path: root/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>
#include <linux/bsearch.h>
#include <linux/btf_ids.h>

#include "kallsyms_internal.h"

/*
 * 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++;
	off++;

	/* If MSB is 1, it is a "big" symbol, so needs an additional byte. */
	if ((len & 0x80) != 0) {
		len = (len & 0x7F) | (*data << 7);
		data++;
		off++;
	}

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

	/*
	 * 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, len;

	/*
	 * 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++) {
		len = *name;

		/*
		 * If MSB is 1, it is a "big" symbol, so we need to look into
		 * the next byte (and skip it, too).
		 */
		if ((len & 0x80) != 0)
			len = ((len & 0x7F) | (name[1] << 7)) + 1;

		name = name + len + 1;
	}

	return name - kallsyms_names;
}

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];
}

static bool cleanup_symbol_name(char *s)
{
	char *res;

	if (!IS_ENABLED(CONFIG_LTO_CLANG))
		return false;

	/*
	 * LLVM appends various suffixes for local functions and variables that
	 * must be promoted to global scope as part of LTO.  This can break
	 * hooking of static functions with kprobes. '.' is not a valid
	 * character in an identifier in C. Suffixes observed:
	 * - foo.llvm.[0-9a-f]+
	 * - foo.[0-9a-f]+
	 */
	res = strchr(s, '.');
	if (res) {
		*res = '\0';
		return true;
	}

	return false;
}

static int compare_symbol_name(const char *name, char *namebuf)
{
	int ret;

	ret = strcmp(name, namebuf);
	if (!ret)
		return ret;

	if (cleanup_symbol_name(namebuf) && !strcmp(name, namebuf))
		return 0;

	return ret;
}

static unsigned int get_symbol_seq(int index)
{
	unsigned int i, seq = 0;

	for (i = 0; i < 3; i++)
		seq = (seq << 8) | kallsyms_seqs_of_names[3 * index + i];

	return seq;
}

static int kallsyms_lookup_names(const char *name,
				 unsigned int *start,
				 unsigned int *end)
{
	int ret;
	int low, mid, high;
	unsigned int seq, off;
	char namebuf[