guix.texi

package from source.  The command:

@example
guix graph -t bag \
  -e '(@@@@ (gnu packages commencement)
          glibc-final-with-bootstrap-bash)' | xdot -
@end example

@noindent
displays the dependency graph leading to the ``final'' C
library@footnote{You may notice the @code{glibc-intermediate} label,
suggesting that it is not @emph{quite} final, but as a good
approximation, we will consider it final.}, depicted below.

@image{images/bootstrap-packages,6in,,Dependency graph of the early packages}

@c See <https://lists.gnu.org/archive/html/gnu-system-discuss/2012-10/msg00000.html>.
The first tool that gets built with the bootstrap binaries is
GNU@tie{}Make---noted @code{make-boot0} above---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 @option{--target} equal to @option{--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 (not shown above) are built.  GCC
uses @command{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}
variable of the @code{(gnu packages commencement)} module, and are
implicitly used by any package that uses @code{gnu-build-system}
(@pxref{Build Systems, @code{gnu-build-system}}).


@unnumberedsec Building the Bootstrap Binaries

@cindex 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
(Binutils, GCC, glibc, for the traditional bootstrap and linux-libre-headers,
bootstrap-mescc-tools, bootstrap-mes for the Reduced Binary Seed bootstrap,
and Guile, 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.

@unnumberedsec Reducing the Set of Bootstrap Binaries

Our traditional bootstrap includes GCC, GNU Libc, Guile, etc.  That's a lot of
binary code!  Why is that a problem?  It's a problem because these big chunks
of binary code are practically non-auditable, which makes it hard to establish
what source code produced them.  Every unauditable binary also leaves us
vulnerable to compiler backdoors as described by Ken Thompson in the 1984
paper @emph{Reflections on Trusting Trust}.

This is mitigated by the fact that our bootstrap binaries were generated
from an earlier Guix revision.  Nevertheless it lacks the level of
transparency that we get in the rest of the package dependency graph,
where Guix always gives us a source-to-binary mapping.  Thus, our goal
is to reduce the set of bootstrap binaries to the bare minimum.

The @uref{https://bootstrappable.org, Bootstrappable.org web site} lists
on-going projects to do that.  One of these is about replacing the
bootstrap GCC with a sequence of assemblers, interpreters, and compilers
of increasing complexity, which could be built from source starting from
a simple and auditable assembler.

Our first major achievement is the replacement of of GCC, the GNU C Library
and Binutils by MesCC-Tools (a simple hex linker and macro assembler) and Mes
(@pxref{Top, GNU Mes Reference Manual,, mes, GNU Mes}, a Scheme interpreter
and C compiler in Scheme).  Neither MesCC-Tools nor Mes can be fully
bootstrapped yet and thus we inject them as binary seeds.  We call this the
Reduced Binary Seed bootstrap, as it has halved the size of our bootstrap
binaries!  Also, it has eliminated the C compiler binary; i686-linux and
x86_64-linux Guix packages are now bootstrapped without any binary C compiler.

Work is ongoing to make MesCC-Tools and Mes fully bootstrappable and we are
also looking at any other bootstrap binaries.  Your help is welcome!

@node Porting
@chapter 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

For this to work, the @code{glibc-dynamic-linker} procedure in
@code{(gnu packages bootstrap)} 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.

Once these are built, the @code{(gnu packages bootstrap)} module needs
to be updated to refer to these binaries on the target platform.  That
is, the hashes and URLs of the bootstrap tarballs for the new platform
must be added alongside those of the currently supported platforms.  The
bootstrap Guile tarball is treated specially: it is expected to be
available locally, and @file{gnu/local.mk} has rules to download it for
the supported architectures; a rule for the new platform must be added
as well.

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 @option{--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 *********************************************************************
@include contributing.texi

@c *********************************************************************
@node Acknowledgments
@chapter Acknowledgments

Guix is based on the @uref{https://nixos.org/nix/, Nix package manager},
which was designed and
implemented by Eelco Dolstra, with contributions from other people (see
the @file{nix/AUTHORS} file in Guix).  Nix pioneered functional package
management, and promoted unprecedented features, such as transactional
package upgrades and rollbacks, per-user profiles, and referentially
transparent build processes.  Without this work, Guix would not exist.

The Nix-based software distributions, Nixpkgs and NixOS, have also been
an inspiration for Guix.

GNU@tie{}Guix itself is a collective work with contributions from a
number of people.  See the @file{AUTHORS} file in Guix for more
information on these fine people.  The @file{THANKS} file lists people
who have helped by reporting bugs, taking care of the infrastructure,
providing artwork and themes, making suggestions, and more---thank you!


@c *********************************************************************
@node GNU Free Documentation License
@appendix GNU Free Documentation License
@cindex license, GNU Free Documentation License
@include fdl-1.3.texi

@c *********************************************************************
@node Concept Index
@unnumbered Concept Index
@printindex cp

@node Programming Index
@unnumbered Programming Index
@syncodeindex tp fn
@syncodeindex vr fn
@printindex fn

@bye

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