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