summaryrefslogtreecommitdiffstats
path: root/arch/arm64/lib/memcmp.S
blob: c0671e793ea9183e5ddc63696d79c8fa2466c2a6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Copyright (C) 2013 ARM Ltd.
 * Copyright (C) 2013 Linaro.
 *
 * This code is based on glibc cortex strings work originally authored by Linaro
 * be found @
 *
 * http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/
 * files/head:/src/aarch64/
 */

#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

SYM_FUNC_START_WEAK_PI(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 difference occurred 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
SYM_FUNC_END_PI(memcmp)
EXPORT_SYMBOL_NOKASAN(memcmp)