arch/sh/kernel/dwarf.c

   1 /*
   2  * Copyright (C) 2009 Matt Fleming <matt@console-pimps.org>
   3  *
   4  * This file is subject to the terms and conditions of the GNU General Public
   5  * License.  See the file "COPYING" in the main directory of this archive
   6  * for more details.
   7  *
   8  * This is an implementation of a DWARF unwinder. Its main purpose is
   9  * for generating stacktrace information. Based on the DWARF 3
  10  * specification from http://www.dwarfstd.org.
  11  *
  12  * TODO:
  13  *      - DWARF64 doesn't work.
  14  */
  15
  16 /* #define DEBUG */
  17 #include <linux/kernel.h>
  18 #include <linux/io.h>
  19 #include <linux/list.h>
  20 #include <linux/mm.h>
  21 #include <asm/dwarf.h>
  22 #include <asm/unwinder.h>
  23 #include <asm/sections.h>
  24 #include <asm-generic/unaligned.h>
  25 #include <asm/dwarf.h>
  26 #include <asm/stacktrace.h>
  27
  28 static LIST_HEAD(dwarf_cie_list);
  29 DEFINE_SPINLOCK(dwarf_cie_lock);
  30
  31 static LIST_HEAD(dwarf_fde_list);
  32 DEFINE_SPINLOCK(dwarf_fde_lock);
  33
  34 static struct dwarf_cie *cached_cie;
  35
  36 /*
  37  * Figure out whether we need to allocate some dwarf registers. If dwarf
  38  * registers have already been allocated then we may need to realloc
  39  * them. "reg" is a register number that we need to be able to access
  40  * after this call.
  41  *
  42  * Register numbers start at zero, therefore we need to allocate space
  43  * for "reg" + 1 registers.
  44  */
  45 static void dwarf_frame_alloc_regs(struct dwarf_frame *frame,
  46                                    unsigned int reg)
  47 {
  48         struct dwarf_reg *regs;
  49         unsigned int num_regs = reg + 1;
  50         size_t new_size;
  51         size_t old_size;
  52
  53         new_size = num_regs * sizeof(*regs);
  54         old_size = frame->num_regs * sizeof(*regs);
  55
  56         /* Fast path: don't allocate any regs if we've already got enough. */
  57         if (frame->num_regs >= num_regs)
  58                 return;
  59
  60         regs = kzalloc(new_size, GFP_KERNEL);
  61         if (!regs) {
  62                 printk(KERN_WARNING "Unable to allocate DWARF registers\n");
  63                 /*
  64                  * Let's just bomb hard here, we have no way to
  65                  * gracefully recover.
  66                  */
  67                 BUG();
  68         }
  69
  70         if (frame->regs) {
  71                 memcpy(regs, frame->regs, old_size);
  72                 kfree(frame->regs);
  73         }
  74
  75         frame->regs = regs;
  76         frame->num_regs = num_regs;
  77 }
  78
  79 /**
  80  *      dwarf_read_addr - read dwarf data
  81  *      @src: source address of data
  82  *      @dst: destination address to store the data to
  83  *
  84  *      Read 'n' bytes from @src, where 'n' is the size of an address on
  85  *      the native machine. We return the number of bytes read, which
  86  *      should always be 'n'. We also have to be careful when reading
  87  *      from @src and writing to @dst, because they can be arbitrarily
  88  *      aligned. Return 'n' - the number of bytes read.
  89  */
  90 static inline int dwarf_read_addr(void *src, void *dst)
  91 {
  92         u32 val = __get_unaligned_cpu32(src);
  93         __put_unaligned_cpu32(val, dst);
  94
  95         return sizeof(unsigned long *);
  96 }
  97
  98 /**
  99  *      dwarf_read_uleb128 - read unsigned LEB128 data
 100  *      @addr: the address where the ULEB128 data is stored
 101  *      @ret: address to store the result
 102  *
 103  *      Decode an unsigned LEB128 encoded datum. The algorithm is taken
 104  *      from Appendix C of the DWARF 3 spec. For information on the
 105  *      encodings refer to section "7.6 - Variable Length Data". Return
 106  *      the number of bytes read.
 107  */
 108 static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
 109 {
 110         unsigned int result;
 111         unsigned char byte;
 112         int shift, count;
 113
 114         result = 0;
 115         shift = 0;
 116         count = 0;
 117
 118         while (1) {
 119                 byte = __raw_readb(addr);
 120                 addr++;
 121                 count++;
 122
 123                 result |= (byte & 0x7f) << shift;
 124                 shift += 7;
 125
 126                 if (!(byte & 0x80))
 127                         break;
 128         }
 129
 130         *ret = result;
 131
 132         return count;
 133 }
 134
 135 /**
 136  *      dwarf_read_leb128 - read signed LEB128 data
 137  *      @addr: the address of the LEB128 encoded data
 138  *      @ret: address to store the result
 139  *
 140  *      Decode signed LEB128 data. The algorithm is taken from Appendix
 141  *      C of the DWARF 3 spec. Return the number of bytes read.
 142  */
 143 static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
 144 {
 145         unsigned char byte;
 146         int result, shift;
 147         int num_bits;
 148         int count;
 149
 150         result = 0;
 151         shift = 0;
 152         count = 0;
 153
 154         while (1) {
 155                 byte = __raw_readb(addr);
 156                 addr++;
 157                 result |= (byte & 0x7f) << shift;
 158                 shift += 7;
 159                 count++;
 160
 161                 if (!(byte & 0x80))
 162                         break;
 163         }
 164
 165         /* The number of bits in a signed integer. */
 166         num_bits = 8 * sizeof(result);
 167
 168         if ((shift < num_bits) && (byte & 0x40))
 169                 result |= (-1 << shift);
 170
 171         *ret = result;
 172
 173         return count;
 174 }
 175
 176 /**
 177  *      dwarf_read_encoded_value - return the decoded value at @addr
 178  *      @addr: the address of the encoded value
 179  *      @val: where to write the decoded value
 180  *      @encoding: the encoding with which we can decode @addr
 181  *
 182  *      GCC emits encoded address in the .eh_frame FDE entries. Decode
 183  *      the value at @addr using @encoding. The decoded value is written
 184  *      to @val and the number of bytes read is returned.
 185  */
 186 static int dwarf_read_encoded_value(char *addr, unsigned long *val,
 187                                     char encoding)
 188 {
 189         unsigned long decoded_addr = 0;
 190         int count = 0;
 191
 192         switch (encoding & 0x70) {
 193         case DW_EH_PE_absptr:
 194                 break;
 195         case DW_EH_PE_pcrel:
 196                 decoded_addr = (unsigned long)addr;
 197                 break;
 198         default:
 199                 pr_debug("encoding=0x%x\n", (encoding & 0x70));
 200                 BUG();
 201         }
 202
 203         if ((encoding & 0x07) == 0x00)
 204                 encoding |= DW_EH_PE_udata4;
 205
 206         switch (encoding & 0x0f) {
 207         case DW_EH_PE_sdata4:
 208         case DW_EH_PE_udata4:
 209                 count += 4;
 210                 decoded_addr += __get_unaligned_cpu32(addr);
 211                 __raw_writel(decoded_addr, val);
 212                 break;
 213         default:
 214                 pr_debug("encoding=0x%x\n", encoding);
 215                 BUG();
 216         }
 217
 218         return count;
 219 }
 220
 221 /**
 222  *      dwarf_entry_len - return the length of an FDE or CIE
 223  *      @addr: the address of the entry
 224  *      @len: the length of the entry
 225  *
 226  *      Read the initial_length field of the entry and store the size of
 227  *      the entry in @len. We return the number of bytes read. Return a
 228  *      count of 0 on error.
 229  */
 230 static inline int dwarf_entry_len(char *addr, unsigned long *len)
 231 {
 232         u32 initial_len;
 233         int count;
 234
 235         initial_len = __get_unaligned_cpu32(addr);
 236         count = 4;
 237
 238         /*
 239          * An initial length field value in the range DW_LEN_EXT_LO -
 240          * DW_LEN_EXT_HI indicates an extension, and should not be
 241          * interpreted as a length. The only extension that we currently
 242          * understand is the use of DWARF64 addresses.
 243          */
 244         if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
 245                 /*
 246                  * The 64-bit length field immediately follows the
 247                  * compulsory 32-bit length field.
 248                  */
 249                 if (initial_len == DW_EXT_DWARF64) {
 250                         *len = __get_unaligned_cpu64(addr + 4);
 251                         count = 12;
 252                 } else {
 253                         printk(KERN_WARNING "Unknown DWARF extension\n");
 254                         count = 0;
 255                 }
 256         } else
 257                 *len = initial_len;
 258
 259         return count;
 260 }
 261
 262 /**
 263  *      dwarf_lookup_cie - locate the cie
 264  *      @cie_ptr: pointer to help with lookup
 265  */
 266 static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
 267 {
 268         struct dwarf_cie *cie, *n;
 269         unsigned long flags;
 270
 271         spin_lock_irqsave(&dwarf_cie_lock, flags);
 272
 273         /*
 274          * We've cached the last CIE we looked up because chances are
 275          * that the FDE wants this CIE.
 276          */
 277         if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
 278                 cie = cached_cie;
 279                 goto out;
 280         }
 281
 282         list_for_each_entry_safe(cie, n, &dwarf_cie_list, link) {
 283                 if (cie->cie_pointer == cie_ptr) {
 284                         cached_cie = cie;
 285                         break;
 286                 }
 287         }
 288
 289         /* Couldn't find the entry in the list. */
 290         if (&cie->link == &dwarf_cie_list)
 291                 cie = NULL;
 292 out:
 293         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 294         return cie;
 295 }
 296
 297 /**
 298  *      dwarf_lookup_fde - locate the FDE that covers pc
 299  *      @pc: the program counter
 300  */
 301 struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
 302 {
 303         unsigned long flags;
 304         struct dwarf_fde *fde, *n;
 305
 306         spin_lock_irqsave(&dwarf_fde_lock, flags);
 307         list_for_each_entry_safe(fde, n, &dwarf_fde_list, link) {
 308                 unsigned long start, end;
 309
 310                 start = fde->initial_location;
 311                 end = fde->initial_location + fde->address_range;
 312
 313                 if (pc >= start && pc < end)
 314                         break;
 315         }
 316
 317         /* Couldn't find the entry in the list. */
 318         if (&fde->link == &dwarf_fde_list)
 319                 fde = NULL;
 320
 321         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 322
 323         return fde;
 324 }
 325
 326 /**
 327  *      dwarf_cfa_execute_insns - execute instructions to calculate a CFA
 328  *      @insn_start: address of the first instruction
 329  *      @insn_end: address of the last instruction
 330  *      @cie: the CIE for this function
 331  *      @fde: the FDE for this function
 332  *      @frame: the instructions calculate the CFA for this frame
 333  *      @pc: the program counter of the address we're interested in
 334  *
 335  *      Execute the Call Frame instruction sequence starting at
 336  *      @insn_start and ending at @insn_end. The instructions describe
 337  *      how to calculate the Canonical Frame Address of a stackframe.
 338  *      Store the results in @frame.
 339  */
 340 static int dwarf_cfa_execute_insns(unsigned char *insn_start,
 341                                    unsigned char *insn_end,
 342                                    struct dwarf_cie *cie,
 343                                    struct dwarf_fde *fde,
 344                                    struct dwarf_frame *frame,
 345                                    unsigned long pc)
 346 {
 347         unsigned char insn;
 348         unsigned char *current_insn;
 349         unsigned int count, delta, reg, expr_len, offset;
 350
 351         current_insn = insn_start;
 352
 353         while (current_insn < insn_end && frame->pc <= pc) {
 354                 insn = __raw_readb(current_insn++);
 355
 356                 /*
 357                  * Firstly, handle the opcodes that embed their operands
 358                  * in the instructions.
 359                  */
 360                 switch (DW_CFA_opcode(insn)) {
 361                 case DW_CFA_advance_loc:
 362                         delta = DW_CFA_operand(insn);
 363                         delta *= cie->code_alignment_factor;
 364                         frame->pc += delta;
 365                         continue;
 366                         /* NOTREACHED */
 367                 case DW_CFA_offset:
 368                         reg = DW_CFA_operand(insn);
 369                         count = dwarf_read_uleb128(current_insn, &offset);
 370                         current_insn += count;
 371                         offset *= cie->data_alignment_factor;
 372                         dwarf_frame_alloc_regs(frame, reg);
 373                         frame->regs[reg].addr = offset;
 374                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 375                         continue;
 376                         /* NOTREACHED */
 377                 case DW_CFA_restore:
 378                         reg = DW_CFA_operand(insn);
 379                         continue;
 380                         /* NOTREACHED */
 381                 }
 382
 383                 /*
 384                  * Secondly, handle the opcodes that don't embed their
 385                  * operands in the instruction.
 386                  */
 387                 switch (insn) {
 388                 case DW_CFA_nop:
 389                         continue;
 390                 case DW_CFA_advance_loc1:
 391                         delta = *current_insn++;
 392                         frame->pc += delta * cie->code_alignment_factor;
 393                         break;
 394                 case DW_CFA_advance_loc2:
 395                         delta = __get_unaligned_cpu16(current_insn);
 396                         current_insn += 2;
 397                         frame->pc += delta * cie->code_alignment_factor;
 398                         break;
 399                 case DW_CFA_advance_loc4:
 400                         delta = __get_unaligned_cpu32(current_insn);
 401                         current_insn += 4;
 402                         frame->pc += delta * cie->code_alignment_factor;
 403                         break;
 404                 case DW_CFA_offset_extended:
 405                         count = dwarf_read_uleb128(current_insn, &reg);
 406                         current_insn += count;
 407                         count = dwarf_read_uleb128(current_insn, &offset);
 408                         current_insn += count;
 409                         offset *= cie->data_alignment_factor;
 410                         break;
 411                 case DW_CFA_restore_extended:
 412                         count = dwarf_read_uleb128(current_insn, &reg);
 413                         current_insn += count;
 414                         break;
 415                 case DW_CFA_undefined:
 416                         count = dwarf_read_uleb128(current_insn, &reg);
 417                         current_insn += count;
 418                         break;
 419                 case DW_CFA_def_cfa:
 420                         count = dwarf_read_uleb128(current_insn,
 421                                                    &frame->cfa_register);
 422                         current_insn += count;
 423                         count = dwarf_read_uleb128(current_insn,
 424                                                    &frame->cfa_offset);
 425                         current_insn += count;
 426
 427                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 428                         break;
 429                 case DW_CFA_def_cfa_register:
 430                         count = dwarf_read_uleb128(current_insn,
 431                                                    &frame->cfa_register);
 432                         current_insn += count;
 433                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 434                         break;
 435                 case DW_CFA_def_cfa_offset:
 436                         count = dwarf_read_uleb128(current_insn, &offset);
 437                         current_insn += count;
 438                         frame->cfa_offset = offset;
 439                         break;
 440                 case DW_CFA_def_cfa_expression:
 441                         count = dwarf_read_uleb128(current_insn, &expr_len);
 442                         current_insn += count;
 443
 444                         frame->cfa_expr = current_insn;
 445                         frame->cfa_expr_len = expr_len;
 446                         current_insn += expr_len;
 447
 448                         frame->flags |= DWARF_FRAME_CFA_REG_EXP;
 449                         break;
 450                 case DW_CFA_offset_extended_sf:
 451                         count = dwarf_read_uleb128(current_insn, &reg);
 452                         current_insn += count;
 453                         count = dwarf_read_leb128(current_insn, &offset);
 454                         current_insn += count;
 455                         offset *= cie->data_alignment_factor;
 456                         dwarf_frame_alloc_regs(frame, reg);
 457                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 458                         frame->regs[reg].addr = offset;
 459                         break;
 460                 case DW_CFA_val_offset:
 461                         count = dwarf_read_uleb128(current_insn, &reg);
 462                         current_insn += count;
 463                         count = dwarf_read_leb128(current_insn, &offset);
 464                         offset *= cie->data_alignment_factor;
 465                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 466                         frame->regs[reg].addr = offset;
 467                         break;
 468                 default:
 469                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
 470                         break;
 471                 }
 472         }
 473
 474         return 0;
 475 }
 476
 477 /**
 478  *      dwarf_unwind_stack - recursively unwind the stack
 479  *      @pc: address of the function to unwind
 480  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
 481  *
 482  *      Return a struct dwarf_frame representing the most recent frame
 483  *      on the callstack. Each of the lower (older) stack frames are
 484  *      linked via the "prev" member.
 485  */
 486 struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
 487                                        struct dwarf_frame *prev)
 488 {
 489         struct dwarf_frame *frame;
 490         struct dwarf_cie *cie;
 491         struct dwarf_fde *fde;
 492         unsigned long addr;
 493         int i, offset;
 494
 495         /*
 496          * If this is the first invocation of this recursive function we
 497          * need get the contents of a physical register to get the CFA
 498          * in order to begin the virtual unwinding of the stack.
 499          *
 500          * The constant DWARF_ARCH_UNWIND_OFFSET is added to the address of
 501          * this function because the return address register
 502          * (DWARF_ARCH_RA_REG) will probably not be initialised until a
 503          * few instructions into the prologue.
 504          */
 505         if (!pc && !prev) {
 506                 pc = (unsigned long)&dwarf_unwind_stack;
 507                 pc += DWARF_ARCH_UNWIND_OFFSET;
 508         }
 509
 510         frame = kzalloc(sizeof(*frame), GFP_KERNEL);
 511         if (!frame)
 512                 return NULL;
 513
 514         frame->prev = prev;
 515
 516         fde = dwarf_lookup_fde(pc);
 517         if (!fde) {
 518                 /*
 519                  * This is our normal exit path - the one that stops the
 520                  * recursion. There's two reasons why we might exit
 521                  * here,
 522                  *
 523                  *      a) pc has no asscociated DWARF frame info and so
 524                  *      we don't know how to unwind this frame. This is
 525                  *      usually the case when we're trying to unwind a
 526                  *      frame that was called from some assembly code
 527                  *      that has no DWARF info, e.g. syscalls.
 528                  *
 529                  *      b) the DEBUG info for pc is bogus. There's
 530                  *      really no way to distinguish this case from the
 531                  *      case above, which sucks because we could print a
 532                  *      warning here.
 533                  */
 534                 return NULL;
 535         }
 536
 537         cie = dwarf_lookup_cie(fde->cie_pointer);
 538
 539         frame->pc = fde->initial_location;
 540
 541         /* CIE initial instructions */
 542         dwarf_cfa_execute_insns(cie->initial_instructions,
 543                                 cie->instructions_end, cie, fde, frame, pc);
 544
 545         /* FDE instructions */
 546         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
 547                                 fde, frame, pc);
 548
 549         /* Calculate the CFA */
 550         switch (frame->flags) {
 551         case DWARF_FRAME_CFA_REG_OFFSET:
 552                 if (prev) {
 553                         BUG_ON(!prev->regs[frame->cfa_register].flags);
 554
 555                         addr = prev->cfa;
 556                         addr += prev->regs[frame->cfa_register].addr;
 557                         frame->cfa = __raw_readl(addr);
 558
 559                 } else {
 560                         /*
 561                          * Again, this is the first invocation of this
 562                          * recurisve function. We need to physically
 563                          * read the contents of a register in order to
 564                          * get the Canonical Frame Address for this
 565                          * function.
 566                          */
 567                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
 568                 }
 569
 570                 frame->cfa += frame->cfa_offset;
 571                 break;
 572         default:
 573                 BUG();
 574         }
 575
 576         /* If we haven't seen the return address reg, we're screwed. */
 577         BUG_ON(!frame->regs[DWARF_ARCH_RA_REG].flags);
 578
 579         for (i = 0; i <= frame->num_regs; i++) {
 580                 struct dwarf_reg *reg = &frame->regs[i];
 581
 582                 if (!reg->flags)
 583                         continue;
 584
 585                 offset = reg->addr;
 586                 offset += frame->cfa;
 587         }
 588
 589         addr = frame->cfa + frame->regs[DWARF_ARCH_RA_REG].addr;
 590         frame->return_addr = __raw_readl(addr);
 591
 592         frame->next = dwarf_unwind_stack(frame->return_addr, frame);
 593         return frame;
 594 }
 595
 596 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
 597                            unsigned char *end)
 598 {
 599         struct dwarf_cie *cie;
 600         unsigned long flags;
 601         int count;
 602
 603         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
 604         if (!cie)
 605                 return -ENOMEM;
 606
 607         cie->length = len;
 608
 609         /*
 610          * Record the offset into the .eh_frame section
 611          * for this CIE. It allows this CIE to be
 612          * quickly and easily looked up from the
 613          * corresponding FDE.
 614          */
 615         cie->cie_pointer = (unsigned long)entry;
 616
 617         cie->version = *(char *)p++;
 618         BUG_ON(cie->version != 1);
 619
 620         cie->augmentation = p;
 621         p += strlen(cie->augmentation) + 1;
 622
 623         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
 624         p += count;
 625
 626         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
 627         p += count;
 628
 629         /*
 630          * Which column in the rule table contains the
 631          * return address?
 632          */
 633         if (cie->version == 1) {
 634                 cie->return_address_reg = __raw_readb(p);
 635                 p++;
 636         } else {
 637                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
 638                 p += count;
 639         }
 640
 641         if (cie->augmentation[0] == 'z') {
 642                 unsigned int length, count;
 643                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
 644
 645                 count = dwarf_read_uleb128(p, &length);
 646                 p += count;
 647
 648                 BUG_ON((unsigned char *)p > end);
 649
 650                 cie->initial_instructions = p + length;
 651                 cie->augmentation++;
 652         }
 653
 654         while (*cie->augmentation) {
 655                 /*
 656                  * "L" indicates a byte showing how the
 657                  * LSDA pointer is encoded. Skip it.
 658                  */
 659                 if (*cie->augmentation == 'L') {
 660                         p++;
 661                         cie->augmentation++;
 662                 } else if (*cie->augmentation == 'R') {
 663                         /*
 664                          * "R" indicates a byte showing
 665                          * how FDE addresses are
 666                          * encoded.
 667                          */
 668                         cie->encoding = *(char *)p++;
 669                         cie->augmentation++;
 670                 } else if (*cie->augmentation == 'P') {
 671                         /*
 672                          * "R" indicates a personality
 673                          * routine in the CIE
 674                          * augmentation.
 675                          */
 676                         BUG();
 677                 } else if (*cie->augmentation == 'S') {
 678                         BUG();
 679                 } else {
 680                         /*
 681                          * Unknown augmentation. Assume
 682                          * 'z' augmentation.
 683                          */
 684                         p = cie->initial_instructions;
 685                         BUG_ON(!p);
 686                         break;
 687                 }
 688         }
 689
 690         cie->initial_instructions = p;
 691         cie->instructions_end = end;
 692
 693         /* Add to list */
 694         spin_lock_irqsave(&dwarf_cie_lock, flags);
 695         list_add_tail(&cie->link, &dwarf_cie_list);
 696         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 697
 698         return 0;
 699 }
 700
 701 static int dwarf_parse_fde(void *entry, u32 entry_type,
 702                            void *start, unsigned long len)
 703 {
 704         struct dwarf_fde *fde;
 705         struct dwarf_cie *cie;
 706         unsigned long flags;
 707         int count;
 708         void *p = start;
 709
 710         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
 711         if (!fde)
 712                 return -ENOMEM;
 713
 714         fde->length = len;
 715
 716         /*
 717          * In a .eh_frame section the CIE pointer is the
 718          * delta between the address within the FDE
 719          */
 720         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
 721
 722         cie = dwarf_lookup_cie(fde->cie_pointer);
 723         fde->cie = cie;
 724
 725         if (cie->encoding)
 726                 count = dwarf_read_encoded_value(p, &fde->initial_location,
 727                                                  cie->encoding);
 728         else
 729                 count = dwarf_read_addr(p, &fde->initial_location);
 730
 731         p += count;
 732
 733         if (cie->encoding)
 734                 count = dwarf_read_encoded_value(p, &fde->address_range,
 735                                                  cie->encoding & 0x0f);
 736         else
 737                 count = dwarf_read_addr(p, &fde->address_range);
 738
 739         p += count;
 740
 741         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
 742                 unsigned int length;
 743                 count = dwarf_read_uleb128(p, &length);
 744                 p += count + length;
 745         }
 746
 747         /* Call frame instructions. */
 748         fde->instructions = p;
 749         fde->end = start + len;
 750
 751         /* Add to list. */
 752         spin_lock_irqsave(&dwarf_fde_lock, flags);
 753         list_add_tail(&fde->link, &dwarf_fde_list);
 754         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 755
 756         return 0;
 757 }
 758
 759 static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
 760                                 unsigned long *sp,
 761                                 const struct stacktrace_ops *ops, void *data)
 762 {
 763         struct dwarf_frame *frame;
 764
 765         frame = dwarf_unwind_stack(0, NULL);
 766
 767         while (frame && frame->return_addr) {
 768                 ops->address(data, frame->return_addr, 1);
 769                 frame = frame->next;
 770         }
 771 }
 772
 773 static struct unwinder dwarf_unwinder = {
 774         .name = "dwarf-unwinder",
 775         .dump = dwarf_unwinder_dump,
 776         .rating = 150,
 777 };
 778
 779 static void dwarf_unwinder_cleanup(void)
 780 {
 781         struct dwarf_cie *cie, *m;
 782         struct dwarf_fde *fde, *n;
 783         unsigned long flags;
 784
 785         /*
 786          * Deallocate all the memory allocated for the DWARF unwinder.
 787          * Traverse all the FDE/CIE lists and remove and free all the
 788          * memory associated with those data structures.
 789          */
 790         spin_lock_irqsave(&dwarf_cie_lock, flags);
 791         list_for_each_entry_safe(cie, m, &dwarf_cie_list, link)
 792                 kfree(cie);
 793         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 794
 795         spin_lock_irqsave(&dwarf_fde_lock, flags);
 796         list_for_each_entry_safe(fde, n, &dwarf_fde_list, link)
 797                 kfree(fde);
 798         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 799 }
 800
 801 /**
 802  *      dwarf_unwinder_init - initialise the dwarf unwinder
 803  *
 804  *      Build the data structures describing the .dwarf_frame section to
 805  *      make it easier to lookup CIE and FDE entries. Because the
 806  *      .eh_frame section is packed as tightly as possible it is not
 807  *      easy to lookup the FDE for a given PC, so we build a list of FDE
 808  *      and CIE entries that make it easier.
 809  */
 810 void dwarf_unwinder_init(void)
 811 {
 812         u32 entry_type;
 813         void *p, *entry;
 814         int count, err;
 815         unsigned long len;
 816         unsigned int c_entries, f_entries;
 817         unsigned char *end;
 818         INIT_LIST_HEAD(&dwarf_cie_list);
 819         INIT_LIST_HEAD(&dwarf_fde_list);
 820
 821         c_entries = 0;
 822         f_entries = 0;
 823         entry = &__start_eh_frame;
 824
 825         while ((char *)entry < __stop_eh_frame) {
 826                 p = entry;
 827
 828                 count = dwarf_entry_len(p, &len);
 829                 if (count == 0) {
 830                         /*
 831                          * We read a bogus length field value. There is
 832                          * nothing we can do here apart from disabling
 833                          * the DWARF unwinder. We can't even skip this
 834                          * entry and move to the next one because 'len'
 835                          * tells us where our next entry is.
 836                          */
 837                         goto out;
 838                 } else
 839                         p += count;
 840
 841                 /* initial length does not include itself */
 842                 end = p + len;
 843
 844                 entry_type = __get_unaligned_cpu32(p);
 845                 p += 4;
 846
 847                 if (entry_type == DW_EH_FRAME_CIE) {
 848                         err = dwarf_parse_cie(entry, p, len, end);
 849                         if (err < 0)
 850                                 goto out;
 851                         else
 852                                 c_entries++;
 853                 } else {
 854                         err = dwarf_parse_fde(entry, entry_type, p, len);
 855                         if (err < 0)
 856                                 goto out;
 857                         else
 858                                 f_entries++;
 859                 }
 860
 861                 entry = (char *)entry + len + 4;
 862         }
 863
 864         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
 865                c_entries, f_entries);
 866
 867         err = unwinder_register(&dwarf_unwinder);
 868         if (err)
 869                 goto out;
 870
 871         return;
 872
 873 out:
 874         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
 875         dwarf_unwinder_cleanup();
 876 }