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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) && !defined(__clang__)
 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         unsigned long sp_high;          /* highest value of sp allowed */
 72         /*
 73          * 1 : check for stack overflow for each register pop.
 74          * 0 : save overhead if there is plenty of stack remaining.
 75          */
 76         int check_each_pop;
 77         int entries;                    /* number of entries left to interpret */
 78         int byte;                       /* current byte number in the instructions word */
 79 };
 80 
 81 enum regs {
 82 #ifdef CONFIG_THUMB2_KERNEL
 83         FP = 7,
 84 #else
 85         FP = 11,
 86 #endif
 87         SP = 13,
 88         LR = 14,
 89         PC = 15
 90 };
 91 
 92 extern const struct unwind_idx __start_unwind_idx[];
 93 static const struct unwind_idx *__origin_unwind_idx;
 94 extern const struct unwind_idx __stop_unwind_idx[];
 95 
 96 static DEFINE_SPINLOCK(unwind_lock);
 97 static LIST_HEAD(unwind_tables);
 98 
 99 /* Convert a prel31 symbol to an absolute address */
100 #define prel31_to_addr(ptr)                             \
101 ({                                                      \
102         /* sign-extend to 32 bits */                    \
103         long offset = (((long)*(ptr)) << 1) >> 1;       \
104         (unsigned long)(ptr) + offset;                  \
105 })
106 
107 /*
108  * Binary search in the unwind index. The entries are
109  * guaranteed to be sorted in ascending order by the linker.
110  *
111  * start = first entry
112  * origin = first entry with positive offset (or stop if there is no such entry)
113  * stop - 1 = last entry
114  */
115 static const struct unwind_idx *search_index(unsigned long addr,
116                                        const struct unwind_idx *start,
117                                        const struct unwind_idx *origin,
118                                        const struct unwind_idx *stop)
119 {
120         unsigned long addr_prel31;
121 
122         pr_debug("%s(%08lx, %p, %p, %p)\n",
123                         __func__, addr, start, origin, stop);
124 
125         /*
126          * only search in the section with the matching sign. This way the
127          * prel31 numbers can be compared as unsigned longs.
128          */
129         if (addr < (unsigned long)start)
130                 /* negative offsets: [start; origin) */
131                 stop = origin;
132         else
133                 /* positive offsets: [origin; stop) */
134                 start = origin;
135 
136         /* prel31 for address relavive to start */
137         addr_prel31 = (addr - (unsigned long)start) & 0x7fffffff;
138 
139         while (start < stop - 1) {
140                 const struct unwind_idx *mid = start + ((stop - start) >> 1);
141 
142                 /*
143                  * As addr_prel31 is relative to start an offset is needed to
144                  * make it relative to mid.
145                  */
146                 if (addr_prel31 - ((unsigned long)mid - (unsigned long)start) <
147                                 mid->addr_offset)
148                         stop = mid;
149                 else {
150                         /* keep addr_prel31 relative to start */
151                         addr_prel31 -= ((unsigned long)mid -
152                                         (unsigned long)start);
153                         start = mid;
154                 }
155         }
156 
157         if (likely(start->addr_offset <= addr_prel31))
158                 return start;
159         else {
160                 pr_warning("unwind: Unknown symbol address %08lx\n", addr);
161                 return NULL;
162         }
163 }
164 
165 static const struct unwind_idx *unwind_find_origin(
166                 const struct unwind_idx *start, const struct unwind_idx *stop)
167 {
168         pr_debug("%s(%p, %p)\n", __func__, start, stop);
169         while (start < stop) {
170                 const struct unwind_idx *mid = start + ((stop - start) >> 1);
171 
172                 if (mid->addr_offset >= 0x40000000)
173                         /* negative offset */
174                         start = mid + 1;
175                 else
176                         /* positive offset */
177                         stop = mid;
178         }
179         pr_debug("%s -> %p\n", __func__, stop);
180         return stop;
181 }
182 
183 static const struct unwind_idx *unwind_find_idx(unsigned long addr)
184 {
185         const struct unwind_idx *idx = NULL;
186         unsigned long flags;
187 
188         pr_debug("%s(%08lx)\n", __func__, addr);
189 
190         if (core_kernel_text(addr)) {
191                 if (unlikely(!__origin_unwind_idx))
192                         __origin_unwind_idx =
193                                 unwind_find_origin(__start_unwind_idx,
194                                                 __stop_unwind_idx);
195 
196                 /* main unwind table */
197                 idx = search_index(addr, __start_unwind_idx,
198                                    __origin_unwind_idx,
199                                    __stop_unwind_idx);
200         } else {
201                 /* module unwind tables */
202                 struct unwind_table *table;
203 
204                 spin_lock_irqsave(&unwind_lock, flags);
205                 list_for_each_entry(table, &unwind_tables, list) {
206                         if (addr >= table->begin_addr &&
207                             addr < table->end_addr) {
208                                 idx = search_index(addr, table->start,
209                                                    table->origin,
210                                                    table->stop);
211                                 /* Move-to-front to exploit common traces */
212                                 list_move(&table->list, &unwind_tables);
213                                 break;
214                         }
215                 }
216                 spin_unlock_irqrestore(&unwind_lock, flags);
217         }
218 
219         pr_debug("%s: idx = %p\n", __func__, idx);
220         return idx;
221 }
222 
223 static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
224 {
225         unsigned long ret;
226 
227         if (ctrl->entries <= 0) {
228                 pr_warning("unwind: Corrupt unwind table\n");
229                 return 0;
230         }
231 
232         ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;
233 
234         if (ctrl->byte == 0) {
235                 ctrl->insn++;
236                 ctrl->entries--;
237                 ctrl->byte = 3;
238         } else
239                 ctrl->byte--;
240 
241         return ret;
242 }
243 
244 /* Before poping a register check whether it is feasible or not */
245 static int unwind_pop_register(struct unwind_ctrl_block *ctrl,
246                                 unsigned long **vsp, unsigned int reg)
247 {
248         if (unlikely(ctrl->check_each_pop))
249                 if (*vsp >= (unsigned long *)ctrl->sp_high)
250                         return -URC_FAILURE;
251 
252         ctrl->vrs[reg] = *(*vsp)++;
253         return URC_OK;
254 }
255 
256 /* Helper functions to execute the instructions */
257 static int unwind_exec_pop_subset_r4_to_r13(struct unwind_ctrl_block *ctrl,
258                                                 unsigned long mask)
259 {
260         unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
261         int load_sp, reg = 4;
262 
263         load_sp = mask & (1 << (13 - 4));
264         while (mask) {
265                 if (mask & 1)
266                         if (unwind_pop_register(ctrl, &vsp, reg))
267                                 return -URC_FAILURE;
268                 mask >>= 1;
269                 reg++;
270         }
271         if (!load_sp)
272                 ctrl->vrs[SP] = (unsigned long)vsp;
273 
274         return URC_OK;
275 }
276 
277 static int unwind_exec_pop_r4_to_rN(struct unwind_ctrl_block *ctrl,
278                                         unsigned long insn)
279 {
280         unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
281         int reg;
282 
283         /* pop R4-R[4+bbb] */
284         for (reg = 4; reg <= 4 + (insn & 7); reg++)
285                 if (unwind_pop_register(ctrl, &vsp, reg))
286                                 return -URC_FAILURE;
287 
288         if (insn & 0x8)
289                 if (unwind_pop_register(ctrl, &vsp, 14))
290                                 return -URC_FAILURE;
291 
292         ctrl->vrs[SP] = (unsigned long)vsp;
293 
294         return URC_OK;
295 }
296 
297 static int unwind_exec_pop_subset_r0_to_r3(struct unwind_ctrl_block *ctrl,
298                                                 unsigned long mask)
299 {
300         unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
301         int reg = 0;
302 
303         /* pop R0-R3 according to mask */
304         while (mask) {
305                 if (mask & 1)
306                         if (unwind_pop_register(ctrl, &vsp, reg))
307                                 return -URC_FAILURE;
308                 mask >>= 1;
309                 reg++;
310         }
311         ctrl->vrs[SP] = (unsigned long)vsp;
312 
313         return URC_OK;
314 }
315 
316 /*
317  * Execute the current unwind instruction.
318  */
319 static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
320 {
321         unsigned long insn = unwind_get_byte(ctrl);
322         int ret = URC_OK;
323 
324         pr_debug("%s: insn = %08lx\n", __func__, insn);
325 
326         if ((insn & 0xc0) == 0x00)
327                 ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
328         else if ((insn & 0xc0) == 0x40)
329                 ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
330         else if ((insn & 0xf0) == 0x80) {
331                 unsigned long mask;
332 
333                 insn = (insn << 8) | unwind_get_byte(ctrl);
334                 mask = insn & 0x0fff;
335                 if (mask == 0) {
336                         pr_warning("unwind: 'Refuse to unwind' instruction %04lx\n",
337                                    insn);
338                         return -URC_FAILURE;
339                 }
340 
341                 ret = unwind_exec_pop_subset_r4_to_r13(ctrl, mask);
342                 if (ret)
343                         goto error;
344         } else if ((insn & 0xf0) == 0x90 &&
345                    (insn & 0x0d) != 0x0d)
346                 ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
347         else if ((insn & 0xf0) == 0xa0) {
348                 ret = unwind_exec_pop_r4_to_rN(ctrl, insn);
349                 if (ret)
350                         goto error;
351         } else if (insn == 0xb0) {
352                 if (ctrl->vrs[PC] == 0)
353                         ctrl->vrs[PC] = ctrl->vrs[LR];
354                 /* no further processing */
355                 ctrl->entries = 0;
356         } else if (insn == 0xb1) {
357                 unsigned long mask = unwind_get_byte(ctrl);
358 
359                 if (mask == 0 || mask & 0xf0) {
360                         pr_warning("unwind: Spare encoding %04lx\n",
361                                (insn << 8) | mask);
362                         return -URC_FAILURE;
363                 }
364 
365                 ret = unwind_exec_pop_subset_r0_to_r3(ctrl, mask);
366                 if (ret)
367                         goto error;
368         } else if (insn == 0xb2) {
369                 unsigned long uleb128 = unwind_get_byte(ctrl);
370 
371                 ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
372         } else {
373                 pr_warning("unwind: Unhandled instruction %02lx\n", insn);
374                 return -URC_FAILURE;
375         }
376 
377         pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
378                  ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);
379 
380 error:
381         return ret;
382 }
383 
384 /*
385  * Unwind a single frame starting with *sp for the symbol at *pc. It
386  * updates the *pc and *sp with the new values.
387  */
388 int unwind_frame(struct stackframe *frame)
389 {
390         unsigned long low;
391         const struct unwind_idx *idx;
392         struct unwind_ctrl_block ctrl;
393 
394         /* store the highest address on the stack to avoid crossing it*/
395         low = frame->sp;
396         ctrl.sp_high = ALIGN(low, THREAD_SIZE);
397 
398         pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
399                  frame->pc, frame->lr, frame->sp);
400 
401         if (!kernel_text_address(frame->pc))
402                 return -URC_FAILURE;
403 
404         idx = unwind_find_idx(frame->pc);
405         if (!idx) {
406                 pr_warning("unwind: Index not found %08lx\n", frame->pc);
407                 return -URC_FAILURE;
408         }
409 
410         ctrl.vrs[FP] = frame->fp;
411         ctrl.vrs[SP] = frame->sp;
412         ctrl.vrs[LR] = frame->lr;
413         ctrl.vrs[PC] = 0;
414 
415         if (idx->insn == 1)
416                 /* can't unwind */
417                 return -URC_FAILURE;
418         else if ((idx->insn & 0x80000000) == 0)
419                 /* prel31 to the unwind table */
420                 ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
421         else if ((idx->insn & 0xff000000) == 0x80000000)
422                 /* only personality routine 0 supported in the index */
423                 ctrl.insn = &idx->insn;
424         else {
425                 pr_warning("unwind: Unsupported personality routine %08lx in the index at %p\n",
426                            idx->insn, idx);
427                 return -URC_FAILURE;
428         }
429 
430         /* check the personality routine */
431         if ((*ctrl.insn & 0xff000000) == 0x80000000) {
432                 ctrl.byte = 2;
433                 ctrl.entries = 1;
434         } else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
435                 ctrl.byte = 1;
436                 ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
437         } else {
438                 pr_warning("unwind: Unsupported personality routine %08lx at %p\n",
439                            *ctrl.insn, ctrl.insn);
440                 return -URC_FAILURE;
441         }
442 
443         ctrl.check_each_pop = 0;
444 
445         while (ctrl.entries > 0) {
446                 int urc;
447                 if ((ctrl.sp_high - ctrl.vrs[SP]) < sizeof(ctrl.vrs))
448                         ctrl.check_each_pop = 1;
449                 urc = unwind_exec_insn(&ctrl);
450                 if (urc < 0)
451                         return urc;
452                 if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= ctrl.sp_high)
453                         return -URC_FAILURE;
454         }
455 
456         if (ctrl.vrs[PC] == 0)
457                 ctrl.vrs[PC] = ctrl.vrs[LR];
458 
459         /* check for infinite loop */
460         if (frame->pc == ctrl.vrs[PC])
461                 return -URC_FAILURE;
462 
463         frame->fp = ctrl.vrs[FP];
464         frame->sp = ctrl.vrs[SP];
465         frame->lr = ctrl.vrs[LR];
466         frame->pc = ctrl.vrs[PC];
467 
468         return URC_OK;
469 }
470 
471 void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
472 {
473         struct stackframe frame;
474         register unsigned long current_sp asm ("sp");
475 
476         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
477 
478         if (!tsk)
479                 tsk = current;
480 
481         if (regs) {
482                 arm_get_current_stackframe(regs, &frame);
483                 /* PC might be corrupted, use LR in that case. */
484                 if (!kernel_text_address(regs->ARM_pc))
485                         frame.pc = regs->ARM_lr;
486         } else if (tsk == current) {
487                 frame.fp = (unsigned long)__builtin_frame_address(0);
488                 frame.sp = current_sp;
489                 frame.lr = (unsigned long)__builtin_return_address(0);
490                 frame.pc = (unsigned long)unwind_backtrace;
491         } else {
492                 /* task blocked in __switch_to */
493                 frame.fp = thread_saved_fp(tsk);
494                 frame.sp = thread_saved_sp(tsk);
495                 /*
496                  * The function calling __switch_to cannot be a leaf function
497                  * so LR is recovered from the stack.
498                  */
499                 frame.lr = 0;
500                 frame.pc = thread_saved_pc(tsk);
501         }
502 
503         while (1) {
504                 int urc;
505                 unsigned long where = frame.pc;
506 
507                 urc = unwind_frame(&frame);
508                 if (urc < 0)
509                         break;
510                 dump_backtrace_entry(where, frame.pc, frame.sp - 4);
511         }
512 }
513 
514 struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
515                                       unsigned long text_addr,
516                                       unsigned long text_size)
517 {
518         unsigned long flags;
519         struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);
520 
521         pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
522                  text_addr, text_size);
523 
524         if (!tab)
525                 return tab;
526 
527         tab->start = (const struct unwind_idx *)start;
528         tab->stop = (const struct unwind_idx *)(start + size);
529         tab->origin = unwind_find_origin(tab->start, tab->stop);
530         tab->begin_addr = text_addr;
531         tab->end_addr = text_addr + text_size;
532 
533         spin_lock_irqsave(&unwind_lock, flags);
534         list_add_tail(&tab->list, &unwind_tables);
535         spin_unlock_irqrestore(&unwind_lock, flags);
536 
537         return tab;
538 }
539 
540 void unwind_table_del(struct unwind_table *tab)
541 {
542         unsigned long flags;
543 
544         if (!tab)
545                 return;
546 
547         spin_lock_irqsave(&unwind_lock, flags);
548         list_del(&tab->list);
549         spin_unlock_irqrestore(&unwind_lock, flags);
550 
551         kfree(tab);
552 }
553 

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