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  *      - 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 <linux/elf.h>
  24 #include <linux/ftrace.h>
  25 #include <linux/module.h>
  26 #include <linux/slab.h>
  27 #include <asm/dwarf.h>
  28 #include <asm/unwinder.h>
  29 #include <asm/sections.h>
  30 #include <asm/unaligned.h>
  31 #include <asm/stacktrace.h>
  32
  33 /* Reserve enough memory for two stack frames */
  34 #define DWARF_FRAME_MIN_REQ     2
  35 /* ... with 4 registers per frame. */
  36 #define DWARF_REG_MIN_REQ       (DWARF_FRAME_MIN_REQ * 4)
  37
  38 static struct kmem_cache *dwarf_frame_cachep;
  39 static mempool_t *dwarf_frame_pool;
  40
  41 static struct kmem_cache *dwarf_reg_cachep;
  42 static mempool_t *dwarf_reg_pool;
  43
  44 static struct rb_root cie_root;
  45 static DEFINE_SPINLOCK(dwarf_cie_lock);
  46
  47 static struct rb_root fde_root;
  48 static DEFINE_SPINLOCK(dwarf_fde_lock);
  49
  50 static struct dwarf_cie *cached_cie;
  51
  52 static unsigned int dwarf_unwinder_ready;
  53
  54 /**
  55  *      dwarf_frame_alloc_reg - allocate memory for a DWARF register
  56  *      @frame: the DWARF frame whose list of registers we insert on
  57  *      @reg_num: the register number
  58  *
  59  *      Allocate space for, and initialise, a dwarf reg from
  60  *      dwarf_reg_pool and insert it onto the (unsorted) linked-list of
  61  *      dwarf registers for @frame.
  62  *
  63  *      Return the initialised DWARF reg.
  64  */
  65 static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
  66                                                unsigned int reg_num)
  67 {
  68         struct dwarf_reg *reg;
  69
  70         reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC);
  71         if (!reg) {
  72                 printk(KERN_WARNING "Unable to allocate a DWARF register\n");
  73                 /*
  74                  * Let's just bomb hard here, we have no way to
  75                  * gracefully recover.
  76                  */
  77                 UNWINDER_BUG();
  78         }
  79
  80         reg->number = reg_num;
  81         reg->addr = 0;
  82         reg->flags = 0;
  83
  84         list_add(&reg->link, &frame->reg_list);
  85
  86         return reg;
  87 }
  88
  89 static void dwarf_frame_free_regs(struct dwarf_frame *frame)
  90 {
  91         struct dwarf_reg *reg, *n;
  92
  93         list_for_each_entry_safe(reg, n, &frame->reg_list, link) {
  94                 list_del(&reg->link);
  95                 mempool_free(reg, dwarf_reg_pool);
  96         }
  97 }
  98
  99 /**
 100  *      dwarf_frame_reg - return a DWARF register
 101  *      @frame: the DWARF frame to search in for @reg_num
 102  *      @reg_num: the register number to search for
 103  *
 104  *      Lookup and return the dwarf reg @reg_num for this frame. Return
 105  *      NULL if @reg_num is an register invalid number.
 106  */
 107 static struct dwarf_reg *dwarf_frame_reg(struct dwarf_frame *frame,
 108                                          unsigned int reg_num)
 109 {
 110         struct dwarf_reg *reg;
 111
 112         list_for_each_entry(reg, &frame->reg_list, link) {
 113                 if (reg->number == reg_num)
 114                         return reg;
 115         }
 116
 117         return NULL;
 118 }
 119
 120 /**
 121  *      dwarf_read_addr - read dwarf data
 122  *      @src: source address of data
 123  *      @dst: destination address to store the data to
 124  *
 125  *      Read 'n' bytes from @src, where 'n' is the size of an address on
 126  *      the native machine. We return the number of bytes read, which
 127  *      should always be 'n'. We also have to be careful when reading
 128  *      from @src and writing to @dst, because they can be arbitrarily
 129  *      aligned. Return 'n' - the number of bytes read.
 130  */
 131 static inline int dwarf_read_addr(unsigned long *src, unsigned long *dst)
 132 {
 133         u32 val = get_unaligned(src);
 134         put_unaligned(val, dst);
 135         return sizeof(unsigned long *);
 136 }
 137
 138 /**
 139  *      dwarf_read_uleb128 - read unsigned LEB128 data
 140  *      @addr: the address where the ULEB128 data is stored
 141  *      @ret: address to store the result
 142  *
 143  *      Decode an unsigned LEB128 encoded datum. The algorithm is taken
 144  *      from Appendix C of the DWARF 3 spec. For information on the
 145  *      encodings refer to section "7.6 - Variable Length Data". Return
 146  *      the number of bytes read.
 147  */
 148 static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
 149 {
 150         unsigned int result;
 151         unsigned char byte;
 152         int shift, count;
 153
 154         result = 0;
 155         shift = 0;
 156         count = 0;
 157
 158         while (1) {
 159                 byte = __raw_readb(addr);
 160                 addr++;
 161                 count++;
 162
 163                 result |= (byte & 0x7f) << shift;
 164                 shift += 7;
 165
 166                 if (!(byte & 0x80))
 167                         break;
 168         }
 169
 170         *ret = result;
 171
 172         return count;
 173 }
 174
 175 /**
 176  *      dwarf_read_leb128 - read signed LEB128 data
 177  *      @addr: the address of the LEB128 encoded data
 178  *      @ret: address to store the result
 179  *
 180  *      Decode signed LEB128 data. The algorithm is taken from Appendix
 181  *      C of the DWARF 3 spec. Return the number of bytes read.
 182  */
 183 static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
 184 {
 185         unsigned char byte;
 186         int result, shift;
 187         int num_bits;
 188         int count;
 189
 190         result = 0;
 191         shift = 0;
 192         count = 0;
 193
 194         while (1) {
 195                 byte = __raw_readb(addr);
 196                 addr++;
 197                 result |= (byte & 0x7f) << shift;
 198                 shift += 7;
 199                 count++;
 200
 201                 if (!(byte & 0x80))
 202                         break;
 203         }
 204
 205         /* The number of bits in a signed integer. */
 206         num_bits = 8 * sizeof(result);
 207
 208         if ((shift < num_bits) && (byte & 0x40))
 209                 result |= (-1 << shift);
 210
 211         *ret = result;
 212
 213         return count;
 214 }
 215
 216 /**
 217  *      dwarf_read_encoded_value - return the decoded value at @addr
 218  *      @addr: the address of the encoded value
 219  *      @val: where to write the decoded value
 220  *      @encoding: the encoding with which we can decode @addr
 221  *
 222  *      GCC emits encoded address in the .eh_frame FDE entries. Decode
 223  *      the value at @addr using @encoding. The decoded value is written
 224  *      to @val and the number of bytes read is returned.
 225  */
 226 static int dwarf_read_encoded_value(char *addr, unsigned long *val,
 227                                     char encoding)
 228 {
 229         unsigned long decoded_addr = 0;
 230         int count = 0;
 231
 232         switch (encoding & 0x70) {
 233         case DW_EH_PE_absptr:
 234                 break;
 235         case DW_EH_PE_pcrel:
 236                 decoded_addr = (unsigned long)addr;
 237                 break;
 238         default:
 239                 pr_debug("encoding=0x%x\n", (encoding & 0x70));
 240                 UNWINDER_BUG();
 241         }
 242
 243         if ((encoding & 0x07) == 0x00)
 244                 encoding |= DW_EH_PE_udata4;
 245
 246         switch (encoding & 0x0f) {
 247         case DW_EH_PE_sdata4:
 248         case DW_EH_PE_udata4:
 249                 count += 4;
 250                 decoded_addr += get_unaligned((u32 *)addr);
 251                 __raw_writel(decoded_addr, val);
 252                 break;
 253         default:
 254                 pr_debug("encoding=0x%x\n", encoding);
 255                 UNWINDER_BUG();
 256         }
 257
 258         return count;
 259 }
 260
 261 /**
 262  *      dwarf_entry_len - return the length of an FDE or CIE
 263  *      @addr: the address of the entry
 264  *      @len: the length of the entry
 265  *
 266  *      Read the initial_length field of the entry and store the size of
 267  *      the entry in @len. We return the number of bytes read. Return a
 268  *      count of 0 on error.
 269  */
 270 static inline int dwarf_entry_len(char *addr, unsigned long *len)
 271 {
 272         u32 initial_len;
 273         int count;
 274
 275         initial_len = get_unaligned((u32 *)addr);
 276         count = 4;
 277
 278         /*
 279          * An initial length field value in the range DW_LEN_EXT_LO -
 280          * DW_LEN_EXT_HI indicates an extension, and should not be
 281          * interpreted as a length. The only extension that we currently
 282          * understand is the use of DWARF64 addresses.
 283          */
 284         if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
 285                 /*
 286                  * The 64-bit length field immediately follows the
 287                  * compulsory 32-bit length field.
 288                  */
 289                 if (initial_len == DW_EXT_DWARF64) {
 290                         *len = get_unaligned((u64 *)addr + 4);
 291                         count = 12;
 292                 } else {
 293                         printk(KERN_WARNING "Unknown DWARF extension\n");
 294                         count = 0;
 295                 }
 296         } else
 297                 *len = initial_len;
 298
 299         return count;
 300 }
 301
 302 /**
 303  *      dwarf_lookup_cie - locate the cie
 304  *      @cie_ptr: pointer to help with lookup
 305  */
 306 static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
 307 {
 308         struct rb_node **rb_node = &cie_root.rb_node;
 309         struct dwarf_cie *cie = NULL;
 310         unsigned long flags;
 311
 312         spin_lock_irqsave(&dwarf_cie_lock, flags);
 313
 314         /*
 315          * We've cached the last CIE we looked up because chances are
 316          * that the FDE wants this CIE.
 317          */
 318         if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
 319                 cie = cached_cie;
 320                 goto out;
 321         }
 322
 323         while (*rb_node) {
 324                 struct dwarf_cie *cie_tmp;
 325
 326                 cie_tmp = rb_entry(*rb_node, struct dwarf_cie, node);
 327                 BUG_ON(!cie_tmp);
 328
 329                 if (cie_ptr == cie_tmp->cie_pointer) {
 330                         cie = cie_tmp;
 331                         cached_cie = cie_tmp;
 332                         goto out;
 333                 } else {
 334                         if (cie_ptr < cie_tmp->cie_pointer)
 335                                 rb_node = &(*rb_node)->rb_left;
 336                         else
 337                                 rb_node = &(*rb_node)->rb_right;
 338                 }
 339         }
 340
 341 out:
 342         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 343         return cie;
 344 }
 345
 346 /**
 347  *      dwarf_lookup_fde - locate the FDE that covers pc
 348  *      @pc: the program counter
 349  */
 350 struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
 351 {
 352         struct rb_node **rb_node = &fde_root.rb_node;
 353         struct dwarf_fde *fde = NULL;
 354         unsigned long flags;
 355
 356         spin_lock_irqsave(&dwarf_fde_lock, flags);
 357
 358         while (*rb_node) {
 359                 struct dwarf_fde *fde_tmp;
 360                 unsigned long tmp_start, tmp_end;
 361
 362                 fde_tmp = rb_entry(*rb_node, struct dwarf_fde, node);
 363                 BUG_ON(!fde_tmp);
 364
 365                 tmp_start = fde_tmp->initial_location;
 366                 tmp_end = fde_tmp->initial_location + fde_tmp->address_range;
 367
 368                 if (pc < tmp_start) {
 369                         rb_node = &(*rb_node)->rb_left;
 370                 } else {
 371                         if (pc < tmp_end) {
 372                                 fde = fde_tmp;
 373                                 goto out;
 374                         } else
 375                                 rb_node = &(*rb_node)->rb_right;
 376                 }
 377         }
 378
 379 out:
 380         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 381
 382         return fde;
 383 }
 384
 385 /**
 386  *      dwarf_cfa_execute_insns - execute instructions to calculate a CFA
 387  *      @insn_start: address of the first instruction
 388  *      @insn_end: address of the last instruction
 389  *      @cie: the CIE for this function
 390  *      @fde: the FDE for this function
 391  *      @frame: the instructions calculate the CFA for this frame
 392  *      @pc: the program counter of the address we're interested in
 393  *
 394  *      Execute the Call Frame instruction sequence starting at
 395  *      @insn_start and ending at @insn_end. The instructions describe
 396  *      how to calculate the Canonical Frame Address of a stackframe.
 397  *      Store the results in @frame.
 398  */
 399 static int dwarf_cfa_execute_insns(unsigned char *insn_start,
 400                                    unsigned char *insn_end,
 401                                    struct dwarf_cie *cie,
 402                                    struct dwarf_fde *fde,
 403                                    struct dwarf_frame *frame,
 404                                    unsigned long pc)
 405 {
 406         unsigned char insn;
 407         unsigned char *current_insn;
 408         unsigned int count, delta, reg, expr_len, offset;
 409         struct dwarf_reg *regp;
 410
 411         current_insn = insn_start;
 412
 413         while (current_insn < insn_end && frame->pc <= pc) {
 414                 insn = __raw_readb(current_insn++);
 415
 416                 /*
 417                  * Firstly, handle the opcodes that embed their operands
 418                  * in the instructions.
 419                  */
 420                 switch (DW_CFA_opcode(insn)) {
 421                 case DW_CFA_advance_loc:
 422                         delta = DW_CFA_operand(insn);
 423                         delta *= cie->code_alignment_factor;
 424                         frame->pc += delta;
 425                         continue;
 426                         /* NOTREACHED */
 427                 case DW_CFA_offset:
 428                         reg = DW_CFA_operand(insn);
 429                         count = dwarf_read_uleb128(current_insn, &offset);
 430                         current_insn += count;
 431                         offset *= cie->data_alignment_factor;
 432                         regp = dwarf_frame_alloc_reg(frame, reg);
 433                         regp->addr = offset;
 434                         regp->flags |= DWARF_REG_OFFSET;
 435                         continue;
 436                         /* NOTREACHED */
 437                 case DW_CFA_restore:
 438                         reg = DW_CFA_operand(insn);
 439                         continue;
 440                         /* NOTREACHED */
 441                 }
 442
 443                 /*
 444                  * Secondly, handle the opcodes that don't embed their
 445                  * operands in the instruction.
 446                  */
 447                 switch (insn) {
 448                 case DW_CFA_nop:
 449                         continue;
 450                 case DW_CFA_advance_loc1:
 451                         delta = *current_insn++;
 452                         frame->pc += delta * cie->code_alignment_factor;
 453                         break;
 454                 case DW_CFA_advance_loc2:
 455                         delta = get_unaligned((u16 *)current_insn);
 456                         current_insn += 2;
 457                         frame->pc += delta * cie->code_alignment_factor;
 458                         break;
 459                 case DW_CFA_advance_loc4:
 460                         delta = get_unaligned((u32 *)current_insn);
 461                         current_insn += 4;
 462                         frame->pc += delta * cie->code_alignment_factor;
 463                         break;
 464                 case DW_CFA_offset_extended:
 465                         count = dwarf_read_uleb128(current_insn, &reg);
 466                         current_insn += count;
 467                         count = dwarf_read_uleb128(current_insn, &offset);
 468                         current_insn += count;
 469                         offset *= cie->data_alignment_factor;
 470                         break;
 471                 case DW_CFA_restore_extended:
 472                         count = dwarf_read_uleb128(current_insn, &reg);
 473                         current_insn += count;
 474                         break;
 475                 case DW_CFA_undefined:
 476                         count = dwarf_read_uleb128(current_insn, &reg);
 477                         current_insn += count;
 478                         regp = dwarf_frame_alloc_reg(frame, reg);
 479                         regp->flags |= DWARF_UNDEFINED;
 480                         break;
 481                 case DW_CFA_def_cfa:
 482                         count = dwarf_read_uleb128(current_insn,
 483                                                    &frame->cfa_register);
 484                         current_insn += count;
 485                         count = dwarf_read_uleb128(current_insn,
 486                                                    &frame->cfa_offset);
 487                         current_insn += count;
 488
 489                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 490                         break;
 491                 case DW_CFA_def_cfa_register:
 492                         count = dwarf_read_uleb128(current_insn,
 493                                                    &frame->cfa_register);
 494                         current_insn += count;
 495                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
 496                         break;
 497                 case DW_CFA_def_cfa_offset:
 498                         count = dwarf_read_uleb128(current_insn, &offset);
 499                         current_insn += count;
 500                         frame->cfa_offset = offset;
 501                         break;
 502                 case DW_CFA_def_cfa_expression:
 503                         count = dwarf_read_uleb128(current_insn, &expr_len);
 504                         current_insn += count;
 505
 506                         frame->cfa_expr = current_insn;
 507                         frame->cfa_expr_len = expr_len;
 508                         current_insn += expr_len;
 509
 510                         frame->flags |= DWARF_FRAME_CFA_REG_EXP;
 511                         break;
 512                 case DW_CFA_offset_extended_sf:
 513                         count = dwarf_read_uleb128(current_insn, &reg);
 514                         current_insn += count;
 515                         count = dwarf_read_leb128(current_insn, &offset);
 516                         current_insn += count;
 517                         offset *= cie->data_alignment_factor;
 518                         regp = dwarf_frame_alloc_reg(frame, reg);
 519                         regp->flags |= DWARF_REG_OFFSET;
 520                         regp->addr = offset;
 521                         break;
 522                 case DW_CFA_val_offset:
 523                         count = dwarf_read_uleb128(current_insn, &reg);
 524                         current_insn += count;
 525                         count = dwarf_read_leb128(current_insn, &offset);
 526                         offset *= cie->data_alignment_factor;
 527                         regp = dwarf_frame_alloc_reg(frame, reg);
 528                         regp->flags |= DWARF_VAL_OFFSET;
 529                         regp->addr = offset;
 530                         break;
 531                 case DW_CFA_GNU_args_size:
 532                         count = dwarf_read_uleb128(current_insn, &offset);
 533                         current_insn += count;
 534                         break;
 535                 case DW_CFA_GNU_negative_offset_extended:
 536                         count = dwarf_read_uleb128(current_insn, &reg);
 537                         current_insn += count;
 538                         count = dwarf_read_uleb128(current_insn, &offset);
 539                         offset *= cie->data_alignment_factor;
 540
 541                         regp = dwarf_frame_alloc_reg(frame, reg);
 542                         regp->flags |= DWARF_REG_OFFSET;
 543                         regp->addr = -offset;
 544                         break;
 545                 default:
 546                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
 547                         UNWINDER_BUG();
 548                         break;
 549                 }
 550         }
 551
 552         return 0;
 553 }
 554
 555 /**
 556  *      dwarf_free_frame - free the memory allocated for @frame
 557  *      @frame: the frame to free
 558  */
 559 void dwarf_free_frame(struct dwarf_frame *frame)
 560 {
 561         dwarf_frame_free_regs(frame);
 562         mempool_free(frame, dwarf_frame_pool);
 563 }
 564
 565 extern void ret_from_irq(void);
 566
 567 /**
 568  *      dwarf_unwind_stack - unwind the stack
 569  *
 570  *      @pc: address of the function to unwind
 571  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
 572  *
 573  *      Return a struct dwarf_frame representing the most recent frame
 574  *      on the callstack. Each of the lower (older) stack frames are
 575  *      linked via the "prev" member.
 576  */
 577 struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
 578                                        struct dwarf_frame *prev)
 579 {
 580         struct dwarf_frame *frame;
 581         struct dwarf_cie *cie;
 582         struct dwarf_fde *fde;
 583         struct dwarf_reg *reg;
 584         unsigned long addr;
 585
 586         /*
 587          * If we've been called in to before initialization has
 588          * completed, bail out immediately.
 589          */
 590         if (!dwarf_unwinder_ready)
 591                 return NULL;
 592
 593         /*
 594          * If we're starting at the top of the stack we need get the
 595          * contents of a physical register to get the CFA in order to
 596          * begin the virtual unwinding of the stack.
 597          *
 598          * NOTE: the return address is guaranteed to be setup by the
 599          * time this function makes its first function call.
 600          */
 601         if (!pc || !prev)
 602                 pc = (unsigned long)current_text_addr();
 603
 604 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 605         /*
 606          * If our stack has been patched by the function graph tracer
 607          * then we might see the address of return_to_handler() where we
 608          * expected to find the real return address.
 609          */
 610         if (pc == (unsigned long)&return_to_handler) {
 611                 int index = current->curr_ret_stack;
 612
 613                 /*
 614                  * We currently have no way of tracking how many
 615                  * return_to_handler()'s we've seen. If there is more
 616                  * than one patched return address on our stack,
 617                  * complain loudly.
 618                  */
 619                 WARN_ON(index > 0);
 620
 621                 pc = current->ret_stack[index].ret;
 622         }
 623 #endif
 624
 625         frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
 626         if (!frame) {
 627                 printk(KERN_ERR "Unable to allocate a dwarf frame\n");
 628                 UNWINDER_BUG();
 629         }
 630
 631         INIT_LIST_HEAD(&frame->reg_list);
 632         frame->flags = 0;
 633         frame->prev = prev;
 634         frame->return_addr = 0;
 635
 636         fde = dwarf_lookup_fde(pc);
 637         if (!fde) {
 638                 /*
 639                  * This is our normal exit path. There are two reasons
 640                  * why we might exit here,
 641                  *
 642                  *      a) pc has no asscociated DWARF frame info and so
 643                  *      we don't know how to unwind this frame. This is
 644                  *      usually the case when we're trying to unwind a
 645                  *      frame that was called from some assembly code
 646                  *      that has no DWARF info, e.g. syscalls.
 647                  *
 648                  *      b) the DEBUG info for pc is bogus. There's
 649                  *      really no way to distinguish this case from the
 650                  *      case above, which sucks because we could print a
 651                  *      warning here.
 652                  */
 653                 goto bail;
 654         }
 655
 656         cie = dwarf_lookup_cie(fde->cie_pointer);
 657
 658         frame->pc = fde->initial_location;
 659
 660         /* CIE initial instructions */
 661         dwarf_cfa_execute_insns(cie->initial_instructions,
 662                                 cie->instructions_end, cie, fde,
 663                                 frame, pc);
 664
 665         /* FDE instructions */
 666         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
 667                                 fde, frame, pc);
 668
 669         /* Calculate the CFA */
 670         switch (frame->flags) {
 671         case DWARF_FRAME_CFA_REG_OFFSET:
 672                 if (prev) {
 673                         reg = dwarf_frame_reg(prev, frame->cfa_register);
 674                         UNWINDER_BUG_ON(!reg);
 675                         UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
 676
 677                         addr = prev->cfa + reg->addr;
 678                         frame->cfa = __raw_readl(addr);
 679
 680                 } else {
 681                         /*
 682                          * Again, we're starting from the top of the
 683                          * stack. We need to physically read
 684                          * the contents of a register in order to get
 685                          * the Canonical Frame Address for this
 686                          * function.
 687                          */
 688                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
 689                 }
 690
 691                 frame->cfa += frame->cfa_offset;
 692                 break;
 693         default:
 694                 UNWINDER_BUG();
 695         }
 696
 697         reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);
 698
 699         /*
 700          * If we haven't seen the return address register or the return
 701          * address column is undefined then we must assume that this is
 702          * the end of the callstack.
 703          */
 704         if (!reg || reg->flags == DWARF_UNDEFINED)
 705                 goto bail;
 706
 707         UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
 708
 709         addr = frame->cfa + reg->addr;
 710         frame->return_addr = __raw_readl(addr);
 711
 712         /*
 713          * Ah, the joys of unwinding through interrupts.
 714          *
 715          * Interrupts are tricky - the DWARF info needs to be _really_
 716          * accurate and unfortunately I'm seeing a lot of bogus DWARF
 717          * info. For example, I've seen interrupts occur in epilogues
 718          * just after the frame pointer (r14) had been restored. The
 719          * problem was that the DWARF info claimed that the CFA could be
 720          * reached by using the value of the frame pointer before it was
 721          * restored.
 722          *
 723          * So until the compiler can be trusted to produce reliable
 724          * DWARF info when it really matters, let's stop unwinding once
 725          * we've calculated the function that was interrupted.
 726          */
 727         if (prev && prev->pc == (unsigned long)ret_from_irq)
 728                 frame->return_addr = 0;
 729
 730         return frame;
 731
 732 bail:
 733         dwarf_free_frame(frame);
 734         return NULL;
 735 }
 736
 737 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
 738                            unsigned char *end, struct module *mod)
 739 {
 740         struct rb_node **rb_node = &cie_root.rb_node;
 741         struct rb_node *parent = *rb_node;
 742         struct dwarf_cie *cie;
 743         unsigned long flags;
 744         int count;
 745
 746         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
 747         if (!cie)
 748                 return -ENOMEM;
 749
 750         cie->length = len;
 751
 752         /*
 753          * Record the offset into the .eh_frame section
 754          * for this CIE. It allows this CIE to be
 755          * quickly and easily looked up from the
 756          * corresponding FDE.
 757          */
 758         cie->cie_pointer = (unsigned long)entry;
 759
 760         cie->version = *(char *)p++;
 761         UNWINDER_BUG_ON(cie->version != 1);
 762
 763         cie->augmentation = p;
 764         p += strlen(cie->augmentation) + 1;
 765
 766         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
 767         p += count;
 768
 769         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
 770         p += count;
 771
 772         /*
 773          * Which column in the rule table contains the
 774          * return address?
 775          */
 776         if (cie->version == 1) {
 777                 cie->return_address_reg = __raw_readb(p);
 778                 p++;
 779         } else {
 780                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
 781                 p += count;
 782         }
 783
 784         if (cie->augmentation[0] == 'z') {
 785                 unsigned int length, count;
 786                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
 787
 788                 count = dwarf_read_uleb128(p, &length);
 789                 p += count;
 790
 791                 UNWINDER_BUG_ON((unsigned char *)p > end);
 792
 793                 cie->initial_instructions = p + length;
 794                 cie->augmentation++;
 795         }
 796
 797         while (*cie->augmentation) {
 798                 /*
 799                  * "L" indicates a byte showing how the
 800                  * LSDA pointer is encoded. Skip it.
 801                  */
 802                 if (*cie->augmentation == 'L') {
 803                         p++;
 804                         cie->augmentation++;
 805                 } else if (*cie->augmentation == 'R') {
 806                         /*
 807                          * "R" indicates a byte showing
 808                          * how FDE addresses are
 809                          * encoded.
 810                          */
 811                         cie->encoding = *(char *)p++;
 812                         cie->augmentation++;
 813                 } else if (*cie->augmentation == 'P') {
 814                         /*
 815                          * "R" indicates a personality
 816                          * routine in the CIE
 817                          * augmentation.
 818                          */
 819                         UNWINDER_BUG();
 820                 } else if (*cie->augmentation == 'S') {
 821                         UNWINDER_BUG();
 822                 } else {
 823                         /*
 824                          * Unknown augmentation. Assume
 825                          * 'z' augmentation.
 826                          */
 827                         p = cie->initial_instructions;
 828                         UNWINDER_BUG_ON(!p);
 829                         break;
 830                 }
 831         }
 832
 833         cie->initial_instructions = p;
 834         cie->instructions_end = end;
 835
 836         /* Add to list */
 837         spin_lock_irqsave(&dwarf_cie_lock, flags);
 838
 839         while (*rb_node) {
 840                 struct dwarf_cie *cie_tmp;
 841
 842                 cie_tmp = rb_entry(*rb_node, struct dwarf_cie, node);
 843
 844                 parent = *rb_node;
 845
 846                 if (cie->cie_pointer < cie_tmp->cie_pointer)
 847                         rb_node = &parent->rb_left;
 848                 else if (cie->cie_pointer >= cie_tmp->cie_pointer)
 849                         rb_node = &parent->rb_right;
 850                 else
 851                         WARN_ON(1);
 852         }
 853
 854         rb_link_node(&cie->node, parent, rb_node);
 855         rb_insert_color(&cie->node, &cie_root);
 856
 857 #ifdef CONFIG_MODULES
 858         if (mod != NULL)
 859                 list_add_tail(&cie->link, &mod->arch.cie_list);
 860 #endif
 861
 862         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
 863
 864         return 0;
 865 }
 866
 867 static int dwarf_parse_fde(void *entry, u32 entry_type,
 868                            void *start, unsigned long len,
 869                            unsigned char *end, struct module *mod)
 870 {
 871         struct rb_node **rb_node = &fde_root.rb_node;
 872         struct rb_node *parent = *rb_node;
 873         struct dwarf_fde *fde;
 874         struct dwarf_cie *cie;
 875         unsigned long flags;
 876         int count;
 877         void *p = start;
 878
 879         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
 880         if (!fde)
 881                 return -ENOMEM;
 882
 883         fde->length = len;
 884
 885         /*
 886          * In a .eh_frame section the CIE pointer is the
 887          * delta between the address within the FDE
 888          */
 889         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
 890
 891         cie = dwarf_lookup_cie(fde->cie_pointer);
 892         fde->cie = cie;
 893
 894         if (cie->encoding)
 895                 count = dwarf_read_encoded_value(p, &fde->initial_location,
 896                                                  cie->encoding);
 897         else
 898                 count = dwarf_read_addr(p, &fde->initial_location);
 899
 900         p += count;
 901
 902         if (cie->encoding)
 903                 count = dwarf_read_encoded_value(p, &fde->address_range,
 904                                                  cie->encoding & 0x0f);
 905         else
 906                 count = dwarf_read_addr(p, &fde->address_range);
 907
 908         p += count;
 909
 910         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
 911                 unsigned int length;
 912                 count = dwarf_read_uleb128(p, &length);
 913                 p += count + length;
 914         }
 915
 916         /* Call frame instructions. */
 917         fde->instructions = p;
 918         fde->end = end;
 919
 920         /* Add to list. */
 921         spin_lock_irqsave(&dwarf_fde_lock, flags);
 922
 923         while (*rb_node) {
 924                 struct dwarf_fde *fde_tmp;
 925                 unsigned long tmp_start, tmp_end;
 926                 unsigned long start, end;
 927
 928                 fde_tmp = rb_entry(*rb_node, struct dwarf_fde, node);
 929
 930                 start = fde->initial_location;
 931                 end = fde->initial_location + fde->address_range;
 932
 933                 tmp_start = fde_tmp->initial_location;
 934                 tmp_end = fde_tmp->initial_location + fde_tmp->address_range;
 935
 936                 parent = *rb_node;
 937
 938                 if (start < tmp_start)
 939                         rb_node = &parent->rb_left;
 940                 else if (start >= tmp_end)
 941                         rb_node = &parent->rb_right;
 942                 else
 943                         WARN_ON(1);
 944         }
 945
 946         rb_link_node(&fde->node, parent, rb_node);
 947         rb_insert_color(&fde->node, &fde_root);
 948
 949 #ifdef CONFIG_MODULES
 950         if (mod != NULL)
 951                 list_add_tail(&fde->link, &mod->arch.fde_list);
 952 #endif
 953
 954         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
 955
 956         return 0;
 957 }
 958
 959 static void dwarf_unwinder_dump(struct task_struct *task,
 960                                 struct pt_regs *regs,
 961                                 unsigned long *sp,
 962                                 const struct stacktrace_ops *ops,
 963                                 void *data)
 964 {
 965         struct dwarf_frame *frame, *_frame;
 966         unsigned long return_addr;
 967
 968         _frame = NULL;
 969         return_addr = 0;
 970
 971         while (1) {
 972                 frame = dwarf_unwind_stack(return_addr, _frame);
 973
 974                 if (_frame)
 975                         dwarf_free_frame(_frame);
 976
 977                 _frame = frame;
 978
 979                 if (!frame || !frame->return_addr)
 980                         break;
 981
 982                 return_addr = frame->return_addr;
 983                 ops->address(data, return_addr, 1);
 984         }
 985
 986         if (frame)
 987                 dwarf_free_frame(frame);
 988 }
 989
 990 static struct unwinder dwarf_unwinder = {
 991         .name = "dwarf-unwinder",
 992         .dump = dwarf_unwinder_dump,
 993         .rating = 150,
 994 };
 995
 996 static void __init dwarf_unwinder_cleanup(void)
 997 {
 998         struct dwarf_fde *fde, *next_fde;
 999         struct dwarf_cie *cie, *next_cie;
1000
1001         /*
1002          * Deallocate all the memory allocated for the DWARF unwinder.
1003          * Traverse all the FDE/CIE lists and remove and free all the
1004          * memory associated with those data structures.
1005          */
1006         rbtree_postorder_for_each_entry_safe(fde, next_fde, &fde_root, node)
1007                 kfree(fde);
1008
1009         rbtree_postorder_for_each_entry_safe(cie, next_cie, &cie_root, node)
1010                 kfree(cie);
1011
1012         mempool_destroy(dwarf_reg_pool);
1013         mempool_destroy(dwarf_frame_pool);
1014         kmem_cache_destroy(dwarf_reg_cachep);
1015         kmem_cache_destroy(dwarf_frame_cachep);
1016 }
1017
1018 /**
1019  *      dwarf_parse_section - parse DWARF section
1020  *      @eh_frame_start: start address of the .eh_frame section
1021  *      @eh_frame_end: end address of the .eh_frame section
1022  *      @mod: the kernel module containing the .eh_frame section
1023  *
1024  *      Parse the information in a .eh_frame section.
1025  */
1026 static int dwarf_parse_section(char *eh_frame_start, char *eh_frame_end,
1027                                struct module *mod)
1028 {
1029         u32 entry_type;
1030         void *p, *entry;
1031         int count, err = 0;
1032         unsigned long len = 0;
1033         unsigned int c_entries, f_entries;
1034         unsigned char *end;
1035
1036         c_entries = 0;
1037         f_entries = 0;
1038         entry = eh_frame_start;
1039
1040         while ((char *)entry < eh_frame_end) {
1041                 p = entry;
1042
1043                 count = dwarf_entry_len(p, &len);
1044                 if (count == 0) {
1045                         /*
1046                          * We read a bogus length field value. There is
1047                          * nothing we can do here apart from disabling
1048                          * the DWARF unwinder. We can't even skip this
1049                          * entry and move to the next one because 'len'
1050                          * tells us where our next entry is.
1051                          */
1052                         err = -EINVAL;
1053                         goto out;
1054                 } else
1055                         p += count;
1056
1057                 /* initial length does not include itself */
1058                 end = p + len;
1059
1060                 entry_type = get_unaligned((u32 *)p);
1061                 p += 4;
1062
1063                 if (entry_type == DW_EH_FRAME_CIE) {
1064                         err = dwarf_parse_cie(entry, p, len, end, mod);
1065                         if (err < 0)
1066                                 goto out;
1067                         else
1068                                 c_entries++;
1069                 } else {
1070                         err = dwarf_parse_fde(entry, entry_type, p, len,
1071                                               end, mod);
1072                         if (err < 0)
1073                                 goto out;
1074                         else
1075                                 f_entries++;
1076                 }
1077
1078                 entry = (char *)entry + len + 4;
1079         }
1080
1081         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
1082                c_entries, f_entries);
1083
1084         return 0;
1085
1086 out:
1087         return err;
1088 }
1089
1090 #ifdef CONFIG_MODULES
1091 int module_dwarf_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
1092                           struct module *me)
1093 {
1094         unsigned int i, err;
1095         unsigned long start, end;
1096         char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
1097
1098         start = end = 0;
1099
1100         for (i = 1; i < hdr->e_shnum; i++) {
1101                 /* Alloc bit cleared means "ignore it." */
1102                 if ((sechdrs[i].sh_flags & SHF_ALLOC)
1103                     && !strcmp(secstrings+sechdrs[i].sh_name, ".eh_frame")) {
1104                         start = sechdrs[i].sh_addr;
1105                         end = start + sechdrs[i].sh_size;
1106                         break;
1107                 }
1108         }
1109
1110         /* Did we find the .eh_frame section? */
1111         if (i != hdr->e_shnum) {
1112                 INIT_LIST_HEAD(&me->arch.cie_list);
1113                 INIT_LIST_HEAD(&me->arch.fde_list);
1114                 err = dwarf_parse_section((char *)start, (char *)end, me);
1115                 if (err) {
1116                         printk(KERN_WARNING "%s: failed to parse DWARF info\n",
1117                                me->name);
1118                         return err;
1119                 }
1120         }
1121
1122         return 0;
1123 }
1124
1125 /**
1126  *      module_dwarf_cleanup - remove FDE/CIEs associated with @mod
1127  *      @mod: the module that is being unloaded
1128  *
1129  *      Remove any FDEs and CIEs from the global lists that came from
1130  *      @mod's .eh_frame section because @mod is being unloaded.
1131  */
1132 void module_dwarf_cleanup(struct module *mod)
1133 {
1134         struct dwarf_fde *fde, *ftmp;
1135         struct dwarf_cie *cie, *ctmp;
1136         unsigned long flags;
1137
1138         spin_lock_irqsave(&dwarf_cie_lock, flags);
1139
1140         list_for_each_entry_safe(cie, ctmp, &mod->arch.cie_list, link) {
1141                 list_del(&cie->link);
1142                 rb_erase(&cie->node, &cie_root);
1143                 kfree(cie);
1144         }
1145
1146         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
1147
1148         spin_lock_irqsave(&dwarf_fde_lock, flags);
1149
1150         list_for_each_entry_safe(fde, ftmp, &mod->arch.fde_list, link) {
1151                 list_del(&fde->link);
1152                 rb_erase(&fde->node, &fde_root);
1153                 kfree(fde);
1154         }
1155
1156         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
1157 }
1158 #endif /* CONFIG_MODULES */
1159
1160 /**
1161  *      dwarf_unwinder_init - initialise the dwarf unwinder
1162  *
1163  *      Build the data structures describing the .dwarf_frame section to
1164  *      make it easier to lookup CIE and FDE entries. Because the
1165  *      .eh_frame section is packed as tightly as possible it is not
1166  *      easy to lookup the FDE for a given PC, so we build a list of FDE
1167  *      and CIE entries that make it easier.
1168  */
1169 static int __init dwarf_unwinder_init(void)
1170 {
1171         int err = -ENOMEM;
1172
1173         dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
1174                         sizeof(struct dwarf_frame), 0,
1175                         SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL);
1176
1177         dwarf_reg_cachep = kmem_cache_create("dwarf_regs",
1178                         sizeof(struct dwarf_reg), 0,
1179                         SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL);
1180
1181         dwarf_frame_pool = mempool_create_slab_pool(DWARF_FRAME_MIN_REQ,
1182                                                     dwarf_frame_cachep);
1183         if (!dwarf_frame_pool)
1184                 goto out;
1185
1186         dwarf_reg_pool = mempool_create_slab_pool(DWARF_REG_MIN_REQ,
1187                                                   dwarf_reg_cachep);
1188         if (!dwarf_reg_pool)
1189                 goto out;
1190
1191         err = dwarf_parse_section(__start_eh_frame, __stop_eh_frame, NULL);
1192         if (err)
1193                 goto out;
1194
1195         err = unwinder_register(&dwarf_unwinder);
1196         if (err)
1197                 goto out;
1198
1199         dwarf_unwinder_ready = 1;
1200
1201         return 0;
1202
1203 out:
1204         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
1205         dwarf_unwinder_cleanup();
1206         return err;
1207 }
1208 early_initcall(dwarf_unwinder_init);