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   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/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(unsigned long *src, unsigned long *dst)
  91 {
  92         u32 val = get_unaligned(src);
  93         put_unaligned(val, dst);
  94         return sizeof(unsigned long *);
  95 }
  96
  97 /**
  98  *      dwarf_read_uleb128 - read unsigned LEB128 data
  99  *      @addr: the address where the ULEB128 data is stored
 100  *      @ret: address to store the result
 101  *
 102  *      Decode an unsigned LEB128 encoded datum. The algorithm is taken
 103  *      from Appendix C of the DWARF 3 spec. For information on the
 104  *      encodings refer to section "7.6 - Variable Length Data". Return
 105  *      the number of bytes read.
 106  */
 107 static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
 108 {
 109         unsigned int result;
 110         unsigned char byte;
 111         int shift, count;
 112
 113         result = 0;
 114         shift = 0;
 115         count = 0;
 116
 117         while (1) {
 118                 byte = __raw_readb(addr);
 119                 addr++;
 120                 count++;
 121
 122                 result |= (byte & 0x7f) << shift;
 123                 shift += 7;
 124
 125                 if (!(byte & 0x80))
 126                         break;
 127         }
 128
 129         *ret = result;
 130
 131         return count;
 132 }
 133
 134 /**
 135  *      dwarf_read_leb128 - read signed LEB128 data
 136  *      @addr: the address of the LEB128 encoded data
 137  *      @ret: address to store the result
 138  *
 139  *      Decode signed LEB128 data. The algorithm is taken from Appendix
 140  *      C of the DWARF 3 spec. Return the number of bytes read.
 141  */
 142 static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
 143 {
 144         unsigned char byte;
 145         int result, shift;
 146         int num_bits;
 147         int count;
 148
 149         result = 0;
 150         shift = 0;
 151         count = 0;
 152
 153         while (1) {
 154                 byte = __raw_readb(addr);
 155                 addr++;
 156                 result |= (byte & 0x7f) << shift;
 157                 shift += 7;
 158                 count++;
 159
 160                 if (!(byte & 0x80))
 161                         break;
 162         }
 163
 164         /* The number of bits in a signed integer. */
 165         num_bits = 8 * sizeof(result);
 166
 167         if ((shift < num_bits) && (byte & 0x40))
 168                 result |= (-1 << shift);
 169
 170         *ret = result;
 171
 172         return count;
 173 }
 174
 175 /**
 176  *      dwarf_read_encoded_value - return the decoded value at @addr
 177  *      @addr: the address of the encoded value
 178  *      @val: where to write the decoded value
 179  *      @encoding: the encoding with which we can decode @addr
 180  *
 181  *      GCC emits encoded address in the .eh_frame FDE entries. Decode
 182  *      the value at @addr using @encoding. The decoded value is written
 183  *      to @val and the number of bytes read is returned.
 184  */
 185 static int dwarf_read_encoded_value(char *addr, unsigned long *val,
 186                                     char encoding)
 187 {
 188         unsigned long decoded_addr = 0;
 189         int count = 0;
 190
 191         switch (encoding & 0x70) {
 192         case DW_EH_PE_absptr:
 193                 break;
 194         case DW_EH_PE_pcrel:
 195                 decoded_addr = (unsigned long)addr;
 196                 break;
 197         default:
 198                 pr_debug("encoding=0x%x\n", (encoding & 0x70));
 199                 BUG();
 200         }
 201
 202         if ((encoding & 0x07) == 0x00)
 203                 encoding |= DW_EH_PE_udata4;
 204
 205         switch (encoding & 0x0f) {
 206         case DW_EH_PE_sdata4:
 207         case DW_EH_PE_udata4:
 208                 count += 4;
 209                 decoded_addr += get_unaligned((u32 *)addr);
 210                 __raw_writel(decoded_addr, val);
 211                 break;
 212         default:
 213                 pr_debug("encoding=0x%x\n", encoding);
 214                 BUG();
 215         }
 216
 217         return count;
 218 }
 219
 220 /**
 221  *      dwarf_entry_len - return the length of an FDE or CIE
 222  *      @addr: the address of the entry
 223  *      @len: the length of the entry
 224  *
 225  *      Read the initial_length field of the entry and store the size of
 226  *      the entry in @len. We return the number of bytes read. Return a
 227  *      count of 0 on error.
 228  */
 229 static inline int dwarf_entry_len(char *addr, unsigned long *len)
 230 {
 231         u32 initial_len;
 232         int count;
 233
 234         initial_len = get_unaligned((u32 *)addr);
 235         count = 4;
 236
 237         /*
 238          * An initial length field value in the range DW_LEN_EXT_LO -
 239          * DW_LEN_EXT_HI indicates an extension, and should not be
 240          * interpreted as a length. The only extension that we currently
 241          * understand is the use of DWARF64 addresses.
 242          */
 243         if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
 244                 /*
 245                  * The 64-bit length field immediately follows the
 246                  * compulsory 32-bit length field.
 247                  */
 248                 if (initial_len == DW_EXT_DWARF64) {
 249                         *len = get_unaligned((u64 *)addr + 4);
 250                         count = 12;
 251                 } else {
 252                         printk(KERN_WARNING "Unknown DWARF extension\n");
 253                         count = 0;
 254                 }
 255         } else
 256                 *len = initial_len;
 257
 258         return count;
 259 }
 260
 261 /**
 262  *      dwarf_lookup_cie - locate the cie
 263  *      @cie_ptr: pointer to help with lookup
 264  */
 265 static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
 266 {
 267         struct dwarf_cie *cie, *n;
 268         unsigned long flags;
 269
 270         spin_lock_irqsave(&dwarf_cie_lock, flags);
 271
 272         /*
 273          * We've cached the last CIE we looked up because chances are
 274          * that the FDE wants this CIE.
 275          */
 276         if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
 277                 cie = cached_cie;
 278                 goto out;
 279         }
 280
 281         list_for_each_entry_safe(cie, n, &dwarf_cie_list, link) {
 282                 if (cie->cie_pointer == cie_ptr) {
 283                         cached_cie = cie;
 284                         break;
 285                 }
 286         }
 287
 288         /* Couldn't find the entry in the list. */
 289         if (&cie->link == &dwarf_cie_list)
 290                 cie = NULL;
 291 out:
 292         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 293         return cie;
 294 }
 295
 296 /**
 297  *      dwarf_lookup_fde - locate the FDE that covers pc
 298  *      @pc: the program counter
 299  */
 300 struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
 301 {
 302         unsigned long flags;
 303         struct dwarf_fde *fde, *n;
 304
 305         spin_lock_irqsave(&dwarf_fde_lock, flags);
 306         list_for_each_entry_safe(fde, n, &dwarf_fde_list, link) {
 307                 unsigned long start, end;
 308
 309                 start = fde->initial_location;
 310                 end = fde->initial_location + fde->address_range;
 311
 312                 if (pc >= start && pc < end)
 313                         break;
 314         }
 315
 316         /* Couldn't find the entry in the list. */
 317         if (&fde->link == &dwarf_fde_list)
 318                 fde = NULL;
 319
 320         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 321
 322         return fde;
 323 }
 324
 325 /**
 326  *      dwarf_cfa_execute_insns - execute instructions to calculate a CFA
 327  *      @insn_start: address of the first instruction
 328  *      @insn_end: address of the last instruction
 329  *      @cie: the CIE for this function
 330  *      @fde: the FDE for this function
 331  *      @frame: the instructions calculate the CFA for this frame
 332  *      @pc: the program counter of the address we're interested in
 333  *
 334  *      Execute the Call Frame instruction sequence starting at
 335  *      @insn_start and ending at @insn_end. The instructions describe
 336  *      how to calculate the Canonical Frame Address of a stackframe.
 337  *      Store the results in @frame.
 338  */
 339 static int dwarf_cfa_execute_insns(unsigned char *insn_start,
 340                                    unsigned char *insn_end,
 341                                    struct dwarf_cie *cie,
 342                                    struct dwarf_fde *fde,
 343                                    struct dwarf_frame *frame,
 344                                    unsigned long pc)
 345 {
 346         unsigned char insn;
 347         unsigned char *current_insn;
 348         unsigned int count, delta, reg, expr_len, offset;
 349
 350         current_insn = insn_start;
 351
 352         while (current_insn < insn_end && frame->pc <= pc) {
 353                 insn = __raw_readb(current_insn++);
 354
 355                 /*
 356                  * Firstly, handle the opcodes that embed their operands
 357                  * in the instructions.
 358                  */
 359                 switch (DW_CFA_opcode(insn)) {
 360                 case DW_CFA_advance_loc:
 361                         delta = DW_CFA_operand(insn);
 362                         delta *= cie->code_alignment_factor;
 363                         frame->pc += delta;
 364                         continue;
 365                         /* NOTREACHED */
 366                 case DW_CFA_offset:
 367                         reg = DW_CFA_operand(insn);
 368                         count = dwarf_read_uleb128(current_insn, &offset);
 369                         current_insn += count;
 370                         offset *= cie->data_alignment_factor;
 371                         dwarf_frame_alloc_regs(frame, reg);
 372                         frame->regs[reg].addr = offset;
 373                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 374                         continue;
 375                         /* NOTREACHED */
 376                 case DW_CFA_restore:
 377                         reg = DW_CFA_operand(insn);
 378                         continue;
 379                         /* NOTREACHED */
 380                 }
 381
 382                 /*
 383                  * Secondly, handle the opcodes that don't embed their
 384                  * operands in the instruction.
 385                  */
 386                 switch (insn) {
 387                 case DW_CFA_nop:
 388                         continue;
 389                 case DW_CFA_advance_loc1:
 390                         delta = *current_insn++;
 391                         frame->pc += delta * cie->code_alignment_factor;
 392                         break;
 393                 case DW_CFA_advance_loc2:
 394                         delta = get_unaligned((u16 *)current_insn);
 395                         current_insn += 2;
 396                         frame->pc += delta * cie->code_alignment_factor;
 397                         break;
 398                 case DW_CFA_advance_loc4:
 399                         delta = get_unaligned((u32 *)current_insn);
 400                         current_insn += 4;
 401                         frame->pc += delta * cie->code_alignment_factor;
 402                         break;
 403                 case DW_CFA_offset_extended:
 404                         count = dwarf_read_uleb128(current_insn, &reg);
 405                         current_insn += count;
 406                         count = dwarf_read_uleb128(current_insn, &offset);
 407                         current_insn += count;
 408                         offset *= cie->data_alignment_factor;
 409                         break;
 410                 case DW_CFA_restore_extended:
 411                         count = dwarf_read_uleb128(current_insn, &reg);
 412                         current_insn += count;
 413                         break;
 414                 case DW_CFA_undefined:
 415                         count = dwarf_read_uleb128(current_insn, &reg);
 416                         current_insn += count;
 417                         break;
 418                 case DW_CFA_def_cfa:
 419                         count = dwarf_read_uleb128(current_insn,
 420                                                    &frame->cfa_register);
 421                         current_insn += count;
 422                         count = dwarf_read_uleb128(current_insn,
 423                                                    &frame->cfa_offset);
 424                         current_insn += count;
 425
 426                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 427                         break;
 428                 case DW_CFA_def_cfa_register:
 429                         count = dwarf_read_uleb128(current_insn,
 430                                                    &frame->cfa_register);
 431                         current_insn += count;
 432                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 433                         break;
 434                 case DW_CFA_def_cfa_offset:
 435                         count = dwarf_read_uleb128(current_insn, &offset);
 436                         current_insn += count;
 437                         frame->cfa_offset = offset;
 438                         break;
 439                 case DW_CFA_def_cfa_expression:
 440                         count = dwarf_read_uleb128(current_insn, &expr_len);
 441                         current_insn += count;
 442
 443                         frame->cfa_expr = current_insn;
 444                         frame->cfa_expr_len = expr_len;
 445                         current_insn += expr_len;
 446
 447                         frame->flags |= DWARF_FRAME_CFA_REG_EXP;
 448                         break;
 449                 case DW_CFA_offset_extended_sf:
 450                         count = dwarf_read_uleb128(current_insn, &reg);
 451                         current_insn += count;
 452                         count = dwarf_read_leb128(current_insn, &offset);
 453                         current_insn += count;
 454                         offset *= cie->data_alignment_factor;
 455                         dwarf_frame_alloc_regs(frame, reg);
 456                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 457                         frame->regs[reg].addr = offset;
 458                         break;
 459                 case DW_CFA_val_offset:
 460                         count = dwarf_read_uleb128(current_insn, &reg);
 461                         current_insn += count;
 462                         count = dwarf_read_leb128(current_insn, &offset);
 463                         offset *= cie->data_alignment_factor;
 464                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 465                         frame->regs[reg].addr = offset;
 466                         break;
 467                 default:
 468                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
 469                         break;
 470                 }
 471         }
 472
 473         return 0;
 474 }
 475
 476 /**
 477  *      dwarf_unwind_stack - recursively unwind the stack
 478  *      @pc: address of the function to unwind
 479  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
 480  *
 481  *      Return a struct dwarf_frame representing the most recent frame
 482  *      on the callstack. Each of the lower (older) stack frames are
 483  *      linked via the "prev" member.
 484  */
 485 struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
 486                                        struct dwarf_frame *prev)
 487 {
 488         struct dwarf_frame *frame;
 489         struct dwarf_cie *cie;
 490         struct dwarf_fde *fde;
 491         unsigned long addr;
 492         int i, offset;
 493
 494         /*
 495          * If this is the first invocation of this recursive function we
 496          * need get the contents of a physical register to get the CFA
 497          * in order to begin the virtual unwinding of the stack.
 498          *
 499          * The constant DWARF_ARCH_UNWIND_OFFSET is added to the address of
 500          * this function because the return address register
 501          * (DWARF_ARCH_RA_REG) will probably not be initialised until a
 502          * few instructions into the prologue.
 503          */
 504         if (!pc && !prev) {
 505                 pc = (unsigned long)&dwarf_unwind_stack;
 506                 pc += DWARF_ARCH_UNWIND_OFFSET;
 507         }
 508
 509         frame = kzalloc(sizeof(*frame), GFP_KERNEL);
 510         if (!frame)
 511                 return NULL;
 512
 513         frame->prev = prev;
 514
 515         fde = dwarf_lookup_fde(pc);
 516         if (!fde) {
 517                 /*
 518                  * This is our normal exit path - the one that stops the
 519                  * recursion. There's two reasons why we might exit
 520                  * here,
 521                  *
 522                  *      a) pc has no asscociated DWARF frame info and so
 523                  *      we don't know how to unwind this frame. This is
 524                  *      usually the case when we're trying to unwind a
 525                  *      frame that was called from some assembly code
 526                  *      that has no DWARF info, e.g. syscalls.
 527                  *
 528                  *      b) the DEBUG info for pc is bogus. There's
 529                  *      really no way to distinguish this case from the
 530                  *      case above, which sucks because we could print a
 531                  *      warning here.
 532                  */
 533                 return NULL;
 534         }
 535
 536         cie = dwarf_lookup_cie(fde->cie_pointer);
 537
 538         frame->pc = fde->initial_location;
 539
 540         /* CIE initial instructions */
 541         dwarf_cfa_execute_insns(cie->initial_instructions,
 542                                 cie->instructions_end, cie, fde, frame, pc);
 543
 544         /* FDE instructions */
 545         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
 546                                 fde, frame, pc);
 547
 548         /* Calculate the CFA */
 549         switch (frame->flags) {
 550         case DWARF_FRAME_CFA_REG_OFFSET:
 551                 if (prev) {
 552                         BUG_ON(!prev->regs[frame->cfa_register].flags);
 553
 554                         addr = prev->cfa;
 555                         addr += prev->regs[frame->cfa_register].addr;
 556                         frame->cfa = __raw_readl(addr);
 557
 558                 } else {
 559                         /*
 560                          * Again, this is the first invocation of this
 561                          * recurisve function. We need to physically
 562                          * read the contents of a register in order to
 563                          * get the Canonical Frame Address for this
 564                          * function.
 565                          */
 566                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
 567                 }
 568
 569                 frame->cfa += frame->cfa_offset;
 570                 break;
 571         default:
 572                 BUG();
 573         }
 574
 575         /* If we haven't seen the return address reg, we're screwed. */
 576         BUG_ON(!frame->regs[DWARF_ARCH_RA_REG].flags);
 577
 578         for (i = 0; i <= frame->num_regs; i++) {
 579                 struct dwarf_reg *reg = &frame->regs[i];
 580
 581                 if (!reg->flags)
 582                         continue;
 583
 584                 offset = reg->addr;
 585                 offset += frame->cfa;
 586         }
 587
 588         addr = frame->cfa + frame->regs[DWARF_ARCH_RA_REG].addr;
 589         frame->return_addr = __raw_readl(addr);
 590
 591         frame->next = dwarf_unwind_stack(frame->return_addr, frame);
 592         return frame;
 593 }
 594
 595 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
 596                            unsigned char *end)
 597 {
 598         struct dwarf_cie *cie;
 599         unsigned long flags;
 600         int count;
 601
 602         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
 603         if (!cie)
 604                 return -ENOMEM;
 605
 606         cie->length = len;
 607
 608         /*
 609          * Record the offset into the .eh_frame section
 610          * for this CIE. It allows this CIE to be
 611          * quickly and easily looked up from the
 612          * corresponding FDE.
 613          */
 614         cie->cie_pointer = (unsigned long)entry;
 615
 616         cie->version = *(char *)p++;
 617         BUG_ON(cie->version != 1);
 618
 619         cie->augmentation = p;
 620         p += strlen(cie->augmentation) + 1;
 621
 622         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
 623         p += count;
 624
 625         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
 626         p += count;
 627
 628         /*
 629          * Which column in the rule table contains the
 630          * return address?
 631          */
 632         if (cie->version == 1) {
 633                 cie->return_address_reg = __raw_readb(p);
 634                 p++;
 635         } else {
 636                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
 637                 p += count;
 638         }
 639
 640         if (cie->augmentation[0] == 'z') {
 641                 unsigned int length, count;
 642                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
 643
 644                 count = dwarf_read_uleb128(p, &length);
 645                 p += count;
 646
 647                 BUG_ON((unsigned char *)p > end);
 648
 649                 cie->initial_instructions = p + length;
 650                 cie->augmentation++;
 651         }
 652
 653         while (*cie->augmentation) {
 654                 /*
 655                  * "L" indicates a byte showing how the
 656                  * LSDA pointer is encoded. Skip it.
 657                  */
 658                 if (*cie->augmentation == 'L') {
 659                         p++;
 660                         cie->augmentation++;
 661                 } else if (*cie->augmentation == 'R') {
 662                         /*
 663                          * "R" indicates a byte showing
 664                          * how FDE addresses are
 665                          * encoded.
 666                          */
 667                         cie->encoding = *(char *)p++;
 668                         cie->augmentation++;
 669                 } else if (*cie->augmentation == 'P') {
 670                         /*
 671                          * "R" indicates a personality
 672                          * routine in the CIE
 673                          * augmentation.
 674                          */
 675                         BUG();
 676                 } else if (*cie->augmentation == 'S') {
 677                         BUG();
 678                 } else {
 679                         /*
 680                          * Unknown augmentation. Assume
 681                          * 'z' augmentation.
 682                          */
 683                         p = cie->initial_instructions;
 684                         BUG_ON(!p);
 685                         break;
 686                 }
 687         }
 688
 689         cie->initial_instructions = p;
 690         cie->instructions_end = end;
 691
 692         /* Add to list */
 693         spin_lock_irqsave(&dwarf_cie_lock, flags);
 694         list_add_tail(&cie->link, &dwarf_cie_list);
 695         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 696
 697         return 0;
 698 }
 699
 700 static int dwarf_parse_fde(void *entry, u32 entry_type,
 701                            void *start, unsigned long len)
 702 {
 703         struct dwarf_fde *fde;
 704         struct dwarf_cie *cie;
 705         unsigned long flags;
 706         int count;
 707         void *p = start;
 708
 709         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
 710         if (!fde)
 711                 return -ENOMEM;
 712
 713         fde->length = len;
 714
 715         /*
 716          * In a .eh_frame section the CIE pointer is the
 717          * delta between the address within the FDE
 718          */
 719         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
 720
 721         cie = dwarf_lookup_cie(fde->cie_pointer);
 722         fde->cie = cie;
 723
 724         if (cie->encoding)
 725                 count = dwarf_read_encoded_value(p, &fde->initial_location,
 726                                                  cie->encoding);
 727         else
 728                 count = dwarf_read_addr(p, &fde->initial_location);
 729
 730         p += count;
 731
 732         if (cie->encoding)
 733                 count = dwarf_read_encoded_value(p, &fde->address_range,
 734                                                  cie->encoding & 0x0f);
 735         else
 736                 count = dwarf_read_addr(p, &fde->address_range);
 737
 738         p += count;
 739
 740         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
 741                 unsigned int length;
 742                 count = dwarf_read_uleb128(p, &length);
 743                 p += count + length;
 744         }
 745
 746         /* Call frame instructions. */
 747         fde->instructions = p;
 748         fde->end = start + len;
 749
 750         /* Add to list. */
 751         spin_lock_irqsave(&dwarf_fde_lock, flags);
 752         list_add_tail(&fde->link, &dwarf_fde_list);
 753         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 754
 755         return 0;
 756 }
 757
 758 static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
 759                                 unsigned long *sp,
 760                                 const struct stacktrace_ops *ops, void *data)
 761 {
 762         struct dwarf_frame *frame;
 763
 764         frame = dwarf_unwind_stack(0, NULL);
 765
 766         while (frame && frame->return_addr) {
 767                 ops->address(data, frame->return_addr, 1);
 768                 frame = frame->next;
 769         }
 770 }
 771
 772 static struct unwinder dwarf_unwinder = {
 773         .name = "dwarf-unwinder",
 774         .dump = dwarf_unwinder_dump,
 775         .rating = 150,
 776 };
 777
 778 static void dwarf_unwinder_cleanup(void)
 779 {
 780         struct dwarf_cie *cie, *m;
 781         struct dwarf_fde *fde, *n;
 782         unsigned long flags;
 783
 784         /*
 785          * Deallocate all the memory allocated for the DWARF unwinder.
 786          * Traverse all the FDE/CIE lists and remove and free all the
 787          * memory associated with those data structures.
 788          */
 789         spin_lock_irqsave(&dwarf_cie_lock, flags);
 790         list_for_each_entry_safe(cie, m, &dwarf_cie_list, link)
 791                 kfree(cie);
 792         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 793
 794         spin_lock_irqsave(&dwarf_fde_lock, flags);
 795         list_for_each_entry_safe(fde, n, &dwarf_fde_list, link)
 796                 kfree(fde);
 797         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 798 }
 799
 800 /**
 801  *      dwarf_unwinder_init - initialise the dwarf unwinder
 802  *
 803  *      Build the data structures describing the .dwarf_frame section to
 804  *      make it easier to lookup CIE and FDE entries. Because the
 805  *      .eh_frame section is packed as tightly as possible it is not
 806  *      easy to lookup the FDE for a given PC, so we build a list of FDE
 807  *      and CIE entries that make it easier.
 808  */
 809 void dwarf_unwinder_init(void)
 810 {
 811         u32 entry_type;
 812         void *p, *entry;
 813         int count, err;
 814         unsigned long len;
 815         unsigned int c_entries, f_entries;
 816         unsigned char *end;
 817         INIT_LIST_HEAD(&dwarf_cie_list);
 818         INIT_LIST_HEAD(&dwarf_fde_list);
 819
 820         c_entries = 0;
 821         f_entries = 0;
 822         entry = &__start_eh_frame;
 823
 824         while ((char *)entry < __stop_eh_frame) {
 825                 p = entry;
 826
 827                 count = dwarf_entry_len(p, &len);
 828                 if (count == 0) {
 829                         /*
 830                          * We read a bogus length field value. There is
 831                          * nothing we can do here apart from disabling
 832                          * the DWARF unwinder. We can't even skip this
 833                          * entry and move to the next one because 'len'
 834                          * tells us where our next entry is.
 835                          */
 836                         goto out;
 837                 } else
 838                         p += count;
 839
 840                 /* initial length does not include itself */
 841                 end = p + len;
 842
 843                 entry_type = get_unaligned((u32 *)p);
 844                 p += 4;
 845
 846                 if (entry_type == DW_EH_FRAME_CIE) {
 847                         err = dwarf_parse_cie(entry, p, len, end);
 848                         if (err < 0)
 849                                 goto out;
 850                         else
 851                                 c_entries++;
 852                 } else {
 853                         err = dwarf_parse_fde(entry, entry_type, p, len);
 854                         if (err < 0)
 855                                 goto out;
 856                         else
 857                                 f_entries++;
 858                 }
 859
 860                 entry = (char *)entry + len + 4;
 861         }
 862
 863         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
 864                c_entries, f_entries);
 865
 866         err = unwinder_register(&dwarf_unwinder);
 867         if (err)
 868                 goto out;
 869
 870         return;
 871
 872 out:
 873         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
 874         dwarf_unwinder_cleanup();
 875 }