common/kallsyms.c

#include <common.h>
#include <init.h>
#include <kallsyms.h>
#include <asm-generic/sections.h>

#ifndef DOXYGEN_SHOULD_SKIP_THIS

/* These will be re-linked against their real values during the second link stage */
extern const unsigned long kallsyms_addresses[] __attribute__((weak));
extern const unsigned long kallsyms_num_syms __attribute__((weak));
extern const u8 kallsyms_names[] __attribute__((weak));

extern const u8 kallsyms_token_table[] __attribute__((weak));
extern const u16 kallsyms_token_index[] __attribute__((weak));

extern const unsigned long kallsyms_markers[] __attribute__((weak));

#endif /* DOXYGEN_SHOULD_SKIP_THIS */

static inline int is_kernel_text(unsigned long addr)
{
	if ((addr >= (unsigned long)_stext && addr <= (unsigned long)_etext))
		return 1;
	return 0;
}

/* expand a compressed symbol data into the resulting uncompressed string,
   given the offset to where the symbol is in the compressed stream */
static unsigned int kallsyms_expand_symbol(unsigned int off, char *result)
{
	int len, skipped_first = 0;
	const u8 *tptr, *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) {
				*result = *tptr;
				result++;
			} else
				skipped_first = 1;
			tptr++;
		}
	}

	*result = '\0';

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

/*
 * 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;
}

/* 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);

		if (strcmp(namebuf, name) == 0)
			return kallsyms_addresses[i];
	}

	/* module kallsyms not yet supported */
	return 0;
}

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. */
	BUG_ON(!kallsyms_addresses);

	/* 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_addresses[mid] <= addr)
			low = mid;
		else
			high = mid;
	}

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

	symbol_start = kallsyms_addresses[low];

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

	/* If we found no next symbol, we use the end of the section. */
	if (!symbol_end) {
		symbol_end = (unsigned long)_etext;
	}

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

	return low;
}

/*
 * 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)
{
	namebuf[KSYM_NAME_LEN - 1] = 0;
	namebuf[0] = 0;

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

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

	/* moduled not yet supported in kallsyms */
	return NULL;
}

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

	name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
	if (!name)
		return sprintf(buffer, "0x%lx", address);

	if (name != buffer)
		strcpy(buffer, name);
	len = strlen(buffer);
	buffer += len;

	if (modname)
		len += sprintf(buffer, "+%#lx/%#lx [%s]",
						offset, size, modname);
	else
		len += sprintf(buffer, "+%#lx/%#lx", offset, size);

	return len;
}
EXPORT_SYMBOL_GPL(sprint_symbol);