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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  *      - Registers with DWARF_VAL_OFFSET rules aren't handled properly.
  15  */
  16
  17 /* #define DEBUG */
  18 #include <linux/kernel.h>
  19 #include <linux/io.h>
  20 #include <linux/list.h>
  21 #include <linux/mempool.h>
  22 #include <linux/mm.h>
  23 #include <asm/dwarf.h>
  24 #include <asm/unwinder.h>
  25 #include <asm/sections.h>
  26 #include <asm/unaligned.h>
  27 #include <asm/dwarf.h>
  28 #include <asm/stacktrace.h>
  29
  30 /* Reserve enough memory for two stack frames */
  31 #define DWARF_FRAME_MIN_REQ     2
  32 /* ... with 4 registers per frame. */
  33 #define DWARF_REG_MIN_REQ       (DWARF_FRAME_MIN_REQ * 4)
  34
  35 static struct kmem_cache *dwarf_frame_cachep;
  36 static mempool_t *dwarf_frame_pool;
  37
  38 static struct kmem_cache *dwarf_reg_cachep;
  39 static mempool_t *dwarf_reg_pool;
  40
  41 static LIST_HEAD(dwarf_cie_list);
  42 static DEFINE_SPINLOCK(dwarf_cie_lock);
  43
  44 static LIST_HEAD(dwarf_fde_list);
  45 static DEFINE_SPINLOCK(dwarf_fde_lock);
  46
  47 static struct dwarf_cie *cached_cie;
  48
  49 /**
  50  *      dwarf_frame_alloc_reg - allocate memory for a DWARF register
  51  *      @frame: the DWARF frame whose list of registers we insert on
  52  *      @reg_num: the register number
  53  *
  54  *      Allocate space for, and initialise, a dwarf reg from
  55  *      dwarf_reg_pool and insert it onto the (unsorted) linked-list of
  56  *      dwarf registers for @frame.
  57  *
  58  *      Return the initialised DWARF reg.
  59  */
  60 static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
  61                                                unsigned int reg_num)
  62 {
  63         struct dwarf_reg *reg;
  64
  65         reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC);
  66         if (!reg) {
  67                 printk(KERN_WARNING "Unable to allocate a DWARF register\n");
  68                 /*
  69                  * Let's just bomb hard here, we have no way to
  70                  * gracefully recover.
  71                  */
  72                 UNWINDER_BUG();
  73         }
  74
  75         reg->number = reg_num;
  76         reg->addr = 0;
  77         reg->flags = 0;
  78
  79         list_add(&reg->link, &frame->reg_list);
  80
  81         return reg;
  82 }
  83
  84 static void dwarf_frame_free_regs(struct dwarf_frame *frame)
  85 {
  86         struct dwarf_reg *reg, *n;
  87
  88         list_for_each_entry_safe(reg, n, &frame->reg_list, link) {
  89                 list_del(&reg->link);
  90                 mempool_free(reg, dwarf_reg_pool);
  91         }
  92 }
  93
  94 /**
  95  *      dwarf_frame_reg - return a DWARF register
  96  *      @frame: the DWARF frame to search in for @reg_num
  97  *      @reg_num: the register number to search for
  98  *
  99  *      Lookup and return the dwarf reg @reg_num for this frame. Return
 100  *      NULL if @reg_num is an register invalid number.
 101  */
 102 static struct dwarf_reg *dwarf_frame_reg(struct dwarf_frame *frame,
 103                                          unsigned int reg_num)
 104 {
 105         struct dwarf_reg *reg;
 106
 107         list_for_each_entry(reg, &frame->reg_list, link) {
 108                 if (reg->number == reg_num)
 109                         return reg;
 110         }
 111
 112         return NULL;
 113 }
 114
 115 /**
 116  *      dwarf_read_addr - read dwarf data
 117  *      @src: source address of data
 118  *      @dst: destination address to store the data to
 119  *
 120  *      Read 'n' bytes from @src, where 'n' is the size of an address on
 121  *      the native machine. We return the number of bytes read, which
 122  *      should always be 'n'. We also have to be careful when reading
 123  *      from @src and writing to @dst, because they can be arbitrarily
 124  *      aligned. Return 'n' - the number of bytes read.
 125  */
 126 static inline int dwarf_read_addr(unsigned long *src, unsigned long *dst)
 127 {
 128         u32 val = get_unaligned(src);
 129         put_unaligned(val, dst);
 130         return sizeof(unsigned long *);
 131 }
 132
 133 /**
 134  *      dwarf_read_uleb128 - read unsigned LEB128 data
 135  *      @addr: the address where the ULEB128 data is stored
 136  *      @ret: address to store the result
 137  *
 138  *      Decode an unsigned LEB128 encoded datum. The algorithm is taken
 139  *      from Appendix C of the DWARF 3 spec. For information on the
 140  *      encodings refer to section "7.6 - Variable Length Data". Return
 141  *      the number of bytes read.
 142  */
 143 static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
 144 {
 145         unsigned int result;
 146         unsigned char byte;
 147         int shift, count;
 148
 149         result = 0;
 150         shift = 0;
 151         count = 0;
 152
 153         while (1) {
 154                 byte = __raw_readb(addr);
 155                 addr++;
 156                 count++;
 157
 158                 result |= (byte & 0x7f) << shift;
 159                 shift += 7;
 160
 161                 if (!(byte & 0x80))
 162                         break;
 163         }
 164
 165         *ret = result;
 166
 167         return count;
 168 }
 169
 170 /**
 171  *      dwarf_read_leb128 - read signed LEB128 data
 172  *      @addr: the address of the LEB128 encoded data
 173  *      @ret: address to store the result
 174  *
 175  *      Decode signed LEB128 data. The algorithm is taken from Appendix
 176  *      C of the DWARF 3 spec. Return the number of bytes read.
 177  */
 178 static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
 179 {
 180         unsigned char byte;
 181         int result, shift;
 182         int num_bits;
 183         int count;
 184
 185         result = 0;
 186         shift = 0;
 187         count = 0;
 188
 189         while (1) {
 190                 byte = __raw_readb(addr);
 191                 addr++;
 192                 result |= (byte & 0x7f) << shift;
 193                 shift += 7;
 194                 count++;
 195
 196                 if (!(byte & 0x80))
 197                         break;
 198         }
 199
 200         /* The number of bits in a signed integer. */
 201         num_bits = 8 * sizeof(result);
 202
 203         if ((shift < num_bits) && (byte & 0x40))
 204                 result |= (-1 << shift);
 205
 206         *ret = result;
 207
 208         return count;
 209 }
 210
 211 /**
 212  *      dwarf_read_encoded_value - return the decoded value at @addr
 213  *      @addr: the address of the encoded value
 214  *      @val: where to write the decoded value
 215  *      @encoding: the encoding with which we can decode @addr
 216  *
 217  *      GCC emits encoded address in the .eh_frame FDE entries. Decode
 218  *      the value at @addr using @encoding. The decoded value is written
 219  *      to @val and the number of bytes read is returned.
 220  */
 221 static int dwarf_read_encoded_value(char *addr, unsigned long *val,
 222                                     char encoding)
 223 {
 224         unsigned long decoded_addr = 0;
 225         int count = 0;
 226
 227         switch (encoding & 0x70) {
 228         case DW_EH_PE_absptr:
 229                 break;
 230         case DW_EH_PE_pcrel:
 231                 decoded_addr = (unsigned long)addr;
 232                 break;
 233         default:
 234                 pr_debug("encoding=0x%x\n", (encoding & 0x70));
 235                 UNWINDER_BUG();
 236         }
 237
 238         if ((encoding & 0x07) == 0x00)
 239                 encoding |= DW_EH_PE_udata4;
 240
 241         switch (encoding & 0x0f) {
 242         case DW_EH_PE_sdata4:
 243         case DW_EH_PE_udata4:
 244                 count += 4;
 245                 decoded_addr += get_unaligned((u32 *)addr);
 246                 __raw_writel(decoded_addr, val);
 247                 break;
 248         default:
 249                 pr_debug("encoding=0x%x\n", encoding);
 250                 UNWINDER_BUG();
 251         }
 252
 253         return count;
 254 }
 255
 256 /**
 257  *      dwarf_entry_len - return the length of an FDE or CIE
 258  *      @addr: the address of the entry
 259  *      @len: the length of the entry
 260  *
 261  *      Read the initial_length field of the entry and store the size of
 262  *      the entry in @len. We return the number of bytes read. Return a
 263  *      count of 0 on error.
 264  */
 265 static inline int dwarf_entry_len(char *addr, unsigned long *len)
 266 {
 267         u32 initial_len;
 268         int count;
 269
 270         initial_len = get_unaligned((u32 *)addr);
 271         count = 4;
 272
 273         /*
 274          * An initial length field value in the range DW_LEN_EXT_LO -
 275          * DW_LEN_EXT_HI indicates an extension, and should not be
 276          * interpreted as a length. The only extension that we currently
 277          * understand is the use of DWARF64 addresses.
 278          */
 279         if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
 280                 /*
 281                  * The 64-bit length field immediately follows the
 282                  * compulsory 32-bit length field.
 283                  */
 284                 if (initial_len == DW_EXT_DWARF64) {
 285                         *len = get_unaligned((u64 *)addr + 4);
 286                         count = 12;
 287                 } else {
 288                         printk(KERN_WARNING "Unknown DWARF extension\n");
 289                         count = 0;
 290                 }
 291         } else
 292                 *len = initial_len;
 293
 294         return count;
 295 }
 296
 297 /**
 298  *      dwarf_lookup_cie - locate the cie
 299  *      @cie_ptr: pointer to help with lookup
 300  */
 301 static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
 302 {
 303         struct dwarf_cie *cie;
 304         unsigned long flags;
 305
 306         spin_lock_irqsave(&dwarf_cie_lock, flags);
 307
 308         /*
 309          * We've cached the last CIE we looked up because chances are
 310          * that the FDE wants this CIE.
 311          */
 312         if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
 313                 cie = cached_cie;
 314                 goto out;
 315         }
 316
 317         list_for_each_entry(cie, &dwarf_cie_list, link) {
 318                 if (cie->cie_pointer == cie_ptr) {
 319                         cached_cie = cie;
 320                         break;
 321                 }
 322         }
 323
 324         /* Couldn't find the entry in the list. */
 325         if (&cie->link == &dwarf_cie_list)
 326                 cie = NULL;
 327 out:
 328         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 329         return cie;
 330 }
 331
 332 /**
 333  *      dwarf_lookup_fde - locate the FDE that covers pc
 334  *      @pc: the program counter
 335  */
 336 struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
 337 {
 338         struct dwarf_fde *fde;
 339         unsigned long flags;
 340
 341         spin_lock_irqsave(&dwarf_fde_lock, flags);
 342
 343         list_for_each_entry(fde, &dwarf_fde_list, link) {
 344                 unsigned long start, end;
 345
 346                 start = fde->initial_location;
 347                 end = fde->initial_location + fde->address_range;
 348
 349                 if (pc >= start && pc < end)
 350                         break;
 351         }
 352
 353         /* Couldn't find the entry in the list. */
 354         if (&fde->link == &dwarf_fde_list)
 355                 fde = NULL;
 356
 357         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 358
 359         return fde;
 360 }
 361
 362 /**
 363  *      dwarf_cfa_execute_insns - execute instructions to calculate a CFA
 364  *      @insn_start: address of the first instruction
 365  *      @insn_end: address of the last instruction
 366  *      @cie: the CIE for this function
 367  *      @fde: the FDE for this function
 368  *      @frame: the instructions calculate the CFA for this frame
 369  *      @pc: the program counter of the address we're interested in
 370  *
 371  *      Execute the Call Frame instruction sequence starting at
 372  *      @insn_start and ending at @insn_end. The instructions describe
 373  *      how to calculate the Canonical Frame Address of a stackframe.
 374  *      Store the results in @frame.
 375  */
 376 static int dwarf_cfa_execute_insns(unsigned char *insn_start,
 377                                    unsigned char *insn_end,
 378                                    struct dwarf_cie *cie,
 379                                    struct dwarf_fde *fde,
 380                                    struct dwarf_frame *frame,
 381                                    unsigned long pc)
 382 {
 383         unsigned char insn;
 384         unsigned char *current_insn;
 385         unsigned int count, delta, reg, expr_len, offset;
 386         struct dwarf_reg *regp;
 387
 388         current_insn = insn_start;
 389
 390         while (current_insn < insn_end && frame->pc <= pc) {
 391                 insn = __raw_readb(current_insn++);
 392
 393                 /*
 394                  * Firstly, handle the opcodes that embed their operands
 395                  * in the instructions.
 396                  */
 397                 switch (DW_CFA_opcode(insn)) {
 398                 case DW_CFA_advance_loc:
 399                         delta = DW_CFA_operand(insn);
 400                         delta *= cie->code_alignment_factor;
 401                         frame->pc += delta;
 402                         continue;
 403                         /* NOTREACHED */
 404                 case DW_CFA_offset:
 405                         reg = DW_CFA_operand(insn);
 406                         count = dwarf_read_uleb128(current_insn, &offset);
 407                         current_insn += count;
 408                         offset *= cie->data_alignment_factor;
 409                         regp = dwarf_frame_alloc_reg(frame, reg);
 410                         regp->addr = offset;
 411                         regp->flags |= DWARF_REG_OFFSET;
 412                         continue;
 413                         /* NOTREACHED */
 414                 case DW_CFA_restore:
 415                         reg = DW_CFA_operand(insn);
 416                         continue;
 417                         /* NOTREACHED */
 418                 }
 419
 420                 /*
 421                  * Secondly, handle the opcodes that don't embed their
 422                  * operands in the instruction.
 423                  */
 424                 switch (insn) {
 425                 case DW_CFA_nop:
 426                         continue;
 427                 case DW_CFA_advance_loc1:
 428                         delta = *current_insn++;
 429                         frame->pc += delta * cie->code_alignment_factor;
 430                         break;
 431                 case DW_CFA_advance_loc2:
 432                         delta = get_unaligned((u16 *)current_insn);
 433                         current_insn += 2;
 434                         frame->pc += delta * cie->code_alignment_factor;
 435                         break;
 436                 case DW_CFA_advance_loc4:
 437                         delta = get_unaligned((u32 *)current_insn);
 438                         current_insn += 4;
 439                         frame->pc += delta * cie->code_alignment_factor;
 440                         break;
 441                 case DW_CFA_offset_extended:
 442                         count = dwarf_read_uleb128(current_insn, &reg);
 443                         current_insn += count;
 444                         count = dwarf_read_uleb128(current_insn, &offset);
 445                         current_insn += count;
 446                         offset *= cie->data_alignment_factor;
 447                         break;
 448                 case DW_CFA_restore_extended:
 449                         count = dwarf_read_uleb128(current_insn, &reg);
 450                         current_insn += count;
 451                         break;
 452                 case DW_CFA_undefined:
 453                         count = dwarf_read_uleb128(current_insn, &reg);
 454                         current_insn += count;
 455                         break;
 456                 case DW_CFA_def_cfa:
 457                         count = dwarf_read_uleb128(current_insn,
 458                                                    &frame->cfa_register);
 459                         current_insn += count;
 460                         count = dwarf_read_uleb128(current_insn,
 461                                                    &frame->cfa_offset);
 462                         current_insn += count;
 463
 464                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 465                         break;
 466                 case DW_CFA_def_cfa_register:
 467                         count = dwarf_read_uleb128(current_insn,
 468                                                    &frame->cfa_register);
 469                         current_insn += count;
 470                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 471                         break;
 472                 case DW_CFA_def_cfa_offset:
 473                         count = dwarf_read_uleb128(current_insn, &offset);
 474                         current_insn += count;
 475                         frame->cfa_offset = offset;
 476                         break;
 477                 case DW_CFA_def_cfa_expression:
 478                         count = dwarf_read_uleb128(current_insn, &expr_len);
 479                         current_insn += count;
 480
 481                         frame->cfa_expr = current_insn;
 482                         frame->cfa_expr_len = expr_len;
 483                         current_insn += expr_len;
 484
 485                         frame->flags |= DWARF_FRAME_CFA_REG_EXP;
 486                         break;
 487                 case DW_CFA_offset_extended_sf:
 488                         count = dwarf_read_uleb128(current_insn, &reg);
 489                         current_insn += count;
 490                         count = dwarf_read_leb128(current_insn, &offset);
 491                         current_insn += count;
 492                         offset *= cie->data_alignment_factor;
 493                         regp = dwarf_frame_alloc_reg(frame, reg);
 494                         regp->flags |= DWARF_REG_OFFSET;
 495                         regp->addr = offset;
 496                         break;
 497                 case DW_CFA_val_offset:
 498                         count = dwarf_read_uleb128(current_insn, &reg);
 499                         current_insn += count;
 500                         count = dwarf_read_leb128(current_insn, &offset);
 501                         offset *= cie->data_alignment_factor;
 502                         regp = dwarf_frame_alloc_reg(frame, reg);
 503                         regp->flags |= DWARF_VAL_OFFSET;
 504                         regp->addr = offset;
 505                         break;
 506                 case DW_CFA_GNU_args_size:
 507                         count = dwarf_read_uleb128(current_insn, &offset);
 508                         current_insn += count;
 509                         break;
 510                 case DW_CFA_GNU_negative_offset_extended:
 511                         count = dwarf_read_uleb128(current_insn, &reg);
 512                         current_insn += count;
 513                         count = dwarf_read_uleb128(current_insn, &offset);
 514                         offset *= cie->data_alignment_factor;
 515
 516                         regp = dwarf_frame_alloc_reg(frame, reg);
 517                         regp->flags |= DWARF_REG_OFFSET;
 518                         regp->addr = -offset;
 519                         break;
 520                 default:
 521                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
 522                         UNWINDER_BUG();
 523                         break;
 524                 }
 525         }
 526
 527         return 0;
 528 }
 529
 530 /**
 531  *      dwarf_unwind_stack - recursively unwind the stack
 532  *      @pc: address of the function to unwind
 533  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
 534  *
 535  *      Return a struct dwarf_frame representing the most recent frame
 536  *      on the callstack. Each of the lower (older) stack frames are
 537  *      linked via the "prev" member.
 538  */
 539 struct dwarf_frame * dwarf_unwind_stack(unsigned long pc,
 540                                         struct dwarf_frame *prev)
 541 {
 542         struct dwarf_frame *frame;
 543         struct dwarf_cie *cie;
 544         struct dwarf_fde *fde;
 545         struct dwarf_reg *reg;
 546         unsigned long addr;
 547
 548         /*
 549          * If this is the first invocation of this recursive function we
 550          * need get the contents of a physical register to get the CFA
 551          * in order to begin the virtual unwinding of the stack.
 552          *
 553          * NOTE: the return address is guaranteed to be setup by the
 554          * time this function makes its first function call.
 555          */
 556         if (!pc && !prev)
 557                 pc = (unsigned long)current_text_addr();
 558
 559         frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
 560         if (!frame) {
 561                 printk(KERN_ERR "Unable to allocate a dwarf frame\n");
 562                 UNWINDER_BUG();
 563         }
 564
 565         INIT_LIST_HEAD(&frame->reg_list);
 566         frame->flags = 0;
 567         frame->prev = prev;
 568         frame->return_addr = 0;
 569
 570         fde = dwarf_lookup_fde(pc);
 571         if (!fde) {
 572                 /*
 573                  * This is our normal exit path - the one that stops the
 574                  * recursion. There's two reasons why we might exit
 575                  * here,
 576                  *
 577                  *      a) pc has no asscociated DWARF frame info and so
 578                  *      we don't know how to unwind this frame. This is
 579                  *      usually the case when we're trying to unwind a
 580                  *      frame that was called from some assembly code
 581                  *      that has no DWARF info, e.g. syscalls.
 582                  *
 583                  *      b) the DEBUG info for pc is bogus. There's
 584                  *      really no way to distinguish this case from the
 585                  *      case above, which sucks because we could print a
 586                  *      warning here.
 587                  */
 588                 goto bail;
 589         }
 590
 591         cie = dwarf_lookup_cie(fde->cie_pointer);
 592
 593         frame->pc = fde->initial_location;
 594
 595         /* CIE initial instructions */
 596         dwarf_cfa_execute_insns(cie->initial_instructions,
 597                                 cie->instructions_end, cie, fde,
 598                                 frame, pc);
 599
 600         /* FDE instructions */
 601         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
 602                                 fde, frame, pc);
 603
 604         /* Calculate the CFA */
 605         switch (frame->flags) {
 606         case DWARF_FRAME_CFA_REG_OFFSET:
 607                 if (prev) {
 608                         reg = dwarf_frame_reg(prev, frame->cfa_register);
 609                         UNWINDER_BUG_ON(!reg);
 610                         UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
 611
 612                         addr = prev->cfa + reg->addr;
 613                         frame->cfa = __raw_readl(addr);
 614
 615                 } else {
 616                         /*
 617                          * Again, this is the first invocation of this
 618                          * recurisve function. We need to physically
 619                          * read the contents of a register in order to
 620                          * get the Canonical Frame Address for this
 621                          * function.
 622                          */
 623                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
 624                 }
 625
 626                 frame->cfa += frame->cfa_offset;
 627                 break;
 628         default:
 629                 UNWINDER_BUG();
 630         }
 631
 632         /* If we haven't seen the return address reg, we're screwed. */
 633         reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);
 634         UNWINDER_BUG_ON(!reg);
 635         UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
 636
 637         addr = frame->cfa + reg->addr;
 638         frame->return_addr = __raw_readl(addr);
 639
 640         return frame;
 641
 642 bail:
 643         dwarf_frame_free_regs(frame);
 644         mempool_free(frame, dwarf_frame_pool);
 645         return NULL;
 646 }
 647
 648 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
 649                            unsigned char *end)
 650 {
 651         struct dwarf_cie *cie;
 652         unsigned long flags;
 653         int count;
 654
 655         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
 656         if (!cie)
 657                 return -ENOMEM;
 658
 659         cie->length = len;
 660
 661         /*
 662          * Record the offset into the .eh_frame section
 663          * for this CIE. It allows this CIE to be
 664          * quickly and easily looked up from the
 665          * corresponding FDE.
 666          */
 667         cie->cie_pointer = (unsigned long)entry;
 668
 669         cie->version = *(char *)p++;
 670         UNWINDER_BUG_ON(cie->version != 1);
 671
 672         cie->augmentation = p;
 673         p += strlen(cie->augmentation) + 1;
 674
 675         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
 676         p += count;
 677
 678         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
 679         p += count;
 680
 681         /*
 682          * Which column in the rule table contains the
 683          * return address?
 684          */
 685         if (cie->version == 1) {
 686                 cie->return_address_reg = __raw_readb(p);
 687                 p++;
 688         } else {
 689                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
 690                 p += count;
 691         }
 692
 693         if (cie->augmentation[0] == 'z') {
 694                 unsigned int length, count;
 695                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
 696
 697                 count = dwarf_read_uleb128(p, &length);
 698                 p += count;
 699
 700                 UNWINDER_BUG_ON((unsigned char *)p > end);
 701
 702                 cie->initial_instructions = p + length;
 703                 cie->augmentation++;
 704         }
 705
 706         while (*cie->augmentation) {
 707                 /*
 708                  * "L" indicates a byte showing how the
 709                  * LSDA pointer is encoded. Skip it.
 710                  */
 711                 if (*cie->augmentation == 'L') {
 712                         p++;
 713                         cie->augmentation++;
 714                 } else if (*cie->augmentation == 'R') {
 715                         /*
 716                          * "R" indicates a byte showing
 717                          * how FDE addresses are
 718                          * encoded.
 719                          */
 720                         cie->encoding = *(char *)p++;
 721                         cie->augmentation++;
 722                 } else if (*cie->augmentation == 'P') {
 723                         /*
 724                          * "R" indicates a personality
 725                          * routine in the CIE
 726                          * augmentation.
 727                          */
 728                         UNWINDER_BUG();
 729                 } else if (*cie->augmentation == 'S') {
 730                         UNWINDER_BUG();
 731                 } else {
 732                         /*
 733                          * Unknown augmentation. Assume
 734                          * 'z' augmentation.
 735                          */
 736                         p = cie->initial_instructions;
 737                         UNWINDER_BUG_ON(!p);
 738                         break;
 739                 }
 740         }
 741
 742         cie->initial_instructions = p;
 743         cie->instructions_end = end;
 744
 745         /* Add to list */
 746         spin_lock_irqsave(&dwarf_cie_lock, flags);
 747         list_add_tail(&cie->link, &dwarf_cie_list);
 748         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 749
 750         return 0;
 751 }
 752
 753 static int dwarf_parse_fde(void *entry, u32 entry_type,
 754                            void *start, unsigned long len,
 755                            unsigned char *end)
 756 {
 757         struct dwarf_fde *fde;
 758         struct dwarf_cie *cie;
 759         unsigned long flags;
 760         int count;
 761         void *p = start;
 762
 763         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
 764         if (!fde)
 765                 return -ENOMEM;
 766
 767         fde->length = len;
 768
 769         /*
 770          * In a .eh_frame section the CIE pointer is the
 771          * delta between the address within the FDE
 772          */
 773         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
 774
 775         cie = dwarf_lookup_cie(fde->cie_pointer);
 776         fde->cie = cie;
 777
 778         if (cie->encoding)
 779                 count = dwarf_read_encoded_value(p, &fde->initial_location,
 780                                                  cie->encoding);
 781         else
 782                 count = dwarf_read_addr(p, &fde->initial_location);
 783
 784         p += count;
 785
 786         if (cie->encoding)
 787                 count = dwarf_read_encoded_value(p, &fde->address_range,
 788                                                  cie->encoding & 0x0f);
 789         else
 790                 count = dwarf_read_addr(p, &fde->address_range);
 791
 792         p += count;
 793
 794         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
 795                 unsigned int length;
 796                 count = dwarf_read_uleb128(p, &length);
 797                 p += count + length;
 798         }
 799
 800         /* Call frame instructions. */
 801         fde->instructions = p;
 802         fde->end = end;
 803
 804         /* Add to list. */
 805         spin_lock_irqsave(&dwarf_fde_lock, flags);
 806         list_add_tail(&fde->link, &dwarf_fde_list);
 807         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 808
 809         return 0;
 810 }
 811
 812 static void dwarf_unwinder_dump(struct task_struct *task,
 813                                 struct pt_regs *regs,
 814                                 unsigned long *sp,
 815                                 const struct stacktrace_ops *ops,
 816                                 void *data)
 817 {
 818         struct dwarf_frame *frame, *_frame;
 819         unsigned long return_addr;
 820
 821         _frame = NULL;
 822         return_addr = 0;
 823
 824         while (1) {
 825                 frame = dwarf_unwind_stack(return_addr, _frame);
 826
 827                 if (_frame) {
 828                         dwarf_frame_free_regs(_frame);
 829                         mempool_free(_frame, dwarf_frame_pool);
 830                 }
 831
 832                 _frame = frame;
 833
 834                 if (!frame || !frame->return_addr)
 835                         break;
 836
 837                 return_addr = frame->return_addr;
 838                 ops->address(data, return_addr, 1);
 839         }
 840 }
 841
 842 static struct unwinder dwarf_unwinder = {
 843         .name = "dwarf-unwinder",
 844         .dump = dwarf_unwinder_dump,
 845         .rating = 150,
 846 };
 847
 848 static void dwarf_unwinder_cleanup(void)
 849 {
 850         struct dwarf_cie *cie;
 851         struct dwarf_fde *fde;
 852
 853         /*
 854          * Deallocate all the memory allocated for the DWARF unwinder.
 855          * Traverse all the FDE/CIE lists and remove and free all the
 856          * memory associated with those data structures.
 857          */
 858         list_for_each_entry(cie, &dwarf_cie_list, link)
 859                 kfree(cie);
 860
 861         list_for_each_entry(fde, &dwarf_fde_list, link)
 862                 kfree(fde);
 863
 864         kmem_cache_destroy(dwarf_reg_cachep);
 865         kmem_cache_destroy(dwarf_frame_cachep);
 866 }
 867
 868 /**
 869  *      dwarf_unwinder_init - initialise the dwarf unwinder
 870  *
 871  *      Build the data structures describing the .dwarf_frame section to
 872  *      make it easier to lookup CIE and FDE entries. Because the
 873  *      .eh_frame section is packed as tightly as possible it is not
 874  *      easy to lookup the FDE for a given PC, so we build a list of FDE
 875  *      and CIE entries that make it easier.
 876  */
 877 static int __init dwarf_unwinder_init(void)
 878 {
 879         u32 entry_type;
 880         void *p, *entry;
 881         int count, err;
 882         unsigned long len;
 883         unsigned int c_entries, f_entries;
 884         unsigned char *end;
 885         INIT_LIST_HEAD(&dwarf_cie_list);
 886         INIT_LIST_HEAD(&dwarf_fde_list);
 887
 888         c_entries = 0;
 889         f_entries = 0;
 890         entry = &__start_eh_frame;
 891
 892         dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
 893                         sizeof(struct dwarf_frame), 0, SLAB_PANIC, NULL);
 894         dwarf_reg_cachep = kmem_cache_create("dwarf_regs",
 895                         sizeof(struct dwarf_reg), 0, SLAB_PANIC, NULL);
 896
 897         dwarf_frame_pool = mempool_create(DWARF_FRAME_MIN_REQ,
 898                                           mempool_alloc_slab,
 899                                           mempool_free_slab,
 900                                           dwarf_frame_cachep);
 901
 902         dwarf_reg_pool = mempool_create(DWARF_REG_MIN_REQ,
 903                                          mempool_alloc_slab,
 904                                          mempool_free_slab,
 905                                          dwarf_reg_cachep);
 906
 907         while ((char *)entry < __stop_eh_frame) {
 908                 p = entry;
 909
 910                 count = dwarf_entry_len(p, &len);
 911                 if (count == 0) {
 912                         /*
 913                          * We read a bogus length field value. There is
 914                          * nothing we can do here apart from disabling
 915                          * the DWARF unwinder. We can't even skip this
 916                          * entry and move to the next one because 'len'
 917                          * tells us where our next entry is.
 918                          */
 919                         goto out;
 920                 } else
 921                         p += count;
 922
 923                 /* initial length does not include itself */
 924                 end = p + len;
 925
 926                 entry_type = get_unaligned((u32 *)p);
 927                 p += 4;
 928
 929                 if (entry_type == DW_EH_FRAME_CIE) {
 930                         err = dwarf_parse_cie(entry, p, len, end);
 931                         if (err < 0)
 932                                 goto out;
 933                         else
 934                                 c_entries++;
 935                 } else {
 936                         err = dwarf_parse_fde(entry, entry_type, p, len, end);
 937                         if (err < 0)
 938                                 goto out;
 939                         else
 940                                 f_entries++;
 941                 }
 942
 943                 entry = (char *)entry + len + 4;
 944         }
 945
 946         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
 947                c_entries, f_entries);
 948
 949         err = unwinder_register(&dwarf_unwinder);
 950         if (err)
 951                 goto out;
 952
 953         return 0;
 954
 955 out:
 956         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
 957         dwarf_unwinder_cleanup();
 958         return -EINVAL;
 959 }
 960 early_initcall(dwarf_unwinder_init);