sh: Tidy up the dwarf module helpers.
[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  *      - Registers with DWARF_VAL_OFFSET rules aren't handled properly.
15  */
16
17 /* #define DEBUG */
18 #include <linux/kernel.h>
19 #include <linux/io.h>
20 #include <linux/list.h>
21 #include <linux/mempool.h>
22 #include <linux/mm.h>
23 #include <linux/elf.h>
24 #include <asm/dwarf.h>
25 #include <asm/unwinder.h>
26 #include <asm/sections.h>
27 #include <asm/unaligned.h>
28 #include <asm/stacktrace.h>
29
30 /* Reserve enough memory for two stack frames */
31 #define DWARF_FRAME_MIN_REQ     2
32 /* ... with 4 registers per frame. */
33 #define DWARF_REG_MIN_REQ       (DWARF_FRAME_MIN_REQ * 4)
34
35 static struct kmem_cache *dwarf_frame_cachep;
36 static mempool_t *dwarf_frame_pool;
37
38 static struct kmem_cache *dwarf_reg_cachep;
39 static mempool_t *dwarf_reg_pool;
40
41 static LIST_HEAD(dwarf_cie_list);
42 static DEFINE_SPINLOCK(dwarf_cie_lock);
43
44 static LIST_HEAD(dwarf_fde_list);
45 static DEFINE_SPINLOCK(dwarf_fde_lock);
46
47 static struct dwarf_cie *cached_cie;
48
49 /**
50  *      dwarf_frame_alloc_reg - allocate memory for a DWARF register
51  *      @frame: the DWARF frame whose list of registers we insert on
52  *      @reg_num: the register number
53  *
54  *      Allocate space for, and initialise, a dwarf reg from
55  *      dwarf_reg_pool and insert it onto the (unsorted) linked-list of
56  *      dwarf registers for @frame.
57  *
58  *      Return the initialised DWARF reg.
59  */
60 static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
61                                                unsigned int reg_num)
62 {
63         struct dwarf_reg *reg;
64
65         reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC);
66         if (!reg) {
67                 printk(KERN_WARNING "Unable to allocate a DWARF register\n");
68                 /*
69                  * Let's just bomb hard here, we have no way to
70                  * gracefully recover.
71                  */
72                 UNWINDER_BUG();
73         }
74
75         reg->number = reg_num;
76         reg->addr = 0;
77         reg->flags = 0;
78
79         list_add(&reg->link, &frame->reg_list);
80
81         return reg;
82 }
83
84 static void dwarf_frame_free_regs(struct dwarf_frame *frame)
85 {
86         struct dwarf_reg *reg, *n;
87
88         list_for_each_entry_safe(reg, n, &frame->reg_list, link) {
89                 list_del(&reg->link);
90                 mempool_free(reg, dwarf_reg_pool);
91         }
92 }
93
94 /**
95  *      dwarf_frame_reg - return a DWARF register
96  *      @frame: the DWARF frame to search in for @reg_num
97  *      @reg_num: the register number to search for
98  *
99  *      Lookup and return the dwarf reg @reg_num for this frame. Return
100  *      NULL if @reg_num is an register invalid number.
101  */
102 static struct dwarf_reg *dwarf_frame_reg(struct dwarf_frame *frame,
103                                          unsigned int reg_num)
104 {
105         struct dwarf_reg *reg;
106
107         list_for_each_entry(reg, &frame->reg_list, link) {
108                 if (reg->number == reg_num)
109                         return reg;
110         }
111
112         return NULL;
113 }
114
115 /**
116  *      dwarf_read_addr - read dwarf data
117  *      @src: source address of data
118  *      @dst: destination address to store the data to
119  *
120  *      Read 'n' bytes from @src, where 'n' is the size of an address on
121  *      the native machine. We return the number of bytes read, which
122  *      should always be 'n'. We also have to be careful when reading
123  *      from @src and writing to @dst, because they can be arbitrarily
124  *      aligned. Return 'n' - the number of bytes read.
125  */
126 static inline int dwarf_read_addr(unsigned long *src, unsigned long *dst)
127 {
128         u32 val = get_unaligned(src);
129         put_unaligned(val, dst);
130         return sizeof(unsigned long *);
131 }
132
133 /**
134  *      dwarf_read_uleb128 - read unsigned LEB128 data
135  *      @addr: the address where the ULEB128 data is stored
136  *      @ret: address to store the result
137  *
138  *      Decode an unsigned LEB128 encoded datum. The algorithm is taken
139  *      from Appendix C of the DWARF 3 spec. For information on the
140  *      encodings refer to section "7.6 - Variable Length Data". Return
141  *      the number of bytes read.
142  */
143 static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
144 {
145         unsigned int result;
146         unsigned char byte;
147         int shift, count;
148
149         result = 0;
150         shift = 0;
151         count = 0;
152
153         while (1) {
154                 byte = __raw_readb(addr);
155                 addr++;
156                 count++;
157
158                 result |= (byte & 0x7f) << shift;
159                 shift += 7;
160
161                 if (!(byte & 0x80))
162                         break;
163         }
164
165         *ret = result;
166
167         return count;
168 }
169
170 /**
171  *      dwarf_read_leb128 - read signed LEB128 data
172  *      @addr: the address of the LEB128 encoded data
173  *      @ret: address to store the result
174  *
175  *      Decode signed LEB128 data. The algorithm is taken from Appendix
176  *      C of the DWARF 3 spec. Return the number of bytes read.
177  */
178 static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
179 {
180         unsigned char byte;
181         int result, shift;
182         int num_bits;
183         int count;
184
185         result = 0;
186         shift = 0;
187         count = 0;
188
189         while (1) {
190                 byte = __raw_readb(addr);
191                 addr++;
192                 result |= (byte & 0x7f) << shift;
193                 shift += 7;
194                 count++;
195
196                 if (!(byte & 0x80))
197                         break;
198         }
199
200         /* The number of bits in a signed integer. */
201         num_bits = 8 * sizeof(result);
202
203         if ((shift < num_bits) && (byte & 0x40))
204                 result |= (-1 << shift);
205
206         *ret = result;
207
208         return count;
209 }
210
211 /**
212  *      dwarf_read_encoded_value - return the decoded value at @addr
213  *      @addr: the address of the encoded value
214  *      @val: where to write the decoded value
215  *      @encoding: the encoding with which we can decode @addr
216  *
217  *      GCC emits encoded address in the .eh_frame FDE entries. Decode
218  *      the value at @addr using @encoding. The decoded value is written
219  *      to @val and the number of bytes read is returned.
220  */
221 static int dwarf_read_encoded_value(char *addr, unsigned long *val,
222                                     char encoding)
223 {
224         unsigned long decoded_addr = 0;
225         int count = 0;
226
227         switch (encoding & 0x70) {
228         case DW_EH_PE_absptr:
229                 break;
230         case DW_EH_PE_pcrel:
231                 decoded_addr = (unsigned long)addr;
232                 break;
233         default:
234                 pr_debug("encoding=0x%x\n", (encoding & 0x70));
235                 UNWINDER_BUG();
236         }
237
238         if ((encoding & 0x07) == 0x00)
239                 encoding |= DW_EH_PE_udata4;
240
241         switch (encoding & 0x0f) {
242         case DW_EH_PE_sdata4:
243         case DW_EH_PE_udata4:
244                 count += 4;
245                 decoded_addr += get_unaligned((u32 *)addr);
246                 __raw_writel(decoded_addr, val);
247                 break;
248         default:
249                 pr_debug("encoding=0x%x\n", encoding);
250                 UNWINDER_BUG();
251         }
252
253         return count;
254 }
255
256 /**
257  *      dwarf_entry_len - return the length of an FDE or CIE
258  *      @addr: the address of the entry
259  *      @len: the length of the entry
260  *
261  *      Read the initial_length field of the entry and store the size of
262  *      the entry in @len. We return the number of bytes read. Return a
263  *      count of 0 on error.
264  */
265 static inline int dwarf_entry_len(char *addr, unsigned long *len)
266 {
267         u32 initial_len;
268         int count;
269
270         initial_len = get_unaligned((u32 *)addr);
271         count = 4;
272
273         /*
274          * An initial length field value in the range DW_LEN_EXT_LO -
275          * DW_LEN_EXT_HI indicates an extension, and should not be
276          * interpreted as a length. The only extension that we currently
277          * understand is the use of DWARF64 addresses.
278          */
279         if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
280                 /*
281                  * The 64-bit length field immediately follows the
282                  * compulsory 32-bit length field.
283                  */
284                 if (initial_len == DW_EXT_DWARF64) {
285                         *len = get_unaligned((u64 *)addr + 4);
286                         count = 12;
287                 } else {
288                         printk(KERN_WARNING "Unknown DWARF extension\n");
289                         count = 0;
290                 }
291         } else
292                 *len = initial_len;
293
294         return count;
295 }
296
297 /**
298  *      dwarf_lookup_cie - locate the cie
299  *      @cie_ptr: pointer to help with lookup
300  */
301 static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
302 {
303         struct dwarf_cie *cie;
304         unsigned long flags;
305
306         spin_lock_irqsave(&dwarf_cie_lock, flags);
307
308         /*
309          * We've cached the last CIE we looked up because chances are
310          * that the FDE wants this CIE.
311          */
312         if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
313                 cie = cached_cie;
314                 goto out;
315         }
316
317         list_for_each_entry(cie, &dwarf_cie_list, link) {
318                 if (cie->cie_pointer == cie_ptr) {
319                         cached_cie = cie;
320                         break;
321                 }
322         }
323
324         /* Couldn't find the entry in the list. */
325         if (&cie->link == &dwarf_cie_list)
326                 cie = NULL;
327 out:
328         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
329         return cie;
330 }
331
332 /**
333  *      dwarf_lookup_fde - locate the FDE that covers pc
334  *      @pc: the program counter
335  */
336 struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
337 {
338         struct dwarf_fde *fde;
339         unsigned long flags;
340
341         spin_lock_irqsave(&dwarf_fde_lock, flags);
342
343         list_for_each_entry(fde, &dwarf_fde_list, link) {
344                 unsigned long start, end;
345
346                 start = fde->initial_location;
347                 end = fde->initial_location + fde->address_range;
348
349                 if (pc >= start && pc < end)
350                         break;
351         }
352
353         /* Couldn't find the entry in the list. */
354         if (&fde->link == &dwarf_fde_list)
355                 fde = NULL;
356
357         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
358
359         return fde;
360 }
361
362 /**
363  *      dwarf_cfa_execute_insns - execute instructions to calculate a CFA
364  *      @insn_start: address of the first instruction
365  *      @insn_end: address of the last instruction
366  *      @cie: the CIE for this function
367  *      @fde: the FDE for this function
368  *      @frame: the instructions calculate the CFA for this frame
369  *      @pc: the program counter of the address we're interested in
370  *
371  *      Execute the Call Frame instruction sequence starting at
372  *      @insn_start and ending at @insn_end. The instructions describe
373  *      how to calculate the Canonical Frame Address of a stackframe.
374  *      Store the results in @frame.
375  */
376 static int dwarf_cfa_execute_insns(unsigned char *insn_start,
377                                    unsigned char *insn_end,
378                                    struct dwarf_cie *cie,
379                                    struct dwarf_fde *fde,
380                                    struct dwarf_frame *frame,
381                                    unsigned long pc)
382 {
383         unsigned char insn;
384         unsigned char *current_insn;
385         unsigned int count, delta, reg, expr_len, offset;
386         struct dwarf_reg *regp;
387
388         current_insn = insn_start;
389
390         while (current_insn < insn_end && frame->pc <= pc) {
391                 insn = __raw_readb(current_insn++);
392
393                 /*
394                  * Firstly, handle the opcodes that embed their operands
395                  * in the instructions.
396                  */
397                 switch (DW_CFA_opcode(insn)) {
398                 case DW_CFA_advance_loc:
399                         delta = DW_CFA_operand(insn);
400                         delta *= cie->code_alignment_factor;
401                         frame->pc += delta;
402                         continue;
403                         /* NOTREACHED */
404                 case DW_CFA_offset:
405                         reg = DW_CFA_operand(insn);
406                         count = dwarf_read_uleb128(current_insn, &offset);
407                         current_insn += count;
408                         offset *= cie->data_alignment_factor;
409                         regp = dwarf_frame_alloc_reg(frame, reg);
410                         regp->addr = offset;
411                         regp->flags |= DWARF_REG_OFFSET;
412                         continue;
413                         /* NOTREACHED */
414                 case DW_CFA_restore:
415                         reg = DW_CFA_operand(insn);
416                         continue;
417                         /* NOTREACHED */
418                 }
419
420                 /*
421                  * Secondly, handle the opcodes that don't embed their
422                  * operands in the instruction.
423                  */
424                 switch (insn) {
425                 case DW_CFA_nop:
426                         continue;
427                 case DW_CFA_advance_loc1:
428                         delta = *current_insn++;
429                         frame->pc += delta * cie->code_alignment_factor;
430                         break;
431                 case DW_CFA_advance_loc2:
432                         delta = get_unaligned((u16 *)current_insn);
433                         current_insn += 2;
434                         frame->pc += delta * cie->code_alignment_factor;
435                         break;
436                 case DW_CFA_advance_loc4:
437                         delta = get_unaligned((u32 *)current_insn);
438                         current_insn += 4;
439                         frame->pc += delta * cie->code_alignment_factor;
440                         break;
441                 case DW_CFA_offset_extended:
442                         count = dwarf_read_uleb128(current_insn, &reg);
443                         current_insn += count;
444                         count = dwarf_read_uleb128(current_insn, &offset);
445                         current_insn += count;
446                         offset *= cie->data_alignment_factor;
447                         break;
448                 case DW_CFA_restore_extended:
449                         count = dwarf_read_uleb128(current_insn, &reg);
450                         current_insn += count;
451                         break;
452                 case DW_CFA_undefined:
453                         count = dwarf_read_uleb128(current_insn, &reg);
454                         current_insn += count;
455                         regp = dwarf_frame_alloc_reg(frame, reg);
456                         regp->flags |= DWARF_UNDEFINED;
457                         break;
458                 case DW_CFA_def_cfa:
459                         count = dwarf_read_uleb128(current_insn,
460                                                    &frame->cfa_register);
461                         current_insn += count;
462                         count = dwarf_read_uleb128(current_insn,
463                                                    &frame->cfa_offset);
464                         current_insn += count;
465
466                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
467                         break;
468                 case DW_CFA_def_cfa_register:
469                         count = dwarf_read_uleb128(current_insn,
470                                                    &frame->cfa_register);
471                         current_insn += count;
472                         frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
473                         break;
474                 case DW_CFA_def_cfa_offset:
475                         count = dwarf_read_uleb128(current_insn, &offset);
476                         current_insn += count;
477                         frame->cfa_offset = offset;
478                         break;
479                 case DW_CFA_def_cfa_expression:
480                         count = dwarf_read_uleb128(current_insn, &expr_len);
481                         current_insn += count;
482
483                         frame->cfa_expr = current_insn;
484                         frame->cfa_expr_len = expr_len;
485                         current_insn += expr_len;
486
487                         frame->flags |= DWARF_FRAME_CFA_REG_EXP;
488                         break;
489                 case DW_CFA_offset_extended_sf:
490                         count = dwarf_read_uleb128(current_insn, &reg);
491                         current_insn += count;
492                         count = dwarf_read_leb128(current_insn, &offset);
493                         current_insn += count;
494                         offset *= cie->data_alignment_factor;
495                         regp = dwarf_frame_alloc_reg(frame, reg);
496                         regp->flags |= DWARF_REG_OFFSET;
497                         regp->addr = offset;
498                         break;
499                 case DW_CFA_val_offset:
500                         count = dwarf_read_uleb128(current_insn, &reg);
501                         current_insn += count;
502                         count = dwarf_read_leb128(current_insn, &offset);
503                         offset *= cie->data_alignment_factor;
504                         regp = dwarf_frame_alloc_reg(frame, reg);
505                         regp->flags |= DWARF_VAL_OFFSET;
506                         regp->addr = offset;
507                         break;
508                 case DW_CFA_GNU_args_size:
509                         count = dwarf_read_uleb128(current_insn, &offset);
510                         current_insn += count;
511                         break;
512                 case DW_CFA_GNU_negative_offset_extended:
513                         count = dwarf_read_uleb128(current_insn, &reg);
514                         current_insn += count;
515                         count = dwarf_read_uleb128(current_insn, &offset);
516                         offset *= cie->data_alignment_factor;
517
518                         regp = dwarf_frame_alloc_reg(frame, reg);
519                         regp->flags |= DWARF_REG_OFFSET;
520                         regp->addr = -offset;
521                         break;
522                 default:
523                         pr_debug("unhandled DWARF instruction 0x%x\n", insn);
524                         UNWINDER_BUG();
525                         break;
526                 }
527         }
528
529         return 0;
530 }
531
532 /**
533  *      dwarf_free_frame - free the memory allocated for @frame
534  *      @frame: the frame to free
535  */
536 void dwarf_free_frame(struct dwarf_frame *frame)
537 {
538         dwarf_frame_free_regs(frame);
539         mempool_free(frame, dwarf_frame_pool);
540 }
541
542 /**
543  *      dwarf_unwind_stack - unwind the stack
544  *
545  *      @pc: address of the function to unwind
546  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
547  *
548  *      Return a struct dwarf_frame representing the most recent frame
549  *      on the callstack. Each of the lower (older) stack frames are
550  *      linked via the "prev" member.
551  */
552 struct dwarf_frame * dwarf_unwind_stack(unsigned long pc,
553                                         struct dwarf_frame *prev)
554 {
555         struct dwarf_frame *frame;
556         struct dwarf_cie *cie;
557         struct dwarf_fde *fde;
558         struct dwarf_reg *reg;
559         unsigned long addr;
560
561         /*
562          * If we're starting at the top of the stack we need get the
563          * contents of a physical register to get the CFA in order to
564          * begin the virtual unwinding of the stack.
565          *
566          * NOTE: the return address is guaranteed to be setup by the
567          * time this function makes its first function call.
568          */
569         if (!pc && !prev)
570                 pc = (unsigned long)current_text_addr();
571
572         frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
573         if (!frame) {
574                 printk(KERN_ERR "Unable to allocate a dwarf frame\n");
575                 UNWINDER_BUG();
576         }
577
578         INIT_LIST_HEAD(&frame->reg_list);
579         frame->flags = 0;
580         frame->prev = prev;
581         frame->return_addr = 0;
582
583         fde = dwarf_lookup_fde(pc);
584         if (!fde) {
585                 /*
586                  * This is our normal exit path. There are two reasons
587                  * why we might exit here,
588                  *
589                  *      a) pc has no asscociated DWARF frame info and so
590                  *      we don't know how to unwind this frame. This is
591                  *      usually the case when we're trying to unwind a
592                  *      frame that was called from some assembly code
593                  *      that has no DWARF info, e.g. syscalls.
594                  *
595                  *      b) the DEBUG info for pc is bogus. There's
596                  *      really no way to distinguish this case from the
597                  *      case above, which sucks because we could print a
598                  *      warning here.
599                  */
600                 goto bail;
601         }
602
603         cie = dwarf_lookup_cie(fde->cie_pointer);
604
605         frame->pc = fde->initial_location;
606
607         /* CIE initial instructions */
608         dwarf_cfa_execute_insns(cie->initial_instructions,
609                                 cie->instructions_end, cie, fde,
610                                 frame, pc);
611
612         /* FDE instructions */
613         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
614                                 fde, frame, pc);
615
616         /* Calculate the CFA */
617         switch (frame->flags) {
618         case DWARF_FRAME_CFA_REG_OFFSET:
619                 if (prev) {
620                         reg = dwarf_frame_reg(prev, frame->cfa_register);
621                         UNWINDER_BUG_ON(!reg);
622                         UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
623
624                         addr = prev->cfa + reg->addr;
625                         frame->cfa = __raw_readl(addr);
626
627                 } else {
628                         /*
629                          * Again, we're starting from the top of the
630                          * stack. We need to physically read
631                          * the contents of a register in order to get
632                          * the Canonical Frame Address for this
633                          * function.
634                          */
635                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
636                 }
637
638                 frame->cfa += frame->cfa_offset;
639                 break;
640         default:
641                 UNWINDER_BUG();
642         }
643
644         reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);
645
646         /*
647          * If we haven't seen the return address register or the return
648          * address column is undefined then we must assume that this is
649          * the end of the callstack.
650          */
651         if (!reg || reg->flags == DWARF_UNDEFINED)
652                 goto bail;
653
654         UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
655
656         addr = frame->cfa + reg->addr;
657         frame->return_addr = __raw_readl(addr);
658
659         return frame;
660
661 bail:
662         dwarf_free_frame(frame);
663         return NULL;
664 }
665
666 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
667                            unsigned char *end, struct module *mod)
668 {
669         struct dwarf_cie *cie;
670         unsigned long flags;
671         int count;
672
673         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
674         if (!cie)
675                 return -ENOMEM;
676
677         cie->length = len;
678
679         /*
680          * Record the offset into the .eh_frame section
681          * for this CIE. It allows this CIE to be
682          * quickly and easily looked up from the
683          * corresponding FDE.
684          */
685         cie->cie_pointer = (unsigned long)entry;
686
687         cie->version = *(char *)p++;
688         UNWINDER_BUG_ON(cie->version != 1);
689
690         cie->augmentation = p;
691         p += strlen(cie->augmentation) + 1;
692
693         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
694         p += count;
695
696         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
697         p += count;
698
699         /*
700          * Which column in the rule table contains the
701          * return address?
702          */
703         if (cie->version == 1) {
704                 cie->return_address_reg = __raw_readb(p);
705                 p++;
706         } else {
707                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
708                 p += count;
709         }
710
711         if (cie->augmentation[0] == 'z') {
712                 unsigned int length, count;
713                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
714
715                 count = dwarf_read_uleb128(p, &length);
716                 p += count;
717
718                 UNWINDER_BUG_ON((unsigned char *)p > end);
719
720                 cie->initial_instructions = p + length;
721                 cie->augmentation++;
722         }
723
724         while (*cie->augmentation) {
725                 /*
726                  * "L" indicates a byte showing how the
727                  * LSDA pointer is encoded. Skip it.
728                  */
729                 if (*cie->augmentation == 'L') {
730                         p++;
731                         cie->augmentation++;
732                 } else if (*cie->augmentation == 'R') {
733                         /*
734                          * "R" indicates a byte showing
735                          * how FDE addresses are
736                          * encoded.
737                          */
738                         cie->encoding = *(char *)p++;
739                         cie->augmentation++;
740                 } else if (*cie->augmentation == 'P') {
741                         /*
742                          * "R" indicates a personality
743                          * routine in the CIE
744                          * augmentation.
745                          */
746                         UNWINDER_BUG();
747                 } else if (*cie->augmentation == 'S') {
748                         UNWINDER_BUG();
749                 } else {
750                         /*
751                          * Unknown augmentation. Assume
752                          * 'z' augmentation.
753                          */
754                         p = cie->initial_instructions;
755                         UNWINDER_BUG_ON(!p);
756                         break;
757                 }
758         }
759
760         cie->initial_instructions = p;
761         cie->instructions_end = end;
762
763         cie->mod = mod;
764
765         /* Add to list */
766         spin_lock_irqsave(&dwarf_cie_lock, flags);
767         list_add_tail(&cie->link, &dwarf_cie_list);
768         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
769
770         return 0;
771 }
772
773 static int dwarf_parse_fde(void *entry, u32 entry_type,
774                            void *start, unsigned long len,
775                            unsigned char *end, struct module *mod)
776 {
777         struct dwarf_fde *fde;
778         struct dwarf_cie *cie;
779         unsigned long flags;
780         int count;
781         void *p = start;
782
783         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
784         if (!fde)
785                 return -ENOMEM;
786
787         fde->length = len;
788
789         /*
790          * In a .eh_frame section the CIE pointer is the
791          * delta between the address within the FDE
792          */
793         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
794
795         cie = dwarf_lookup_cie(fde->cie_pointer);
796         fde->cie = cie;
797
798         if (cie->encoding)
799                 count = dwarf_read_encoded_value(p, &fde->initial_location,
800                                                  cie->encoding);
801         else
802                 count = dwarf_read_addr(p, &fde->initial_location);
803
804         p += count;
805
806         if (cie->encoding)
807                 count = dwarf_read_encoded_value(p, &fde->address_range,
808                                                  cie->encoding & 0x0f);
809         else
810                 count = dwarf_read_addr(p, &fde->address_range);
811
812         p += count;
813
814         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
815                 unsigned int length;
816                 count = dwarf_read_uleb128(p, &length);
817                 p += count + length;
818         }
819
820         /* Call frame instructions. */
821         fde->instructions = p;
822         fde->end = end;
823
824         fde->mod = mod;
825
826         /* Add to list. */
827         spin_lock_irqsave(&dwarf_fde_lock, flags);
828         list_add_tail(&fde->link, &dwarf_fde_list);
829         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
830
831         return 0;
832 }
833
834 static void dwarf_unwinder_dump(struct task_struct *task,
835                                 struct pt_regs *regs,
836                                 unsigned long *sp,
837                                 const struct stacktrace_ops *ops,
838                                 void *data)
839 {
840         struct dwarf_frame *frame, *_frame;
841         unsigned long return_addr;
842
843         _frame = NULL;
844         return_addr = 0;
845
846         while (1) {
847                 frame = dwarf_unwind_stack(return_addr, _frame);
848
849                 if (_frame)
850                         dwarf_free_frame(_frame);
851
852                 _frame = frame;
853
854                 if (!frame || !frame->return_addr)
855                         break;
856
857                 return_addr = frame->return_addr;
858                 ops->address(data, return_addr, 1);
859         }
860
861         if (frame)
862                 dwarf_free_frame(frame);
863 }
864
865 static struct unwinder dwarf_unwinder = {
866         .name = "dwarf-unwinder",
867         .dump = dwarf_unwinder_dump,
868         .rating = 150,
869 };
870
871 static void dwarf_unwinder_cleanup(void)
872 {
873         struct dwarf_cie *cie;
874         struct dwarf_fde *fde;
875
876         /*
877          * Deallocate all the memory allocated for the DWARF unwinder.
878          * Traverse all the FDE/CIE lists and remove and free all the
879          * memory associated with those data structures.
880          */
881         list_for_each_entry(cie, &dwarf_cie_list, link)
882                 kfree(cie);
883
884         list_for_each_entry(fde, &dwarf_fde_list, link)
885                 kfree(fde);
886
887         kmem_cache_destroy(dwarf_reg_cachep);
888         kmem_cache_destroy(dwarf_frame_cachep);
889 }
890
891 /**
892  *      dwarf_parse_section - parse DWARF section
893  *      @eh_frame_start: start address of the .eh_frame section
894  *      @eh_frame_end: end address of the .eh_frame section
895  *      @mod: the kernel module containing the .eh_frame section
896  *
897  *      Parse the information in a .eh_frame section.
898  */
899 static int dwarf_parse_section(char *eh_frame_start, char *eh_frame_end,
900                                struct module *mod)
901 {
902         u32 entry_type;
903         void *p, *entry;
904         int count, err = 0;
905         unsigned long len;
906         unsigned int c_entries, f_entries;
907         unsigned char *end;
908
909         c_entries = 0;
910         f_entries = 0;
911         entry = eh_frame_start;
912
913         while ((char *)entry < eh_frame_end) {
914                 p = entry;
915
916                 count = dwarf_entry_len(p, &len);
917                 if (count == 0) {
918                         /*
919                          * We read a bogus length field value. There is
920                          * nothing we can do here apart from disabling
921                          * the DWARF unwinder. We can't even skip this
922                          * entry and move to the next one because 'len'
923                          * tells us where our next entry is.
924                          */
925                         err = -EINVAL;
926                         goto out;
927                 } else
928                         p += count;
929
930                 /* initial length does not include itself */
931                 end = p + len;
932
933                 entry_type = get_unaligned((u32 *)p);
934                 p += 4;
935
936                 if (entry_type == DW_EH_FRAME_CIE) {
937                         err = dwarf_parse_cie(entry, p, len, end, mod);
938                         if (err < 0)
939                                 goto out;
940                         else
941                                 c_entries++;
942                 } else {
943                         err = dwarf_parse_fde(entry, entry_type, p, len,
944                                               end, mod);
945                         if (err < 0)
946                                 goto out;
947                         else
948                                 f_entries++;
949                 }
950
951                 entry = (char *)entry + len + 4;
952         }
953
954         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
955                c_entries, f_entries);
956
957         return 0;
958
959 out:
960         return err;
961 }
962
963 #ifdef CONFIG_MODULES
964 int module_dwarf_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
965                           struct module *me)
966 {
967         unsigned int i, err;
968         unsigned long start, end;
969         char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
970
971         start = end = 0;
972
973         for (i = 1; i < hdr->e_shnum; i++) {
974                 /* Alloc bit cleared means "ignore it." */
975                 if ((sechdrs[i].sh_flags & SHF_ALLOC)
976                     && !strcmp(secstrings+sechdrs[i].sh_name, ".eh_frame")) {
977                         start = sechdrs[i].sh_addr;
978                         end = start + sechdrs[i].sh_size;
979                         break;
980                 }
981         }
982
983         /* Did we find the .eh_frame section? */
984         if (i != hdr->e_shnum) {
985                 err = dwarf_parse_section((char *)start, (char *)end, me);
986                 if (err) {
987                         printk(KERN_WARNING "%s: failed to parse DWARF info\n",
988                                me->name);
989                         return err;
990                 }
991         }
992
993         return 0;
994 }
995
996 /**
997  *      module_dwarf_cleanup - remove FDE/CIEs associated with @mod
998  *      @mod: the module that is being unloaded
999  *
1000  *      Remove any FDEs and CIEs from the global lists that came from
1001  *      @mod's .eh_frame section because @mod is being unloaded.
1002  */
1003 void module_dwarf_cleanup(struct module *mod)
1004 {
1005         struct dwarf_fde *fde;
1006         struct dwarf_cie *cie;
1007         unsigned long flags;
1008
1009         spin_lock_irqsave(&dwarf_cie_lock, flags);
1010
1011 again_cie:
1012         list_for_each_entry(cie, &dwarf_cie_list, link) {
1013                 if (cie->mod == mod)
1014                         break;
1015         }
1016
1017         if (&cie->link != &dwarf_cie_list) {
1018                 list_del(&cie->link);
1019                 kfree(cie);
1020                 goto again_cie;
1021         }
1022
1023         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
1024
1025         spin_lock_irqsave(&dwarf_fde_lock, flags);
1026
1027 again_fde:
1028         list_for_each_entry(fde, &dwarf_fde_list, link) {
1029                 if (fde->mod == mod)
1030                         break;
1031         }
1032
1033         if (&fde->link != &dwarf_fde_list) {
1034                 list_del(&fde->link);
1035                 kfree(fde);
1036                 goto again_fde;
1037         }
1038
1039         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
1040 }
1041 #endif /* CONFIG_MODULES */
1042
1043 /**
1044  *      dwarf_unwinder_init - initialise the dwarf unwinder
1045  *
1046  *      Build the data structures describing the .dwarf_frame section to
1047  *      make it easier to lookup CIE and FDE entries. Because the
1048  *      .eh_frame section is packed as tightly as possible it is not
1049  *      easy to lookup the FDE for a given PC, so we build a list of FDE
1050  *      and CIE entries that make it easier.
1051  */
1052 static int __init dwarf_unwinder_init(void)
1053 {
1054         int err;
1055         INIT_LIST_HEAD(&dwarf_cie_list);
1056         INIT_LIST_HEAD(&dwarf_fde_list);
1057
1058         dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
1059                         sizeof(struct dwarf_frame), 0,
1060                         SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);
1061
1062         dwarf_reg_cachep = kmem_cache_create("dwarf_regs",
1063                         sizeof(struct dwarf_reg), 0,
1064                         SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);
1065
1066         dwarf_frame_pool = mempool_create(DWARF_FRAME_MIN_REQ,
1067                                           mempool_alloc_slab,
1068                                           mempool_free_slab,
1069                                           dwarf_frame_cachep);
1070
1071         dwarf_reg_pool = mempool_create(DWARF_REG_MIN_REQ,
1072                                          mempool_alloc_slab,
1073                                          mempool_free_slab,
1074                                          dwarf_reg_cachep);
1075
1076         err = dwarf_parse_section(__start_eh_frame, __stop_eh_frame, NULL);
1077         if (err)
1078                 goto out;
1079
1080         err = unwinder_register(&dwarf_unwinder);
1081         if (err)
1082                 goto out;
1083
1084         return 0;
1085
1086 out:
1087         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
1088         dwarf_unwinder_cleanup();
1089         return -EINVAL;
1090 }
1091 early_initcall(dwarf_unwinder_init);