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_warn("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_warn("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_warn("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_warn("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_warn("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_warn("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_warn("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_warn("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
 475         pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 476
 477         if (!tsk)
 478                 tsk = current;
 479
 480         if (regs) {
 481                 arm_get_current_stackframe(regs, &frame);
 482                 /* PC might be corrupted, use LR in that case. */
 483                 if (!kernel_text_address(regs->ARM_pc))
 484                         frame.pc = regs->ARM_lr;
 485         } else if (tsk == current) {
 486                 frame.fp = (unsigned long)__builtin_frame_address(0);
 487                 frame.sp = current_stack_pointer;
 488                 frame.lr = (unsigned long)__builtin_return_address(0);
 489                 frame.pc = (unsigned long)unwind_backtrace;
 490         } else {
 491                 /* task blocked in __switch_to */
 492                 frame.fp = thread_saved_fp(tsk);
 493                 frame.sp = thread_saved_sp(tsk);
 494                 /*
 495                  * The function calling __switch_to cannot be a leaf function
 496                  * so LR is recovered from the stack.
 497                  */
 498                 frame.lr = 0;
 499                 frame.pc = thread_saved_pc(tsk);
 500         }
 501
 502         while (1) {
 503                 int urc;
 504                 unsigned long where = frame.pc;
 505
 506                 urc = unwind_frame(&frame);
 507                 if (urc < 0)
 508                         break;
 509                 dump_backtrace_entry(where, frame.pc, frame.sp - 4);
 510         }
 511 }
 512
 513 struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
 514                                       unsigned long text_addr,
 515                                       unsigned long text_size)
 516 {
 517         unsigned long flags;
 518         struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);
 519
 520         pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
 521                  text_addr, text_size);
 522
 523         if (!tab)
 524                 return tab;
 525
 526         tab->start = (const struct unwind_idx *)start;
 527         tab->stop = (const struct unwind_idx *)(start + size);
 528         tab->origin = unwind_find_origin(tab->start, tab->stop);
 529         tab->begin_addr = text_addr;
 530         tab->end_addr = text_addr + text_size;
 531
 532         spin_lock_irqsave(&unwind_lock, flags);
 533         list_add_tail(&tab->list, &unwind_tables);
 534         spin_unlock_irqrestore(&unwind_lock, flags);
 535
 536         return tab;
 537 }
 538
 539 void unwind_table_del(struct unwind_table *tab)
 540 {
 541         unsigned long flags;
 542
 543         if (!tab)
 544                 return;
 545
 546         spin_lock_irqsave(&unwind_lock, flags);
 547         list_del(&tab->list);
 548         spin_unlock_irqrestore(&unwind_lock, flags);
 549
 550         kfree(tab);
 551 }