sh: Set the cfa_offset to 0 if we see a DW_CFA_def_cfa_register op
[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_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, *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  *      @define_ra: keep executing insns until the return addr reg is defined?
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                                    bool define_ra)
347 {
348         unsigned char insn;
349         unsigned char *current_insn;
350         unsigned int count, delta, reg, expr_len, offset;
351         bool seen_ra_reg;
352
353         current_insn = insn_start;
354
355         /*
356          * If we're executing instructions for the dwarf_unwind_stack()
357          * FDE we need to keep executing instructions until the value of
358          * DWARF_ARCH_RA_REG is defined. See the comment in
359          * dwarf_unwind_stack() for more details.
360          */
361         if (define_ra)
362                 seen_ra_reg = false;
363         else
364                 seen_ra_reg = true;
365
366         while (current_insn < insn_end && (frame->pc <= pc || !seen_ra_reg) ) {
367                 insn = __raw_readb(current_insn++);
368
369                 if (!seen_ra_reg) {
370                         if (frame->num_regs >= DWARF_ARCH_RA_REG &&
371                             frame->regs[DWARF_ARCH_RA_REG].flags)
372                                 seen_ra_reg = true;
373                 }
374
375                 /*
376                  * Firstly, handle the opcodes that embed their operands
377                  * in the instructions.
378                  */
379                 switch (DW_CFA_opcode(insn)) {
380                 case DW_CFA_advance_loc:
381                         delta = DW_CFA_operand(insn);
382                         delta *= cie->code_alignment_factor;
383                         frame->pc += delta;
384                         continue;
385                         /* NOTREACHED */
386                 case DW_CFA_offset:
387                         reg = DW_CFA_operand(insn);
388                         count = dwarf_read_uleb128(current_insn, &offset);
389                         current_insn += count;
390                         offset *= cie->data_alignment_factor;
391                         dwarf_frame_alloc_regs(frame, reg);
392                         frame->regs[reg].addr = offset;
393                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
394                         continue;
395                         /* NOTREACHED */
396                 case DW_CFA_restore:
397                         reg = DW_CFA_operand(insn);
398                         continue;
399                         /* NOTREACHED */
400                 }
401
402                 /*
403                  * Secondly, handle the opcodes that don't embed their
404                  * operands in the instruction.
405                  */
406                 switch (insn) {
407                 case DW_CFA_nop:
408                         continue;
409                 case DW_CFA_advance_loc1:
410                         delta = *current_insn++;
411                         frame->pc += delta * cie->code_alignment_factor;
412                         break;
413                 case DW_CFA_advance_loc2:
414                         delta = get_unaligned((u16 *)current_insn);
415                         current_insn += 2;
416                         frame->pc += delta * cie->code_alignment_factor;
417                         break;
418                 case DW_CFA_advance_loc4:
419                         delta = get_unaligned((u32 *)current_insn);
420                         current_insn += 4;
421                         frame->pc += delta * cie->code_alignment_factor;
422                         break;
423                 case DW_CFA_offset_extended:
424                         count = dwarf_read_uleb128(current_insn, &reg);
425                         current_insn += count;
426                         count = dwarf_read_uleb128(current_insn, &offset);
427                         current_insn += count;
428                         offset *= cie->data_alignment_factor;
429                         break;
430                 case DW_CFA_restore_extended:
431                         count = dwarf_read_uleb128(current_insn, &reg);
432                         current_insn += count;
433                         break;
434                 case DW_CFA_undefined:
435                         count = dwarf_read_uleb128(current_insn, &reg);
436                         current_insn += count;
437                         break;
438                 case DW_CFA_def_cfa:
439                         count = dwarf_read_uleb128(current_insn,
440                                                    &frame->cfa_register);
441                         current_insn += count;
442                         count = dwarf_read_uleb128(current_insn,
443                                                    &frame->cfa_offset);
444                         current_insn += count;
445
446                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
447                         break;
448                 case DW_CFA_def_cfa_register:
449                         count = dwarf_read_uleb128(current_insn,
450                                                    &frame->cfa_register);
451                         current_insn += count;
452                         frame->cfa_offset = 0;
453                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
454                         break;
455                 case DW_CFA_def_cfa_offset:
456                         count = dwarf_read_uleb128(current_insn, &offset);
457                         current_insn += count;
458                         frame->cfa_offset = offset;
459                         break;
460                 case DW_CFA_def_cfa_expression:
461                         count = dwarf_read_uleb128(current_insn, &expr_len);
462                         current_insn += count;
463
464                         frame->cfa_expr = current_insn;
465                         frame->cfa_expr_len = expr_len;
466                         current_insn += expr_len;
467
468                         frame->flags |= DWARF_FRAME_CFA_REG_EXP;
469                         break;
470                 case DW_CFA_offset_extended_sf:
471                         count = dwarf_read_uleb128(current_insn, &reg);
472                         current_insn += count;
473                         count = dwarf_read_leb128(current_insn, &offset);
474                         current_insn += count;
475                         offset *= cie->data_alignment_factor;
476                         dwarf_frame_alloc_regs(frame, reg);
477                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
478                         frame->regs[reg].addr = offset;
479                         break;
480                 case DW_CFA_val_offset:
481                         count = dwarf_read_uleb128(current_insn, &reg);
482                         current_insn += count;
483                         count = dwarf_read_leb128(current_insn, &offset);
484                         offset *= cie->data_alignment_factor;
485                         frame->regs[reg].flags |= DWARF_REG_OFFSET;
486                         frame->regs[reg].addr = offset;
487                         break;
488                 default:
489                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
490                         break;
491                 }
492         }
493
494         return 0;
495 }
496
497 /**
498  *      dwarf_unwind_stack - recursively unwind the stack
499  *      @pc: address of the function to unwind
500  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
501  *
502  *      Return a struct dwarf_frame representing the most recent frame
503  *      on the callstack. Each of the lower (older) stack frames are
504  *      linked via the "prev" member.
505  */
506 struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
507                                        struct dwarf_frame *prev)
508 {
509         struct dwarf_frame *frame;
510         struct dwarf_cie *cie;
511         struct dwarf_fde *fde;
512         unsigned long addr;
513         int i, offset;
514         bool define_ra = false;
515
516         /*
517          * If this is the first invocation of this recursive function we
518          * need get the contents of a physical register to get the CFA
519          * in order to begin the virtual unwinding of the stack.
520          *
521          * Setting "define_ra" to true indictates that we want
522          * dwarf_cfa_execute_insns() to continue executing instructions
523          * until we know how to calculate the value of DWARF_ARCH_RA_REG
524          * (which we need in order to kick off the whole unwinding
525          * process).
526          *
527          * NOTE: the return address is guaranteed to be setup by the
528          * time this function makes its first function call.
529          */
530         if (!pc && !prev) {
531                 pc = (unsigned long)&dwarf_unwind_stack;
532                 define_ra = true;
533         }
534
535         frame = kzalloc(sizeof(*frame), GFP_ATOMIC);
536         if (!frame)
537                 return NULL;
538
539         frame->prev = prev;
540
541         fde = dwarf_lookup_fde(pc);
542         if (!fde) {
543                 /*
544                  * This is our normal exit path - the one that stops the
545                  * recursion. There's two reasons why we might exit
546                  * here,
547                  *
548                  *      a) pc has no asscociated DWARF frame info and so
549                  *      we don't know how to unwind this frame. This is
550                  *      usually the case when we're trying to unwind a
551                  *      frame that was called from some assembly code
552                  *      that has no DWARF info, e.g. syscalls.
553                  *
554                  *      b) the DEBUG info for pc is bogus. There's
555                  *      really no way to distinguish this case from the
556                  *      case above, which sucks because we could print a
557                  *      warning here.
558                  */
559                 return NULL;
560         }
561
562         cie = dwarf_lookup_cie(fde->cie_pointer);
563
564         frame->pc = fde->initial_location;
565
566         /* CIE initial instructions */
567         dwarf_cfa_execute_insns(cie->initial_instructions,
568                                 cie->instructions_end, cie, fde,
569                                 frame, pc, false);
570
571         /* FDE instructions */
572         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
573                                 fde, frame, pc, define_ra);
574
575         /* Calculate the CFA */
576         switch (frame->flags) {
577         case DWARF_FRAME_CFA_REG_OFFSET:
578                 if (prev) {
579                         BUG_ON(!prev->regs[frame->cfa_register].flags);
580
581                         addr = prev->cfa;
582                         addr += prev->regs[frame->cfa_register].addr;
583                         frame->cfa = __raw_readl(addr);
584
585                 } else {
586                         /*
587                          * Again, this is the first invocation of this
588                          * recurisve function. We need to physically
589                          * read the contents of a register in order to
590                          * get the Canonical Frame Address for this
591                          * function.
592                          */
593                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
594                 }
595
596                 frame->cfa += frame->cfa_offset;
597                 break;
598         default:
599                 BUG();
600         }
601
602         /* If we haven't seen the return address reg, we're screwed. */
603         BUG_ON(!frame->regs[DWARF_ARCH_RA_REG].flags);
604
605         for (i = 0; i <= frame->num_regs; i++) {
606                 struct dwarf_reg *reg = &frame->regs[i];
607
608                 if (!reg->flags)
609                         continue;
610
611                 offset = reg->addr;
612                 offset += frame->cfa;
613         }
614
615         addr = frame->cfa + frame->regs[DWARF_ARCH_RA_REG].addr;
616         frame->return_addr = __raw_readl(addr);
617
618         frame->next = dwarf_unwind_stack(frame->return_addr, frame);
619         return frame;
620 }
621
622 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
623                            unsigned char *end)
624 {
625         struct dwarf_cie *cie;
626         unsigned long flags;
627         int count;
628
629         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
630         if (!cie)
631                 return -ENOMEM;
632
633         cie->length = len;
634
635         /*
636          * Record the offset into the .eh_frame section
637          * for this CIE. It allows this CIE to be
638          * quickly and easily looked up from the
639          * corresponding FDE.
640          */
641         cie->cie_pointer = (unsigned long)entry;
642
643         cie->version = *(char *)p++;
644         BUG_ON(cie->version != 1);
645
646         cie->augmentation = p;
647         p += strlen(cie->augmentation) + 1;
648
649         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
650         p += count;
651
652         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
653         p += count;
654
655         /*
656          * Which column in the rule table contains the
657          * return address?
658          */
659         if (cie->version == 1) {
660                 cie->return_address_reg = __raw_readb(p);
661                 p++;
662         } else {
663                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
664                 p += count;
665         }
666
667         if (cie->augmentation[0] == 'z') {
668                 unsigned int length, count;
669                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
670
671                 count = dwarf_read_uleb128(p, &length);
672                 p += count;
673
674                 BUG_ON((unsigned char *)p > end);
675
676                 cie->initial_instructions = p + length;
677                 cie->augmentation++;
678         }
679
680         while (*cie->augmentation) {
681                 /*
682                  * "L" indicates a byte showing how the
683                  * LSDA pointer is encoded. Skip it.
684                  */
685                 if (*cie->augmentation == 'L') {
686                         p++;
687                         cie->augmentation++;
688                 } else if (*cie->augmentation == 'R') {
689                         /*
690                          * "R" indicates a byte showing
691                          * how FDE addresses are
692                          * encoded.
693                          */
694                         cie->encoding = *(char *)p++;
695                         cie->augmentation++;
696                 } else if (*cie->augmentation == 'P') {
697                         /*
698                          * "R" indicates a personality
699                          * routine in the CIE
700                          * augmentation.
701                          */
702                         BUG();
703                 } else if (*cie->augmentation == 'S') {
704                         BUG();
705                 } else {
706                         /*
707                          * Unknown augmentation. Assume
708                          * 'z' augmentation.
709                          */
710                         p = cie->initial_instructions;
711                         BUG_ON(!p);
712                         break;
713                 }
714         }
715
716         cie->initial_instructions = p;
717         cie->instructions_end = end;
718
719         /* Add to list */
720         spin_lock_irqsave(&dwarf_cie_lock, flags);
721         list_add_tail(&cie->link, &dwarf_cie_list);
722         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
723
724         return 0;
725 }
726
727 static int dwarf_parse_fde(void *entry, u32 entry_type,
728                            void *start, unsigned long len)
729 {
730         struct dwarf_fde *fde;
731         struct dwarf_cie *cie;
732         unsigned long flags;
733         int count;
734         void *p = start;
735
736         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
737         if (!fde)
738                 return -ENOMEM;
739
740         fde->length = len;
741
742         /*
743          * In a .eh_frame section the CIE pointer is the
744          * delta between the address within the FDE
745          */
746         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
747
748         cie = dwarf_lookup_cie(fde->cie_pointer);
749         fde->cie = cie;
750
751         if (cie->encoding)
752                 count = dwarf_read_encoded_value(p, &fde->initial_location,
753                                                  cie->encoding);
754         else
755                 count = dwarf_read_addr(p, &fde->initial_location);
756
757         p += count;
758
759         if (cie->encoding)
760                 count = dwarf_read_encoded_value(p, &fde->address_range,
761                                                  cie->encoding & 0x0f);
762         else
763                 count = dwarf_read_addr(p, &fde->address_range);
764
765         p += count;
766
767         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
768                 unsigned int length;
769                 count = dwarf_read_uleb128(p, &length);
770                 p += count + length;
771         }
772
773         /* Call frame instructions. */
774         fde->instructions = p;
775         fde->end = start + len;
776
777         /* Add to list. */
778         spin_lock_irqsave(&dwarf_fde_lock, flags);
779         list_add_tail(&fde->link, &dwarf_fde_list);
780         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
781
782         return 0;
783 }
784
785 static void dwarf_unwinder_dump(struct task_struct *task, struct pt_regs *regs,
786                                 unsigned long *sp,
787                                 const struct stacktrace_ops *ops, void *data)
788 {
789         struct dwarf_frame *frame;
790
791         frame = dwarf_unwind_stack(0, NULL);
792
793         while (frame && frame->return_addr) {
794                 ops->address(data, frame->return_addr, 1);
795                 frame = frame->next;
796         }
797 }
798
799 static struct unwinder dwarf_unwinder = {
800         .name = "dwarf-unwinder",
801         .dump = dwarf_unwinder_dump,
802         .rating = 150,
803 };
804
805 static void dwarf_unwinder_cleanup(void)
806 {
807         struct dwarf_cie *cie, *m;
808         struct dwarf_fde *fde, *n;
809         unsigned long flags;
810
811         /*
812          * Deallocate all the memory allocated for the DWARF unwinder.
813          * Traverse all the FDE/CIE lists and remove and free all the
814          * memory associated with those data structures.
815          */
816         spin_lock_irqsave(&dwarf_cie_lock, flags);
817         list_for_each_entry_safe(cie, m, &dwarf_cie_list, link)
818                 kfree(cie);
819         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
820
821         spin_lock_irqsave(&dwarf_fde_lock, flags);
822         list_for_each_entry_safe(fde, n, &dwarf_fde_list, link)
823                 kfree(fde);
824         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
825 }
826
827 /**
828  *      dwarf_unwinder_init - initialise the dwarf unwinder
829  *
830  *      Build the data structures describing the .dwarf_frame section to
831  *      make it easier to lookup CIE and FDE entries. Because the
832  *      .eh_frame section is packed as tightly as possible it is not
833  *      easy to lookup the FDE for a given PC, so we build a list of FDE
834  *      and CIE entries that make it easier.
835  */
836 void dwarf_unwinder_init(void)
837 {
838         u32 entry_type;
839         void *p, *entry;
840         int count, err;
841         unsigned long len;
842         unsigned int c_entries, f_entries;
843         unsigned char *end;
844         INIT_LIST_HEAD(&dwarf_cie_list);
845         INIT_LIST_HEAD(&dwarf_fde_list);
846
847         c_entries = 0;
848         f_entries = 0;
849         entry = &__start_eh_frame;
850
851         while ((char *)entry < __stop_eh_frame) {
852                 p = entry;
853
854                 count = dwarf_entry_len(p, &len);
855                 if (count == 0) {
856                         /*
857                          * We read a bogus length field value. There is
858                          * nothing we can do here apart from disabling
859                          * the DWARF unwinder. We can't even skip this
860                          * entry and move to the next one because 'len'
861                          * tells us where our next entry is.
862                          */
863                         goto out;
864                 } else
865                         p += count;
866
867                 /* initial length does not include itself */
868                 end = p + len;
869
870                 entry_type = get_unaligned((u32 *)p);
871                 p += 4;
872
873                 if (entry_type == DW_EH_FRAME_CIE) {
874                         err = dwarf_parse_cie(entry, p, len, end);
875                         if (err < 0)
876                                 goto out;
877                         else
878                                 c_entries++;
879                 } else {
880                         err = dwarf_parse_fde(entry, entry_type, p, len);
881                         if (err < 0)
882                                 goto out;
883                         else
884                                 f_entries++;
885                 }
886
887                 entry = (char *)entry + len + 4;
888         }
889
890         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
891                c_entries, f_entries);
892
893         err = unwinder_register(&dwarf_unwinder);
894         if (err)
895                 goto out;
896
897         return;
898
899 out:
900         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
901         dwarf_unwinder_cleanup();
902 }