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(®->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(®->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, ®); 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, ®); 473 current_insn += count; 474 break; 475 case DW_CFA_undefined: 476 count = dwarf_read_uleb128(current_insn, ®); 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, ®); 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, ®); 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, ®); 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 = _THIS_IP_; 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 struct ftrace_ret_stack *ret_stack; 612 613 ret_stack = ftrace_graph_get_ret_stack(current, 0); 614 if (ret_stack) 615 pc = ret_stack->ret; 616 /* 617 * We currently have no way of tracking how many 618 * return_to_handler()'s we've seen. If there is more 619 * than one patched return address on our stack, 620 * complain loudly. 621 */ 622 WARN_ON(ftrace_graph_get_ret_stack(current, 1)); 623 } 624 #endif 625 626 frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC); 627 if (!frame) { 628 printk(KERN_ERR "Unable to allocate a dwarf frame\n"); 629 UNWINDER_BUG(); 630 } 631 632 INIT_LIST_HEAD(&frame->reg_list); 633 frame->flags = 0; 634 frame->prev = prev; 635 frame->return_addr = 0; 636 637 fde = dwarf_lookup_fde(pc); 638 if (!fde) { 639 /* 640 * This is our normal exit path. There are two reasons 641 * why we might exit here, 642 * 643 * a) pc has no asscociated DWARF frame info and so 644 * we don't know how to unwind this frame. This is 645 * usually the case when we're trying to unwind a 646 * frame that was called from some assembly code 647 * that has no DWARF info, e.g. syscalls. 648 * 649 * b) the DEBUG info for pc is bogus. There's 650 * really no way to distinguish this case from the 651 * case above, which sucks because we could print a 652 * warning here. 653 */ 654 goto bail; 655 } 656 657 cie = dwarf_lookup_cie(fde->cie_pointer); 658 659 frame->pc = fde->initial_location; 660 661 /* CIE initial instructions */ 662 dwarf_cfa_execute_insns(cie->initial_instructions, 663 cie->instructions_end, cie, fde, 664 frame, pc); 665 666 /* FDE instructions */ 667 dwarf_cfa_execute_insns(fde->instructions, fde->end, cie, 668 fde, frame, pc); 669 670 /* Calculate the CFA */ 671 switch (frame->flags) { 672 case DWARF_FRAME_CFA_REG_OFFSET: 673 if (prev) { 674 reg = dwarf_frame_reg(prev, frame->cfa_register); 675 UNWINDER_BUG_ON(!reg); 676 UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET); 677 678 addr = prev->cfa + reg->addr; 679 frame->cfa = __raw_readl(addr); 680 681 } else { 682 /* 683 * Again, we're starting from the top of the 684 * stack. We need to physically read 685 * the contents of a register in order to get 686 * the Canonical Frame Address for this 687 * function. 688 */ 689 frame->cfa = dwarf_read_arch_reg(frame->cfa_register); 690 } 691 692 frame->cfa += frame->cfa_offset; 693 break; 694 default: 695 UNWINDER_BUG(); 696 } 697 698 reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG); 699 700 /* 701 * If we haven't seen the return address register or the return 702 * address column is undefined then we must assume that this is 703 * the end of the callstack. 704 */ 705 if (!reg || reg->flags == DWARF_UNDEFINED) 706 goto bail; 707 708 UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET); 709 710 addr = frame->cfa + reg->addr; 711 frame->return_addr = __raw_readl(addr); 712 713 /* 714 * Ah, the joys of unwinding through interrupts. 715 * 716 * Interrupts are tricky - the DWARF info needs to be _really_ 717 * accurate and unfortunately I'm seeing a lot of bogus DWARF 718 * info. For example, I've seen interrupts occur in epilogues 719 * just after the frame pointer (r14) had been restored. The 720 * problem was that the DWARF info claimed that the CFA could be 721 * reached by using the value of the frame pointer before it was 722 * restored. 723 * 724 * So until the compiler can be trusted to produce reliable 725 * DWARF info when it really matters, let's stop unwinding once 726 * we've calculated the function that was interrupted. 727 */ 728 if (prev && prev->pc == (unsigned long)ret_from_irq) 729 frame->return_addr = 0; 730 731 return frame; 732 733 bail: 734 dwarf_free_frame(frame); 735 return NULL; 736 } 737 738 static int dwarf_parse_cie(void *entry, void *p, unsigned long len, 739 unsigned char *end, struct module *mod) 740 { 741 struct rb_node **rb_node = &cie_root.rb_node; 742 struct rb_node *parent = *rb_node; 743 struct dwarf_cie *cie; 744 unsigned long flags; 745 int count; 746 747 cie = kzalloc(sizeof(*cie), GFP_KERNEL); 748 if (!cie) 749 return -ENOMEM; 750 751 cie->length = len; 752 753 /* 754 * Record the offset into the .eh_frame section 755 * for this CIE. It allows this CIE to be 756 * quickly and easily looked up from the 757 * corresponding FDE. 758 */ 759 cie->cie_pointer = (unsigned long)entry; 760 761 cie->version = *(char *)p++; 762 UNWINDER_BUG_ON(cie->version != 1); 763 764 cie->augmentation = p; 765 p += strlen(cie->augmentation) + 1; 766 767 count = dwarf_read_uleb128(p, &cie->code_alignment_factor); 768 p += count; 769 770 count = dwarf_read_leb128(p, &cie->data_alignment_factor); 771 p += count; 772 773 /* 774 * Which column in the rule table contains the 775 * return address? 776 */ 777 if (cie->version == 1) { 778 cie->return_address_reg = __raw_readb(p); 779 p++; 780 } else { 781 count = dwarf_read_uleb128(p, &cie->return_address_reg); 782 p += count; 783 } 784 785 if (cie->augmentation[0] == 'z') { 786 unsigned int length, count; 787 cie->flags |= DWARF_CIE_Z_AUGMENTATION; 788 789 count = dwarf_read_uleb128(p, &length); 790 p += count; 791 792 UNWINDER_BUG_ON((unsigned char *)p > end); 793 794 cie->initial_instructions = p + length; 795 cie->augmentation++; 796 } 797 798 while (*cie->augmentation) { 799 /* 800 * "L" indicates a byte showing how the 801 * LSDA pointer is encoded. Skip it. 802 */ 803 if (*cie->augmentation == 'L') { 804 p++; 805 cie->augmentation++; 806 } else if (*cie->augmentation == 'R') { 807 /* 808 * "R" indicates a byte showing 809 * how FDE addresses are 810 * encoded. 811 */ 812 cie->encoding = *(char *)p++; 813 cie->augmentation++; 814 } else if (*cie->augmentation == 'P') { 815 /* 816 * "R" indicates a personality 817 * routine in the CIE 818 * augmentation. 819 */ 820 UNWINDER_BUG(); 821 } else if (*cie->augmentation == 'S') { 822 UNWINDER_BUG(); 823 } else { 824 /* 825 * Unknown augmentation. Assume 826 * 'z' augmentation. 827 */ 828 p = cie->initial_instructions; 829 UNWINDER_BUG_ON(!p); 830 break; 831 } 832 } 833 834 cie->initial_instructions = p; 835 cie->instructions_end = end; 836 837 /* Add to list */ 838 spin_lock_irqsave(&dwarf_cie_lock, flags); 839 840 while (*rb_node) { 841 struct dwarf_cie *cie_tmp; 842 843 cie_tmp = rb_entry(*rb_node, struct dwarf_cie, node); 844 845 parent = *rb_node; 846 847 if (cie->cie_pointer < cie_tmp->cie_pointer) 848 rb_node = &parent->rb_left; 849 else if (cie->cie_pointer >= cie_tmp->cie_pointer) 850 rb_node = &parent->rb_right; 851 else 852 WARN_ON(1); 853 } 854 855 rb_link_node(&cie->node, parent, rb_node); 856 rb_insert_color(&cie->node, &cie_root); 857 858 #ifdef CONFIG_MODULES 859 if (mod != NULL) 860 list_add_tail(&cie->link, &mod->arch.cie_list); 861 #endif 862 863 spin_unlock_irqrestore(&dwarf_cie_lock, flags); 864 865 return 0; 866 } 867 868 static int dwarf_parse_fde(void *entry, u32 entry_type, 869 void *start, unsigned long len, 870 unsigned char *end, struct module *mod) 871 { 872 struct rb_node **rb_node = &fde_root.rb_node; 873 struct rb_node *parent = *rb_node; 874 struct dwarf_fde *fde; 875 struct dwarf_cie *cie; 876 unsigned long flags; 877 int count; 878 void *p = start; 879 880 fde = kzalloc(sizeof(*fde), GFP_KERNEL); 881 if (!fde) 882 return -ENOMEM; 883 884 fde->length = len; 885 886 /* 887 * In a .eh_frame section the CIE pointer is the 888 * delta between the address within the FDE 889 */ 890 fde->cie_pointer = (unsigned long)(p - entry_type - 4); 891 892 cie = dwarf_lookup_cie(fde->cie_pointer); 893 fde->cie = cie; 894 895 if (cie->encoding) 896 count = dwarf_read_encoded_value(p, &fde->initial_location, 897 cie->encoding); 898 else 899 count = dwarf_read_addr(p, &fde->initial_location); 900 901 p += count; 902 903 if (cie->encoding) 904 count = dwarf_read_encoded_value(p, &fde->address_range, 905 cie->encoding & 0x0f); 906 else 907 count = dwarf_read_addr(p, &fde->address_range); 908 909 p += count; 910 911 if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) { 912 unsigned int length; 913 count = dwarf_read_uleb128(p, &length); 914 p += count + length; 915 } 916 917 /* Call frame instructions. */ 918 fde->instructions = p; 919 fde->end = end; 920 921 /* Add to list. */ 922 spin_lock_irqsave(&dwarf_fde_lock, flags); 923 924 while (*rb_node) { 925 struct dwarf_fde *fde_tmp; 926 unsigned long tmp_start, tmp_end; 927 unsigned long start, end; 928 929 fde_tmp = rb_entry(*rb_node, struct dwarf_fde, node); 930 931 start = fde->initial_location; 932 end = fde->initial_location + fde->address_range; 933 934 tmp_start = fde_tmp->initial_location; 935 tmp_end = fde_tmp->initial_location + fde_tmp->address_range; 936 937 parent = *rb_node; 938 939 if (start < tmp_start) 940 rb_node = &parent->rb_left; 941 else if (start >= tmp_end) 942 rb_node = &parent->rb_right; 943 else 944 WARN_ON(1); 945 } 946 947 rb_link_node(&fde->node, parent, rb_node); 948 rb_insert_color(&fde->node, &fde_root); 949 950 #ifdef CONFIG_MODULES 951 if (mod != NULL) 952 list_add_tail(&fde->link, &mod->arch.fde_list); 953 #endif 954 955 spin_unlock_irqrestore(&dwarf_fde_lock, flags); 956 957 return 0; 958 } 959 960 static void dwarf_unwinder_dump(struct task_struct *task, 961 struct pt_regs *regs, 962 unsigned long *sp, 963 const struct stacktrace_ops *ops, 964 void *data) 965 { 966 struct dwarf_frame *frame, *_frame; 967 unsigned long return_addr; 968 969 _frame = NULL; 970 return_addr = 0; 971 972 while (1) { 973 frame = dwarf_unwind_stack(return_addr, _frame); 974 975 if (_frame) 976 dwarf_free_frame(_frame); 977 978 _frame = frame; 979 980 if (!frame || !frame->return_addr) 981 break; 982 983 return_addr = frame->return_addr; 984 ops->address(data, return_addr, 1); 985 } 986 987 if (frame) 988 dwarf_free_frame(frame); 989 } 990 991 static struct unwinder dwarf_unwinder = { 992 .name = "dwarf-unwinder", 993 .dump = dwarf_unwinder_dump, 994 .rating = 150, 995 }; 996 997 static void __init dwarf_unwinder_cleanup(void) 998 { 999 struct dwarf_fde *fde, *next_fde; 1000 struct dwarf_cie *cie, *next_cie; 1001 1002 /* 1003 * Deallocate all the memory allocated for the DWARF unwinder. 1004 * Traverse all the FDE/CIE lists and remove and free all the 1005 * memory associated with those data structures. 1006 */ 1007 rbtree_postorder_for_each_entry_safe(fde, next_fde, &fde_root, node) 1008 kfree(fde); 1009 1010 rbtree_postorder_for_each_entry_safe(cie, next_cie, &cie_root, node) 1011 kfree(cie); 1012 1013 mempool_destroy(dwarf_reg_pool); 1014 mempool_destroy(dwarf_frame_pool); 1015 kmem_cache_destroy(dwarf_reg_cachep); 1016 kmem_cache_destroy(dwarf_frame_cachep); 1017 } 1018 1019 /** 1020 * dwarf_parse_section - parse DWARF section 1021 * @eh_frame_start: start address of the .eh_frame section 1022 * @eh_frame_end: end address of the .eh_frame section 1023 * @mod: the kernel module containing the .eh_frame section 1024 * 1025 * Parse the information in a .eh_frame section. 1026 */ 1027 static int dwarf_parse_section(char *eh_frame_start, char *eh_frame_end, 1028 struct module *mod) 1029 { 1030 u32 entry_type; 1031 void *p, *entry; 1032 int count, err = 0; 1033 unsigned long len = 0; 1034 unsigned int c_entries, f_entries; 1035 unsigned char *end; 1036 1037 c_entries = 0; 1038 f_entries = 0; 1039 entry = eh_frame_start; 1040 1041 while ((char *)entry < eh_frame_end) { 1042 p = entry; 1043 1044 count = dwarf_entry_len(p, &len); 1045 if (count == 0) { 1046 /* 1047 * We read a bogus length field value. There is 1048 * nothing we can do here apart from disabling 1049 * the DWARF unwinder. We can't even skip this 1050 * entry and move to the next one because 'len' 1051 * tells us where our next entry is. 1052 */ 1053 err = -EINVAL; 1054 goto out; 1055 } else 1056 p += count; 1057 1058 /* initial length does not include itself */ 1059 end = p + len; 1060 1061 entry_type = get_unaligned((u32 *)p); 1062 p += 4; 1063 1064 if (entry_type == DW_EH_FRAME_CIE) { 1065 err = dwarf_parse_cie(entry, p, len, end, mod); 1066 if (err < 0) 1067 goto out; 1068 else 1069 c_entries++; 1070 } else { 1071 err = dwarf_parse_fde(entry, entry_type, p, len, 1072 end, mod); 1073 if (err < 0) 1074 goto out; 1075 else 1076 f_entries++; 1077 } 1078 1079 entry = (char *)entry + len + 4; 1080 } 1081 1082 printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n", 1083 c_entries, f_entries); 1084 1085 return 0; 1086 1087 out: 1088 return err; 1089 } 1090 1091 #ifdef CONFIG_MODULES 1092 int module_dwarf_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs, 1093 struct module *me) 1094 { 1095 unsigned int i, err; 1096 unsigned long start, end; 1097 char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset; 1098 1099 start = end = 0; 1100 1101 for (i = 1; i < hdr->e_shnum; i++) { 1102 /* Alloc bit cleared means "ignore it." */ 1103 if ((sechdrs[i].sh_flags & SHF_ALLOC) 1104 && !strcmp(secstrings+sechdrs[i].sh_name, ".eh_frame")) { 1105 start = sechdrs[i].sh_addr; 1106 end = start + sechdrs[i].sh_size; 1107 break; 1108 } 1109 } 1110 1111 /* Did we find the .eh_frame section? */ 1112 if (i != hdr->e_shnum) { 1113 INIT_LIST_HEAD(&me->arch.cie_list); 1114 INIT_LIST_HEAD(&me->arch.fde_list); 1115 err = dwarf_parse_section((char *)start, (char *)end, me); 1116 if (err) { 1117 printk(KERN_WARNING "%s: failed to parse DWARF info\n", 1118 me->name); 1119 return err; 1120 } 1121 } 1122 1123 return 0; 1124 } 1125 1126 /** 1127 * module_dwarf_cleanup - remove FDE/CIEs associated with @mod 1128 * @mod: the module that is being unloaded 1129 * 1130 * Remove any FDEs and CIEs from the global lists that came from 1131 * @mod's .eh_frame section because @mod is being unloaded. 1132 */ 1133 void module_dwarf_cleanup(struct module *mod) 1134 { 1135 struct dwarf_fde *fde, *ftmp; 1136 struct dwarf_cie *cie, *ctmp; 1137 unsigned long flags; 1138 1139 spin_lock_irqsave(&dwarf_cie_lock, flags); 1140 1141 list_for_each_entry_safe(cie, ctmp, &mod->arch.cie_list, link) { 1142 list_del(&cie->link); 1143 rb_erase(&cie->node, &cie_root); 1144 kfree(cie); 1145 } 1146 1147 spin_unlock_irqrestore(&dwarf_cie_lock, flags); 1148 1149 spin_lock_irqsave(&dwarf_fde_lock, flags); 1150 1151 list_for_each_entry_safe(fde, ftmp, &mod->arch.fde_list, link) { 1152 list_del(&fde->link); 1153 rb_erase(&fde->node, &fde_root); 1154 kfree(fde); 1155 } 1156 1157 spin_unlock_irqrestore(&dwarf_fde_lock, flags); 1158 } 1159 #endif /* CONFIG_MODULES */ 1160 1161 /** 1162 * dwarf_unwinder_init - initialise the dwarf unwinder 1163 * 1164 * Build the data structures describing the .dwarf_frame section to 1165 * make it easier to lookup CIE and FDE entries. Because the 1166 * .eh_frame section is packed as tightly as possible it is not 1167 * easy to lookup the FDE for a given PC, so we build a list of FDE 1168 * and CIE entries that make it easier. 1169 */ 1170 static int __init dwarf_unwinder_init(void) 1171 { 1172 int err = -ENOMEM; 1173 1174 dwarf_frame_cachep = kmem_cache_create("dwarf_frames", 1175 sizeof(struct dwarf_frame), 0, 1176 SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL); 1177 1178 dwarf_reg_cachep = kmem_cache_create("dwarf_regs", 1179 sizeof(struct dwarf_reg), 0, 1180 SLAB_PANIC | SLAB_HWCACHE_ALIGN, NULL); 1181 1182 dwarf_frame_pool = mempool_create_slab_pool(DWARF_FRAME_MIN_REQ, 1183 dwarf_frame_cachep); 1184 if (!dwarf_frame_pool) 1185 goto out; 1186 1187 dwarf_reg_pool = mempool_create_slab_pool(DWARF_REG_MIN_REQ, 1188 dwarf_reg_cachep); 1189 if (!dwarf_reg_pool) 1190 goto out; 1191 1192 err = dwarf_parse_section(__start_eh_frame, __stop_eh_frame, NULL); 1193 if (err) 1194 goto out; 1195 1196 err = unwinder_register(&dwarf_unwinder); 1197 if (err) 1198 goto out; 1199 1200 dwarf_unwinder_ready = 1; 1201 1202 return 0; 1203 1204 out: 1205 printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err); 1206 dwarf_unwinder_cleanup(); 1207 return err; 1208 } 1209 early_initcall(dwarf_unwinder_init); 1210