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[hh.org.git] / kernel / unwind.c

/*
 * Copyright (C) 2002-2006 Novell, Inc.
 *      Jan Beulich <jbeulich@novell.com>
 * This code is released under version 2 of the GNU GPL.
 *
 * A simple API for unwinding kernel stacks.  This is used for
 * debugging and error reporting purposes.  The kernel doesn't need
 * full-blown stack unwinding with all the bells and whistles, so there
 * is not much point in implementing the full Dwarf2 unwind API.
 */

#include <linux/unwind.h>
#include <linux/module.h>
#include <linux/bootmem.h>
#include <linux/sort.h>
#include <linux/stop_machine.h>
#include <asm/sections.h>
#include <asm/uaccess.h>
#include <asm/unaligned.h>

extern char __start_unwind[], __end_unwind[];
extern const u8 __start_unwind_hdr[], __end_unwind_hdr[];

#define MAX_STACK_DEPTH 8

#define EXTRA_INFO(f) { \
                BUILD_BUG_ON_ZERO(offsetof(struct unwind_frame_info, f) \
                                  % FIELD_SIZEOF(struct unwind_frame_info, f)) \
                + offsetof(struct unwind_frame_info, f) \
                  / FIELD_SIZEOF(struct unwind_frame_info, f), \
                FIELD_SIZEOF(struct unwind_frame_info, f) \
        }
#define PTREGS_INFO(f) EXTRA_INFO(regs.f)

static const struct {
        unsigned offs:BITS_PER_LONG / 2;
        unsigned width:BITS_PER_LONG / 2;
} reg_info[] = {
        UNW_REGISTER_INFO
};

#undef PTREGS_INFO
#undef EXTRA_INFO

#ifndef REG_INVALID
#define REG_INVALID(r) (reg_info[r].width == 0)
#endif

#define DW_CFA_nop                          0x00
#define DW_CFA_set_loc                      0x01
#define DW_CFA_advance_loc1                 0x02
#define DW_CFA_advance_loc2                 0x03
#define DW_CFA_advance_loc4                 0x04
#define DW_CFA_offset_extended              0x05
#define DW_CFA_restore_extended             0x06
#define DW_CFA_undefined                    0x07
#define DW_CFA_same_value                   0x08
#define DW_CFA_register                     0x09
#define DW_CFA_remember_state               0x0a
#define DW_CFA_restore_state                0x0b
#define DW_CFA_def_cfa                      0x0c
#define DW_CFA_def_cfa_register             0x0d
#define DW_CFA_def_cfa_offset               0x0e
#define DW_CFA_def_cfa_expression           0x0f
#define DW_CFA_expression                   0x10
#define DW_CFA_offset_extended_sf           0x11
#define DW_CFA_def_cfa_sf                   0x12
#define DW_CFA_def_cfa_offset_sf            0x13
#define DW_CFA_val_offset                   0x14
#define DW_CFA_val_offset_sf                0x15
#define DW_CFA_val_expression               0x16
#define DW_CFA_lo_user                      0x1c
#define DW_CFA_GNU_window_save              0x2d
#define DW_CFA_GNU_args_size                0x2e
#define DW_CFA_GNU_negative_offset_extended 0x2f
#define DW_CFA_hi_user                      0x3f

#define DW_EH_PE_FORM     0x07
#define DW_EH_PE_native   0x00
#define DW_EH_PE_leb128   0x01
#define DW_EH_PE_data2    0x02
#define DW_EH_PE_data4    0x03
#define DW_EH_PE_data8    0x04
#define DW_EH_PE_signed   0x08
#define DW_EH_PE_ADJUST   0x70
#define DW_EH_PE_abs      0x00
#define DW_EH_PE_pcrel    0x10
#define DW_EH_PE_textrel  0x20
#define DW_EH_PE_datarel  0x30
#define DW_EH_PE_funcrel  0x40
#define DW_EH_PE_aligned  0x50
#define DW_EH_PE_indirect 0x80
#define DW_EH_PE_omit     0xff

typedef unsigned long uleb128_t;
typedef   signed long sleb128_t;

static struct unwind_table {
        struct {
                unsigned long pc;
                unsigned long range;
        } core, init;
        const void *address;
        unsigned long size;
        const unsigned char *header;
        unsigned long hdrsz;
        struct unwind_table *link;
        const char *name;
} root_table;

struct unwind_item {
        enum item_location {
                Nowhere,
                Memory,
                Register,
                Value
        } where;
        uleb128_t value;
};

struct unwind_state {
        uleb128_t loc, org;
        const u8 *cieStart, *cieEnd;
        uleb128_t codeAlign;
        sleb128_t dataAlign;
        struct cfa {
                uleb128_t reg, offs;
        } cfa;
        struct unwind_item regs[ARRAY_SIZE(reg_info)];
        unsigned stackDepth:8;
        unsigned version:8;
        const u8 *label;
        const u8 *stack[MAX_STACK_DEPTH];
};

static const struct cfa badCFA = { ARRAY_SIZE(reg_info), 1 };

static struct unwind_table *find_table(unsigned long pc)
{
        struct unwind_table *table;

        for (table = &root_table; table; table = table->link)
                if ((pc >= table->core.pc
                     && pc < table->core.pc + table->core.range)
                    || (pc >= table->init.pc
                        && pc < table->init.pc + table->init.range))
                        break;

        return table;
}

static unsigned long read_pointer(const u8 **pLoc,
                                  const void *end,
                                  signed ptrType);

static void init_unwind_table(struct unwind_table *table,
                              const char *name,
                              const void *core_start,
                              unsigned long core_size,
                              const void *init_start,
                              unsigned long init_size,
                              const void *table_start,
                              unsigned long table_size,
                              const u8 *header_start,
                              unsigned long header_size)
{
        const u8 *ptr = header_start + 4;
        const u8 *end = header_start + header_size;

        table->core.pc = (unsigned long)core_start;
        table->core.range = core_size;
        table->init.pc = (unsigned long)init_start;
        table->init.range = init_size;
        table->address = table_start;
        table->size = table_size;
        /* See if the linker provided table looks valid. */
        if (header_size <= 4
            || header_start[0] != 1
            || (void *)read_pointer(&ptr, end, header_start[1]) != table_start
            || header_start[2] == DW_EH_PE_omit
            || read_pointer(&ptr, end, header_start[2]) <= 0
            || header_start[3] == DW_EH_PE_omit)
                header_start = NULL;
        table->hdrsz = header_size;
        smp_wmb();
        table->header = header_start;
        table->link = NULL;
        table->name = name;
}

void __init unwind_init(void)
{
        init_unwind_table(&root_table, "kernel",
                          _text, _end - _text,
                          NULL, 0,
                          __start_unwind, __end_unwind - __start_unwind,
                          __start_unwind_hdr, __end_unwind_hdr - __start_unwind_hdr);
}

static const u32 bad_cie, not_fde;
static const u32 *cie_for_fde(const u32 *fde, const struct unwind_table *);
static signed fde_pointer_type(const u32 *cie);

struct eh_frame_hdr_table_entry {
        unsigned long start, fde;
};

static int cmp_eh_frame_hdr_table_entries(const void *p1, const void *p2)
{
        const struct eh_frame_hdr_table_entry *e1 = p1;
        const struct eh_frame_hdr_table_entry *e2 = p2;

        return (e1->start > e2->start) - (e1->start < e2->start);
}

static void swap_eh_frame_hdr_table_entries(void *p1, void *p2, int size)
{
        struct eh_frame_hdr_table_entry *e1 = p1;
        struct eh_frame_hdr_table_entry *e2 = p2;
        unsigned long v;

        v = e1->start;
        e1->start = e2->start;
        e2->start = v;
        v = e1->fde;
        e1->fde = e2->fde;
        e2->fde = v;
}

static void __init setup_unwind_table(struct unwind_table *table,
                                        void *(*alloc)(unsigned long))
{
        const u8 *ptr;
        unsigned long tableSize = table->size, hdrSize;
        unsigned n;
        const u32 *fde;
        struct {
                u8 version;
                u8 eh_frame_ptr_enc;
                u8 fde_count_enc;
                u8 table_enc;
                unsigned long eh_frame_ptr;
                unsigned int fde_count;
                struct eh_frame_hdr_table_entry table[];
        } __attribute__((__packed__)) *header;

        if (table->header)
                return;

        if (table->hdrsz)
                printk(KERN_WARNING ".eh_frame_hdr for '%s' present but unusable\n",
                       table->name);

        if (tableSize & (sizeof(*fde) - 1))
                return;

        for (fde = table->address, n = 0;
             tableSize > sizeof(*fde) && tableSize - sizeof(*fde) >= *fde;
             tableSize -= sizeof(*fde) + *fde, fde += 1 + *fde / sizeof(*fde)) {
                const u32 *cie = cie_for_fde(fde, table);
                signed ptrType;

                if (cie == &not_fde)
                        continue;
                if (cie == NULL
                    || cie == &bad_cie
                    || (ptrType = fde_pointer_type(cie)) < 0)
                        return;
                ptr = (const u8 *)(fde + 2);
                if (!read_pointer(&ptr,
                                  (const u8 *)(fde + 1) + *fde,
                                  ptrType))
                        return;
                ++n;
        }

        if (tableSize || !n)
                return;

        hdrSize = 4 + sizeof(unsigned long) + sizeof(unsigned int)
                + 2 * n * sizeof(unsigned long);
        header = alloc(hdrSize);
        if (!header)
                return;
        header->version          = 1;
        header->eh_frame_ptr_enc = DW_EH_PE_abs|DW_EH_PE_native;
        header->fde_count_enc    = DW_EH_PE_abs|DW_EH_PE_data4;
        header->table_enc        = DW_EH_PE_abs|DW_EH_PE_native;
        put_unaligned((unsigned long)table->address, &header->eh_frame_ptr);
        BUILD_BUG_ON(offsetof(typeof(*header), fde_count)
                     % __alignof(typeof(header->fde_count)));
        header->fde_count        = n;

        BUILD_BUG_ON(offsetof(typeof(*header), table)
                     % __alignof(typeof(*header->table)));
        for (fde = table->address, tableSize = table->size, n = 0;
             tableSize;
             tableSize -= sizeof(*fde) + *fde, fde += 1 + *fde / sizeof(*fde)) {
                const u32 *cie = fde + 1 - fde[1] / sizeof(*fde);

                if (!fde[1])
                        continue; /* this is a CIE */
                ptr = (const u8 *)(fde + 2);
                header->table[n].start = read_pointer(&ptr,
                                                      (const u8 *)(fde + 1) + *fde,
                                                      fde_pointer_type(cie));
                header->table[n].fde = (unsigned long)fde;
                ++n;
        }
        WARN_ON(n != header->fde_count);

        sort(header->table,
             n,
             sizeof(*header->table),
             cmp_eh_frame_hdr_table_entries,
             swap_eh_frame_hdr_table_entries);

        table->hdrsz = hdrSize;
        smp_wmb();
        table->header = (const void *)header;
}

static void *__init balloc(unsigned long sz)
{
        return __alloc_bootmem_nopanic(sz,
                                       sizeof(unsigned int),
                                       __pa(MAX_DMA_ADDRESS));
}

void __init unwind_setup(void)
{
        setup_unwind_table(&root_table, balloc);
}

#ifdef CONFIG_MODULES

static struct unwind_table *last_table;

/* Must be called with module_mutex held. */
void *unwind_add_table(struct module *module,
                       const void *table_start,
                       unsigned long table_size)
{
        struct unwind_table *table;

        if (table_size <= 0)
                return NULL;

        table = kmalloc(sizeof(*table), GFP_KERNEL);
        if (!table)
                return NULL;

        init_unwind_table(table, module->name,
                          module->module_core, module->core_size,
                          module->module_init, module->init_size,
                          table_start, table_size,
                          NULL, 0);

        if (last_table)
                last_table->link = table;
        else
                root_table.link = table;
        last_table = table;

        return table;
}

struct unlink_table_info
{
        struct unwind_table *table;
        int init_only;
};

static int unlink_table(void *arg)
{
        struct unlink_table_info *info = arg;
        struct unwind_table *table = info->table, *prev;

        for (prev = &root_table; prev->link && prev->link != table; prev = prev->link)
                ;

        if (prev->link) {
                if (info->init_only) {
                        table->init.pc = 0;
                        table->init.range = 0;
                        info->table = NULL;
                } else {
                        prev->link = table->link;
                        if (!prev->link)
                                last_table = prev;
                }
        } else
                info->table = NULL;

        return 0;
}

/* Must be called with module_mutex held. */
void unwind_remove_table(void *handle, int init_only)
{
        struct unwind_table *table = handle;
        struct unlink_table_info info;

        if (!table || table == &root_table)
                return;

        if (init_only && table == last_table) {
                table->init.pc = 0;
                table->init.range = 0;
                return;
        }

        info.table = table;
        info.init_only = init_only;
        stop_machine_run(unlink_table, &info, NR_CPUS);

        if (info.table)
                kfree(table);
}

#endif /* CONFIG_MODULES */

static uleb128_t get_uleb128(const u8 **pcur, const u8 *end)
{
        const u8 *cur = *pcur;
        uleb128_t value;
        unsigned shift;

        for (shift = 0, value = 0; cur < end; shift += 7) {
                if (shift + 7 > 8 * sizeof(value)
                    && (*cur & 0x7fU) >= (1U << (8 * sizeof(value) - shift))) {
                        cur = end + 1;
                        break;
                }
                value |= (uleb128_t)(*cur & 0x7f) << shift;
                if (!(*cur++ & 0x80))
                        break;
        }
        *pcur = cur;

        return value;
}

static sleb128_t get_sleb128(const u8 **pcur, const u8 *end)
{
        const u8 *cur = *pcur;
        sleb128_t value;
        unsigned shift;

        for (shift = 0, value = 0; cur < end; shift += 7) {
                if (shift + 7 > 8 * sizeof(value)
                    && (*cur & 0x7fU) >= (1U << (8 * sizeof(value) - shift))) {
                        cur = end + 1;
                        break;
                }
                value |= (sleb128_t)(*cur & 0x7f) << shift;
                if (!(*cur & 0x80)) {
                        value |= -(*cur++ & 0x40) << shift;
                        break;
                }
        }
        *pcur = cur;

        return value;
}

static const u32 *cie_for_fde(const u32 *fde, const struct unwind_table *table)
{
        const u32 *cie;

        if (!*fde || (*fde & (sizeof(*fde) - 1)))
                return &bad_cie;
        if (!fde[1])
                return &not_fde; /* this is a CIE */
        if ((fde[1] & (sizeof(*fde) - 1))
            || fde[1] > (unsigned long)(fde + 1) - (unsigned long)table->address)
                return NULL; /* this is not a valid FDE */
        cie = fde + 1 - fde[1] / sizeof(*fde);
        if (*cie <= sizeof(*cie) + 4
            || *cie >= fde[1] - sizeof(*fde)
            || (*cie & (sizeof(*cie) - 1))
            || cie[1])
                return NULL; /* this is not a (valid) CIE */
        return cie;
}

static unsigned long read_pointer(const u8 **pLoc,
                                  const void *end,
                                  signed ptrType)
{
        unsigned long value = 0;
        union {
                const u8 *p8;
                const u16 *p16u;
                const s16 *p16s;
                const u32 *p32u;
                const s32 *p32s;
                const unsigned long *pul;
        } ptr;

        if (ptrType < 0 || ptrType == DW_EH_PE_omit)
                return 0;
        ptr.p8 = *pLoc;
        switch(ptrType & DW_EH_PE_FORM) {
        case DW_EH_PE_data2:
                if (end < (const void *)(ptr.p16u + 1))
                        return 0;
                if(ptrType & DW_EH_PE_signed)
                        value = get_unaligned(ptr.p16s++);
                else
                        value = get_unaligned(ptr.p16u++);
                break;
        case DW_EH_PE_data4:
#ifdef CONFIG_64BIT
                if (end < (const void *)(ptr.p32u + 1))
                        return 0;
                if(ptrType & DW_EH_PE_signed)
                        value = get_unaligned(ptr.p32s++);
                else
                        value = get_unaligned(ptr.p32u++);
                break;
        case DW_EH_PE_data8:
                BUILD_BUG_ON(sizeof(u64) != sizeof(value));
#else
                BUILD_BUG_ON(sizeof(u32) != sizeof(value));
#endif
        case DW_EH_PE_native:
                if (end < (const void *)(ptr.pul + 1))
                        return 0;
                value = get_unaligned(ptr.pul++);
                break;
        case DW_EH_PE_leb128:
                BUILD_BUG_ON(sizeof(uleb128_t) > sizeof(value));
                value = ptrType & DW_EH_PE_signed
                        ? get_sleb128(&ptr.p8, end)
                        : get_uleb128(&ptr.p8, end);
                if ((const void *)ptr.p8 > end)
                        return 0;
                break;
        default:
                return 0;
        }
        switch(ptrType & DW_EH_PE_ADJUST) {
        case DW_EH_PE_abs:
                break;
        case DW_EH_PE_pcrel:
                value += (unsigned long)*pLoc;
                break;
        default:
                return 0;
        }
        if ((ptrType & DW_EH_PE_indirect)
            && __get_user(value, (unsigned long *)value))
                return 0;
        *pLoc = ptr.p8;

        return value;
}

static signed fde_pointer_type(const u32 *cie)
{
        const u8 *ptr = (const u8 *)(cie + 2);
        unsigned version = *ptr;

        if (version != 1)
                return -1; /* unsupported */
        if (*++ptr) {
                const char *aug;
                const u8 *end = (const u8 *)(cie + 1) + *cie;
                uleb128_t len;

                /* check if augmentation size is first (and thus present) */
                if (*ptr != 'z')
                        return -1;
                /* check if augmentation string is nul-terminated */
                if ((ptr = memchr(aug = (const void *)ptr, 0, end - ptr)) == NULL)
                        return -1;
                ++ptr; /* skip terminator */
                get_uleb128(&ptr, end); /* skip code alignment */
                get_sleb128(&ptr, end); /* skip data alignment */
                /* skip return address column */
                version <= 1 ? (void)++ptr : (void)get_uleb128(&ptr, end);
                len = get_uleb128(&ptr, end); /* augmentation length */
                if (ptr + len < ptr || ptr + len > end)
                        return -1;
                end = ptr + len;
                while (*++aug) {
                        if (ptr >= end)
                                return -1;
                        switch(*aug) {
                        case 'L':
                                ++ptr;
                                break;
                        case 'P': {
                                        signed ptrType = *ptr++;

                                        if (!read_pointer(&ptr, end, ptrType) || ptr > end)
                                                return -1;
                                }
                                break;
                        case 'R':
                                return *ptr;
                        default:
                                return -1;
                        }
                }
        }
        return DW_EH_PE_native|DW_EH_PE_abs;
}

static int advance_loc(unsigned long delta, struct unwind_state *state)
{
        state->loc += delta * state->codeAlign;

        return delta > 0;
}

static void set_rule(uleb128_t reg,
                     enum item_location where,
                     uleb128_t value,
                     struct unwind_state *state)
{
        if (reg < ARRAY_SIZE(state->regs)) {
                state->regs[reg].where = where;
                state->regs[reg].value = value;
        }
}

static int processCFI(const u8 *start,
                      const u8 *end,
                      unsigned long targetLoc,
                      signed ptrType,
                      struct unwind_state *state)
{
        union {
                const u8 *p8;
                const u16 *p16;
                const u32 *p32;
        } ptr;
        int result = 1;

        if (start != state->cieStart) {
                state->loc = state->org;
                result = processCFI(state->cieStart, state->cieEnd, 0, ptrType, state);
                if (targetLoc == 0 && state->label == NULL)
                        return result;
        }
        for (ptr.p8 = start; result && ptr.p8 < end; ) {
                switch(*ptr.p8 >> 6) {
                        uleb128_t value;

                case 0:
                        switch(*ptr.p8++) {
                        case DW_CFA_nop:
                                break;
                        case DW_CFA_set_loc:
                                if ((state->loc = read_pointer(&ptr.p8, end, ptrType)) == 0)
                                        result = 0;
                                break;
                        case DW_CFA_advance_loc1:
                                result = ptr.p8 < end && advance_loc(*ptr.p8++, state);
                                break;
                        case DW_CFA_advance_loc2:
                                result = ptr.p8 <= end + 2
                                         && advance_loc(*ptr.p16++, state);
                                break;
                        case DW_CFA_advance_loc4:
                                result = ptr.p8 <= end + 4
                                         && advance_loc(*ptr.p32++, state);
                                break;
                        case DW_CFA_offset_extended:
                                value = get_uleb128(&ptr.p8, end);
                                set_rule(value, Memory, get_uleb128(&ptr.p8, end), state);
                                break;
                        case DW_CFA_val_offset:
                                value = get_uleb128(&ptr.p8, end);
                                set_rule(value, Value, get_uleb128(&ptr.p8, end), state);
                                break;
                        case DW_CFA_offset_extended_sf:
                                value = get_uleb128(&ptr.p8, end);
                                set_rule(value, Memory, get_sleb128(&ptr.p8, end), state);
                                break;
                        case DW_CFA_val_offset_sf:
                                value = get_uleb128(&ptr.p8, end);
                                set_rule(value, Value, get_sleb128(&ptr.p8, end), state);
                                break;
                        case DW_CFA_restore_extended:
                        case DW_CFA_undefined:
                        case DW_CFA_same_value:
                                set_rule(get_uleb128(&ptr.p8, end), Nowhere, 0, state);
                                break;
                        case DW_CFA_register:
                                value = get_uleb128(&ptr.p8, end);
                                set_rule(value,
                                         Register,
                                         get_uleb128(&ptr.p8, end), state);
                                break;
                        case DW_CFA_remember_state:
                                if (ptr.p8 == state->label) {
                                        state->label = NULL;
                                        return 1;
                                }
                                if (state->stackDepth >= MAX_STACK_DEPTH)
                                        return 0;
                                state->stack[state->stackDepth++] = ptr.p8;
                                break;
                        case DW_CFA_restore_state:
                                if (state->stackDepth) {
                                        const uleb128_t loc = state->loc;
                                        const u8 *label = state->label;

                                        state->label = state->stack[state->stackDepth - 1];
                                        memcpy(&state->cfa, &badCFA, sizeof(state->cfa));
                                        memset(state->regs, 0, sizeof(state->regs));
                                        state->stackDepth = 0;
                                        result = processCFI(start, end, 0, ptrType, state);
                                        state->loc = loc;
                                        state->label = label;
                                } else
                                        return 0;
                                break;
                        case DW_CFA_def_cfa:
                                state->cfa.reg = get_uleb128(&ptr.p8, end);
                                /*nobreak*/
                        case DW_CFA_def_cfa_offset:
                                state->cfa.offs = get_uleb128(&ptr.p8, end);
                                break;
                        case DW_CFA_def_cfa_sf:
                                state->cfa.reg = get_uleb128(&ptr.p8, end);
                                /*nobreak*/
                        case DW_CFA_def_cfa_offset_sf:
                                state->cfa.offs = get_sleb128(&ptr.p8, end)
                                                  * state->dataAlign;
                                break;
                        case DW_CFA_def_cfa_register:
                                state->cfa.reg = get_uleb128(&ptr.p8, end);
                                break;
                        /*todo case DW_CFA_def_cfa_expression: */
                        /*todo case DW_CFA_expression: */
                        /*todo case DW_CFA_val_expression: */
                        case DW_CFA_GNU_args_size:
                                get_uleb128(&ptr.p8, end);
                                break;
                        case DW_CFA_GNU_negative_offset_extended:
                                value = get_uleb128(&ptr.p8, end);
                                set_rule(value,
                                         Memory,
                                         (uleb128_t)0 - get_uleb128(&ptr.p8, end), state);
                                break;
                        case DW_CFA_GNU_window_save:
                        default:
                                result = 0;
                                break;
                        }
                        break;
                case 1:
                        result = advance_loc(*ptr.p8++ & 0x3f, state);
                        break;
                case 2:
                        value = *ptr.p8++ & 0x3f;
                        set_rule(value, Memory, get_uleb128(&ptr.p8, end), state);
                        break;
                case 3:
                        set_rule(*ptr.p8++ & 0x3f, Nowhere, 0, state);
                        break;
                }
                if (ptr.p8 > end)
                        result = 0;
                if (result && targetLoc != 0 && targetLoc < state->loc)
                        return 1;
        }

        return result
           && ptr.p8 == end
           && (targetLoc == 0
            || (/*todo While in theory this should apply, gcc in practice omits
                  everything past the function prolog, and hence the location
                  never reaches the end of the function.
                targetLoc < state->loc &&*/ state->label == NULL));
}

/* Unwind to previous to frame.  Returns 0 if successful, negative
 * number in case of an error. */
int unwind(struct unwind_frame_info *frame)
{
#define FRAME_REG(r, t) (((t *)frame)[reg_info[r].offs])
        const u32 *fde = NULL, *cie = NULL;
        const u8 *ptr = NULL, *end = NULL;
        unsigned long pc = UNW_PC(frame) - frame->call_frame;
        unsigned long startLoc = 0, endLoc = 0, cfa;
        unsigned i;
        signed ptrType = -1;
        uleb128_t retAddrReg = 0;
        const struct unwind_table *table;
        struct unwind_state state;

        if (UNW_PC(frame) == 0)
                return -EINVAL;
        if ((table = find_table(pc)) != NULL
            && !(table->size & (sizeof(*fde) - 1))) {
                const u8 *hdr = table->header;
                unsigned long tableSize;

                smp_rmb();
                if (hdr && hdr[0] == 1) {
                        switch(hdr[3] & DW_EH_PE_FORM) {
                        case DW_EH_PE_native: tableSize = sizeof(unsigned long); break;
                        case DW_EH_PE_data2: tableSize = 2; break;
                        case DW_EH_PE_data4: tableSize = 4; break;
                        case DW_EH_PE_data8: tableSize = 8; break;
                        default: tableSize = 0; break;
                        }
                        ptr = hdr + 4;
                        end = hdr + table->hdrsz;
                        if (tableSize
                            && read_pointer(&ptr, end, hdr[1])
                               == (unsigned long)table->address
                            && (i = read_pointer(&ptr, end, hdr[2])) > 0
                            && i == (end - ptr) / (2 * tableSize)
                            && !((end - ptr) % (2 * tableSize))) {
                                do {
                                        const u8 *cur = ptr + (i / 2) * (2 * tableSize);

                                        startLoc = read_pointer(&cur,
                                                                cur + tableSize,
                                                                hdr[3]);
                                        if (pc < startLoc)
                                                i /= 2;
                                        else {
                                                ptr = cur - tableSize;
                                                i = (i + 1) / 2;
                                        }
                                } while (startLoc && i > 1);
                                if (i == 1
                                    && (startLoc = read_pointer(&ptr,
                                                                ptr + tableSize,
                                                                hdr[3])) != 0
                                    && pc >= startLoc)
                                        fde = (void *)read_pointer(&ptr,
                                                                   ptr + tableSize,
                                                                   hdr[3]);
                        }
                }

                if (fde != NULL) {
                        cie = cie_for_fde(fde, table);
                        ptr = (const u8 *)(fde + 2);
                        if(cie != NULL
                           && cie != &bad_cie
                           && cie != &not_fde
                           && (ptrType = fde_pointer_type(cie)) >= 0
                           && read_pointer(&ptr,
                                           (const u8 *)(fde + 1) + *fde,
                                           ptrType) == startLoc) {
                                if (!(ptrType & DW_EH_PE_indirect))
                                        ptrType &= DW_EH_PE_FORM|DW_EH_PE_signed;
                                endLoc = startLoc
                                         + read_pointer(&ptr,
                                                        (const u8 *)(fde + 1) + *fde,
                                                        ptrType);
                                if(pc >= endLoc)
                                        fde = NULL;
                        } else
                                fde = NULL;
                }
                if (fde == NULL) {
                        for (fde = table->address, tableSize = table->size;
                             cie = NULL, tableSize > sizeof(*fde)
                             && tableSize - sizeof(*fde) >= *fde;
                             tableSize -= sizeof(*fde) + *fde,
                             fde += 1 + *fde / sizeof(*fde)) {
                                cie = cie_for_fde(fde, table);
                                if (cie == &bad_cie) {
                                        cie = NULL;
                                        break;
                                }
                                if (cie == NULL
                                    || cie == &not_fde
                                    || (ptrType = fde_pointer_type(cie)) < 0)
                                        continue;
                                ptr = (const u8 *)(fde + 2);
                                startLoc = read_pointer(&ptr,
                                                        (const u8 *)(fde + 1) + *fde,
                                                        ptrType);
                                if (!startLoc)
                                        continue;
                                if (!(ptrType & DW_EH_PE_indirect))
                                        ptrType &= DW_EH_PE_FORM|DW_EH_PE_signed;
                                endLoc = startLoc
                                         + read_pointer(&ptr,
                                                        (const u8 *)(fde + 1) + *fde,
                                                        ptrType);
                                if (pc >= startLoc && pc < endLoc)
                                        break;
                        }
                }
        }
        if (cie != NULL) {
                memset(&state, 0, sizeof(state));
                state.cieEnd = ptr; /* keep here temporarily */
                ptr = (const u8 *)(cie + 2);
                end = (const u8 *)(cie + 1) + *cie;
                frame->call_frame = 1;
                if ((state.version = *ptr) != 1)
                        cie = NULL; /* unsupported version */
                else if (*++ptr) {
                        /* check if augmentation size is first (and thus present) */
                        if (*ptr == 'z') {
                                while (++ptr < end && *ptr) {
                                        switch(*ptr) {
                                        /* check for ignorable (or already handled)
                                         * nul-terminated augmentation string */
                                        case 'L':
                                        case 'P':
                                        case 'R':
                                                continue;
                                        case 'S':
                                                frame->call_frame = 0;
                                                continue;
                                        default:
                                                break;
                                        }
                                        break;
                                }
                        }
                        if (ptr >= end || *ptr)
                                cie = NULL;
                }
                ++ptr;
        }
        if (cie != NULL) {
                /* get code aligment factor */
                state.codeAlign = get_uleb128(&ptr, end);
                /* get data aligment factor */
                state.dataAlign = get_sleb128(&ptr, end);
                if (state.codeAlign == 0 || state.dataAlign == 0 || ptr >= end)
                        cie = NULL;
                else {
                        retAddrReg = state.version <= 1 ? *ptr++ : get_uleb128(&ptr, end);
                        /* skip augmentation */
                        if (((const char *)(cie + 2))[1] == 'z') {
                                uleb128_t augSize = get_uleb128(&ptr, end);

                                ptr += augSize;
                        }
                        if (ptr > end
                           || retAddrReg >= ARRAY_SIZE(reg_info)
                           || REG_INVALID(retAddrReg)
                           || reg_info[retAddrReg].width != sizeof(unsigned long))
                                cie = NULL;
                }
        }
        if (cie != NULL) {
                state.cieStart = ptr;
                ptr = state.cieEnd;
                state.cieEnd = end;
                end = (const u8 *)(fde + 1) + *fde;
                /* skip augmentation */
                if (((const char *)(cie + 2))[1] == 'z') {
                        uleb128_t augSize = get_uleb128(&ptr, end);

                        if ((ptr += augSize) > end)
                                fde = NULL;
                }
        }
        if (cie == NULL || fde == NULL) {
#ifdef CONFIG_FRAME_POINTER
                unsigned long top, bottom;

                top = STACK_TOP(frame->task);
                bottom = STACK_BOTTOM(frame->task);
# if FRAME_RETADDR_OFFSET < 0
                if (UNW_SP(frame) < top
                    && UNW_FP(frame) <= UNW_SP(frame)
                    && bottom < UNW_FP(frame)
# else
                if (UNW_SP(frame) > top
                    && UNW_FP(frame) >= UNW_SP(frame)
                    && bottom > UNW_FP(frame)
# endif
                   && !((UNW_SP(frame) | UNW_FP(frame))
                        & (sizeof(unsigned long) - 1))) {
                        unsigned long link;

                        if (!__get_user(link,
                                        (unsigned long *)(UNW_FP(frame)
                                                          + FRAME_LINK_OFFSET))
# if FRAME_RETADDR_OFFSET < 0
                           && link > bottom && link < UNW_FP(frame)
# else
                           && link > UNW_FP(frame) && link < bottom
# endif
                           && !(link & (sizeof(link) - 1))
                           && !__get_user(UNW_PC(frame),
                                          (unsigned long *)(UNW_FP(frame)
                                                            + FRAME_RETADDR_OFFSET))) {
                                UNW_SP(frame) = UNW_FP(frame) + FRAME_RETADDR_OFFSET
# if FRAME_RETADDR_OFFSET < 0
                                        -
# else
                                        +
# endif
                                          sizeof(UNW_PC(frame));
                                UNW_FP(frame) = link;
                                return 0;
                        }
                }
#endif
                return -ENXIO;
        }
        state.org = startLoc;
        memcpy(&state.cfa, &badCFA, sizeof(state.cfa));
        /* process instructions */
        if (!processCFI(ptr, end, pc, ptrType, &state)
           || state.loc > endLoc
           || state.regs[retAddrReg].where == Nowhere
           || state.cfa.reg >= ARRAY_SIZE(reg_info)
           || reg_info[state.cfa.reg].width != sizeof(unsigned long)
           || state.cfa.offs % sizeof(unsigned long))
                return -EIO;
        /* update frame */
#ifndef CONFIG_AS_CFI_SIGNAL_FRAME
        if(frame->call_frame
           && !UNW_DEFAULT_RA(state.regs[retAddrReg], state.dataAlign))
                frame->call_frame = 0;
#endif
        cfa = FRAME_REG(state.cfa.reg, unsigned long) + state.cfa.offs;
        startLoc = min((unsigned long)UNW_SP(frame), cfa);
        endLoc = max((unsigned long)UNW_SP(frame), cfa);
        if (STACK_LIMIT(startLoc) != STACK_LIMIT(endLoc)) {
                startLoc = min(STACK_LIMIT(cfa), cfa);
                endLoc = max(STACK_LIMIT(cfa), cfa);
        }
#ifndef CONFIG_64BIT
# define CASES CASE(8); CASE(16); CASE(32)
#else
# define CASES CASE(8); CASE(16); CASE(32); CASE(64)
#endif
        for (i = 0; i < ARRAY_SIZE(state.regs); ++i) {
                if (REG_INVALID(i)) {
                        if (state.regs[i].where == Nowhere)
                                continue;
                        return -EIO;
                }
                switch(state.regs[i].where) {
                default:
                        break;
                case Register:
                        if (state.regs[i].value >= ARRAY_SIZE(reg_info)
                           || REG_INVALID(state.regs[i].value)
                           || reg_info[i].width > reg_info[state.regs[i].value].width)
                                return -EIO;
                        switch(reg_info[state.regs[i].value].width) {
#define CASE(n) \
                        case sizeof(u##n): \
                                state.regs[i].value = FRAME_REG(state.regs[i].value, \
                                                                const u##n); \
                                break
                        CASES;
#undef CASE
                        default:
                                return -EIO;
                        }
                        break;
                }
        }
        for (i = 0; i < ARRAY_SIZE(state.regs); ++i) {
                if (REG_INVALID(i))
                        continue;
                switch(state.regs[i].where) {
                case Nowhere:
                        if (reg_info[i].width != sizeof(UNW_SP(frame))
                           || &FRAME_REG(i, __typeof__(UNW_SP(frame)))
                              != &UNW_SP(frame))
                                continue;
                        UNW_SP(frame) = cfa;
                        break;
                case Register:
                        switch(reg_info[i].width) {
#define CASE(n) case sizeof(u##n): \
                                FRAME_REG(i, u##n) = state.regs[i].value; \
                                break
                        CASES;
#undef CASE
                        default:
                                return -EIO;
                        }
                        break;
                case Value:
                        if (reg_info[i].width != sizeof(unsigned long))
                                return -EIO;
                        FRAME_REG(i, unsigned long) = cfa + state.regs[i].value
                                                            * state.dataAlign;
                        break;
                case Memory: {
                                unsigned long addr = cfa + state.regs[i].value
                                                           * state.dataAlign;

                                if ((state.regs[i].value * state.dataAlign)
                                    % sizeof(unsigned long)
                                    || addr < startLoc
                                    || addr + sizeof(unsigned long) < addr
                                    || addr + sizeof(unsigned long) > endLoc)
                                        return -EIO;
                                switch(reg_info[i].width) {
#define CASE(n)     case sizeof(u##n): \
                                        __get_user(FRAME_REG(i, u##n), (u##n *)addr); \
                                        break
                                CASES;
#undef CASE
                                default:
                                        return -EIO;
                                }
                        }
                        break;
                }
        }

        return 0;
#undef CASES
#undef FRAME_REG
}
EXPORT_SYMBOL(unwind);

int unwind_init_frame_info(struct unwind_frame_info *info,
                           struct task_struct *tsk,
                           /*const*/ struct pt_regs *regs)
{
        info->task = tsk;
        info->call_frame = 0;
        arch_unw_init_frame_info(info, regs);

        return 0;
}
EXPORT_SYMBOL(unwind_init_frame_info);

/*
 * Prepare to unwind a blocked task.
 */
int unwind_init_blocked(struct unwind_frame_info *info,
                        struct task_struct *tsk)
{
        info->task = tsk;
        info->call_frame = 0;
        arch_unw_init_blocked(info);

        return 0;
}
EXPORT_SYMBOL(unwind_init_blocked);

/*
 * Prepare to unwind the currently running thread.
 */
int unwind_init_running(struct unwind_frame_info *info,
                        asmlinkage int (*callback)(struct unwind_frame_info *,
                                                   void *arg),
                        void *arg)
{
        info->task = current;
        info->call_frame = 0;

        return arch_unwind_init_running(info, callback, arg);
}
EXPORT_SYMBOL(unwind_init_running);

/*
 * Unwind until the return pointer is in user-land (or until an error
 * occurs).  Returns 0 if successful, negative number in case of
 * error.
 */
int unwind_to_user(struct unwind_frame_info *info)
{
        while (!arch_unw_user_mode(info)) {
                int err = unwind(info);

                if (err < 0)
                        return err;
        }

        return 0;
}
EXPORT_SYMBOL(unwind_to_user);