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Linux/arch/arm/kernel/unwind.c

  1 /*
  2  * arch/arm/kernel/unwind.c
  3  *
  4  * Copyright (C) 2008 ARM Limited
  5  *
  6  * This program is free software; you can redistribute it and/or modify
  7  * it under the terms of the GNU General Public License version 2 as
  8  * published by the Free Software Foundation.
  9  *
 10  * This program is distributed in the hope that it will be useful,
 11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 13  * GNU General Public License for more details.
 14  *
 15  * You should have received a copy of the GNU General Public License
 16  * along with this program; if not, write to the Free Software
 17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 18  *
 19  *
 20  * Stack unwinding support for ARM
 21  *
 22  * An ARM EABI version of gcc is required to generate the unwind
 23  * tables. For information about the structure of the unwind tables,
 24  * see "Exception Handling ABI for the ARM Architecture" at:
 25  *
 26  * http://infocenter.arm.com/help/topic/com.arm.doc.subset.swdev.abi/index.html
 27  */
 28 
 29 #ifndef __CHECKER__
 30 #if !defined (__ARM_EABI__)
 31 #warning Your compiler does not have EABI support.
 32 #warning    ARM unwind is known to compile only with EABI compilers.
 33 #warning    Change compiler or disable ARM_UNWIND option.
 34 #elif (__GNUC__ == 4 && __GNUC_MINOR__ <= 2)
 35 #warning Your compiler is too buggy; it is known to not compile ARM unwind support.
 36 #warning    Change compiler or disable ARM_UNWIND option.
 37 #endif
 38 #endif /* __CHECKER__ */
 39 
 40 #include <linux/kernel.h>
 41 #include <linux/init.h>
 42 #include <linux/export.h>
 43 #include <linux/sched.h>
 44 #include <linux/slab.h>
 45 #include <linux/spinlock.h>
 46 #include <linux/list.h>
 47 
 48 #include <asm/stacktrace.h>
 49 #include <asm/traps.h>
 50 #include <asm/unwind.h>
 51 
 52 /* Dummy functions to avoid linker complaints */
 53 void __aeabi_unwind_cpp_pr0(void)
 54 {
 55 };
 56 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);
 57 
 58 void __aeabi_unwind_cpp_pr1(void)
 59 {
 60 };
 61 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);
 62 
 63 void __aeabi_unwind_cpp_pr2(void)
 64 {
 65 };
 66 EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);
 67 
 68 struct unwind_ctrl_block {
 69         unsigned long vrs[16];          /* virtual register set */
 70         const unsigned long *insn;      /* pointer to the current instructions word */
 71         int entries;                    /* number of entries left to interpret */
 72         int byte;                       /* current byte number in the instructions word */
 73 };
 74 
 75 enum regs {
 76 #ifdef CONFIG_THUMB2_KERNEL
 77         FP = 7,
 78 #else
 79         FP = 11,
 80 #endif
 81         SP = 13,
 82         LR = 14,
 83         PC = 15
 84 };
 85 
 86 extern const struct unwind_idx __start_unwind_idx[];
 87 static const struct unwind_idx *__origin_unwind_idx;
 88 extern const struct unwind_idx __stop_unwind_idx[];
 89 
 90 static DEFINE_SPINLOCK(unwind_lock);
 91 static LIST_HEAD(unwind_tables);
 92 
 93 /* Convert a prel31 symbol to an absolute address */
 94 #define prel31_to_addr(ptr)                             \
 95 ({                                                      \
 96         /* sign-extend to 32 bits */                    \
 97         long offset = (((long)*(ptr)) << 1) >> 1;       \
 98         (unsigned long)(ptr) + offset;                  \
 99 })
100 
101 /*
102  * Binary search in the unwind index. The entries are
103  * guaranteed to be sorted in ascending order by the linker.
104  *
105  * start = first entry
106  * origin = first entry with positive offset (or stop if there is no such entry)
107  * stop - 1 = last entry
108  */
109 static const struct unwind_idx *search_index(unsigned long addr,
110                                        const struct unwind_idx *start,
111                                        const struct unwind_idx *origin,
112                                        const struct unwind_idx *stop)
113 {
114         unsigned long addr_prel31;
115 
116         pr_debug("%s(%08lx, %p, %p, %p)\n",
117                         __func__, addr, start, origin, stop);
118 
119         /*
120          * only search in the section with the matching sign. This way the
121          * prel31 numbers can be compared as unsigned longs.
122          */
123         if (addr < (unsigned long)start)
124                 /* negative offsets: [start; origin) */
125                 stop = origin;
126         else
127                 /* positive offsets: [origin; stop) */
128                 start = origin;
129 
130         /* prel31 for address relavive to start */
131         addr_prel31 = (addr - (unsigned long)start) & 0x7fffffff;
132 
133         while (start < stop - 1) {
134                 const struct unwind_idx *mid = start + ((stop - start) >> 1);
135 
136                 /*
137                  * As addr_prel31 is relative to start an offset is needed to
138                  * make it relative to mid.
139                  */
140                 if (addr_prel31 - ((unsigned long)mid - (unsigned long)start) <
141                                 mid->addr_offset)
142                         stop = mid;
143                 else {
144                         /* keep addr_prel31 relative to start */
145                         addr_prel31 -= ((unsigned long)mid -
146                                         (unsigned long)start);
147                         start = mid;
148                 }
149         }
150 
151         if (likely(start->addr_offset <= addr_prel31))
152                 return start;
153         else {
154                 pr_warning("unwind: Unknown symbol address %08lx\n", addr);
155                 return NULL;
156         }
157 }
158 
159 static const struct unwind_idx *unwind_find_origin(
160                 const struct unwind_idx *start, const struct unwind_idx *stop)
161 {
162         pr_debug("%s(%p, %p)\n", __func__, start, stop);
163         while (start < stop) {
164                 const struct unwind_idx *mid = start + ((stop - start) >> 1);
165 
166                 if (mid->addr_offset >= 0x40000000)
167                         /* negative offset */
168                         start = mid + 1;
169                 else
170                         /* positive offset */
171                         stop = mid;
172         }
173         pr_debug("%s -> %p\n", __func__, stop);
174         return stop;
175 }
176 
177 static const struct unwind_idx *unwind_find_idx(unsigned long addr)
178 {
179         const struct unwind_idx *idx = NULL;
180         unsigned long flags;
181 
182         pr_debug("%s(%08lx)\n", __func__, addr);
183 
184         if (core_kernel_text(addr)) {
185                 if (unlikely(!__origin_unwind_idx))
186                         __origin_unwind_idx =
187                                 unwind_find_origin(__start_unwind_idx,
188                                                 __stop_unwind_idx);
189 
190                 /* main unwind table */
191                 idx = search_index(addr, __start_unwind_idx,
192                                    __origin_unwind_idx,
193                                    __stop_unwind_idx);
194         } else {
195                 /* module unwind tables */
196                 struct unwind_table *table;
197 
198                 spin_lock_irqsave(&unwind_lock, flags);
199                 list_for_each_entry(table, &unwind_tables, list) {
200                         if (addr >= table->begin_addr &&
201                             addr < table->end_addr) {
202                                 idx = search_index(addr, table->start,
203                                                    table->origin,
204                                                    table->stop);
205                                 /* Move-to-front to exploit common traces */
206                                 list_move(&table->list, &unwind_tables);
207                                 break;
208                         }
209                 }
210                 spin_unlock_irqrestore(&unwind_lock, flags);
211         }
212 
213         pr_debug("%s: idx = %p\n", __func__, idx);
214         return idx;
215 }
216 
217 static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
218 {
219         unsigned long ret;
220 
221         if (ctrl->entries <= 0) {
222                 pr_warning("unwind: Corrupt unwind table\n");
223                 return 0;
224         }
225 
226         ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;
227 
228         if (ctrl->byte == 0) {
229                 ctrl->insn++;
230                 ctrl->entries--;
231                 ctrl->byte = 3;
232         } else
233                 ctrl->byte--;
234 
235         return ret;
236 }
237 
238 /*
239  * Execute the current unwind instruction.
240  */
241 static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
242 {
243         unsigned long insn = unwind_get_byte(ctrl);
244 
245         pr_debug("%s: insn = %08lx\n", __func__, insn);
246 
247         if ((insn & 0xc0) == 0x00)
248                 ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
249         else if ((insn & 0xc0) == 0x40)
250                 ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
251         else if ((insn & 0xf0) == 0x80) {
252                 unsigned long mask;
253                 unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
254                 int load_sp, reg = 4;
255 
256                 insn = (insn << 8) | unwind_get_byte(ctrl);
257                 mask = insn & 0x0fff;
258                 if (mask == 0) {
259                         pr_warning("unwind: 'Refuse to unwind' instruction %04lx\n",
260                                    insn);
261                         return -URC_FAILURE;
262                 }
263 
264                 /* pop R4-R15 according to mask */
265                 load_sp = mask & (1 << (13 - 4));
266                 while (mask) {
267                         if (mask & 1)
268                                 ctrl->vrs[reg] = *vsp++;
269                         mask >>= 1;
270                         reg++;
271                 }
272                 if (!load_sp)
273                         ctrl->vrs[SP] = (unsigned long)vsp;
274         } else if ((insn & 0xf0) == 0x90 &&
275                    (insn & 0x0d) != 0x0d)
276                 ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
277         else if ((insn & 0xf0) == 0xa0) {
278                 unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
279                 int reg;
280 
281                 /* pop R4-R[4+bbb] */
282                 for (reg = 4; reg <= 4 + (insn & 7); reg++)
283                         ctrl->vrs[reg] = *vsp++;
284                 if (insn & 0x80)
285                         ctrl->vrs[14] = *vsp++;
286                 ctrl->vrs[SP] = (unsigned long)vsp;
287         } else if (insn == 0xb0) {
288                 if (ctrl->vrs[PC] == 0)
289                         ctrl->vrs[PC] = ctrl->vrs[LR];
290                 /* no further processing */
291                 ctrl->entries = 0;
292         } else if (insn == 0xb1) {
293                 unsigned long mask = unwind_get_byte(ctrl);
294                 unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
295                 int reg = 0;
296 
297                 if (mask == 0 || mask & 0xf0) {
298                         pr_warning("unwind: Spare encoding %04lx\n",
299                                (insn << 8) | mask);
300                         return -URC_FAILURE;
301                 }
302 
303                 /* pop R0-R3 according to mask */
304                 while (mask) {
305                         if (mask & 1)
306                                 ctrl->vrs[reg] = *vsp++;
307                         mask >>= 1;
308                         reg++;
309                 }
310                 ctrl->vrs[SP] = (unsigned long)vsp;
311         } else if (insn == 0xb2) {
312                 unsigned long uleb128 = unwind_get_byte(ctrl);
313 
314                 ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
315         } else {
316                 pr_warning("unwind: Unhandled instruction %02lx\n", insn);
317                 return -URC_FAILURE;
318         }
319 
320         pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
321                  ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);
322 
323         return URC_OK;
324 }
325 
326 /*
327  * Unwind a single frame starting with *sp for the symbol at *pc. It
328  * updates the *pc and *sp with the new values.
329  */
330 int unwind_frame(struct stackframe *frame)
331 {
332         unsigned long high, low;
333         const struct unwind_idx *idx;
334         struct unwind_ctrl_block ctrl;
335 
336         /* only go to a higher address on the stack */
337         low = frame->sp;
338         high = ALIGN(low, THREAD_SIZE);
339 
340         pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
341                  frame->pc, frame->lr, frame->sp);
342 
343         if (!kernel_text_address(frame->pc))
344                 return -URC_FAILURE;
345 
346         idx = unwind_find_idx(frame->pc);
347         if (!idx) {
348                 pr_warning("unwind: Index not found %08lx\n", frame->pc);
349                 return -URC_FAILURE;
350         }
351 
352         ctrl.vrs[FP] = frame->fp;
353         ctrl.vrs[SP] = frame->sp;
354         ctrl.vrs[LR] = frame->lr;
355         ctrl.vrs[PC] = 0;
356 
357         if (idx->insn == 1)
358                 /* can't unwind */
359                 return -URC_FAILURE;
360         else if ((idx->insn & 0x80000000) == 0)
361                 /* prel31 to the unwind table */
362                 ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
363         else if ((idx->insn & 0xff000000) == 0x80000000)
364                 /* only personality routine 0 supported in the index */
365                 ctrl.insn = &idx->insn;
366         else {
367                 pr_warning("unwind: Unsupported personality routine %08lx in the index at %p\n",
368                            idx->insn, idx);
369                 return -URC_FAILURE;
370         }
371 
372         /* check the personality routine */
373         if ((*ctrl.insn & 0xff000000) == 0x80000000) {
374                 ctrl.byte = 2;
375                 ctrl.entries = 1;
376         } else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
377                 ctrl.byte = 1;
378                 ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
379         } else {
380                 pr_warning("unwind: Unsupported personality routine %08lx at %p\n",
381                            *ctrl.insn, ctrl.insn);
382                 return -URC_FAILURE;
383         }
384 
385         while (ctrl.entries > 0) {
386                 int urc = unwind_exec_insn(&ctrl);
387                 if (urc < 0)
388                         return urc;
389                 if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= high)
390                         return -URC_FAILURE;
391         }
392 
393         if (ctrl.vrs[PC] == 0)
394                 ctrl.vrs[PC] = ctrl.vrs[LR];
395 
396         /* check for infinite loop */
397         if (frame->pc == ctrl.vrs[PC])
398                 return -URC_FAILURE;
399 
400         frame->fp = ctrl.vrs[FP];
401         frame->sp = ctrl.vrs[SP];
402         frame->lr = ctrl.vrs[LR];
403         frame->pc = ctrl.vrs[PC];
404 
405         return URC_OK;
406 }
407 
408 void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
409 {
410         struct stackframe frame;
411         register unsigned long current_sp asm ("sp");
412 
413         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
414 
415         if (!tsk)
416                 tsk = current;
417 
418         if (regs) {
419                 frame.fp = regs->ARM_fp;
420                 frame.sp = regs->ARM_sp;
421                 frame.lr = regs->ARM_lr;
422                 /* PC might be corrupted, use LR in that case. */
423                 frame.pc = kernel_text_address(regs->ARM_pc)
424                          ? regs->ARM_pc : regs->ARM_lr;
425         } else if (tsk == current) {
426                 frame.fp = (unsigned long)__builtin_frame_address(0);
427                 frame.sp = current_sp;
428                 frame.lr = (unsigned long)__builtin_return_address(0);
429                 frame.pc = (unsigned long)unwind_backtrace;
430         } else {
431                 /* task blocked in __switch_to */
432                 frame.fp = thread_saved_fp(tsk);
433                 frame.sp = thread_saved_sp(tsk);
434                 /*
435                  * The function calling __switch_to cannot be a leaf function
436                  * so LR is recovered from the stack.
437                  */
438                 frame.lr = 0;
439                 frame.pc = thread_saved_pc(tsk);
440         }
441 
442         while (1) {
443                 int urc;
444                 unsigned long where = frame.pc;
445 
446                 urc = unwind_frame(&frame);
447                 if (urc < 0)
448                         break;
449                 dump_backtrace_entry(where, frame.pc, frame.sp - 4);
450         }
451 }
452 
453 struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
454                                       unsigned long text_addr,
455                                       unsigned long text_size)
456 {
457         unsigned long flags;
458         struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);
459 
460         pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
461                  text_addr, text_size);
462 
463         if (!tab)
464                 return tab;
465 
466         tab->start = (const struct unwind_idx *)start;
467         tab->stop = (const struct unwind_idx *)(start + size);
468         tab->origin = unwind_find_origin(tab->start, tab->stop);
469         tab->begin_addr = text_addr;
470         tab->end_addr = text_addr + text_size;
471 
472         spin_lock_irqsave(&unwind_lock, flags);
473         list_add_tail(&tab->list, &unwind_tables);
474         spin_unlock_irqrestore(&unwind_lock, flags);
475 
476         return tab;
477 }
478 
479 void unwind_table_del(struct unwind_table *tab)
480 {
481         unsigned long flags;
482 
483         if (!tab)
484                 return;
485 
486         spin_lock_irqsave(&unwind_lock, flags);
487         list_del(&tab->list);
488         spin_unlock_irqrestore(&unwind_lock, flags);
489 
490         kfree(tab);
491 }
492 

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