1/* Prologue value handling for GDB. 2 Copyright (C) 2003-2023 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 24/* Constructors. */ 25 26pv_t 27pv_unknown (void) 28{ 29 pv_t v = { pvk_unknown, 0, 0 }; 30 31 return v; 32} 33 34 35pv_t 36pv_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 48pv_t 49pv_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 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. */ 68static void 69constant_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 81pv_t 82pv_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 104pv_t 105pv_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 113pv_t 114pv_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 152pv_t 153pv_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} 183 184 185 186/* Examining prologue values. */ 187 188int 189pv_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 208int 209pv_is_constant (pv_t a) 210{ 211 return (a.kind == pvk_constant); 212} 213 214 215int 216pv_is_register (pv_t a, int r) 217{ 218 return (a.kind == pvk_register 219 && a.reg == r); 220} 221 222 223int 224pv_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 232enum pv_boolean 233pv_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} 266 267 268 269/* 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. */ 281struct 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 301pv_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 312void 313pv_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 336pv_area::~pv_area () 337{ 338 clear_entries (); 339} 340 341 342/* See prologue-value.h. */ 343 344bool 345pv_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 360struct pv_area::area_entry * 361pv_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 397int 398pv_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 408void 409pv_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 470pv_t 471pv_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 495bool 496pv_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 523void 524pv_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} 545