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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  *      @define_ra: keep executing insns until the return addr reg is defined?
 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                                    bool define_ra)
 347 {
 348         unsigned char insn;
 349         unsigned char *current_insn;
 350         unsigned int count, delta, reg, expr_len, offset;
 351         bool seen_ra_reg;
 352
 353         current_insn = insn_start;
 354
 355         /*
 356          * If we're executing instructions for the dwarf_unwind_stack()
 357          * FDE we need to keep executing instructions until the value of
 358          * DWARF_ARCH_RA_REG is defined. See the comment in
 359          * dwarf_unwind_stack() for more details.
 360          */
 361         if (define_ra)
 362                 seen_ra_reg = false;
 363         else
 364                 seen_ra_reg = true;
 365
 366         while (current_insn < insn_end && (frame->pc <= pc || !seen_ra_reg) ) {
 367                 insn = __raw_readb(current_insn++);
 368
 369                 if (!seen_ra_reg) {
 370                         if (frame->num_regs >= DWARF_ARCH_RA_REG &&
 371                             frame->regs[DWARF_ARCH_RA_REG].flags)
 372                                 seen_ra_reg = true;
 373                 }
 374
 375                 /*
 376                  * Firstly, handle the opcodes that embed their operands
 377                  * in the instructions.
 378                  */
 379                 switch (DW_CFA_opcode(insn)) {
 380                 case DW_CFA_advance_loc:
 381                         delta = DW_CFA_operand(insn);
 382                         delta *= cie->code_alignment_factor;
 383                         frame->pc += delta;
 384                         continue;
 385                         /* NOTREACHED */
 386                 case DW_CFA_offset:
 387                         reg = DW_CFA_operand(insn);
 388                         count = dwarf_read_uleb128(current_insn, &offset);
 389                         current_insn += count;
 390                         offset *= cie->data_alignment_factor;
 391                         dwarf_frame_alloc_regs(frame, reg);
 392                         frame->regs[reg].addr = offset;
 393                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 394                         continue;
 395                         /* NOTREACHED */
 396                 case DW_CFA_restore:
 397                         reg = DW_CFA_operand(insn);
 398                         continue;
 399                         /* NOTREACHED */
 400                 }
 401
 402                 /*
 403                  * Secondly, handle the opcodes that don't embed their
 404                  * operands in the instruction.
 405                  */
 406                 switch (insn) {
 407                 case DW_CFA_nop:
 408                         continue;
 409                 case DW_CFA_advance_loc1:
 410                         delta = *current_insn++;
 411                         frame->pc += delta * cie->code_alignment_factor;
 412                         break;
 413                 case DW_CFA_advance_loc2:
 414                         delta = get_unaligned((u16 *)current_insn);
 415                         current_insn += 2;
 416                         frame->pc += delta * cie->code_alignment_factor;
 417                         break;
 418                 case DW_CFA_advance_loc4:
 419                         delta = get_unaligned((u32 *)current_insn);
 420                         current_insn += 4;
 421                         frame->pc += delta * cie->code_alignment_factor;
 422                         break;
 423                 case DW_CFA_offset_extended:
 424                         count = dwarf_read_uleb128(current_insn, &reg);
 425                         current_insn += count;
 426                         count = dwarf_read_uleb128(current_insn, &offset);
 427                         current_insn += count;
 428                         offset *= cie->data_alignment_factor;
 429                         break;
 430                 case DW_CFA_restore_extended:
 431                         count = dwarf_read_uleb128(current_insn, &reg);
 432                         current_insn += count;
 433                         break;
 434                 case DW_CFA_undefined:
 435                         count = dwarf_read_uleb128(current_insn, &reg);
 436                         current_insn += count;
 437                         break;
 438                 case DW_CFA_def_cfa:
 439                         count = dwarf_read_uleb128(current_insn,
 440                                                    &frame->cfa_register);
 441                         current_insn += count;
 442                         count = dwarf_read_uleb128(current_insn,
 443                                                    &frame->cfa_offset);
 444                         current_insn += count;
 445
 446                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 447                         break;
 448                 case DW_CFA_def_cfa_register:
 449                         count = dwarf_read_uleb128(current_insn,
 450                                                    &frame->cfa_register);
 451                         current_insn += count;
 452                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 453                         break;
 454                 case DW_CFA_def_cfa_offset:
 455                         count = dwarf_read_uleb128(current_insn, &offset);
 456                         current_insn += count;
 457                         frame->cfa_offset = offset;
 458                         break;
 459                 case DW_CFA_def_cfa_expression:
 460                         count = dwarf_read_uleb128(current_insn, &expr_len);
 461                         current_insn += count;
 462
 463                         frame->cfa_expr = current_insn;
 464                         frame->cfa_expr_len = expr_len;
 465                         current_insn += expr_len;
 466
 467                         frame->flags |= DWARF_FRAME_CFA_REG_EXP;
 468                         break;
 469                 case DW_CFA_offset_extended_sf:
 470                         count = dwarf_read_uleb128(current_insn, &reg);
 471                         current_insn += count;
 472                         count = dwarf_read_leb128(current_insn, &offset);
 473                         current_insn += count;
 474                         offset *= cie->data_alignment_factor;
 475                         dwarf_frame_alloc_regs(frame, reg);
 476                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 477                         frame->regs[reg].addr = offset;
 478                         break;
 479                 case DW_CFA_val_offset:
 480                         count = dwarf_read_uleb128(current_insn, &reg);
 481                         current_insn += count;
 482                         count = dwarf_read_leb128(current_insn, &offset);
 483                         offset *= cie->data_alignment_factor;
 484                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 485                         frame->regs[reg].addr = offset;
 486                         break;
 487                 default:
 488                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
 489                         break;
 490                 }
 491         }
 492
 493         return 0;
 494 }
 495
 496 /**
 497  *      dwarf_unwind_stack - recursively unwind the stack
 498  *      @pc: address of the function to unwind
 499  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
 500  *
 501  *      Return a struct dwarf_frame representing the most recent frame
 502  *      on the callstack. Each of the lower (older) stack frames are
 503  *      linked via the "prev" member.
 504  */
 505 struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
 506                                        struct dwarf_frame *prev)
 507 {
 508         struct dwarf_frame *frame;
 509         struct dwarf_cie *cie;
 510         struct dwarf_fde *fde;
 511         unsigned long addr;
 512         int i, offset;
 513         bool define_ra = false;
 514
 515         /*
 516          * If this is the first invocation of this recursive function we
 517          * need get the contents of a physical register to get the CFA
 518          * in order to begin the virtual unwinding of the stack.
 519          *
 520          * Setting "define_ra" to true indictates that we want
 521          * dwarf_cfa_execute_insns() to continue executing instructions
 522          * until we know how to calculate the value of DWARF_ARCH_RA_REG
 523          * (which we need in order to kick off the whole unwinding
 524          * process).
 525          *
 526          * NOTE: the return address is guaranteed to be setup by the
 527          * time this function makes its first function call.
 528          */
 529         if (!pc && !prev) {
 530                 pc = (unsigned long)&dwarf_unwind_stack;
 531                 define_ra = true;
 532         }
 533
 534         frame = kzalloc(sizeof(*frame), GFP_KERNEL);
 535         if (!frame)
 536                 return NULL;
 537
 538         frame->prev = prev;
 539
 540         fde = dwarf_lookup_fde(pc);
 541         if (!fde) {
 542                 /*
 543                  * This is our normal exit path - the one that stops the
 544                  * recursion. There's two reasons why we might exit
 545                  * here,
 546                  *
 547                  *      a) pc has no asscociated DWARF frame info and so
 548                  *      we don't know how to unwind this frame. This is
 549                  *      usually the case when we're trying to unwind a
 550                  *      frame that was called from some assembly code
 551                  *      that has no DWARF info, e.g. syscalls.
 552                  *
 553                  *      b) the DEBUG info for pc is bogus. There's
 554                  *      really no way to distinguish this case from the
 555                  *      case above, which sucks because we could print a
 556                  *      warning here.
 557                  */
 558                 return NULL;
 559         }
 560
 561         cie = dwarf_lookup_cie(fde->cie_pointer);
 562
 563         frame->pc = fde->initial_location;
 564
 565         /* CIE initial instructions */
 566         dwarf_cfa_execute_insns(cie->initial_instructions,
 567                                 cie->instructions_end, cie, fde,
 568                                 frame, pc, false);
 569
 570         /* FDE instructions */
 571         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
 572                                 fde, frame, pc, define_ra);
 573
 574         /* Calculate the CFA */
 575         switch (frame->flags) {
 576         case DWARF_FRAME_CFA_REG_OFFSET:
 577                 if (prev) {
 578                         BUG_ON(!prev->regs[frame->cfa_register].flags);
 579
 580                         addr = prev->cfa;
 581                         addr += prev->regs[frame->cfa_register].addr;
 582                         frame->cfa = __raw_readl(addr);
 583
 584                 } else {
 585                         /*
 586                          * Again, this is the first invocation of this
 587                          * recurisve function. We need to physically
 588                          * read the contents of a register in order to
 589                          * get the Canonical Frame Address for this
 590                          * function.
 591                          */
 592                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
 593                 }
 594
 595                 frame->cfa += frame->cfa_offset;
 596                 break;
 597         default:
 598                 BUG();
 599         }
 600
 601         /* If we haven't seen the return address reg, we're screwed. */
 602         BUG_ON(!frame->regs[DWARF_ARCH_RA_REG].flags);
 603
 604         for (i = 0; i <= frame->num_regs; i++) {
 605                 struct dwarf_reg *reg = &frame->regs[i];
 606
 607                 if (!reg->flags)
 608                         continue;
 609
 610                 offset = reg->addr;
 611                 offset += frame->cfa;
 612         }
 613
 614         addr = frame->cfa + frame->regs[DWARF_ARCH_RA_REG].addr;
 615         frame->return_addr = __raw_readl(addr);
 616
 617         frame->next = dwarf_unwind_stack(frame->return_addr, frame);
 618         return frame;
 619 }
 620
 621 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
 622                            unsigned char *end)
 623 {
 624         struct dwarf_cie *cie;
 625         unsigned long flags;
 626         int count;
 627
 628         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
 629         if (!cie)
 630                 return -ENOMEM;
 631
 632         cie->length = len;
 633
 634         /*
 635          * Record the offset into the .eh_frame section
 636          * for this CIE. It allows this CIE to be
 637          * quickly and easily looked up from the
 638          * corresponding FDE.
 639          */
 640         cie->cie_pointer = (unsigned long)entry;
 641
 642         cie->version = *(char *)p++;
 643         BUG_ON(cie->version != 1);
 644
 645         cie->augmentation = p;
 646         p += strlen(cie->augmentation) + 1;
 647
 648         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
 649         p += count;
 650
 651         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
 652         p += count;
 653
 654         /*
 655          * Which column in the rule table contains the
 656          * return address?
 657          */
 658         if (cie->version == 1) {
 659                 cie->return_address_reg = __raw_readb(p);
 660                 p++;
 661         } else {
 662                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
 663                 p += count;
 664         }
 665
 666         if (cie->augmentation[0] == 'z') {
 667                 unsigned int length, count;
 668                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
 669
 670                 count = dwarf_read_uleb128(p, &length);
 671                 p += count;
 672
 673                 BUG_ON((unsigned char *)p > end);
 674
 675                 cie->initial_instructions = p + length;
 676                 cie->augmentation++;
 677         }
 678
 679         while (*cie->augmentation) {
 680                 /*
 681                  * "L" indicates a byte showing how the
 682                  * LSDA pointer is encoded. Skip it.
 683                  */
 684                 if (*cie->augmentation == 'L') {
 685                         p++;
 686                         cie->augmentation++;
 687                 } else if (*cie->augmentation == 'R') {
 688                         /*
 689                          * "R" indicates a byte showing
 690                          * how FDE addresses are
 691                          * encoded.
 692                          */
 693                         cie->encoding = *(char *)p++;
 694                         cie->augmentation++;
 695                 } else if (*cie->augmentation == 'P') {
 696                         /*
 697                          * "R" indicates a personality
 698                          * routine in the CIE
 699                          * augmentation.
 700                          */
 701                         BUG();
 702                 } else if (*cie->augmentation == 'S') {
 703                         BUG();
 704                 } else {
 705                         /*
 706                          * Unknown augmentation. Assume
 707                          * 'z' augmentation.
 708                          */
 709                         p = cie->initial_instructions;
 710                         BUG_ON(!p);
 711                         break;
 712                 }
 713         }
 714
 715         cie->initial_instructions = p;
 716         cie->instructions_end = end;
 717
 718         /* Add to list */
 719         spin_lock_irqsave(&dwarf_cie_lock, flags);
 720         list_add_tail(&cie->link, &dwarf_cie_list);
 721         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 722
 723         return 0;
 724 }
 725
 726 static int dwarf_parse_fde(void *entry, u32 entry_type,
 727                            void *start, unsigned long len)
 728 {
 729         struct dwarf_fde *fde;
 730         struct dwarf_cie *cie;
 731         unsigned long flags;
 732         int count;
 733         void *p = start;
 734
 735         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
 736         if (!fde)
 737                 return -ENOMEM;
 738
 739         fde->length = len;
 740
 741         /*
 742          * In a .eh_frame section the CIE pointer is the
 743          * delta between the address within the FDE
 744          */
 745         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
 746
 747         cie = dwarf_lookup_cie(fde->cie_pointer);
 748         fde->cie = cie;
 749
 750         if (cie->encoding)
 751                 count = dwarf_read_encoded_value(p, &fde->initial_location,
 752                                                  cie->encoding);
 753         else
 754                 count = dwarf_read_addr(p, &fde->initial_location);
 755
 756         p += count;
 757
 758         if (cie->encoding)
 759                 count = dwarf_read_encoded_value(p, &fde->address_range,
 760                                                  cie->encoding & 0x0f);
 761         else
 762                 count = dwarf_read_addr(p, &fde->address_range);
 763
 764         p += count;
 765
 766         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
 767                 unsigned int length;
 768                 count = dwarf_read_uleb128(p, &length);
 769                 p += count + length;
 770         }
 771
 772         /* Call frame instructions. */
 773         fde->instructions = p;
 774         fde->end = start + len;
 775
 776         /* Add to list. */
 777         spin_lock_irqsave(&dwarf_fde_lock, flags);
 778         list_add_tail(&fde->link, &dwarf_fde_list);
 779         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 780
 781         return 0;
 782 }
 783
 784 static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
 785                                 unsigned long *sp,
 786                                 const struct stacktrace_ops *ops, void *data)
 787 {
 788         struct dwarf_frame *frame;
 789
 790         frame = dwarf_unwind_stack(0, NULL);
 791
 792         while (frame && frame->return_addr) {
 793                 ops->address(data, frame->return_addr, 1);
 794                 frame = frame->next;
 795         }
 796 }
 797
 798 static struct unwinder dwarf_unwinder = {
 799         .name = "dwarf-unwinder",
 800         .dump = dwarf_unwinder_dump,
 801         .rating = 150,
 802 };
 803
 804 static void dwarf_unwinder_cleanup(void)
 805 {
 806         struct dwarf_cie *cie, *m;
 807         struct dwarf_fde *fde, *n;
 808         unsigned long flags;
 809
 810         /*
 811          * Deallocate all the memory allocated for the DWARF unwinder.
 812          * Traverse all the FDE/CIE lists and remove and free all the
 813          * memory associated with those data structures.
 814          */
 815         spin_lock_irqsave(&dwarf_cie_lock, flags);
 816         list_for_each_entry_safe(cie, m, &dwarf_cie_list, link)
 817                 kfree(cie);
 818         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 819
 820         spin_lock_irqsave(&dwarf_fde_lock, flags);
 821         list_for_each_entry_safe(fde, n, &dwarf_fde_list, link)
 822                 kfree(fde);
 823         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 824 }
 825
 826 /**
 827  *      dwarf_unwinder_init - initialise the dwarf unwinder
 828  *
 829  *      Build the data structures describing the .dwarf_frame section to
 830  *      make it easier to lookup CIE and FDE entries. Because the
 831  *      .eh_frame section is packed as tightly as possible it is not
 832  *      easy to lookup the FDE for a given PC, so we build a list of FDE
 833  *      and CIE entries that make it easier.
 834  */
 835 void dwarf_unwinder_init(void)
 836 {
 837         u32 entry_type;
 838         void *p, *entry;
 839         int count, err;
 840         unsigned long len;
 841         unsigned int c_entries, f_entries;
 842         unsigned char *end;
 843         INIT_LIST_HEAD(&dwarf_cie_list);
 844         INIT_LIST_HEAD(&dwarf_fde_list);
 845
 846         c_entries = 0;
 847         f_entries = 0;
 848         entry = &__start_eh_frame;
 849
 850         while ((char *)entry < __stop_eh_frame) {
 851                 p = entry;
 852
 853                 count = dwarf_entry_len(p, &len);
 854                 if (count == 0) {
 855                         /*
 856                          * We read a bogus length field value. There is
 857                          * nothing we can do here apart from disabling
 858                          * the DWARF unwinder. We can't even skip this
 859                          * entry and move to the next one because 'len'
 860                          * tells us where our next entry is.
 861                          */
 862                         goto out;
 863                 } else
 864                         p += count;
 865
 866                 /* initial length does not include itself */
 867                 end = p + len;
 868
 869                 entry_type = get_unaligned((u32 *)p);
 870                 p += 4;
 871
 872                 if (entry_type == DW_EH_FRAME_CIE) {
 873                         err = dwarf_parse_cie(entry, p, len, end);
 874                         if (err < 0)
 875                                 goto out;
 876                         else
 877                                 c_entries++;
 878                 } else {
 879                         err = dwarf_parse_fde(entry, entry_type, p, len);
 880                         if (err < 0)
 881                                 goto out;
 882                         else
 883                                 f_entries++;
 884                 }
 885
 886                 entry = (char *)entry + len + 4;
 887         }
 888
 889         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
 890                c_entries, f_entries);
 891
 892         err = unwinder_register(&dwarf_unwinder);
 893         if (err)
 894                 goto out;
 895
 896         return;
 897
 898 out:
 899         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
 900         dwarf_unwinder_cleanup();
 901 }