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.
17 #include <linux/kernel.h>
19 #include <linux/list.h>
21 #include <asm/dwarf.h>
22 #include <asm/unwinder.h>
23 #include <asm/sections.h>
24 #include <asm-generic/unaligned.h>
25 #include <asm/dwarf.h>
26 #include <asm/stacktrace.h>
28 static LIST_HEAD(dwarf_cie_list
);
29 DEFINE_SPINLOCK(dwarf_cie_lock
);
31 static LIST_HEAD(dwarf_fde_list
);
32 DEFINE_SPINLOCK(dwarf_fde_lock
);
34 static struct dwarf_cie
*cached_cie
;
37 * Figure out whether we need to allocate some dwarf registers. If dwarf
38 * registers have already been allocated then we may need to realloc
39 * them. "reg" is a register number that we need to be able to access
42 * Register numbers start at zero, therefore we need to allocate space
43 * for "reg" + 1 registers.
45 static void dwarf_frame_alloc_regs(struct dwarf_frame
*frame
,
48 struct dwarf_reg
*regs
;
49 unsigned int num_regs
= reg
+ 1;
53 new_size
= num_regs
* sizeof(*regs
);
54 old_size
= frame
->num_regs
* sizeof(*regs
);
56 /* Fast path: don't allocate any regs if we've already got enough. */
57 if (frame
->num_regs
>= num_regs
)
60 regs
= kzalloc(new_size
, GFP_KERNEL
);
62 printk(KERN_WARNING
"Unable to allocate DWARF registers\n");
64 * Let's just bomb hard here, we have no way to
71 memcpy(regs
, frame
->regs
, old_size
);
76 frame
->num_regs
= num_regs
;
80 * dwarf_read_addr - read dwarf data
81 * @src: source address of data
82 * @dst: destination address to store the data to
84 * Read 'n' bytes from @src, where 'n' is the size of an address on
85 * the native machine. We return the number of bytes read, which
86 * should always be 'n'. We also have to be careful when reading
87 * from @src and writing to @dst, because they can be arbitrarily
88 * aligned. Return 'n' - the number of bytes read.
90 static inline int dwarf_read_addr(void *src
, void *dst
)
92 u32 val
= __get_unaligned_cpu32(src
);
93 __put_unaligned_cpu32(val
, dst
);
95 return sizeof(unsigned long *);
99 * dwarf_read_uleb128 - read unsigned LEB128 data
100 * @addr: the address where the ULEB128 data is stored
101 * @ret: address to store the result
103 * Decode an unsigned LEB128 encoded datum. The algorithm is taken
104 * from Appendix C of the DWARF 3 spec. For information on the
105 * encodings refer to section "7.6 - Variable Length Data". Return
106 * the number of bytes read.
108 static inline unsigned long dwarf_read_uleb128(char *addr
, unsigned int *ret
)
119 byte
= __raw_readb(addr
);
123 result
|= (byte
& 0x7f) << shift
;
136 * dwarf_read_leb128 - read signed LEB128 data
137 * @addr: the address of the LEB128 encoded data
138 * @ret: address to store the result
140 * Decode signed LEB128 data. The algorithm is taken from Appendix
141 * C of the DWARF 3 spec. Return the number of bytes read.
143 static inline unsigned long dwarf_read_leb128(char *addr
, int *ret
)
155 byte
= __raw_readb(addr
);
157 result
|= (byte
& 0x7f) << shift
;
165 /* The number of bits in a signed integer. */
166 num_bits
= 8 * sizeof(result
);
168 if ((shift
< num_bits
) && (byte
& 0x40))
169 result
|= (-1 << shift
);
177 * dwarf_read_encoded_value - return the decoded value at @addr
178 * @addr: the address of the encoded value
179 * @val: where to write the decoded value
180 * @encoding: the encoding with which we can decode @addr
182 * GCC emits encoded address in the .eh_frame FDE entries. Decode
183 * the value at @addr using @encoding. The decoded value is written
184 * to @val and the number of bytes read is returned.
186 static int dwarf_read_encoded_value(char *addr
, unsigned long *val
,
189 unsigned long decoded_addr
= 0;
192 switch (encoding
& 0x70) {
193 case DW_EH_PE_absptr
:
196 decoded_addr
= (unsigned long)addr
;
199 pr_debug("encoding=0x%x\n", (encoding
& 0x70));
203 if ((encoding
& 0x07) == 0x00)
204 encoding
|= DW_EH_PE_udata4
;
206 switch (encoding
& 0x0f) {
207 case DW_EH_PE_sdata4
:
208 case DW_EH_PE_udata4
:
210 decoded_addr
+= __get_unaligned_cpu32(addr
);
211 __raw_writel(decoded_addr
, val
);
214 pr_debug("encoding=0x%x\n", encoding
);
222 * dwarf_entry_len - return the length of an FDE or CIE
223 * @addr: the address of the entry
224 * @len: the length of the entry
226 * Read the initial_length field of the entry and store the size of
227 * the entry in @len. We return the number of bytes read. Return a
228 * count of 0 on error.
230 static inline int dwarf_entry_len(char *addr
, unsigned long *len
)
235 initial_len
= __get_unaligned_cpu32(addr
);
239 * An initial length field value in the range DW_LEN_EXT_LO -
240 * DW_LEN_EXT_HI indicates an extension, and should not be
241 * interpreted as a length. The only extension that we currently
242 * understand is the use of DWARF64 addresses.
244 if (initial_len
>= DW_EXT_LO
&& initial_len
<= DW_EXT_HI
) {
246 * The 64-bit length field immediately follows the
247 * compulsory 32-bit length field.
249 if (initial_len
== DW_EXT_DWARF64
) {
250 *len
= __get_unaligned_cpu64(addr
+ 4);
253 printk(KERN_WARNING
"Unknown DWARF extension\n");
263 * dwarf_lookup_cie - locate the cie
264 * @cie_ptr: pointer to help with lookup
266 static struct dwarf_cie
*dwarf_lookup_cie(unsigned long cie_ptr
)
268 struct dwarf_cie
*cie
, *n
;
271 spin_lock_irqsave(&dwarf_cie_lock
, flags
);
274 * We've cached the last CIE we looked up because chances are
275 * that the FDE wants this CIE.
277 if (cached_cie
&& cached_cie
->cie_pointer
== cie_ptr
) {
282 list_for_each_entry_safe(cie
, n
, &dwarf_cie_list
, link
) {
283 if (cie
->cie_pointer
== cie_ptr
) {
289 /* Couldn't find the entry in the list. */
290 if (&cie
->link
== &dwarf_cie_list
)
293 spin_unlock_irqrestore(&dwarf_cie_lock
, flags
);
298 * dwarf_lookup_fde - locate the FDE that covers pc
299 * @pc: the program counter
301 struct dwarf_fde
*dwarf_lookup_fde(unsigned long pc
)
304 struct dwarf_fde
*fde
, *n
;
306 spin_lock_irqsave(&dwarf_fde_lock
, flags
);
307 list_for_each_entry_safe(fde
, n
, &dwarf_fde_list
, link
) {
308 unsigned long start
, end
;
310 start
= fde
->initial_location
;
311 end
= fde
->initial_location
+ fde
->address_range
;
313 if (pc
>= start
&& pc
< end
)
317 /* Couldn't find the entry in the list. */
318 if (&fde
->link
== &dwarf_fde_list
)
321 spin_unlock_irqrestore(&dwarf_fde_lock
, flags
);
327 * dwarf_cfa_execute_insns - execute instructions to calculate a CFA
328 * @insn_start: address of the first instruction
329 * @insn_end: address of the last instruction
330 * @cie: the CIE for this function
331 * @fde: the FDE for this function
332 * @frame: the instructions calculate the CFA for this frame
333 * @pc: the program counter of the address we're interested in
335 * Execute the Call Frame instruction sequence starting at
336 * @insn_start and ending at @insn_end. The instructions describe
337 * how to calculate the Canonical Frame Address of a stackframe.
338 * Store the results in @frame.
340 static int dwarf_cfa_execute_insns(unsigned char *insn_start
,
341 unsigned char *insn_end
,
342 struct dwarf_cie
*cie
,
343 struct dwarf_fde
*fde
,
344 struct dwarf_frame
*frame
,
348 unsigned char *current_insn
;
349 unsigned int count
, delta
, reg
, expr_len
, offset
;
351 current_insn
= insn_start
;
353 while (current_insn
< insn_end
&& frame
->pc
<= pc
) {
354 insn
= __raw_readb(current_insn
++);
357 * Firstly, handle the opcodes that embed their operands
358 * in the instructions.
360 switch (DW_CFA_opcode(insn
)) {
361 case DW_CFA_advance_loc
:
362 delta
= DW_CFA_operand(insn
);
363 delta
*= cie
->code_alignment_factor
;
368 reg
= DW_CFA_operand(insn
);
369 count
= dwarf_read_uleb128(current_insn
, &offset
);
370 current_insn
+= count
;
371 offset
*= cie
->data_alignment_factor
;
372 dwarf_frame_alloc_regs(frame
, reg
);
373 frame
->regs
[reg
].addr
= offset
;
374 frame
->regs
[reg
].flags
|= DWARF_REG_OFFSET
;
378 reg
= DW_CFA_operand(insn
);
384 * Secondly, handle the opcodes that don't embed their
385 * operands in the instruction.
390 case DW_CFA_advance_loc1
:
391 delta
= *current_insn
++;
392 frame
->pc
+= delta
* cie
->code_alignment_factor
;
394 case DW_CFA_advance_loc2
:
395 delta
= __get_unaligned_cpu16(current_insn
);
397 frame
->pc
+= delta
* cie
->code_alignment_factor
;
399 case DW_CFA_advance_loc4
:
400 delta
= __get_unaligned_cpu32(current_insn
);
402 frame
->pc
+= delta
* cie
->code_alignment_factor
;
404 case DW_CFA_offset_extended
:
405 count
= dwarf_read_uleb128(current_insn
, ®
);
406 current_insn
+= count
;
407 count
= dwarf_read_uleb128(current_insn
, &offset
);
408 current_insn
+= count
;
409 offset
*= cie
->data_alignment_factor
;
411 case DW_CFA_restore_extended
:
412 count
= dwarf_read_uleb128(current_insn
, ®
);
413 current_insn
+= count
;
415 case DW_CFA_undefined
:
416 count
= dwarf_read_uleb128(current_insn
, ®
);
417 current_insn
+= count
;
420 count
= dwarf_read_uleb128(current_insn
,
421 &frame
->cfa_register
);
422 current_insn
+= count
;
423 count
= dwarf_read_uleb128(current_insn
,
425 current_insn
+= count
;
427 frame
->flags
|= DWARF_FRAME_CFA_REG_OFFSET
;
429 case DW_CFA_def_cfa_register
:
430 count
= dwarf_read_uleb128(current_insn
,
431 &frame
->cfa_register
);
432 current_insn
+= count
;
433 frame
->flags
|= DWARF_FRAME_CFA_REG_OFFSET
;
435 case DW_CFA_def_cfa_offset
:
436 count
= dwarf_read_uleb128(current_insn
, &offset
);
437 current_insn
+= count
;
438 frame
->cfa_offset
= offset
;
440 case DW_CFA_def_cfa_expression
:
441 count
= dwarf_read_uleb128(current_insn
, &expr_len
);
442 current_insn
+= count
;
444 frame
->cfa_expr
= current_insn
;
445 frame
->cfa_expr_len
= expr_len
;
446 current_insn
+= expr_len
;
448 frame
->flags
|= DWARF_FRAME_CFA_REG_EXP
;
450 case DW_CFA_offset_extended_sf
:
451 count
= dwarf_read_uleb128(current_insn
, ®
);
452 current_insn
+= count
;
453 count
= dwarf_read_leb128(current_insn
, &offset
);
454 current_insn
+= count
;
455 offset
*= cie
->data_alignment_factor
;
456 dwarf_frame_alloc_regs(frame
, reg
);
457 frame
->regs
[reg
].flags
|= DWARF_REG_OFFSET
;
458 frame
->regs
[reg
].addr
= offset
;
460 case DW_CFA_val_offset
:
461 count
= dwarf_read_uleb128(current_insn
, ®
);
462 current_insn
+= count
;
463 count
= dwarf_read_leb128(current_insn
, &offset
);
464 offset
*= cie
->data_alignment_factor
;
465 frame
->regs
[reg
].flags
|= DWARF_REG_OFFSET
;
466 frame
->regs
[reg
].addr
= offset
;
469 pr_debug("unhandled DWARF instruction 0x%x\n", insn
);
478 * dwarf_unwind_stack - recursively unwind the stack
479 * @pc: address of the function to unwind
480 * @prev: struct dwarf_frame of the previous stackframe on the callstack
482 * Return a struct dwarf_frame representing the most recent frame
483 * on the callstack. Each of the lower (older) stack frames are
484 * linked via the "prev" member.
486 struct dwarf_frame
*dwarf_unwind_stack(unsigned long pc
,
487 struct dwarf_frame
*prev
)
489 struct dwarf_frame
*frame
;
490 struct dwarf_cie
*cie
;
491 struct dwarf_fde
*fde
;
496 * If this is the first invocation of this recursive function we
497 * need get the contents of a physical register to get the CFA
498 * in order to begin the virtual unwinding of the stack.
500 * The constant DWARF_ARCH_UNWIND_OFFSET is added to the address of
501 * this function because the return address register
502 * (DWARF_ARCH_RA_REG) will probably not be initialised until a
503 * few instructions into the prologue.
506 pc
= (unsigned long)&dwarf_unwind_stack
;
507 pc
+= DWARF_ARCH_UNWIND_OFFSET
;
510 frame
= kzalloc(sizeof(*frame
), GFP_KERNEL
);
516 fde
= dwarf_lookup_fde(pc
);
519 * This is our normal exit path - the one that stops the
520 * recursion. There's two reasons why we might exit
523 * a) pc has no asscociated DWARF frame info and so
524 * we don't know how to unwind this frame. This is
525 * usually the case when we're trying to unwind a
526 * frame that was called from some assembly code
527 * that has no DWARF info, e.g. syscalls.
529 * b) the DEBUG info for pc is bogus. There's
530 * really no way to distinguish this case from the
531 * case above, which sucks because we could print a
537 cie
= dwarf_lookup_cie(fde
->cie_pointer
);
539 frame
->pc
= fde
->initial_location
;
541 /* CIE initial instructions */
542 dwarf_cfa_execute_insns(cie
->initial_instructions
,
543 cie
->instructions_end
, cie
, fde
, frame
, pc
);
545 /* FDE instructions */
546 dwarf_cfa_execute_insns(fde
->instructions
, fde
->end
, cie
,
549 /* Calculate the CFA */
550 switch (frame
->flags
) {
551 case DWARF_FRAME_CFA_REG_OFFSET
:
553 BUG_ON(!prev
->regs
[frame
->cfa_register
].flags
);
556 addr
+= prev
->regs
[frame
->cfa_register
].addr
;
557 frame
->cfa
= __raw_readl(addr
);
561 * Again, this is the first invocation of this
562 * recurisve function. We need to physically
563 * read the contents of a register in order to
564 * get the Canonical Frame Address for this
567 frame
->cfa
= dwarf_read_arch_reg(frame
->cfa_register
);
570 frame
->cfa
+= frame
->cfa_offset
;
576 /* If we haven't seen the return address reg, we're screwed. */
577 BUG_ON(!frame
->regs
[DWARF_ARCH_RA_REG
].flags
);
579 for (i
= 0; i
<= frame
->num_regs
; i
++) {
580 struct dwarf_reg
*reg
= &frame
->regs
[i
];
586 offset
+= frame
->cfa
;
589 addr
= frame
->cfa
+ frame
->regs
[DWARF_ARCH_RA_REG
].addr
;
590 frame
->return_addr
= __raw_readl(addr
);
592 frame
->next
= dwarf_unwind_stack(frame
->return_addr
, frame
);
596 static int dwarf_parse_cie(void *entry
, void *p
, unsigned long len
,
599 struct dwarf_cie
*cie
;
603 cie
= kzalloc(sizeof(*cie
), GFP_KERNEL
);
610 * Record the offset into the .eh_frame section
611 * for this CIE. It allows this CIE to be
612 * quickly and easily looked up from the
615 cie
->cie_pointer
= (unsigned long)entry
;
617 cie
->version
= *(char *)p
++;
618 BUG_ON(cie
->version
!= 1);
620 cie
->augmentation
= p
;
621 p
+= strlen(cie
->augmentation
) + 1;
623 count
= dwarf_read_uleb128(p
, &cie
->code_alignment_factor
);
626 count
= dwarf_read_leb128(p
, &cie
->data_alignment_factor
);
630 * Which column in the rule table contains the
633 if (cie
->version
== 1) {
634 cie
->return_address_reg
= __raw_readb(p
);
637 count
= dwarf_read_uleb128(p
, &cie
->return_address_reg
);
641 if (cie
->augmentation
[0] == 'z') {
642 unsigned int length
, count
;
643 cie
->flags
|= DWARF_CIE_Z_AUGMENTATION
;
645 count
= dwarf_read_uleb128(p
, &length
);
648 BUG_ON((unsigned char *)p
> end
);
650 cie
->initial_instructions
= p
+ length
;
654 while (*cie
->augmentation
) {
656 * "L" indicates a byte showing how the
657 * LSDA pointer is encoded. Skip it.
659 if (*cie
->augmentation
== 'L') {
662 } else if (*cie
->augmentation
== 'R') {
664 * "R" indicates a byte showing
665 * how FDE addresses are
668 cie
->encoding
= *(char *)p
++;
670 } else if (*cie
->augmentation
== 'P') {
672 * "R" indicates a personality
677 } else if (*cie
->augmentation
== 'S') {
681 * Unknown augmentation. Assume
684 p
= cie
->initial_instructions
;
690 cie
->initial_instructions
= p
;
691 cie
->instructions_end
= end
;
694 spin_lock_irqsave(&dwarf_cie_lock
, flags
);
695 list_add_tail(&cie
->link
, &dwarf_cie_list
);
696 spin_unlock_irqrestore(&dwarf_cie_lock
, flags
);
701 static int dwarf_parse_fde(void *entry
, u32 entry_type
,
702 void *start
, unsigned long len
)
704 struct dwarf_fde
*fde
;
705 struct dwarf_cie
*cie
;
710 fde
= kzalloc(sizeof(*fde
), GFP_KERNEL
);
717 * In a .eh_frame section the CIE pointer is the
718 * delta between the address within the FDE
720 fde
->cie_pointer
= (unsigned long)(p
- entry_type
- 4);
722 cie
= dwarf_lookup_cie(fde
->cie_pointer
);
726 count
= dwarf_read_encoded_value(p
, &fde
->initial_location
,
729 count
= dwarf_read_addr(p
, &fde
->initial_location
);
734 count
= dwarf_read_encoded_value(p
, &fde
->address_range
,
735 cie
->encoding
& 0x0f);
737 count
= dwarf_read_addr(p
, &fde
->address_range
);
741 if (fde
->cie
->flags
& DWARF_CIE_Z_AUGMENTATION
) {
743 count
= dwarf_read_uleb128(p
, &length
);
747 /* Call frame instructions. */
748 fde
->instructions
= p
;
749 fde
->end
= start
+ len
;
752 spin_lock_irqsave(&dwarf_fde_lock
, flags
);
753 list_add_tail(&fde
->link
, &dwarf_fde_list
);
754 spin_unlock_irqrestore(&dwarf_fde_lock
, flags
);
759 static void dwarf_unwinder_dump(struct task_struct
*task
, struct pt_regs
*regs
,
761 const struct stacktrace_ops
*ops
, void *data
)
763 struct dwarf_frame
*frame
;
765 frame
= dwarf_unwind_stack(0, NULL
);
767 while (frame
&& frame
->return_addr
) {
768 ops
->address(data
, frame
->return_addr
, 1);
773 static struct unwinder dwarf_unwinder
= {
774 .name
= "dwarf-unwinder",
775 .dump
= dwarf_unwinder_dump
,
779 static void dwarf_unwinder_cleanup(void)
781 struct dwarf_cie
*cie
, *m
;
782 struct dwarf_fde
*fde
, *n
;
786 * Deallocate all the memory allocated for the DWARF unwinder.
787 * Traverse all the FDE/CIE lists and remove and free all the
788 * memory associated with those data structures.
790 spin_lock_irqsave(&dwarf_cie_lock
, flags
);
791 list_for_each_entry_safe(cie
, m
, &dwarf_cie_list
, link
)
793 spin_unlock_irqrestore(&dwarf_cie_lock
, flags
);
795 spin_lock_irqsave(&dwarf_fde_lock
, flags
);
796 list_for_each_entry_safe(fde
, n
, &dwarf_fde_list
, link
)
798 spin_unlock_irqrestore(&dwarf_fde_lock
, flags
);
802 * dwarf_unwinder_init - initialise the dwarf unwinder
804 * Build the data structures describing the .dwarf_frame section to
805 * make it easier to lookup CIE and FDE entries. Because the
806 * .eh_frame section is packed as tightly as possible it is not
807 * easy to lookup the FDE for a given PC, so we build a list of FDE
808 * and CIE entries that make it easier.
810 void dwarf_unwinder_init(void)
816 unsigned int c_entries
, f_entries
;
818 INIT_LIST_HEAD(&dwarf_cie_list
);
819 INIT_LIST_HEAD(&dwarf_fde_list
);
823 entry
= &__start_eh_frame
;
825 while ((char *)entry
< __stop_eh_frame
) {
828 count
= dwarf_entry_len(p
, &len
);
831 * We read a bogus length field value. There is
832 * nothing we can do here apart from disabling
833 * the DWARF unwinder. We can't even skip this
834 * entry and move to the next one because 'len'
835 * tells us where our next entry is.
841 /* initial length does not include itself */
844 entry_type
= __get_unaligned_cpu32(p
);
847 if (entry_type
== DW_EH_FRAME_CIE
) {
848 err
= dwarf_parse_cie(entry
, p
, len
, end
);
854 err
= dwarf_parse_fde(entry
, entry_type
, p
, len
);
861 entry
= (char *)entry
+ len
+ 4;
864 printk(KERN_INFO
"DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
865 c_entries
, f_entries
);
867 err
= unwinder_register(&dwarf_unwinder
);
874 printk(KERN_ERR
"Failed to initialise DWARF unwinder: %d\n", err
);
875 dwarf_unwinder_cleanup();