arm64: lib: Implement optimized memcmp routine

This patch, based on Linaro's Cortex Strings library, adds
an assembly optimized memcmp() function.
Signed-off-by: Zhichang Yuan <zhichang.yuan@linaro.org>
Signed-off-by: Deepak Saxena <dsaxena@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/string.h

@@ -34,4 +34,7 @@ extern void *memchr(const void *, int, __kernel_size_t);
 #define __HAVE_ARCH_MEMSET
 extern void *memset(void *, int, __kernel_size_t);
 
+#define __HAVE_ARCH_MEMCMP
+extern int memcmp(const void *, const void *, size_t);
+
 #endif

arch/arm64/kernel/arm64ksyms.c

@@ -48,6 +48,7 @@ EXPORT_SYMBOL(memset);
 EXPORT_SYMBOL(memcpy);
 EXPORT_SYMBOL(memmove);
 EXPORT_SYMBOL(memchr);
+EXPORT_SYMBOL(memcmp);
 
 	/* atomic bitops */
 EXPORT_SYMBOL(set_bit);

arch/arm64/lib/Makefile

 lib-y		:= bitops.o clear_user.o delay.o copy_from_user.o	\
 		   copy_to_user.o copy_in_user.o copy_page.o		\
 		   clear_page.o memchr.o memcpy.o memmove.o memset.o	\
-		   strchr.o strrchr.o
+		   memcmp.o strchr.o strrchr.o

arch/arm64/lib/memcmp.S

+/*
+ * Copyright (C) 2013 ARM Ltd.
+ * Copyright (C) 2013 Linaro.
+ *
+ * This code is based on glibc cortex strings work originally authored by Linaro
+ * and re-licensed under GPLv2 for the Linux kernel. The original code can
+ * be found @
+ *
+ * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
+ * files/head:/src/aarch64/
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/*
+* compare memory areas(when two memory areas' offset are different,
+* alignment handled by the hardware)
+*
+* Parameters:
+*  x0 - const memory area 1 pointer
+*  x1 - const memory area 2 pointer
+*  x2 - the maximal compare byte length
+* Returns:
+*  x0 - a compare result, maybe less than, equal to, or greater than ZERO
+*/
+
+/* Parameters and result.  */
+src1		.req	x0
+src2		.req	x1
+limit		.req	x2
+result		.req	x0
+
+/* Internal variables.  */
+data1		.req	x3
+data1w		.req	w3
+data2		.req	x4
+data2w		.req	w4
+has_nul		.req	x5
+diff		.req	x6
+endloop		.req	x7
+tmp1		.req	x8
+tmp2		.req	x9
+tmp3		.req	x10
+pos		.req	x11
+limit_wd	.req	x12
+mask		.req	x13
+
+ENTRY(memcmp)
+	cbz	limit, .Lret0
+	eor	tmp1, src1, src2
+	tst	tmp1, #7
+	b.ne	.Lmisaligned8
+	ands	tmp1, src1, #7
+	b.ne	.Lmutual_align
+	sub	limit_wd, limit, #1 /* limit != 0, so no underflow.  */
+	lsr	limit_wd, limit_wd, #3 /* Convert to Dwords.  */
+	/*
+	* The input source addresses are at alignment boundary.
+	* Directly compare eight bytes each time.
+	*/
+.Lloop_aligned:
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+.Lstart_realigned:
+	subs	limit_wd, limit_wd, #1
+	eor	diff, data1, data2	/* Non-zero if differences found.  */
+	csinv	endloop, diff, xzr, cs	/* Last Dword or differences.  */
+	cbz	endloop, .Lloop_aligned
+
+	/* Not reached the limit, must have found a diff.  */
+	tbz	limit_wd, #63, .Lnot_limit
+
+	/* Limit % 8 == 0 => the diff is in the last 8 bytes. */
+	ands	limit, limit, #7
+	b.eq	.Lnot_limit
+	/*
+	* The remained bytes less than 8. It is needed to extract valid data
+	* from last eight bytes of the intended memory range.
+	*/
+	lsl	limit, limit, #3	/* bytes-> bits.  */
+	mov	mask, #~0
+CPU_BE( lsr	mask, mask, limit )
+CPU_LE( lsl	mask, mask, limit )
+	bic	data1, data1, mask
+	bic	data2, data2, mask
+
+	orr	diff, diff, mask
+	b	.Lnot_limit
+
+.Lmutual_align:
+	/*
+	* Sources are mutually aligned, but are not currently at an
+	* alignment boundary. Round down the addresses and then mask off
+	* the bytes that precede the start point.
+	*/
+	bic	src1, src1, #7
+	bic	src2, src2, #7
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+	/*
+	* We can not add limit with alignment offset(tmp1) here. Since the
+	* addition probably make the limit overflown.
+	*/
+	sub	limit_wd, limit, #1/*limit != 0, so no underflow.*/
+	and	tmp3, limit_wd, #7
+	lsr	limit_wd, limit_wd, #3
+	add	tmp3, tmp3, tmp1
+	add	limit_wd, limit_wd, tmp3, lsr #3
+	add	limit, limit, tmp1/* Adjust the limit for the extra.  */
+
+	lsl	tmp1, tmp1, #3/* Bytes beyond alignment -> bits.*/
+	neg	tmp1, tmp1/* Bits to alignment -64.  */
+	mov	tmp2, #~0
+	/*mask off the non-intended bytes before the start address.*/
+CPU_BE( lsl	tmp2, tmp2, tmp1 )/*Big-endian.Early bytes are at MSB*/
+	/* Little-endian.  Early bytes are at LSB.  */
+CPU_LE( lsr	tmp2, tmp2, tmp1 )
+
+	orr	data1, data1, tmp2
+	orr	data2, data2, tmp2
+	b	.Lstart_realigned
+
+	/*src1 and src2 have different alignment offset.*/
+.Lmisaligned8:
+	cmp	limit, #8
+	b.lo	.Ltiny8proc /*limit < 8: compare byte by byte*/
+
+	and	tmp1, src1, #7
+	neg	tmp1, tmp1
+	add	tmp1, tmp1, #8/*valid length in the first 8 bytes of src1*/
+	and	tmp2, src2, #7
+	neg	tmp2, tmp2
+	add	tmp2, tmp2, #8/*valid length in the first 8 bytes of src2*/
+	subs	tmp3, tmp1, tmp2
+	csel	pos, tmp1, tmp2, hi /*Choose the maximum.*/
+
+	sub	limit, limit, pos
+	/*compare the proceeding bytes in the first 8 byte segment.*/
+.Ltinycmp:
+	ldrb	data1w, [src1], #1
+	ldrb	data2w, [src2], #1
+	subs	pos, pos, #1
+	ccmp	data1w, data2w, #0, ne  /* NZCV = 0b0000.  */
+	b.eq	.Ltinycmp
+	cbnz	pos, 1f /*diff occurred before the last byte.*/
+	cmp	data1w, data2w
+	b.eq	.Lstart_align
+1:
+	sub	result, data1, data2
+	ret
+
+.Lstart_align:
+	lsr	limit_wd, limit, #3
+	cbz	limit_wd, .Lremain8
+
+	ands	xzr, src1, #7
+	b.eq	.Lrecal_offset
+	/*process more leading bytes to make src1 aligned...*/
+	add	src1, src1, tmp3 /*backwards src1 to alignment boundary*/
+	add	src2, src2, tmp3
+	sub	limit, limit, tmp3
+	lsr	limit_wd, limit, #3
+	cbz	limit_wd, .Lremain8
+	/*load 8 bytes from aligned SRC1..*/
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+
+	subs	limit_wd, limit_wd, #1
+	eor	diff, data1, data2  /*Non-zero if differences found.*/
+	csinv	endloop, diff, xzr, ne
+	cbnz	endloop, .Lunequal_proc
+	/*How far is the current SRC2 from the alignment boundary...*/
+	and	tmp3, tmp3, #7
+
+.Lrecal_offset:/*src1 is aligned now..*/
+	neg	pos, tmp3
+.Lloopcmp_proc:
+	/*
+	* Divide the eight bytes into two parts. First,backwards the src2
+	* to an alignment boundary,load eight bytes and compare from
+	* the SRC2 alignment boundary. If all 8 bytes are equal,then start
+	* the second part's comparison. Otherwise finish the comparison.
+	* This special handle can garantee all the accesses are in the
+	* thread/task space in avoid to overrange access.
+	*/
+	ldr	data1, [src1,pos]
+	ldr	data2, [src2,pos]
+	eor	diff, data1, data2  /* Non-zero if differences found.  */
+	cbnz	diff, .Lnot_limit
+
+	/*The second part process*/
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+	eor	diff, data1, data2  /* Non-zero if differences found.  */
+	subs	limit_wd, limit_wd, #1
+	csinv	endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
+	cbz	endloop, .Lloopcmp_proc
+.Lunequal_proc:
+	cbz	diff, .Lremain8
+
+/*There is differnence occured in the latest comparison.*/
+.Lnot_limit:
+/*
+* For little endian,reverse the low significant equal bits into MSB,then
+* following CLZ can find how many equal bits exist.
+*/
+CPU_LE( rev	diff, diff )
+CPU_LE( rev	data1, data1 )
+CPU_LE( rev	data2, data2 )
+
+	/*
+	* The MS-non-zero bit of DIFF marks either the first bit
+	* that is different, or the end of the significant data.
+	* Shifting left now will bring the critical information into the
+	* top bits.
+	*/
+	clz	pos, diff
+	lsl	data1, data1, pos
+	lsl	data2, data2, pos
+	/*
+	* We need to zero-extend (char is unsigned) the value and then
+	* perform a signed subtraction.
+	*/
+	lsr	data1, data1, #56
+	sub	result, data1, data2, lsr #56
+	ret
+
+.Lremain8:
+	/* Limit % 8 == 0 =>. all data are equal.*/
+	ands	limit, limit, #7
+	b.eq	.Lret0
+
+.Ltiny8proc:
+	ldrb	data1w, [src1], #1
+	ldrb	data2w, [src2], #1
+	subs	limit, limit, #1
+
+	ccmp	data1w, data2w, #0, ne  /* NZCV = 0b0000. */
+	b.eq	.Ltiny8proc
+	sub	result, data1, data2
+	ret
+.Lret0:
+	mov	result, #0
+	ret
+ENDPROC(memcmp)