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unwind.c

/*
 * arch/arm/kernel/unwind.c
 *
 * Copyright (C) 2008 ARM Limited
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 *
 * Stack unwinding support for ARM
 *
 * An ARM EABI version of gcc is required to generate the unwind
 * tables. For information about the structure of the unwind tables,
 * see "Exception Handling ABI for the ARM Architecture" at:
 *
 * http://infocenter.arm.com/help/topic/com.arm.doc.subset.swdev.abi/index.html
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/list.h>

#include <asm/stacktrace.h>
#include <asm/traps.h>
#include <asm/unwind.h>

/* Dummy functions to avoid linker complaints */
void __aeabi_unwind_cpp_pr0(void)
{
};
EXPORT_SYMBOL(__aeabi_unwind_cpp_pr0);

void __aeabi_unwind_cpp_pr1(void)
{
};
EXPORT_SYMBOL(__aeabi_unwind_cpp_pr1);

void __aeabi_unwind_cpp_pr2(void)
{
};
EXPORT_SYMBOL(__aeabi_unwind_cpp_pr2);

00057 struct unwind_ctrl_block {
      unsigned long vrs[16];        /* virtual register set */
      unsigned long *insn;          /* pointer to the current instructions word */
      int entries;                  /* number of entries left to interpret */
      int byte;               /* current byte number in the instructions word */
};

enum regs {
      FP = 11,
      SP = 13,
      LR = 14,
      PC = 15
};

extern struct unwind_idx __start_unwind_idx[];
extern struct unwind_idx __stop_unwind_idx[];

static DEFINE_SPINLOCK(unwind_lock);
static LIST_HEAD(unwind_tables);

/* Convert a prel31 symbol to an absolute address */
#define prel31_to_addr(ptr)                     \
({                                        \
      /* sign-extend to 32 bits */              \
      long offset = (((long)*(ptr)) << 1) >> 1; \
      (unsigned long)(ptr) + offset;                  \
})

/*
 * Binary search in the unwind index. The entries entries are
 * guaranteed to be sorted in ascending order by the linker.
 */
static struct unwind_idx *search_index(unsigned long addr,
                               struct unwind_idx *first,
                               struct unwind_idx *last)
{
      pr_debug("%s(%08lx, %p, %p)\n", __func__, addr, first, last);

      if (addr < first->addr) {
            pr_warning("unwind: Unknown symbol address %08lx\n", addr);
            return NULL;
      } else if (addr >= last->addr)
            return last;

      while (first < last - 1) {
            struct unwind_idx *mid = first + ((last - first + 1) >> 1);

            if (addr < mid->addr)
                  last = mid;
            else
                  first = mid;
      }

      return first;
}

static struct unwind_idx *unwind_find_idx(unsigned long addr)
{
      struct unwind_idx *idx = NULL;
      unsigned long flags;

      pr_debug("%s(%08lx)\n", __func__, addr);

      if (core_kernel_text(addr))
            /* main unwind table */
            idx = search_index(addr, __start_unwind_idx,
                           __stop_unwind_idx - 1);
      else {
            /* module unwind tables */
            struct unwind_table *table;

            spin_lock_irqsave(&unwind_lock, flags);
            list_for_each_entry(table, &unwind_tables, list) {
                  if (addr >= table->begin_addr &&
                      addr < table->end_addr) {
                        idx = search_index(addr, table->start,
                                       table->stop - 1);
                        break;
                  }
            }
            spin_unlock_irqrestore(&unwind_lock, flags);
      }

      pr_debug("%s: idx = %p\n", __func__, idx);
      return idx;
}

static unsigned long unwind_get_byte(struct unwind_ctrl_block *ctrl)
{
      unsigned long ret;

      if (ctrl->entries <= 0) {
            pr_warning("unwind: Corrupt unwind table\n");
            return 0;
      }

      ret = (*ctrl->insn >> (ctrl->byte * 8)) & 0xff;

      if (ctrl->byte == 0) {
            ctrl->insn++;
            ctrl->entries--;
            ctrl->byte = 3;
      } else
            ctrl->byte--;

      return ret;
}

/*
 * Execute the current unwind instruction.
 */
static int unwind_exec_insn(struct unwind_ctrl_block *ctrl)
{
      unsigned long insn = unwind_get_byte(ctrl);

      pr_debug("%s: insn = %08lx\n", __func__, insn);

      if ((insn & 0xc0) == 0x00)
            ctrl->vrs[SP] += ((insn & 0x3f) << 2) + 4;
      else if ((insn & 0xc0) == 0x40)
            ctrl->vrs[SP] -= ((insn & 0x3f) << 2) + 4;
      else if ((insn & 0xf0) == 0x80) {
            unsigned long mask;
            unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
            int load_sp, reg = 4;

            insn = (insn << 8) | unwind_get_byte(ctrl);
            mask = insn & 0x0fff;
            if (mask == 0) {
                  pr_warning("unwind: 'Refuse to unwind' instruction %04lx\n",
                           insn);
                  return -URC_FAILURE;
            }

            /* pop R4-R15 according to mask */
            load_sp = mask & (1 << (13 - 4));
            while (mask) {
                  if (mask & 1)
                        ctrl->vrs[reg] = *vsp++;
                  mask >>= 1;
                  reg++;
            }
            if (!load_sp)
                  ctrl->vrs[SP] = (unsigned long)vsp;
      } else if ((insn & 0xf0) == 0x90 &&
               (insn & 0x0d) != 0x0d)
            ctrl->vrs[SP] = ctrl->vrs[insn & 0x0f];
      else if ((insn & 0xf0) == 0xa0) {
            unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
            int reg;

            /* pop R4-R[4+bbb] */
            for (reg = 4; reg <= 4 + (insn & 7); reg++)
                  ctrl->vrs[reg] = *vsp++;
            if (insn & 0x80)
                  ctrl->vrs[14] = *vsp++;
            ctrl->vrs[SP] = (unsigned long)vsp;
      } else if (insn == 0xb0) {
            if (ctrl->vrs[PC] == 0)
                  ctrl->vrs[PC] = ctrl->vrs[LR];
            /* no further processing */
            ctrl->entries = 0;
      } else if (insn == 0xb1) {
            unsigned long mask = unwind_get_byte(ctrl);
            unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
            int reg = 0;

            if (mask == 0 || mask & 0xf0) {
                  pr_warning("unwind: Spare encoding %04lx\n",
                         (insn << 8) | mask);
                  return -URC_FAILURE;
            }

            /* pop R0-R3 according to mask */
            while (mask) {
                  if (mask & 1)
                        ctrl->vrs[reg] = *vsp++;
                  mask >>= 1;
                  reg++;
            }
            ctrl->vrs[SP] = (unsigned long)vsp;
      } else if (insn == 0xb2) {
            unsigned long uleb128 = unwind_get_byte(ctrl);

            ctrl->vrs[SP] += 0x204 + (uleb128 << 2);
      } else {
            pr_warning("unwind: Unhandled instruction %02lx\n", insn);
            return -URC_FAILURE;
      }

      pr_debug("%s: fp = %08lx sp = %08lx lr = %08lx pc = %08lx\n", __func__,
             ctrl->vrs[FP], ctrl->vrs[SP], ctrl->vrs[LR], ctrl->vrs[PC]);

      return URC_OK;
}

/*
 * Unwind a single frame starting with *sp for the symbol at *pc. It
 * updates the *pc and *sp with the new values.
 */
int unwind_frame(struct stackframe *frame)
{
      unsigned long high, low;
      struct unwind_idx *idx;
      struct unwind_ctrl_block ctrl;

      /* only go to a higher address on the stack */
      low = frame->sp;
      high = ALIGN(low, THREAD_SIZE) + THREAD_SIZE;

      pr_debug("%s(pc = %08lx lr = %08lx sp = %08lx)\n", __func__,
             frame->pc, frame->lr, frame->sp);

      if (!kernel_text_address(frame->pc))
            return -URC_FAILURE;

      idx = unwind_find_idx(frame->pc);
      if (!idx) {
            pr_warning("unwind: Index not found %08lx\n", frame->pc);
            return -URC_FAILURE;
      }

      ctrl.vrs[FP] = frame->fp;
      ctrl.vrs[SP] = frame->sp;
      ctrl.vrs[LR] = frame->lr;
      ctrl.vrs[PC] = 0;

      if (idx->insn == 1)
            /* can't unwind */
            return -URC_FAILURE;
      else if ((idx->insn & 0x80000000) == 0)
            /* prel31 to the unwind table */
            ctrl.insn = (unsigned long *)prel31_to_addr(&idx->insn);
      else if ((idx->insn & 0xff000000) == 0x80000000)
            /* only personality routine 0 supported in the index */
            ctrl.insn = &idx->insn;
      else {
            pr_warning("unwind: Unsupported personality routine %08lx in the index at %p\n",
                     idx->insn, idx);
            return -URC_FAILURE;
      }

      /* check the personality routine */
      if ((*ctrl.insn & 0xff000000) == 0x80000000) {
            ctrl.byte = 2;
            ctrl.entries = 1;
      } else if ((*ctrl.insn & 0xff000000) == 0x81000000) {
            ctrl.byte = 1;
            ctrl.entries = 1 + ((*ctrl.insn & 0x00ff0000) >> 16);
      } else {
            pr_warning("unwind: Unsupported personality routine %08lx at %p\n",
                     *ctrl.insn, ctrl.insn);
            return -URC_FAILURE;
      }

      while (ctrl.entries > 0) {
            int urc = unwind_exec_insn(&ctrl);
            if (urc < 0)
                  return urc;
            if (ctrl.vrs[SP] < low || ctrl.vrs[SP] >= high)
                  return -URC_FAILURE;
      }

      if (ctrl.vrs[PC] == 0)
            ctrl.vrs[PC] = ctrl.vrs[LR];

      /* check for infinite loop */
      if (frame->pc == ctrl.vrs[PC])
            return -URC_FAILURE;

      frame->fp = ctrl.vrs[FP];
      frame->sp = ctrl.vrs[SP];
      frame->lr = ctrl.vrs[LR];
      frame->pc = ctrl.vrs[PC];

      return URC_OK;
}

void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
      struct stackframe frame;
      register unsigned long current_sp asm ("sp");

      pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

      if (!tsk)
            tsk = current;

      if (regs) {
            frame.fp = regs->ARM_fp;
            frame.sp = regs->ARM_sp;
            frame.lr = regs->ARM_lr;
            frame.pc = regs->ARM_pc;
      } else if (tsk == current) {
            frame.fp = (unsigned long)__builtin_frame_address(0);
            frame.sp = current_sp;
            frame.lr = (unsigned long)__builtin_return_address(0);
            frame.pc = (unsigned long)unwind_backtrace;
      } else {
            /* task blocked in __switch_to */
            frame.fp = thread_saved_fp(tsk);
            frame.sp = thread_saved_sp(tsk);
            /*
             * The function calling __switch_to cannot be a leaf function
             * so LR is recovered from the stack.
             */
            frame.lr = 0;
            frame.pc = thread_saved_pc(tsk);
      }

      while (1) {
            int urc;
            unsigned long where = frame.pc;

            urc = unwind_frame(&frame);
            if (urc < 0)
                  break;
            dump_backtrace_entry(where, frame.pc, frame.sp - 4);
      }
}

struct unwind_table *unwind_table_add(unsigned long start, unsigned long size,
                              unsigned long text_addr,
                              unsigned long text_size)
{
      unsigned long flags;
      struct unwind_idx *idx;
      struct unwind_table *tab = kmalloc(sizeof(*tab), GFP_KERNEL);

      pr_debug("%s(%08lx, %08lx, %08lx, %08lx)\n", __func__, start, size,
             text_addr, text_size);

      if (!tab)
            return tab;

      tab->start = (struct unwind_idx *)start;
      tab->stop = (struct unwind_idx *)(start + size);
      tab->begin_addr = text_addr;
      tab->end_addr = text_addr + text_size;

      /* Convert the symbol addresses to absolute values */
      for (idx = tab->start; idx < tab->stop; idx++)
            idx->addr = prel31_to_addr(&idx->addr);

      spin_lock_irqsave(&unwind_lock, flags);
      list_add_tail(&tab->list, &unwind_tables);
      spin_unlock_irqrestore(&unwind_lock, flags);

      return tab;
}

void unwind_table_del(struct unwind_table *tab)
{
      unsigned long flags;

      if (!tab)
            return;

      spin_lock_irqsave(&unwind_lock, flags);
      list_del(&tab->list);
      spin_unlock_irqrestore(&unwind_lock, flags);

      kfree(tab);
}

int __init unwind_init(void)
{
      struct unwind_idx *idx;

      /* Convert the symbol addresses to absolute values */
      for (idx = __start_unwind_idx; idx < __stop_unwind_idx; idx++)
            idx->addr = prel31_to_addr(&idx->addr);

      pr_debug("unwind: ARM stack unwinding initialised\n");

      return 0;
}

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