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