1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * arch/alpha/lib/ev6-stxcpy.S
4 * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
5 *
6 * Copy a null-terminated string from SRC to DST.
7 *
8 * This is an internal routine used by strcpy, stpcpy, and strcat.
9 * As such, it uses special linkage conventions to make implementation
10 * of these public functions more efficient.
11 *
12 * On input:
13 *	t9 = return address
14 *	a0 = DST
15 *	a1 = SRC
16 *
17 * On output:
18 *	t12 = bitmask (with one bit set) indicating the last byte written
19 *	a0  = unaligned address of the last *word* written
20 *
21 * Furthermore, v0, a3-a5, t11, and t12 are untouched.
22 *
23 * Much of the information about 21264 scheduling/coding comes from:
24 *	Compiler Writer's Guide for the Alpha 21264
25 *	abbreviated as 'CWG' in other comments here
26 *	ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
27 * Scheduling notation:
28 *	E	- either cluster
29 *	U	- upper subcluster; U0 - subcluster U0; U1 - subcluster U1
30 *	L	- lower subcluster; L0 - subcluster L0; L1 - subcluster L1
31 * Try not to change the actual algorithm if possible for consistency.
32 */
33
34#include <asm/regdef.h>
35
36	.set noat
37	.set noreorder
38
39	.text
40
41/* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that
42   doesn't like putting the entry point for a procedure somewhere in the
43   middle of the procedure descriptor.  Work around this by putting the
44   aligned copy in its own procedure descriptor */
45
46
47	.ent stxcpy_aligned
48	.align 4
49stxcpy_aligned:
50	.frame sp, 0, t9
51	.prologue 0
52
53	/* On entry to this basic block:
54	   t0 == the first destination word for masking back in
55	   t1 == the first source word.  */
56
57	/* Create the 1st output word and detect 0's in the 1st input word.  */
58	lda	t2, -1		# E : build a mask against false zero
59	mskqh	t2, a1, t2	# U :   detection in the src word (stall)
60	mskqh	t1, a1, t3	# U :
61	ornot	t1, t2, t2	# E : (stall)
62
63	mskql	t0, a1, t0	# U : assemble the first output word
64	cmpbge	zero, t2, t8	# E : bits set iff null found
65	or	t0, t3, t1	# E : (stall)
66	bne	t8, $a_eos	# U : (stall)
67
68	/* On entry to this basic block:
69	   t0 == the first destination word for masking back in
70	   t1 == a source word not containing a null.  */
71	/* Nops here to separate store quads from load quads */
72
73$a_loop:
74	stq_u	t1, 0(a0)	# L :
75	addq	a0, 8, a0	# E :
76	nop
77	nop
78
79	ldq_u	t1, 0(a1)	# L : Latency=3
80	addq	a1, 8, a1	# E :
81	cmpbge	zero, t1, t8	# E : (3 cycle stall)
82	beq	t8, $a_loop	# U : (stall for t8)
83
84	/* Take care of the final (partial) word store.
85	   On entry to this basic block we have:
86	   t1 == the source word containing the null
87	   t8 == the cmpbge mask that found it.  */
88$a_eos:
89	negq	t8, t6		# E : find low bit set
90	and	t8, t6, t12	# E : (stall)
91	/* For the sake of the cache, don't read a destination word
92	   if we're not going to need it.  */
93	and	t12, 0x80, t6	# E : (stall)
94	bne	t6, 1f		# U : (stall)
95
96	/* We're doing a partial word store and so need to combine
97	   our source and original destination words.  */
98	ldq_u	t0, 0(a0)	# L : Latency=3
99	subq	t12, 1, t6	# E :
100	zapnot	t1, t6, t1	# U : clear src bytes >= null (stall)
101	or	t12, t6, t8	# E : (stall)
102
103	zap	t0, t8, t0	# E : clear dst bytes <= null
104	or	t0, t1, t1	# E : (stall)
105	nop
106	nop
107
1081:	stq_u	t1, 0(a0)	# L :
109	ret	(t9)		# L0 : Latency=3
110	nop
111	nop
112
113	.end stxcpy_aligned
114
115	.align 4
116	.ent __stxcpy
117	.globl __stxcpy
118__stxcpy:
119	.frame sp, 0, t9
120	.prologue 0
121
122	/* Are source and destination co-aligned?  */
123	xor	a0, a1, t0	# E :
124	unop			# E :
125	and	t0, 7, t0	# E : (stall)
126	bne	t0, $unaligned	# U : (stall)
127
128	/* We are co-aligned; take care of a partial first word.  */
129	ldq_u	t1, 0(a1)		# L : load first src word
130	and	a0, 7, t0		# E : take care not to load a word ...
131	addq	a1, 8, a1		# E :
132	beq	t0, stxcpy_aligned	# U : ... if we wont need it (stall)
133
134	ldq_u	t0, 0(a0)	# L :
135	br	stxcpy_aligned	# L0 : Latency=3
136	nop
137	nop
138
139
140/* The source and destination are not co-aligned.  Align the destination
141   and cope.  We have to be very careful about not reading too much and
142   causing a SEGV.  */
143
144	.align 4
145$u_head:
146	/* We know just enough now to be able to assemble the first
147	   full source word.  We can still find a zero at the end of it
148	   that prevents us from outputting the whole thing.
149
150	   On entry to this basic block:
151	   t0 == the first dest word, for masking back in, if needed else 0
152	   t1 == the low bits of the first source word
153	   t6 == bytemask that is -1 in dest word bytes */
154
155	ldq_u	t2, 8(a1)	# L :
156	addq	a1, 8, a1	# E :
157	extql	t1, a1, t1	# U : (stall on a1)
158	extqh	t2, a1, t4	# U : (stall on a1)
159
160	mskql	t0, a0, t0	# U :
161	or	t1, t4, t1	# E :
162	mskqh	t1, a0, t1	# U : (stall on t1)
163	or	t0, t1, t1	# E : (stall on t1)
164
165	or	t1, t6, t6	# E :
166	cmpbge	zero, t6, t8	# E : (stall)
167	lda	t6, -1		# E : for masking just below
168	bne	t8, $u_final	# U : (stall)
169
170	mskql	t6, a1, t6		# U : mask out the bits we have
171	or	t6, t2, t2		# E :   already extracted before (stall)
172	cmpbge	zero, t2, t8		# E :   testing eos (stall)
173	bne	t8, $u_late_head_exit	# U : (stall)
174
175	/* Finally, we've got all the stupid leading edge cases taken care
176	   of and we can set up to enter the main loop.  */
177
178	stq_u	t1, 0(a0)	# L : store first output word
179	addq	a0, 8, a0	# E :
180	extql	t2, a1, t0	# U : position ho-bits of lo word
181	ldq_u	t2, 8(a1)	# U : read next high-order source word
182
183	addq	a1, 8, a1	# E :
184	cmpbge	zero, t2, t8	# E : (stall for t2)
185	nop			# E :
186	bne	t8, $u_eos	# U : (stall)
187
188	/* Unaligned copy main loop.  In order to avoid reading too much,
189	   the loop is structured to detect zeros in aligned source words.
190	   This has, unfortunately, effectively pulled half of a loop
191	   iteration out into the head and half into the tail, but it does
192	   prevent nastiness from accumulating in the very thing we want
193	   to run as fast as possible.
194
195	   On entry to this basic block:
196	   t0 == the shifted high-order bits from the previous source word
197	   t2 == the unshifted current source word
198
199	   We further know that t2 does not contain a null terminator.  */
200
201	.align 3
202$u_loop:
203	extqh	t2, a1, t1	# U : extract high bits for current word
204	addq	a1, 8, a1	# E : (stall)
205	extql	t2, a1, t3	# U : extract low bits for next time (stall)
206	addq	a0, 8, a0	# E :
207
208	or	t0, t1, t1	# E : current dst word now complete
209	ldq_u	t2, 0(a1)	# L : Latency=3 load high word for next time
210	stq_u	t1, -8(a0)	# L : save the current word (stall)
211	mov	t3, t0		# E :
212
213	cmpbge	zero, t2, t8	# E : test new word for eos
214	beq	t8, $u_loop	# U : (stall)
215	nop
216	nop
217
218	/* We've found a zero somewhere in the source word we just read.
219	   If it resides in the lower half, we have one (probably partial)
220	   word to write out, and if it resides in the upper half, we
221	   have one full and one partial word left to write out.
222
223	   On entry to this basic block:
224	   t0 == the shifted high-order bits from the previous source word
225	   t2 == the unshifted current source word.  */
226$u_eos:
227	extqh	t2, a1, t1	# U :
228	or	t0, t1, t1	# E : first (partial) source word complete (stall)
229	cmpbge	zero, t1, t8	# E : is the null in this first bit? (stall)
230	bne	t8, $u_final	# U : (stall)
231
232$u_late_head_exit:
233	stq_u	t1, 0(a0)	# L : the null was in the high-order bits
234	addq	a0, 8, a0	# E :
235	extql	t2, a1, t1	# U :
236	cmpbge	zero, t1, t8	# E : (stall)
237
238	/* Take care of a final (probably partial) result word.
239	   On entry to this basic block:
240	   t1 == assembled source word
241	   t8 == cmpbge mask that found the null.  */
242$u_final:
243	negq	t8, t6		# E : isolate low bit set
244	and	t6, t8, t12	# E : (stall)
245	and	t12, 0x80, t6	# E : avoid dest word load if we can (stall)
246	bne	t6, 1f		# U : (stall)
247
248	ldq_u	t0, 0(a0)	# E :
249	subq	t12, 1, t6	# E :
250	or	t6, t12, t8	# E : (stall)
251	zapnot	t1, t6, t1	# U : kill source bytes >= null (stall)
252
253	zap	t0, t8, t0	# U : kill dest bytes <= null (2 cycle data stall)
254	or	t0, t1, t1	# E : (stall)
255	nop
256	nop
257
2581:	stq_u	t1, 0(a0)	# L :
259	ret	(t9)		# L0 : Latency=3
260	nop
261	nop
262
263	/* Unaligned copy entry point.  */
264	.align 4
265$unaligned:
266
267	ldq_u	t1, 0(a1)	# L : load first source word
268	and	a0, 7, t4	# E : find dest misalignment
269	and	a1, 7, t5	# E : find src misalignment
270	/* Conditionally load the first destination word and a bytemask
271	   with 0xff indicating that the destination byte is sacrosanct.  */
272	mov	zero, t0	# E :
273
274	mov	zero, t6	# E :
275	beq	t4, 1f		# U :
276	ldq_u	t0, 0(a0)	# L :
277	lda	t6, -1		# E :
278
279	mskql	t6, a0, t6	# U :
280	nop
281	nop
282	nop
2831:
284	subq	a1, t4, a1	# E : sub dest misalignment from src addr
285	/* If source misalignment is larger than dest misalignment, we need
286	   extra startup checks to avoid SEGV.  */
287	cmplt	t4, t5, t12	# E :
288	beq	t12, $u_head	# U :
289	lda	t2, -1		# E : mask out leading garbage in source
290
291	mskqh	t2, t5, t2	# U :
292	ornot	t1, t2, t3	# E : (stall)
293	cmpbge	zero, t3, t8	# E : is there a zero? (stall)
294	beq	t8, $u_head	# U : (stall)
295
296	/* At this point we've found a zero in the first partial word of
297	   the source.  We need to isolate the valid source data and mask
298	   it into the original destination data.  (Incidentally, we know
299	   that we'll need at least one byte of that original dest word.) */
300
301	ldq_u	t0, 0(a0)	# L :
302	negq	t8, t6		# E : build bitmask of bytes <= zero
303	and	t6, t8, t12	# E : (stall)
304	and	a1, 7, t5	# E :
305
306	subq	t12, 1, t6	# E :
307	or	t6, t12, t8	# E : (stall)
308	srl	t12, t5, t12	# U : adjust final null return value
309	zapnot	t2, t8, t2	# U : prepare source word; mirror changes (stall)
310
311	and	t1, t2, t1	# E : to source validity mask
312	extql	t2, a1, t2	# U :
313	extql	t1, a1, t1	# U : (stall)
314	andnot	t0, t2, t0	# .. e1 : zero place for source to reside (stall)
315
316	or	t0, t1, t1	# e1    : and put it there
317	stq_u	t1, 0(a0)	# .. e0 : (stall)
318	ret	(t9)		# e1    :
319	nop
320
321	.end __stxcpy
322
323