2 * Copyright (C) 2009 Matt Fleming <matt@console-pimps.org>
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
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.
13 * - DWARF64 doesn't work.
14 * - Registers with DWARF_VAL_OFFSET rules aren't handled properly.
18 #include <linux/kernel.h>
20 #include <linux/list.h>
21 #include <linux/mempool.h>
23 #include <asm/dwarf.h>
24 #include <asm/unwinder.h>
25 #include <asm/sections.h>
26 #include <asm/unaligned.h>
27 #include <asm/stacktrace.h>
29 /* Reserve enough memory for two stack frames */
30 #define DWARF_FRAME_MIN_REQ 2
31 /* ... with 4 registers per frame. */
32 #define DWARF_REG_MIN_REQ (DWARF_FRAME_MIN_REQ * 4)
34 static struct kmem_cache *dwarf_frame_cachep;
35 static mempool_t *dwarf_frame_pool;
37 static struct kmem_cache *dwarf_reg_cachep;
38 static mempool_t *dwarf_reg_pool;
40 static LIST_HEAD(dwarf_cie_list);
41 static DEFINE_SPINLOCK(dwarf_cie_lock);
43 static LIST_HEAD(dwarf_fde_list);
44 static DEFINE_SPINLOCK(dwarf_fde_lock);
46 static struct dwarf_cie *cached_cie;
49 * dwarf_frame_alloc_reg - allocate memory for a DWARF register
50 * @frame: the DWARF frame whose list of registers we insert on
51 * @reg_num: the register number
53 * Allocate space for, and initialise, a dwarf reg from
54 * dwarf_reg_pool and insert it onto the (unsorted) linked-list of
55 * dwarf registers for @frame.
57 * Return the initialised DWARF reg.
59 static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
62 struct dwarf_reg *reg;
64 reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC);
66 printk(KERN_WARNING "Unable to allocate a DWARF register\n");
68 * Let's just bomb hard here, we have no way to
74 reg->number = reg_num;
78 list_add(®->link, &frame->reg_list);
83 static void dwarf_frame_free_regs(struct dwarf_frame *frame)
85 struct dwarf_reg *reg, *n;
87 list_for_each_entry_safe(reg, n, &frame->reg_list, link) {
89 mempool_free(reg, dwarf_reg_pool);
94 * dwarf_frame_reg - return a DWARF register
95 * @frame: the DWARF frame to search in for @reg_num
96 * @reg_num: the register number to search for
98 * Lookup and return the dwarf reg @reg_num for this frame. Return
99 * NULL if @reg_num is an register invalid number.
101 static struct dwarf_reg *dwarf_frame_reg(struct dwarf_frame *frame,
102 unsigned int reg_num)
104 struct dwarf_reg *reg;
106 list_for_each_entry(reg, &frame->reg_list, link) {
107 if (reg->number == reg_num)
115 * dwarf_read_addr - read dwarf data
116 * @src: source address of data
117 * @dst: destination address to store the data to
119 * Read 'n' bytes from @src, where 'n' is the size of an address on
120 * the native machine. We return the number of bytes read, which
121 * should always be 'n'. We also have to be careful when reading
122 * from @src and writing to @dst, because they can be arbitrarily
123 * aligned. Return 'n' - the number of bytes read.
125 static inline int dwarf_read_addr(unsigned long *src, unsigned long *dst)
127 u32 val = get_unaligned(src);
128 put_unaligned(val, dst);
129 return sizeof(unsigned long *);
133 * dwarf_read_uleb128 - read unsigned LEB128 data
134 * @addr: the address where the ULEB128 data is stored
135 * @ret: address to store the result
137 * Decode an unsigned LEB128 encoded datum. The algorithm is taken
138 * from Appendix C of the DWARF 3 spec. For information on the
139 * encodings refer to section "7.6 - Variable Length Data". Return
140 * the number of bytes read.
142 static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
153 byte = __raw_readb(addr);
157 result |= (byte & 0x7f) << shift;
170 * dwarf_read_leb128 - read signed LEB128 data
171 * @addr: the address of the LEB128 encoded data
172 * @ret: address to store the result
174 * Decode signed LEB128 data. The algorithm is taken from Appendix
175 * C of the DWARF 3 spec. Return the number of bytes read.
177 static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
189 byte = __raw_readb(addr);
191 result |= (byte & 0x7f) << shift;
199 /* The number of bits in a signed integer. */
200 num_bits = 8 * sizeof(result);
202 if ((shift < num_bits) && (byte & 0x40))
203 result |= (-1 << shift);
211 * dwarf_read_encoded_value - return the decoded value at @addr
212 * @addr: the address of the encoded value
213 * @val: where to write the decoded value
214 * @encoding: the encoding with which we can decode @addr
216 * GCC emits encoded address in the .eh_frame FDE entries. Decode
217 * the value at @addr using @encoding. The decoded value is written
218 * to @val and the number of bytes read is returned.
220 static int dwarf_read_encoded_value(char *addr, unsigned long *val,
223 unsigned long decoded_addr = 0;
226 switch (encoding & 0x70) {
227 case DW_EH_PE_absptr:
230 decoded_addr = (unsigned long)addr;
233 pr_debug("encoding=0x%x\n", (encoding & 0x70));
237 if ((encoding & 0x07) == 0x00)
238 encoding |= DW_EH_PE_udata4;
240 switch (encoding & 0x0f) {
241 case DW_EH_PE_sdata4:
242 case DW_EH_PE_udata4:
244 decoded_addr += get_unaligned((u32 *)addr);
245 __raw_writel(decoded_addr, val);
248 pr_debug("encoding=0x%x\n", encoding);
256 * dwarf_entry_len - return the length of an FDE or CIE
257 * @addr: the address of the entry
258 * @len: the length of the entry
260 * Read the initial_length field of the entry and store the size of
261 * the entry in @len. We return the number of bytes read. Return a
262 * count of 0 on error.
264 static inline int dwarf_entry_len(char *addr, unsigned long *len)
269 initial_len = get_unaligned((u32 *)addr);
273 * An initial length field value in the range DW_LEN_EXT_LO -
274 * DW_LEN_EXT_HI indicates an extension, and should not be
275 * interpreted as a length. The only extension that we currently
276 * understand is the use of DWARF64 addresses.
278 if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
280 * The 64-bit length field immediately follows the
281 * compulsory 32-bit length field.
283 if (initial_len == DW_EXT_DWARF64) {
284 *len = get_unaligned((u64 *)addr + 4);
287 printk(KERN_WARNING "Unknown DWARF extension\n");
297 * dwarf_lookup_cie - locate the cie
298 * @cie_ptr: pointer to help with lookup
300 static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
302 struct dwarf_cie *cie;
305 spin_lock_irqsave(&dwarf_cie_lock, flags);
308 * We've cached the last CIE we looked up because chances are
309 * that the FDE wants this CIE.
311 if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
316 list_for_each_entry(cie, &dwarf_cie_list, link) {
317 if (cie->cie_pointer == cie_ptr) {
323 /* Couldn't find the entry in the list. */
324 if (&cie->link == &dwarf_cie_list)
327 spin_unlock_irqrestore(&dwarf_cie_lock, flags);
332 * dwarf_lookup_fde - locate the FDE that covers pc
333 * @pc: the program counter
335 struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
337 struct dwarf_fde *fde;
340 spin_lock_irqsave(&dwarf_fde_lock, flags);
342 list_for_each_entry(fde, &dwarf_fde_list, link) {
343 unsigned long start, end;
345 start = fde->initial_location;
346 end = fde->initial_location + fde->address_range;
348 if (pc >= start && pc < end)
352 /* Couldn't find the entry in the list. */
353 if (&fde->link == &dwarf_fde_list)
356 spin_unlock_irqrestore(&dwarf_fde_lock, flags);
362 * dwarf_cfa_execute_insns - execute instructions to calculate a CFA
363 * @insn_start: address of the first instruction
364 * @insn_end: address of the last instruction
365 * @cie: the CIE for this function
366 * @fde: the FDE for this function
367 * @frame: the instructions calculate the CFA for this frame
368 * @pc: the program counter of the address we're interested in
370 * Execute the Call Frame instruction sequence starting at
371 * @insn_start and ending at @insn_end. The instructions describe
372 * how to calculate the Canonical Frame Address of a stackframe.
373 * Store the results in @frame.
375 static int dwarf_cfa_execute_insns(unsigned char *insn_start,
376 unsigned char *insn_end,
377 struct dwarf_cie *cie,
378 struct dwarf_fde *fde,
379 struct dwarf_frame *frame,
383 unsigned char *current_insn;
384 unsigned int count, delta, reg, expr_len, offset;
385 struct dwarf_reg *regp;
387 current_insn = insn_start;
389 while (current_insn < insn_end && frame->pc <= pc) {
390 insn = __raw_readb(current_insn++);
393 * Firstly, handle the opcodes that embed their operands
394 * in the instructions.
396 switch (DW_CFA_opcode(insn)) {
397 case DW_CFA_advance_loc:
398 delta = DW_CFA_operand(insn);
399 delta *= cie->code_alignment_factor;
404 reg = DW_CFA_operand(insn);
405 count = dwarf_read_uleb128(current_insn, &offset);
406 current_insn += count;
407 offset *= cie->data_alignment_factor;
408 regp = dwarf_frame_alloc_reg(frame, reg);
410 regp->flags |= DWARF_REG_OFFSET;
414 reg = DW_CFA_operand(insn);
420 * Secondly, handle the opcodes that don't embed their
421 * operands in the instruction.
426 case DW_CFA_advance_loc1:
427 delta = *current_insn++;
428 frame->pc += delta * cie->code_alignment_factor;
430 case DW_CFA_advance_loc2:
431 delta = get_unaligned((u16 *)current_insn);
433 frame->pc += delta * cie->code_alignment_factor;
435 case DW_CFA_advance_loc4:
436 delta = get_unaligned((u32 *)current_insn);
438 frame->pc += delta * cie->code_alignment_factor;
440 case DW_CFA_offset_extended:
441 count = dwarf_read_uleb128(current_insn, ®);
442 current_insn += count;
443 count = dwarf_read_uleb128(current_insn, &offset);
444 current_insn += count;
445 offset *= cie->data_alignment_factor;
447 case DW_CFA_restore_extended:
448 count = dwarf_read_uleb128(current_insn, ®);
449 current_insn += count;
451 case DW_CFA_undefined:
452 count = dwarf_read_uleb128(current_insn, ®);
453 current_insn += count;
454 regp = dwarf_frame_alloc_reg(frame, reg);
455 regp->flags |= DWARF_UNDEFINED;
458 count = dwarf_read_uleb128(current_insn,
459 &frame->cfa_register);
460 current_insn += count;
461 count = dwarf_read_uleb128(current_insn,
463 current_insn += count;
465 frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
467 case DW_CFA_def_cfa_register:
468 count = dwarf_read_uleb128(current_insn,
469 &frame->cfa_register);
470 current_insn += count;
471 frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
473 case DW_CFA_def_cfa_offset:
474 count = dwarf_read_uleb128(current_insn, &offset);
475 current_insn += count;
476 frame->cfa_offset = offset;
478 case DW_CFA_def_cfa_expression:
479 count = dwarf_read_uleb128(current_insn, &expr_len);
480 current_insn += count;
482 frame->cfa_expr = current_insn;
483 frame->cfa_expr_len = expr_len;
484 current_insn += expr_len;
486 frame->flags |= DWARF_FRAME_CFA_REG_EXP;
488 case DW_CFA_offset_extended_sf:
489 count = dwarf_read_uleb128(current_insn, ®);
490 current_insn += count;
491 count = dwarf_read_leb128(current_insn, &offset);
492 current_insn += count;
493 offset *= cie->data_alignment_factor;
494 regp = dwarf_frame_alloc_reg(frame, reg);
495 regp->flags |= DWARF_REG_OFFSET;
498 case DW_CFA_val_offset:
499 count = dwarf_read_uleb128(current_insn, ®);
500 current_insn += count;
501 count = dwarf_read_leb128(current_insn, &offset);
502 offset *= cie->data_alignment_factor;
503 regp = dwarf_frame_alloc_reg(frame, reg);
504 regp->flags |= DWARF_VAL_OFFSET;
507 case DW_CFA_GNU_args_size:
508 count = dwarf_read_uleb128(current_insn, &offset);
509 current_insn += count;
511 case DW_CFA_GNU_negative_offset_extended:
512 count = dwarf_read_uleb128(current_insn, ®);
513 current_insn += count;
514 count = dwarf_read_uleb128(current_insn, &offset);
515 offset *= cie->data_alignment_factor;
517 regp = dwarf_frame_alloc_reg(frame, reg);
518 regp->flags |= DWARF_REG_OFFSET;
519 regp->addr = -offset;
522 pr_debug("unhandled DWARF instruction 0x%x\n", insn);
532 * dwarf_unwind_stack - recursively unwind the stack
533 * @pc: address of the function to unwind
534 * @prev: struct dwarf_frame of the previous stackframe on the callstack
536 * Return a struct dwarf_frame representing the most recent frame
537 * on the callstack. Each of the lower (older) stack frames are
538 * linked via the "prev" member.
540 struct dwarf_frame * dwarf_unwind_stack(unsigned long pc,
541 struct dwarf_frame *prev)
543 struct dwarf_frame *frame;
544 struct dwarf_cie *cie;
545 struct dwarf_fde *fde;
546 struct dwarf_reg *reg;
550 * If this is the first invocation of this recursive function we
551 * need get the contents of a physical register to get the CFA
552 * in order to begin the virtual unwinding of the stack.
554 * NOTE: the return address is guaranteed to be setup by the
555 * time this function makes its first function call.
558 pc = (unsigned long)current_text_addr();
560 frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
562 printk(KERN_ERR "Unable to allocate a dwarf frame\n");
566 INIT_LIST_HEAD(&frame->reg_list);
569 frame->return_addr = 0;
571 fde = dwarf_lookup_fde(pc);
574 * This is our normal exit path - the one that stops the
575 * recursion. There's two reasons why we might exit
578 * a) pc has no asscociated DWARF frame info and so
579 * we don't know how to unwind this frame. This is
580 * usually the case when we're trying to unwind a
581 * frame that was called from some assembly code
582 * that has no DWARF info, e.g. syscalls.
584 * b) the DEBUG info for pc is bogus. There's
585 * really no way to distinguish this case from the
586 * case above, which sucks because we could print a
592 cie = dwarf_lookup_cie(fde->cie_pointer);
594 frame->pc = fde->initial_location;
596 /* CIE initial instructions */
597 dwarf_cfa_execute_insns(cie->initial_instructions,
598 cie->instructions_end, cie, fde,
601 /* FDE instructions */
602 dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
605 /* Calculate the CFA */
606 switch (frame->flags) {
607 case DWARF_FRAME_CFA_REG_OFFSET:
609 reg = dwarf_frame_reg(prev, frame->cfa_register);
610 UNWINDER_BUG_ON(!reg);
611 UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
613 addr = prev->cfa + reg->addr;
614 frame->cfa = __raw_readl(addr);
618 * Again, this is the first invocation of this
619 * recurisve function. We need to physically
620 * read the contents of a register in order to
621 * get the Canonical Frame Address for this
624 frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
627 frame->cfa += frame->cfa_offset;
633 reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);
636 * If we haven't seen the return address register or the return
637 * address column is undefined then we must assume that this is
638 * the end of the callstack.
640 if (!reg || reg->flags == DWARF_UNDEFINED)
643 UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
645 addr = frame->cfa + reg->addr;
646 frame->return_addr = __raw_readl(addr);
651 dwarf_frame_free_regs(frame);
652 mempool_free(frame, dwarf_frame_pool);
656 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
659 struct dwarf_cie *cie;
663 cie = kzalloc(sizeof(*cie), GFP_KERNEL);
670 * Record the offset into the .eh_frame section
671 * for this CIE. It allows this CIE to be
672 * quickly and easily looked up from the
675 cie->cie_pointer = (unsigned long)entry;
677 cie->version = *(char *)p++;
678 UNWINDER_BUG_ON(cie->version != 1);
680 cie->augmentation = p;
681 p += strlen(cie->augmentation) + 1;
683 count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
686 count = dwarf_read_leb128(p, &cie->data_alignment_factor);
690 * Which column in the rule table contains the
693 if (cie->version == 1) {
694 cie->return_address_reg = __raw_readb(p);
697 count = dwarf_read_uleb128(p, &cie->return_address_reg);
701 if (cie->augmentation[0] == 'z') {
702 unsigned int length, count;
703 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
705 count = dwarf_read_uleb128(p, &length);
708 UNWINDER_BUG_ON((unsigned char *)p > end);
710 cie->initial_instructions = p + length;
714 while (*cie->augmentation) {
716 * "L" indicates a byte showing how the
717 * LSDA pointer is encoded. Skip it.
719 if (*cie->augmentation == 'L') {
722 } else if (*cie->augmentation == 'R') {
724 * "R" indicates a byte showing
725 * how FDE addresses are
728 cie->encoding = *(char *)p++;
730 } else if (*cie->augmentation == 'P') {
732 * "R" indicates a personality
737 } else if (*cie->augmentation == 'S') {
741 * Unknown augmentation. Assume
744 p = cie->initial_instructions;
750 cie->initial_instructions = p;
751 cie->instructions_end = end;
754 spin_lock_irqsave(&dwarf_cie_lock, flags);
755 list_add_tail(&cie->link, &dwarf_cie_list);
756 spin_unlock_irqrestore(&dwarf_cie_lock, flags);
761 static int dwarf_parse_fde(void *entry, u32 entry_type,
762 void *start, unsigned long len,
765 struct dwarf_fde *fde;
766 struct dwarf_cie *cie;
771 fde = kzalloc(sizeof(*fde), GFP_KERNEL);
778 * In a .eh_frame section the CIE pointer is the
779 * delta between the address within the FDE
781 fde->cie_pointer = (unsigned long)(p - entry_type - 4);
783 cie = dwarf_lookup_cie(fde->cie_pointer);
787 count = dwarf_read_encoded_value(p, &fde->initial_location,
790 count = dwarf_read_addr(p, &fde->initial_location);
795 count = dwarf_read_encoded_value(p, &fde->address_range,
796 cie->encoding & 0x0f);
798 count = dwarf_read_addr(p, &fde->address_range);
802 if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
804 count = dwarf_read_uleb128(p, &length);
808 /* Call frame instructions. */
809 fde->instructions = p;
813 spin_lock_irqsave(&dwarf_fde_lock, flags);
814 list_add_tail(&fde->link, &dwarf_fde_list);
815 spin_unlock_irqrestore(&dwarf_fde_lock, flags);
820 static void dwarf_unwinder_dump(struct task_struct *task,
821 struct pt_regs *regs,
823 const struct stacktrace_ops *ops,
826 struct dwarf_frame *frame, *_frame;
827 unsigned long return_addr;
833 frame = dwarf_unwind_stack(return_addr, _frame);
836 dwarf_frame_free_regs(_frame);
837 mempool_free(_frame, dwarf_frame_pool);
842 if (!frame || !frame->return_addr)
845 return_addr = frame->return_addr;
846 ops->address(data, return_addr, 1);
850 static struct unwinder dwarf_unwinder = {
851 .name = "dwarf-unwinder",
852 .dump = dwarf_unwinder_dump,
856 static void dwarf_unwinder_cleanup(void)
858 struct dwarf_cie *cie;
859 struct dwarf_fde *fde;
862 * Deallocate all the memory allocated for the DWARF unwinder.
863 * Traverse all the FDE/CIE lists and remove and free all the
864 * memory associated with those data structures.
866 list_for_each_entry(cie, &dwarf_cie_list, link)
869 list_for_each_entry(fde, &dwarf_fde_list, link)
872 kmem_cache_destroy(dwarf_reg_cachep);
873 kmem_cache_destroy(dwarf_frame_cachep);
877 * dwarf_unwinder_init - initialise the dwarf unwinder
879 * Build the data structures describing the .dwarf_frame section to
880 * make it easier to lookup CIE and FDE entries. Because the
881 * .eh_frame section is packed as tightly as possible it is not
882 * easy to lookup the FDE for a given PC, so we build a list of FDE
883 * and CIE entries that make it easier.
885 static int __init dwarf_unwinder_init(void)
891 unsigned int c_entries, f_entries;
893 INIT_LIST_HEAD(&dwarf_cie_list);
894 INIT_LIST_HEAD(&dwarf_fde_list);
898 entry = &__start_eh_frame;
900 dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
901 sizeof(struct dwarf_frame), 0,
902 SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);
904 dwarf_reg_cachep = kmem_cache_create("dwarf_regs",
905 sizeof(struct dwarf_reg), 0,
906 SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);
908 dwarf_frame_pool = mempool_create(DWARF_FRAME_MIN_REQ,
913 dwarf_reg_pool = mempool_create(DWARF_REG_MIN_REQ,
918 while ((char *)entry < __stop_eh_frame) {
921 count = dwarf_entry_len(p, &len);
924 * We read a bogus length field value. There is
925 * nothing we can do here apart from disabling
926 * the DWARF unwinder. We can't even skip this
927 * entry and move to the next one because 'len'
928 * tells us where our next entry is.
934 /* initial length does not include itself */
937 entry_type = get_unaligned((u32 *)p);
940 if (entry_type == DW_EH_FRAME_CIE) {
941 err = dwarf_parse_cie(entry, p, len, end);
947 err = dwarf_parse_fde(entry, entry_type, p, len, end);
954 entry = (char *)entry + len + 4;
957 printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
958 c_entries, f_entries);
960 err = unwinder_register(&dwarf_unwinder);
967 printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
968 dwarf_unwinder_cleanup();
971 early_initcall(dwarf_unwinder_init);