build-system/meson: Support cross-compilation.

For cross-compilation, meson needs to be passed a
‘cross file’ with information on the architecture,
CPU type, endianness and operating system, and the
name of the cross-compiler binaries.

The new module (guix build meson-configuration) has
some utilities for writing these cross files, used
by 'make-cross-file' in a G-exp.  The values for
the cross file are generated by 'make-machine-alist'
and 'make-binaries-alist'.

'make-machine-alist' and 'make-binaries-alist' live
on the host side, such that new architectures and operating
systems can be added without causing rebuilds for old
architectures.

All operating systems and targets supported by Guix are
theoretically supported, but only aarch64-linux-gnu,
powerpc64le-linux-gnu and arm-linux-gnueabihf have been
tested.  i686-linux-gnu has also been tested with a previous
version of this patch series but required some changes
to 'cross-base.scm'.

This has been tested with:

$ ./pre-inst-env guix build glib --target=TARGET

* guix/build/meson-configuration.scm
  (write-section-header): New procedure.
  (write-assignment): New procedure.
  (write-assignments): New procedure.
* guix/build-system/meson.scm
  (target-hurd?): New predicate.
  (make-machine-alist): New procedure.
  (make-binaries-alist): New procedure.
  (make-cross-file): New procedure.
  (meson-cross-build): New procedure.
  (lower)[build-inputs]: Add standard cross packages when cross-compiling.
  Do not include regular 'inputs' when cross-compiling.
  (lower)[host-inputs]: Include 'inputs' when cross-compiling.
  (lower)[target-inputs]: Add cross packages when cross-compiling.
  (lower)[build]: Call 'meson-cross-build' instead of 'cross-build'
  when cross-compiling.
  (lower)[target]: Set it.
  (lower)[private-keywords]: Do not remove #:target when cross-compiling.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/guix/build/meson-configuration.scm b/guix/build/meson-configuration.scm
new file mode 100644
index 0000000000..1aac5f8f0a
--- /dev/null
+++ b/guix/build/meson-configuration.scm
@@ -0,0 +1,56 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2021 Maxime Devos <maximedevos@telenet.be>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix build meson-configuration)
+  #:use-module (ice-9 match)
+  #:export (write-section-header write-assignment write-assignments))
+
+;; Commentary:
+;;
+;; Utilities for generating a ‘Cross build definition file’ for
+;; the Meson build system.  Configuration values are currently
+;; never escaped.  In practice this is unlikely to be a problem
+;; in the build environment.
+;;
+;; Code:
+
+(define (write-section-header port section-name)
+  "Write a section header for a section named SECTION-NAME to PORT."
+  (format port "[~a]~%" section-name))
+
+(define (write-assignment port key value)
+  "Write an assignment of VALUE to KEY to PORT.
+
+VALUE must be a string (without any special characters such as quotes),
+a boolean or an integer.  Lists are currently not supported"
+  (match value
+    ((? string?)
+     (format port "~a = '~a'~%" key value))
+    ((? integer?)
+     (format port "~a = ~a~%" key value))
+    (#f
+     (format port "~a = true~%" key))
+    (#t
+     (format port "~a = false~%" key))))
+
+(define* (write-assignments port alist)
+  "Write the assignments in ALIST, an association list, to PORT."
+  (for-each (match-lambda
+              ((key . value)
+               (write-assignment port key value)))
+            alist))