1 /* Prologue value handling for GDB. 2 Copyright (C) 2003-2013 Free Software Foundation, Inc. 3 4 This file is part of GDB. 5 6 This program is free software; you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 3 of the License, or 9 (at your option) any later version. 10 11 This program is distributed in the hope that it will be useful, 12 but WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 GNU General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with this program. If not, see <http://www.gnu.org/licenses/>. */ 18 19 #include "defs.h" 20 #include "gdb_string.h" 21 #include "gdb_assert.h" 22 #include "prologue-value.h" 23 #include "regcache.h" 24 25 26 /* Constructors. */ 27 28 pv_t 29 pv_unknown (void) 30 { 31 pv_t v = { pvk_unknown, 0, 0 }; 32 33 return v; 34 } 35 36 37 pv_t 38 pv_constant (CORE_ADDR k) 39 { 40 pv_t v; 41 42 v.kind = pvk_constant; 43 v.reg = -1; /* for debugging */ 44 v.k = k; 45 46 return v; 47 } 48 49 50 pv_t 51 pv_register (int reg, CORE_ADDR k) 52 { 53 pv_t v; 54 55 v.kind = pvk_register; 56 v.reg = reg; 57 v.k = k; 58 59 return v; 60 } 61 62 63 64 /* Arithmetic operations. */ 65 66 /* If one of *A and *B is a constant, and the other isn't, swap the 67 values as necessary to ensure that *B is the constant. This can 68 reduce the number of cases we need to analyze in the functions 69 below. */ 70 static void 71 constant_last (pv_t *a, pv_t *b) 72 { 73 if (a->kind == pvk_constant 74 && b->kind != pvk_constant) 75 { 76 pv_t temp = *a; 77 *a = *b; 78 *b = temp; 79 } 80 } 81 82 83 pv_t 84 pv_add (pv_t a, pv_t b) 85 { 86 constant_last (&a, &b); 87 88 /* We can add a constant to a register. */ 89 if (a.kind == pvk_register 90 && b.kind == pvk_constant) 91 return pv_register (a.reg, a.k + b.k); 92 93 /* We can add a constant to another constant. */ 94 else if (a.kind == pvk_constant 95 && b.kind == pvk_constant) 96 return pv_constant (a.k + b.k); 97 98 /* Anything else we don't know how to add. We don't have a 99 representation for, say, the sum of two registers, or a multiple 100 of a register's value (adding a register to itself). */ 101 else 102 return pv_unknown (); 103 } 104 105 106 pv_t 107 pv_add_constant (pv_t v, CORE_ADDR k) 108 { 109 /* Rather than thinking of all the cases we can and can't handle, 110 we'll just let pv_add take care of that for us. */ 111 return pv_add (v, pv_constant (k)); 112 } 113 114 115 pv_t 116 pv_subtract (pv_t a, pv_t b) 117 { 118 /* This isn't quite the same as negating B and adding it to A, since 119 we don't have a representation for the negation of anything but a 120 constant. For example, we can't negate { pvk_register, R1, 10 }, 121 but we do know that { pvk_register, R1, 10 } minus { pvk_register, 122 R1, 5 } is { pvk_constant, <ignored>, 5 }. 123 124 This means, for example, that we could subtract two stack 125 addresses; they're both relative to the original SP. Since the 126 frame pointer is set based on the SP, its value will be the 127 original SP plus some constant (probably zero), so we can use its 128 value just fine, too. */ 129 130 constant_last (&a, &b); 131 132 /* We can subtract two constants. */ 133 if (a.kind == pvk_constant 134 && b.kind == pvk_constant) 135 return pv_constant (a.k - b.k); 136 137 /* We can subtract a constant from a register. */ 138 else if (a.kind == pvk_register 139 && b.kind == pvk_constant) 140 return pv_register (a.reg, a.k - b.k); 141 142 /* We can subtract a register from itself, yielding a constant. */ 143 else if (a.kind == pvk_register 144 && b.kind == pvk_register 145 && a.reg == b.reg) 146 return pv_constant (a.k - b.k); 147 148 /* We don't know how to subtract anything else. */ 149 else 150 return pv_unknown (); 151 } 152 153 154 pv_t 155 pv_logical_and (pv_t a, pv_t b) 156 { 157 constant_last (&a, &b); 158 159 /* We can 'and' two constants. */ 160 if (a.kind == pvk_constant 161 && b.kind == pvk_constant) 162 return pv_constant (a.k & b.k); 163 164 /* We can 'and' anything with the constant zero. */ 165 else if (b.kind == pvk_constant 166 && b.k == 0) 167 return pv_constant (0); 168 169 /* We can 'and' anything with ~0. */ 170 else if (b.kind == pvk_constant 171 && b.k == ~ (CORE_ADDR) 0) 172 return a; 173 174 /* We can 'and' a register with itself. */ 175 else if (a.kind == pvk_register 176 && b.kind == pvk_register 177 && a.reg == b.reg 178 && a.k == b.k) 179 return a; 180 181 /* Otherwise, we don't know. */ 182 else 183 return pv_unknown (); 184 } 185 186 187 188 /* Examining prologue values. */ 189 190 int 191 pv_is_identical (pv_t a, pv_t b) 192 { 193 if (a.kind != b.kind) 194 return 0; 195 196 switch (a.kind) 197 { 198 case pvk_unknown: 199 return 1; 200 case pvk_constant: 201 return (a.k == b.k); 202 case pvk_register: 203 return (a.reg == b.reg && a.k == b.k); 204 default: 205 gdb_assert_not_reached ("unexpected prologue value kind"); 206 } 207 } 208 209 210 int 211 pv_is_constant (pv_t a) 212 { 213 return (a.kind == pvk_constant); 214 } 215 216 217 int 218 pv_is_register (pv_t a, int r) 219 { 220 return (a.kind == pvk_register 221 && a.reg == r); 222 } 223 224 225 int 226 pv_is_register_k (pv_t a, int r, CORE_ADDR k) 227 { 228 return (a.kind == pvk_register 229 && a.reg == r 230 && a.k == k); 231 } 232 233 234 enum pv_boolean 235 pv_is_array_ref (pv_t addr, CORE_ADDR size, 236 pv_t array_addr, CORE_ADDR array_len, 237 CORE_ADDR elt_size, 238 int *i) 239 { 240 /* Note that, since .k is a CORE_ADDR, and CORE_ADDR is unsigned, if 241 addr is *before* the start of the array, then this isn't going to 242 be negative... */ 243 pv_t offset = pv_subtract (addr, array_addr); 244 245 if (offset.kind == pvk_constant) 246 { 247 /* This is a rather odd test. We want to know if the SIZE bytes 248 at ADDR don't overlap the array at all, so you'd expect it to 249 be an || expression: "if we're completely before || we're 250 completely after". But with unsigned arithmetic, things are 251 different: since it's a number circle, not a number line, the 252 right values for offset.k are actually one contiguous range. */ 253 if (offset.k <= -size 254 && offset.k >= array_len * elt_size) 255 return pv_definite_no; 256 else if (offset.k % elt_size != 0 257 || size != elt_size) 258 return pv_maybe; 259 else 260 { 261 *i = offset.k / elt_size; 262 return pv_definite_yes; 263 } 264 } 265 else 266 return pv_maybe; 267 } 268 269 270 271 /* Areas. */ 272 273 274 /* A particular value known to be stored in an area. 275 276 Entries form a ring, sorted by unsigned offset from the area's base 277 register's value. Since entries can straddle the wrap-around point, 278 unsigned offsets form a circle, not a number line, so the list 279 itself is structured the same way --- there is no inherent head. 280 The entry with the lowest offset simply follows the entry with the 281 highest offset. Entries may abut, but never overlap. The area's 282 'entry' pointer points to an arbitrary node in the ring. */ 283 struct area_entry 284 { 285 /* Links in the doubly-linked ring. */ 286 struct area_entry *prev, *next; 287 288 /* Offset of this entry's address from the value of the base 289 register. */ 290 CORE_ADDR offset; 291 292 /* The size of this entry. Note that an entry may wrap around from 293 the end of the address space to the beginning. */ 294 CORE_ADDR size; 295 296 /* The value stored here. */ 297 pv_t value; 298 }; 299 300 301 struct pv_area 302 { 303 /* This area's base register. */ 304 int base_reg; 305 306 /* The mask to apply to addresses, to make the wrap-around happen at 307 the right place. */ 308 CORE_ADDR addr_mask; 309 310 /* An element of the doubly-linked ring of entries, or zero if we 311 have none. */ 312 struct area_entry *entry; 313 }; 314 315 316 struct pv_area * 317 make_pv_area (int base_reg, int addr_bit) 318 { 319 struct pv_area *a = (struct pv_area *) xmalloc (sizeof (*a)); 320 321 memset (a, 0, sizeof (*a)); 322 323 a->base_reg = base_reg; 324 a->entry = 0; 325 326 /* Remember that shift amounts equal to the type's width are 327 undefined. */ 328 a->addr_mask = ((((CORE_ADDR) 1 << (addr_bit - 1)) - 1) << 1) | 1; 329 330 return a; 331 } 332 333 334 /* Delete all entries from AREA. */ 335 static void 336 clear_entries (struct pv_area *area) 337 { 338 struct area_entry *e = area->entry; 339 340 if (e) 341 { 342 /* This needs to be a do-while loop, in order to actually 343 process the node being checked for in the terminating 344 condition. */ 345 do 346 { 347 struct area_entry *next = e->next; 348 349 xfree (e); 350 e = next; 351 } 352 while (e != area->entry); 353 354 area->entry = 0; 355 } 356 } 357 358 359 void 360 free_pv_area (struct pv_area *area) 361 { 362 clear_entries (area); 363 xfree (area); 364 } 365 366 367 static void 368 do_free_pv_area_cleanup (void *arg) 369 { 370 free_pv_area ((struct pv_area *) arg); 371 } 372 373 374 struct cleanup * 375 make_cleanup_free_pv_area (struct pv_area *area) 376 { 377 return make_cleanup (do_free_pv_area_cleanup, (void *) area); 378 } 379 380 381 int 382 pv_area_store_would_trash (struct pv_area *area, pv_t addr) 383 { 384 /* It may seem odd that pvk_constant appears here --- after all, 385 that's the case where we know the most about the address! But 386 pv_areas are always relative to a register, and we don't know the 387 value of the register, so we can't compare entry addresses to 388 constants. */ 389 return (addr.kind == pvk_unknown 390 || addr.kind == pvk_constant 391 || (addr.kind == pvk_register && addr.reg != area->base_reg)); 392 } 393 394 395 /* Return a pointer to the first entry we hit in AREA starting at 396 OFFSET and going forward. 397 398 This may return zero, if AREA has no entries. 399 400 And since the entries are a ring, this may return an entry that 401 entirely precedes OFFSET. This is the correct behavior: depending 402 on the sizes involved, we could still overlap such an area, with 403 wrap-around. */ 404 static struct area_entry * 405 find_entry (struct pv_area *area, CORE_ADDR offset) 406 { 407 struct area_entry *e = area->entry; 408 409 if (! e) 410 return 0; 411 412 /* If the next entry would be better than the current one, then scan 413 forward. Since we use '<' in this loop, it always terminates. 414 415 Note that, even setting aside the addr_mask stuff, we must not 416 simplify this, in high school algebra fashion, to 417 (e->next->offset < e->offset), because of the way < interacts 418 with wrap-around. We have to subtract offset from both sides to 419 make sure both things we're comparing are on the same side of the 420 discontinuity. */ 421 while (((e->next->offset - offset) & area->addr_mask) 422 < ((e->offset - offset) & area->addr_mask)) 423 e = e->next; 424 425 /* If the previous entry would be better than the current one, then 426 scan backwards. */ 427 while (((e->prev->offset - offset) & area->addr_mask) 428 < ((e->offset - offset) & area->addr_mask)) 429 e = e->prev; 430 431 /* In case there's some locality to the searches, set the area's 432 pointer to the entry we've found. */ 433 area->entry = e; 434 435 return e; 436 } 437 438 439 /* Return non-zero if the SIZE bytes at OFFSET would overlap ENTRY; 440 return zero otherwise. AREA is the area to which ENTRY belongs. */ 441 static int 442 overlaps (struct pv_area *area, 443 struct area_entry *entry, 444 CORE_ADDR offset, 445 CORE_ADDR size) 446 { 447 /* Think carefully about wrap-around before simplifying this. */ 448 return (((entry->offset - offset) & area->addr_mask) < size 449 || ((offset - entry->offset) & area->addr_mask) < entry->size); 450 } 451 452 453 void 454 pv_area_store (struct pv_area *area, 455 pv_t addr, 456 CORE_ADDR size, 457 pv_t value) 458 { 459 /* Remove any (potentially) overlapping entries. */ 460 if (pv_area_store_would_trash (area, addr)) 461 clear_entries (area); 462 else 463 { 464 CORE_ADDR offset = addr.k; 465 struct area_entry *e = find_entry (area, offset); 466 467 /* Delete all entries that we would overlap. */ 468 while (e && overlaps (area, e, offset, size)) 469 { 470 struct area_entry *next = (e->next == e) ? 0 : e->next; 471 472 e->prev->next = e->next; 473 e->next->prev = e->prev; 474 475 xfree (e); 476 e = next; 477 } 478 479 /* Move the area's pointer to the next remaining entry. This 480 will also zero the pointer if we've deleted all the entries. */ 481 area->entry = e; 482 } 483 484 /* Now, there are no entries overlapping us, and area->entry is 485 either zero or pointing at the closest entry after us. We can 486 just insert ourselves before that. 487 488 But if we're storing an unknown value, don't bother --- that's 489 the default. */ 490 if (value.kind == pvk_unknown) 491 return; 492 else 493 { 494 CORE_ADDR offset = addr.k; 495 struct area_entry *e = (struct area_entry *) xmalloc (sizeof (*e)); 496 497 e->offset = offset; 498 e->size = size; 499 e->value = value; 500 501 if (area->entry) 502 { 503 e->prev = area->entry->prev; 504 e->next = area->entry; 505 e->prev->next = e->next->prev = e; 506 } 507 else 508 { 509 e->prev = e->next = e; 510 area->entry = e; 511 } 512 } 513 } 514 515 516 pv_t 517 pv_area_fetch (struct pv_area *area, pv_t addr, CORE_ADDR size) 518 { 519 /* If we have no entries, or we can't decide how ADDR relates to the 520 entries we do have, then the value is unknown. */ 521 if (! area->entry 522 || pv_area_store_would_trash (area, addr)) 523 return pv_unknown (); 524 else 525 { 526 CORE_ADDR offset = addr.k; 527 struct area_entry *e = find_entry (area, offset); 528 529 /* If this entry exactly matches what we're looking for, then 530 we're set. Otherwise, say it's unknown. */ 531 if (e->offset == offset && e->size == size) 532 return e->value; 533 else 534 return pv_unknown (); 535 } 536 } 537 538 539 int 540 pv_area_find_reg (struct pv_area *area, 541 struct gdbarch *gdbarch, 542 int reg, 543 CORE_ADDR *offset_p) 544 { 545 struct area_entry *e = area->entry; 546 547 if (e) 548 do 549 { 550 if (e->value.kind == pvk_register 551 && e->value.reg == reg 552 && e->value.k == 0 553 && e->size == register_size (gdbarch, reg)) 554 { 555 if (offset_p) 556 *offset_p = e->offset; 557 return 1; 558 } 559 560 e = e->next; 561 } 562 while (e != area->entry); 563 564 return 0; 565 } 566 567 568 void 569 pv_area_scan (struct pv_area *area, 570 void (*func) (void *closure, 571 pv_t addr, 572 CORE_ADDR size, 573 pv_t value), 574 void *closure) 575 { 576 struct area_entry *e = area->entry; 577 pv_t addr; 578 579 addr.kind = pvk_register; 580 addr.reg = area->base_reg; 581 582 if (e) 583 do 584 { 585 addr.k = e->offset; 586 func (closure, addr, e->size, e->value); 587 e = e->next; 588 } 589 while (e != area->entry); 590 } 591