arm64: lib: Implement optimized string compare routines

This patch, based on Linaro's Cortex Strings library, adds
an assembly optimized strcmp() and strncmp() functions.

Signed-off-by: Zhichang Yuan <[e-mail]>
Signed-off-by: Deepak Saxena <[e-mail]>
Signed-off-by: Catalin Marinas <[e-mail]>

arch/arm64/include/asm/string.h

···
 #define __HAVE_ARCH_STRCHR
 extern char *strchr(const char *, int c);
 
+#define __HAVE_ARCH_STRCMP
+extern int strcmp(const char *, const char *);
+
+#define __HAVE_ARCH_STRNCMP
+extern int strncmp(const char *, const char *, __kernel_size_t);
+
 #define __HAVE_ARCH_MEMCPY
 extern void *memcpy(void *, const void *, __kernel_size_t);
 

arch/arm64/kernel/arm64ksyms.c

···
 	/* string / mem functions */
 EXPORT_SYMBOL(strchr);
 EXPORT_SYMBOL(strrchr);
+EXPORT_SYMBOL(strcmp);
+EXPORT_SYMBOL(strncmp);
 EXPORT_SYMBOL(memset);
 EXPORT_SYMBOL(memcpy);
 EXPORT_SYMBOL(memmove);

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	\
-		   memcmp.o strchr.o strrchr.o
+		   memcmp.o strcmp.o strncmp.o strchr.o strrchr.o

arch/arm64/lib/strcmp.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 two strings
+ *
+ * Parameters:
+ *	x0 - const string 1 pointer
+ *    x1 - const string 2 pointer
+ * Returns:
+ * x0 - an integer less than, equal to, or greater than zero
+ * if  s1  is  found, respectively, to be less than, to match,
+ * or be greater than s2.
+ */
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+/* Parameters and result.  */
+src1		.req	x0
+src2		.req	x1
+result		.req	x0
+
+/* Internal variables.  */
+data1		.req	x2
+data1w		.req	w2
+data2		.req	x3
+data2w		.req	w3
+has_nul		.req	x4
+diff		.req	x5
+syndrome	.req	x6
+tmp1		.req	x7
+tmp2		.req	x8
+tmp3		.req	x9
+zeroones	.req	x10
+pos		.req	x11
+
+ENTRY(strcmp)
+	eor	tmp1, src1, src2
+	mov	zeroones, #REP8_01
+	tst	tmp1, #7
+	b.ne	.Lmisaligned8
+	ands	tmp1, src1, #7
+	b.ne	.Lmutual_align
+
+	/*
+	* NUL detection works on the principle that (X - 1) & (~X) & 0x80
+	* (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
+	* can be done in parallel across the entire word.
+	*/
+.Lloop_aligned:
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+.Lstart_realigned:
+	sub	tmp1, data1, zeroones
+	orr	tmp2, data1, #REP8_7f
+	eor	diff, data1, data2	/* Non-zero if differences found.  */
+	bic	has_nul, tmp1, tmp2	/* Non-zero if NUL terminator.  */
+	orr	syndrome, diff, has_nul
+	cbz	syndrome, .Lloop_aligned
+	b	.Lcal_cmpresult
+
+.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 preceed the start point.
+	*/
+	bic	src1, src1, #7
+	bic	src2, src2, #7
+	lsl	tmp1, tmp1, #3		/* Bytes beyond alignment -> bits.  */
+	ldr	data1, [src1], #8
+	neg	tmp1, tmp1		/* Bits to alignment -64.  */
+	ldr	data2, [src2], #8
+	mov	tmp2, #~0
+	/* Big-endian.  Early bytes are at MSB.  */
+CPU_BE( lsl	tmp2, tmp2, tmp1 )	/* Shift (tmp1 & 63).  */
+	/* Little-endian.  Early bytes are at LSB.  */
+CPU_LE( lsr	tmp2, tmp2, tmp1 )	/* Shift (tmp1 & 63).  */
+
+	orr	data1, data1, tmp2
+	orr	data2, data2, tmp2
+	b	.Lstart_realigned
+
+.Lmisaligned8:
+	/*
+	* Get the align offset length to compare per byte first.
+	* After this process, one string's address will be aligned.
+	*/
+	and	tmp1, src1, #7
+	neg	tmp1, tmp1
+	add	tmp1, tmp1, #8
+	and	tmp2, src2, #7
+	neg	tmp2, tmp2
+	add	tmp2, tmp2, #8
+	subs	tmp3, tmp1, tmp2
+	csel	pos, tmp1, tmp2, hi /*Choose the maximum. */
+.Ltinycmp:
+	ldrb	data1w, [src1], #1
+	ldrb	data2w, [src2], #1
+	subs	pos, pos, #1
+	ccmp	data1w, #1, #0, ne  /* NZCV = 0b0000.  */
+	ccmp	data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
+	b.eq	.Ltinycmp
+	cbnz	pos, 1f /*find the null or unequal...*/
+	cmp	data1w, #1
+	ccmp	data1w, data2w, #0, cs
+	b.eq	.Lstart_align /*the last bytes are equal....*/
+1:
+	sub	result, data1, data2
+	ret
+
+.Lstart_align:
+	ands	xzr, src1, #7
+	b.eq	.Lrecal_offset
+	/*process more leading bytes to make str1 aligned...*/
+	add	src1, src1, tmp3
+	add	src2, src2, tmp3
+	/*load 8 bytes from aligned str1 and non-aligned str2..*/
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+
+	sub	tmp1, data1, zeroones
+	orr	tmp2, data1, #REP8_7f
+	bic	has_nul, tmp1, tmp2
+	eor	diff, data1, data2 /* Non-zero if differences found.  */
+	orr	syndrome, diff, has_nul
+	cbnz	syndrome, .Lcal_cmpresult
+	/*How far is the current str2 from the alignment boundary...*/
+	and	tmp3, tmp3, #7
+.Lrecal_offset:
+	neg	pos, tmp3
+.Lloopcmp_proc:
+	/*
+	* Divide the eight bytes into two parts. First,backwards the src2
+	* to an alignment boundary,load eight bytes from the SRC2 alignment
+	* boundary,then compare with the relative bytes from SRC1.
+	* 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]
+	sub	tmp1, data1, zeroones
+	orr	tmp2, data1, #REP8_7f
+	bic	has_nul, tmp1, tmp2
+	eor	diff, data1, data2  /* Non-zero if differences found.  */
+	orr	syndrome, diff, has_nul
+	cbnz	syndrome, .Lcal_cmpresult
+
+	/*The second part process*/
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+	sub	tmp1, data1, zeroones
+	orr	tmp2, data1, #REP8_7f
+	bic	has_nul, tmp1, tmp2
+	eor	diff, data1, data2  /* Non-zero if differences found.  */
+	orr	syndrome, diff, has_nul
+	cbz	syndrome, .Lloopcmp_proc
+
+.Lcal_cmpresult:
+	/*
+	* reversed the byte-order as big-endian,then CLZ can find the most
+	* significant zero bits.
+	*/
+CPU_LE( rev	syndrome, syndrome )
+CPU_LE( rev	data1, data1 )
+CPU_LE( rev	data2, data2 )
+
+	/*
+	* For big-endian we cannot use the trick with the syndrome value
+	* as carry-propagation can corrupt the upper bits if the trailing
+	* bytes in the string contain 0x01.
+	* However, if there is no NUL byte in the dword, we can generate
+	* the result directly.  We ca not just subtract the bytes as the
+	* MSB might be significant.
+	*/
+CPU_BE( cbnz	has_nul, 1f )
+CPU_BE( cmp	data1, data2 )
+CPU_BE( cset	result, ne )
+CPU_BE( cneg	result, result, lo )
+CPU_BE( ret )
+CPU_BE( 1: )
+	/*Re-compute the NUL-byte detection, using a byte-reversed value. */
+CPU_BE(	rev	tmp3, data1 )
+CPU_BE(	sub	tmp1, tmp3, zeroones )
+CPU_BE(	orr	tmp2, tmp3, #REP8_7f )
+CPU_BE(	bic	has_nul, tmp1, tmp2 )
+CPU_BE(	rev	has_nul, has_nul )
+CPU_BE(	orr	syndrome, diff, has_nul )
+
+	clz	pos, syndrome
+	/*
+	* The MS-non-zero bit of the syndrome marks either the first bit
+	* that is different, or the top bit of the first zero byte.
+	* Shifting left now will bring the critical information into the
+	* top bits.
+	*/
+	lsl	data1, data1, pos
+	lsl	data2, data2, pos
+	/*
+	* But we need to zero-extend (char is unsigned) the value and then
+	* perform a signed 32-bit subtraction.
+	*/
+	lsr	data1, data1, #56
+	sub	result, data1, data2, lsr #56
+	ret
+ENDPROC(strcmp)

arch/arm64/lib/strncmp.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 two strings
+ *
+ * Parameters:
+ *  x0 - const string 1 pointer
+ *  x1 - const string 2 pointer
+ *  x2 - the maximal length to be compared
+ * Returns:
+ *  x0 - an integer less than, equal to, or greater than zero if s1 is found,
+ *     respectively, to be less than, to match, or be greater than s2.
+ */
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+/* 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
+syndrome	.req	x7
+tmp1		.req	x8
+tmp2		.req	x9
+tmp3		.req	x10
+zeroones	.req	x11
+pos		.req	x12
+limit_wd	.req	x13
+mask		.req	x14
+endloop		.req	x15
+
+ENTRY(strncmp)
+	cbz	limit, .Lret0
+	eor	tmp1, src1, src2
+	mov	zeroones, #REP8_01
+	tst	tmp1, #7
+	b.ne	.Lmisaligned8
+	ands	tmp1, src1, #7
+	b.ne	.Lmutual_align
+	/* Calculate the number of full and partial words -1.  */
+	/*
+	* when limit is mulitply of 8, if not sub 1,
+	* the judgement of last dword will wrong.
+	*/
+	sub	limit_wd, limit, #1 /* limit != 0, so no underflow.  */
+	lsr	limit_wd, limit_wd, #3  /* Convert to Dwords.  */
+
+	/*
+	* NUL detection works on the principle that (X - 1) & (~X) & 0x80
+	* (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
+	* can be done in parallel across the entire word.
+	*/
+.Lloop_aligned:
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+.Lstart_realigned:
+	subs	limit_wd, limit_wd, #1
+	sub	tmp1, data1, zeroones
+	orr	tmp2, data1, #REP8_7f
+	eor	diff, data1, data2  /* Non-zero if differences found.  */
+	csinv	endloop, diff, xzr, pl  /* Last Dword or differences.*/
+	bics	has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
+	ccmp	endloop, #0, #0, eq
+	b.eq	.Lloop_aligned
+
+	/*Not reached the limit, must have found the end or a diff.  */
+	tbz	limit_wd, #63, .Lnot_limit
+
+	/* Limit % 8 == 0 => all bytes significant.  */
+	ands	limit, limit, #7
+	b.eq	.Lnot_limit
+
+	lsl	limit, limit, #3    /* Bits -> bytes.  */
+	mov	mask, #~0
+CPU_BE( lsr	mask, mask, limit )
+CPU_LE( lsl	mask, mask, limit )
+	bic	data1, data1, mask
+	bic	data2, data2, mask
+
+	/* Make sure that the NUL byte is marked in the syndrome.  */
+	orr	has_nul, has_nul, mask
+
+.Lnot_limit:
+	orr	syndrome, diff, has_nul
+	b	.Lcal_cmpresult
+
+.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.
+	* We also need to adjust the limit calculations, but without
+	* overflowing if the limit is near ULONG_MAX.
+	*/
+	bic	src1, src1, #7
+	bic	src2, src2, #7
+	ldr	data1, [src1], #8
+	neg	tmp3, tmp1, lsl #3  /* 64 - bits(bytes beyond align). */
+	ldr	data2, [src2], #8
+	mov	tmp2, #~0
+	sub	limit_wd, limit, #1 /* limit != 0, so no underflow.  */
+	/* Big-endian.  Early bytes are at MSB.  */
+CPU_BE( lsl	tmp2, tmp2, tmp3 )	/* Shift (tmp1 & 63).  */
+	/* Little-endian.  Early bytes are at LSB.  */
+CPU_LE( lsr	tmp2, tmp2, tmp3 )	/* Shift (tmp1 & 63).  */
+
+	and	tmp3, limit_wd, #7
+	lsr	limit_wd, limit_wd, #3
+	/* Adjust the limit. Only low 3 bits used, so overflow irrelevant.*/
+	add	limit, limit, tmp1
+	add	tmp3, tmp3, tmp1
+	orr	data1, data1, tmp2
+	orr	data2, data2, tmp2
+	add	limit_wd, limit_wd, tmp3, lsr #3
+	b	.Lstart_realigned
+
+/*when src1 offset is not equal to src2 offset...*/
+.Lmisaligned8:
+	cmp	limit, #8
+	b.lo	.Ltiny8proc /*limit < 8... */
+	/*
+	* Get the align offset length to compare per byte first.
+	* After this process, one string's address will be aligned.*/
+	and	tmp1, src1, #7
+	neg	tmp1, tmp1
+	add	tmp1, tmp1, #8
+	and	tmp2, src2, #7
+	neg	tmp2, tmp2
+	add	tmp2, tmp2, #8
+	subs	tmp3, tmp1, tmp2
+	csel	pos, tmp1, tmp2, hi /*Choose the maximum. */
+	/*
+	* Here, limit is not less than 8, so directly run .Ltinycmp
+	* without checking the limit.*/
+	sub	limit, limit, pos
+.Ltinycmp:
+	ldrb	data1w, [src1], #1
+	ldrb	data2w, [src2], #1
+	subs	pos, pos, #1
+	ccmp	data1w, #1, #0, ne  /* NZCV = 0b0000.  */
+	ccmp	data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
+	b.eq	.Ltinycmp
+	cbnz	pos, 1f /*find the null or unequal...*/
+	cmp	data1w, #1
+	ccmp	data1w, data2w, #0, cs
+	b.eq	.Lstart_align /*the last bytes are equal....*/
+1:
+	sub	result, data1, data2
+	ret
+
+.Lstart_align:
+	lsr	limit_wd, limit, #3
+	cbz	limit_wd, .Lremain8
+	/*process more leading bytes to make str1 aligned...*/
+	ands	xzr, src1, #7
+	b.eq	.Lrecal_offset
+	add	src1, src1, tmp3	/*tmp3 is positive in this branch.*/
+	add	src2, src2, tmp3
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+
+	sub	limit, limit, tmp3
+	lsr	limit_wd, limit, #3
+	subs	limit_wd, limit_wd, #1
+
+	sub	tmp1, data1, zeroones
+	orr	tmp2, data1, #REP8_7f
+	eor	diff, data1, data2  /* Non-zero if differences found.  */
+	csinv	endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
+	bics	has_nul, tmp1, tmp2
+	ccmp	endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
+	b.ne	.Lunequal_proc
+	/*How far is the current str2 from the alignment boundary...*/
+	and	tmp3, tmp3, #7
+.Lrecal_offset:
+	neg	pos, tmp3
+.Lloopcmp_proc:
+	/*
+	* Divide the eight bytes into two parts. First,backwards the src2
+	* to an alignment boundary,load eight bytes from the SRC2 alignment
+	* boundary,then compare with the relative bytes from SRC1.
+	* 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]
+	sub	tmp1, data1, zeroones
+	orr	tmp2, data1, #REP8_7f
+	bics	has_nul, tmp1, tmp2 /* Non-zero if NUL terminator.  */
+	eor	diff, data1, data2  /* Non-zero if differences found.  */
+	csinv	endloop, diff, xzr, eq
+	cbnz	endloop, .Lunequal_proc
+
+	/*The second part process*/
+	ldr	data1, [src1], #8
+	ldr	data2, [src2], #8
+	subs	limit_wd, limit_wd, #1
+	sub	tmp1, data1, zeroones
+	orr	tmp2, data1, #REP8_7f
+	eor	diff, data1, data2  /* Non-zero if differences found.  */
+	csinv	endloop, diff, xzr, ne/*if limit_wd is 0,will finish the cmp*/
+	bics	has_nul, tmp1, tmp2
+	ccmp	endloop, #0, #0, eq /*has_null is ZERO: no null byte*/
+	b.eq	.Lloopcmp_proc
+
+.Lunequal_proc:
+	orr	syndrome, diff, has_nul
+	cbz	syndrome, .Lremain8
+.Lcal_cmpresult:
+	/*
+	* reversed the byte-order as big-endian,then CLZ can find the most
+	* significant zero bits.
+	*/
+CPU_LE( rev	syndrome, syndrome )
+CPU_LE( rev	data1, data1 )
+CPU_LE( rev	data2, data2 )
+	/*
+	* For big-endian we cannot use the trick with the syndrome value
+	* as carry-propagation can corrupt the upper bits if the trailing
+	* bytes in the string contain 0x01.
+	* However, if there is no NUL byte in the dword, we can generate
+	* the result directly.  We can't just subtract the bytes as the
+	* MSB might be significant.
+	*/
+CPU_BE( cbnz	has_nul, 1f )
+CPU_BE( cmp	data1, data2 )
+CPU_BE( cset	result, ne )
+CPU_BE( cneg	result, result, lo )
+CPU_BE( ret )
+CPU_BE( 1: )
+	/* Re-compute the NUL-byte detection, using a byte-reversed value.*/
+CPU_BE( rev	tmp3, data1 )
+CPU_BE( sub	tmp1, tmp3, zeroones )
+CPU_BE( orr	tmp2, tmp3, #REP8_7f )
+CPU_BE( bic	has_nul, tmp1, tmp2 )
+CPU_BE( rev	has_nul, has_nul )
+CPU_BE( orr	syndrome, diff, has_nul )
+	/*
+	* The MS-non-zero bit of the syndrome marks either the first bit
+	* that is different, or the top bit of the first zero byte.
+	* Shifting left now will bring the critical information into the
+	* top bits.
+	*/
+	clz	pos, syndrome
+	lsl	data1, data1, pos
+	lsl	data2, data2, pos
+	/*
+	* But we need to zero-extend (char is unsigned) the value and then
+	* perform a signed 32-bit subtraction.
+	*/
+	lsr	data1, data1, #56
+	sub	result, data1, data2, lsr #56
+	ret
+
+.Lremain8:
+	/* Limit % 8 == 0 => all bytes significant.  */
+	ands	limit, limit, #7
+	b.eq	.Lret0
+.Ltiny8proc:
+	ldrb	data1w, [src1], #1
+	ldrb	data2w, [src2], #1
+	subs	limit, limit, #1
+
+	ccmp	data1w, #1, #0, ne  /* NZCV = 0b0000.  */
+	ccmp	data1w, data2w, #0, cs  /* NZCV = 0b0000.  */
+	b.eq	.Ltiny8proc
+	sub	result, data1, data2
+	ret
+
+.Lret0:
+	mov	result, #0
+	ret
+ENDPROC(strncmp)