dwarf.c

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/*
 * Copyright (C) 2009 Matt Fleming <[email protected]>
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * This is an implementation of a DWARF unwinder. Its main purpose is
 * for generating stacktrace information. Based on the DWARF 3
 * specification from http://www.dwarfstd.org.
 *
 * TODO:
 *  - DWARF64 doesn't work.
 *  - Registers with DWARF_VAL_OFFSET rules aren't handled properly.
 */

/* #define DEBUG */
#include <linux/kernel.h>
#include <linux/io.h>
#include <linux/list.h>
#include <linux/mempool.h>
#include <linux/mm.h>
#include <linux/elf.h>
#include <linux/ftrace.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <asm/dwarf.h>
#include <asm/unwinder.h>
#include <asm/sections.h>
#include <asm/unaligned.h>
#include <asm/stacktrace.h>

/* Reserve enough memory for two stack frames */
#define DWARF_FRAME_MIN_REQ 2
/* ... with 4 registers per frame. */
#define DWARF_REG_MIN_REQ   (DWARF_FRAME_MIN_REQ * 4)

static struct kmem_cache *dwarf_frame_cachep;
static mempool_t *dwarf_frame_pool;

static struct kmem_cache *dwarf_reg_cachep;
static mempool_t *dwarf_reg_pool;

static struct rb_root cie_root;
static DEFINE_SPINLOCK(dwarf_cie_lock);

static struct rb_root fde_root;
static DEFINE_SPINLOCK(dwarf_fde_lock);

static struct dwarf_cie *cached_cie;

static unsigned int dwarf_unwinder_ready;

static struct dwarf_reg *dwarf_frame_alloc_reg(struct dwarf_frame *frame,
                           unsigned int reg_num)
{
    struct dwarf_reg *reg;

    reg = mempool_alloc(dwarf_reg_pool, GFP_ATOMIC);
    if (!reg) {
        printk(KERN_WARNING "Unable to allocate a DWARF register\n");
        /*
         * Let's just bomb hard here, we have no way to
         * gracefully recover.
         */
        UNWINDER_BUG();
    }

    reg->number = reg_num;
    reg->addr = 0;
    reg->flags = 0;

    list_add(&reg->link, &frame->reg_list);

    return reg;
}

static void dwarf_frame_free_regs(struct dwarf_frame *frame)
{
    struct dwarf_reg *reg, *n;

    list_for_each_entry_safe(reg, n, &frame->reg_list, link) {
        list_del(&reg->link);
        mempool_free(reg, dwarf_reg_pool);
    }
}

static struct dwarf_reg *dwarf_frame_reg(struct dwarf_frame *frame,
                     unsigned int reg_num)
{
    struct dwarf_reg *reg;

    list_for_each_entry(reg, &frame->reg_list, link) {
        if (reg->number == reg_num)
            return reg;
    }

    return NULL;
}

static inline int dwarf_read_addr(unsigned long *src, unsigned long *dst)
{
    u32 val = get_unaligned(src);
    put_unaligned(val, dst);
    return sizeof(unsigned long *);
}

static inline unsigned long dwarf_read_uleb128(char *addr, unsigned int *ret)
{
    unsigned int result;
    unsigned char byte;
    int shift, count;

    result = 0;
    shift = 0;
    count = 0;

    while (1) {
        byte = __raw_readb(addr);
        addr++;
        count++;

        result |= (byte & 0x7f) << shift;
        shift += 7;

        if (!(byte & 0x80))
            break;
    }

    *ret = result;

    return count;
}

static inline unsigned long dwarf_read_leb128(char *addr, int *ret)
{
    unsigned char byte;
    int result, shift;
    int num_bits;
    int count;

    result = 0;
    shift = 0;
    count = 0;

    while (1) {
        byte = __raw_readb(addr);
        addr++;
        result |= (byte & 0x7f) << shift;
        shift += 7;
        count++;

        if (!(byte & 0x80))
            break;
    }

    /* The number of bits in a signed integer. */
    num_bits = 8 * sizeof(result);

    if ((shift < num_bits) && (byte & 0x40))
        result |= (-1 << shift);

    *ret = result;

    return count;
}

static int dwarf_read_encoded_value(char *addr, unsigned long *val,
                    char encoding)
{
    unsigned long decoded_addr = 0;
    int count = 0;

    switch (encoding & 0x70) {
    case DW_EH_PE_absptr:
        break;
    case DW_EH_PE_pcrel:
        decoded_addr = (unsigned long)addr;
        break;
    default:
        pr_debug("encoding=0x%x\n", (encoding & 0x70));
        UNWINDER_BUG();
    }

    if ((encoding & 0x07) == 0x00)
        encoding |= DW_EH_PE_udata4;

    switch (encoding & 0x0f) {
    case DW_EH_PE_sdata4:
    case DW_EH_PE_udata4:
        count += 4;
        decoded_addr += get_unaligned((u32 *)addr);
        __raw_writel(decoded_addr, val);
        break;
    default:
        pr_debug("encoding=0x%x\n", encoding);
        UNWINDER_BUG();
    }

    return count;
}

static inline int dwarf_entry_len(char *addr, unsigned long *len)
{
    u32 initial_len;
    int count;

    initial_len = get_unaligned((u32 *)addr);
    count = 4;

    /*
     * An initial length field value in the range DW_LEN_EXT_LO -
     * DW_LEN_EXT_HI indicates an extension, and should not be
     * interpreted as a length. The only extension that we currently
     * understand is the use of DWARF64 addresses.
     */
    if (initial_len >= DW_EXT_LO && initial_len <= DW_EXT_HI) {
        /*
         * The 64-bit length field immediately follows the
         * compulsory 32-bit length field.
         */
        if (initial_len == DW_EXT_DWARF64) {
            *len = get_unaligned((u64 *)addr + 4);
            count = 12;
        } else {
            printk(KERN_WARNING "Unknown DWARF extension\n");
            count = 0;
        }
    } else
        *len = initial_len;

    return count;
}

static struct dwarf_cie *dwarf_lookup_cie(unsigned long cie_ptr)
{
    struct rb_node **rb_node = &cie_root.rb_node;
    struct dwarf_cie *cie = NULL;
    unsigned long flags;

    spin_lock_irqsave(&dwarf_cie_lock, flags);

    /*
     * We've cached the last CIE we looked up because chances are
     * that the FDE wants this CIE.
     */
    if (cached_cie && cached_cie->cie_pointer == cie_ptr) {
        cie = cached_cie;
        goto out;
    }

    while (*rb_node) {
        struct dwarf_cie *cie_tmp;

        cie_tmp = rb_entry(*rb_node, struct dwarf_cie, node);
        BUG_ON(!cie_tmp);

        if (cie_ptr == cie_tmp->cie_pointer) {
            cie = cie_tmp;
            cached_cie = cie_tmp;
            goto out;
        } else {
            if (cie_ptr < cie_tmp->cie_pointer)
                rb_node = &(*rb_node)->rb_left;
            else
                rb_node = &(*rb_node)->rb_right;
        }
    }

out:
    spin_unlock_irqrestore(&dwarf_cie_lock, flags);
    return cie;
}

struct dwarf_fde *dwarf_lookup_fde(unsigned long pc)
{
    struct rb_node **rb_node = &fde_root.rb_node;
    struct dwarf_fde *fde = NULL;
    unsigned long flags;

    spin_lock_irqsave(&dwarf_fde_lock, flags);

    while (*rb_node) {
        struct dwarf_fde *fde_tmp;
        unsigned long tmp_start, tmp_end;

        fde_tmp = rb_entry(*rb_node, struct dwarf_fde, node);
        BUG_ON(!fde_tmp);

        tmp_start = fde_tmp->initial_location;
        tmp_end = fde_tmp->initial_location + fde_tmp->address_range;

        if (pc < tmp_start) {
            rb_node = &(*rb_node)->rb_left;
        } else {
            if (pc < tmp_end) {
                fde = fde_tmp;
                goto out;
            } else
                rb_node = &(*rb_node)->rb_right;
        }
    }

out:
    spin_unlock_irqrestore(&dwarf_fde_lock, flags);

    return fde;
}

static int dwarf_cfa_execute_insns(unsigned char *insn_start,
                   unsigned char *insn_end,
                   struct dwarf_cie *cie,
                   struct dwarf_fde *fde,
                   struct dwarf_frame *frame,
                   unsigned long pc)
{
    unsigned char insn;
    unsigned char *current_insn;
    unsigned int count, delta, reg, expr_len, offset;
    struct dwarf_reg *regp;

    current_insn = insn_start;

    while (current_insn < insn_end && frame->pc <= pc) {
        insn = __raw_readb(current_insn++);

        /*
         * Firstly, handle the opcodes that embed their operands
         * in the instructions.
         */
        switch (DW_CFA_opcode(insn)) {
        case DW_CFA_advance_loc:
            delta = DW_CFA_operand(insn);
            delta *= cie->code_alignment_factor;
            frame->pc += delta;
            continue;
            /* NOTREACHED */
        case DW_CFA_offset:
            reg = DW_CFA_operand(insn);
            count = dwarf_read_uleb128(current_insn, &offset);
            current_insn += count;
            offset *= cie->data_alignment_factor;
            regp = dwarf_frame_alloc_reg(frame, reg);
            regp->addr = offset;
            regp->flags |= DWARF_REG_OFFSET;
            continue;
            /* NOTREACHED */
        case DW_CFA_restore:
            reg = DW_CFA_operand(insn);
            continue;
            /* NOTREACHED */
        }

        /*
         * Secondly, handle the opcodes that don't embed their
         * operands in the instruction.
         */
        switch (insn) {
        case DW_CFA_nop:
            continue;
        case DW_CFA_advance_loc1:
            delta = *current_insn++;
            frame->pc += delta * cie->code_alignment_factor;
            break;
        case DW_CFA_advance_loc2:
            delta = get_unaligned((u16 *)current_insn);
            current_insn += 2;
            frame->pc += delta * cie->code_alignment_factor;
            break;
        case DW_CFA_advance_loc4:
            delta = get_unaligned((u32 *)current_insn);
            current_insn += 4;
            frame->pc += delta * cie->code_alignment_factor;
            break;
        case DW_CFA_offset_extended:
            count = dwarf_read_uleb128(current_insn, &reg);
            current_insn += count;
            count = dwarf_read_uleb128(current_insn, &offset);
            current_insn += count;
            offset *= cie->data_alignment_factor;
            break;
        case DW_CFA_restore_extended:
            count = dwarf_read_uleb128(current_insn, &reg);
            current_insn += count;
            break;
        case DW_CFA_undefined:
            count = dwarf_read_uleb128(current_insn, &reg);
            current_insn += count;
            regp = dwarf_frame_alloc_reg(frame, reg);
            regp->flags |= DWARF_UNDEFINED;
            break;
        case DW_CFA_def_cfa:
            count = dwarf_read_uleb128(current_insn,
                           &frame->cfa_register);
            current_insn += count;
            count = dwarf_read_uleb128(current_insn,
                           &frame->cfa_offset);
            current_insn += count;

            frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
            break;
        case DW_CFA_def_cfa_register:
            count = dwarf_read_uleb128(current_insn,
                           &frame->cfa_register);
            current_insn += count;
            frame->flags |= DWARF_FRAME_CFA_REG_OFFSET;
            break;
        case DW_CFA_def_cfa_offset:
            count = dwarf_read_uleb128(current_insn, &offset);
            current_insn += count;
            frame->cfa_offset = offset;
            break;
        case DW_CFA_def_cfa_expression:
            count = dwarf_read_uleb128(current_insn, &expr_len);
            current_insn += count;

            frame->cfa_expr = current_insn;
            frame->cfa_expr_len = expr_len;
            current_insn += expr_len;

            frame->flags |= DWARF_FRAME_CFA_REG_EXP;
            break;
        case DW_CFA_offset_extended_sf:
            count = dwarf_read_uleb128(current_insn, &reg);
            current_insn += count;
            count = dwarf_read_leb128(current_insn, &offset);
            current_insn += count;
            offset *= cie->data_alignment_factor;
            regp = dwarf_frame_alloc_reg(frame, reg);
            regp->flags |= DWARF_REG_OFFSET;
            regp->addr = offset;
            break;
        case DW_CFA_val_offset:
            count = dwarf_read_uleb128(current_insn, &reg);
            current_insn += count;
            count = dwarf_read_leb128(current_insn, &offset);
            offset *= cie->data_alignment_factor;
            regp = dwarf_frame_alloc_reg(frame, reg);
            regp->flags |= DWARF_VAL_OFFSET;
            regp->addr = offset;
            break;
        case DW_CFA_GNU_args_size:
            count = dwarf_read_uleb128(current_insn, &offset);
            current_insn += count;
            break;
        case DW_CFA_GNU_negative_offset_extended:
            count = dwarf_read_uleb128(current_insn, &reg);
            current_insn += count;
            count = dwarf_read_uleb128(current_insn, &offset);
            offset *= cie->data_alignment_factor;

            regp = dwarf_frame_alloc_reg(frame, reg);
            regp->flags |= DWARF_REG_OFFSET;
            regp->addr = -offset;
            break;
        default:
            pr_debug("unhandled DWARF instruction 0x%x\n", insn);
            UNWINDER_BUG();
            break;
        }
    }

    return 0;
}

void dwarf_free_frame(struct dwarf_frame *frame)
{
    dwarf_frame_free_regs(frame);
    mempool_free(frame, dwarf_frame_pool);
}

extern void ret_from_irq(void);

struct dwarf_frame *dwarf_unwind_stack(unsigned long pc,
                       struct dwarf_frame *prev)
{
    struct dwarf_frame *frame;
    struct dwarf_cie *cie;
    struct dwarf_fde *fde;
    struct dwarf_reg *reg;
    unsigned long addr;

    /*
     * If we've been called in to before initialization has
     * completed, bail out immediately.
     */
    if (!dwarf_unwinder_ready)
        return NULL;

    /*
     * If we're starting at the top of the stack we need get the
     * contents of a physical register to get the CFA in order to
     * begin the virtual unwinding of the stack.
     *
     * NOTE: the return address is guaranteed to be setup by the
     * time this function makes its first function call.
     */
    if (!pc || !prev)
        pc = (unsigned long)current_text_addr();

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
    /*
     * If our stack has been patched by the function graph tracer
     * then we might see the address of return_to_handler() where we
     * expected to find the real return address.
     */
    if (pc == (unsigned long)&return_to_handler) {
        int index = current->curr_ret_stack;

        /*
         * We currently have no way of tracking how many
         * return_to_handler()'s we've seen. If there is more
         * than one patched return address on our stack,
         * complain loudly.
         */
        WARN_ON(index > 0);

        pc = current->ret_stack[index].ret;
    }
#endif

    frame = mempool_alloc(dwarf_frame_pool, GFP_ATOMIC);
    if (!frame) {
        printk(KERN_ERR "Unable to allocate a dwarf frame\n");
        UNWINDER_BUG();
    }

    INIT_LIST_HEAD(&frame->reg_list);
    frame->flags = 0;
    frame->prev = prev;
    frame->return_addr = 0;

    fde = dwarf_lookup_fde(pc);
    if (!fde) {
        /*
         * This is our normal exit path. There are two reasons
         * why we might exit here,
         *
         *  a) pc has no asscociated DWARF frame info and so
         *  we don't know how to unwind this frame. This is
         *  usually the case when we're trying to unwind a
         *  frame that was called from some assembly code
         *  that has no DWARF info, e.g. syscalls.
         *
         *  b) the DEBUG info for pc is bogus. There's
         *  really no way to distinguish this case from the
         *  case above, which sucks because we could print a
         *  warning here.
         */
        goto bail;
    }

    cie = dwarf_lookup_cie(fde->cie_pointer);

    frame->pc = fde->initial_location;

    /* CIE initial instructions */
    dwarf_cfa_execute_insns(cie->initial_instructions,
                cie->instructions_end, cie, fde,
                frame, pc);

    /* FDE instructions */
    dwarf_cfa_execute_insns(fde->instructions, fde->end, cie,
                fde, frame, pc);

    /* Calculate the CFA */
    switch (frame->flags) {
    case DWARF_FRAME_CFA_REG_OFFSET:
        if (prev) {
            reg = dwarf_frame_reg(prev, frame->cfa_register);
            UNWINDER_BUG_ON(!reg);
            UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);

            addr = prev->cfa + reg->addr;
            frame->cfa = __raw_readl(addr);

        } else {
            /*
             * Again, we're starting from the top of the
             * stack. We need to physically read
             * the contents of a register in order to get
             * the Canonical Frame Address for this
             * function.
             */
            frame->cfa = dwarf_read_arch_reg(frame->cfa_register);
        }

        frame->cfa += frame->cfa_offset;
        break;
    default:
        UNWINDER_BUG();
    }

    reg = dwarf_frame_reg(frame, DWARF_ARCH_RA_REG);

    /*
     * If we haven't seen the return address register or the return
     * address column is undefined then we must assume that this is
     * the end of the callstack.
     */
    if (!reg || reg->flags == DWARF_UNDEFINED)
        goto bail;

    UNWINDER_BUG_ON(reg->flags != DWARF_REG_OFFSET);

    addr = frame->cfa + reg->addr;
    frame->return_addr = __raw_readl(addr);

    /*
     * Ah, the joys of unwinding through interrupts.
     *
     * Interrupts are tricky - the DWARF info needs to be _really_
     * accurate and unfortunately I'm seeing a lot of bogus DWARF
     * info. For example, I've seen interrupts occur in epilogues
     * just after the frame pointer (r14) had been restored. The
     * problem was that the DWARF info claimed that the CFA could be
     * reached by using the value of the frame pointer before it was
     * restored.
     *
     * So until the compiler can be trusted to produce reliable
     * DWARF info when it really matters, let's stop unwinding once
     * we've calculated the function that was interrupted.
     */
    if (prev && prev->pc == (unsigned long)ret_from_irq)
        frame->return_addr = 0;

    return frame;

bail:
    dwarf_free_frame(frame);
    return NULL;
}

static int dwarf_parse_cie(void *entry, void *p, unsigned long len,
               unsigned char *end, struct module *mod)
{
    struct rb_node **rb_node = &cie_root.rb_node;
    struct rb_node *parent = *rb_node;
    struct dwarf_cie *cie;
    unsigned long flags;
    int count;

    cie = kzalloc(sizeof(*cie), GFP_KERNEL);
    if (!cie)
        return -ENOMEM;

    cie->length = len;

    /*
     * Record the offset into the .eh_frame section
     * for this CIE. It allows this CIE to be
     * quickly and easily looked up from the
     * corresponding FDE.
     */
    cie->cie_pointer = (unsigned long)entry;

    cie->version = *(char *)p++;
    UNWINDER_BUG_ON(cie->version != 1);

    cie->augmentation = p;
    p += strlen(cie->augmentation) + 1;

    count = dwarf_read_uleb128(p, &cie->code_alignment_factor);
    p += count;

    count = dwarf_read_leb128(p, &cie->data_alignment_factor);
    p += count;

    /*
     * Which column in the rule table contains the
     * return address?
     */
    if (cie->version == 1) {
        cie->return_address_reg = __raw_readb(p);
        p++;
    } else {
        count = dwarf_read_uleb128(p, &cie->return_address_reg);
        p += count;
    }

    if (cie->augmentation[0] == 'z') {
        unsigned int length, count;
        cie->flags |= DWARF_CIE_Z_AUGMENTATION;

        count = dwarf_read_uleb128(p, &length);
        p += count;

        UNWINDER_BUG_ON((unsigned char *)p > end);

        cie->initial_instructions = p + length;
        cie->augmentation++;
    }

    while (*cie->augmentation) {
        /*
         * "L" indicates a byte showing how the
         * LSDA pointer is encoded. Skip it.
         */
        if (*cie->augmentation == 'L') {
            p++;
            cie->augmentation++;
        } else if (*cie->augmentation == 'R') {
            /*
             * "R" indicates a byte showing
             * how FDE addresses are
             * encoded.
             */
            cie->encoding = *(char *)p++;
            cie->augmentation++;
        } else if (*cie->augmentation == 'P') {
            /*
             * "R" indicates a personality
             * routine in the CIE
             * augmentation.
             */
            UNWINDER_BUG();
        } else if (*cie->augmentation == 'S') {
            UNWINDER_BUG();
        } else {
            /*
             * Unknown augmentation. Assume
             * 'z' augmentation.
             */
            p = cie->initial_instructions;
            UNWINDER_BUG_ON(!p);
            break;
        }
    }

    cie->initial_instructions = p;
    cie->instructions_end = end;

    /* Add to list */
    spin_lock_irqsave(&dwarf_cie_lock, flags);

    while (*rb_node) {
        struct dwarf_cie *cie_tmp;

        cie_tmp = rb_entry(*rb_node, struct dwarf_cie, node);

        parent = *rb_node;

        if (cie->cie_pointer < cie_tmp->cie_pointer)
            rb_node = &parent->rb_left;
        else if (cie->cie_pointer >= cie_tmp->cie_pointer)
            rb_node = &parent->rb_right;
        else
            WARN_ON(1);
    }

    rb_link_node(&cie->node, parent, rb_node);
    rb_insert_color(&cie->node, &cie_root);

#ifdef CONFIG_MODULES
    if (mod != NULL)
        list_add_tail(&cie->link, &mod->arch.cie_list);
#endif

    spin_unlock_irqrestore(&dwarf_cie_lock, flags);

    return 0;
}

static int dwarf_parse_fde(void *entry, u32 entry_type,
               void *start, unsigned long len,
               unsigned char *end, struct module *mod)
{
    struct rb_node **rb_node = &fde_root.rb_node;
    struct rb_node *parent = *rb_node;
    struct dwarf_fde *fde;
    struct dwarf_cie *cie;
    unsigned long flags;
    int count;
    void *p = start;

    fde = kzalloc(sizeof(*fde), GFP_KERNEL);
    if (!fde)
        return -ENOMEM;

    fde->length = len;

    /*
     * In a .eh_frame section the CIE pointer is the
     * delta between the address within the FDE
     */
    fde->cie_pointer = (unsigned long)(p - entry_type - 4);

    cie = dwarf_lookup_cie(fde->cie_pointer);
    fde->cie = cie;

    if (cie->encoding)
        count = dwarf_read_encoded_value(p, &fde->initial_location,
                         cie->encoding);
    else
        count = dwarf_read_addr(p, &fde->initial_location);

    p += count;

    if (cie->encoding)
        count = dwarf_read_encoded_value(p, &fde->address_range,
                         cie->encoding & 0x0f);
    else
        count = dwarf_read_addr(p, &fde->address_range);

    p += count;

    if (fde->cie->flags & DWARF_CIE_Z_AUGMENTATION) {
        unsigned int length;
        count = dwarf_read_uleb128(p, &length);
        p += count + length;
    }

    /* Call frame instructions. */
    fde->instructions = p;
    fde->end = end;

    /* Add to list. */
    spin_lock_irqsave(&dwarf_fde_lock, flags);

    while (*rb_node) {
        struct dwarf_fde *fde_tmp;
        unsigned long tmp_start, tmp_end;
        unsigned long start, end;

        fde_tmp = rb_entry(*rb_node, struct dwarf_fde, node);

        start = fde->initial_location;
        end = fde->initial_location + fde->address_range;

        tmp_start = fde_tmp->initial_location;
        tmp_end = fde_tmp->initial_location + fde_tmp->address_range;

        parent = *rb_node;

        if (start < tmp_start)
            rb_node = &parent->rb_left;
        else if (start >= tmp_end)
            rb_node = &parent->rb_right;
        else
            WARN_ON(1);
    }

    rb_link_node(&fde->node, parent, rb_node);
    rb_insert_color(&fde->node, &fde_root);

#ifdef CONFIG_MODULES
    if (mod != NULL)
        list_add_tail(&fde->link, &mod->arch.fde_list);
#endif

    spin_unlock_irqrestore(&dwarf_fde_lock, flags);

    return 0;
}

static void dwarf_unwinder_dump(struct task_struct *task,
                struct pt_regs *regs,
                unsigned long *sp,
                const struct stacktrace_ops *ops,
                void *data)
{
    struct dwarf_frame *frame, *_frame;
    unsigned long return_addr;

    _frame = NULL;
    return_addr = 0;

    while (1) {
        frame = dwarf_unwind_stack(return_addr, _frame);

        if (_frame)
            dwarf_free_frame(_frame);

        _frame = frame;

        if (!frame || !frame->return_addr)
            break;

        return_addr = frame->return_addr;
        ops->address(data, return_addr, 1);
    }

    if (frame)
        dwarf_free_frame(frame);
}

static struct unwinder dwarf_unwinder = {
    .name = "dwarf-unwinder",
    .dump = dwarf_unwinder_dump,
    .rating = 150,
};

static void dwarf_unwinder_cleanup(void)
{
    struct rb_node **fde_rb_node = &fde_root.rb_node;
    struct rb_node **cie_rb_node = &cie_root.rb_node;

    /*
     * Deallocate all the memory allocated for the DWARF unwinder.
     * Traverse all the FDE/CIE lists and remove and free all the
     * memory associated with those data structures.
     */
    while (*fde_rb_node) {
        struct dwarf_fde *fde;

        fde = rb_entry(*fde_rb_node, struct dwarf_fde, node);
        rb_erase(*fde_rb_node, &fde_root);
        kfree(fde);
    }

    while (*cie_rb_node) {
        struct dwarf_cie *cie;

        cie = rb_entry(*cie_rb_node, struct dwarf_cie, node);
        rb_erase(*cie_rb_node, &cie_root);
        kfree(cie);
    }

    kmem_cache_destroy(dwarf_reg_cachep);
    kmem_cache_destroy(dwarf_frame_cachep);
}

static int dwarf_parse_section(char *eh_frame_start, char *eh_frame_end,
                   struct module *mod)
{
    u32 entry_type;
    void *p, *entry;
    int count, err = 0;
    unsigned long len = 0;
    unsigned int c_entries, f_entries;
    unsigned char *end;

    c_entries = 0;
    f_entries = 0;
    entry = eh_frame_start;

    while ((char *)entry < eh_frame_end) {
        p = entry;

        count = dwarf_entry_len(p, &len);
        if (count == 0) {
            /*
             * We read a bogus length field value. There is
             * nothing we can do here apart from disabling
             * the DWARF unwinder. We can't even skip this
             * entry and move to the next one because 'len'
             * tells us where our next entry is.
             */
            err = -EINVAL;
            goto out;
        } else
            p += count;

        /* initial length does not include itself */
        end = p + len;

        entry_type = get_unaligned((u32 *)p);
        p += 4;

        if (entry_type == DW_EH_FRAME_CIE) {
            err = dwarf_parse_cie(entry, p, len, end, mod);
            if (err < 0)
                goto out;
            else
                c_entries++;
        } else {
            err = dwarf_parse_fde(entry, entry_type, p, len,
                          end, mod);
            if (err < 0)
                goto out;
            else
                f_entries++;
        }

        entry = (char *)entry + len + 4;
    }

    printk(KERN_INFO "DWARF unwinder initialised: read %u CIEs, %u FDEs\n",
           c_entries, f_entries);

    return 0;

out:
    return err;
}

#ifdef CONFIG_MODULES
int module_dwarf_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
              struct module *me)
{
    unsigned int i, err;
    unsigned long start, end;
    char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;

    start = end = 0;

    for (i = 1; i < hdr->e_shnum; i++) {
        /* Alloc bit cleared means "ignore it." */
        if ((sechdrs[i].sh_flags & SHF_ALLOC)
            && !strcmp(secstrings+sechdrs[i].sh_name, ".eh_frame")) {
            start = sechdrs[i].sh_addr;
            end = start + sechdrs[i].sh_size;
            break;
        }
    }

    /* Did we find the .eh_frame section? */
    if (i != hdr->e_shnum) {
        INIT_LIST_HEAD(&me->arch.cie_list);
        INIT_LIST_HEAD(&me->arch.fde_list);
        err = dwarf_parse_section((char *)start, (char *)end, me);
        if (err) {
            printk(KERN_WARNING "%s: failed to parse DWARF info\n",
                   me->name);
            return err;
        }
    }

    return 0;
}

void module_dwarf_cleanup(struct module *mod)
{
    struct dwarf_fde *fde, *ftmp;
    struct dwarf_cie *cie, *ctmp;
    unsigned long flags;

    spin_lock_irqsave(&dwarf_cie_lock, flags);

    list_for_each_entry_safe(cie, ctmp, &mod->arch.cie_list, link) {
        list_del(&cie->link);
        rb_erase(&cie->node, &cie_root);
        kfree(cie);
    }

    spin_unlock_irqrestore(&dwarf_cie_lock, flags);

    spin_lock_irqsave(&dwarf_fde_lock, flags);

    list_for_each_entry_safe(fde, ftmp, &mod->arch.fde_list, link) {
        list_del(&fde->link);
        rb_erase(&fde->node, &fde_root);
        kfree(fde);
    }

    spin_unlock_irqrestore(&dwarf_fde_lock, flags);
}
#endif /* CONFIG_MODULES */

static int __init dwarf_unwinder_init(void)
{
    int err = -ENOMEM;

    dwarf_frame_cachep = kmem_cache_create("dwarf_frames",
            sizeof(struct dwarf_frame), 0,
            SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);

    dwarf_reg_cachep = kmem_cache_create("dwarf_regs",
            sizeof(struct dwarf_reg), 0,
            SLAB_PANIC | SLAB_HWCACHE_ALIGN | SLAB_NOTRACK, NULL);

    dwarf_frame_pool = mempool_create(DWARF_FRAME_MIN_REQ,
                      mempool_alloc_slab,
                      mempool_free_slab,
                      dwarf_frame_cachep);
    if (!dwarf_frame_pool)
        goto out;

    dwarf_reg_pool = mempool_create(DWARF_REG_MIN_REQ,
                     mempool_alloc_slab,
                     mempool_free_slab,
                     dwarf_reg_cachep);
    if (!dwarf_reg_pool)
        goto out;

    err = dwarf_parse_section(__start_eh_frame, __stop_eh_frame, NULL);
    if (err)
        goto out;

    err = unwinder_register(&dwarf_unwinder);
    if (err)
        goto out;

    dwarf_unwinder_ready = 1;

    return 0;

out:
    printk(KERN_ERR "Failed to initialise DWARF unwinder: %d\n", err);
    dwarf_unwinder_cleanup();
    return err;
}
early_initcall(dwarf_unwinder_init);