nds32: make code build with gcc 8.1

*** 21744 bytes still available in flash on reef_it8320 ****

BUG=b:65441143
BRANCH=none
TEST=make BOARD=reef_it8320 builds with gcc 8.1. not tested at all

Change-Id: Ie79ee23452574fd883c7f9425b8614346e46fdd7
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1077207
Commit-Ready: Patrick Georgi <pgeorgi@chromium.org>
Tested-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-by: Stefan Reinauer <reinauer@google.com>

core/nds32/abort.S

@@ -0,0 +1,26 @@
+/* Copyright 2018 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * abort() handler
+ */
+
+#include "config.h"
+#define PSW_INTL_SHIFT	1        /* Interrupt Stack Level */
+#define PSW_INTL_MASK	(0x3 << PSW_INTL_SHIFT)
+
+.text
+
+.global abort
+abort:
+	movi55 $r6, 3 // assert
+	movi55 $r7, 0 // no info. doubles for the equality test below
+
+	// in interrupt context -> $r5 != 0
+	mfsr $r5, $PSW
+	andi $r5, $r5, PSW_INTL_MASK
+
+	beq $r5, $r7, .L1
+	j excep_handler
+.L1:
+	break 0

core/nds32/build.mk

@@ -20,5 +20,8 @@ CFLAGS_CPU+=-flto
 LDFLAGS_EXTRA+=-flto
 endif
 
+LDFLAGS_EXTRA+=-Wl,--relax
+
 core-y=cpu.o init.o panic.o task.o switch.o __muldi3.o math.o __builtin.o
+core-y+=abort.o
 core-$(CONFIG_FPU)+=__libsoftfpu.o