sh: unwinder: Move initialization to early_initcall() and tidy up locking.
[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 static DEFINE_SPINLOCK(dwarf_cie_lock);
30
31 static LIST_HEAD(dwarf_fde_list);
32 static 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_ATOMIC);
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;
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(cie, &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         struct dwarf_fde *fde;
303         unsigned long flags;
304
305         spin_lock_irqsave(&dwarf_fde_lock, flags);
306
307         list_for_each_entry(fde, &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((u16 *)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((u32 *)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                 case DW_CFA_GNU_args_size:
469                         count = dwarf_read_uleb128(current_insn, &offset);
470                         current_insn += count;
471                         break;
472                 case DW_CFA_GNU_negative_offset_extended:
473                         count = dwarf_read_uleb128(current_insn, &reg);
474                         current_insn += count;
475                         count = dwarf_read_uleb128(current_insn, &offset);
476                         offset *= cie->data_alignment_factor;
477                         dwarf_frame_alloc_regs(frame, reg);
478                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
479                         frame->regs[reg].addr = -offset;
480                         break;
481                 default:
482                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
483                         break;
484                 }
485         }
486
487         return 0;
488 }
489
490 /**
491  *      dwarf_unwind_stack - recursively unwind the stack
492  *      @pc: address of the function to unwind
493  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
494  *
495  *      Return a struct dwarf_frame representing the most recent frame
496  *      on the callstack. Each of the lower (older) stack frames are
497  *      linked via the "prev" member.
498  */
499 struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
500                                        struct dwarf_frame *prev)
501 {
502         struct dwarf_frame *frame;
503         struct dwarf_cie *cie;
504         struct dwarf_fde *fde;
505         unsigned long addr;
506         int i, offset;
507
508         /*
509          * If this is the first invocation of this recursive function we
510          * need get the contents of a physical register to get the CFA
511          * in order to begin the virtual unwinding of the stack.
512          *
513          * NOTE: the return address is guaranteed to be setup by the
514          * time this function makes its first function call.
515          */
516         if (!pc && !prev)
517                 pc = (unsigned long)current_text_addr();
518
519         frame = kzalloc(sizeof(*frame), GFP_ATOMIC);
520         if (!frame)
521                 return NULL;
522
523         frame->prev = prev;
524
525         fde = dwarf_lookup_fde(pc);
526         if (!fde) {
527                 /*
528                  * This is our normal exit path - the one that stops the
529                  * recursion. There's two reasons why we might exit
530                  * here,
531                  *
532                  *      a) pc has no asscociated DWARF frame info and so
533                  *      we don't know how to unwind this frame. This is
534                  *      usually the case when we're trying to unwind a
535                  *      frame that was called from some assembly code
536                  *      that has no DWARF info, e.g. syscalls.
537                  *
538                  *      b) the DEBUG info for pc is bogus. There's
539                  *      really no way to distinguish this case from the
540                  *      case above, which sucks because we could print a
541                  *      warning here.
542                  */
543                 return NULL;
544         }
545
546         cie = dwarf_lookup_cie(fde->cie_pointer);
547
548         frame->pc = fde->initial_location;
549
550         /* CIE initial instructions */
551         dwarf_cfa_execute_insns(cie->initial_instructions,
552                                 cie->instructions_end, cie, fde,
553                                 frame, pc);
554
555         /* FDE instructions */
556         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
557                                 fde, frame, pc);
558
559         /* Calculate the CFA */
560         switch (frame->flags) {
561         case DWARF_FRAME_CFA_REG_OFFSET:
562                 if (prev) {
563                         BUG_ON(!prev->regs[frame->cfa_register].flags);
564
565                         addr = prev->cfa;
566                         addr += prev->regs[frame->cfa_register].addr;
567                         frame->cfa = __raw_readl(addr);
568
569                 } else {
570                         /*
571                          * Again, this is the first invocation of this
572                          * recurisve function. We need to physically
573                          * read the contents of a register in order to
574                          * get the Canonical Frame Address for this
575                          * function.
576                          */
577                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
578                 }
579
580                 frame->cfa += frame->cfa_offset;
581                 break;
582         default:
583                 BUG();
584         }
585
586         /* If we haven't seen the return address reg, we're screwed. */
587         BUG_ON(!frame->regs[DWARF_ARCH_RA_REG].flags);
588
589         for (i = 0; i <= frame->num_regs; i++) {
590                 struct dwarf_reg *reg = &frame->regs[i];
591
592                 if (!reg->flags)
593                         continue;
594
595                 offset = reg->addr;
596                 offset += frame->cfa;
597         }
598
599         addr = frame->cfa + frame->regs[DWARF_ARCH_RA_REG].addr;
600         frame->return_addr = __raw_readl(addr);
601
602         frame->next = dwarf_unwind_stack(frame->return_addr, frame);
603         return frame;
604 }
605
606 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
607                            unsigned char *end)
608 {
609         struct dwarf_cie *cie;
610         unsigned long flags;
611         int count;
612
613         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
614         if (!cie)
615                 return -ENOMEM;
616
617         cie->length = len;
618
619         /*
620          * Record the offset into the .eh_frame section
621          * for this CIE. It allows this CIE to be
622          * quickly and easily looked up from the
623          * corresponding FDE.
624          */
625         cie->cie_pointer = (unsigned long)entry;
626
627         cie->version = *(char *)p++;
628         BUG_ON(cie->version != 1);
629
630         cie->augmentation = p;
631         p += strlen(cie->augmentation) + 1;
632
633         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
634         p += count;
635
636         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
637         p += count;
638
639         /*
640          * Which column in the rule table contains the
641          * return address?
642          */
643         if (cie->version == 1) {
644                 cie->return_address_reg = __raw_readb(p);
645                 p++;
646         } else {
647                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
648                 p += count;
649         }
650
651         if (cie->augmentation[0] == 'z') {
652                 unsigned int length, count;
653                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
654
655                 count = dwarf_read_uleb128(p, &length);
656                 p += count;
657
658                 BUG_ON((unsigned char *)p > end);
659
660                 cie->initial_instructions = p + length;
661                 cie->augmentation++;
662         }
663
664         while (*cie->augmentation) {
665                 /*
666                  * "L" indicates a byte showing how the
667                  * LSDA pointer is encoded. Skip it.
668                  */
669                 if (*cie->augmentation == 'L') {
670                         p++;
671                         cie->augmentation++;
672                 } else if (*cie->augmentation == 'R') {
673                         /*
674                          * "R" indicates a byte showing
675                          * how FDE addresses are
676                          * encoded.
677                          */
678                         cie->encoding = *(char *)p++;
679                         cie->augmentation++;
680                 } else if (*cie->augmentation == 'P') {
681                         /*
682                          * "R" indicates a personality
683                          * routine in the CIE
684                          * augmentation.
685                          */
686                         BUG();
687                 } else if (*cie->augmentation == 'S') {
688                         BUG();
689                 } else {
690                         /*
691                          * Unknown augmentation. Assume
692                          * 'z' augmentation.
693                          */
694                         p = cie->initial_instructions;
695                         BUG_ON(!p);
696                         break;
697                 }
698         }
699
700         cie->initial_instructions = p;
701         cie->instructions_end = end;
702
703         /* Add to list */
704         spin_lock_irqsave(&dwarf_cie_lock, flags);
705         list_add_tail(&cie->link, &dwarf_cie_list);
706         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
707
708         return 0;
709 }
710
711 static int dwarf_parse_fde(void *entry, u32 entry_type,
712                            void *start, unsigned long len)
713 {
714         struct dwarf_fde *fde;
715         struct dwarf_cie *cie;
716         unsigned long flags;
717         int count;
718         void *p = start;
719
720         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
721         if (!fde)
722                 return -ENOMEM;
723
724         fde->length = len;
725
726         /*
727          * In a .eh_frame section the CIE pointer is the
728          * delta between the address within the FDE
729          */
730         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
731
732         cie = dwarf_lookup_cie(fde->cie_pointer);
733         fde->cie = cie;
734
735         if (cie->encoding)
736                 count = dwarf_read_encoded_value(p, &fde->initial_location,
737                                                  cie->encoding);
738         else
739                 count = dwarf_read_addr(p, &fde->initial_location);
740
741         p += count;
742
743         if (cie->encoding)
744                 count = dwarf_read_encoded_value(p, &fde->address_range,
745                                                  cie->encoding & 0x0f);
746         else
747                 count = dwarf_read_addr(p, &fde->address_range);
748
749         p += count;
750
751         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
752                 unsigned int length;
753                 count = dwarf_read_uleb128(p, &length);
754                 p += count + length;
755         }
756
757         /* Call frame instructions. */
758         fde->instructions = p;
759         fde->end = start + len;
760
761         /* Add to list. */
762         spin_lock_irqsave(&dwarf_fde_lock, flags);
763         list_add_tail(&fde->link, &dwarf_fde_list);
764         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
765
766         return 0;
767 }
768
769 static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
770                                 unsigned long *sp,
771                                 const struct stacktrace_ops *ops, void *data)
772 {
773         struct dwarf_frame *frame;
774
775         frame = dwarf_unwind_stack(0, NULL);
776
777         while (frame && frame->return_addr) {
778                 ops->address(data, frame->return_addr, 1);
779                 frame = frame->next;
780         }
781 }
782
783 static struct unwinder dwarf_unwinder = {
784         .name = "dwarf-unwinder",
785         .dump = dwarf_unwinder_dump,
786         .rating = 150,
787 };
788
789 static void dwarf_unwinder_cleanup(void)
790 {
791         struct dwarf_cie *cie;
792         struct dwarf_fde *fde;
793
794         /*
795          * Deallocate all the memory allocated for the DWARF unwinder.
796          * Traverse all the FDE/CIE lists and remove and free all the
797          * memory associated with those data structures.
798          */
799         list_for_each_entry(cie, &dwarf_cie_list, link)
800                 kfree(cie);
801
802         list_for_each_entry(fde, &dwarf_fde_list, link)
803                 kfree(fde);
804 }
805
806 /**
807  *      dwarf_unwinder_init - initialise the dwarf unwinder
808  *
809  *      Build the data structures describing the .dwarf_frame section to
810  *      make it easier to lookup CIE and FDE entries. Because the
811  *      .eh_frame section is packed as tightly as possible it is not
812  *      easy to lookup the FDE for a given PC, so we build a list of FDE
813  *      and CIE entries that make it easier.
814  */
815 static int __init dwarf_unwinder_init(void)
816 {
817         u32 entry_type;
818         void *p, *entry;
819         int count, err;
820         unsigned long len;
821         unsigned int c_entries, f_entries;
822         unsigned char *end;
823         INIT_LIST_HEAD(&dwarf_cie_list);
824         INIT_LIST_HEAD(&dwarf_fde_list);
825
826         c_entries = 0;
827         f_entries = 0;
828         entry = &__start_eh_frame;
829
830         while ((char *)entry < __stop_eh_frame) {
831                 p = entry;
832
833                 count = dwarf_entry_len(p, &len);
834                 if (count == 0) {
835                         /*
836                          * We read a bogus length field value. There is
837                          * nothing we can do here apart from disabling
838                          * the DWARF unwinder. We can't even skip this
839                          * entry and move to the next one because 'len'
840                          * tells us where our next entry is.
841                          */
842                         goto out;
843                 } else
844                         p += count;
845
846                 /* initial length does not include itself */
847                 end = p + len;
848
849                 entry_type = get_unaligned((u32 *)p);
850                 p += 4;
851
852                 if (entry_type == DW_EH_FRAME_CIE) {
853                         err = dwarf_parse_cie(entry, p, len, end);
854                         if (err < 0)
855                                 goto out;
856                         else
857                                 c_entries++;
858                 } else {
859                         err = dwarf_parse_fde(entry, entry_type, p, len);
860                         if (err < 0)
861                                 goto out;
862                         else
863                                 f_entries++;
864                 }
865
866                 entry = (char *)entry + len + 4;
867         }
868
869         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
870                c_entries, f_entries);
871
872         err = unwinder_register(&dwarf_unwinder);
873         if (err)
874                 goto out;
875
876         return 0;
877
878 out:
879         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
880         dwarf_unwinder_cleanup();
881         return -EINVAL;
882 }
883 early_initcall(dwarf_unwinder_init);