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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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 | /* * arch/alpha/lib/ev6-strncpy_from_user.S * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com> * * Just like strncpy except in the return value: * * -EFAULT if an exception occurs before the terminator is copied. * N if the buffer filled. * * Otherwise the length of the string is returned. * * Much of the information about 21264 scheduling/coding comes from: * Compiler Writer's Guide for the Alpha 21264 * abbreviated as 'CWG' in other comments here * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html * Scheduling notation: * E - either cluster * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1 * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1 * A bunch of instructions got moved and temp registers were changed * to aid in scheduling. Control flow was also re-arranged to eliminate * branches, and to provide longer code sequences to enable better scheduling. * A total rewrite (using byte load/stores for start & tail sequences) * is desirable, but very difficult to do without a from-scratch rewrite. * Save that for the future. */ #include <asm/errno.h> #include <alpha/regdef.h> /* Allow an exception for an insn; exit if we get one. */ #define EX(x,y...) \ 99: x,##y; \ .section __ex_table,"a"; \ .gprel32 99b; \ lda $31, $exception-99b($0); \ .previous .set noat .set noreorder .text .globl __strncpy_from_user .ent __strncpy_from_user .frame $30, 0, $26 .prologue 1 .align 4 __strncpy_from_user: ldgp $29, 0($27) # E E : becomes 2 instructions (for exceptions) and a0, 7, t3 # E : find dest misalignment beq a2, $zerolength # U : /* Are source and destination co-aligned? */ mov a0, v0 # E : save the string start xor a0, a1, t4 # E : EX( ldq_u t1, 0(a1) ) # L : Latency=3 load first quadword ldq_u t0, 0(a0) # L : load first (partial) aligned dest quadword addq a2, t3, a2 # E : bias count by dest misalignment subq a2, 1, a3 # E : addq zero, 1, t10 # E : and t4, 7, t4 # E : misalignment between the two and a3, 7, t6 # E : number of tail bytes sll t10, t6, t10 # E : t10 = bitmask of last count byte bne t4, $unaligned # U : lda t2, -1 # E : build a mask against false zero /* * We are co-aligned; take care of a partial first word. * On entry to this basic block: * t0 == the first destination word for masking back in * t1 == the first source word. */ srl a3, 3, a2 # E : a2 = loop counter = (count - 1)/8 addq a1, 8, a1 # E : mskqh t2, a1, t2 # U : detection in the src word nop /* Create the 1st output word and detect 0's in the 1st input word. */ mskqh t1, a1, t3 # U : mskql t0, a1, t0 # U : assemble the first output word ornot t1, t2, t2 # E : nop cmpbge zero, t2, t8 # E : bits set iff null found or t0, t3, t0 # E : beq a2, $a_eoc # U : bne t8, $a_eos # U : 2nd branch in a quad. Bad. /* On entry to this basic block: * t0 == a source quad not containing a null. * a0 - current aligned destination address * a1 - current aligned source address * a2 - count of quadwords to move. * NOTE: Loop improvement - unrolling this is going to be * a huge win, since we're going to stall otherwise. * Fix this later. For _really_ large copies, look * at using wh64 on a look-ahead basis. See the code * in clear_user.S and copy_user.S. * Presumably, since (a0) and (a1) do not overlap (by C definition) * Lots of nops here: * - Separate loads from stores * - Keep it to 1 branch/quadpack so the branch predictor * can train. */ $a_loop: stq_u t0, 0(a0) # L : addq a0, 8, a0 # E : nop subq a2, 1, a2 # E : EX( ldq_u t0, 0(a1) ) # L : addq a1, 8, a1 # E : cmpbge zero, t0, t8 # E : Stall 2 cycles on t0 beq a2, $a_eoc # U : beq t8, $a_loop # U : nop nop nop /* Take care of the final (partial) word store. At this point * the end-of-count bit is set in t8 iff it applies. * * On entry to this basic block we have: * t0 == the source word containing the null * t8 == the cmpbge mask that found it. */ $a_eos: negq t8, t12 # E : find low bit set and t8, t12, t12 # E : /* We're doing a partial word store and so need to combine our source and original destination words. */ ldq_u t1, 0(a0) # L : subq t12, 1, t6 # E : or t12, t6, t8 # E : zapnot t0, t8, t0 # U : clear src bytes > null zap t1, t8, t1 # U : clear dst bytes <= null or t0, t1, t0 # E : stq_u t0, 0(a0) # L : br $finish_up # L0 : nop nop /* Add the end-of-count bit to the eos detection bitmask. */ .align 4 $a_eoc: or t10, t8, t8 br $a_eos nop nop /* The source and destination are not co-aligned. Align the destination and cope. We have to be very careful about not reading too much and causing a SEGV. */ .align 4 $u_head: /* We know just enough now to be able to assemble the first full source word. We can still find a zero at the end of it that prevents us from outputting the whole thing. On entry to this basic block: t0 == the first dest word, unmasked t1 == the shifted low bits of the first source word t6 == bytemask that is -1 in dest word bytes */ EX( ldq_u t2, 8(a1) ) # L : load second src word addq a1, 8, a1 # E : mskql t0, a0, t0 # U : mask trailing garbage in dst extqh t2, a1, t4 # U : or t1, t4, t1 # E : first aligned src word complete mskqh t1, a0, t1 # U : mask leading garbage in src or t0, t1, t0 # E : first output word complete or t0, t6, t6 # E : mask original data for zero test cmpbge zero, t6, t8 # E : beq a2, $u_eocfin # U : bne t8, $u_final # U : bad news - 2nd branch in a quad lda t6, -1 # E : mask out the bits we have mskql t6, a1, t6 # U : already seen stq_u t0, 0(a0) # L : store first output word or t6, t2, t2 # E : cmpbge zero, t2, t8 # E : find nulls in second partial addq a0, 8, a0 # E : subq a2, 1, a2 # E : bne t8, $u_late_head_exit # U : nop /* Finally, we've got all the stupid leading edge cases taken care of and we can set up to enter the main loop. */ extql t2, a1, t1 # U : position hi-bits of lo word EX( ldq_u t2, 8(a1) ) # L : read next high-order source word addq a1, 8, a1 # E : cmpbge zero, t2, t8 # E : beq a2, $u_eoc # U : bne t8, $u_eos # U : nop nop /* Unaligned copy main loop. In order to avoid reading too much, the loop is structured to detect zeros in aligned source words. This has, unfortunately, effectively pulled half of a loop iteration out into the head and half into the tail, but it does prevent nastiness from accumulating in the very thing we want to run as fast as possible. On entry to this basic block: t1 == the shifted high-order bits from the previous source word t2 == the unshifted current source word We further know that t2 does not contain a null terminator. */ /* * Extra nops here: * separate load quads from store quads * only one branch/quad to permit predictor training */ .align 4 $u_loop: extqh t2, a1, t0 # U : extract high bits for current word addq a1, 8, a1 # E : extql t2, a1, t3 # U : extract low bits for next time addq a0, 8, a0 # E : or t0, t1, t0 # E : current dst word now complete EX( ldq_u t2, 0(a1) ) # L : load high word for next time subq a2, 1, a2 # E : nop stq_u t0, -8(a0) # L : save the current word mov t3, t1 # E : cmpbge zero, t2, t8 # E : test new word for eos beq a2, $u_eoc # U : beq t8, $u_loop # U : nop nop nop /* We've found a zero somewhere in the source word we just read. If it resides in the lower half, we have one (probably partial) word to write out, and if it resides in the upper half, we have one full and one partial word left to write out. On entry to this basic block: t1 == the shifted high-order bits from the previous source word t2 == the unshifted current source word. */ .align 4 $u_eos: extqh t2, a1, t0 # U : or t0, t1, t0 # E : first (partial) source word complete cmpbge zero, t0, t8 # E : is the null in this first bit? nop bne t8, $u_final # U : stq_u t0, 0(a0) # L : the null was in the high-order bits addq a0, 8, a0 # E : subq a2, 1, a2 # E : .align 4 $u_late_head_exit: extql t2, a1, t0 # U : cmpbge zero, t0, t8 # E : or t8, t10, t6 # E : cmoveq a2, t6, t8 # E : /* Take care of a final (probably partial) result word. On entry to this basic block: t0 == assembled source word t8 == cmpbge mask that found the null. */ .align 4 $u_final: negq t8, t6 # E : isolate low bit set and t6, t8, t12 # E : ldq_u t1, 0(a0) # L : subq t12, 1, t6 # E : or t6, t12, t8 # E : zapnot t0, t8, t0 # U : kill source bytes > null zap t1, t8, t1 # U : kill dest bytes <= null or t0, t1, t0 # E : stq_u t0, 0(a0) # E : br $finish_up # U : nop nop .align 4 $u_eoc: # end-of-count extqh t2, a1, t0 # U : or t0, t1, t0 # E : cmpbge zero, t0, t8 # E : nop .align 4 $u_eocfin: # end-of-count, final word or t10, t8, t8 # E : br $u_final # U : nop nop /* Unaligned copy entry point. */ .align 4 $unaligned: srl a3, 3, a2 # U : a2 = loop counter = (count - 1)/8 and a0, 7, t4 # E : find dest misalignment and a1, 7, t5 # E : find src misalignment mov zero, t0 # E : /* Conditionally load the first destination word and a bytemask with 0xff indicating that the destination byte is sacrosanct. */ mov zero, t6 # E : beq t4, 1f # U : ldq_u t0, 0(a0) # L : lda t6, -1 # E : mskql t6, a0, t6 # E : nop nop nop .align 4 1: subq a1, t4, a1 # E : sub dest misalignment from src addr /* If source misalignment is larger than dest misalignment, we need extra startup checks to avoid SEGV. */ cmplt t4, t5, t12 # E : extql t1, a1, t1 # U : shift src into place lda t2, -1 # E : for creating masks later beq t12, $u_head # U : mskqh t2, t5, t2 # U : begin src byte validity mask cmpbge zero, t1, t8 # E : is there a zero? nop extql t2, a1, t2 # U : or t8, t10, t5 # E : test for end-of-count too cmpbge zero, t2, t3 # E : cmoveq a2, t5, t8 # E : Latency=2, extra map slot nop # E : goes with cmov andnot t8, t3, t8 # E : beq t8, $u_head # U : nop /* At this point we've found a zero in the first partial word of the source. We need to isolate the valid source data and mask it into the original destination data. (Incidentally, we know that we'll need at least one byte of that original dest word.) */ ldq_u t0, 0(a0) # L : negq t8, t6 # E : build bitmask of bytes <= zero mskqh t1, t4, t1 # U : and t6, t8, t12 # E : subq t12, 1, t6 # E : or t6, t12, t8 # E : zapnot t2, t8, t2 # U : prepare source word; mirror changes zapnot t1, t8, t1 # U : to source validity mask andnot t0, t2, t0 # E : zero place for source to reside or t0, t1, t0 # E : and put it there stq_u t0, 0(a0) # L : nop .align 4 $finish_up: zapnot t0, t12, t4 # U : was last byte written null? and t12, 0xf0, t3 # E : binary search for the address of the cmovne t4, 1, t4 # E : Latency=2, extra map slot nop # E : with cmovne and t12, 0xcc, t2 # E : last byte written and t12, 0xaa, t1 # E : cmovne t3, 4, t3 # E : Latency=2, extra map slot nop # E : with cmovne bic a0, 7, t0 cmovne t2, 2, t2 # E : Latency=2, extra map slot nop # E : with cmovne nop cmovne t1, 1, t1 # E : Latency=2, extra map slot nop # E : with cmovne addq t0, t3, t0 # E : addq t1, t2, t1 # E : addq t0, t1, t0 # E : addq t0, t4, t0 # add one if we filled the buffer subq t0, v0, v0 # find string length ret # L0 : .align 4 $zerolength: nop nop nop clr v0 $exception: nop nop nop ret .end __strncpy_from_user |