doc: Add a "Porting" section.

* HACKING (Porting the Guix distro on a new platform): Remove.
* doc/guix.texi (Porting): New node.  Describe cross-compilation as the
  only approach.

1 files changed, 30 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 4d674b1b20..c217416b0a 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -1434,6 +1434,7 @@ tools that help users exert that freedom.
 @menu
 * Package Modules::             Packages from the programmer's viewpoint.
 * Bootstrapping::               GNU/Linux built from scratch.
+* Porting::                     Targeting another platform or kernel.
 @end menu
 
 Building this distribution is a cooperative effort, and you are invited
@@ -1588,6 +1589,35 @@ 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
+
+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