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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2013, 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2014, 2015 Mark H Weaver <mhw@netris.org>
+;;; Copyright © 2016 Jan Nieuwenhuizen <janneke@gnu.org>
+;;; Copyright © 2016 Manolis Fragkiskos Ragkousis <manolis837@gmail.com>
+;;;
+;;; 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 (gnu build cross-toolchain)
+  #:use-module (guix build utils)
+  #:use-module (guix build gnu-build-system)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26)
+  #:use-module (ice-9 match)
+  #:use-module (ice-9 ftw)
+  #:export (cross-gcc-build-phases))
+
+;;; Commentary:
+;;;
+;;; This module provides tools to build a cross-compiler.
+;;;
+;;; Code:
+
+(define %gcc-include-paths
+  ;; Environment variables for header search paths.
+  ;; Note: See <http://bugs.gnu.org/22186> for why not 'CPATH'.
+  '("C_INCLUDE_PATH"
+    "CPLUS_INCLUDE_PATH"
+    "OBJC_INCLUDE_PATH"
+    "OBJCPLUS_INCLUDE_PATH"))
+
+(define %gcc-cross-include-paths
+  ;; Search path for target headers when cross-compiling.
+  (map (cut string-append "CROSS_" <>) %gcc-include-paths))
+
+(define* (make-cross-binutils-visible #:key outputs inputs target
+                                      #:allow-other-keys)
+  "Create symlinks for 'as', 'nm', and 'ld' in the \"out\" output, under
+libexec/gcc, so that the cross-GCC can find them."
+  (let* ((out      (assoc-ref outputs "out"))
+         (libexec  (string-append out "/libexec/gcc/" target))
+         (binutils (string-append (assoc-ref inputs "binutils-cross")
+                                  "/bin/" target "-"))
+         (wrapper  (string-append (assoc-ref inputs "ld-wrapper-cross")
+                                  "/bin/" target "-ld")))
+    (for-each (lambda (file)
+                (symlink (string-append binutils file)
+                         (string-append libexec "/" file)))
+              '("as" "nm"))
+    (symlink wrapper (string-append libexec "/ld"))
+    #t))
+
+(define* (set-cross-path #:key inputs #:allow-other-keys)
+  "Add the cross kernel headers to CROSS_CPATH, and remove them from
+C_INCLUDE_PATH et al."
+  (match (assoc-ref inputs "libc")
+    ((? string? libc)
+     (let ((kernel (assoc-ref inputs "xkernel-headers")))
+       (define (cross? x)
+         ;; Return #t if X is a cross-libc or cross Linux.
+         (or (string-prefix? libc x)
+             (string-prefix? kernel x)))
+
+       (let ((cpath (string-append libc "/include"
+                                   ":" kernel "/include")))
+         (for-each (cut setenv <> cpath)
+                   %gcc-cross-include-paths))
+
+       (setenv "CROSS_LIBRARY_PATH"
+               (string-append libc "/lib:" kernel "/lib")) ;for Hurd's libihash
+
+       (for-each (lambda (var)
+                   (and=> (getenv var)
+                          (lambda (value)
+                            (let* ((path (search-path-as-string->list value))
+                                   (native-path (list->search-path-as-string
+                                                 (remove cross? path) ":")))
+                              (setenv var native-path)))))
+                 (cons "LIBRARY_PATH" %gcc-include-paths))
+       #t))
+    (#f
+     ;; We're building the sans-libc cross-compiler, so nothing to do.
+     #t)))
+
+(define* (set-cross-path/mingw #:key inputs #:allow-other-keys)
+  "Add the cross MinGW headers to CROSS_C_*_INCLUDE_PATH, and remove them from
+C_*INCLUDE_PATH."
+  (let ((libc (assoc-ref inputs "libc"))
+        (gcc (assoc-ref inputs "gcc")))
+    (define (cross? x)
+      (and libc (string-prefix? libc x)))
+
+    (define (unpacked-mingw-dir)
+      (match (scandir "." (lambda (name)
+                            (string-contains name "mingw-w64")))
+        ((mingw-dir)
+         (string-append
+          (getcwd) "/" mingw-dir "/mingw-w64-headers"))))
+
+    (if libc
+        (let ((cpath (string-append libc "/include"
+                                    ":" libc "/i686-w64-mingw32/include")))
+          (for-each (cut setenv <> cpath)
+                    %gcc-cross-include-paths))
+
+        ;; libc is false, so we are building xgcc-sans-libc.
+        ;; Add essential headers from mingw-w64.
+        (let ((mingw-source (assoc-ref inputs "mingw-source")))
+          (system* "tar" "xvf" mingw-source)
+          (let ((mingw-headers (unpacked-mingw-dir)))
+            ;; We need _mingw.h which will gets built from _mingw.h.in by
+            ;; mingw-w64's configure.  We cannot configure mingw-w64 until we
+            ;; have xgcc-sans-libc; substitute to the rescue.
+            (copy-file (string-append mingw-headers "/crt/_mingw.h.in")
+                       (string-append mingw-headers "/crt/_mingw.h"))
+
+            (substitute* (string-append mingw-headers "/crt/_mingw.h")
+              (("@MINGW_HAS_SECURE_API@")
+               "#define MINGW_HAS_SECURE_API 1"))
+
+            (let ((cpath (string-append mingw-headers "/include"
+                                        ":" mingw-headers "/crt"
+                                        ":" mingw-headers
+                                        "/defaults/include")))
+              (for-each (cut setenv <> cpath)
+                        (cons "CROSS_LIBRARY_PATH"
+                              %gcc-cross-include-paths))))))
+
+    (when libc
+      (setenv "CROSS_LIBRARY_PATH"
+              (string-append libc "/lib"
+                             ":" libc "/i686-w64-mingw32/lib")))
+
+    (setenv "CPP" (string-append gcc "/bin/cpp"))
+    (for-each (lambda (var)
+                (and=> (getenv var)
+                       (lambda (value)
+                         (let* ((path (search-path-as-string->list
+                                       value))
+                                (native-path (list->search-path-as-string
+                                              (remove cross? path) ":")))
+                           (setenv var native-path)))))
+              (cons "LIBRARY_PATH" %gcc-include-paths))
+    #t))
+
+(define (install-strip . _)
+  "Install a stripped GCC."
+  ;; Unlike our 'strip' phase, this will do the right thing for
+  ;; cross-compilers.
+  (zero? (system* "make" "install-strip")))
+
+(define* (cross-gcc-build-phases target
+                                 #:optional (phases %standard-phases))
+  "Modify PHASES to include everything needed to build a cross-GCC for TARGET,
+a target triplet."
+  (modify-phases phases
+    (add-before 'configure 'set-cross-path
+      (if (string-contains target "mingw")
+          set-cross-path/mingw
+          set-cross-path))
+    (add-after 'install 'make-cross-binutils-visible
+      (cut make-cross-binutils-visible #:target target <...>))
+    (replace 'install install-strip)))
+
+;;; cross-toolchain.scm ends here