on pre-built binaries of Guile, GCC,
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Binutils, libc, and the other packages mentioned above---the
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@dfn{bootstrap binaries}.
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These bootstrap binaries are ``taken for granted'', though we can also
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re-create them if needed (more on that later).
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@unnumberedsubsec Preparing to Use the Bootstrap Binaries
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@c As of Emacs 24.3, Info-mode displays the image, but since it's a
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@c large image, it's hard to scroll. Oh well.
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@image{images/bootstrap-graph,6in,,Dependency graph of the early bootstrap derivations}
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The figure above shows the very beginning of the dependency graph of the
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distribution, corresponding to the package definitions of the @code{(gnu
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packages bootstrap)} module. At this level of detail, things are
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slightly complex. First, Guile itself consists of an ELF executable,
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along with many source and compiled Scheme files that are dynamically
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loaded when it runs. This gets stored in the @file{guile-2.0.7.tar.xz}
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tarball shown in this graph. This tarball is part of Guix's ``source''
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distribution, and gets inserted into the store with @code{add-to-store}
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(@pxref{The Store}).
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But how do we write a derivation that unpacks this tarball and adds it
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to the store? To solve this problem, the @code{guile-bootstrap-2.0.drv}
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derivation---the first one that gets built---uses @code{bash} as its
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builder, which runs @code{build-bootstrap-guile.sh}, which in turn calls
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@code{tar} to unpack the tarball. Thus, @file{bash}, @file{tar},
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@file{xz}, and @file{mkdir} are statically-linked binaries, also part of
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the Guix source distribution, whose sole purpose is to allow the Guile
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tarball to be unpacked.
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Once @code{guile-bootstrap-2.0.drv} is built, we have a functioning
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Guile that can be used to run subsequent build programs. Its first task
|
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is to download tarballs containing the other pre-built binaries---this
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is what the @code{.tar.xz.drv} derivations do. Guix modules such as
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@code{ftp-client.scm} are used for this purpose. The
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@code{module-import.drv} derivations import those modules in a directory
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in the store, using the original layout. The
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@code{module-import-compiled.drv} derivations compile those modules, and
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write them in an output directory with the right layout. This
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corresponds to the @code{#:modules} argument of
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@code{build-expression->derivation} (@pxref{Derivations}).
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Finally, the various tarballs are unpacked by the
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derivations @code{gcc-bootstrap-0.drv}, @code{glibc-bootstrap-0.drv},
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etc., at which point we have a working C tool chain.
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@unnumberedsubsec Building the Build Tools
|
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@c TODO: Add a package-level dependency graph generated from (gnu
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@c packages base).
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|
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Bootstrapping is complete when we have a full tool chain that does not
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depend on the pre-built bootstrap tools discussed above. This
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no-dependency requirement is verified by checking whether the files of
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the final tool chain contain references to the @file{/gnu/store}
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directories of the bootstrap inputs. The process that leads to this
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``final'' tool chain is described by the package definitions found in
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the @code{(gnu packages base)} module.
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@c See <http://lists.gnu.org/archive/html/gnu-system-discuss/2012-10/msg00000.html>.
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The first tool that gets built with the bootstrap binaries is
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GNU Make, which is a prerequisite for all the following packages.
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From there Findutils and Diffutils get built.
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Then come the first-stage Binutils and GCC, built as pseudo cross
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tools---i.e., with @code{--target} equal to @code{--host}. They are
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used to build libc. Thanks to this cross-build trick, this libc is
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guaranteed not to hold any reference to the initial tool chain.
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From there the final Binutils and GCC are built. GCC uses @code{ld}
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from the final Binutils, and links programs against the just-built libc.
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This tool chain is used to build the other packages used by Guix and by
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the GNU Build System: Guile, Bash, Coreutils, etc.
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And voilà! At this point we have the complete set of build tools that
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the GNU Build System expects. These are in the @code{%final-inputs}
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variables of the @code{(gnu packages base)} module, and are implicitly
|
||||
used by any package that uses @code{gnu-build-system} (@pxref{Defining
|
||||
Packages}).
|
||||
|
||||
|
||||
@unnumberedsubsec Building the Bootstrap Binaries
|
||||
|
||||
Because the final tool chain does not depend on the bootstrap binaries,
|
||||
those rarely need to be updated. Nevertheless, it is useful to have an
|
||||
automated way to produce them, should an update occur, and this is what
|
||||
the @code{(gnu packages make-bootstrap)} module provides.
|
||||
|
||||
The following command builds the tarballs containing the bootstrap
|
||||
binaries (Guile, Binutils, GCC, libc, and a tarball containing a mixture
|
||||
of Coreutils and other basic command-line tools):
|
||||
|
||||
@example
|
||||
guix build bootstrap-tarballs
|
||||
@end example
|
||||
|
||||
The generated tarballs are those that should be referred to in the
|
||||
@code{(gnu packages bootstrap)} module mentioned at the beginning of
|
||||
this section.
|
||||
|
||||
Still here? Then perhaps by now you've started to wonder: when do we
|
||||
reach a fixed point? That is an interesting question! The answer is
|
||||
unknown, but if you would like to investigate further (and have
|
||||
significant computational and storage resources to do so), then let us
|
||||
know.
|
||||
|
||||
@node Porting
|
||||
@section Porting to a New Platform
|
||||
|
||||
As discussed above, the GNU distribution is self-contained, and
|
||||
self-containment is achieved by relying on pre-built ``bootstrap
|
||||
binaries'' (@pxref{Bootstrapping}). These binaries are specific to an
|
||||
operating system kernel, CPU architecture, and application binary
|
||||
interface (ABI). Thus, to port the distribution to a platform that is
|
||||
not yet supported, one must build those bootstrap binaries, and update
|
||||
the @code{(gnu packages bootstrap)} module to use them on that platform.
|
||||
|
||||
Fortunately, Guix can @emph{cross compile} those bootstrap binaries.
|
||||
When everything goes well, and assuming the GNU tool chain supports the
|
||||
target platform, this can be as simple as running a command like this
|
||||
one:
|
||||
|
||||
@example
|
||||
guix build --target=armv5tel-linux-gnueabi bootstrap-tarballs
|
||||
@end example
|
||||
|
||||
Once these are built, the @code{(gnu packages bootstrap)} module needs
|
||||
to be updated to refer to these binaries on the target platform. In
|
||||
addition, the @code{glibc-dynamic-linker} procedure in that module must
|
||||
be augmented to return the right file name for libc's dynamic linker on
|
||||
that platform; likewise, @code{system->linux-architecture} in @code{(gnu
|
||||
packages linux)} must be taught about the new platform.
|
||||
|
||||
In practice, there may be some complications. First, it may be that the
|
||||
extended GNU triplet that specifies an ABI (like the @code{eabi} suffix
|
||||
above) is not recognized by all the GNU tools. Typically, glibc
|
||||
recognizes some of these, whereas GCC uses an extra @code{--with-abi}
|
||||
configure flag (see @code{gcc.scm} for examples of how to handle this).
|
||||
Second, some of the required packages could fail to build for that
|
||||
platform. Lastly, the generated binaries could be broken for some
|
||||
reason.
|
||||
|
||||
|
||||
@node System Configuration
|
||||
@section System Configuration
|
||||
|
||||
|
|
@ -3846,6 +3379,472 @@ on-line documentation. Thus, the commands @command{deco start ncsd},
|
|||
would expect (@pxref{Invoking deco,,, dmd, GNU dmd Manual}).
|
||||
|
||||
|
||||
@node Installing Debugging Files
|
||||
@section Installing Debugging Files
|
||||
|
||||
@cindex debugging files
|
||||
Program binaries, as produced by the GCC compilers for instance, are
|
||||
typically written in the ELF format, with a section containing
|
||||
@dfn{debugging information}. Debugging information is what allows the
|
||||
debugger, GDB, to map binary code to source code; it is required to
|
||||
debug a compiled program in good conditions.
|
||||
|
||||
The problem with debugging information is that is takes up a fair amount
|
||||
of disk space. For example, debugging information for the GNU C Library
|
||||
weighs in at more than 60 MiB. Thus, as a user, keeping all the
|
||||
debugging info of all the installed programs is usually not an option.
|
||||
Yet, space savings should not come at the cost of an impediment to
|
||||
debugging---especially in the GNU system, which should make it easier
|
||||
for users to exert their computing freedom (@pxref{GNU Distribution}).
|
||||
|
||||
Thankfully, the GNU Binary Utilities (Binutils) and GDB provide a
|
||||
mechanism that allows users to get the best of both worlds: debugging
|
||||
information can be stripped from the binaries and stored in separate
|
||||
files. GDB is then able to load debugging information from those files,
|
||||
when they are available (@pxref{Separate Debug Files,,, gdb, Debugging
|
||||
with GDB}).
|
||||
|
||||
The GNU distribution takes advantage of this by storing debugging
|
||||
information in the @code{lib/debug} sub-directory of a separate package
|
||||
output unimaginatively called @code{debug} (@pxref{Packages with
|
||||
Multiple Outputs}). Users can choose to install the @code{debug} output
|
||||
of a package when they need it. For instance, the following command
|
||||
installs the debugging information for the GNU C Library and for GNU
|
||||
Guile:
|
||||
|
||||
@example
|
||||
guix package -i glibc:debug guile:debug
|
||||
@end example
|
||||
|
||||
GDB must then be told to look for debug files in the user's profile, by
|
||||
setting the @code{debug-file-directory} variable (consider setting it
|
||||
from the @file{~/.gdbinit} file, @pxref{Startup,,, gdb, Debugging with
|
||||
GDB}):
|
||||
|
||||
@example
|
||||
(gdb) set debug-file-directory ~/.guix-profile/lib/debug
|
||||
@end example
|
||||
|
||||
From there on, GDB will pick up debugging information from the
|
||||
@code{.debug} files under @file{~/.guix-profile/lib/debug}.
|
||||
|
||||
In addition, you will most likely want GDB to be able to show the source
|
||||
code being debugged. To do that, you will have to unpack the source
|
||||
code of the package of interest (obtained with @code{guix build
|
||||
--source}, @pxref{Invoking guix build}), and to point GDB to that source
|
||||
directory using the @code{directory} command (@pxref{Source Path,
|
||||
@code{directory},, gdb, Debugging with GDB}).
|
||||
|
||||
@c XXX: keep me up-to-date
|
||||
The @code{debug} output mechanism in Guix is implemented by the
|
||||
@code{gnu-build-system} (@pxref{Build Systems}). Currently, it is
|
||||
opt-in---debugging information is available only for those packages
|
||||
whose definition explicitly declares a @code{debug} output. This may be
|
||||
changed to opt-out in the future, if our build farm servers can handle
|
||||
the load. To check whether a package has a @code{debug} output, use
|
||||
@command{guix package --list-available} (@pxref{Invoking guix package}).
|
||||
|
||||
|
||||
@node Package Modules
|
||||
@section Package Modules
|
||||
|
||||
From a programming viewpoint, the package definitions of the
|
||||
GNU distribution are provided by Guile modules in the @code{(gnu packages
|
||||
@dots{})} name space@footnote{Note that packages under the @code{(gnu
|
||||
packages @dots{})} module name space are not necessarily ``GNU
|
||||
packages''. This module naming scheme follows the usual Guile module
|
||||
naming convention: @code{gnu} means that these modules are distributed
|
||||
as part of the GNU system, and @code{packages} identifies modules that
|
||||
define packages.} (@pxref{Modules, Guile modules,, guile, GNU Guile
|
||||
Reference Manual}). For instance, the @code{(gnu packages emacs)}
|
||||
module exports a variable named @code{emacs}, which is bound to a
|
||||
@code{<package>} object (@pxref{Defining Packages}).
|
||||
|
||||
The @code{(gnu packages @dots{})} module name space is special: it is
|
||||
automatically scanned for packages by the command-line tools. For
|
||||
instance, when running @code{guix package -i emacs}, all the @code{(gnu
|
||||
packages @dots{})} modules are scanned until one that exports a package
|
||||
object whose name is @code{emacs} is found. This package search
|
||||
facility is implemented in the @code{(gnu packages)} module.
|
||||
|
||||
Users can store package definitions in modules with different
|
||||
names---e.g., @code{(my-packages emacs)}. In that case, commands such
|
||||
as @command{guix package} and @command{guix build} have to be used with
|
||||
the @code{-e} option so that they know where to find the package.
|
||||
|
||||
The distribution is fully @dfn{bootstrapped} and @dfn{self-contained}:
|
||||
each package is built based solely on other packages in the
|
||||
distribution. The root of this dependency graph is a small set of
|
||||
@dfn{bootstrap binaries}, provided by the @code{(gnu packages
|
||||
bootstrap)} module. For more information on bootstrapping,
|
||||
@ref{Bootstrapping}.
|
||||
|
||||
@node Packaging Guidelines
|
||||
@section Packaging Guidelines
|
||||
|
||||
The GNU distribution is nascent and may well lack some of your favorite
|
||||
packages. This section describes how you can help make the distribution
|
||||
grow. @xref{Contributing}, for additional information on how you can
|
||||
help.
|
||||
|
||||
Free software packages are usually distributed in the form of
|
||||
@dfn{source code tarballs}---typically @file{tar.gz} files that contain
|
||||
all the source files. Adding a package to the distribution means
|
||||
essentially two things: adding a @dfn{recipe} that describes how to
|
||||
build the package, including a list of other packages required to build
|
||||
it, and adding @dfn{package meta-data} along with that recipe, such as a
|
||||
description and licensing information.
|
||||
|
||||
In Guix all this information is embodied in @dfn{package definitions}.
|
||||
Package definitions provide a high-level view of the package. They are
|
||||
written using the syntax of the Scheme programming language; in fact,
|
||||
for each package we define a variable bound to the package definition,
|
||||
and export that variable from a module (@pxref{Package Modules}).
|
||||
However, in-depth Scheme knowledge is @emph{not} a prerequisite for
|
||||
creating packages. For more information on package definitions,
|
||||
@ref{Defining Packages}.
|
||||
|
||||
Once a package definition is in place, stored in a file in the Guix
|
||||
source tree, it can be tested using the @command{guix build} command
|
||||
(@pxref{Invoking guix build}). For example, assuming the new package is
|
||||
called @code{gnew}, you may run this command from the Guix build tree:
|
||||
|
||||
@example
|
||||
./pre-inst-env guix build gnew --keep-failed
|
||||
@end example
|
||||
|
||||
Using @code{--keep-failed} makes it easier to debug build failures since
|
||||
it provides access to the failed build tree. Another useful
|
||||
command-line option when debugging is @code{--log-file}, to access the
|
||||
build log.
|
||||
|
||||
If the package is unknown to the @command{guix} command, it may be that
|
||||
the source file contains a syntax error, or lacks a @code{define-public}
|
||||
clause to export the package variable. To figure it out, you may load
|
||||
the module from Guile to get more information about the actual error:
|
||||
|
||||
@example
|
||||
./pre-inst-env guile -c '(use-modules (gnu packages gnew))'
|
||||
@end example
|
||||
|
||||
Once your package builds correctly, please send us a patch
|
||||
(@pxref{Contributing}). Well, if you need help, we will be happy to
|
||||
help you too. Once the patch is committed in the Guix repository, the
|
||||
new package automatically gets built on the supported platforms by
|
||||
@url{http://hydra.gnu.org/gnu/master, our continuous integration
|
||||
system}.
|
||||
|
||||
@cindex substituter
|
||||
Users can obtain the new package definition simply by running
|
||||
@command{guix pull} (@pxref{Invoking guix pull}). When
|
||||
@code{hydra.gnu.org} is done building the package, installing the
|
||||
package automatically downloads binaries from there
|
||||
(@pxref{Substitutes}). The only place where human intervention is
|
||||
needed is to review and apply the patch.
|
||||
|
||||
|
||||
@menu
|
||||
* Software Freedom:: What may go into the distribution.
|
||||
* Package Naming:: What's in a name?
|
||||
* Version Numbers:: When the name is not enough.
|
||||
* Python Modules:: Taming the snake.
|
||||
* Perl Modules:: Little pearls.
|
||||
@end menu
|
||||
|
||||
@node Software Freedom
|
||||
@subsection Software Freedom
|
||||
|
||||
@c Adapted from http://www.gnu.org/philosophy/philosophy.html.
|
||||
|
||||
The GNU operating system has been developed so that users can have
|
||||
freedom in their computing. GNU is @dfn{free software}, meaning that
|
||||
users have the @url{http://www.gnu.org/philosophy/free-sw.html,four
|
||||
essential freedoms}: to run the program, to study and change the program
|
||||
in source code form, to redistribute exact copies, and to distribute
|
||||
modified versions. Packages found in the GNU distribution provide only
|
||||
software that conveys these four freedoms.
|
||||
|
||||
In addition, the GNU distribution follow the
|
||||
@url{http://www.gnu.org/distros/free-system-distribution-guidelines.html,free
|
||||
software distribution guidelines}. Among other things, these guidelines
|
||||
reject non-free firmware, recommendations of non-free software, and
|
||||
discuss ways to deal with trademarks and patents.
|
||||
|
||||
Some packages contain a small and optional subset that violates the
|
||||
above guidelines, for instance because this subset is itself non-free
|
||||
code. When that happens, the offending items are removed with
|
||||
appropriate patches or code snippets in the package definition's
|
||||
@code{origin} form (@pxref{Defining Packages}). That way, @code{guix
|
||||
build --source} returns the ``freed'' source rather than the unmodified
|
||||
upstream source.
|
||||
|
||||
|
||||
@node Package Naming
|
||||
@subsection Package Naming
|
||||
|
||||
A package has actually two names associated with it:
|
||||
First, there is the name of the @emph{Scheme variable}, the one following
|
||||
@code{define-public}. By this name, the package can be made known in the
|
||||
Scheme code, for instance as input to another package. Second, there is
|
||||
the string in the @code{name} field of a package definition. This name
|
||||
is used by package management commands such as
|
||||
@command{guix package} and @command{guix build}.
|
||||
|
||||
Both are usually the same and correspond to the lowercase conversion of
|
||||
the project name chosen upstream, with underscores replaced with
|
||||
hyphens. For instance, GNUnet is available as @code{gnunet}, and
|
||||
SDL_net as @code{sdl-net}.
|
||||
|
||||
We do not add @code{lib} prefixes for library packages, unless these are
|
||||
already part of the official project name. But see @pxref{Python
|
||||
Modules} and @ref{Perl Modules} for special rules concerning modules for
|
||||
the Python and Perl languages.
|
||||
|
||||
|
||||
@node Version Numbers
|
||||
@subsection Version Numbers
|
||||
|
||||
We usually package only the latest version of a given free software
|
||||
project. But sometimes, for instance for incompatible library versions,
|
||||
two (or more) versions of the same package are needed. These require
|
||||
different Scheme variable names. We use the name as defined
|
||||
in @ref{Package Naming}
|
||||
for the most recent version; previous versions use the same name, suffixed
|
||||
by @code{-} and the smallest prefix of the version number that may
|
||||
distinguish the two versions.
|
||||
|
||||
The name inside the package definition is the same for all versions of a
|
||||
package and does not contain any version number.
|
||||
|
||||
For instance, the versions 2.24.20 and 3.9.12 of GTK+ may be packaged as follows:
|
||||
|
||||
@example
|
||||
(define-public gtk+
|
||||
(package
|
||||
(name "gtk+")
|
||||
(version "3.9.12")
|
||||
...))
|
||||
(define-public gtk+-2
|
||||
(package
|
||||
(name "gtk+")
|
||||
(version "2.24.20")
|
||||
...))
|
||||
@end example
|
||||
If we also wanted GTK+ 3.8.2, this would be packaged as
|
||||
@example
|
||||
(define-public gtk+-3.8
|
||||
(package
|
||||
(name "gtk+")
|
||||
(version "3.8.2")
|
||||
...))
|
||||
@end example
|
||||
|
||||
|
||||
@node Python Modules
|
||||
@subsection Python Modules
|
||||
|
||||
We currently package Python 2 and Python 3, under the Scheme variable names
|
||||
@code{python-2} and @code{python} as explained in @ref{Version Numbers}.
|
||||
To avoid confusion and naming clashes with other programming languages, it
|
||||
seems desirable that the name of a package for a Python module contains
|
||||
the word @code{python}.
|
||||
|
||||
Some modules are compatible with only one version of Python, others with both.
|
||||
If the package Foo compiles only with Python 3, we name it
|
||||
@code{python-foo}; if it compiles only with Python 2, we name it
|
||||
@code{python2-foo}. If it is compatible with both versions, we create two
|
||||
packages with the corresponding names.
|
||||
|
||||
If a project already contains the word @code{python}, we drop this;
|
||||
for instance, the module python-dateutil is packaged under the names
|
||||
@code{python-dateutil} and @code{python2-dateutil}.
|
||||
|
||||
|
||||
@node Perl Modules
|
||||
@subsection Perl Modules
|
||||
|
||||
Perl programs standing for themselves are named as any other package,
|
||||
using the lowercase upstream name.
|
||||
For Perl packages containing a single class, we use the lowercase class name,
|
||||
replace all occurrences of @code{::} by dashes and prepend the prefix
|
||||
@code{perl-}.
|
||||
So the class @code{XML::Parser} becomes @code{perl-xml-parser}.
|
||||
Modules containing several classes keep their lowercase upstream name and
|
||||
are also prepended by @code{perl-}. Such modules tend to have the word
|
||||
@code{perl} somewhere in their name, which gets dropped in favor of the
|
||||
prefix. For instance, @code{libwww-perl} becomes @code{perl-libwww}.
|
||||
|
||||
|
||||
|
||||
@node Bootstrapping
|
||||
@section Bootstrapping
|
||||
|
||||
@c Adapted from the ELS 2013 paper.
|
||||
|
||||
@cindex bootstrapping
|
||||
|
||||
Bootstrapping in our context refers to how the distribution gets built
|
||||
``from nothing''. Remember that the build environment of a derivation
|
||||
contains nothing but its declared inputs (@pxref{Introduction}). So
|
||||
there's an obvious chicken-and-egg problem: how does the first package
|
||||
get built? How does the first compiler get compiled? Note that this is
|
||||
a question of interest only to the curious hacker, not to the regular
|
||||
user, so you can shamelessly skip this section if you consider yourself
|
||||
a ``regular user''.
|
||||
|
||||
@cindex bootstrap binaries
|
||||
The GNU system is primarily made of C code, with libc at its core. The
|
||||
GNU build system itself assumes the availability of a Bourne shell and
|
||||
command-line tools provided by GNU Coreutils, Awk, Findutils, `sed', and
|
||||
`grep'. Furthermore, build programs---programs that run
|
||||
@code{./configure}, @code{make}, etc.---are written in Guile Scheme
|
||||
(@pxref{Derivations}). Consequently, to be able to build anything at
|
||||
all, from scratch, Guix relies on pre-built binaries of Guile, GCC,
|
||||
Binutils, libc, and the other packages mentioned above---the
|
||||
@dfn{bootstrap binaries}.
|
||||
|
||||
These bootstrap binaries are ``taken for granted'', though we can also
|
||||
re-create them if needed (more on that later).
|
||||
|
||||
@unnumberedsubsec Preparing to Use the Bootstrap Binaries
|
||||
|
||||
@c As of Emacs 24.3, Info-mode displays the image, but since it's a
|
||||
@c large image, it's hard to scroll. Oh well.
|
||||
@image{images/bootstrap-graph,6in,,Dependency graph of the early bootstrap derivations}
|
||||
|
||||
The figure above shows the very beginning of the dependency graph of the
|
||||
distribution, corresponding to the package definitions of the @code{(gnu
|
||||
packages bootstrap)} module. At this level of detail, things are
|
||||
slightly complex. First, Guile itself consists of an ELF executable,
|
||||
along with many source and compiled Scheme files that are dynamically
|
||||
loaded when it runs. This gets stored in the @file{guile-2.0.7.tar.xz}
|
||||
tarball shown in this graph. This tarball is part of Guix's ``source''
|
||||
distribution, and gets inserted into the store with @code{add-to-store}
|
||||
(@pxref{The Store}).
|
||||
|
||||
But how do we write a derivation that unpacks this tarball and adds it
|
||||
to the store? To solve this problem, the @code{guile-bootstrap-2.0.drv}
|
||||
derivation---the first one that gets built---uses @code{bash} as its
|
||||
builder, which runs @code{build-bootstrap-guile.sh}, which in turn calls
|
||||
@code{tar} to unpack the tarball. Thus, @file{bash}, @file{tar},
|
||||
@file{xz}, and @file{mkdir} are statically-linked binaries, also part of
|
||||
the Guix source distribution, whose sole purpose is to allow the Guile
|
||||
tarball to be unpacked.
|
||||
|
||||
Once @code{guile-bootstrap-2.0.drv} is built, we have a functioning
|
||||
Guile that can be used to run subsequent build programs. Its first task
|
||||
is to download tarballs containing the other pre-built binaries---this
|
||||
is what the @code{.tar.xz.drv} derivations do. Guix modules such as
|
||||
@code{ftp-client.scm} are used for this purpose. The
|
||||
@code{module-import.drv} derivations import those modules in a directory
|
||||
in the store, using the original layout. The
|
||||
@code{module-import-compiled.drv} derivations compile those modules, and
|
||||
write them in an output directory with the right layout. This
|
||||
corresponds to the @code{#:modules} argument of
|
||||
@code{build-expression->derivation} (@pxref{Derivations}).
|
||||
|
||||
Finally, the various tarballs are unpacked by the
|
||||
derivations @code{gcc-bootstrap-0.drv}, @code{glibc-bootstrap-0.drv},
|
||||
etc., at which point we have a working C tool chain.
|
||||
|
||||
|
||||
@unnumberedsubsec Building the Build Tools
|
||||
|
||||
@c TODO: Add a package-level dependency graph generated from (gnu
|
||||
@c packages base).
|
||||
|
||||
Bootstrapping is complete when we have a full tool chain that does not
|
||||
depend on the pre-built bootstrap tools discussed above. This
|
||||
no-dependency requirement is verified by checking whether the files of
|
||||
the final tool chain contain references to the @file{/gnu/store}
|
||||
directories of the bootstrap inputs. The process that leads to this
|
||||
``final'' tool chain is described by the package definitions found in
|
||||
the @code{(gnu packages base)} module.
|
||||
|
||||
@c See <http://lists.gnu.org/archive/html/gnu-system-discuss/2012-10/msg00000.html>.
|
||||
The first tool that gets built with the bootstrap binaries is
|
||||
GNU Make, which is a prerequisite for all the following packages.
|
||||
From there Findutils and Diffutils get built.
|
||||
|
||||
Then come the first-stage Binutils and GCC, built as pseudo cross
|
||||
tools---i.e., with @code{--target} equal to @code{--host}. They are
|
||||
used to build libc. Thanks to this cross-build trick, this libc is
|
||||
guaranteed not to hold any reference to the initial tool chain.
|
||||
|
||||
From there the final Binutils and GCC are built. GCC uses @code{ld}
|
||||
from the final Binutils, and links programs against the just-built libc.
|
||||
This tool chain is used to build the other packages used by Guix and by
|
||||
the GNU Build System: Guile, Bash, Coreutils, etc.
|
||||
|
||||
And voilà! At this point we have the complete set of build tools that
|
||||
the GNU Build System expects. These are in the @code{%final-inputs}
|
||||
variables of the @code{(gnu packages base)} module, and are implicitly
|
||||
used by any package that uses @code{gnu-build-system} (@pxref{Defining
|
||||
Packages}).
|
||||
|
||||
|
||||
@unnumberedsubsec Building the Bootstrap Binaries
|
||||
|
||||
Because the final tool chain does not depend on the bootstrap binaries,
|
||||
those rarely need to be updated. Nevertheless, it is useful to have an
|
||||
automated way to produce them, should an update occur, and this is what
|
||||
the @code{(gnu packages make-bootstrap)} module provides.
|
||||
|
||||
The following command builds the tarballs containing the bootstrap
|
||||
binaries (Guile, Binutils, GCC, libc, and a tarball containing a mixture
|
||||
of Coreutils and other basic command-line tools):
|
||||
|
||||
@example
|
||||
guix build bootstrap-tarballs
|
||||
@end example
|
||||
|
||||
The generated tarballs are those that should be referred to in the
|
||||
@code{(gnu packages bootstrap)} module mentioned at the beginning of
|
||||
this section.
|
||||
|
||||
Still here? Then perhaps by now you've started to wonder: when do we
|
||||
reach a fixed point? That is an interesting question! The answer is
|
||||
unknown, but if you would like to investigate further (and have
|
||||
significant computational and storage resources to do so), then let us
|
||||
know.
|
||||
|
||||
@node Porting
|
||||
@section Porting to a New Platform
|
||||
|
||||
As discussed above, the GNU distribution is self-contained, and
|
||||
self-containment is achieved by relying on pre-built ``bootstrap
|
||||
binaries'' (@pxref{Bootstrapping}). These binaries are specific to an
|
||||
operating system kernel, CPU architecture, and application binary
|
||||
interface (ABI). Thus, to port the distribution to a platform that is
|
||||
not yet supported, one must build those bootstrap binaries, and update
|
||||
the @code{(gnu packages bootstrap)} module to use them on that platform.
|
||||
|
||||
Fortunately, Guix can @emph{cross compile} those bootstrap binaries.
|
||||
When everything goes well, and assuming the GNU tool chain supports the
|
||||
target platform, this can be as simple as running a command like this
|
||||
one:
|
||||
|
||||
@example
|
||||
guix build --target=armv5tel-linux-gnueabi bootstrap-tarballs
|
||||
@end example
|
||||
|
||||
Once these are built, the @code{(gnu packages bootstrap)} module needs
|
||||
to be updated to refer to these binaries on the target platform. In
|
||||
addition, the @code{glibc-dynamic-linker} procedure in that module must
|
||||
be augmented to return the right file name for libc's dynamic linker on
|
||||
that platform; likewise, @code{system->linux-architecture} in @code{(gnu
|
||||
packages linux)} must be taught about the new platform.
|
||||
|
||||
In practice, there may be some complications. First, it may be that the
|
||||
extended GNU triplet that specifies an ABI (like the @code{eabi} suffix
|
||||
above) is not recognized by all the GNU tools. Typically, glibc
|
||||
recognizes some of these, whereas GCC uses an extra @code{--with-abi}
|
||||
configure flag (see @code{gcc.scm} for examples of how to handle this).
|
||||
Second, some of the required packages could fail to build for that
|
||||
platform. Lastly, the generated binaries could be broken for some
|
||||
reason.
|
||||
|
||||
|
||||
@c *********************************************************************
|
||||
@node Contributing
|
||||
@chapter Contributing
|
||||
|
|
|
|||
Reference in a new issue