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1/*
2 * arch/alpha/lib/ev6-strncpy_from_user.S
3 * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
4 *
5 * Just like strncpy except in the return value:
6 *
7 * -EFAULT if an exception occurs before the terminator is copied.
8 * N if the buffer filled.
9 *
10 * Otherwise the length of the string is returned.
11 *
12 * Much of the information about 21264 scheduling/coding comes from:
13 * Compiler Writer's Guide for the Alpha 21264
14 * abbreviated as 'CWG' in other comments here
15 * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
16 * Scheduling notation:
17 * E - either cluster
18 * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
19 * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
20 * A bunch of instructions got moved and temp registers were changed
21 * to aid in scheduling. Control flow was also re-arranged to eliminate
22 * branches, and to provide longer code sequences to enable better scheduling.
23 * A total rewrite (using byte load/stores for start & tail sequences)
24 * is desirable, but very difficult to do without a from-scratch rewrite.
25 * Save that for the future.
26 */
27
28
29#include <asm/errno.h>
30#include <asm/regdef.h>
31
32
33/* Allow an exception for an insn; exit if we get one. */
34#define EX(x,y...) \
35 99: x,##y; \
36 .section __ex_table,"a"; \
37 .long 99b - .; \
38 lda $31, $exception-99b($0); \
39 .previous
40
41
42 .set noat
43 .set noreorder
44 .text
45
46 .globl __strncpy_from_user
47 .ent __strncpy_from_user
48 .frame $30, 0, $26
49 .prologue 0
50
51 .align 4
52__strncpy_from_user:
53 and a0, 7, t3 # E : find dest misalignment
54 beq a2, $zerolength # U :
55
56 /* Are source and destination co-aligned? */
57 mov a0, v0 # E : save the string start
58 xor a0, a1, t4 # E :
59 EX( ldq_u t1, 0(a1) ) # L : Latency=3 load first quadword
60 ldq_u t0, 0(a0) # L : load first (partial) aligned dest quadword
61
62 addq a2, t3, a2 # E : bias count by dest misalignment
63 subq a2, 1, a3 # E :
64 addq zero, 1, t10 # E :
65 and t4, 7, t4 # E : misalignment between the two
66
67 and a3, 7, t6 # E : number of tail bytes
68 sll t10, t6, t10 # E : t10 = bitmask of last count byte
69 bne t4, $unaligned # U :
70 lda t2, -1 # E : build a mask against false zero
71
72 /*
73 * We are co-aligned; take care of a partial first word.
74 * On entry to this basic block:
75 * t0 == the first destination word for masking back in
76 * t1 == the first source word.
77 */
78
79 srl a3, 3, a2 # E : a2 = loop counter = (count - 1)/8
80 addq a1, 8, a1 # E :
81 mskqh t2, a1, t2 # U : detection in the src word
82 nop
83
84 /* Create the 1st output word and detect 0's in the 1st input word. */
85 mskqh t1, a1, t3 # U :
86 mskql t0, a1, t0 # U : assemble the first output word
87 ornot t1, t2, t2 # E :
88 nop
89
90 cmpbge zero, t2, t8 # E : bits set iff null found
91 or t0, t3, t0 # E :
92 beq a2, $a_eoc # U :
93 bne t8, $a_eos # U : 2nd branch in a quad. Bad.
94
95 /* On entry to this basic block:
96 * t0 == a source quad not containing a null.
97 * a0 - current aligned destination address
98 * a1 - current aligned source address
99 * a2 - count of quadwords to move.
100 * NOTE: Loop improvement - unrolling this is going to be
101 * a huge win, since we're going to stall otherwise.
102 * Fix this later. For _really_ large copies, look
103 * at using wh64 on a look-ahead basis. See the code
104 * in clear_user.S and copy_user.S.
105 * Presumably, since (a0) and (a1) do not overlap (by C definition)
106 * Lots of nops here:
107 * - Separate loads from stores
108 * - Keep it to 1 branch/quadpack so the branch predictor
109 * can train.
110 */
111$a_loop:
112 stq_u t0, 0(a0) # L :
113 addq a0, 8, a0 # E :
114 nop
115 subq a2, 1, a2 # E :
116
117 EX( ldq_u t0, 0(a1) ) # L :
118 addq a1, 8, a1 # E :
119 cmpbge zero, t0, t8 # E : Stall 2 cycles on t0
120 beq a2, $a_eoc # U :
121
122 beq t8, $a_loop # U :
123 nop
124 nop
125 nop
126
127 /* Take care of the final (partial) word store. At this point
128 * the end-of-count bit is set in t8 iff it applies.
129 *
130 * On entry to this basic block we have:
131 * t0 == the source word containing the null
132 * t8 == the cmpbge mask that found it.
133 */
134$a_eos:
135 negq t8, t12 # E : find low bit set
136 and t8, t12, t12 # E :
137
138 /* We're doing a partial word store and so need to combine
139 our source and original destination words. */
140 ldq_u t1, 0(a0) # L :
141 subq t12, 1, t6 # E :
142
143 or t12, t6, t8 # E :
144 zapnot t0, t8, t0 # U : clear src bytes > null
145 zap t1, t8, t1 # U : clear dst bytes <= null
146 or t0, t1, t0 # E :
147
148 stq_u t0, 0(a0) # L :
149 br $finish_up # L0 :
150 nop
151 nop
152
153 /* Add the end-of-count bit to the eos detection bitmask. */
154 .align 4
155$a_eoc:
156 or t10, t8, t8
157 br $a_eos
158 nop
159 nop
160
161
162/* The source and destination are not co-aligned. Align the destination
163 and cope. We have to be very careful about not reading too much and
164 causing a SEGV. */
165
166 .align 4
167$u_head:
168 /* We know just enough now to be able to assemble the first
169 full source word. We can still find a zero at the end of it
170 that prevents us from outputting the whole thing.
171
172 On entry to this basic block:
173 t0 == the first dest word, unmasked
174 t1 == the shifted low bits of the first source word
175 t6 == bytemask that is -1 in dest word bytes */
176
177 EX( ldq_u t2, 8(a1) ) # L : load second src word
178 addq a1, 8, a1 # E :
179 mskql t0, a0, t0 # U : mask trailing garbage in dst
180 extqh t2, a1, t4 # U :
181
182 or t1, t4, t1 # E : first aligned src word complete
183 mskqh t1, a0, t1 # U : mask leading garbage in src
184 or t0, t1, t0 # E : first output word complete
185 or t0, t6, t6 # E : mask original data for zero test
186
187 cmpbge zero, t6, t8 # E :
188 beq a2, $u_eocfin # U :
189 bne t8, $u_final # U : bad news - 2nd branch in a quad
190 lda t6, -1 # E : mask out the bits we have
191
192 mskql t6, a1, t6 # U : already seen
193 stq_u t0, 0(a0) # L : store first output word
194 or t6, t2, t2 # E :
195 cmpbge zero, t2, t8 # E : find nulls in second partial
196
197 addq a0, 8, a0 # E :
198 subq a2, 1, a2 # E :
199 bne t8, $u_late_head_exit # U :
200 nop
201
202 /* Finally, we've got all the stupid leading edge cases taken care
203 of and we can set up to enter the main loop. */
204
205 extql t2, a1, t1 # U : position hi-bits of lo word
206 EX( ldq_u t2, 8(a1) ) # L : read next high-order source word
207 addq a1, 8, a1 # E :
208 cmpbge zero, t2, t8 # E :
209
210 beq a2, $u_eoc # U :
211 bne t8, $u_eos # U :
212 nop
213 nop
214
215 /* Unaligned copy main loop. In order to avoid reading too much,
216 the loop is structured to detect zeros in aligned source words.
217 This has, unfortunately, effectively pulled half of a loop
218 iteration out into the head and half into the tail, but it does
219 prevent nastiness from accumulating in the very thing we want
220 to run as fast as possible.
221
222 On entry to this basic block:
223 t1 == the shifted high-order bits from the previous source word
224 t2 == the unshifted current source word
225
226 We further know that t2 does not contain a null terminator. */
227
228 /*
229 * Extra nops here:
230 * separate load quads from store quads
231 * only one branch/quad to permit predictor training
232 */
233
234 .align 4
235$u_loop:
236 extqh t2, a1, t0 # U : extract high bits for current word
237 addq a1, 8, a1 # E :
238 extql t2, a1, t3 # U : extract low bits for next time
239 addq a0, 8, a0 # E :
240
241 or t0, t1, t0 # E : current dst word now complete
242 EX( ldq_u t2, 0(a1) ) # L : load high word for next time
243 subq a2, 1, a2 # E :
244 nop
245
246 stq_u t0, -8(a0) # L : save the current word
247 mov t3, t1 # E :
248 cmpbge zero, t2, t8 # E : test new word for eos
249 beq a2, $u_eoc # U :
250
251 beq t8, $u_loop # U :
252 nop
253 nop
254 nop
255
256 /* We've found a zero somewhere in the source word we just read.
257 If it resides in the lower half, we have one (probably partial)
258 word to write out, and if it resides in the upper half, we
259 have one full and one partial word left to write out.
260
261 On entry to this basic block:
262 t1 == the shifted high-order bits from the previous source word
263 t2 == the unshifted current source word. */
264 .align 4
265$u_eos:
266 extqh t2, a1, t0 # U :
267 or t0, t1, t0 # E : first (partial) source word complete
268 cmpbge zero, t0, t8 # E : is the null in this first bit?
269 nop
270
271 bne t8, $u_final # U :
272 stq_u t0, 0(a0) # L : the null was in the high-order bits
273 addq a0, 8, a0 # E :
274 subq a2, 1, a2 # E :
275
276 .align 4
277$u_late_head_exit:
278 extql t2, a1, t0 # U :
279 cmpbge zero, t0, t8 # E :
280 or t8, t10, t6 # E :
281 cmoveq a2, t6, t8 # E :
282
283 /* Take care of a final (probably partial) result word.
284 On entry to this basic block:
285 t0 == assembled source word
286 t8 == cmpbge mask that found the null. */
287 .align 4
288$u_final:
289 negq t8, t6 # E : isolate low bit set
290 and t6, t8, t12 # E :
291 ldq_u t1, 0(a0) # L :
292 subq t12, 1, t6 # E :
293
294 or t6, t12, t8 # E :
295 zapnot t0, t8, t0 # U : kill source bytes > null
296 zap t1, t8, t1 # U : kill dest bytes <= null
297 or t0, t1, t0 # E :
298
299 stq_u t0, 0(a0) # E :
300 br $finish_up # U :
301 nop
302 nop
303
304 .align 4
305$u_eoc: # end-of-count
306 extqh t2, a1, t0 # U :
307 or t0, t1, t0 # E :
308 cmpbge zero, t0, t8 # E :
309 nop
310
311 .align 4
312$u_eocfin: # end-of-count, final word
313 or t10, t8, t8 # E :
314 br $u_final # U :
315 nop
316 nop
317
318 /* Unaligned copy entry point. */
319 .align 4
320$unaligned:
321
322 srl a3, 3, a2 # U : a2 = loop counter = (count - 1)/8
323 and a0, 7, t4 # E : find dest misalignment
324 and a1, 7, t5 # E : find src misalignment
325 mov zero, t0 # E :
326
327 /* Conditionally load the first destination word and a bytemask
328 with 0xff indicating that the destination byte is sacrosanct. */
329
330 mov zero, t6 # E :
331 beq t4, 1f # U :
332 ldq_u t0, 0(a0) # L :
333 lda t6, -1 # E :
334
335 mskql t6, a0, t6 # E :
336 nop
337 nop
338 nop
339
340 .align 4
3411:
342 subq a1, t4, a1 # E : sub dest misalignment from src addr
343 /* If source misalignment is larger than dest misalignment, we need
344 extra startup checks to avoid SEGV. */
345 cmplt t4, t5, t12 # E :
346 extql t1, a1, t1 # U : shift src into place
347 lda t2, -1 # E : for creating masks later
348
349 beq t12, $u_head # U :
350 mskqh t2, t5, t2 # U : begin src byte validity mask
351 cmpbge zero, t1, t8 # E : is there a zero?
352 nop
353
354 extql t2, a1, t2 # U :
355 or t8, t10, t5 # E : test for end-of-count too
356 cmpbge zero, t2, t3 # E :
357 cmoveq a2, t5, t8 # E : Latency=2, extra map slot
358
359 nop # E : goes with cmov
360 andnot t8, t3, t8 # E :
361 beq t8, $u_head # U :
362 nop
363
364 /* At this point we've found a zero in the first partial word of
365 the source. We need to isolate the valid source data and mask
366 it into the original destination data. (Incidentally, we know
367 that we'll need at least one byte of that original dest word.) */
368
369 ldq_u t0, 0(a0) # L :
370 negq t8, t6 # E : build bitmask of bytes <= zero
371 mskqh t1, t4, t1 # U :
372 and t6, t8, t12 # E :
373
374 subq t12, 1, t6 # E :
375 or t6, t12, t8 # E :
376 zapnot t2, t8, t2 # U : prepare source word; mirror changes
377 zapnot t1, t8, t1 # U : to source validity mask
378
379 andnot t0, t2, t0 # E : zero place for source to reside
380 or t0, t1, t0 # E : and put it there
381 stq_u t0, 0(a0) # L :
382 nop
383
384 .align 4
385$finish_up:
386 zapnot t0, t12, t4 # U : was last byte written null?
387 and t12, 0xf0, t3 # E : binary search for the address of the
388 cmovne t4, 1, t4 # E : Latency=2, extra map slot
389 nop # E : with cmovne
390
391 and t12, 0xcc, t2 # E : last byte written
392 and t12, 0xaa, t1 # E :
393 cmovne t3, 4, t3 # E : Latency=2, extra map slot
394 nop # E : with cmovne
395
396 bic a0, 7, t0
397 cmovne t2, 2, t2 # E : Latency=2, extra map slot
398 nop # E : with cmovne
399 nop
400
401 cmovne t1, 1, t1 # E : Latency=2, extra map slot
402 nop # E : with cmovne
403 addq t0, t3, t0 # E :
404 addq t1, t2, t1 # E :
405
406 addq t0, t1, t0 # E :
407 addq t0, t4, t0 # add one if we filled the buffer
408 subq t0, v0, v0 # find string length
409 ret # L0 :
410
411 .align 4
412$zerolength:
413 nop
414 nop
415 nop
416 clr v0
417
418$exception:
419 nop
420 nop
421 nop
422 ret
423
424 .end __strncpy_from_user
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