1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * arch/alpha/lib/ev6-copy_user.S
4 *
5 * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
6 *
7 * Copy to/from user space, handling exceptions as we go.. This
8 * isn't exactly pretty.
9 *
10 * This is essentially the same as "memcpy()", but with a few twists.
11 * Notably, we have to make sure that $0 is always up-to-date and
12 * contains the right "bytes left to copy" value (and that it is updated
13 * only _after_ a successful copy). There is also some rather minor
14 * exception setup stuff..
15 *
16 * Much of the information about 21264 scheduling/coding comes from:
17 * Compiler Writer's Guide for the Alpha 21264
18 * abbreviated as 'CWG' in other comments here
19 * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
20 * Scheduling notation:
21 * E - either cluster
22 * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
23 * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
24 */
25
26#include <linux/export.h>
27/* Allow an exception for an insn; exit if we get one. */
28#define EXI(x,y...) \
29 99: x,##y; \
30 .section __ex_table,"a"; \
31 .long 99b - .; \
32 lda $31, $exitin-99b($31); \
33 .previous
34
35#define EXO(x,y...) \
36 99: x,##y; \
37 .section __ex_table,"a"; \
38 .long 99b - .; \
39 lda $31, $exitout-99b($31); \
40 .previous
41
42 .set noat
43 .align 4
44 .globl __copy_user
45 .ent __copy_user
46 # Pipeline info: Slotting & Comments
47__copy_user:
48 .prologue 0
49 mov $18, $0 # .. .. .. E
50 subq $18, 32, $1 # .. .. E. .. : Is this going to be a small copy?
51 nop # .. E .. ..
52 beq $18, $zerolength # U .. .. .. : U L U L
53
54 and $16,7,$3 # .. .. .. E : is leading dest misalignment
55 ble $1, $onebyteloop # .. .. U .. : 1st branch : small amount of data
56 beq $3, $destaligned # .. U .. .. : 2nd (one cycle fetcher stall)
57 subq $3, 8, $3 # E .. .. .. : L U U L : trip counter
58/*
59 * The fetcher stall also hides the 1 cycle cross-cluster stall for $3 (L --> U)
60 * This loop aligns the destination a byte at a time
61 * We know we have at least one trip through this loop
62 */
63$aligndest:
64 EXI( ldbu $1,0($17) ) # .. .. .. L : Keep loads separate from stores
65 addq $16,1,$16 # .. .. E .. : Section 3.8 in the CWG
66 addq $3,1,$3 # .. E .. .. :
67 nop # E .. .. .. : U L U L
68
69/*
70 * the -1 is to compensate for the inc($16) done in a previous quadpack
71 * which allows us zero dependencies within either quadpack in the loop
72 */
73 EXO( stb $1,-1($16) ) # .. .. .. L :
74 addq $17,1,$17 # .. .. E .. : Section 3.8 in the CWG
75 subq $0,1,$0 # .. E .. .. :
76 bne $3, $aligndest # U .. .. .. : U L U L
77
78/*
79 * If we fell through into here, we have a minimum of 33 - 7 bytes
80 * If we arrived via branch, we have a minimum of 32 bytes
81 */
82$destaligned:
83 and $17,7,$1 # .. .. .. E : Check _current_ source alignment
84 bic $0,7,$4 # .. .. E .. : number bytes as a quadword loop
85 EXI( ldq_u $3,0($17) ) # .. L .. .. : Forward fetch for fallthrough code
86 beq $1,$quadaligned # U .. .. .. : U L U L
87
88/*
89 * In the worst case, we've just executed an ldq_u here from 0($17)
90 * and we'll repeat it once if we take the branch
91 */
92
93/* Misaligned quadword loop - not unrolled. Leave it that way. */
94$misquad:
95 EXI( ldq_u $2,8($17) ) # .. .. .. L :
96 subq $4,8,$4 # .. .. E .. :
97 extql $3,$17,$3 # .. U .. .. :
98 extqh $2,$17,$1 # U .. .. .. : U U L L
99
100 bis $3,$1,$1 # .. .. .. E :
101 EXO( stq $1,0($16) ) # .. .. L .. :
102 addq $17,8,$17 # .. E .. .. :
103 subq $0,8,$0 # E .. .. .. : U L L U
104
105 addq $16,8,$16 # .. .. .. E :
106 bis $2,$2,$3 # .. .. E .. :
107 nop # .. E .. .. :
108 bne $4,$misquad # U .. .. .. : U L U L
109
110 nop # .. .. .. E
111 nop # .. .. E ..
112 nop # .. E .. ..
113 beq $0,$zerolength # U .. .. .. : U L U L
114
115/* We know we have at least one trip through the byte loop */
116 EXI ( ldbu $2,0($17) ) # .. .. .. L : No loads in the same quad
117 addq $16,1,$16 # .. .. E .. : as the store (Section 3.8 in CWG)
118 nop # .. E .. .. :
119 br $31, $dirtyentry # L0 .. .. .. : L U U L
120/* Do the trailing byte loop load, then hop into the store part of the loop */
121
122/*
123 * A minimum of (33 - 7) bytes to do a quad at a time.
124 * Based upon the usage context, it's worth the effort to unroll this loop
125 * $0 - number of bytes to be moved
126 * $4 - number of bytes to move as quadwords
127 * $16 is current destination address
128 * $17 is current source address
129 */
130$quadaligned:
131 subq $4, 32, $2 # .. .. .. E : do not unroll for small stuff
132 nop # .. .. E ..
133 nop # .. E .. ..
134 blt $2, $onequad # U .. .. .. : U L U L
135
136/*
137 * There is a significant assumption here that the source and destination
138 * addresses differ by more than 32 bytes. In this particular case, a
139 * sparsity of registers further bounds this to be a minimum of 8 bytes.
140 * But if this isn't met, then the output result will be incorrect.
141 * Furthermore, due to a lack of available registers, we really can't
142 * unroll this to be an 8x loop (which would enable us to use the wh64
143 * instruction memory hint instruction).
144 */
145$unroll4:
146 EXI( ldq $1,0($17) ) # .. .. .. L
147 EXI( ldq $2,8($17) ) # .. .. L ..
148 subq $4,32,$4 # .. E .. ..
149 nop # E .. .. .. : U U L L
150
151 addq $17,16,$17 # .. .. .. E
152 EXO( stq $1,0($16) ) # .. .. L ..
153 EXO( stq $2,8($16) ) # .. L .. ..
154 subq $0,16,$0 # E .. .. .. : U L L U
155
156 addq $16,16,$16 # .. .. .. E
157 EXI( ldq $1,0($17) ) # .. .. L ..
158 EXI( ldq $2,8($17) ) # .. L .. ..
159 subq $4, 32, $3 # E .. .. .. : U U L L : is there enough for another trip?
160
161 EXO( stq $1,0($16) ) # .. .. .. L
162 EXO( stq $2,8($16) ) # .. .. L ..
163 subq $0,16,$0 # .. E .. ..
164 addq $17,16,$17 # E .. .. .. : U L L U
165
166 nop # .. .. .. E
167 nop # .. .. E ..
168 addq $16,16,$16 # .. E .. ..
169 bgt $3,$unroll4 # U .. .. .. : U L U L
170
171 nop
172 nop
173 nop
174 beq $4, $noquads
175
176$onequad:
177 EXI( ldq $1,0($17) )
178 subq $4,8,$4
179 addq $17,8,$17
180 nop
181
182 EXO( stq $1,0($16) )
183 subq $0,8,$0
184 addq $16,8,$16
185 bne $4,$onequad
186
187$noquads:
188 nop
189 nop
190 nop
191 beq $0,$zerolength
192
193/*
194 * For small copies (or the tail of a larger copy), do a very simple byte loop.
195 * There's no point in doing a lot of complex alignment calculations to try to
196 * to quadword stuff for a small amount of data.
197 * $0 - remaining number of bytes left to copy
198 * $16 - current dest addr
199 * $17 - current source addr
200 */
201
202$onebyteloop:
203 EXI ( ldbu $2,0($17) ) # .. .. .. L : No loads in the same quad
204 addq $16,1,$16 # .. .. E .. : as the store (Section 3.8 in CWG)
205 nop # .. E .. .. :
206 nop # E .. .. .. : U L U L
207
208$dirtyentry:
209/*
210 * the -1 is to compensate for the inc($16) done in a previous quadpack
211 * which allows us zero dependencies within either quadpack in the loop
212 */
213 EXO ( stb $2,-1($16) ) # .. .. .. L :
214 addq $17,1,$17 # .. .. E .. : quadpack as the load
215 subq $0,1,$0 # .. E .. .. : change count _after_ copy
216 bgt $0,$onebyteloop # U .. .. .. : U L U L
217
218$zerolength:
219$exitin:
220$exitout: # Destination for exception recovery(?)
221 nop # .. .. .. E
222 nop # .. .. E ..
223 nop # .. E .. ..
224 ret $31,($26),1 # L0 .. .. .. : L U L U
225
226 .end __copy_user
227 EXPORT_SYMBOL(__copy_user)
228

source code of linux/arch/alpha/lib/ev6-copy_user.S