| 1 | /* Prologue value handling for GDB. |
| 2 | Copyright (C) 2003-2019 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 "prologue-value.h" |
| 21 | #include "regcache.h" |
| 22 | |
| 23 | \f |
| 24 | /* Constructors. */ |
| 25 | |
| 26 | pv_t |
| 27 | pv_unknown (void) |
| 28 | { |
| 29 | pv_t v = { pvk_unknown, 0, 0 }; |
| 30 | |
| 31 | return v; |
| 32 | } |
| 33 | |
| 34 | |
| 35 | pv_t |
| 36 | pv_constant (CORE_ADDR k) |
| 37 | { |
| 38 | pv_t v; |
| 39 | |
| 40 | v.kind = pvk_constant; |
| 41 | v.reg = -1; /* for debugging */ |
| 42 | v.k = k; |
| 43 | |
| 44 | return v; |
| 45 | } |
| 46 | |
| 47 | |
| 48 | pv_t |
| 49 | pv_register (int reg, CORE_ADDR k) |
| 50 | { |
| 51 | pv_t v; |
| 52 | |
| 53 | v.kind = pvk_register; |
| 54 | v.reg = reg; |
| 55 | v.k = k; |
| 56 | |
| 57 | return v; |
| 58 | } |
| 59 | |
| 60 | |
| 61 | \f |
| 62 | /* Arithmetic operations. */ |
| 63 | |
| 64 | /* If one of *A and *B is a constant, and the other isn't, swap the |
| 65 | values as necessary to ensure that *B is the constant. This can |
| 66 | reduce the number of cases we need to analyze in the functions |
| 67 | below. */ |
| 68 | static void |
| 69 | constant_last (pv_t *a, pv_t *b) |
| 70 | { |
| 71 | if (a->kind == pvk_constant |
| 72 | && b->kind != pvk_constant) |
| 73 | { |
| 74 | pv_t temp = *a; |
| 75 | *a = *b; |
| 76 | *b = temp; |
| 77 | } |
| 78 | } |
| 79 | |
| 80 | |
| 81 | pv_t |
| 82 | pv_add (pv_t a, pv_t b) |
| 83 | { |
| 84 | constant_last (&a, &b); |
| 85 | |
| 86 | /* We can add a constant to a register. */ |
| 87 | if (a.kind == pvk_register |
| 88 | && b.kind == pvk_constant) |
| 89 | return pv_register (a.reg, a.k + b.k); |
| 90 | |
| 91 | /* We can add a constant to another constant. */ |
| 92 | else if (a.kind == pvk_constant |
| 93 | && b.kind == pvk_constant) |
| 94 | return pv_constant (a.k + b.k); |
| 95 | |
| 96 | /* Anything else we don't know how to add. We don't have a |
| 97 | representation for, say, the sum of two registers, or a multiple |
| 98 | of a register's value (adding a register to itself). */ |
| 99 | else |
| 100 | return pv_unknown (); |
| 101 | } |
| 102 | |
| 103 | |
| 104 | pv_t |
| 105 | pv_add_constant (pv_t v, CORE_ADDR k) |
| 106 | { |
| 107 | /* Rather than thinking of all the cases we can and can't handle, |
| 108 | we'll just let pv_add take care of that for us. */ |
| 109 | return pv_add (v, pv_constant (k)); |
| 110 | } |
| 111 | |
| 112 | |
| 113 | pv_t |
| 114 | pv_subtract (pv_t a, pv_t b) |
| 115 | { |
| 116 | /* This isn't quite the same as negating B and adding it to A, since |
| 117 | we don't have a representation for the negation of anything but a |
| 118 | constant. For example, we can't negate { pvk_register, R1, 10 }, |
| 119 | but we do know that { pvk_register, R1, 10 } minus { pvk_register, |
| 120 | R1, 5 } is { pvk_constant, <ignored>, 5 }. |
| 121 | |
| 122 | This means, for example, that we could subtract two stack |
| 123 | addresses; they're both relative to the original SP. Since the |
| 124 | frame pointer is set based on the SP, its value will be the |
| 125 | original SP plus some constant (probably zero), so we can use its |
| 126 | value just fine, too. */ |
| 127 | |
| 128 | constant_last (&a, &b); |
| 129 | |
| 130 | /* We can subtract two constants. */ |
| 131 | if (a.kind == pvk_constant |
| 132 | && b.kind == pvk_constant) |
| 133 | return pv_constant (a.k - b.k); |
| 134 | |
| 135 | /* We can subtract a constant from a register. */ |
| 136 | else if (a.kind == pvk_register |
| 137 | && b.kind == pvk_constant) |
| 138 | return pv_register (a.reg, a.k - b.k); |
| 139 | |
| 140 | /* We can subtract a register from itself, yielding a constant. */ |
| 141 | else if (a.kind == pvk_register |
| 142 | && b.kind == pvk_register |
| 143 | && a.reg == b.reg) |
| 144 | return pv_constant (a.k - b.k); |
| 145 | |
| 146 | /* We don't know how to subtract anything else. */ |
| 147 | else |
| 148 | return pv_unknown (); |
| 149 | } |
| 150 | |
| 151 | |
| 152 | pv_t |
| 153 | pv_logical_and (pv_t a, pv_t b) |
| 154 | { |
| 155 | constant_last (&a, &b); |
| 156 | |
| 157 | /* We can 'and' two constants. */ |
| 158 | if (a.kind == pvk_constant |
| 159 | && b.kind == pvk_constant) |
| 160 | return pv_constant (a.k & b.k); |
| 161 | |
| 162 | /* We can 'and' anything with the constant zero. */ |
| 163 | else if (b.kind == pvk_constant |
| 164 | && b.k == 0) |
| 165 | return pv_constant (0); |
| 166 | |
| 167 | /* We can 'and' anything with ~0. */ |
| 168 | else if (b.kind == pvk_constant |
| 169 | && b.k == ~ (CORE_ADDR) 0) |
| 170 | return a; |
| 171 | |
| 172 | /* We can 'and' a register with itself. */ |
| 173 | else if (a.kind == pvk_register |
| 174 | && b.kind == pvk_register |
| 175 | && a.reg == b.reg |
| 176 | && a.k == b.k) |
| 177 | return a; |
| 178 | |
| 179 | /* Otherwise, we don't know. */ |
| 180 | else |
| 181 | return pv_unknown (); |
| 182 | } |
| 183 | |
| 184 | |
| 185 | \f |
| 186 | /* Examining prologue values. */ |
| 187 | |
| 188 | int |
| 189 | pv_is_identical (pv_t a, pv_t b) |
| 190 | { |
| 191 | if (a.kind != b.kind) |
| 192 | return 0; |
| 193 | |
| 194 | switch (a.kind) |
| 195 | { |
| 196 | case pvk_unknown: |
| 197 | return 1; |
| 198 | case pvk_constant: |
| 199 | return (a.k == b.k); |
| 200 | case pvk_register: |
| 201 | return (a.reg == b.reg && a.k == b.k); |
| 202 | default: |
| 203 | gdb_assert_not_reached ("unexpected prologue value kind"); |
| 204 | } |
| 205 | } |
| 206 | |
| 207 | |
| 208 | int |
| 209 | pv_is_constant (pv_t a) |
| 210 | { |
| 211 | return (a.kind == pvk_constant); |
| 212 | } |
| 213 | |
| 214 | |
| 215 | int |
| 216 | pv_is_register (pv_t a, int r) |
| 217 | { |
| 218 | return (a.kind == pvk_register |
| 219 | && a.reg == r); |
| 220 | } |
| 221 | |
| 222 | |
| 223 | int |
| 224 | pv_is_register_k (pv_t a, int r, CORE_ADDR k) |
| 225 | { |
| 226 | return (a.kind == pvk_register |
| 227 | && a.reg == r |
| 228 | && a.k == k); |
| 229 | } |
| 230 | |
| 231 | |
| 232 | enum pv_boolean |
| 233 | pv_is_array_ref (pv_t addr, CORE_ADDR size, |
| 234 | pv_t array_addr, CORE_ADDR array_len, |
| 235 | CORE_ADDR elt_size, |
| 236 | int *i) |
| 237 | { |
| 238 | /* Note that, since .k is a CORE_ADDR, and CORE_ADDR is unsigned, if |
| 239 | addr is *before* the start of the array, then this isn't going to |
| 240 | be negative... */ |
| 241 | pv_t offset = pv_subtract (addr, array_addr); |
| 242 | |
| 243 | if (offset.kind == pvk_constant) |
| 244 | { |
| 245 | /* This is a rather odd test. We want to know if the SIZE bytes |
| 246 | at ADDR don't overlap the array at all, so you'd expect it to |
| 247 | be an || expression: "if we're completely before || we're |
| 248 | completely after". But with unsigned arithmetic, things are |
| 249 | different: since it's a number circle, not a number line, the |
| 250 | right values for offset.k are actually one contiguous range. */ |
| 251 | if (offset.k <= -size |
| 252 | && offset.k >= array_len * elt_size) |
| 253 | return pv_definite_no; |
| 254 | else if (offset.k % elt_size != 0 |
| 255 | || size != elt_size) |
| 256 | return pv_maybe; |
| 257 | else |
| 258 | { |
| 259 | *i = offset.k / elt_size; |
| 260 | return pv_definite_yes; |
| 261 | } |
| 262 | } |
| 263 | else |
| 264 | return pv_maybe; |
| 265 | } |
| 266 | |
| 267 | |
| 268 | \f |
| 269 | /* Areas. */ |
| 270 | |
| 271 | |
| 272 | /* A particular value known to be stored in an area. |
| 273 | |
| 274 | Entries form a ring, sorted by unsigned offset from the area's base |
| 275 | register's value. Since entries can straddle the wrap-around point, |
| 276 | unsigned offsets form a circle, not a number line, so the list |
| 277 | itself is structured the same way --- there is no inherent head. |
| 278 | The entry with the lowest offset simply follows the entry with the |
| 279 | highest offset. Entries may abut, but never overlap. The area's |
| 280 | 'entry' pointer points to an arbitrary node in the ring. */ |
| 281 | struct pv_area::area_entry |
| 282 | { |
| 283 | /* Links in the doubly-linked ring. */ |
| 284 | struct area_entry *prev, *next; |
| 285 | |
| 286 | /* Offset of this entry's address from the value of the base |
| 287 | register. */ |
| 288 | CORE_ADDR offset; |
| 289 | |
| 290 | /* The size of this entry. Note that an entry may wrap around from |
| 291 | the end of the address space to the beginning. */ |
| 292 | CORE_ADDR size; |
| 293 | |
| 294 | /* The value stored here. */ |
| 295 | pv_t value; |
| 296 | }; |
| 297 | |
| 298 | |
| 299 | /* See prologue-value.h. */ |
| 300 | |
| 301 | pv_area::pv_area (int base_reg, int addr_bit) |
| 302 | : m_base_reg (base_reg), |
| 303 | /* Remember that shift amounts equal to the type's width are |
| 304 | undefined. */ |
| 305 | m_addr_mask (((((CORE_ADDR) 1 << (addr_bit - 1)) - 1) << 1) | 1), |
| 306 | m_entry (nullptr) |
| 307 | { |
| 308 | } |
| 309 | |
| 310 | /* See prologue-value.h. */ |
| 311 | |
| 312 | void |
| 313 | pv_area::clear_entries () |
| 314 | { |
| 315 | struct area_entry *e = m_entry; |
| 316 | |
| 317 | if (e) |
| 318 | { |
| 319 | /* This needs to be a do-while loop, in order to actually |
| 320 | process the node being checked for in the terminating |
| 321 | condition. */ |
| 322 | do |
| 323 | { |
| 324 | struct area_entry *next = e->next; |
| 325 | |
| 326 | xfree (e); |
| 327 | e = next; |
| 328 | } |
| 329 | while (e != m_entry); |
| 330 | |
| 331 | m_entry = 0; |
| 332 | } |
| 333 | } |
| 334 | |
| 335 | |
| 336 | pv_area::~pv_area () |
| 337 | { |
| 338 | clear_entries (); |
| 339 | } |
| 340 | |
| 341 | |
| 342 | /* See prologue-value.h. */ |
| 343 | |
| 344 | bool |
| 345 | pv_area::store_would_trash (pv_t addr) |
| 346 | { |
| 347 | /* It may seem odd that pvk_constant appears here --- after all, |
| 348 | that's the case where we know the most about the address! But |
| 349 | pv_areas are always relative to a register, and we don't know the |
| 350 | value of the register, so we can't compare entry addresses to |
| 351 | constants. */ |
| 352 | return (addr.kind == pvk_unknown |
| 353 | || addr.kind == pvk_constant |
| 354 | || (addr.kind == pvk_register && addr.reg != m_base_reg)); |
| 355 | } |
| 356 | |
| 357 | |
| 358 | /* See prologue-value.h. */ |
| 359 | |
| 360 | struct pv_area::area_entry * |
| 361 | pv_area::find_entry (CORE_ADDR offset) |
| 362 | { |
| 363 | struct area_entry *e = m_entry; |
| 364 | |
| 365 | if (! e) |
| 366 | return 0; |
| 367 | |
| 368 | /* If the next entry would be better than the current one, then scan |
| 369 | forward. Since we use '<' in this loop, it always terminates. |
| 370 | |
| 371 | Note that, even setting aside the addr_mask stuff, we must not |
| 372 | simplify this, in high school algebra fashion, to |
| 373 | (e->next->offset < e->offset), because of the way < interacts |
| 374 | with wrap-around. We have to subtract offset from both sides to |
| 375 | make sure both things we're comparing are on the same side of the |
| 376 | discontinuity. */ |
| 377 | while (((e->next->offset - offset) & m_addr_mask) |
| 378 | < ((e->offset - offset) & m_addr_mask)) |
| 379 | e = e->next; |
| 380 | |
| 381 | /* If the previous entry would be better than the current one, then |
| 382 | scan backwards. */ |
| 383 | while (((e->prev->offset - offset) & m_addr_mask) |
| 384 | < ((e->offset - offset) & m_addr_mask)) |
| 385 | e = e->prev; |
| 386 | |
| 387 | /* In case there's some locality to the searches, set the area's |
| 388 | pointer to the entry we've found. */ |
| 389 | m_entry = e; |
| 390 | |
| 391 | return e; |
| 392 | } |
| 393 | |
| 394 | |
| 395 | /* See prologue-value.h. */ |
| 396 | |
| 397 | int |
| 398 | pv_area::overlaps (struct area_entry *entry, CORE_ADDR offset, CORE_ADDR size) |
| 399 | { |
| 400 | /* Think carefully about wrap-around before simplifying this. */ |
| 401 | return (((entry->offset - offset) & m_addr_mask) < size |
| 402 | || ((offset - entry->offset) & m_addr_mask) < entry->size); |
| 403 | } |
| 404 | |
| 405 | |
| 406 | /* See prologue-value.h. */ |
| 407 | |
| 408 | void |
| 409 | pv_area::store (pv_t addr, CORE_ADDR size, pv_t value) |
| 410 | { |
| 411 | /* Remove any (potentially) overlapping entries. */ |
| 412 | if (store_would_trash (addr)) |
| 413 | clear_entries (); |
| 414 | else |
| 415 | { |
| 416 | CORE_ADDR offset = addr.k; |
| 417 | struct area_entry *e = find_entry (offset); |
| 418 | |
| 419 | /* Delete all entries that we would overlap. */ |
| 420 | while (e && overlaps (e, offset, size)) |
| 421 | { |
| 422 | struct area_entry *next = (e->next == e) ? 0 : e->next; |
| 423 | |
| 424 | e->prev->next = e->next; |
| 425 | e->next->prev = e->prev; |
| 426 | |
| 427 | xfree (e); |
| 428 | e = next; |
| 429 | } |
| 430 | |
| 431 | /* Move the area's pointer to the next remaining entry. This |
| 432 | will also zero the pointer if we've deleted all the entries. */ |
| 433 | m_entry = e; |
| 434 | } |
| 435 | |
| 436 | /* Now, there are no entries overlapping us, and m_entry is |
| 437 | either zero or pointing at the closest entry after us. We can |
| 438 | just insert ourselves before that. |
| 439 | |
| 440 | But if we're storing an unknown value, don't bother --- that's |
| 441 | the default. */ |
| 442 | if (value.kind == pvk_unknown) |
| 443 | return; |
| 444 | else |
| 445 | { |
| 446 | CORE_ADDR offset = addr.k; |
| 447 | struct area_entry *e = XNEW (struct area_entry); |
| 448 | |
| 449 | e->offset = offset; |
| 450 | e->size = size; |
| 451 | e->value = value; |
| 452 | |
| 453 | if (m_entry) |
| 454 | { |
| 455 | e->prev = m_entry->prev; |
| 456 | e->next = m_entry; |
| 457 | e->prev->next = e->next->prev = e; |
| 458 | } |
| 459 | else |
| 460 | { |
| 461 | e->prev = e->next = e; |
| 462 | m_entry = e; |
| 463 | } |
| 464 | } |
| 465 | } |
| 466 | |
| 467 | |
| 468 | /* See prologue-value.h. */ |
| 469 | |
| 470 | pv_t |
| 471 | pv_area::fetch (pv_t addr, CORE_ADDR size) |
| 472 | { |
| 473 | /* If we have no entries, or we can't decide how ADDR relates to the |
| 474 | entries we do have, then the value is unknown. */ |
| 475 | if (! m_entry |
| 476 | || store_would_trash (addr)) |
| 477 | return pv_unknown (); |
| 478 | else |
| 479 | { |
| 480 | CORE_ADDR offset = addr.k; |
| 481 | struct area_entry *e = find_entry (offset); |
| 482 | |
| 483 | /* If this entry exactly matches what we're looking for, then |
| 484 | we're set. Otherwise, say it's unknown. */ |
| 485 | if (e->offset == offset && e->size == size) |
| 486 | return e->value; |
| 487 | else |
| 488 | return pv_unknown (); |
| 489 | } |
| 490 | } |
| 491 | |
| 492 | |
| 493 | /* See prologue-value.h. */ |
| 494 | |
| 495 | bool |
| 496 | pv_area::find_reg (struct gdbarch *gdbarch, int reg, CORE_ADDR *offset_p) |
| 497 | { |
| 498 | struct area_entry *e = m_entry; |
| 499 | |
| 500 | if (e) |
| 501 | do |
| 502 | { |
| 503 | if (e->value.kind == pvk_register |
| 504 | && e->value.reg == reg |
| 505 | && e->value.k == 0 |
| 506 | && e->size == register_size (gdbarch, reg)) |
| 507 | { |
| 508 | if (offset_p) |
| 509 | *offset_p = e->offset; |
| 510 | return true; |
| 511 | } |
| 512 | |
| 513 | e = e->next; |
| 514 | } |
| 515 | while (e != m_entry); |
| 516 | |
| 517 | return false; |
| 518 | } |
| 519 | |
| 520 | |
| 521 | /* See prologue-value.h. */ |
| 522 | |
| 523 | void |
| 524 | pv_area::scan (void (*func) (void *closure, |
| 525 | pv_t addr, |
| 526 | CORE_ADDR size, |
| 527 | pv_t value), |
| 528 | void *closure) |
| 529 | { |
| 530 | struct area_entry *e = m_entry; |
| 531 | pv_t addr; |
| 532 | |
| 533 | addr.kind = pvk_register; |
| 534 | addr.reg = m_base_reg; |
| 535 | |
| 536 | if (e) |
| 537 | do |
| 538 | { |
| 539 | addr.k = e->offset; |
| 540 | func (closure, addr, e->size, e->value); |
| 541 | e = e->next; |
| 542 | } |
| 543 | while (e != m_entry); |
| 544 | } |