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/unaligned.h>
  25 #include <asm/dwarf.h>
  26 #include <asm/stacktrace.h>
  27
  28 static LIST_HEAD(dwarf_cie_list);
  29 static DEFINE_SPINLOCK(dwarf_cie_lock);
  30
  31 static LIST_HEAD(dwarf_fde_list);
  32 static 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_ATOMIC);
  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;
 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(cie, &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         struct dwarf_fde *fde;
 303         unsigned long flags;
 304
 305         spin_lock_irqsave(&dwarf_fde_lock, flags);
 306
 307         list_for_each_entry(fde, &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((u16 *)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((u32 *)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                 case DW_CFA_GNU_args_size:
 469                         count = dwarf_read_uleb128(current_insn, &offset);
 470                         current_insn += count;
 471                         break;
 472                 case DW_CFA_GNU_negative_offset_extended:
 473                         count = dwarf_read_uleb128(current_insn, &reg);
 474                         current_insn += count;
 475                         count = dwarf_read_uleb128(current_insn, &offset);
 476                         offset *= cie->data_alignment_factor;
 477                         dwarf_frame_alloc_regs(frame, reg);
 478                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
 479                         frame->regs[reg].addr = -offset;
 480                         break;
 481                 default:
 482                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
 483                         break;
 484                 }
 485         }
 486
 487         return 0;
 488 }
 489
 490 /**
 491  *      dwarf_unwind_stack - recursively unwind the stack
 492  *      @pc: address of the function to unwind
 493  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
 494  *
 495  *      Return a struct dwarf_frame representing the most recent frame
 496  *      on the callstack. Each of the lower (older) stack frames are
 497  *      linked via the "prev" member.
 498  */
 499 struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
 500                                        struct dwarf_frame *prev)
 501 {
 502         struct dwarf_frame *frame;
 503         struct dwarf_cie *cie;
 504         struct dwarf_fde *fde;
 505         unsigned long addr;
 506         int i, offset;
 507
 508         /*
 509          * If this is the first invocation of this recursive function we
 510          * need get the contents of a physical register to get the CFA
 511          * in order to begin the virtual unwinding of the stack.
 512          *
 513          * NOTE: the return address is guaranteed to be setup by the
 514          * time this function makes its first function call.
 515          */
 516         if (!pc && !prev)
 517                 pc = (unsigned long)current_text_addr();
 518
 519         frame = kzalloc(sizeof(*frame), GFP_ATOMIC);
 520         if (!frame)
 521                 return NULL;
 522
 523         frame->prev = prev;
 524
 525         fde = dwarf_lookup_fde(pc);
 526         if (!fde) {
 527                 /*
 528                  * This is our normal exit path - the one that stops the
 529                  * recursion. There's two reasons why we might exit
 530                  * here,
 531                  *
 532                  *      a) pc has no asscociated DWARF frame info and so
 533                  *      we don't know how to unwind this frame. This is
 534                  *      usually the case when we're trying to unwind a
 535                  *      frame that was called from some assembly code
 536                  *      that has no DWARF info, e.g. syscalls.
 537                  *
 538                  *      b) the DEBUG info for pc is bogus. There's
 539                  *      really no way to distinguish this case from the
 540                  *      case above, which sucks because we could print a
 541                  *      warning here.
 542                  */
 543                 return NULL;
 544         }
 545
 546         cie = dwarf_lookup_cie(fde->cie_pointer);
 547
 548         frame->pc = fde->initial_location;
 549
 550         /* CIE initial instructions */
 551         dwarf_cfa_execute_insns(cie->initial_instructions,
 552                                 cie->instructions_end, cie, fde,
 553                                 frame, pc);
 554
 555         /* FDE instructions */
 556         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
 557                                 fde, frame, pc);
 558
 559         /* Calculate the CFA */
 560         switch (frame->flags) {
 561         case DWARF_FRAME_CFA_REG_OFFSET:
 562                 if (prev) {
 563                         BUG_ON(!prev->regs[frame->cfa_register].flags);
 564
 565                         addr = prev->cfa;
 566                         addr += prev->regs[frame->cfa_register].addr;
 567                         frame->cfa = __raw_readl(addr);
 568
 569                 } else {
 570                         /*
 571                          * Again, this is the first invocation of this
 572                          * recurisve function. We need to physically
 573                          * read the contents of a register in order to
 574                          * get the Canonical Frame Address for this
 575                          * function.
 576                          */
 577                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
 578                 }
 579
 580                 frame->cfa += frame->cfa_offset;
 581                 break;
 582         default:
 583                 BUG();
 584         }
 585
 586         /* If we haven't seen the return address reg, we're screwed. */
 587         BUG_ON(!frame->regs[DWARF_ARCH_RA_REG].flags);
 588
 589         for (i = 0; i <= frame->num_regs; i++) {
 590                 struct dwarf_reg *reg = &frame->regs[i];
 591
 592                 if (!reg->flags)
 593                         continue;
 594
 595                 offset = reg->addr;
 596                 offset += frame->cfa;
 597         }
 598
 599         addr = frame->cfa + frame->regs[DWARF_ARCH_RA_REG].addr;
 600         frame->return_addr = __raw_readl(addr);
 601
 602         frame->next = dwarf_unwind_stack(frame->return_addr, frame);
 603         return frame;
 604 }
 605
 606 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
 607                            unsigned char *end)
 608 {
 609         struct dwarf_cie *cie;
 610         unsigned long flags;
 611         int count;
 612
 613         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
 614         if (!cie)
 615                 return -ENOMEM;
 616
 617         cie->length = len;
 618
 619         /*
 620          * Record the offset into the .eh_frame section
 621          * for this CIE. It allows this CIE to be
 622          * quickly and easily looked up from the
 623          * corresponding FDE.
 624          */
 625         cie->cie_pointer = (unsigned long)entry;
 626
 627         cie->version = *(char *)p++;
 628         BUG_ON(cie->version != 1);
 629
 630         cie->augmentation = p;
 631         p += strlen(cie->augmentation) + 1;
 632
 633         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
 634         p += count;
 635
 636         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
 637         p += count;
 638
 639         /*
 640          * Which column in the rule table contains the
 641          * return address?
 642          */
 643         if (cie->version == 1) {
 644                 cie->return_address_reg = __raw_readb(p);
 645                 p++;
 646         } else {
 647                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
 648                 p += count;
 649         }
 650
 651         if (cie->augmentation[0] == 'z') {
 652                 unsigned int length, count;
 653                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
 654
 655                 count = dwarf_read_uleb128(p, &length);
 656                 p += count;
 657
 658                 BUG_ON((unsigned char *)p > end);
 659
 660                 cie->initial_instructions = p + length;
 661                 cie->augmentation++;
 662         }
 663
 664         while (*cie->augmentation) {
 665                 /*
 666                  * "L" indicates a byte showing how the
 667                  * LSDA pointer is encoded. Skip it.
 668                  */
 669                 if (*cie->augmentation == 'L') {
 670                         p++;
 671                         cie->augmentation++;
 672                 } else if (*cie->augmentation == 'R') {
 673                         /*
 674                          * "R" indicates a byte showing
 675                          * how FDE addresses are
 676                          * encoded.
 677                          */
 678                         cie->encoding = *(char *)p++;
 679                         cie->augmentation++;
 680                 } else if (*cie->augmentation == 'P') {
 681                         /*
 682                          * "R" indicates a personality
 683                          * routine in the CIE
 684                          * augmentation.
 685                          */
 686                         BUG();
 687                 } else if (*cie->augmentation == 'S') {
 688                         BUG();
 689                 } else {
 690                         /*
 691                          * Unknown augmentation. Assume
 692                          * 'z' augmentation.
 693                          */
 694                         p = cie->initial_instructions;
 695                         BUG_ON(!p);
 696                         break;
 697                 }
 698         }
 699
 700         cie->initial_instructions = p;
 701         cie->instructions_end = end;
 702
 703         /* Add to list */
 704         spin_lock_irqsave(&dwarf_cie_lock, flags);
 705         list_add_tail(&cie->link, &dwarf_cie_list);
 706         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 707
 708         return 0;
 709 }
 710
 711 static int dwarf_parse_fde(void *entry, u32 entry_type,
 712                            void *start, unsigned long len)
 713 {
 714         struct dwarf_fde *fde;
 715         struct dwarf_cie *cie;
 716         unsigned long flags;
 717         int count;
 718         void *p = start;
 719
 720         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
 721         if (!fde)
 722                 return -ENOMEM;
 723
 724         fde->length = len;
 725
 726         /*
 727          * In a .eh_frame section the CIE pointer is the
 728          * delta between the address within the FDE
 729          */
 730         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
 731
 732         cie = dwarf_lookup_cie(fde->cie_pointer);
 733         fde->cie = cie;
 734
 735         if (cie->encoding)
 736                 count = dwarf_read_encoded_value(p, &fde->initial_location,
 737                                                  cie->encoding);
 738         else
 739                 count = dwarf_read_addr(p, &fde->initial_location);
 740
 741         p += count;
 742
 743         if (cie->encoding)
 744                 count = dwarf_read_encoded_value(p, &fde->address_range,
 745                                                  cie->encoding & 0x0f);
 746         else
 747                 count = dwarf_read_addr(p, &fde->address_range);
 748
 749         p += count;
 750
 751         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
 752                 unsigned int length;
 753                 count = dwarf_read_uleb128(p, &length);
 754                 p += count + length;
 755         }
 756
 757         /* Call frame instructions. */
 758         fde->instructions = p;
 759         fde->end = start + len;
 760
 761         /* Add to list. */
 762         spin_lock_irqsave(&dwarf_fde_lock, flags);
 763         list_add_tail(&fde->link, &dwarf_fde_list);
 764         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 765
 766         return 0;
 767 }
 768
 769 static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
 770                                 unsigned long *sp,
 771                                 const struct stacktrace_ops *ops, void *data)
 772 {
 773         struct dwarf_frame *frame;
 774
 775         frame = dwarf_unwind_stack(0, NULL);
 776
 777         while (frame && frame->return_addr) {
 778                 ops->address(data, frame->return_addr, 1);
 779                 frame = frame->next;
 780         }
 781 }
 782
 783 static struct unwinder dwarf_unwinder = {
 784         .name = "dwarf-unwinder",
 785         .dump = dwarf_unwinder_dump,
 786         .rating = 150,
 787 };
 788
 789 static void dwarf_unwinder_cleanup(void)
 790 {
 791         struct dwarf_cie *cie;
 792         struct dwarf_fde *fde;
 793
 794         /*
 795          * Deallocate all the memory allocated for the DWARF unwinder.
 796          * Traverse all the FDE/CIE lists and remove and free all the
 797          * memory associated with those data structures.
 798          */
 799         list_for_each_entry(cie, &dwarf_cie_list, link)
 800                 kfree(cie);
 801
 802         list_for_each_entry(fde, &dwarf_fde_list, link)
 803                 kfree(fde);
 804 }
 805
 806 /**
 807  *      dwarf_unwinder_init - initialise the dwarf unwinder
 808  *
 809  *      Build the data structures describing the .dwarf_frame section to
 810  *      make it easier to lookup CIE and FDE entries. Because the
 811  *      .eh_frame section is packed as tightly as possible it is not
 812  *      easy to lookup the FDE for a given PC, so we build a list of FDE
 813  *      and CIE entries that make it easier.
 814  */
 815 static int __init dwarf_unwinder_init(void)
 816 {
 817         u32 entry_type;
 818         void *p, *entry;
 819         int count, err;
 820         unsigned long len;
 821         unsigned int c_entries, f_entries;
 822         unsigned char *end;
 823         INIT_LIST_HEAD(&dwarf_cie_list);
 824         INIT_LIST_HEAD(&dwarf_fde_list);
 825
 826         c_entries = 0;
 827         f_entries = 0;
 828         entry = &__start_eh_frame;
 829
 830         while ((char *)entry < __stop_eh_frame) {
 831                 p = entry;
 832
 833                 count = dwarf_entry_len(p, &len);
 834                 if (count == 0) {
 835                         /*
 836                          * We read a bogus length field value. There is
 837                          * nothing we can do here apart from disabling
 838                          * the DWARF unwinder. We can't even skip this
 839                          * entry and move to the next one because 'len'
 840                          * tells us where our next entry is.
 841                          */
 842                         goto out;
 843                 } else
 844                         p += count;
 845
 846                 /* initial length does not include itself */
 847                 end = p + len;
 848
 849                 entry_type = get_unaligned((u32 *)p);
 850                 p += 4;
 851
 852                 if (entry_type == DW_EH_FRAME_CIE) {
 853                         err = dwarf_parse_cie(entry, p, len, end);
 854                         if (err < 0)
 855                                 goto out;
 856                         else
 857                                 c_entries++;
 858                 } else {
 859                         err = dwarf_parse_fde(entry, entry_type, p, len);
 860                         if (err < 0)
 861                                 goto out;
 862                         else
 863                                 f_entries++;
 864                 }
 865
 866                 entry = (char *)entry + len + 4;
 867         }
 868
 869         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
 870                c_entries, f_entries);
 871
 872         err = unwinder_register(&dwarf_unwinder);
 873         if (err)
 874                 goto out;
 875
 876         return 0;
 877
 878 out:
 879         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
 880         dwarf_unwinder_cleanup();
 881         return -EINVAL;
 882 }
 883 early_initcall(dwarf_unwinder_init);