kallsyms.c 16.5 KB
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/*
 * 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/module.h>
#include <linux/init.h>
#include <linux/seq_file.h>
#include <linux/fs.h>
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#include <linux/kdb.h>
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#include <linux/err.h>
#include <linux/proc_fs.h>
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#include <linux/sched.h>	/* for cond_resched */
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#include <linux/mm.h>
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#include <linux/ctype.h>
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#include <linux/slab.h>
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#include <linux/filter.h>
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#include <linux/compiler.h>
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#include <asm/sections.h>

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/*
 * These will be re-linked against their real values
 * during the second link stage.
 */
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extern const unsigned long kallsyms_addresses[] __weak;
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extern const int kallsyms_offsets[] __weak;
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extern const u8 kallsyms_names[] __weak;
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/*
 * Tell the compiler that the count isn't in the small data section if the arch
 * has one (eg: FRV).
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 */
extern const unsigned long kallsyms_num_syms
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__attribute__((weak, section(".rodata")));
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extern const unsigned long kallsyms_relative_base
__attribute__((weak, section(".rodata")));

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extern const u8 kallsyms_token_table[] __weak;
extern const u16 kallsyms_token_index[] __weak;
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extern const unsigned long kallsyms_markers[] __weak;
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static inline int is_kernel_inittext(unsigned long addr)
{
	if (addr >= (unsigned long)_sinittext
	    && addr <= (unsigned long)_einittext)
		return 1;
	return 0;
}

static inline int is_kernel_text(unsigned long addr)
{
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	if ((addr >= (unsigned long)_stext && addr <= (unsigned long)_etext) ||
	    arch_is_kernel_text(addr))
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		return 1;
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	return in_gate_area_no_mm(addr);
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}

static inline int is_kernel(unsigned long addr)
{
	if (addr >= (unsigned long)_stext && addr <= (unsigned long)_end)
		return 1;
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	return in_gate_area_no_mm(addr);
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}

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static int is_ksym_addr(unsigned long addr)
{
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	if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
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		return is_kernel(addr);

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	return is_kernel_text(addr) || is_kernel_inittext(addr);
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}

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

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

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	/*
	 * 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]];
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		data++;
		len--;

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

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tail:
	if (maxlen)
		*result = '\0';
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	/* Return to offset to the next symbol. */
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	return off;
}

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/*
 * Get symbol type information. This is encoded as a single char at the
 * beginning of the symbol name.
 */
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static char kallsyms_get_symbol_type(unsigned int off)
{
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	/*
	 * 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]]];
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}


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

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	/*
	 * 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]];
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	/*
	 * 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++)
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		name = name + (*name) + 1;

	return name - kallsyms_names;
}

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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];
}

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

	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
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		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
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		if (strcmp(namebuf, name) == 0)
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			return kallsyms_sym_address(i);
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	}
	return module_kallsyms_lookup_name(name);
}
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EXPORT_SYMBOL_GPL(kallsyms_lookup_name);
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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++) {
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		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
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		ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
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		if (ret != 0)
			return ret;
	}
	return module_kallsyms_on_each_symbol(fn, data);
}
EXPORT_SYMBOL_GPL(kallsyms_on_each_symbol);

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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;

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	/* This kernel should never had been booted. */
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	if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
		BUG_ON(!kallsyms_addresses);
	else
		BUG_ON(!kallsyms_offsets);
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	/* Do a binary search on the sorted kallsyms_addresses array. */
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	low = 0;
	high = kallsyms_num_syms;

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

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

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

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

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	if (symbolsize)
		*symbolsize = symbol_end - symbol_start;
	if (offset)
		*offset = addr - symbol_start;
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	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)
{
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	char namebuf[KSYM_NAME_LEN];
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	if (is_ksym_addr(addr))
		return !!get_symbol_pos(addr, symbolsize, offset);
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	return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
	       !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
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}

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/*
 * Lookup an address
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 * - 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.
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 */
const char *kallsyms_lookup(unsigned long addr,
			    unsigned long *symbolsize,
			    unsigned long *offset,
			    char **modname, char *namebuf)
{
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	const char *ret;

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

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	if (is_ksym_addr(addr)) {
		unsigned long pos;
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		pos = get_symbol_pos(addr, symbolsize, offset);
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		/* Grab name */
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		kallsyms_expand_symbol(get_symbol_offset(pos),
				       namebuf, KSYM_NAME_LEN);
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		if (modname)
			*modname = NULL;
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		return namebuf;
	}

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

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int lookup_symbol_name(unsigned long addr, char *symname)
{
	symname[0] = '\0';
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	symname[KSYM_NAME_LEN - 1] = '\0';
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	if (is_ksym_addr(addr)) {
		unsigned long pos;

		pos = get_symbol_pos(addr, NULL, NULL);
		/* Grab name */
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		kallsyms_expand_symbol(get_symbol_offset(pos),
				       symname, KSYM_NAME_LEN);
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		return 0;
	}
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	/* See if it's in a module. */
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	return lookup_module_symbol_name(addr, symname);
}

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int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
			unsigned long *offset, char *modname, char *name)
{
	name[0] = '\0';
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	name[KSYM_NAME_LEN - 1] = '\0';
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	if (is_ksym_addr(addr)) {
		unsigned long pos;

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

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/* Look up a kernel symbol and return it in a text buffer. */
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static int __sprint_symbol(char *buffer, unsigned long address,
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			   int symbol_offset, int add_offset)
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{
	char *modname;
	const char *name;
	unsigned long offset, size;
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	int len;
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	address += symbol_offset;
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	name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
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	if (!name)
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		return sprintf(buffer, "0x%lx", address - symbol_offset);
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	if (name != buffer)
		strcpy(buffer, name);
	len = strlen(buffer);
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	offset -= symbol_offset;
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	if (add_offset)
		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);

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	if (modname)
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		len += sprintf(buffer + len, " [%s]", modname);
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	return len;
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}
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/**
 * 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)
{
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	return __sprint_symbol(buffer, address, 0, 1);
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}
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EXPORT_SYMBOL_GPL(sprint_symbol);
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/**
 * 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);
}
EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);

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/**
 * 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)
{
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	return __sprint_symbol(buffer, address, -1, 1);
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}

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/* Look up a kernel symbol and print it to the kernel messages. */
void __print_symbol(const char *fmt, unsigned long address)
{
	char buffer[KSYM_SYMBOL_LEN];

	sprint_symbol(buffer, address);

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	printk(fmt, buffer);
}
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EXPORT_SYMBOL(__print_symbol);
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/* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
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struct kallsym_iter {
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	loff_t pos;
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	loff_t pos_mod_end;
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	unsigned long value;
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	unsigned int nameoff; /* If iterating in core kernel symbols. */
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	char type;
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	char name[KSYM_NAME_LEN];
	char module_name[MODULE_NAME_LEN];
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	int exported;
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};

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

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	return 1;
}

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static int get_ksymbol_bpf(struct kallsym_iter *iter)
{
	iter->module_name[0] = '\0';
	iter->exported = 0;
	return bpf_get_kallsym(iter->pos - iter->pos_mod_end,
			       &iter->value, &iter->type,
			       iter->name) < 0 ? 0 : 1;
}

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

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

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	off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
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	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;
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	if (new_pos == 0)
		iter->pos_mod_end = 0;
}

static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
{
	iter->pos = pos;

	if (iter->pos_mod_end > 0 &&
	    iter->pos_mod_end < iter->pos)
		return get_ksymbol_bpf(iter);

	if (!get_ksymbol_mod(iter))
		return get_ksymbol_bpf(iter);

	return 1;
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}

/* 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. */
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	if (pos >= kallsyms_num_syms)
		return update_iter_mod(iter, pos);
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	/* 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)
{
	struct kallsym_iter *iter = m->private;

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

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

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

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

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

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	return 0;
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}

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#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 */

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static const struct file_operations kallsyms_operations = {
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	.open = kallsyms_open,
	.read = seq_read,
	.llseek = seq_lseek,
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	.release = seq_release_private,
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};

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