gnu: Python: Fix test failure on ARMv7.

* gnu/packages/patches/python-3-arm-alignment.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/python.scm (python-3.8)[source](patches): Add it when the
current system is ARM.

gnu/local.mk

@@ -1344,6 +1344,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/python-2.7-search-paths.patch		\
   %D%/packages/patches/python-2.7-site-prefixes.patch		\
   %D%/packages/patches/python-2.7-source-date-epoch.patch	\
+  %D%/packages/patches/python-3-arm-alignment.patch		\
   %D%/packages/patches/python-3-deterministic-build-info.patch	\
   %D%/packages/patches/python-3-search-paths.patch		\
   %D%/packages/patches/python-3-fix-tests.patch			\

gnu/packages/patches/python-3-arm-alignment.patch

@@ -0,0 +1,21 @@
+Ensure memory accesses in the sha3 module are aligned on ARM as it causes
+problems when running 32-bit code on a 64-bit kernel.
+
+Patch taken from upstream bug report:
+https://bugs.python.org/issue36515
+
+--- a/Modules/_sha3/sha3module.c
++++ b/Modules/_sha3/sha3module.c
+@@ -64,6 +64,12 @@
+ #define PLATFORM_BYTE_ORDER IS_BIG_ENDIAN
+ #endif
+ 
++/* Bus error on 32-bit ARM due to un-aligned memory accesses; 64-bit ARM
++ * doesn't complain but un-aligned memory accesses are sub-optimal */
++#if defined(__arm__) || defined(__aarch64__)
++#define NO_MISALIGNED_ACCESSES
++#endif
++
+ /* mangle names */
+ #define KeccakF1600_FastLoop_Absorb _PySHA3_KeccakF1600_FastLoop_Absorb
+ #define Keccak_HashFinal _PySHA3_Keccak_HashFinal

gnu/packages/python.scm

@@ -26,7 +26,7 @@
 ;;; Copyright © 2016, 2017 ng0 <ng0@n0.is>
 ;;; Copyright © 2016 Dylan Jeffers <sapientech@sapientech@openmailbox.org>
 ;;; Copyright © 2016 David Craven <david@craven.ch>
-;;; Copyright © 2016, 2017, 2018, 2019 Marius Bakke <mbakke@fastmail.com>
+;;; Copyright © 2016, 2017, 2018, 2019, 2020 Marius Bakke <mbakke@fastmail.com>
 ;;; Copyright © 2016, 2017 Stefan Reichör <stefan@xsteve.at>
 ;;; Copyright © 2016 Dylan Jeffers <sapientech@sapientech@openmailbox.org>
 ;;; Copyright © 2016, 2017 Alex Vong <alexvong1995@gmail.com>
@@ -92,7 +92,9 @@
   #:use-module (guix download)
   #:use-module (guix utils)
   #:use-module (guix build-system gnu)
-  #:use-module (guix build-system trivial))
+  #:use-module (guix build-system trivial)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-26))
 
 (define-public python-2.7
   (package
@@ -352,11 +354,22 @@ data types.")
               (method url-fetch)
               (uri (string-append "https://www.python.org/ftp/python/"
                                   version "/Python-" version ".tar.xz"))
-              (patches (search-patches
+              (patches (append
-                        "python-3-fix-tests.patch"
+                        ;; Disable unaligned accesses in the sha3 module on ARM as
-                        "python-3.8-fix-tests.patch"
+                        ;; it causes a test failure when building 32-bit Python on a
-                        "python-3-deterministic-build-info.patch"
+                        ;; 64-bit kernel.  See <https://bugs.python.org/issue36515>.
-                        "python-3-search-paths.patch"))
+                        ;; TODO: Remove the conditional on the next rebuild cycle.
+                        (let ((system (or (%current-target-system)
+                                          (%current-system))))
+                          (if (any (cute string-prefix? <> system)
+                                   '("arm" "aarch64"))
+                              (list (search-patch "python-3-arm-alignment.patch"))
+                              '()))
+                        (search-patches
+                         "python-3-fix-tests.patch"
+                         "python-3.8-fix-tests.patch"
+                         "python-3-deterministic-build-info.patch"
+                         "python-3-search-paths.patch")))
               (sha256
                (base32
                 "1ps5v323cp5czfshqjmbsqw7nvrdpcbk06f62jbzaqik4gfffii6"))