sh: dwarf unwinder support.
[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-generic/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(void *src, void *dst)
91 {
92         u32 val = __get_unaligned_cpu32(src);
93         __put_unaligned_cpu32(val, dst);
94
95         return sizeof(unsigned long *);
96 }
97
98 /**
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
102  *
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.
107  */
108 static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
109 {
110         unsigned int result;
111         unsigned char byte;
112         int shift, count;
113
114         result = 0;
115         shift = 0;
116         count = 0;
117
118         while (1) {
119                 byte = __raw_readb(addr);
120                 addr++;
121                 count++;
122
123                 result |= (byte & 0x7f) << shift;
124                 shift += 7;
125
126                 if (!(byte & 0x80))
127                         break;
128         }
129
130         *ret = result;
131
132         return count;
133 }
134
135 /**
136  *      dwarf_read_leb128 - read signed LEB128 data
137  *      @addr: the address of the LEB128 encoded data
138  *      @ret: address to store the result
139  *
140  *      Decode signed LEB128 data. The algorithm is taken from Appendix
141  *      C of the DWARF 3 spec. Return the number of bytes read.
142  */
143 static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
144 {
145         unsigned char byte;
146         int result, shift;
147         int num_bits;
148         int count;
149
150         result = 0;
151         shift = 0;
152         count = 0;
153
154         while (1) {
155                 byte = __raw_readb(addr);
156                 addr++;
157                 result |= (byte & 0x7f) << shift;
158                 shift += 7;
159                 count++;
160
161                 if (!(byte & 0x80))
162                         break;
163         }
164
165         /* The number of bits in a signed integer. */
166         num_bits = 8 * sizeof(result);
167
168         if ((shift < num_bits) && (byte & 0x40))
169                 result |= (-1 << shift);
170
171         *ret = result;
172
173         return count;
174 }
175
176 /**
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
181  *
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.
185  */
186 static int dwarf_read_encoded_value(char *addr, unsigned long *val,
187                                     char encoding)
188 {
189         unsigned long decoded_addr = 0;
190         int count = 0;
191
192         switch (encoding & 0x70) {
193         case DW_EH_PE_absptr:
194                 break;
195         case DW_EH_PE_pcrel:
196                 decoded_addr = (unsigned long)addr;
197                 break;
198         default:
199                 pr_debug("encoding=0x%x\n", (encoding & 0x70));
200                 BUG();
201         }
202
203         if ((encoding & 0x07) == 0x00)
204                 encoding |= DW_EH_PE_udata4;
205
206         switch (encoding & 0x0f) {
207         case DW_EH_PE_sdata4:
208         case DW_EH_PE_udata4:
209                 count += 4;
210                 decoded_addr += __get_unaligned_cpu32(addr);
211                 __raw_writel(decoded_addr, val);
212                 break;
213         default:
214                 pr_debug("encoding=0x%x\n", encoding);
215                 BUG();
216         }
217
218         return count;
219 }
220
221 /**
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
225  *
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.
229  */
230 static inline int dwarf_entry_len(char *addr, unsigned long *len)
231 {
232         u32 initial_len;
233         int count;
234
235         initial_len = __get_unaligned_cpu32(addr);
236         count = 4;
237
238         /*
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.
243          */
244         if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
245                 /*
246                  * The 64-bit length field immediately follows the
247                  * compulsory 32-bit length field.
248                  */
249                 if (initial_len == DW_EXT_DWARF64) {
250                         *len = __get_unaligned_cpu64(addr + 4);
251                         count = 12;
252                 } else {
253                         printk(KERN_WARNING "Unknown DWARF extension\n");
254                         count = 0;
255                 }
256         } else
257                 *len = initial_len;
258
259         return count;
260 }
261
262 /**
263  *      dwarf_lookup_cie - locate the cie
264  *      @cie_ptr: pointer to help with lookup
265  */
266 static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
267 {
268         struct dwarf_cie *cie, *n;
269         unsigned long flags;
270
271         spin_lock_irqsave(&dwarf_cie_lock, flags);
272
273         /*
274          * We've cached the last CIE we looked up because chances are
275          * that the FDE wants this CIE.
276          */
277         if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
278                 cie = cached_cie;
279                 goto out;
280         }
281
282         list_for_each_entry_safe(cie, n, &dwarf_cie_list, link) {
283                 if (cie->cie_pointer == cie_ptr) {
284                         cached_cie = cie;
285                         break;
286                 }
287         }
288
289         /* Couldn't find the entry in the list. */
290         if (&cie->link == &dwarf_cie_list)
291                 cie = NULL;
292 out:
293         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
294         return cie;
295 }
296
297 /**
298  *      dwarf_lookup_fde - locate the FDE that covers pc
299  *      @pc: the program counter
300  */
301 struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
302 {
303         unsigned long flags;
304         struct dwarf_fde *fde, *n;
305
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;
309
310                 start = fde->initial_location;
311                 end = fde->initial_location + fde->address_range;
312
313                 if (pc >= start && pc < end)
314                         break;
315         }
316
317         /* Couldn't find the entry in the list. */
318         if (&fde->link == &dwarf_fde_list)
319                 fde = NULL;
320
321         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
322
323         return fde;
324 }
325
326 /**
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
334  *
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.
339  */
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,
345                                    unsigned long pc)
346 {
347         unsigned char insn;
348         unsigned char *current_insn;
349         unsigned int count, delta, reg, expr_len, offset;
350
351         current_insn = insn_start;
352
353         while (current_insn < insn_end && frame->pc <= pc) {
354                 insn = __raw_readb(current_insn++);
355
356                 /*
357                  * Firstly, handle the opcodes that embed their operands
358                  * in the instructions.
359                  */
360                 switch (DW_CFA_opcode(insn)) {
361                 case DW_CFA_advance_loc:
362                         delta = DW_CFA_operand(insn);
363                         delta *= cie->code_alignment_factor;
364                         frame->pc += delta;
365                         continue;
366                         /* NOTREACHED */
367                 case DW_CFA_offset:
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;
375                         continue;
376                         /* NOTREACHED */
377                 case DW_CFA_restore:
378                         reg = DW_CFA_operand(insn);
379                         continue;
380                         /* NOTREACHED */
381                 }
382
383                 /*
384                  * Secondly, handle the opcodes that don't embed their
385                  * operands in the instruction.
386                  */
387                 switch (insn) {
388                 case DW_CFA_nop:
389                         continue;
390                 case DW_CFA_advance_loc1:
391                         delta = *current_insn++;
392                         frame->pc += delta * cie->code_alignment_factor;
393                         break;
394                 case DW_CFA_advance_loc2:
395                         delta = __get_unaligned_cpu16(current_insn);
396                         current_insn += 2;
397                         frame->pc += delta * cie->code_alignment_factor;
398                         break;
399                 case DW_CFA_advance_loc4:
400                         delta = __get_unaligned_cpu32(current_insn);
401                         current_insn += 4;
402                         frame->pc += delta * cie->code_alignment_factor;
403                         break;
404                 case DW_CFA_offset_extended:
405                         count = dwarf_read_uleb128(current_insn, &reg);
406                         current_insn += count;
407                         count = dwarf_read_uleb128(current_insn, &offset);
408                         current_insn += count;
409                         offset *= cie->data_alignment_factor;
410                         break;
411                 case DW_CFA_restore_extended:
412                         count = dwarf_read_uleb128(current_insn, &reg);
413                         current_insn += count;
414                         break;
415                 case DW_CFA_undefined:
416                         count = dwarf_read_uleb128(current_insn, &reg);
417                         current_insn += count;
418                         break;
419                 case DW_CFA_def_cfa:
420                         count = dwarf_read_uleb128(current_insn,
421                                                    &frame->cfa_register);
422                         current_insn += count;
423                         count = dwarf_read_uleb128(current_insn,
424                                                    &frame->cfa_offset);
425                         current_insn += count;
426
427                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
428                         break;
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;
434                         break;
435                 case DW_CFA_def_cfa_offset:
436                         count = dwarf_read_uleb128(current_insn, &offset);
437                         current_insn += count;
438                         frame->cfa_offset = offset;
439                         break;
440                 case DW_CFA_def_cfa_expression:
441                         count = dwarf_read_uleb128(current_insn, &expr_len);
442                         current_insn += count;
443
444                         frame->cfa_expr = current_insn;
445                         frame->cfa_expr_len = expr_len;
446                         current_insn += expr_len;
447
448                         frame->flags |= DWARF_FRAME_CFA_REG_EXP;
449                         break;
450                 case DW_CFA_offset_extended_sf:
451                         count = dwarf_read_uleb128(current_insn, &reg);
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;
459                         break;
460                 case DW_CFA_val_offset:
461                         count = dwarf_read_uleb128(current_insn, &reg);
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;
467                         break;
468                 default:
469                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
470                         break;
471                 }
472         }
473
474         return 0;
475 }
476
477 /**
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
481  *
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.
485  */
486 struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
487                                        struct dwarf_frame *prev)
488 {
489         struct dwarf_frame *frame;
490         struct dwarf_cie *cie;
491         struct dwarf_fde *fde;
492         unsigned long addr;
493         int i, offset;
494
495         /*
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.
499          *
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.
504          */
505         if (!pc && !prev) {
506                 pc = (unsigned long)&dwarf_unwind_stack;
507                 pc += DWARF_ARCH_UNWIND_OFFSET;
508         }
509
510         frame = kzalloc(sizeof(*frame), GFP_KERNEL);
511         if (!frame)
512                 return NULL;
513
514         frame->prev = prev;
515
516         fde = dwarf_lookup_fde(pc);
517         if (!fde) {
518                 /*
519                  * This is our normal exit path - the one that stops the
520                  * recursion. There's two reasons why we might exit
521                  * here,
522                  *
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.
528                  *
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
532                  *      warning here.
533                  */
534                 return NULL;
535         }
536
537         cie = dwarf_lookup_cie(fde->cie_pointer);
538
539         frame->pc = fde->initial_location;
540
541         /* CIE initial instructions */
542         dwarf_cfa_execute_insns(cie->initial_instructions,
543                                 cie->instructions_end, cie, fde, frame, pc);
544
545         /* FDE instructions */
546         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
547                                 fde, frame, pc);
548
549         /* Calculate the CFA */
550         switch (frame->flags) {
551         case DWARF_FRAME_CFA_REG_OFFSET:
552                 if (prev) {
553                         BUG_ON(!prev->regs[frame->cfa_register].flags);
554
555                         addr = prev->cfa;
556                         addr += prev->regs[frame->cfa_register].addr;
557                         frame->cfa = __raw_readl(addr);
558
559                 } else {
560                         /*
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
565                          * function.
566                          */
567                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
568                 }
569
570                 frame->cfa += frame->cfa_offset;
571                 break;
572         default:
573                 BUG();
574         }
575
576         /* If we haven't seen the return address reg, we're screwed. */
577         BUG_ON(!frame->regs[DWARF_ARCH_RA_REG].flags);
578
579         for (i = 0; i <= frame->num_regs; i++) {
580                 struct dwarf_reg *reg = &frame->regs[i];
581
582                 if (!reg->flags)
583                         continue;
584
585                 offset = reg->addr;
586                 offset += frame->cfa;
587         }
588
589         addr = frame->cfa + frame->regs[DWARF_ARCH_RA_REG].addr;
590         frame->return_addr = __raw_readl(addr);
591
592         frame->next = dwarf_unwind_stack(frame->return_addr, frame);
593         return frame;
594 }
595
596 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
597                            unsigned char *end)
598 {
599         struct dwarf_cie *cie;
600         unsigned long flags;
601         int count;
602
603         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
604         if (!cie)
605                 return -ENOMEM;
606
607         cie->length = len;
608
609         /*
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
613          * corresponding FDE.
614          */
615         cie->cie_pointer = (unsigned long)entry;
616
617         cie->version = *(char *)p++;
618         BUG_ON(cie->version != 1);
619
620         cie->augmentation = p;
621         p += strlen(cie->augmentation) + 1;
622
623         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
624         p += count;
625
626         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
627         p += count;
628
629         /*
630          * Which column in the rule table contains the
631          * return address?
632          */
633         if (cie->version == 1) {
634                 cie->return_address_reg = __raw_readb(p);
635                 p++;
636         } else {
637                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
638                 p += count;
639         }
640
641         if (cie->augmentation[0] == 'z') {
642                 unsigned int length, count;
643                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
644
645                 count = dwarf_read_uleb128(p, &length);
646                 p += count;
647
648                 BUG_ON((unsigned char *)p > end);
649
650                 cie->initial_instructions = p + length;
651                 cie->augmentation++;
652         }
653
654         while (*cie->augmentation) {
655                 /*
656                  * "L" indicates a byte showing how the
657                  * LSDA pointer is encoded. Skip it.
658                  */
659                 if (*cie->augmentation == 'L') {
660                         p++;
661                         cie->augmentation++;
662                 } else if (*cie->augmentation == 'R') {
663                         /*
664                          * "R" indicates a byte showing
665                          * how FDE addresses are
666                          * encoded.
667                          */
668                         cie->encoding = *(char *)p++;
669                         cie->augmentation++;
670                 } else if (*cie->augmentation == 'P') {
671                         /*
672                          * "R" indicates a personality
673                          * routine in the CIE
674                          * augmentation.
675                          */
676                         BUG();
677                 } else if (*cie->augmentation == 'S') {
678                         BUG();
679                 } else {
680                         /*
681                          * Unknown augmentation. Assume
682                          * 'z' augmentation.
683                          */
684                         p = cie->initial_instructions;
685                         BUG_ON(!p);
686                         break;
687                 }
688         }
689
690         cie->initial_instructions = p;
691         cie->instructions_end = end;
692
693         /* Add to list */
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);
697
698         return 0;
699 }
700
701 static int dwarf_parse_fde(void *entry, u32 entry_type,
702                            void *start, unsigned long len)
703 {
704         struct dwarf_fde *fde;
705         struct dwarf_cie *cie;
706         unsigned long flags;
707         int count;
708         void *p = start;
709
710         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
711         if (!fde)
712                 return -ENOMEM;
713
714         fde->length = len;
715
716         /*
717          * In a .eh_frame section the CIE pointer is the
718          * delta between the address within the FDE
719          */
720         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
721
722         cie = dwarf_lookup_cie(fde->cie_pointer);
723         fde->cie = cie;
724
725         if (cie->encoding)
726                 count = dwarf_read_encoded_value(p, &fde->initial_location,
727                                                  cie->encoding);
728         else
729                 count = dwarf_read_addr(p, &fde->initial_location);
730
731         p += count;
732
733         if (cie->encoding)
734                 count = dwarf_read_encoded_value(p, &fde->address_range,
735                                                  cie->encoding & 0x0f);
736         else
737                 count = dwarf_read_addr(p, &fde->address_range);
738
739         p += count;
740
741         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
742                 unsigned int length;
743                 count = dwarf_read_uleb128(p, &length);
744                 p += count + length;
745         }
746
747         /* Call frame instructions. */
748         fde->instructions = p;
749         fde->end = start + len;
750
751         /* Add to list. */
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);
755
756         return 0;
757 }
758
759 static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
760                                 unsigned long *sp,
761                                 const struct stacktrace_ops *ops, void *data)
762 {
763         struct dwarf_frame *frame;
764
765         frame = dwarf_unwind_stack(0, NULL);
766
767         while (frame && frame->return_addr) {
768                 ops->address(data, frame->return_addr, 1);
769                 frame = frame->next;
770         }
771 }
772
773 static struct unwinder dwarf_unwinder = {
774         .name = "dwarf-unwinder",
775         .dump = dwarf_unwinder_dump,
776         .rating = 150,
777 };
778
779 static void dwarf_unwinder_cleanup(void)
780 {
781         struct dwarf_cie *cie, *m;
782         struct dwarf_fde *fde, *n;
783         unsigned long flags;
784
785         /*
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.
789          */
790         spin_lock_irqsave(&dwarf_cie_lock, flags);
791         list_for_each_entry_safe(cie, m, &dwarf_cie_list, link)
792                 kfree(cie);
793         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
794
795         spin_lock_irqsave(&dwarf_fde_lock, flags);
796         list_for_each_entry_safe(fde, n, &dwarf_fde_list, link)
797                 kfree(fde);
798         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
799 }
800
801 /**
802  *      dwarf_unwinder_init - initialise the dwarf unwinder
803  *
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.
809  */
810 void dwarf_unwinder_init(void)
811 {
812         u32 entry_type;
813         void *p, *entry;
814         int count, err;
815         unsigned long len;
816         unsigned int c_entries, f_entries;
817         unsigned char *end;
818         INIT_LIST_HEAD(&dwarf_cie_list);
819         INIT_LIST_HEAD(&dwarf_fde_list);
820
821         c_entries = 0;
822         f_entries = 0;
823         entry = &__start_eh_frame;
824
825         while ((char *)entry < __stop_eh_frame) {
826                 p = entry;
827
828                 count = dwarf_entry_len(p, &len);
829                 if (count == 0) {
830                         /*
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.
836                          */
837                         goto out;
838                 } else
839                         p += count;
840
841                 /* initial length does not include itself */
842                 end = p + len;
843
844                 entry_type = __get_unaligned_cpu32(p);
845                 p += 4;
846
847                 if (entry_type == DW_EH_FRAME_CIE) {
848                         err = dwarf_parse_cie(entry, p, len, end);
849                         if (err < 0)
850                                 goto out;
851                         else
852                                 c_entries++;
853                 } else {
854                         err = dwarf_parse_fde(entry, entry_type, p, len);
855                         if (err < 0)
856                                 goto out;
857                         else
858                                 f_entries++;
859                 }
860
861                 entry = (char *)entry + len + 4;
862         }
863
864         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
865                c_entries, f_entries);
866
867         err = unwinder_register(&dwarf_unwinder);
868         if (err)
869                 goto out;
870
871         return;
872
873 out:
874         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
875         dwarf_unwinder_cleanup();
876 }