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/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(unsigned long *src
, unsigned long *dst
)
92 *dst
= get_unaligned(src
);
93 return sizeof(unsigned long *);
97 * dwarf_read_uleb128 - read unsigned LEB128 data
98 * @addr: the address where the ULEB128 data is stored
99 * @ret: address to store the result
101 * Decode an unsigned LEB128 encoded datum. The algorithm is taken
102 * from Appendix C of the DWARF 3 spec. For information on the
103 * encodings refer to section "7.6 - Variable Length Data". Return
104 * the number of bytes read.
106 static inline unsigned long dwarf_read_uleb128(char *addr
, unsigned int *ret
)
117 byte
= __raw_readb(addr
);
121 result
|= (byte
& 0x7f) << shift
;
134 * dwarf_read_leb128 - read signed LEB128 data
135 * @addr: the address of the LEB128 encoded data
136 * @ret: address to store the result
138 * Decode signed LEB128 data. The algorithm is taken from Appendix
139 * C of the DWARF 3 spec. Return the number of bytes read.
141 static inline unsigned long dwarf_read_leb128(char *addr
, int *ret
)
153 byte
= __raw_readb(addr
);
155 result
|= (byte
& 0x7f) << shift
;
163 /* The number of bits in a signed integer. */
164 num_bits
= 8 * sizeof(result
);
166 if ((shift
< num_bits
) && (byte
& 0x40))
167 result
|= (-1 << shift
);
175 * dwarf_read_encoded_value - return the decoded value at @addr
176 * @addr: the address of the encoded value
177 * @val: where to write the decoded value
178 * @encoding: the encoding with which we can decode @addr
180 * GCC emits encoded address in the .eh_frame FDE entries. Decode
181 * the value at @addr using @encoding. The decoded value is written
182 * to @val and the number of bytes read is returned.
184 static int dwarf_read_encoded_value(char *addr
, unsigned long *val
,
187 unsigned long decoded_addr
= 0;
190 switch (encoding
& 0x70) {
191 case DW_EH_PE_absptr
:
194 decoded_addr
= (unsigned long)addr
;
197 pr_debug("encoding=0x%x\n", (encoding
& 0x70));
201 if ((encoding
& 0x07) == 0x00)
202 encoding
|= DW_EH_PE_udata4
;
204 switch (encoding
& 0x0f) {
205 case DW_EH_PE_sdata4
:
206 case DW_EH_PE_udata4
:
208 decoded_addr
+= get_unaligned((u32
*)addr
);
209 __raw_writel(decoded_addr
, val
);
212 pr_debug("encoding=0x%x\n", encoding
);
220 * dwarf_entry_len - return the length of an FDE or CIE
221 * @addr: the address of the entry
222 * @len: the length of the entry
224 * Read the initial_length field of the entry and store the size of
225 * the entry in @len. We return the number of bytes read. Return a
226 * count of 0 on error.
228 static inline int dwarf_entry_len(char *addr
, unsigned long *len
)
233 initial_len
= get_unaligned((u32
*)addr
);
237 * An initial length field value in the range DW_LEN_EXT_LO -
238 * DW_LEN_EXT_HI indicates an extension, and should not be
239 * interpreted as a length. The only extension that we currently
240 * understand is the use of DWARF64 addresses.
242 if (initial_len
>= DW_EXT_LO
&& initial_len
<= DW_EXT_HI
) {
244 * The 64-bit length field immediately follows the
245 * compulsory 32-bit length field.
247 if (initial_len
== DW_EXT_DWARF64
) {
248 *len
= get_unaligned((u64
*)addr
+ 4);
251 printk(KERN_WARNING
"Unknown DWARF extension\n");
261 * dwarf_lookup_cie - locate the cie
262 * @cie_ptr: pointer to help with lookup
264 static struct dwarf_cie
*dwarf_lookup_cie(unsigned long cie_ptr
)
266 struct dwarf_cie
*cie
, *n
;
269 spin_lock_irqsave(&dwarf_cie_lock
, flags
);
272 * We've cached the last CIE we looked up because chances are
273 * that the FDE wants this CIE.
275 if (cached_cie
&& cached_cie
->cie_pointer
== cie_ptr
) {
280 list_for_each_entry_safe(cie
, n
, &dwarf_cie_list
, link
) {
281 if (cie
->cie_pointer
== cie_ptr
) {
287 /* Couldn't find the entry in the list. */
288 if (&cie
->link
== &dwarf_cie_list
)
291 spin_unlock_irqrestore(&dwarf_cie_lock
, flags
);
296 * dwarf_lookup_fde - locate the FDE that covers pc
297 * @pc: the program counter
299 struct dwarf_fde
*dwarf_lookup_fde(unsigned long pc
)
302 struct dwarf_fde
*fde
, *n
;
304 spin_lock_irqsave(&dwarf_fde_lock
, flags
);
305 list_for_each_entry_safe(fde
, n
, &dwarf_fde_list
, link
) {
306 unsigned long start
, end
;
308 start
= fde
->initial_location
;
309 end
= fde
->initial_location
+ fde
->address_range
;
311 if (pc
>= start
&& pc
< end
)
315 /* Couldn't find the entry in the list. */
316 if (&fde
->link
== &dwarf_fde_list
)
319 spin_unlock_irqrestore(&dwarf_fde_lock
, flags
);
325 * dwarf_cfa_execute_insns - execute instructions to calculate a CFA
326 * @insn_start: address of the first instruction
327 * @insn_end: address of the last instruction
328 * @cie: the CIE for this function
329 * @fde: the FDE for this function
330 * @frame: the instructions calculate the CFA for this frame
331 * @pc: the program counter of the address we're interested in
333 * Execute the Call Frame instruction sequence starting at
334 * @insn_start and ending at @insn_end. The instructions describe
335 * how to calculate the Canonical Frame Address of a stackframe.
336 * Store the results in @frame.
338 static int dwarf_cfa_execute_insns(unsigned char *insn_start
,
339 unsigned char *insn_end
,
340 struct dwarf_cie
*cie
,
341 struct dwarf_fde
*fde
,
342 struct dwarf_frame
*frame
,
346 unsigned char *current_insn
;
347 unsigned int count
, delta
, reg
, expr_len
, offset
;
349 current_insn
= insn_start
;
351 while (current_insn
< insn_end
&& frame
->pc
<= pc
) {
352 insn
= __raw_readb(current_insn
++);
355 * Firstly, handle the opcodes that embed their operands
356 * in the instructions.
358 switch (DW_CFA_opcode(insn
)) {
359 case DW_CFA_advance_loc
:
360 delta
= DW_CFA_operand(insn
);
361 delta
*= cie
->code_alignment_factor
;
366 reg
= DW_CFA_operand(insn
);
367 count
= dwarf_read_uleb128(current_insn
, &offset
);
368 current_insn
+= count
;
369 offset
*= cie
->data_alignment_factor
;
370 dwarf_frame_alloc_regs(frame
, reg
);
371 frame
->regs
[reg
].addr
= offset
;
372 frame
->regs
[reg
].flags
|= DWARF_REG_OFFSET
;
376 reg
= DW_CFA_operand(insn
);
382 * Secondly, handle the opcodes that don't embed their
383 * operands in the instruction.
388 case DW_CFA_advance_loc1
:
389 delta
= *current_insn
++;
390 frame
->pc
+= delta
* cie
->code_alignment_factor
;
392 case DW_CFA_advance_loc2
:
393 delta
= get_unaligned((u16
*)current_insn
);
395 frame
->pc
+= delta
* cie
->code_alignment_factor
;
397 case DW_CFA_advance_loc4
:
398 delta
= get_unaligned((u32
*)current_insn
);
400 frame
->pc
+= delta
* cie
->code_alignment_factor
;
402 case DW_CFA_offset_extended
:
403 count
= dwarf_read_uleb128(current_insn
, ®
);
404 current_insn
+= count
;
405 count
= dwarf_read_uleb128(current_insn
, &offset
);
406 current_insn
+= count
;
407 offset
*= cie
->data_alignment_factor
;
409 case DW_CFA_restore_extended
:
410 count
= dwarf_read_uleb128(current_insn
, ®
);
411 current_insn
+= count
;
413 case DW_CFA_undefined
:
414 count
= dwarf_read_uleb128(current_insn
, ®
);
415 current_insn
+= count
;
418 count
= dwarf_read_uleb128(current_insn
,
419 &frame
->cfa_register
);
420 current_insn
+= count
;
421 count
= dwarf_read_uleb128(current_insn
,
423 current_insn
+= count
;
425 frame
->flags
|= DWARF_FRAME_CFA_REG_OFFSET
;
427 case DW_CFA_def_cfa_register
:
428 count
= dwarf_read_uleb128(current_insn
,
429 &frame
->cfa_register
);
430 current_insn
+= count
;
431 frame
->flags
|= DWARF_FRAME_CFA_REG_OFFSET
;
433 case DW_CFA_def_cfa_offset
:
434 count
= dwarf_read_uleb128(current_insn
, &offset
);
435 current_insn
+= count
;
436 frame
->cfa_offset
= offset
;
438 case DW_CFA_def_cfa_expression
:
439 count
= dwarf_read_uleb128(current_insn
, &expr_len
);
440 current_insn
+= count
;
442 frame
->cfa_expr
= current_insn
;
443 frame
->cfa_expr_len
= expr_len
;
444 current_insn
+= expr_len
;
446 frame
->flags
|= DWARF_FRAME_CFA_REG_EXP
;
448 case DW_CFA_offset_extended_sf
:
449 count
= dwarf_read_uleb128(current_insn
, ®
);
450 current_insn
+= count
;
451 count
= dwarf_read_leb128(current_insn
, &offset
);
452 current_insn
+= count
;
453 offset
*= cie
->data_alignment_factor
;
454 dwarf_frame_alloc_regs(frame
, reg
);
455 frame
->regs
[reg
].flags
|= DWARF_REG_OFFSET
;
456 frame
->regs
[reg
].addr
= offset
;
458 case DW_CFA_val_offset
:
459 count
= dwarf_read_uleb128(current_insn
, ®
);
460 current_insn
+= count
;
461 count
= dwarf_read_leb128(current_insn
, &offset
);
462 offset
*= cie
->data_alignment_factor
;
463 frame
->regs
[reg
].flags
|= DWARF_REG_OFFSET
;
464 frame
->regs
[reg
].addr
= offset
;
467 pr_debug("unhandled DWARF instruction 0x%x\n", insn
);
476 * dwarf_unwind_stack - recursively unwind the stack
477 * @pc: address of the function to unwind
478 * @prev: struct dwarf_frame of the previous stackframe on the callstack
480 * Return a struct dwarf_frame representing the most recent frame
481 * on the callstack. Each of the lower (older) stack frames are
482 * linked via the "prev" member.
484 struct dwarf_frame
*dwarf_unwind_stack(unsigned long pc
,
485 struct dwarf_frame
*prev
)
487 struct dwarf_frame
*frame
;
488 struct dwarf_cie
*cie
;
489 struct dwarf_fde
*fde
;
494 * If this is the first invocation of this recursive function we
495 * need get the contents of a physical register to get the CFA
496 * in order to begin the virtual unwinding of the stack.
498 * The constant DWARF_ARCH_UNWIND_OFFSET is added to the address of
499 * this function because the return address register
500 * (DWARF_ARCH_RA_REG) will probably not be initialised until a
501 * few instructions into the prologue.
504 pc
= (unsigned long)&dwarf_unwind_stack
;
505 pc
+= DWARF_ARCH_UNWIND_OFFSET
;
508 frame
= kzalloc(sizeof(*frame
), GFP_KERNEL
);
514 fde
= dwarf_lookup_fde(pc
);
517 * This is our normal exit path - the one that stops the
518 * recursion. There's two reasons why we might exit
521 * a) pc has no asscociated DWARF frame info and so
522 * we don't know how to unwind this frame. This is
523 * usually the case when we're trying to unwind a
524 * frame that was called from some assembly code
525 * that has no DWARF info, e.g. syscalls.
527 * b) the DEBUG info for pc is bogus. There's
528 * really no way to distinguish this case from the
529 * case above, which sucks because we could print a
535 cie
= dwarf_lookup_cie(fde
->cie_pointer
);
537 frame
->pc
= fde
->initial_location
;
539 /* CIE initial instructions */
540 dwarf_cfa_execute_insns(cie
->initial_instructions
,
541 cie
->instructions_end
, cie
, fde
, frame
, pc
);
543 /* FDE instructions */
544 dwarf_cfa_execute_insns(fde
->instructions
, fde
->end
, cie
,
547 /* Calculate the CFA */
548 switch (frame
->flags
) {
549 case DWARF_FRAME_CFA_REG_OFFSET
:
551 BUG_ON(!prev
->regs
[frame
->cfa_register
].flags
);
554 addr
+= prev
->regs
[frame
->cfa_register
].addr
;
555 frame
->cfa
= __raw_readl(addr
);
559 * Again, this is the first invocation of this
560 * recurisve function. We need to physically
561 * read the contents of a register in order to
562 * get the Canonical Frame Address for this
565 frame
->cfa
= dwarf_read_arch_reg(frame
->cfa_register
);
568 frame
->cfa
+= frame
->cfa_offset
;
574 /* If we haven't seen the return address reg, we're screwed. */
575 BUG_ON(!frame
->regs
[DWARF_ARCH_RA_REG
].flags
);
577 for (i
= 0; i
<= frame
->num_regs
; i
++) {
578 struct dwarf_reg
*reg
= &frame
->regs
[i
];
584 offset
+= frame
->cfa
;
587 addr
= frame
->cfa
+ frame
->regs
[DWARF_ARCH_RA_REG
].addr
;
588 frame
->return_addr
= __raw_readl(addr
);
590 frame
->next
= dwarf_unwind_stack(frame
->return_addr
, frame
);
594 static int dwarf_parse_cie(void *entry
, void *p
, unsigned long len
,
597 struct dwarf_cie
*cie
;
601 cie
= kzalloc(sizeof(*cie
), GFP_KERNEL
);
608 * Record the offset into the .eh_frame section
609 * for this CIE. It allows this CIE to be
610 * quickly and easily looked up from the
613 cie
->cie_pointer
= (unsigned long)entry
;
615 cie
->version
= *(char *)p
++;
616 BUG_ON(cie
->version
!= 1);
618 cie
->augmentation
= p
;
619 p
+= strlen(cie
->augmentation
) + 1;
621 count
= dwarf_read_uleb128(p
, &cie
->code_alignment_factor
);
624 count
= dwarf_read_leb128(p
, &cie
->data_alignment_factor
);
628 * Which column in the rule table contains the
631 if (cie
->version
== 1) {
632 cie
->return_address_reg
= __raw_readb(p
);
635 count
= dwarf_read_uleb128(p
, &cie
->return_address_reg
);
639 if (cie
->augmentation
[0] == 'z') {
640 unsigned int length
, count
;
641 cie
->flags
|= DWARF_CIE_Z_AUGMENTATION
;
643 count
= dwarf_read_uleb128(p
, &length
);
646 BUG_ON((unsigned char *)p
> end
);
648 cie
->initial_instructions
= p
+ length
;
652 while (*cie
->augmentation
) {
654 * "L" indicates a byte showing how the
655 * LSDA pointer is encoded. Skip it.
657 if (*cie
->augmentation
== 'L') {
660 } else if (*cie
->augmentation
== 'R') {
662 * "R" indicates a byte showing
663 * how FDE addresses are
666 cie
->encoding
= *(char *)p
++;
668 } else if (*cie
->augmentation
== 'P') {
670 * "R" indicates a personality
675 } else if (*cie
->augmentation
== 'S') {
679 * Unknown augmentation. Assume
682 p
= cie
->initial_instructions
;
688 cie
->initial_instructions
= p
;
689 cie
->instructions_end
= end
;
692 spin_lock_irqsave(&dwarf_cie_lock
, flags
);
693 list_add_tail(&cie
->link
, &dwarf_cie_list
);
694 spin_unlock_irqrestore(&dwarf_cie_lock
, flags
);
699 static int dwarf_parse_fde(void *entry
, u32 entry_type
,
700 void *start
, unsigned long len
)
702 struct dwarf_fde
*fde
;
703 struct dwarf_cie
*cie
;
708 fde
= kzalloc(sizeof(*fde
), GFP_KERNEL
);
715 * In a .eh_frame section the CIE pointer is the
716 * delta between the address within the FDE
718 fde
->cie_pointer
= (unsigned long)(p
- entry_type
- 4);
720 cie
= dwarf_lookup_cie(fde
->cie_pointer
);
724 count
= dwarf_read_encoded_value(p
, &fde
->initial_location
,
727 count
= dwarf_read_addr(p
, &fde
->initial_location
);
732 count
= dwarf_read_encoded_value(p
, &fde
->address_range
,
733 cie
->encoding
& 0x0f);
735 count
= dwarf_read_addr(p
, &fde
->address_range
);
739 if (fde
->cie
->flags
& DWARF_CIE_Z_AUGMENTATION
) {
741 count
= dwarf_read_uleb128(p
, &length
);
745 /* Call frame instructions. */
746 fde
->instructions
= p
;
747 fde
->end
= start
+ len
;
750 spin_lock_irqsave(&dwarf_fde_lock
, flags
);
751 list_add_tail(&fde
->link
, &dwarf_fde_list
);
752 spin_unlock_irqrestore(&dwarf_fde_lock
, flags
);
757 static void dwarf_unwinder_dump(struct task_struct
*task
, struct pt_regs
*regs
,
759 const struct stacktrace_ops
*ops
, void *data
)
761 struct dwarf_frame
*frame
;
763 frame
= dwarf_unwind_stack(0, NULL
);
765 while (frame
&& frame
->return_addr
) {
766 ops
->address(data
, frame
->return_addr
, 1);
771 static struct unwinder dwarf_unwinder
= {
772 .name
= "dwarf-unwinder",
773 .dump
= dwarf_unwinder_dump
,
777 static void dwarf_unwinder_cleanup(void)
779 struct dwarf_cie
*cie
, *m
;
780 struct dwarf_fde
*fde
, *n
;
784 * Deallocate all the memory allocated for the DWARF unwinder.
785 * Traverse all the FDE/CIE lists and remove and free all the
786 * memory associated with those data structures.
788 spin_lock_irqsave(&dwarf_cie_lock
, flags
);
789 list_for_each_entry_safe(cie
, m
, &dwarf_cie_list
, link
)
791 spin_unlock_irqrestore(&dwarf_cie_lock
, flags
);
793 spin_lock_irqsave(&dwarf_fde_lock
, flags
);
794 list_for_each_entry_safe(fde
, n
, &dwarf_fde_list
, link
)
796 spin_unlock_irqrestore(&dwarf_fde_lock
, flags
);
800 * dwarf_unwinder_init - initialise the dwarf unwinder
802 * Build the data structures describing the .dwarf_frame section to
803 * make it easier to lookup CIE and FDE entries. Because the
804 * .eh_frame section is packed as tightly as possible it is not
805 * easy to lookup the FDE for a given PC, so we build a list of FDE
806 * and CIE entries that make it easier.
808 void dwarf_unwinder_init(void)
814 unsigned int c_entries
, f_entries
;
816 INIT_LIST_HEAD(&dwarf_cie_list
);
817 INIT_LIST_HEAD(&dwarf_fde_list
);
821 entry
= &__start_eh_frame
;
823 while ((char *)entry
< __stop_eh_frame
) {
826 count
= dwarf_entry_len(p
, &len
);
829 * We read a bogus length field value. There is
830 * nothing we can do here apart from disabling
831 * the DWARF unwinder. We can't even skip this
832 * entry and move to the next one because 'len'
833 * tells us where our next entry is.
839 /* initial length does not include itself */
842 entry_type
= get_unaligned((u32
*)p
);
845 if (entry_type
== DW_EH_FRAME_CIE
) {
846 err
= dwarf_parse_cie(entry
, p
, len
, end
);
852 err
= dwarf_parse_fde(entry
, entry_type
, p
, len
);
859 entry
= (char *)entry
+ len
+ 4;
862 printk(KERN_INFO
"DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
863 c_entries
, f_entries
);
865 err
= unwinder_register(&dwarf_unwinder
);
872 printk(KERN_ERR
"Failed to initialise DWARF unwinder: %d\n", err
);
873 dwarf_unwinder_cleanup();