linux/arch/arm/kernel/unwind.c
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   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 */
  53void __aeabi_unwind_cpp_pr0(void)
  54{
  55};
  56EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);
  57
  58void __aeabi_unwind_cpp_pr1(void)
  59{
  60};
  61EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);
  62
  63void __aeabi_unwind_cpp_pr2(void)
  64{
  65};
  66EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);
  67
  68struct 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
  81enum 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
  92extern const struct unwind_idx __start_unwind_idx[];
  93static const struct unwind_idx *__origin_unwind_idx;
  94extern const struct unwind_idx __stop_unwind_idx[];
  95
  96static DEFINE_SPINLOCK(unwind_lock);
  97static 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 */
 115static 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
 165static 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
 183static 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
 223static 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 */
 245static 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 */
 257static 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
 277static 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
 297static 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 */
 319static 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
 380error:
 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 */
 388int 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
 471void 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
 514struct 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
 540void 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