perf/core: Fix address filter parser for multiple filters

[mirror_ubuntu-jammy-kernel.git] / kernel / kallsyms.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * kallsyms.c: in-kernel printing of symbolic oopses and stack traces.
 *
 * Rewritten and vastly simplified by Rusty Russell for in-kernel
 * module loader:
 *   Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
 *
 * ChangeLog:
 *
 * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
 *      Changed the compression method from stem compression to "table lookup"
 *      compression (see scripts/kallsyms.c for a more complete description)
 */
#include <linux/kallsyms.h>
#include <linux/init.h>
#include <linux/seq_file.h>
#include <linux/fs.h>
#include <linux/kdb.h>
#include <linux/err.h>
#include <linux/proc_fs.h>
#include <linux/sched.h>        /* for cond_resched */
#include <linux/ctype.h>
#include <linux/slab.h>
#include <linux/filter.h>
#include <linux/ftrace.h>
#include <linux/kprobes.h>
#include <linux/build_bug.h>
#include <linux/compiler.h>
#include <linux/module.h>
#include <linux/kernel.h>

/*
 * These will be re-linked against their real values
 * during the second link stage.
 */
extern const unsigned long kallsyms_addresses[] __weak;
extern const int kallsyms_offsets[] __weak;
extern const u8 kallsyms_names[] __weak;

/*
 * Tell the compiler that the count isn't in the small data section if the arch
 * has one (eg: FRV).
 */
extern const unsigned int kallsyms_num_syms
__section(".rodata") __attribute__((weak));

extern const unsigned long kallsyms_relative_base
__section(".rodata") __attribute__((weak));

extern const char kallsyms_token_table[] __weak;
extern const u16 kallsyms_token_index[] __weak;

extern const unsigned int kallsyms_markers[] __weak;

/*
 * Expand a compressed symbol data into the resulting uncompressed string,
 * if uncompressed string is too long (>= maxlen), it will be truncated,
 * given the offset to where the symbol is in the compressed stream.
 */
static unsigned int kallsyms_expand_symbol(unsigned int off,
                                           char *result, size_t maxlen)
{
        int len, skipped_first = 0;
        const char *tptr;
        const u8 *data;

        /* Get the compressed symbol length from the first symbol byte. */
        data = &kallsyms_names[off];
        len = *data;
        data++;

        /*
         * Update the offset to return the offset for the next symbol on
         * the compressed stream.
         */
        off += len + 1;

        /*
         * For every byte on the compressed symbol data, copy the table
         * entry for that byte.
         */
        while (len) {
                tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
                data++;
                len--;

                while (*tptr) {
                        if (skipped_first) {
                                if (maxlen <= 1)
                                        goto tail;
                                *result = *tptr;
                                result++;
                                maxlen--;
                        } else
                                skipped_first = 1;
                        tptr++;
                }
        }

tail:
        if (maxlen)
                *result = '\0';

        /* Return to offset to the next symbol. */
        return off;
}

/*
 * Get symbol type information. This is encoded as a single char at the
 * beginning of the symbol name.
 */
static char kallsyms_get_symbol_type(unsigned int off)
{
        /*
         * Get just the first code, look it up in the token table,
         * and return the first char from this token.
         */
        return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
}


/*
 * Find the offset on the compressed stream given and index in the
 * kallsyms array.
 */
static unsigned int get_symbol_offset(unsigned long pos)
{
        const u8 *name;
        int i;

        /*
         * Use the closest marker we have. We have markers every 256 positions,
         * so that should be close enough.
         */
        name = &kallsyms_names[kallsyms_markers[pos >> 8]];

        /*
         * Sequentially scan all the symbols up to the point we're searching
         * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
         * so we just need to add the len to the current pointer for every
         * symbol we wish to skip.
         */
        for (i = 0; i < (pos & 0xFF); i++)
                name = name + (*name) + 1;

        return name - kallsyms_names;
}

static unsigned long kallsyms_sym_address(int idx)
{
        if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
                return kallsyms_addresses[idx];

        /* values are unsigned offsets if --absolute-percpu is not in effect */
        if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
                return kallsyms_relative_base + (u32)kallsyms_offsets[idx];

        /* ...otherwise, positive offsets are absolute values */
        if (kallsyms_offsets[idx] >= 0)
                return kallsyms_offsets[idx];

        /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
        return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
}

#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
/*
 * LLVM appends a hash to static function names when ThinLTO and CFI are
 * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b.
 * This causes confusion and potentially breaks user space tools, so we
 * strip the suffix from expanded symbol names.
 */
static inline bool cleanup_symbol_name(char *s)
{
        char *res;

        res = strrchr(s, '$');
        if (res)
                *res = '\0';

        return res != NULL;
}
#else
static inline bool cleanup_symbol_name(char *s) { return false; }
#endif

/* Lookup the address for this symbol. Returns 0 if not found. */
unsigned long kallsyms_lookup_name(const char *name)
{
        char namebuf[KSYM_NAME_LEN];
        unsigned long i;
        unsigned int off;

        for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
                off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));

                if (strcmp(namebuf, name) == 0)
                        return kallsyms_sym_address(i);

                if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)
                        return kallsyms_sym_address(i);
        }
        return module_kallsyms_lookup_name(name);
}

#ifdef CONFIG_LIVEPATCH
/*
 * Iterate over all symbols in vmlinux.  For symbols from modules use
 * module_kallsyms_on_each_symbol instead.
 */
int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
                                      unsigned long),
                            void *data)
{
        char namebuf[KSYM_NAME_LEN];
        unsigned long i;
        unsigned int off;
        int ret;

        for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
                off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
                ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
                if (ret != 0)
                        return ret;
        }
        return 0;
}
#endif /* CONFIG_LIVEPATCH */

static unsigned long get_symbol_pos(unsigned long addr,
                                    unsigned long *symbolsize,
                                    unsigned long *offset)
{
        unsigned long symbol_start = 0, symbol_end = 0;
        unsigned long i, low, high, mid;

        /* This kernel should never had been booted. */
        if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
                BUG_ON(!kallsyms_addresses);
        else
                BUG_ON(!kallsyms_offsets);

        /* Do a binary search on the sorted kallsyms_addresses array. */
        low = 0;
        high = kallsyms_num_syms;

        while (high - low > 1) {
                mid = low + (high - low) / 2;
                if (kallsyms_sym_address(mid) <= addr)
                        low = mid;
                else
                        high = mid;
        }

        /*
         * Search for the first aliased symbol. Aliased
         * symbols are symbols with the same address.
         */
        while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
                --low;

        symbol_start = kallsyms_sym_address(low);

        /* Search for next non-aliased symbol. */
        for (i = low + 1; i < kallsyms_num_syms; i++) {
                if (kallsyms_sym_address(i) > symbol_start) {
                        symbol_end = kallsyms_sym_address(i);
                        break;
                }
        }

        /* If we found no next symbol, we use the end of the section. */
        if (!symbol_end) {
                if (is_kernel_inittext(addr))
                        symbol_end = (unsigned long)_einittext;
                else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
                        symbol_end = (unsigned long)_end;
                else
                        symbol_end = (unsigned long)_etext;
        }

        if (symbolsize)
                *symbolsize = symbol_end - symbol_start;
        if (offset)
                *offset = addr - symbol_start;

        return low;
}

/*
 * Lookup an address but don't bother to find any names.
 */
int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
                                unsigned long *offset)
{
        char namebuf[KSYM_NAME_LEN];

        if (is_ksym_addr(addr)) {
                get_symbol_pos(addr, symbolsize, offset);
                return 1;
        }
        return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
               !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
}

static const char *kallsyms_lookup_buildid(unsigned long addr,
                        unsigned long *symbolsize,
                        unsigned long *offset, char **modname,
                        const unsigned char **modbuildid, char *namebuf)
{
        const char *ret;

        namebuf[KSYM_NAME_LEN - 1] = 0;
        namebuf[0] = 0;

        if (is_ksym_addr(addr)) {
                unsigned long pos;

                pos = get_symbol_pos(addr, symbolsize, offset);
                /* Grab name */
                kallsyms_expand_symbol(get_symbol_offset(pos),
                                       namebuf, KSYM_NAME_LEN);
                if (modname)
                        *modname = NULL;
                if (modbuildid)
                        *modbuildid = NULL;

                ret = namebuf;
                goto found;
        }

        /* See if it's in a module or a BPF JITed image. */
        ret = module_address_lookup(addr, symbolsize, offset,
                                    modname, modbuildid, namebuf);
        if (!ret)
                ret = bpf_address_lookup(addr, symbolsize,
                                         offset, modname, namebuf);

        if (!ret)
                ret = ftrace_mod_address_lookup(addr, symbolsize,
                                                offset, modname, namebuf);

found:
        cleanup_symbol_name(namebuf);
        return ret;
}

/*
 * Lookup an address
 * - modname is set to NULL if it's in the kernel.
 * - We guarantee that the returned name is valid until we reschedule even if.
 *   It resides in a module.
 * - We also guarantee that modname will be valid until rescheduled.
 */
const char *kallsyms_lookup(unsigned long addr,
                            unsigned long *symbolsize,
                            unsigned long *offset,
                            char **modname, char *namebuf)
{
        return kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
                                       NULL, namebuf);
}

int lookup_symbol_name(unsigned long addr, char *symname)
{
        int res;

        symname[0] = '\0';
        symname[KSYM_NAME_LEN - 1] = '\0';

        if (is_ksym_addr(addr)) {
                unsigned long pos;

                pos = get_symbol_pos(addr, NULL, NULL);
                /* Grab name */
                kallsyms_expand_symbol(get_symbol_offset(pos),
                                       symname, KSYM_NAME_LEN);
                goto found;
        }
        /* See if it's in a module. */
        res = lookup_module_symbol_name(addr, symname);
        if (res)
                return res;

found:
        cleanup_symbol_name(symname);
        return 0;
}

int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
                        unsigned long *offset, char *modname, char *name)
{
        int res;

        name[0] = '\0';
        name[KSYM_NAME_LEN - 1] = '\0';

        if (is_ksym_addr(addr)) {
                unsigned long pos;

                pos = get_symbol_pos(addr, size, offset);
                /* Grab name */
                kallsyms_expand_symbol(get_symbol_offset(pos),
                                       name, KSYM_NAME_LEN);
                modname[0] = '\0';
                goto found;
        }
        /* See if it's in a module. */
        res = lookup_module_symbol_attrs(addr, size, offset, modname, name);
        if (res)
                return res;

found:
        cleanup_symbol_name(name);
        return 0;
}

/* Look up a kernel symbol and return it in a text buffer. */
static int __sprint_symbol(char *buffer, unsigned long address,
                           int symbol_offset, int add_offset, int add_buildid)
{
        char *modname;
        const unsigned char *buildid;
        const char *name;
        unsigned long offset, size;
        int len;

        address += symbol_offset;
        name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
                                       buffer);
        if (!name)
                return sprintf(buffer, "0x%lx", address - symbol_offset);

        if (name != buffer)
                strcpy(buffer, name);
        len = strlen(buffer);
        offset -= symbol_offset;

        if (add_offset)
                len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);

        if (modname) {
                len += sprintf(buffer + len, " [%s", modname);
#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
                if (add_buildid && buildid) {
                        /* build ID should match length of sprintf */
#if IS_ENABLED(CONFIG_MODULES)
                        static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
#endif
                        len += sprintf(buffer + len, " %20phN", buildid);
                }
#endif
                len += sprintf(buffer + len, "]");
        }

        return len;
}

/**
 * sprint_symbol - Look up a kernel symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function looks up a kernel symbol with @address and stores its name,
 * offset, size and module name to @buffer if possible. If no symbol was found,
 * just saves its @address as is.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_symbol(char *buffer, unsigned long address)
{
        return __sprint_symbol(buffer, address, 0, 1, 0);
}
EXPORT_SYMBOL_GPL(sprint_symbol);

/**
 * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function looks up a kernel symbol with @address and stores its name,
 * offset, size, module name and module build ID to @buffer if possible. If no
 * symbol was found, just saves its @address as is.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_symbol_build_id(char *buffer, unsigned long address)
{
        return __sprint_symbol(buffer, address, 0, 1, 1);
}
EXPORT_SYMBOL_GPL(sprint_symbol_build_id);

/**
 * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function looks up a kernel symbol with @address and stores its name
 * and module name to @buffer if possible. If no symbol was found, just saves
 * its @address as is.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_symbol_no_offset(char *buffer, unsigned long address)
{
        return __sprint_symbol(buffer, address, 0, 0, 0);
}
EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);

/**
 * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function is for stack backtrace and does the same thing as
 * sprint_symbol() but with modified/decreased @address. If there is a
 * tail-call to the function marked "noreturn", gcc optimized out code after
 * the call so that the stack-saved return address could point outside of the
 * caller. This function ensures that kallsyms will find the original caller
 * by decreasing @address.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_backtrace(char *buffer, unsigned long address)
{
        return __sprint_symbol(buffer, address, -1, 1, 0);
}

/**
 * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function is for stack backtrace and does the same thing as
 * sprint_symbol() but with modified/decreased @address. If there is a
 * tail-call to the function marked "noreturn", gcc optimized out code after
 * the call so that the stack-saved return address could point outside of the
 * caller. This function ensures that kallsyms will find the original caller
 * by decreasing @address. This function also appends the module build ID to
 * the @buffer if @address is within a kernel module.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_backtrace_build_id(char *buffer, unsigned long address)
{
        return __sprint_symbol(buffer, address, -1, 1, 1);
}

/* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
struct kallsym_iter {
        loff_t pos;
        loff_t pos_arch_end;
        loff_t pos_mod_end;
        loff_t pos_ftrace_mod_end;
        loff_t pos_bpf_end;
        unsigned long value;
        unsigned int nameoff; /* If iterating in core kernel symbols. */
        char type;
        char name[KSYM_NAME_LEN];
        char module_name[MODULE_NAME_LEN];
        int exported;
        int show_value;
};

int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
                            char *type, char *name)
{
        return -EINVAL;
}

static int get_ksymbol_arch(struct kallsym_iter *iter)
{
        int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
                                   &iter->value, &iter->type,
                                   iter->name);

        if (ret < 0) {
                iter->pos_arch_end = iter->pos;
                return 0;
        }

        return 1;
}

static int get_ksymbol_mod(struct kallsym_iter *iter)
{
        int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
                                     &iter->value, &iter->type,
                                     iter->name, iter->module_name,
                                     &iter->exported);
        if (ret < 0) {
                iter->pos_mod_end = iter->pos;
                return 0;
        }

        return 1;
}

/*
 * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
 * purposes. In that case "__builtin__ftrace" is used as a module name, even
 * though "__builtin__ftrace" is not a module.
 */
static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
{
        int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
                                         &iter->value, &iter->type,
                                         iter->name, iter->module_name,
                                         &iter->exported);
        if (ret < 0) {
                iter->pos_ftrace_mod_end = iter->pos;
                return 0;
        }

        return 1;
}

static int get_ksymbol_bpf(struct kallsym_iter *iter)
{
        int ret;

        strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
        iter->exported = 0;
        ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
                              &iter->value, &iter->type,
                              iter->name);
        if (ret < 0) {
                iter->pos_bpf_end = iter->pos;
                return 0;
        }

        return 1;
}

/*
 * This uses "__builtin__kprobes" as a module name for symbols for pages
 * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
 * module.
 */
static int get_ksymbol_kprobe(struct kallsym_iter *iter)
{
        strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
        iter->exported = 0;
        return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
                                  &iter->value, &iter->type,
                                  iter->name) < 0 ? 0 : 1;
}

/* Returns space to next name. */
static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
{
        unsigned off = iter->nameoff;

        iter->module_name[0] = '\0';
        iter->value = kallsyms_sym_address(iter->pos);

        iter->type = kallsyms_get_symbol_type(off);

        off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));

        return off - iter->nameoff;
}

static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
{
        iter->name[0] = '\0';
        iter->nameoff = get_symbol_offset(new_pos);
        iter->pos = new_pos;
        if (new_pos == 0) {
                iter->pos_arch_end = 0;
                iter->pos_mod_end = 0;
                iter->pos_ftrace_mod_end = 0;
                iter->pos_bpf_end = 0;
        }
}

/*
 * The end position (last + 1) of each additional kallsyms section is recorded
 * in iter->pos_..._end as each section is added, and so can be used to
 * determine which get_ksymbol_...() function to call next.
 */
static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
{
        iter->pos = pos;

        if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
            get_ksymbol_arch(iter))
                return 1;

        if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
            get_ksymbol_mod(iter))
                return 1;

        if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
            get_ksymbol_ftrace_mod(iter))
                return 1;

        if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
            get_ksymbol_bpf(iter))
                return 1;

        return get_ksymbol_kprobe(iter);
}

/* Returns false if pos at or past end of file. */
static int update_iter(struct kallsym_iter *iter, loff_t pos)
{
        /* Module symbols can be accessed randomly. */
        if (pos >= kallsyms_num_syms)
                return update_iter_mod(iter, pos);

        /* If we're not on the desired position, reset to new position. */
        if (pos != iter->pos)
                reset_iter(iter, pos);

        iter->nameoff += get_ksymbol_core(iter);
        iter->pos++;

        return 1;
}

static void *s_next(struct seq_file *m, void *p, loff_t *pos)
{
        (*pos)++;

        if (!update_iter(m->private, *pos))
                return NULL;
        return p;
}

static void *s_start(struct seq_file *m, loff_t *pos)
{
        if (!update_iter(m->private, *pos))
                return NULL;
        return m->private;
}

static void s_stop(struct seq_file *m, void *p)
{
}

static int s_show(struct seq_file *m, void *p)
{
        void *value;
        struct kallsym_iter *iter = m->private;

        /* Some debugging symbols have no name.  Ignore them. */
        if (!iter->name[0])
                return 0;

        value = iter->show_value ? (void *)iter->value : NULL;

        if (iter->module_name[0]) {
                char type;

                /*
                 * Label it "global" if it is exported,
                 * "local" if not exported.
                 */
                type = iter->exported ? toupper(iter->type) :
                                        tolower(iter->type);
                seq_printf(m, "%px %c %s\t[%s]\n", value,
                           type, iter->name, iter->module_name);
        } else
                seq_printf(m, "%px %c %s\n", value,
                           iter->type, iter->name);
        return 0;
}

static const struct seq_operations kallsyms_op = {
        .start = s_start,
        .next = s_next,
        .stop = s_stop,
        .show = s_show
};

static inline int kallsyms_for_perf(void)
{
#ifdef CONFIG_PERF_EVENTS
        extern int sysctl_perf_event_paranoid;
        if (sysctl_perf_event_paranoid <= 1)
                return 1;
#endif
        return 0;
}

/*
 * We show kallsyms information even to normal users if we've enabled
 * kernel profiling and are explicitly not paranoid (so kptr_restrict
 * is clear, and sysctl_perf_event_paranoid isn't set).
 *
 * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
 * block even that).
 */
bool kallsyms_show_value(const struct cred *cred)
{
        switch (kptr_restrict) {
        case 0:
                if (kallsyms_for_perf())
                        return true;
                fallthrough;
        case 1:
                if (security_capable(cred, &init_user_ns, CAP_SYSLOG,
                                     CAP_OPT_NOAUDIT) == 0)
                        return true;
                fallthrough;
        default:
                return false;
        }
}

static int kallsyms_open(struct inode *inode, struct file *file)
{
        /*
         * We keep iterator in m->private, since normal case is to
         * s_start from where we left off, so we avoid doing
         * using get_symbol_offset for every symbol.
         */
        struct kallsym_iter *iter;
        iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
        if (!iter)
                return -ENOMEM;
        reset_iter(iter, 0);

        /*
         * Instead of checking this on every s_show() call, cache
         * the result here at open time.
         */
        iter->show_value = kallsyms_show_value(file->f_cred);
        return 0;
}

#ifdef  CONFIG_KGDB_KDB
const char *kdb_walk_kallsyms(loff_t *pos)
{
        static struct kallsym_iter kdb_walk_kallsyms_iter;
        if (*pos == 0) {
                memset(&kdb_walk_kallsyms_iter, 0,
                       sizeof(kdb_walk_kallsyms_iter));
                reset_iter(&kdb_walk_kallsyms_iter, 0);
        }
        while (1) {
                if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
                        return NULL;
                ++*pos;
                /* Some debugging symbols have no name.  Ignore them. */
                if (kdb_walk_kallsyms_iter.name[0])
                        return kdb_walk_kallsyms_iter.name;
        }
}
#endif  /* CONFIG_KGDB_KDB */

static const struct proc_ops kallsyms_proc_ops = {
        .proc_open      = kallsyms_open,
        .proc_read      = seq_read,
        .proc_lseek     = seq_lseek,
        .proc_release   = seq_release_private,
};

static int __init kallsyms_init(void)
{
        proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
        return 0;
}
device_initcall(kallsyms_init);