kernel/arch/tile/kernel/backtrace.c

   1 /*
   2  * Copyright 2011 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  */
  14
  15 #include <linux/kernel.h>
  16 #include <linux/string.h>
  17 #include <asm/byteorder.h>
  18 #include <asm/backtrace.h>
  19 #include <asm/tile-desc.h>
  20 #include <arch/abi.h>
  21
  22 #ifdef __tilegx__
  23 #define TILE_MAX_INSTRUCTIONS_PER_BUNDLE TILEGX_MAX_INSTRUCTIONS_PER_BUNDLE
  24 #define tile_decoded_instruction tilegx_decoded_instruction
  25 #define tile_mnemonic tilegx_mnemonic
  26 #define parse_insn_tile parse_insn_tilegx
  27 #define TILE_OPC_IRET TILEGX_OPC_IRET
  28 #define TILE_OPC_ADDI TILEGX_OPC_ADDI
  29 #define TILE_OPC_ADDLI TILEGX_OPC_ADDLI
  30 #define TILE_OPC_INFO TILEGX_OPC_INFO
  31 #define TILE_OPC_INFOL TILEGX_OPC_INFOL
  32 #define TILE_OPC_JRP TILEGX_OPC_JRP
  33 #define TILE_OPC_MOVE TILEGX_OPC_MOVE
  34 #define OPCODE_STORE TILEGX_OPC_ST
  35 typedef long long bt_int_reg_t;
  36 #else
  37 #define TILE_MAX_INSTRUCTIONS_PER_BUNDLE TILEPRO_MAX_INSTRUCTIONS_PER_BUNDLE
  38 #define tile_decoded_instruction tilepro_decoded_instruction
  39 #define tile_mnemonic tilepro_mnemonic
  40 #define parse_insn_tile parse_insn_tilepro
  41 #define TILE_OPC_IRET TILEPRO_OPC_IRET
  42 #define TILE_OPC_ADDI TILEPRO_OPC_ADDI
  43 #define TILE_OPC_ADDLI TILEPRO_OPC_ADDLI
  44 #define TILE_OPC_INFO TILEPRO_OPC_INFO
  45 #define TILE_OPC_INFOL TILEPRO_OPC_INFOL
  46 #define TILE_OPC_JRP TILEPRO_OPC_JRP
  47 #define TILE_OPC_MOVE TILEPRO_OPC_MOVE
  48 #define OPCODE_STORE TILEPRO_OPC_SW
  49 typedef int bt_int_reg_t;
  50 #endif
  51
  52 /* A decoded bundle used for backtracer analysis. */
  53 struct BacktraceBundle {
  54         tile_bundle_bits bits;
  55         int num_insns;
  56         struct tile_decoded_instruction
  57         insns[TILE_MAX_INSTRUCTIONS_PER_BUNDLE];
  58 };
  59
  60
  61 /* Locates an instruction inside the given bundle that
  62  * has the specified mnemonic, and whose first 'num_operands_to_match'
  63  * operands exactly match those in 'operand_values'.
  64  */
  65 static const struct tile_decoded_instruction *find_matching_insn(
  66         const struct BacktraceBundle *bundle,
  67         tile_mnemonic mnemonic,
  68         const int *operand_values,
  69         int num_operands_to_match)
  70 {
  71         int i, j;
  72         bool match;
  73
  74         for (i = 0; i < bundle->num_insns; i++) {
  75                 const struct tile_decoded_instruction *insn =
  76                         &bundle->insns[i];
  77
  78                 if (insn->opcode->mnemonic != mnemonic)
  79                         continue;
  80
  81                 match = true;
  82                 for (j = 0; j < num_operands_to_match; j++) {
  83                         if (operand_values[j] != insn->operand_values[j]) {
  84                                 match = false;
  85                                 break;
  86                         }
  87                 }
  88
  89                 if (match)
  90                         return insn;
  91         }
  92
  93         return NULL;
  94 }
  95
  96 /* Does this bundle contain an 'iret' instruction? */
  97 static inline bool bt_has_iret(const struct BacktraceBundle *bundle)
  98 {
  99         return find_matching_insn(bundle, TILE_OPC_IRET, NULL, 0) != NULL;
 100 }
 101
 102 /* Does this bundle contain an 'addi sp, sp, OFFSET' or
 103  * 'addli sp, sp, OFFSET' instruction, and if so, what is OFFSET?
 104  */
 105 static bool bt_has_addi_sp(const struct BacktraceBundle *bundle, int *adjust)
 106 {
 107         static const int vals[2] = { TREG_SP, TREG_SP };
 108
 109         const struct tile_decoded_instruction *insn =
 110                 find_matching_insn(bundle, TILE_OPC_ADDI, vals, 2);
 111         if (insn == NULL)
 112                 insn = find_matching_insn(bundle, TILE_OPC_ADDLI, vals, 2);
 113 #ifdef __tilegx__
 114         if (insn == NULL)
 115                 insn = find_matching_insn(bundle, TILEGX_OPC_ADDXLI, vals, 2);
 116         if (insn == NULL)
 117                 insn = find_matching_insn(bundle, TILEGX_OPC_ADDXI, vals, 2);
 118 #endif
 119         if (insn == NULL)
 120                 return false;
 121
 122         *adjust = insn->operand_values[2];
 123         return true;
 124 }
 125
 126 /* Does this bundle contain any 'info OP' or 'infol OP'
 127  * instruction, and if so, what are their OP?  Note that OP is interpreted
 128  * as an unsigned value by this code since that's what the caller wants.
 129  * Returns the number of info ops found.
 130  */
 131 static int bt_get_info_ops(const struct BacktraceBundle *bundle,
 132                 int operands[MAX_INFO_OPS_PER_BUNDLE])
 133 {
 134         int num_ops = 0;
 135         int i;
 136
 137         for (i = 0; i < bundle->num_insns; i++) {
 138                 const struct tile_decoded_instruction *insn =
 139                         &bundle->insns[i];
 140
 141                 if (insn->opcode->mnemonic == TILE_OPC_INFO ||
 142                     insn->opcode->mnemonic == TILE_OPC_INFOL) {
 143                         operands[num_ops++] = insn->operand_values[0];
 144                 }
 145         }
 146
 147         return num_ops;
 148 }
 149
 150 /* Does this bundle contain a jrp instruction, and if so, to which
 151  * register is it jumping?
 152  */
 153 static bool bt_has_jrp(const struct BacktraceBundle *bundle, int *target_reg)
 154 {
 155         const struct tile_decoded_instruction *insn =
 156                 find_matching_insn(bundle, TILE_OPC_JRP, NULL, 0);
 157         if (insn == NULL)
 158                 return false;
 159
 160         *target_reg = insn->operand_values[0];
 161         return true;
 162 }
 163
 164 /* Does this bundle modify the specified register in any way? */
 165 static bool bt_modifies_reg(const struct BacktraceBundle *bundle, int reg)
 166 {
 167         int i, j;
 168         for (i = 0; i < bundle->num_insns; i++) {
 169                 const struct tile_decoded_instruction *insn =
 170                         &bundle->insns[i];
 171
 172                 if (insn->opcode->implicitly_written_register == reg)
 173                         return true;
 174
 175                 for (j = 0; j < insn->opcode->num_operands; j++)
 176                         if (insn->operands[j]->is_dest_reg &&
 177                             insn->operand_values[j] == reg)
 178                                 return true;
 179         }
 180
 181         return false;
 182 }
 183
 184 /* Does this bundle modify sp? */
 185 static inline bool bt_modifies_sp(const struct BacktraceBundle *bundle)
 186 {
 187         return bt_modifies_reg(bundle, TREG_SP);
 188 }
 189
 190 /* Does this bundle modify lr? */
 191 static inline bool bt_modifies_lr(const struct BacktraceBundle *bundle)
 192 {
 193         return bt_modifies_reg(bundle, TREG_LR);
 194 }
 195
 196 /* Does this bundle contain the instruction 'move fp, sp'? */
 197 static inline bool bt_has_move_r52_sp(const struct BacktraceBundle *bundle)
 198 {
 199         static const int vals[2] = { 52, TREG_SP };
 200         return find_matching_insn(bundle, TILE_OPC_MOVE, vals, 2) != NULL;
 201 }
 202
 203 /* Does this bundle contain a store of lr to sp? */
 204 static inline bool bt_has_sw_sp_lr(const struct BacktraceBundle *bundle)
 205 {
 206         static const int vals[2] = { TREG_SP, TREG_LR };
 207         return find_matching_insn(bundle, OPCODE_STORE, vals, 2) != NULL;
 208 }
 209
 210 #ifdef __tilegx__
 211 /* Track moveli values placed into registers. */
 212 static inline void bt_update_moveli(const struct BacktraceBundle *bundle,
 213                                     int moveli_args[])
 214 {
 215         int i;
 216         for (i = 0; i < bundle->num_insns; i++) {
 217                 const struct tile_decoded_instruction *insn =
 218                         &bundle->insns[i];
 219
 220                 if (insn->opcode->mnemonic == TILEGX_OPC_MOVELI) {
 221                         int reg = insn->operand_values[0];
 222                         moveli_args[reg] = insn->operand_values[1];
 223                 }
 224         }
 225 }
 226
 227 /* Does this bundle contain an 'add sp, sp, reg' instruction
 228  * from a register that we saw a moveli into, and if so, what
 229  * is the value in the register?
 230  */
 231 static bool bt_has_add_sp(const struct BacktraceBundle *bundle, int *adjust,
 232                           int moveli_args[])
 233 {
 234         static const int vals[2] = { TREG_SP, TREG_SP };
 235
 236         const struct tile_decoded_instruction *insn =
 237                 find_matching_insn(bundle, TILEGX_OPC_ADDX, vals, 2);
 238         if (insn) {
 239                 int reg = insn->operand_values[2];
 240                 if (moveli_args[reg]) {
 241                         *adjust = moveli_args[reg];
 242                         return true;
 243                 }
 244         }
 245         return false;
 246 }
 247 #endif
 248
 249 /* Locates the caller's PC and SP for a program starting at the
 250  * given address.
 251  */
 252 static void find_caller_pc_and_caller_sp(CallerLocation *location,
 253                                          const unsigned long start_pc,
 254                                          BacktraceMemoryReader read_memory_func,
 255                                          void *read_memory_func_extra)
 256 {
 257         /* Have we explicitly decided what the sp is,
 258          * rather than just the default?
 259          */
 260         bool sp_determined = false;
 261
 262         /* Has any bundle seen so far modified lr? */
 263         bool lr_modified = false;
 264
 265         /* Have we seen a move from sp to fp? */
 266         bool sp_moved_to_r52 = false;
 267
 268         /* Have we seen a terminating bundle? */
 269         bool seen_terminating_bundle = false;
 270
 271         /* Cut down on round-trip reading overhead by reading several
 272          * bundles at a time.
 273          */
 274         tile_bundle_bits prefetched_bundles[32];
 275         int num_bundles_prefetched = 0;
 276         int next_bundle = 0;
 277         unsigned long pc;
 278
 279 #ifdef __tilegx__
 280         /* Naively try to track moveli values to support addx for -m32. */
 281         int moveli_args[TILEGX_NUM_REGISTERS] = { 0 };
 282 #endif
 283
 284         /* Default to assuming that the caller's sp is the current sp.
 285          * This is necessary to handle the case where we start backtracing
 286          * right at the end of the epilog.
 287          */
 288         location->sp_location = SP_LOC_OFFSET;
 289         location->sp_offset = 0;
 290
 291         /* Default to having no idea where the caller PC is. */
 292         location->pc_location = PC_LOC_UNKNOWN;
 293
 294         /* Don't even try if the PC is not aligned. */
 295         if (start_pc % TILE_BUNDLE_ALIGNMENT_IN_BYTES != 0)
 296                 return;
 297
 298         for (pc = start_pc;; pc += sizeof(tile_bundle_bits)) {
 299
 300                 struct BacktraceBundle bundle;
 301                 int num_info_ops, info_operands[MAX_INFO_OPS_PER_BUNDLE];
 302                 int one_ago, jrp_reg;
 303                 bool has_jrp;
 304
 305                 if (next_bundle >= num_bundles_prefetched) {
 306                         /* Prefetch some bytes, but don't cross a page
 307                          * boundary since that might cause a read failure we
 308                          * don't care about if we only need the first few
 309                          * bytes. Note: we don't care what the actual page
 310                          * size is; using the minimum possible page size will
 311                          * prevent any problems.
 312                          */
 313                         unsigned int bytes_to_prefetch = 4096 - (pc & 4095);
 314                         if (bytes_to_prefetch > sizeof prefetched_bundles)
 315                                 bytes_to_prefetch = sizeof prefetched_bundles;
 316
 317                         if (!read_memory_func(prefetched_bundles, pc,
 318                                               bytes_to_prefetch,
 319                                               read_memory_func_extra)) {
 320                                 if (pc == start_pc) {
 321                                         /* The program probably called a bad
 322                                          * address, such as a NULL pointer.
 323                                          * So treat this as if we are at the
 324                                          * start of the function prolog so the
 325                                          * backtrace will show how we got here.
 326                                          */
 327                                         location->pc_location = PC_LOC_IN_LR;
 328                                         return;
 329                                 }
 330
 331                                 /* Unreadable address. Give up. */
 332                                 break;
 333                         }
 334
 335                         next_bundle = 0;
 336                         num_bundles_prefetched =
 337                                 bytes_to_prefetch / sizeof(tile_bundle_bits);
 338                 }
 339
 340                 /*
 341                  * Decode the next bundle.
 342                  * TILE always stores instruction bundles in little-endian
 343                  * mode, even when the chip is running in big-endian mode.
 344                  */
 345                 bundle.bits = le64_to_cpu(prefetched_bundles[next_bundle++]);
 346                 bundle.num_insns =
 347                         parse_insn_tile(bundle.bits, pc, bundle.insns);
 348                 num_info_ops = bt_get_info_ops(&bundle, info_operands);
 349
 350                 /* First look at any one_ago info ops if they are interesting,
 351                  * since they should shadow any non-one-ago info ops.
 352                  */
 353                 for (one_ago = (pc != start_pc) ? 1 : 0;
 354                      one_ago >= 0; one_ago--) {
 355                         int i;
 356                         for (i = 0; i < num_info_ops; i++) {
 357                                 int info_operand = info_operands[i];
 358                                 if (info_operand < CALLER_UNKNOWN_BASE) {
 359                                         /* Weird; reserved value, ignore it. */
 360                                         continue;
 361                                 }
 362
 363                                 /* Skip info ops which are not in the
 364                                  * "one_ago" mode we want right now.
 365                                  */
 366                                 if (((info_operand & ONE_BUNDLE_AGO_FLAG) != 0)
 367                                     != (one_ago != 0))
 368                                         continue;
 369
 370                                 /* Clear the flag to make later checking
 371                                  * easier. */
 372                                 info_operand &= ~ONE_BUNDLE_AGO_FLAG;
 373
 374                                 /* Default to looking at PC_IN_LR_FLAG. */
 375                                 if (info_operand & PC_IN_LR_FLAG)
 376                                         location->pc_location =
 377                                                 PC_LOC_IN_LR;
 378                                 else
 379                                         location->pc_location =
 380                                                 PC_LOC_ON_STACK;
 381
 382                                 switch (info_operand) {
 383                                 case CALLER_UNKNOWN_BASE:
 384                                         location->pc_location = PC_LOC_UNKNOWN;
 385                                         location->sp_location = SP_LOC_UNKNOWN;
 386                                         return;
 387
 388                                 case CALLER_SP_IN_R52_BASE:
 389                                 case CALLER_SP_IN_R52_BASE | PC_IN_LR_FLAG:
 390                                         location->sp_location = SP_LOC_IN_R52;
 391                                         return;
 392
 393                                 default:
 394                                 {
 395                                         const unsigned int val = info_operand
 396                                                 - CALLER_SP_OFFSET_BASE;
 397                                         const unsigned int sp_offset =
 398                                                 (val >> NUM_INFO_OP_FLAGS) * 8;
 399                                         if (sp_offset < 32768) {
 400                                                 /* This is a properly encoded
 401                                                  * SP offset. */
 402                                                 location->sp_location =
 403                                                         SP_LOC_OFFSET;
 404                                                 location->sp_offset =
 405                                                         sp_offset;
 406                                                 return;
 407                                         } else {
 408                                                 /* This looked like an SP
 409                                                  * offset, but it's outside
 410                                                  * the legal range, so this
 411                                                  * must be an unrecognized
 412                                                  * info operand.  Ignore it.
 413                                                  */
 414                                         }
 415                                 }
 416                                 break;
 417                                 }
 418                         }
 419                 }
 420
 421                 if (seen_terminating_bundle) {
 422                         /* We saw a terminating bundle during the previous
 423                          * iteration, so we were only looking for an info op.
 424                          */
 425                         break;
 426                 }
 427
 428                 if (bundle.bits == 0) {
 429                         /* Wacky terminating bundle. Stop looping, and hope
 430                          * we've already seen enough to find the caller.
 431                          */
 432                         break;
 433                 }
 434
 435                 /*
 436                  * Try to determine caller's SP.
 437                  */
 438
 439                 if (!sp_determined) {
 440                         int adjust;
 441                         if (bt_has_addi_sp(&bundle, &adjust)
 442 #ifdef __tilegx__
 443                             || bt_has_add_sp(&bundle, &adjust, moveli_args)
 444 #endif
 445                                 ) {
 446                                 location->sp_location = SP_LOC_OFFSET;
 447
 448                                 if (adjust <= 0) {
 449                                         /* We are in prolog about to adjust
 450                                          * SP. */
 451                                         location->sp_offset = 0;
 452                                 } else {
 453                                         /* We are in epilog restoring SP. */
 454                                         location->sp_offset = adjust;
 455                                 }
 456
 457                                 sp_determined = true;
 458                         } else {
 459                                 if (bt_has_move_r52_sp(&bundle)) {
 460                                         /* Maybe in prolog, creating an
 461                                          * alloca-style frame.  But maybe in
 462                                          * the middle of a fixed-size frame
 463                                          * clobbering r52 with SP.
 464                                          */
 465                                         sp_moved_to_r52 = true;
 466                                 }
 467
 468                                 if (bt_modifies_sp(&bundle)) {
 469                                         if (sp_moved_to_r52) {
 470                                                 /* We saw SP get saved into
 471                                                  * r52 earlier (or now), which
 472                                                  * must have been in the
 473                                                  * prolog, so we now know that
 474                                                  * SP is still holding the
 475                                                  * caller's sp value.
 476                                                  */
 477                                                 location->sp_location =
 478                                                         SP_LOC_OFFSET;
 479                                                 location->sp_offset = 0;
 480                                         } else {
 481                                                 /* Someone must have saved
 482                                                  * aside the caller's SP value
 483                                                  * into r52, so r52 holds the
 484                                                  * current value.
 485                                                  */
 486                                                 location->sp_location =
 487                                                         SP_LOC_IN_R52;
 488                                         }
 489                                         sp_determined = true;
 490                                 }
 491                         }
 492
 493 #ifdef __tilegx__
 494                         /* Track moveli arguments for -m32 mode. */
 495                         bt_update_moveli(&bundle, moveli_args);
 496 #endif
 497                 }
 498
 499                 if (bt_has_iret(&bundle)) {
 500                         /* This is a terminating bundle. */
 501                         seen_terminating_bundle = true;
 502                         continue;
 503                 }
 504
 505                 /*
 506                  * Try to determine caller's PC.
 507                  */
 508
 509                 jrp_reg = -1;
 510                 has_jrp = bt_has_jrp(&bundle, &jrp_reg);
 511                 if (has_jrp)
 512                         seen_terminating_bundle = true;
 513
 514                 if (location->pc_location == PC_LOC_UNKNOWN) {
 515                         if (has_jrp) {
 516                                 if (jrp_reg == TREG_LR && !lr_modified) {
 517                                         /* Looks like a leaf function, or else
 518                                          * lr is already restored. */
 519                                         location->pc_location =
 520                                                 PC_LOC_IN_LR;
 521                                 } else {
 522                                         location->pc_location =
 523                                                 PC_LOC_ON_STACK;
 524                                 }
 525                         } else if (bt_has_sw_sp_lr(&bundle)) {
 526                                 /* In prolog, spilling initial lr to stack. */
 527                                 location->pc_location = PC_LOC_IN_LR;
 528                         } else if (bt_modifies_lr(&bundle)) {
 529                                 lr_modified = true;
 530                         }
 531                 }
 532         }
 533 }
 534
 535 /* Initializes a backtracer to start from the given location.
 536  *
 537  * If the frame pointer cannot be determined it is set to -1.
 538  *
 539  * state: The state to be filled in.
 540  * read_memory_func: A callback that reads memory.
 541  * read_memory_func_extra: An arbitrary argument to read_memory_func.
 542  * pc: The current PC.
 543  * lr: The current value of the 'lr' register.
 544  * sp: The current value of the 'sp' register.
 545  * r52: The current value of the 'r52' register.
 546  */
 547 void backtrace_init(BacktraceIterator *state,
 548                     BacktraceMemoryReader read_memory_func,
 549                     void *read_memory_func_extra,
 550                     unsigned long pc, unsigned long lr,
 551                     unsigned long sp, unsigned long r52)
 552 {
 553         CallerLocation location;
 554         unsigned long fp, initial_frame_caller_pc;
 555
 556         /* Find out where we are in the initial frame. */
 557         find_caller_pc_and_caller_sp(&location, pc,
 558                                      read_memory_func, read_memory_func_extra);
 559
 560         switch (location.sp_location) {
 561         case SP_LOC_UNKNOWN:
 562                 /* Give up. */
 563                 fp = -1;
 564                 break;
 565
 566         case SP_LOC_IN_R52:
 567                 fp = r52;
 568                 break;
 569
 570         case SP_LOC_OFFSET:
 571                 fp = sp + location.sp_offset;
 572                 break;
 573
 574         default:
 575                 /* Give up. */
 576                 fp = -1;
 577                 break;
 578         }
 579
 580         /* If the frame pointer is not aligned to the basic word size
 581          * something terrible happened and we should mark it as invalid.
 582          */
 583         if (fp % sizeof(bt_int_reg_t) != 0)
 584                 fp = -1;
 585
 586         /* -1 means "don't know initial_frame_caller_pc". */
 587         initial_frame_caller_pc = -1;
 588
 589         switch (location.pc_location) {
 590         case PC_LOC_UNKNOWN:
 591                 /* Give up. */
 592                 fp = -1;
 593                 break;
 594
 595         case PC_LOC_IN_LR:
 596                 if (lr == 0 || lr % TILE_BUNDLE_ALIGNMENT_IN_BYTES != 0) {
 597                         /* Give up. */
 598                         fp = -1;
 599                 } else {
 600                         initial_frame_caller_pc = lr;
 601                 }
 602                 break;
 603
 604         case PC_LOC_ON_STACK:
 605                 /* Leave initial_frame_caller_pc as -1,
 606                  * meaning check the stack.
 607                  */
 608                 break;
 609
 610         default:
 611                 /* Give up. */
 612                 fp = -1;
 613                 break;
 614         }
 615
 616         state->pc = pc;
 617         state->sp = sp;
 618         state->fp = fp;
 619         state->initial_frame_caller_pc = initial_frame_caller_pc;
 620         state->read_memory_func = read_memory_func;
 621         state->read_memory_func_extra = read_memory_func_extra;
 622 }
 623
 624 /* Handle the case where the register holds more bits than the VA. */
 625 static bool valid_addr_reg(bt_int_reg_t reg)
 626 {
 627         return ((unsigned long)reg == reg);
 628 }
 629
 630 /* Advances the backtracing state to the calling frame, returning
 631  * true iff successful.
 632  */
 633 bool backtrace_next(BacktraceIterator *state)
 634 {
 635         unsigned long next_fp, next_pc;
 636         bt_int_reg_t next_frame[2];
 637
 638         if (state->fp == -1) {
 639                 /* No parent frame. */
 640                 return false;
 641         }
 642
 643         /* Try to read the frame linkage data chaining to the next function. */
 644         if (!state->read_memory_func(&next_frame, state->fp, sizeof next_frame,
 645                                      state->read_memory_func_extra)) {
 646                 return false;
 647         }
 648
 649         next_fp = next_frame[1];
 650         if (!valid_addr_reg(next_frame[1]) ||
 651             next_fp % sizeof(bt_int_reg_t) != 0) {
 652                 /* Caller's frame pointer is suspect, so give up. */
 653                 return false;
 654         }
 655
 656         if (state->initial_frame_caller_pc != -1) {
 657                 /* We must be in the initial stack frame and already know the
 658                  * caller PC.
 659                  */
 660                 next_pc = state->initial_frame_caller_pc;
 661
 662                 /* Force reading stack next time, in case we were in the
 663                  * initial frame.  We don't do this above just to paranoidly
 664                  * avoid changing the struct at all when we return false.
 665                  */
 666                 state->initial_frame_caller_pc = -1;
 667         } else {
 668                 /* Get the caller PC from the frame linkage area. */
 669                 next_pc = next_frame[0];
 670                 if (!valid_addr_reg(next_frame[0]) || next_pc == 0 ||
 671                     next_pc % TILE_BUNDLE_ALIGNMENT_IN_BYTES != 0) {
 672                         /* The PC is suspect, so give up. */
 673                         return false;
 674                 }
 675         }
 676
 677         /* Update state to become the caller's stack frame. */
 678         state->pc = next_pc;
 679         state->sp = state->fp;
 680         state->fp = next_fp;
 681
 682         return true;
 683 }