sh: unwinder: Restore put_unaligned() for an unaligned destination.
[linux-2.6.git] / arch / sh / kernel / dwarf.c
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  */
15
16 /* #define DEBUG */
17 #include <linux/kernel.h>
18 #include <linux/io.h>
19 #include <linux/list.h>
20 #include <linux/mm.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>
27
28 static LIST_HEAD(dwarf_cie_list);
29 DEFINE_SPINLOCK(dwarf_cie_lock);
30
31 static LIST_HEAD(dwarf_fde_list);
32 DEFINE_SPINLOCK(dwarf_fde_lock);
33
34 static struct dwarf_cie *cached_cie;
35
36 /*
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
40  * after this call.
41  *
42  * Register numbers start at zero, therefore we need to allocate space
43  * for "reg" + 1 registers.
44  */
45 static void dwarf_frame_alloc_regs(struct dwarf_frame *frame,
46                                    unsigned int reg)
47 {
48         struct dwarf_reg *regs;
49         unsigned int num_regs = reg + 1;
50         size_t new_size;
51         size_t old_size;
52
53         new_size = num_regs * sizeof(*regs);
54         old_size = frame->num_regs * sizeof(*regs);
55
56         /* Fast path: don't allocate any regs if we've already got enough. */
57         if (frame->num_regs >= num_regs)
58                 return;
59
60         regs = kzalloc(new_size, GFP_KERNEL);
61         if (!regs) {
62                 printk(KERN_WARNING "Unable to allocate DWARF registers\n");
63                 /*
64                  * Let's just bomb hard here, we have no way to
65                  * gracefully recover.
66                  */
67                 BUG();
68         }
69
70         if (frame->regs) {
71                 memcpy(regs, frame->regs, old_size);
72                 kfree(frame->regs);
73         }
74
75         frame->regs = regs;
76         frame->num_regs = num_regs;
77 }
78
79 /**
80  *      dwarf_read_addr - read dwarf data
81  *      @src: source address of data
82  *      @dst: destination address to store the data to
83  *
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.
89  */
90 static inline int dwarf_read_addr(unsigned long *src, unsigned long *dst)
91 {
92         u32 val = get_unaligned(src);
93         put_unaligned(val, dst);
94         return sizeof(unsigned long *);
95 }
96
97 /**
98  *      dwarf_read_uleb128 - read unsigned LEB128 data
99  *      @addr: the address where the ULEB128 data is stored
100  *      @ret: address to store the result
101  *
102  *      Decode an unsigned LEB128 encoded datum. The algorithm is taken
103  *      from Appendix C of the DWARF 3 spec. For information on the
104  *      encodings refer to section "7.6 - Variable Length Data". Return
105  *      the number of bytes read.
106  */
107 static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
108 {
109         unsigned int result;
110         unsigned char byte;
111         int shift, count;
112
113         result = 0;
114         shift = 0;
115         count = 0;
116
117         while (1) {
118                 byte = __raw_readb(addr);
119                 addr++;
120                 count++;
121
122                 result |= (byte & 0x7f) << shift;
123                 shift += 7;
124
125                 if (!(byte & 0x80))
126                         break;
127         }
128
129         *ret = result;
130
131         return count;
132 }
133
134 /**
135  *      dwarf_read_leb128 - read signed LEB128 data
136  *      @addr: the address of the LEB128 encoded data
137  *      @ret: address to store the result
138  *
139  *      Decode signed LEB128 data. The algorithm is taken from Appendix
140  *      C of the DWARF 3 spec. Return the number of bytes read.
141  */
142 static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
143 {
144         unsigned char byte;
145         int result, shift;
146         int num_bits;
147         int count;
148
149         result = 0;
150         shift = 0;
151         count = 0;
152
153         while (1) {
154                 byte = __raw_readb(addr);
155                 addr++;
156                 result |= (byte & 0x7f) << shift;
157                 shift += 7;
158                 count++;
159
160                 if (!(byte & 0x80))
161                         break;
162         }
163
164         /* The number of bits in a signed integer. */
165         num_bits = 8 * sizeof(result);
166
167         if ((shift < num_bits) && (byte & 0x40))
168                 result |= (-1 << shift);
169
170         *ret = result;
171
172         return count;
173 }
174
175 /**
176  *      dwarf_read_encoded_value - return the decoded value at @addr
177  *      @addr: the address of the encoded value
178  *      @val: where to write the decoded value
179  *      @encoding: the encoding with which we can decode @addr
180  *
181  *      GCC emits encoded address in the .eh_frame FDE entries. Decode
182  *      the value at @addr using @encoding. The decoded value is written
183  *      to @val and the number of bytes read is returned.
184  */
185 static int dwarf_read_encoded_value(char *addr, unsigned long *val,
186                                     char encoding)
187 {
188         unsigned long decoded_addr = 0;
189         int count = 0;
190
191         switch (encoding & 0x70) {
192         case DW_EH_PE_absptr:
193                 break;
194         case DW_EH_PE_pcrel:
195                 decoded_addr = (unsigned long)addr;
196                 break;
197         default:
198                 pr_debug("encoding=0x%x\n", (encoding & 0x70));
199                 BUG();
200         }
201
202         if ((encoding & 0x07) == 0x00)
203                 encoding |= DW_EH_PE_udata4;
204
205         switch (encoding & 0x0f) {
206         case DW_EH_PE_sdata4:
207         case DW_EH_PE_udata4:
208                 count += 4;
209                 decoded_addr += get_unaligned((u32 *)addr);
210                 __raw_writel(decoded_addr, val);
211                 break;
212         default:
213                 pr_debug("encoding=0x%x\n", encoding);
214                 BUG();
215         }
216
217         return count;
218 }
219
220 /**
221  *      dwarf_entry_len - return the length of an FDE or CIE
222  *      @addr: the address of the entry
223  *      @len: the length of the entry
224  *
225  *      Read the initial_length field of the entry and store the size of
226  *      the entry in @len. We return the number of bytes read. Return a
227  *      count of 0 on error.
228  */
229 static inline int dwarf_entry_len(char *addr, unsigned long *len)
230 {
231         u32 initial_len;
232         int count;
233
234         initial_len = get_unaligned((u32 *)addr);
235         count = 4;
236
237         /*
238          * An initial length field value in the range DW_LEN_EXT_LO -
239          * DW_LEN_EXT_HI indicates an extension, and should not be
240          * interpreted as a length. The only extension that we currently
241          * understand is the use of DWARF64 addresses.
242          */
243         if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
244                 /*
245                  * The 64-bit length field immediately follows the
246                  * compulsory 32-bit length field.
247                  */
248                 if (initial_len == DW_EXT_DWARF64) {
249                         *len = get_unaligned((u64 *)addr + 4);
250                         count = 12;
251                 } else {
252                         printk(KERN_WARNING "Unknown DWARF extension\n");
253                         count = 0;
254                 }
255         } else
256                 *len = initial_len;
257
258         return count;
259 }
260
261 /**
262  *      dwarf_lookup_cie - locate the cie
263  *      @cie_ptr: pointer to help with lookup
264  */
265 static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
266 {
267         struct dwarf_cie *cie, *n;
268         unsigned long flags;
269
270         spin_lock_irqsave(&dwarf_cie_lock, flags);
271
272         /*
273          * We've cached the last CIE we looked up because chances are
274          * that the FDE wants this CIE.
275          */
276         if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
277                 cie = cached_cie;
278                 goto out;
279         }
280
281         list_for_each_entry_safe(cie, n, &dwarf_cie_list, link) {
282                 if (cie->cie_pointer == cie_ptr) {
283                         cached_cie = cie;
284                         break;
285                 }
286         }
287
288         /* Couldn't find the entry in the list. */
289         if (&cie->link == &dwarf_cie_list)
290                 cie = NULL;
291 out:
292         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
293         return cie;
294 }
295
296 /**
297  *      dwarf_lookup_fde - locate the FDE that covers pc
298  *      @pc: the program counter
299  */
300 struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
301 {
302         unsigned long flags;
303         struct dwarf_fde *fde, *n;
304
305         spin_lock_irqsave(&dwarf_fde_lock, flags);
306         list_for_each_entry_safe(fde, n, &dwarf_fde_list, link) {
307                 unsigned long start, end;
308
309                 start = fde->initial_location;
310                 end = fde->initial_location + fde->address_range;
311
312                 if (pc >= start && pc < end)
313                         break;
314         }
315
316         /* Couldn't find the entry in the list. */
317         if (&fde->link == &dwarf_fde_list)
318                 fde = NULL;
319
320         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
321
322         return fde;
323 }
324
325 /**
326  *      dwarf_cfa_execute_insns - execute instructions to calculate a CFA
327  *      @insn_start: address of the first instruction
328  *      @insn_end: address of the last instruction
329  *      @cie: the CIE for this function
330  *      @fde: the FDE for this function
331  *      @frame: the instructions calculate the CFA for this frame
332  *      @pc: the program counter of the address we're interested in
333  *
334  *      Execute the Call Frame instruction sequence starting at
335  *      @insn_start and ending at @insn_end. The instructions describe
336  *      how to calculate the Canonical Frame Address of a stackframe.
337  *      Store the results in @frame.
338  */
339 static int dwarf_cfa_execute_insns(unsigned char *insn_start,
340                                    unsigned char *insn_end,
341                                    struct dwarf_cie *cie,
342                                    struct dwarf_fde *fde,
343                                    struct dwarf_frame *frame,
344                                    unsigned long pc)
345 {
346         unsigned char insn;
347         unsigned char *current_insn;
348         unsigned int count, delta, reg, expr_len, offset;
349
350         current_insn = insn_start;
351
352         while (current_insn < insn_end && frame->pc <= pc) {
353                 insn = __raw_readb(current_insn++);
354
355                 /*
356                  * Firstly, handle the opcodes that embed their operands
357                  * in the instructions.
358                  */
359                 switch (DW_CFA_opcode(insn)) {
360                 case DW_CFA_advance_loc:
361                         delta = DW_CFA_operand(insn);
362                         delta *= cie->code_alignment_factor;
363                         frame->pc += delta;
364                         continue;
365                         /* NOTREACHED */
366                 case DW_CFA_offset:
367                         reg = DW_CFA_operand(insn);
368                         count = dwarf_read_uleb128(current_insn, &offset);
369                         current_insn += count;
370                         offset *= cie->data_alignment_factor;
371                         dwarf_frame_alloc_regs(frame, reg);
372                         frame->regs[reg].addr = offset;
373                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
374                         continue;
375                         /* NOTREACHED */
376                 case DW_CFA_restore:
377                         reg = DW_CFA_operand(insn);
378                         continue;
379                         /* NOTREACHED */
380                 }
381
382                 /*
383                  * Secondly, handle the opcodes that don't embed their
384                  * operands in the instruction.
385                  */
386                 switch (insn) {
387                 case DW_CFA_nop:
388                         continue;
389                 case DW_CFA_advance_loc1:
390                         delta = *current_insn++;
391                         frame->pc += delta * cie->code_alignment_factor;
392                         break;
393                 case DW_CFA_advance_loc2:
394                         delta = get_unaligned((u16 *)current_insn);
395                         current_insn += 2;
396                         frame->pc += delta * cie->code_alignment_factor;
397                         break;
398                 case DW_CFA_advance_loc4:
399                         delta = get_unaligned((u32 *)current_insn);
400                         current_insn += 4;
401                         frame->pc += delta * cie->code_alignment_factor;
402                         break;
403                 case DW_CFA_offset_extended:
404                         count = dwarf_read_uleb128(current_insn, &reg);
405                         current_insn += count;
406                         count = dwarf_read_uleb128(current_insn, &offset);
407                         current_insn += count;
408                         offset *= cie->data_alignment_factor;
409                         break;
410                 case DW_CFA_restore_extended:
411                         count = dwarf_read_uleb128(current_insn, &reg);
412                         current_insn += count;
413                         break;
414                 case DW_CFA_undefined:
415                         count = dwarf_read_uleb128(current_insn, &reg);
416                         current_insn += count;
417                         break;
418                 case DW_CFA_def_cfa:
419                         count = dwarf_read_uleb128(current_insn,
420                                                    &frame->cfa_register);
421                         current_insn += count;
422                         count = dwarf_read_uleb128(current_insn,
423                                                    &frame->cfa_offset);
424                         current_insn += count;
425
426                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
427                         break;
428                 case DW_CFA_def_cfa_register:
429                         count = dwarf_read_uleb128(current_insn,
430                                                    &frame->cfa_register);
431                         current_insn += count;
432                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
433                         break;
434                 case DW_CFA_def_cfa_offset:
435                         count = dwarf_read_uleb128(current_insn, &offset);
436                         current_insn += count;
437                         frame->cfa_offset = offset;
438                         break;
439                 case DW_CFA_def_cfa_expression:
440                         count = dwarf_read_uleb128(current_insn, &expr_len);
441                         current_insn += count;
442
443                         frame->cfa_expr = current_insn;
444                         frame->cfa_expr_len = expr_len;
445                         current_insn += expr_len;
446
447                         frame->flags |= DWARF_FRAME_CFA_REG_EXP;
448                         break;
449                 case DW_CFA_offset_extended_sf:
450                         count = dwarf_read_uleb128(current_insn, &reg);
451                         current_insn += count;
452                         count = dwarf_read_leb128(current_insn, &offset);
453                         current_insn += count;
454                         offset *= cie->data_alignment_factor;
455                         dwarf_frame_alloc_regs(frame, reg);
456                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
457                         frame->regs[reg].addr = offset;
458                         break;
459                 case DW_CFA_val_offset:
460                         count = dwarf_read_uleb128(current_insn, &reg);
461                         current_insn += count;
462                         count = dwarf_read_leb128(current_insn, &offset);
463                         offset *= cie->data_alignment_factor;
464                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
465                         frame->regs[reg].addr = offset;
466                         break;
467                 default:
468                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
469                         break;
470                 }
471         }
472
473         return 0;
474 }
475
476 /**
477  *      dwarf_unwind_stack - recursively unwind the stack
478  *      @pc: address of the function to unwind
479  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
480  *
481  *      Return a struct dwarf_frame representing the most recent frame
482  *      on the callstack. Each of the lower (older) stack frames are
483  *      linked via the "prev" member.
484  */
485 struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
486                                        struct dwarf_frame *prev)
487 {
488         struct dwarf_frame *frame;
489         struct dwarf_cie *cie;
490         struct dwarf_fde *fde;
491         unsigned long addr;
492         int i, offset;
493
494         /*
495          * If this is the first invocation of this recursive function we
496          * need get the contents of a physical register to get the CFA
497          * in order to begin the virtual unwinding of the stack.
498          *
499          * The constant DWARF_ARCH_UNWIND_OFFSET is added to the address of
500          * this function because the return address register
501          * (DWARF_ARCH_RA_REG) will probably not be initialised until a
502          * few instructions into the prologue.
503          */
504         if (!pc && !prev) {
505                 pc = (unsigned long)&dwarf_unwind_stack;
506                 pc += DWARF_ARCH_UNWIND_OFFSET;
507         }
508
509         frame = kzalloc(sizeof(*frame), GFP_KERNEL);
510         if (!frame)
511                 return NULL;
512
513         frame->prev = prev;
514
515         fde = dwarf_lookup_fde(pc);
516         if (!fde) {
517                 /*
518                  * This is our normal exit path - the one that stops the
519                  * recursion. There's two reasons why we might exit
520                  * here,
521                  *
522                  *      a) pc has no asscociated DWARF frame info and so
523                  *      we don't know how to unwind this frame. This is
524                  *      usually the case when we're trying to unwind a
525                  *      frame that was called from some assembly code
526                  *      that has no DWARF info, e.g. syscalls.
527                  *
528                  *      b) the DEBUG info for pc is bogus. There's
529                  *      really no way to distinguish this case from the
530                  *      case above, which sucks because we could print a
531                  *      warning here.
532                  */
533                 return NULL;
534         }
535
536         cie = dwarf_lookup_cie(fde->cie_pointer);
537
538         frame->pc = fde->initial_location;
539
540         /* CIE initial instructions */
541         dwarf_cfa_execute_insns(cie->initial_instructions,
542                                 cie->instructions_end, cie, fde, frame, pc);
543
544         /* FDE instructions */
545         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
546                                 fde, frame, pc);
547
548         /* Calculate the CFA */
549         switch (frame->flags) {
550         case DWARF_FRAME_CFA_REG_OFFSET:
551                 if (prev) {
552                         BUG_ON(!prev->regs[frame->cfa_register].flags);
553
554                         addr = prev->cfa;
555                         addr += prev->regs[frame->cfa_register].addr;
556                         frame->cfa = __raw_readl(addr);
557
558                 } else {
559                         /*
560                          * Again, this is the first invocation of this
561                          * recurisve function. We need to physically
562                          * read the contents of a register in order to
563                          * get the Canonical Frame Address for this
564                          * function.
565                          */
566                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
567                 }
568
569                 frame->cfa += frame->cfa_offset;
570                 break;
571         default:
572                 BUG();
573         }
574
575         /* If we haven't seen the return address reg, we're screwed. */
576         BUG_ON(!frame->regs[DWARF_ARCH_RA_REG].flags);
577
578         for (i = 0; i <= frame->num_regs; i++) {
579                 struct dwarf_reg *reg = &frame->regs[i];
580
581                 if (!reg->flags)
582                         continue;
583
584                 offset = reg->addr;
585                 offset += frame->cfa;
586         }
587
588         addr = frame->cfa + frame->regs[DWARF_ARCH_RA_REG].addr;
589         frame->return_addr = __raw_readl(addr);
590
591         frame->next = dwarf_unwind_stack(frame->return_addr, frame);
592         return frame;
593 }
594
595 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
596                            unsigned char *end)
597 {
598         struct dwarf_cie *cie;
599         unsigned long flags;
600         int count;
601
602         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
603         if (!cie)
604                 return -ENOMEM;
605
606         cie->length = len;
607
608         /*
609          * Record the offset into the .eh_frame section
610          * for this CIE. It allows this CIE to be
611          * quickly and easily looked up from the
612          * corresponding FDE.
613          */
614         cie->cie_pointer = (unsigned long)entry;
615
616         cie->version = *(char *)p++;
617         BUG_ON(cie->version != 1);
618
619         cie->augmentation = p;
620         p += strlen(cie->augmentation) + 1;
621
622         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
623         p += count;
624
625         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
626         p += count;
627
628         /*
629          * Which column in the rule table contains the
630          * return address?
631          */
632         if (cie->version == 1) {
633                 cie->return_address_reg = __raw_readb(p);
634                 p++;
635         } else {
636                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
637                 p += count;
638         }
639
640         if (cie->augmentation[0] == 'z') {
641                 unsigned int length, count;
642                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
643
644                 count = dwarf_read_uleb128(p, &length);
645                 p += count;
646
647                 BUG_ON((unsigned char *)p > end);
648
649                 cie->initial_instructions = p + length;
650                 cie->augmentation++;
651         }
652
653         while (*cie->augmentation) {
654                 /*
655                  * "L" indicates a byte showing how the
656                  * LSDA pointer is encoded. Skip it.
657                  */
658                 if (*cie->augmentation == 'L') {
659                         p++;
660                         cie->augmentation++;
661                 } else if (*cie->augmentation == 'R') {
662                         /*
663                          * "R" indicates a byte showing
664                          * how FDE addresses are
665                          * encoded.
666                          */
667                         cie->encoding = *(char *)p++;
668                         cie->augmentation++;
669                 } else if (*cie->augmentation == 'P') {
670                         /*
671                          * "R" indicates a personality
672                          * routine in the CIE
673                          * augmentation.
674                          */
675                         BUG();
676                 } else if (*cie->augmentation == 'S') {
677                         BUG();
678                 } else {
679                         /*
680                          * Unknown augmentation. Assume
681                          * 'z' augmentation.
682                          */
683                         p = cie->initial_instructions;
684                         BUG_ON(!p);
685                         break;
686                 }
687         }
688
689         cie->initial_instructions = p;
690         cie->instructions_end = end;
691
692         /* Add to list */
693         spin_lock_irqsave(&dwarf_cie_lock, flags);
694         list_add_tail(&cie->link, &dwarf_cie_list);
695         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
696
697         return 0;
698 }
699
700 static int dwarf_parse_fde(void *entry, u32 entry_type,
701                            void *start, unsigned long len)
702 {
703         struct dwarf_fde *fde;
704         struct dwarf_cie *cie;
705         unsigned long flags;
706         int count;
707         void *p = start;
708
709         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
710         if (!fde)
711                 return -ENOMEM;
712
713         fde->length = len;
714
715         /*
716          * In a .eh_frame section the CIE pointer is the
717          * delta between the address within the FDE
718          */
719         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
720
721         cie = dwarf_lookup_cie(fde->cie_pointer);
722         fde->cie = cie;
723
724         if (cie->encoding)
725                 count = dwarf_read_encoded_value(p, &fde->initial_location,
726                                                  cie->encoding);
727         else
728                 count = dwarf_read_addr(p, &fde->initial_location);
729
730         p += count;
731
732         if (cie->encoding)
733                 count = dwarf_read_encoded_value(p, &fde->address_range,
734                                                  cie->encoding & 0x0f);
735         else
736                 count = dwarf_read_addr(p, &fde->address_range);
737
738         p += count;
739
740         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
741                 unsigned int length;
742                 count = dwarf_read_uleb128(p, &length);
743                 p += count + length;
744         }
745
746         /* Call frame instructions. */
747         fde->instructions = p;
748         fde->end = start + len;
749
750         /* Add to list. */
751         spin_lock_irqsave(&dwarf_fde_lock, flags);
752         list_add_tail(&fde->link, &dwarf_fde_list);
753         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
754
755         return 0;
756 }
757
758 static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
759                                 unsigned long *sp,
760                                 const struct stacktrace_ops *ops, void *data)
761 {
762         struct dwarf_frame *frame;
763
764         frame = dwarf_unwind_stack(0, NULL);
765
766         while (frame && frame->return_addr) {
767                 ops->address(data, frame->return_addr, 1);
768                 frame = frame->next;
769         }
770 }
771
772 static struct unwinder dwarf_unwinder = {
773         .name = "dwarf-unwinder",
774         .dump = dwarf_unwinder_dump,
775         .rating = 150,
776 };
777
778 static void dwarf_unwinder_cleanup(void)
779 {
780         struct dwarf_cie *cie, *m;
781         struct dwarf_fde *fde, *n;
782         unsigned long flags;
783
784         /*
785          * Deallocate all the memory allocated for the DWARF unwinder.
786          * Traverse all the FDE/CIE lists and remove and free all the
787          * memory associated with those data structures.
788          */
789         spin_lock_irqsave(&dwarf_cie_lock, flags);
790         list_for_each_entry_safe(cie, m, &dwarf_cie_list, link)
791                 kfree(cie);
792         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
793
794         spin_lock_irqsave(&dwarf_fde_lock, flags);
795         list_for_each_entry_safe(fde, n, &dwarf_fde_list, link)
796                 kfree(fde);
797         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
798 }
799
800 /**
801  *      dwarf_unwinder_init - initialise the dwarf unwinder
802  *
803  *      Build the data structures describing the .dwarf_frame section to
804  *      make it easier to lookup CIE and FDE entries. Because the
805  *      .eh_frame section is packed as tightly as possible it is not
806  *      easy to lookup the FDE for a given PC, so we build a list of FDE
807  *      and CIE entries that make it easier.
808  */
809 void dwarf_unwinder_init(void)
810 {
811         u32 entry_type;
812         void *p, *entry;
813         int count, err;
814         unsigned long len;
815         unsigned int c_entries, f_entries;
816         unsigned char *end;
817         INIT_LIST_HEAD(&dwarf_cie_list);
818         INIT_LIST_HEAD(&dwarf_fde_list);
819
820         c_entries = 0;
821         f_entries = 0;
822         entry = &__start_eh_frame;
823
824         while ((char *)entry < __stop_eh_frame) {
825                 p = entry;
826
827                 count = dwarf_entry_len(p, &len);
828                 if (count == 0) {
829                         /*
830                          * We read a bogus length field value. There is
831                          * nothing we can do here apart from disabling
832                          * the DWARF unwinder. We can't even skip this
833                          * entry and move to the next one because 'len'
834                          * tells us where our next entry is.
835                          */
836                         goto out;
837                 } else
838                         p += count;
839
840                 /* initial length does not include itself */
841                 end = p + len;
842
843                 entry_type = get_unaligned((u32 *)p);
844                 p += 4;
845
846                 if (entry_type == DW_EH_FRAME_CIE) {
847                         err = dwarf_parse_cie(entry, p, len, end);
848                         if (err < 0)
849                                 goto out;
850                         else
851                                 c_entries++;
852                 } else {
853                         err = dwarf_parse_fde(entry, entry_type, p, len);
854                         if (err < 0)
855                                 goto out;
856                         else
857                                 f_entries++;
858                 }
859
860                 entry = (char *)entry + len + 4;
861         }
862
863         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
864                c_entries, f_entries);
865
866         err = unwinder_register(&dwarf_unwinder);
867         if (err)
868                 goto out;
869
870         return;
871
872 out:
873         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
874         dwarf_unwinder_cleanup();
875 }