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1 | /* | ||
2 | * arch/alpha/lib/ev6-stxncpy.S | ||
3 | * 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com> | ||
4 | * | ||
5 | * Copy no more than COUNT bytes of the null-terminated string from | ||
6 | * SRC to DST. | ||
7 | * | ||
8 | * This is an internal routine used by strncpy, stpncpy, and strncat. | ||
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 | * a2 = COUNT | ||
17 | * | ||
18 | * Furthermore, COUNT may not be zero. | ||
19 | * | ||
20 | * On output: | ||
21 | * t0 = last word written | ||
22 | * t10 = bitmask (with one bit set) indicating the byte position of | ||
23 | * the end of the range specified by COUNT | ||
24 | * t12 = bitmask (with one bit set) indicating the last byte written | ||
25 | * a0 = unaligned address of the last *word* written | ||
26 | * a2 = the number of full words left in COUNT | ||
27 | * | ||
28 | * Furthermore, v0, a3-a5, t11, and $at are untouched. | ||
29 | * | ||
30 | * Much of the information about 21264 scheduling/coding comes from: | ||
31 | * Compiler Writer's Guide for the Alpha 21264 | ||
32 | * abbreviated as 'CWG' in other comments here | ||
33 | * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html | ||
34 | * Scheduling notation: | ||
35 | * E - either cluster | ||
36 | * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1 | ||
37 | * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1 | ||
38 | * Try not to change the actual algorithm if possible for consistency. | ||
39 | */ | ||
40 | |||
41 | #include <asm/regdef.h> | ||
42 | |||
43 | .set noat | ||
44 | .set noreorder | ||
45 | |||
46 | .text | ||
47 | |||
48 | /* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that | ||
49 | doesn't like putting the entry point for a procedure somewhere in the | ||
50 | middle of the procedure descriptor. Work around this by putting the | ||
51 | aligned copy in its own procedure descriptor */ | ||
52 | |||
53 | |||
54 | .ent stxncpy_aligned | ||
55 | .align 4 | ||
56 | stxncpy_aligned: | ||
57 | .frame sp, 0, t9, 0 | ||
58 | .prologue 0 | ||
59 | |||
60 | /* On entry to this basic block: | ||
61 | t0 == the first destination word for masking back in | ||
62 | t1 == the first source word. */ | ||
63 | |||
64 | /* Create the 1st output word and detect 0's in the 1st input word. */ | ||
65 | lda t2, -1 # E : build a mask against false zero | ||
66 | mskqh t2, a1, t2 # U : detection in the src word (stall) | ||
67 | mskqh t1, a1, t3 # U : | ||
68 | ornot t1, t2, t2 # E : (stall) | ||
69 | |||
70 | mskql t0, a1, t0 # U : assemble the first output word | ||
71 | cmpbge zero, t2, t8 # E : bits set iff null found | ||
72 | or t0, t3, t0 # E : (stall) | ||
73 | beq a2, $a_eoc # U : | ||
74 | |||
75 | bne t8, $a_eos # U : | ||
76 | nop | ||
77 | nop | ||
78 | nop | ||
79 | |||
80 | /* On entry to this basic block: | ||
81 | t0 == a source word not containing a null. */ | ||
82 | |||
83 | /* | ||
84 | * nops here to: | ||
85 | * separate store quads from load quads | ||
86 | * limit of 1 bcond/quad to permit training | ||
87 | */ | ||
88 | $a_loop: | ||
89 | stq_u t0, 0(a0) # L : | ||
90 | addq a0, 8, a0 # E : | ||
91 | subq a2, 1, a2 # E : | ||
92 | nop | ||
93 | |||
94 | ldq_u t0, 0(a1) # L : | ||
95 | addq a1, 8, a1 # E : | ||
96 | cmpbge zero, t0, t8 # E : | ||
97 | beq a2, $a_eoc # U : | ||
98 | |||
99 | beq t8, $a_loop # U : | ||
100 | nop | ||
101 | nop | ||
102 | nop | ||
103 | |||
104 | /* Take care of the final (partial) word store. At this point | ||
105 | the end-of-count bit is set in t8 iff it applies. | ||
106 | |||
107 | On entry to this basic block we have: | ||
108 | t0 == the source word containing the null | ||
109 | t8 == the cmpbge mask that found it. */ | ||
110 | |||
111 | $a_eos: | ||
112 | negq t8, t12 # E : find low bit set | ||
113 | and t8, t12, t12 # E : (stall) | ||
114 | /* For the sake of the cache, don't read a destination word | ||
115 | if we're not going to need it. */ | ||
116 | and t12, 0x80, t6 # E : (stall) | ||
117 | bne t6, 1f # U : (stall) | ||
118 | |||
119 | /* We're doing a partial word store and so need to combine | ||
120 | our source and original destination words. */ | ||
121 | ldq_u t1, 0(a0) # L : | ||
122 | subq t12, 1, t6 # E : | ||
123 | or t12, t6, t8 # E : (stall) | ||
124 | zapnot t0, t8, t0 # U : clear src bytes > null (stall) | ||
125 | |||
126 | zap t1, t8, t1 # .. e1 : clear dst bytes <= null | ||
127 | or t0, t1, t0 # e1 : (stall) | ||
128 | nop | ||
129 | nop | ||
130 | |||
131 | 1: stq_u t0, 0(a0) # L : | ||
132 | ret (t9) # L0 : Latency=3 | ||
133 | nop | ||
134 | nop | ||
135 | |||
136 | /* Add the end-of-count bit to the eos detection bitmask. */ | ||
137 | $a_eoc: | ||
138 | or t10, t8, t8 # E : | ||
139 | br $a_eos # L0 : Latency=3 | ||
140 | nop | ||
141 | nop | ||
142 | |||
143 | .end stxncpy_aligned | ||
144 | |||
145 | .align 4 | ||
146 | .ent __stxncpy | ||
147 | .globl __stxncpy | ||
148 | __stxncpy: | ||
149 | .frame sp, 0, t9, 0 | ||
150 | .prologue 0 | ||
151 | |||
152 | /* Are source and destination co-aligned? */ | ||
153 | xor a0, a1, t1 # E : | ||
154 | and a0, 7, t0 # E : find dest misalignment | ||
155 | and t1, 7, t1 # E : (stall) | ||
156 | addq a2, t0, a2 # E : bias count by dest misalignment (stall) | ||
157 | |||
158 | subq a2, 1, a2 # E : | ||
159 | and a2, 7, t2 # E : (stall) | ||
160 | srl a2, 3, a2 # U : a2 = loop counter = (count - 1)/8 (stall) | ||
161 | addq zero, 1, t10 # E : | ||
162 | |||
163 | sll t10, t2, t10 # U : t10 = bitmask of last count byte | ||
164 | bne t1, $unaligned # U : | ||
165 | /* We are co-aligned; take care of a partial first word. */ | ||
166 | ldq_u t1, 0(a1) # L : load first src word | ||
167 | addq a1, 8, a1 # E : | ||
168 | |||
169 | beq t0, stxncpy_aligned # U : avoid loading dest word if not needed | ||
170 | ldq_u t0, 0(a0) # L : | ||
171 | nop | ||
172 | nop | ||
173 | |||
174 | br stxncpy_aligned # .. e1 : | ||
175 | nop | ||
176 | nop | ||
177 | nop | ||
178 | |||
179 | |||
180 | |||
181 | /* The source and destination are not co-aligned. Align the destination | ||
182 | and cope. We have to be very careful about not reading too much and | ||
183 | causing a SEGV. */ | ||
184 | |||
185 | .align 4 | ||
186 | $u_head: | ||
187 | /* We know just enough now to be able to assemble the first | ||
188 | full source word. We can still find a zero at the end of it | ||
189 | that prevents us from outputting the whole thing. | ||
190 | |||
191 | On entry to this basic block: | ||
192 | t0 == the first dest word, unmasked | ||
193 | t1 == the shifted low bits of the first source word | ||
194 | t6 == bytemask that is -1 in dest word bytes */ | ||
195 | |||
196 | ldq_u t2, 8(a1) # L : Latency=3 load second src word | ||
197 | addq a1, 8, a1 # E : | ||
198 | mskql t0, a0, t0 # U : mask trailing garbage in dst | ||
199 | extqh t2, a1, t4 # U : (3 cycle stall on t2) | ||
200 | |||
201 | or t1, t4, t1 # E : first aligned src word complete (stall) | ||
202 | mskqh t1, a0, t1 # U : mask leading garbage in src (stall) | ||
203 | or t0, t1, t0 # E : first output word complete (stall) | ||
204 | or t0, t6, t6 # E : mask original data for zero test (stall) | ||
205 | |||
206 | cmpbge zero, t6, t8 # E : | ||
207 | beq a2, $u_eocfin # U : | ||
208 | lda t6, -1 # E : | ||
209 | nop | ||
210 | |||
211 | bne t8, $u_final # U : | ||
212 | mskql t6, a1, t6 # U : mask out bits already seen | ||
213 | stq_u t0, 0(a0) # L : store first output word | ||
214 | or t6, t2, t2 # E : (stall) | ||
215 | |||
216 | cmpbge zero, t2, t8 # E : find nulls in second partial | ||
217 | addq a0, 8, a0 # E : | ||
218 | subq a2, 1, a2 # E : | ||
219 | bne t8, $u_late_head_exit # U : | ||
220 | |||
221 | /* Finally, we've got all the stupid leading edge cases taken care | ||
222 | of and we can set up to enter the main loop. */ | ||
223 | extql t2, a1, t1 # U : position hi-bits of lo word | ||
224 | beq a2, $u_eoc # U : | ||
225 | ldq_u t2, 8(a1) # L : read next high-order source word | ||
226 | addq a1, 8, a1 # E : | ||
227 | |||
228 | extqh t2, a1, t0 # U : position lo-bits of hi word (stall) | ||
229 | cmpbge zero, t2, t8 # E : | ||
230 | nop | ||
231 | bne t8, $u_eos # U : | ||
232 | |||
233 | /* Unaligned copy main loop. In order to avoid reading too much, | ||
234 | the loop is structured to detect zeros in aligned source words. | ||
235 | This has, unfortunately, effectively pulled half of a loop | ||
236 | iteration out into the head and half into the tail, but it does | ||
237 | prevent nastiness from accumulating in the very thing we want | ||
238 | to run as fast as possible. | ||
239 | |||
240 | On entry to this basic block: | ||
241 | t0 == the shifted low-order bits from the current source word | ||
242 | t1 == the shifted high-order bits from the previous source word | ||
243 | t2 == the unshifted current source word | ||
244 | |||
245 | We further know that t2 does not contain a null terminator. */ | ||
246 | |||
247 | .align 4 | ||
248 | $u_loop: | ||
249 | or t0, t1, t0 # E : current dst word now complete | ||
250 | subq a2, 1, a2 # E : decrement word count | ||
251 | extql t2, a1, t1 # U : extract low bits for next time | ||
252 | addq a0, 8, a0 # E : | ||
253 | |||
254 | stq_u t0, -8(a0) # U : save the current word | ||
255 | beq a2, $u_eoc # U : | ||
256 | ldq_u t2, 8(a1) # U : Latency=3 load high word for next time | ||
257 | addq a1, 8, a1 # E : | ||
258 | |||
259 | extqh t2, a1, t0 # U : extract low bits (2 cycle stall) | ||
260 | cmpbge zero, t2, t8 # E : test new word for eos | ||
261 | nop | ||
262 | beq t8, $u_loop # U : | ||
263 | |||
264 | /* We've found a zero somewhere in the source word we just read. | ||
265 | If it resides in the lower half, we have one (probably partial) | ||
266 | word to write out, and if it resides in the upper half, we | ||
267 | have one full and one partial word left to write out. | ||
268 | |||
269 | On entry to this basic block: | ||
270 | t0 == the shifted low-order bits from the current source word | ||
271 | t1 == the shifted high-order bits from the previous source word | ||
272 | t2 == the unshifted current source word. */ | ||
273 | $u_eos: | ||
274 | or t0, t1, t0 # E : first (partial) source word complete | ||
275 | nop | ||
276 | cmpbge zero, t0, t8 # E : is the null in this first bit? (stall) | ||
277 | bne t8, $u_final # U : (stall) | ||
278 | |||
279 | stq_u t0, 0(a0) # L : the null was in the high-order bits | ||
280 | addq a0, 8, a0 # E : | ||
281 | subq a2, 1, a2 # E : | ||
282 | nop | ||
283 | |||
284 | $u_late_head_exit: | ||
285 | extql t2, a1, t0 # U : | ||
286 | cmpbge zero, t0, t8 # E : | ||
287 | or t8, t10, t6 # E : (stall) | ||
288 | cmoveq a2, t6, t8 # E : Latency=2, extra map slot (stall) | ||
289 | |||
290 | /* Take care of a final (probably partial) result word. | ||
291 | On entry to this basic block: | ||
292 | t0 == assembled source word | ||
293 | t8 == cmpbge mask that found the null. */ | ||
294 | $u_final: | ||
295 | negq t8, t6 # E : isolate low bit set | ||
296 | and t6, t8, t12 # E : (stall) | ||
297 | and t12, 0x80, t6 # E : avoid dest word load if we can (stall) | ||
298 | bne t6, 1f # U : (stall) | ||
299 | |||
300 | ldq_u t1, 0(a0) # L : | ||
301 | subq t12, 1, t6 # E : | ||
302 | or t6, t12, t8 # E : (stall) | ||
303 | zapnot t0, t8, t0 # U : kill source bytes > null | ||
304 | |||
305 | zap t1, t8, t1 # U : kill dest bytes <= null | ||
306 | or t0, t1, t0 # E : (stall) | ||
307 | nop | ||
308 | nop | ||
309 | |||
310 | 1: stq_u t0, 0(a0) # L : | ||
311 | ret (t9) # L0 : Latency=3 | ||
312 | |||
313 | /* Got to end-of-count before end of string. | ||
314 | On entry to this basic block: | ||
315 | t1 == the shifted high-order bits from the previous source word */ | ||
316 | $u_eoc: | ||
317 | and a1, 7, t6 # E : avoid final load if possible | ||
318 | sll t10, t6, t6 # U : (stall) | ||
319 | and t6, 0xff, t6 # E : (stall) | ||
320 | bne t6, 1f # U : (stall) | ||
321 | |||
322 | ldq_u t2, 8(a1) # L : load final src word | ||
323 | nop | ||
324 | extqh t2, a1, t0 # U : extract low bits for last word (stall) | ||
325 | or t1, t0, t1 # E : (stall) | ||
326 | |||
327 | 1: cmpbge zero, t1, t8 # E : | ||
328 | mov t1, t0 # E : | ||
329 | |||
330 | $u_eocfin: # end-of-count, final word | ||
331 | or t10, t8, t8 # E : | ||
332 | br $u_final # L0 : Latency=3 | ||
333 | |||
334 | /* Unaligned copy entry point. */ | ||
335 | .align 4 | ||
336 | $unaligned: | ||
337 | |||
338 | ldq_u t1, 0(a1) # L : load first source word | ||
339 | and a0, 7, t4 # E : find dest misalignment | ||
340 | and a1, 7, t5 # E : find src misalignment | ||
341 | /* Conditionally load the first destination word and a bytemask | ||
342 | with 0xff indicating that the destination byte is sacrosanct. */ | ||
343 | mov zero, t0 # E : | ||
344 | |||
345 | mov zero, t6 # E : | ||
346 | beq t4, 1f # U : | ||
347 | ldq_u t0, 0(a0) # L : | ||
348 | lda t6, -1 # E : | ||
349 | |||
350 | mskql t6, a0, t6 # U : | ||
351 | nop | ||
352 | nop | ||
353 | subq a1, t4, a1 # E : sub dest misalignment from src addr | ||
354 | |||
355 | /* If source misalignment is larger than dest misalignment, we need | ||
356 | extra startup checks to avoid SEGV. */ | ||
357 | |||
358 | 1: cmplt t4, t5, t12 # E : | ||
359 | extql t1, a1, t1 # U : shift src into place | ||
360 | lda t2, -1 # E : for creating masks later | ||
361 | beq t12, $u_head # U : (stall) | ||
362 | |||
363 | extql t2, a1, t2 # U : | ||
364 | cmpbge zero, t1, t8 # E : is there a zero? | ||
365 | andnot t2, t6, t12 # E : dest mask for a single word copy | ||
366 | or t8, t10, t5 # E : test for end-of-count too | ||
367 | |||
368 | cmpbge zero, t12, t3 # E : | ||
369 | cmoveq a2, t5, t8 # E : Latency=2, extra map slot | ||
370 | nop # E : keep with cmoveq | ||
371 | andnot t8, t3, t8 # E : (stall) | ||
372 | |||
373 | beq t8, $u_head # U : | ||
374 | /* At this point we've found a zero in the first partial word of | ||
375 | the source. We need to isolate the valid source data and mask | ||
376 | it into the original destination data. (Incidentally, we know | ||
377 | that we'll need at least one byte of that original dest word.) */ | ||
378 | ldq_u t0, 0(a0) # L : | ||
379 | negq t8, t6 # E : build bitmask of bytes <= zero | ||
380 | mskqh t1, t4, t1 # U : | ||
381 | |||
382 | and t6, t8, t2 # E : | ||
383 | subq t2, 1, t6 # E : (stall) | ||
384 | or t6, t2, t8 # E : (stall) | ||
385 | zapnot t12, t8, t12 # U : prepare source word; mirror changes (stall) | ||
386 | |||
387 | zapnot t1, t8, t1 # U : to source validity mask | ||
388 | andnot t0, t12, t0 # E : zero place for source to reside | ||
389 | or t0, t1, t0 # E : and put it there (stall both t0, t1) | ||
390 | stq_u t0, 0(a0) # L : (stall) | ||
391 | |||
392 | ret (t9) # L0 : Latency=3 | ||
393 | nop | ||
394 | nop | ||
395 | nop | ||
396 | |||
397 | .end __stxncpy | ||