sh: Check for return_to_handler when unwinding the stack
[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/ftrace.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_unwind_stack - recursively unwind the stack
534  *      @pc: address of the function to unwind
535  *      @prev: struct dwarf_frame of the previous stackframe on the callstack
536  *
537  *      Return a struct dwarf_frame representing the most recent frame
538  *      on the callstack. Each of the lower (older) stack frames are
539  *      linked via the "prev" member.
540  */
541 struct dwarf_frame * dwarf_unwind_stack(unsigned long pc,
542                                         struct dwarf_frame *prev)
543 {
544         struct dwarf_frame *frame;
545         struct dwarf_cie *cie;
546         struct dwarf_fde *fde;
547         struct dwarf_reg *reg;
548         unsigned long addr;
549
550         /*
551          * If this is the first invocation of this recursive function we
552          * need get the contents of a physical register to get the CFA
553          * in order to begin the virtual unwinding of the stack.
554          *
555          * NOTE: the return address is guaranteed to be setup by the
556          * time this function makes its first function call.
557          */
558         if (!pc && !prev)
559                 pc = (unsigned long)current_text_addr();
560
561 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
562         /*
563          * If our stack has been patched by the function graph tracer
564          * then we might see the address of return_to_handler() where we
565          * expected to find the real return address.
566          */
567         if (pc == (unsigned long)&return_to_handler) {
568                 int index = current->curr_ret_stack;
569
570                 /*
571                  * We currently have no way of tracking how many
572                  * return_to_handler()'s we've seen. If there is more
573                  * than one patched return address on our stack,
574                  * complain loudly.
575                  */
576                 WARN_ON(index > 0);
577
578                 pc = current->ret_stack[index].ret;
579         }
580 #endif
581
582         frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
583         if (!frame) {
584                 printk(KERN_ERR "Unable to allocate a dwarf frame\n");
585                 UNWINDER_BUG();
586         }
587
588         INIT_LIST_HEAD(&frame->reg_list);
589         frame->flags = 0;
590         frame->prev = prev;
591         frame->return_addr = 0;
592
593         fde = dwarf_lookup_fde(pc);
594         if (!fde) {
595                 /*
596                  * This is our normal exit path - the one that stops the
597                  * recursion. There's two reasons why we might exit
598                  * here,
599                  *
600                  *      a) pc has no asscociated DWARF frame info and so
601                  *      we don't know how to unwind this frame. This is
602                  *      usually the case when we're trying to unwind a
603                  *      frame that was called from some assembly code
604                  *      that has no DWARF info, e.g. syscalls.
605                  *
606                  *      b) the DEBUG info for pc is bogus. There's
607                  *      really no way to distinguish this case from the
608                  *      case above, which sucks because we could print a
609                  *      warning here.
610                  */
611                 goto bail;
612         }
613
614         cie = dwarf_lookup_cie(fde->cie_pointer);
615
616         frame->pc = fde->initial_location;
617
618         /* CIE initial instructions */
619         dwarf_cfa_execute_insns(cie->initial_instructions,
620                                 cie->instructions_end, cie, fde,
621                                 frame, pc);
622
623         /* FDE instructions */
624         dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
625                                 fde, frame, pc);
626
627         /* Calculate the CFA */
628         switch (frame->flags) {
629         case DWARF_FRAME_CFA_REG_OFFSET:
630                 if (prev) {
631                         reg = dwarf_frame_reg(prev, frame->cfa_register);
632                         UNWINDER_BUG_ON(!reg);
633                         UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
634
635                         addr = prev->cfa + reg->addr;
636                         frame->cfa = __raw_readl(addr);
637
638                 } else {
639                         /*
640                          * Again, this is the first invocation of this
641                          * recurisve function. We need to physically
642                          * read the contents of a register in order to
643                          * get the Canonical Frame Address for this
644                          * function.
645                          */
646                         frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
647                 }
648
649                 frame->cfa += frame->cfa_offset;
650                 break;
651         default:
652                 UNWINDER_BUG();
653         }
654
655         reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);
656
657         /*
658          * If we haven't seen the return address register or the return
659          * address column is undefined then we must assume that this is
660          * the end of the callstack.
661          */
662         if (!reg || reg->flags == DWARF_UNDEFINED)
663                 goto bail;
664
665         UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);
666
667         addr = frame->cfa + reg->addr;
668         frame->return_addr = __raw_readl(addr);
669
670         return frame;
671
672 bail:
673         dwarf_frame_free_regs(frame);
674         mempool_free(frame, dwarf_frame_pool);
675         return NULL;
676 }
677
678 static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
679                            unsigned char *end)
680 {
681         struct dwarf_cie *cie;
682         unsigned long flags;
683         int count;
684
685         cie = kzalloc(sizeof(*cie), GFP_KERNEL);
686         if (!cie)
687                 return -ENOMEM;
688
689         cie->length = len;
690
691         /*
692          * Record the offset into the .eh_frame section
693          * for this CIE. It allows this CIE to be
694          * quickly and easily looked up from the
695          * corresponding FDE.
696          */
697         cie->cie_pointer = (unsigned long)entry;
698
699         cie->version = *(char *)p++;
700         UNWINDER_BUG_ON(cie->version != 1);
701
702         cie->augmentation = p;
703         p += strlen(cie->augmentation) + 1;
704
705         count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
706         p += count;
707
708         count = dwarf_read_leb128(p, &cie->data_alignment_factor);
709         p += count;
710
711         /*
712          * Which column in the rule table contains the
713          * return address?
714          */
715         if (cie->version == 1) {
716                 cie->return_address_reg = __raw_readb(p);
717                 p++;
718         } else {
719                 count = dwarf_read_uleb128(p, &cie->return_address_reg);
720                 p += count;
721         }
722
723         if (cie->augmentation[0] == 'z') {
724                 unsigned int length, count;
725                 cie->flags |= DWARF_CIE_Z_AUGMENTATION;
726
727                 count = dwarf_read_uleb128(p, &length);
728                 p += count;
729
730                 UNWINDER_BUG_ON((unsigned char *)p > end);
731
732                 cie->initial_instructions = p + length;
733                 cie->augmentation++;
734         }
735
736         while (*cie->augmentation) {
737                 /*
738                  * "L" indicates a byte showing how the
739                  * LSDA pointer is encoded. Skip it.
740                  */
741                 if (*cie->augmentation == 'L') {
742                         p++;
743                         cie->augmentation++;
744                 } else if (*cie->augmentation == 'R') {
745                         /*
746                          * "R" indicates a byte showing
747                          * how FDE addresses are
748                          * encoded.
749                          */
750                         cie->encoding = *(char *)p++;
751                         cie->augmentation++;
752                 } else if (*cie->augmentation == 'P') {
753                         /*
754                          * "R" indicates a personality
755                          * routine in the CIE
756                          * augmentation.
757                          */
758                         UNWINDER_BUG();
759                 } else if (*cie->augmentation == 'S') {
760                         UNWINDER_BUG();
761                 } else {
762                         /*
763                          * Unknown augmentation. Assume
764                          * 'z' augmentation.
765                          */
766                         p = cie->initial_instructions;
767                         UNWINDER_BUG_ON(!p);
768                         break;
769                 }
770         }
771
772         cie->initial_instructions = p;
773         cie->instructions_end = end;
774
775         /* Add to list */
776         spin_lock_irqsave(&dwarf_cie_lock, flags);
777         list_add_tail(&cie->link, &dwarf_cie_list);
778         spin_unlock_irqrestore(&dwarf_cie_lock, flags);
779
780         return 0;
781 }
782
783 static int dwarf_parse_fde(void *entry, u32 entry_type,
784                            void *start, unsigned long len,
785                            unsigned char *end)
786 {
787         struct dwarf_fde *fde;
788         struct dwarf_cie *cie;
789         unsigned long flags;
790         int count;
791         void *p = start;
792
793         fde = kzalloc(sizeof(*fde), GFP_KERNEL);
794         if (!fde)
795                 return -ENOMEM;
796
797         fde->length = len;
798
799         /*
800          * In a .eh_frame section the CIE pointer is the
801          * delta between the address within the FDE
802          */
803         fde->cie_pointer = (unsigned long)(p - entry_type - 4);
804
805         cie = dwarf_lookup_cie(fde->cie_pointer);
806         fde->cie = cie;
807
808         if (cie->encoding)
809                 count = dwarf_read_encoded_value(p, &fde->initial_location,
810                                                  cie->encoding);
811         else
812                 count = dwarf_read_addr(p, &fde->initial_location);
813
814         p += count;
815
816         if (cie->encoding)
817                 count = dwarf_read_encoded_value(p, &fde->address_range,
818                                                  cie->encoding & 0x0f);
819         else
820                 count = dwarf_read_addr(p, &fde->address_range);
821
822         p += count;
823
824         if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
825                 unsigned int length;
826                 count = dwarf_read_uleb128(p, &length);
827                 p += count + length;
828         }
829
830         /* Call frame instructions. */
831         fde->instructions = p;
832         fde->end = end;
833
834         /* Add to list. */
835         spin_lock_irqsave(&dwarf_fde_lock, flags);
836         list_add_tail(&fde->link, &dwarf_fde_list);
837         spin_unlock_irqrestore(&dwarf_fde_lock, flags);
838
839         return 0;
840 }
841
842 static void dwarf_unwinder_dump(struct task_struct *task,
843                                 struct pt_regs *regs,
844                                 unsigned long *sp,
845                                 const struct stacktrace_ops *ops,
846                                 void *data)
847 {
848         struct dwarf_frame *frame, *_frame;
849         unsigned long return_addr;
850
851         _frame = NULL;
852         return_addr = 0;
853
854         while (1) {
855                 frame = dwarf_unwind_stack(return_addr, _frame);
856
857                 if (_frame) {
858                         dwarf_frame_free_regs(_frame);
859                         mempool_free(_frame, dwarf_frame_pool);
860                 }
861
862                 _frame = frame;
863
864                 if (!frame || !frame->return_addr)
865                         break;
866
867                 return_addr = frame->return_addr;
868                 ops->address(data, return_addr, 1);
869         }
870 }
871
872 static struct unwinder dwarf_unwinder = {
873         .name = "dwarf-unwinder",
874         .dump = dwarf_unwinder_dump,
875         .rating = 150,
876 };
877
878 static void dwarf_unwinder_cleanup(void)
879 {
880         struct dwarf_cie *cie;
881         struct dwarf_fde *fde;
882
883         /*
884          * Deallocate all the memory allocated for the DWARF unwinder.
885          * Traverse all the FDE/CIE lists and remove and free all the
886          * memory associated with those data structures.
887          */
888         list_for_each_entry(cie, &dwarf_cie_list, link)
889                 kfree(cie);
890
891         list_for_each_entry(fde, &dwarf_fde_list, link)
892                 kfree(fde);
893
894         kmem_cache_destroy(dwarf_reg_cachep);
895         kmem_cache_destroy(dwarf_frame_cachep);
896 }
897
898 /**
899  *      dwarf_unwinder_init - initialise the dwarf unwinder
900  *
901  *      Build the data structures describing the .dwarf_frame section to
902  *      make it easier to lookup CIE and FDE entries. Because the
903  *      .eh_frame section is packed as tightly as possible it is not
904  *      easy to lookup the FDE for a given PC, so we build a list of FDE
905  *      and CIE entries that make it easier.
906  */
907 static int __init dwarf_unwinder_init(void)
908 {
909         u32 entry_type;
910         void *p, *entry;
911         int count, err = 0;
912         unsigned long len;
913         unsigned int c_entries, f_entries;
914         unsigned char *end;
915         INIT_LIST_HEAD(&dwarf_cie_list);
916         INIT_LIST_HEAD(&dwarf_fde_list);
917
918         c_entries = 0;
919         f_entries = 0;
920         entry = &__start_eh_frame;
921
922         dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
923                         sizeof(struct dwarf_frame), 0,
924                         SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);
925
926         dwarf_reg_cachep = kmem_cache_create("dwarf_regs",
927                         sizeof(struct dwarf_reg), 0,
928                         SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);
929
930         dwarf_frame_pool = mempool_create(DWARF_FRAME_MIN_REQ,
931                                           mempool_alloc_slab,
932                                           mempool_free_slab,
933                                           dwarf_frame_cachep);
934
935         dwarf_reg_pool = mempool_create(DWARF_REG_MIN_REQ,
936                                          mempool_alloc_slab,
937                                          mempool_free_slab,
938                                          dwarf_reg_cachep);
939
940         while ((char *)entry < __stop_eh_frame) {
941                 p = entry;
942
943                 count = dwarf_entry_len(p, &len);
944                 if (count == 0) {
945                         /*
946                          * We read a bogus length field value. There is
947                          * nothing we can do here apart from disabling
948                          * the DWARF unwinder. We can't even skip this
949                          * entry and move to the next one because 'len'
950                          * tells us where our next entry is.
951                          */
952                         goto out;
953                 } else
954                         p += count;
955
956                 /* initial length does not include itself */
957                 end = p + len;
958
959                 entry_type = get_unaligned((u32 *)p);
960                 p += 4;
961
962                 if (entry_type == DW_EH_FRAME_CIE) {
963                         err = dwarf_parse_cie(entry, p, len, end);
964                         if (err < 0)
965                                 goto out;
966                         else
967                                 c_entries++;
968                 } else {
969                         err = dwarf_parse_fde(entry, entry_type, p, len, end);
970                         if (err < 0)
971                                 goto out;
972                         else
973                                 f_entries++;
974                 }
975
976                 entry = (char *)entry + len + 4;
977         }
978
979         printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
980                c_entries, f_entries);
981
982         err = unwinder_register(&dwarf_unwinder);
983         if (err)
984                 goto out;
985
986         return 0;
987
988 out:
989         printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
990         dwarf_unwinder_cleanup();
991         return -EINVAL;
992 }
993 early_initcall(dwarf_unwinder_init);