cortex-m0: add 64-bit multiplication

Import code to do 64-bit multiplication on Cortex-M0 core without SMULL
instruction.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=none
TEST=make buildall
add a 64-bit multiplication and see it compiled properly.
verify in .map files that the code is discarded for cortex-M0 based
platforms not using the 64-bit multiplication.

Change-Id: I0a91b3502f4bee4bb79b193fe0854e56a7d498f7
Reviewed-on: https://chromium-review.googlesource.com/207132
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>

core/cortex-m0/build.mk

@@ -13,7 +13,7 @@ CROSS_COMPILE?=arm-none-eabi-
 CFLAGS_CPU+=-mthumb -Os -mno-sched-prolog
 CFLAGS_CPU+=-mno-unaligned-access
 
-core-y=cpu.o init.o thumb_case.o div.o
+core-y=cpu.o init.o thumb_case.o div.o lmul.o
 core-$(CONFIG_COMMON_PANIC_OUTPUT)+=panic.o
 core-$(CONFIG_COMMON_RUNTIME)+=switch.o task.o
 core-$(CONFIG_WATCHDOG)+=watchdog.o

core/cortex-m0/lmul.S

@@ -0,0 +1,74 @@
+/* Runtime ABI for the ARM Cortex-M0
+ * lmul.S: 64 bit multiplication
+ *
+ * Copyright (c) 2013 Jörg Mische <bobbl@gmx.de>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
+ * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+
+
+	.syntax unified
+	.text
+	.thumb
+	.cpu cortex-m0
+
+
+
+@ long long __muldi3(long long, long long)
+@
+@ libgcc wrapper: just an alias for __aeabi_lmul()
+@
+	.thumb_func
+	.global __muldi3
+__muldi3:
+
+
+
+@ long long __aeabi_lmul(long long r1:r0, long long r3:r2)
+@
+@ Multiply r1:r0 and r3:r2 and return the product in r1:r0
+@ Can also be used for unsigned long product
+@
+	.thumb_func
+	.global __aeabi_lmul
+__aeabi_lmul:
+
+	push	{r4, lr}
+	muls	r1, r2
+	muls	r3, r0
+	adds	r1, r3
+
+	lsrs	r3, r0, #16
+	lsrs	r4, r2, #16
+	muls	r3, r4
+	adds	r1, r3
+
+	lsrs	r3, r0, #16
+	uxth	r0, r0
+	uxth	r2, r2
+	muls	r3, r2
+	muls	r4, r0
+	muls	r0, r2
+
+	movs	r2, #0
+	adds	r3, r4
+	adcs	r2, r2
+	lsls	r2, #16
+	adds	r1, r2
+
+	lsls	r2, r3, #16
+	lsrs	r3, #16
+	adds	r0, r2
+	adcs	r1, r3
+	pop	{r4, pc}