/* * Copyright (C) 2009 Matt Fleming * * This file is subject to the terms and conditions of the GNU General Public * License. See the file "COPYING" in the main directory of this archive * for more details. * * This is an implementation of a DWARF unwinder. Its main purpose is * for generating stacktrace information. Based on the DWARF 3 * specification from http://www.dwarfstd.org. * * TODO: * - DWARF64 doesn't work. * - Registers with DWARF_VAL_OFFSET rules aren't handled properly. */ /* #define DEBUG */ #include #include #include #include #include #include #include #include #include #include #include /* Reserve enough memory for two stack frames */ #define DWARF_FRAME_MIN_REQ 2 /* ... with 4 registers per frame. */ #define DWARF_REG_MIN_REQ (DWARF_FRAME_MIN_REQ * 4) static struct kmem_cache *dwarf_frame_cachep; static mempool_t *dwarf_frame_pool; static struct kmem_cache *dwarf_reg_cachep; static mempool_t *dwarf_reg_pool; static LIST_HEAD(dwarf_cie_list); static DEFINE_SPINLOCK(dwarf_cie_lock); static LIST_HEAD(dwarf_fde_list); static DEFINE_SPINLOCK(dwarf_fde_lock); static struct dwarf_cie *cached_cie; /** * dwarf_frame_alloc_reg - allocate memory for a DWARF register * @frame: the DWARF frame whose list of registers we insert on * @reg_num: the register number * * Allocate space for, and initialise, a dwarf reg from * dwarf_reg_pool and insert it onto the (unsorted) linked-list of * dwarf registers for @frame. * * Return the initialised DWARF reg. */ static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame, unsigned int reg_num) { struct dwarf_reg *reg; reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC); if (!reg) { printk(KERN_WARNING "Unable to allocate a DWARF register\n"); /* * Let's just bomb hard here, we have no way to * gracefully recover. */ UNWINDER_BUG(); } reg->number = reg_num; reg->addr = 0; reg->flags = 0; list_add(®->link, &frame->reg_list); return reg; } static void dwarf_frame_free_regs(struct dwarf_frame *frame) { struct dwarf_reg *reg, *n; list_for_each_entry_safe(reg, n, &frame->reg_list, link) { list_del(®->link); mempool_free(reg, dwarf_reg_pool); } } /** * dwarf_frame_reg - return a DWARF register * @frame: the DWARF frame to search in for @reg_num * @reg_num: the register number to search for * * Lookup and return the dwarf reg @reg_num for this frame. Return * NULL if @reg_num is an register invalid number. */ static struct dwarf_reg *dwarf_frame_reg(struct dwarf_frame *frame, unsigned int reg_num) { struct dwarf_reg *reg; list_for_each_entry(reg, &frame->reg_list, link) { if (reg->number == reg_num) return reg; } return NULL; } /** * dwarf_read_addr - read dwarf data * @src: source address of data * @dst: destination address to store the data to * * Read 'n' bytes from @src, where 'n' is the size of an address on * the native machine. We return the number of bytes read, which * should always be 'n'. We also have to be careful when reading * from @src and writing to @dst, because they can be arbitrarily * aligned. Return 'n' - the number of bytes read. */ static inline int dwarf_read_addr(unsigned long *src, unsigned long *dst) { u32 val = get_unaligned(src); put_unaligned(val, dst); return sizeof(unsigned long *); } /** * dwarf_read_uleb128 - read unsigned LEB128 data * @addr: the address where the ULEB128 data is stored * @ret: address to store the result * * Decode an unsigned LEB128 encoded datum. The algorithm is taken * from Appendix C of the DWARF 3 spec. For information on the * encodings refer to section "7.6 - Variable Length Data". Return * the number of bytes read. */ static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret) { unsigned int result; unsigned char byte; int shift, count; result = 0; shift = 0; count = 0; while (1) { byte = __raw_readb(addr); addr++; count++; result |= (byte & 0x7f) << shift; shift += 7; if (!(byte & 0x80)) break; } *ret = result; return count; } /** * dwarf_read_leb128 - read signed LEB128 data * @addr: the address of the LEB128 encoded data * @ret: address to store the result * * Decode signed LEB128 data. The algorithm is taken from Appendix * C of the DWARF 3 spec. Return the number of bytes read. */ static inline unsigned long dwarf_read_leb128(char *addr, int *ret) { unsigned char byte; int result, shift; int num_bits; int count; result = 0; shift = 0; count = 0; while (1) { byte = __raw_readb(addr); addr++; result |= (byte & 0x7f) << shift; shift += 7; count++; if (!(byte & 0x80)) break; } /* The number of bits in a signed integer. */ num_bits = 8 * sizeof(result); if ((shift < num_bits) && (byte & 0x40)) result |= (-1 << shift); *ret = result; return count; } /** * dwarf_read_encoded_value - return the decoded value at @addr * @addr: the address of the encoded value * @val: where to write the decoded value * @encoding: the encoding with which we can decode @addr * * GCC emits encoded address in the .eh_frame FDE entries. Decode * the value at @addr using @encoding. The decoded value is written * to @val and the number of bytes read is returned. */ static int dwarf_read_encoded_value(char *addr, unsigned long *val, char encoding) { unsigned long decoded_addr = 0; int count = 0; switch (encoding & 0x70) { case DW_EH_PE_absptr: break; case DW_EH_PE_pcrel: decoded_addr = (unsigned long)addr; break; default: pr_debug("encoding=0x%x\n", (encoding & 0x70)); UNWINDER_BUG(); } if ((encoding & 0x07) == 0x00) encoding |= DW_EH_PE_udata4; switch (encoding & 0x0f) { case DW_EH_PE_sdata4: case DW_EH_PE_udata4: count += 4; decoded_addr += get_unaligned((u32 *)addr); __raw_writel(decoded_addr, val); break; default: pr_debug("encoding=0x%x\n", encoding); UNWINDER_BUG(); } return count; } /** * dwarf_entry_len - return the length of an FDE or CIE * @addr: the address of the entry * @len: the length of the entry * * Read the initial_length field of the entry and store the size of * the entry in @len. We return the number of bytes read. Return a * count of 0 on error. */ static inline int dwarf_entry_len(char *addr, unsigned long *len) { u32 initial_len; int count; initial_len = get_unaligned((u32 *)addr); count = 4; /* * An initial length field value in the range DW_LEN_EXT_LO - * DW_LEN_EXT_HI indicates an extension, and should not be * interpreted as a length. The only extension that we currently * understand is the use of DWARF64 addresses. */ if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) { /* * The 64-bit length field immediately follows the * compulsory 32-bit length field. */ if (initial_len == DW_EXT_DWARF64) { *len = get_unaligned((u64 *)addr + 4); count = 12; } else { printk(KERN_WARNING "Unknown DWARF extension\n"); count = 0; } } else *len = initial_len; return count; } /** * dwarf_lookup_cie - locate the cie * @cie_ptr: pointer to help with lookup */ static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr) { struct dwarf_cie *cie; unsigned long flags; spin_lock_irqsave(&dwarf_cie_lock, flags); /* * We've cached the last CIE we looked up because chances are * that the FDE wants this CIE. */ if (cached_cie && cached_cie->cie_pointer == cie_ptr) { cie = cached_cie; goto out; } list_for_each_entry(cie, &dwarf_cie_list, link) { if (cie->cie_pointer == cie_ptr) { cached_cie = cie; break; } } /* Couldn't find the entry in the list. */ if (&cie->link == &dwarf_cie_list) cie = NULL; out: spin_unlock_irqrestore(&dwarf_cie_lock, flags); return cie; } /** * dwarf_lookup_fde - locate the FDE that covers pc * @pc: the program counter */ struct dwarf_fde *dwarf_lookup_fde(unsigned long pc) { struct dwarf_fde *fde; unsigned long flags; spin_lock_irqsave(&dwarf_fde_lock, flags); list_for_each_entry(fde, &dwarf_fde_list, link) { unsigned long start, end; start = fde->initial_location; end = fde->initial_location + fde->address_range; if (pc >= start && pc < end) break; } /* Couldn't find the entry in the list. */ if (&fde->link == &dwarf_fde_list) fde = NULL; spin_unlock_irqrestore(&dwarf_fde_lock, flags); return fde; } /** * dwarf_cfa_execute_insns - execute instructions to calculate a CFA * @insn_start: address of the first instruction * @insn_end: address of the last instruction * @cie: the CIE for this function * @fde: the FDE for this function * @frame: the instructions calculate the CFA for this frame * @pc: the program counter of the address we're interested in * * Execute the Call Frame instruction sequence starting at * @insn_start and ending at @insn_end. The instructions describe * how to calculate the Canonical Frame Address of a stackframe. * Store the results in @frame. */ static int dwarf_cfa_execute_insns(unsigned char *insn_start, unsigned char *insn_end, struct dwarf_cie *cie, struct dwarf_fde *fde, struct dwarf_frame *frame, unsigned long pc) { unsigned char insn; unsigned char *current_insn; unsigned int count, delta, reg, expr_len, offset; struct dwarf_reg *regp; current_insn = insn_start; while (current_insn < insn_end && frame->pc <= pc) { insn = __raw_readb(current_insn++); /* * Firstly, handle the opcodes that embed their operands * in the instructions. */ switch (DW_CFA_opcode(insn)) { case DW_CFA_advance_loc: delta = DW_CFA_operand(insn); delta *= cie->code_alignment_factor; frame->pc += delta; continue; /* NOTREACHED */ case DW_CFA_offset: reg = DW_CFA_operand(insn); count = dwarf_read_uleb128(current_insn, &offset); current_insn += count; offset *= cie->data_alignment_factor; regp = dwarf_frame_alloc_reg(frame, reg); regp->addr = offset; regp->flags |= DWARF_REG_OFFSET; continue; /* NOTREACHED */ case DW_CFA_restore: reg = DW_CFA_operand(insn); continue; /* NOTREACHED */ } /* * Secondly, handle the opcodes that don't embed their * operands in the instruction. */ switch (insn) { case DW_CFA_nop: continue; case DW_CFA_advance_loc1: delta = *current_insn++; frame->pc += delta * cie->code_alignment_factor; break; case DW_CFA_advance_loc2: delta = get_unaligned((u16 *)current_insn); current_insn += 2; frame->pc += delta * cie->code_alignment_factor; break; case DW_CFA_advance_loc4: delta = get_unaligned((u32 *)current_insn); current_insn += 4; frame->pc += delta * cie->code_alignment_factor; break; case DW_CFA_offset_extended: count = dwarf_read_uleb128(current_insn, ®); current_insn += count; count = dwarf_read_uleb128(current_insn, &offset); current_insn += count; offset *= cie->data_alignment_factor; break; case DW_CFA_restore_extended: count = dwarf_read_uleb128(current_insn, ®); current_insn += count; break; case DW_CFA_undefined: count = dwarf_read_uleb128(current_insn, ®); current_insn += count; break; case DW_CFA_def_cfa: count = dwarf_read_uleb128(current_insn, &frame->cfa_register); current_insn += count; count = dwarf_read_uleb128(current_insn, &frame->cfa_offset); current_insn += count; frame->flags |= DWARF_FRAME_CFA_REG_OFFSET; break; case DW_CFA_def_cfa_register: count = dwarf_read_uleb128(current_insn, &frame->cfa_register); current_insn += count; frame->flags |= DWARF_FRAME_CFA_REG_OFFSET; break; case DW_CFA_def_cfa_offset: count = dwarf_read_uleb128(current_insn, &offset); current_insn += count; frame->cfa_offset = offset; break; case DW_CFA_def_cfa_expression: count = dwarf_read_uleb128(current_insn, &expr_len); current_insn += count; frame->cfa_expr = current_insn; frame->cfa_expr_len = expr_len; current_insn += expr_len; frame->flags |= DWARF_FRAME_CFA_REG_EXP; break; case DW_CFA_offset_extended_sf: count = dwarf_read_uleb128(current_insn, ®); current_insn += count; count = dwarf_read_leb128(current_insn, &offset); current_insn += count; offset *= cie->data_alignment_factor; regp = dwarf_frame_alloc_reg(frame, reg); regp->flags |= DWARF_REG_OFFSET; regp->addr = offset; break; case DW_CFA_val_offset: count = dwarf_read_uleb128(current_insn, ®); current_insn += count; count = dwarf_read_leb128(current_insn, &offset); offset *= cie->data_alignment_factor; regp = dwarf_frame_alloc_reg(frame, reg); regp->flags |= DWARF_VAL_OFFSET; regp->addr = offset; break; case DW_CFA_GNU_args_size: count = dwarf_read_uleb128(current_insn, &offset); current_insn += count; break; case DW_CFA_GNU_negative_offset_extended: count = dwarf_read_uleb128(current_insn, ®); current_insn += count; count = dwarf_read_uleb128(current_insn, &offset); offset *= cie->data_alignment_factor; regp = dwarf_frame_alloc_reg(frame, reg); regp->flags |= DWARF_REG_OFFSET; regp->addr = -offset; break; default: pr_debug("unhandled DWARF instruction 0x%x\n", insn); UNWINDER_BUG(); break; } } return 0; } /** * dwarf_unwind_stack - recursively unwind the stack * @pc: address of the function to unwind * @prev: struct dwarf_frame of the previous stackframe on the callstack * * Return a struct dwarf_frame representing the most recent frame * on the callstack. Each of the lower (older) stack frames are * linked via the "prev" member. */ struct dwarf_frame * dwarf_unwind_stack(unsigned long pc, struct dwarf_frame *prev) { struct dwarf_frame *frame; struct dwarf_cie *cie; struct dwarf_fde *fde; struct dwarf_reg *reg; unsigned long addr; /* * If this is the first invocation of this recursive function we * need get the contents of a physical register to get the CFA * in order to begin the virtual unwinding of the stack. * * NOTE: the return address is guaranteed to be setup by the * time this function makes its first function call. */ if (!pc && !prev) pc = (unsigned long)current_text_addr(); frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC); if (!frame) { printk(KERN_ERR "Unable to allocate a dwarf frame\n"); UNWINDER_BUG(); } INIT_LIST_HEAD(&frame->reg_list); frame->flags = 0; frame->prev = prev; frame->return_addr = 0; fde = dwarf_lookup_fde(pc); if (!fde) { /* * This is our normal exit path - the one that stops the * recursion. There's two reasons why we might exit * here, * * a) pc has no asscociated DWARF frame info and so * we don't know how to unwind this frame. This is * usually the case when we're trying to unwind a * frame that was called from some assembly code * that has no DWARF info, e.g. syscalls. * * b) the DEBUG info for pc is bogus. There's * really no way to distinguish this case from the * case above, which sucks because we could print a * warning here. */ goto bail; } cie = dwarf_lookup_cie(fde->cie_pointer); frame->pc = fde->initial_location; /* CIE initial instructions */ dwarf_cfa_execute_insns(cie->initial_instructions, cie->instructions_end, cie, fde, frame, pc); /* FDE instructions */ dwarf_cfa_execute_insns(fde->instructions, fde->end, cie, fde, frame, pc); /* Calculate the CFA */ switch (frame->flags) { case DWARF_FRAME_CFA_REG_OFFSET: if (prev) { reg = dwarf_frame_reg(prev, frame->cfa_register); UNWINDER_BUG_ON(!reg); UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET); addr = prev->cfa + reg->addr; frame->cfa = __raw_readl(addr); } else { /* * Again, this is the first invocation of this * recurisve function. We need to physically * read the contents of a register in order to * get the Canonical Frame Address for this * function. */ frame->cfa = dwarf_read_arch_reg(frame->cfa_register); } frame->cfa += frame->cfa_offset; break; default: UNWINDER_BUG(); } /* If we haven't seen the return address reg, we're screwed. */ reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG); UNWINDER_BUG_ON(!reg); UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET); addr = frame->cfa + reg->addr; frame->return_addr = __raw_readl(addr); return frame; bail: dwarf_frame_free_regs(frame); mempool_free(frame, dwarf_frame_pool); return NULL; } static int dwarf_parse_cie(void *entry, void *p, unsigned long len, unsigned char *end) { struct dwarf_cie *cie; unsigned long flags; int count; cie = kzalloc(sizeof(*cie), GFP_KERNEL); if (!cie) return -ENOMEM; cie->length = len; /* * Record the offset into the .eh_frame section * for this CIE. It allows this CIE to be * quickly and easily looked up from the * corresponding FDE. */ cie->cie_pointer = (unsigned long)entry; cie->version = *(char *)p++; UNWINDER_BUG_ON(cie->version != 1); cie->augmentation = p; p += strlen(cie->augmentation) + 1; count = dwarf_read_uleb128(p, &cie->code_alignment_factor); p += count; count = dwarf_read_leb128(p, &cie->data_alignment_factor); p += count; /* * Which column in the rule table contains the * return address? */ if (cie->version == 1) { cie->return_address_reg = __raw_readb(p); p++; } else { count = dwarf_read_uleb128(p, &cie->return_address_reg); p += count; } if (cie->augmentation[0] == 'z') { unsigned int length, count; cie->flags |= DWARF_CIE_Z_AUGMENTATION; count = dwarf_read_uleb128(p, &length); p += count; UNWINDER_BUG_ON((unsigned char *)p > end); cie->initial_instructions = p + length; cie->augmentation++; } while (*cie->augmentation) { /* * "L" indicates a byte showing how the * LSDA pointer is encoded. Skip it. */ if (*cie->augmentation == 'L') { p++; cie->augmentation++; } else if (*cie->augmentation == 'R') { /* * "R" indicates a byte showing * how FDE addresses are * encoded. */ cie->encoding = *(char *)p++; cie->augmentation++; } else if (*cie->augmentation == 'P') { /* * "R" indicates a personality * routine in the CIE * augmentation. */ UNWINDER_BUG(); } else if (*cie->augmentation == 'S') { UNWINDER_BUG(); } else { /* * Unknown augmentation. Assume * 'z' augmentation. */ p = cie->initial_instructions; UNWINDER_BUG_ON(!p); break; } } cie->initial_instructions = p; cie->instructions_end = end; /* Add to list */ spin_lock_irqsave(&dwarf_cie_lock, flags); list_add_tail(&cie->link, &dwarf_cie_list); spin_unlock_irqrestore(&dwarf_cie_lock, flags); return 0; } static int dwarf_parse_fde(void *entry, u32 entry_type, void *start, unsigned long len, unsigned char *end) { struct dwarf_fde *fde; struct dwarf_cie *cie; unsigned long flags; int count; void *p = start; fde = kzalloc(sizeof(*fde), GFP_KERNEL); if (!fde) return -ENOMEM; fde->length = len; /* * In a .eh_frame section the CIE pointer is the * delta between the address within the FDE */ fde->cie_pointer = (unsigned long)(p - entry_type - 4); cie = dwarf_lookup_cie(fde->cie_pointer); fde->cie = cie; if (cie->encoding) count = dwarf_read_encoded_value(p, &fde->initial_location, cie->encoding); else count = dwarf_read_addr(p, &fde->initial_location); p += count; if (cie->encoding) count = dwarf_read_encoded_value(p, &fde->address_range, cie->encoding & 0x0f); else count = dwarf_read_addr(p, &fde->address_range); p += count; if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) { unsigned int length; count = dwarf_read_uleb128(p, &length); p += count + length; } /* Call frame instructions. */ fde->instructions = p; fde->end = end; /* Add to list. */ spin_lock_irqsave(&dwarf_fde_lock, flags); list_add_tail(&fde->link, &dwarf_fde_list); spin_unlock_irqrestore(&dwarf_fde_lock, flags); return 0; } static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs, unsigned long *sp, const struct stacktrace_ops *ops, void *data) { struct dwarf_frame *frame, *_frame; unsigned long return_addr; _frame = NULL; return_addr = 0; while (1) { frame = dwarf_unwind_stack(return_addr, _frame); if (_frame) { dwarf_frame_free_regs(_frame); mempool_free(_frame, dwarf_frame_pool); } _frame = frame; if (!frame || !frame->return_addr) break; return_addr = frame->return_addr; ops->address(data, return_addr, 1); } } static struct unwinder dwarf_unwinder = { .name = "dwarf-unwinder", .dump = dwarf_unwinder_dump, .rating = 150, }; static void dwarf_unwinder_cleanup(void) { struct dwarf_cie *cie; struct dwarf_fde *fde; /* * Deallocate all the memory allocated for the DWARF unwinder. * Traverse all the FDE/CIE lists and remove and free all the * memory associated with those data structures. */ list_for_each_entry(cie, &dwarf_cie_list, link) kfree(cie); list_for_each_entry(fde, &dwarf_fde_list, link) kfree(fde); kmem_cache_destroy(dwarf_reg_cachep); kmem_cache_destroy(dwarf_frame_cachep); } /** * dwarf_unwinder_init - initialise the dwarf unwinder * * Build the data structures describing the .dwarf_frame section to * make it easier to lookup CIE and FDE entries. Because the * .eh_frame section is packed as tightly as possible it is not * easy to lookup the FDE for a given PC, so we build a list of FDE * and CIE entries that make it easier. */ static int __init dwarf_unwinder_init(void) { u32 entry_type; void *p, *entry; int count, err; unsigned long len; unsigned int c_entries, f_entries; unsigned char *end; INIT_LIST_HEAD(&dwarf_cie_list); INIT_LIST_HEAD(&dwarf_fde_list); c_entries = 0; f_entries = 0; entry = &__start_eh_frame; dwarf_frame_cachep = kmem_cache_create("dwarf_frames", sizeof(struct dwarf_frame), 0, SLAB_PANIC, NULL); dwarf_reg_cachep = kmem_cache_create("dwarf_regs", sizeof(struct dwarf_reg), 0, SLAB_PANIC, NULL); dwarf_frame_pool = mempool_create(DWARF_FRAME_MIN_REQ, mempool_alloc_slab, mempool_free_slab, dwarf_frame_cachep); dwarf_reg_pool = mempool_create(DWARF_REG_MIN_REQ, mempool_alloc_slab, mempool_free_slab, dwarf_reg_cachep); while ((char *)entry < __stop_eh_frame) { p = entry; count = dwarf_entry_len(p, &len); if (count == 0) { /* * We read a bogus length field value. There is * nothing we can do here apart from disabling * the DWARF unwinder. We can't even skip this * entry and move to the next one because 'len' * tells us where our next entry is. */ goto out; } else p += count; /* initial length does not include itself */ end = p + len; entry_type = get_unaligned((u32 *)p); p += 4; if (entry_type == DW_EH_FRAME_CIE) { err = dwarf_parse_cie(entry, p, len, end); if (err < 0) goto out; else c_entries++; } else { err = dwarf_parse_fde(entry, entry_type, p, len, end); if (err < 0) goto out; else f_entries++; } entry = (char *)entry + len + 4; } printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n", c_entries, f_entries); err = unwinder_register(&dwarf_unwinder); if (err) goto out; return 0; out: printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err); dwarf_unwinder_cleanup(); return -EINVAL; } early_initcall(dwarf_unwinder_init);