xref: /linux/kernel/kallsyms.c (revision 4413e16d9d21673bb5048a2e542f1aaa00015c2e)
1 /*
2  * kallsyms.c: in-kernel printing of symbolic oopses and stack traces.
3  *
4  * Rewritten and vastly simplified by Rusty Russell for in-kernel
5  * module loader:
6  *   Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
7  *
8  * ChangeLog:
9  *
10  * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
11  *      Changed the compression method from stem compression to "table lookup"
12  *      compression (see scripts/kallsyms.c for a more complete description)
13  */
14 #include <linux/kallsyms.h>
15 #include <linux/module.h>
16 #include <linux/init.h>
17 #include <linux/seq_file.h>
18 #include <linux/fs.h>
19 #include <linux/kdb.h>
20 #include <linux/err.h>
21 #include <linux/proc_fs.h>
22 #include <linux/sched.h>	/* for cond_resched */
23 #include <linux/mm.h>
24 #include <linux/ctype.h>
25 #include <linux/slab.h>
26 
27 #include <asm/sections.h>
28 
29 #ifdef CONFIG_KALLSYMS_ALL
30 #define all_var 1
31 #else
32 #define all_var 0
33 #endif
34 
35 /*
36  * These will be re-linked against their real values
37  * during the second link stage.
38  */
39 extern const unsigned long kallsyms_addresses[] __attribute__((weak));
40 extern const u8 kallsyms_names[] __attribute__((weak));
41 
42 /*
43  * Tell the compiler that the count isn't in the small data section if the arch
44  * has one (eg: FRV).
45  */
46 extern const unsigned long kallsyms_num_syms
47 __attribute__((weak, section(".rodata")));
48 
49 extern const u8 kallsyms_token_table[] __attribute__((weak));
50 extern const u16 kallsyms_token_index[] __attribute__((weak));
51 
52 extern const unsigned long kallsyms_markers[] __attribute__((weak));
53 
54 static inline int is_kernel_inittext(unsigned long addr)
55 {
56 	if (addr >= (unsigned long)_sinittext
57 	    && addr <= (unsigned long)_einittext)
58 		return 1;
59 	return 0;
60 }
61 
62 static inline int is_kernel_text(unsigned long addr)
63 {
64 	if ((addr >= (unsigned long)_stext && addr <= (unsigned long)_etext) ||
65 	    arch_is_kernel_text(addr))
66 		return 1;
67 	return in_gate_area_no_mm(addr);
68 }
69 
70 static inline int is_kernel(unsigned long addr)
71 {
72 	if (addr >= (unsigned long)_stext && addr <= (unsigned long)_end)
73 		return 1;
74 	return in_gate_area_no_mm(addr);
75 }
76 
77 static int is_ksym_addr(unsigned long addr)
78 {
79 	if (all_var)
80 		return is_kernel(addr);
81 
82 	return is_kernel_text(addr) || is_kernel_inittext(addr);
83 }
84 
85 /*
86  * Expand a compressed symbol data into the resulting uncompressed string,
87  * given the offset to where the symbol is in the compressed stream.
88  */
89 static unsigned int kallsyms_expand_symbol(unsigned int off, char *result)
90 {
91 	int len, skipped_first = 0;
92 	const u8 *tptr, *data;
93 
94 	/* Get the compressed symbol length from the first symbol byte. */
95 	data = &kallsyms_names[off];
96 	len = *data;
97 	data++;
98 
99 	/*
100 	 * Update the offset to return the offset for the next symbol on
101 	 * the compressed stream.
102 	 */
103 	off += len + 1;
104 
105 	/*
106 	 * For every byte on the compressed symbol data, copy the table
107 	 * entry for that byte.
108 	 */
109 	while (len) {
110 		tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
111 		data++;
112 		len--;
113 
114 		while (*tptr) {
115 			if (skipped_first) {
116 				*result = *tptr;
117 				result++;
118 			} else
119 				skipped_first = 1;
120 			tptr++;
121 		}
122 	}
123 
124 	*result = '\0';
125 
126 	/* Return to offset to the next symbol. */
127 	return off;
128 }
129 
130 /*
131  * Get symbol type information. This is encoded as a single char at the
132  * beginning of the symbol name.
133  */
134 static char kallsyms_get_symbol_type(unsigned int off)
135 {
136 	/*
137 	 * Get just the first code, look it up in the token table,
138 	 * and return the first char from this token.
139 	 */
140 	return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
141 }
142 
143 
144 /*
145  * Find the offset on the compressed stream given and index in the
146  * kallsyms array.
147  */
148 static unsigned int get_symbol_offset(unsigned long pos)
149 {
150 	const u8 *name;
151 	int i;
152 
153 	/*
154 	 * Use the closest marker we have. We have markers every 256 positions,
155 	 * so that should be close enough.
156 	 */
157 	name = &kallsyms_names[kallsyms_markers[pos >> 8]];
158 
159 	/*
160 	 * Sequentially scan all the symbols up to the point we're searching
161 	 * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
162 	 * so we just need to add the len to the current pointer for every
163 	 * symbol we wish to skip.
164 	 */
165 	for (i = 0; i < (pos & 0xFF); i++)
166 		name = name + (*name) + 1;
167 
168 	return name - kallsyms_names;
169 }
170 
171 /* Lookup the address for this symbol. Returns 0 if not found. */
172 unsigned long kallsyms_lookup_name(const char *name)
173 {
174 	char namebuf[KSYM_NAME_LEN];
175 	unsigned long i;
176 	unsigned int off;
177 
178 	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
179 		off = kallsyms_expand_symbol(off, namebuf);
180 
181 		if (strcmp(namebuf, name) == 0)
182 			return kallsyms_addresses[i];
183 	}
184 	return module_kallsyms_lookup_name(name);
185 }
186 EXPORT_SYMBOL_GPL(kallsyms_lookup_name);
187 
188 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
189 				      unsigned long),
190 			    void *data)
191 {
192 	char namebuf[KSYM_NAME_LEN];
193 	unsigned long i;
194 	unsigned int off;
195 	int ret;
196 
197 	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
198 		off = kallsyms_expand_symbol(off, namebuf);
199 		ret = fn(data, namebuf, NULL, kallsyms_addresses[i]);
200 		if (ret != 0)
201 			return ret;
202 	}
203 	return module_kallsyms_on_each_symbol(fn, data);
204 }
205 EXPORT_SYMBOL_GPL(kallsyms_on_each_symbol);
206 
207 static unsigned long get_symbol_pos(unsigned long addr,
208 				    unsigned long *symbolsize,
209 				    unsigned long *offset)
210 {
211 	unsigned long symbol_start = 0, symbol_end = 0;
212 	unsigned long i, low, high, mid;
213 
214 	/* This kernel should never had been booted. */
215 	BUG_ON(!kallsyms_addresses);
216 
217 	/* Do a binary search on the sorted kallsyms_addresses array. */
218 	low = 0;
219 	high = kallsyms_num_syms;
220 
221 	while (high - low > 1) {
222 		mid = low + (high - low) / 2;
223 		if (kallsyms_addresses[mid] <= addr)
224 			low = mid;
225 		else
226 			high = mid;
227 	}
228 
229 	/*
230 	 * Search for the first aliased symbol. Aliased
231 	 * symbols are symbols with the same address.
232 	 */
233 	while (low && kallsyms_addresses[low-1] == kallsyms_addresses[low])
234 		--low;
235 
236 	symbol_start = kallsyms_addresses[low];
237 
238 	/* Search for next non-aliased symbol. */
239 	for (i = low + 1; i < kallsyms_num_syms; i++) {
240 		if (kallsyms_addresses[i] > symbol_start) {
241 			symbol_end = kallsyms_addresses[i];
242 			break;
243 		}
244 	}
245 
246 	/* If we found no next symbol, we use the end of the section. */
247 	if (!symbol_end) {
248 		if (is_kernel_inittext(addr))
249 			symbol_end = (unsigned long)_einittext;
250 		else if (all_var)
251 			symbol_end = (unsigned long)_end;
252 		else
253 			symbol_end = (unsigned long)_etext;
254 	}
255 
256 	if (symbolsize)
257 		*symbolsize = symbol_end - symbol_start;
258 	if (offset)
259 		*offset = addr - symbol_start;
260 
261 	return low;
262 }
263 
264 /*
265  * Lookup an address but don't bother to find any names.
266  */
267 int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
268 				unsigned long *offset)
269 {
270 	char namebuf[KSYM_NAME_LEN];
271 	if (is_ksym_addr(addr))
272 		return !!get_symbol_pos(addr, symbolsize, offset);
273 
274 	return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf);
275 }
276 
277 /*
278  * Lookup an address
279  * - modname is set to NULL if it's in the kernel.
280  * - We guarantee that the returned name is valid until we reschedule even if.
281  *   It resides in a module.
282  * - We also guarantee that modname will be valid until rescheduled.
283  */
284 const char *kallsyms_lookup(unsigned long addr,
285 			    unsigned long *symbolsize,
286 			    unsigned long *offset,
287 			    char **modname, char *namebuf)
288 {
289 	namebuf[KSYM_NAME_LEN - 1] = 0;
290 	namebuf[0] = 0;
291 
292 	if (is_ksym_addr(addr)) {
293 		unsigned long pos;
294 
295 		pos = get_symbol_pos(addr, symbolsize, offset);
296 		/* Grab name */
297 		kallsyms_expand_symbol(get_symbol_offset(pos), namebuf);
298 		if (modname)
299 			*modname = NULL;
300 		return namebuf;
301 	}
302 
303 	/* See if it's in a module. */
304 	return module_address_lookup(addr, symbolsize, offset, modname,
305 				     namebuf);
306 }
307 
308 int lookup_symbol_name(unsigned long addr, char *symname)
309 {
310 	symname[0] = '\0';
311 	symname[KSYM_NAME_LEN - 1] = '\0';
312 
313 	if (is_ksym_addr(addr)) {
314 		unsigned long pos;
315 
316 		pos = get_symbol_pos(addr, NULL, NULL);
317 		/* Grab name */
318 		kallsyms_expand_symbol(get_symbol_offset(pos), symname);
319 		return 0;
320 	}
321 	/* See if it's in a module. */
322 	return lookup_module_symbol_name(addr, symname);
323 }
324 
325 int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
326 			unsigned long *offset, char *modname, char *name)
327 {
328 	name[0] = '\0';
329 	name[KSYM_NAME_LEN - 1] = '\0';
330 
331 	if (is_ksym_addr(addr)) {
332 		unsigned long pos;
333 
334 		pos = get_symbol_pos(addr, size, offset);
335 		/* Grab name */
336 		kallsyms_expand_symbol(get_symbol_offset(pos), name);
337 		modname[0] = '\0';
338 		return 0;
339 	}
340 	/* See if it's in a module. */
341 	return lookup_module_symbol_attrs(addr, size, offset, modname, name);
342 }
343 
344 /* Look up a kernel symbol and return it in a text buffer. */
345 static int __sprint_symbol(char *buffer, unsigned long address,
346 			   int symbol_offset, int add_offset)
347 {
348 	char *modname;
349 	const char *name;
350 	unsigned long offset, size;
351 	int len;
352 
353 	address += symbol_offset;
354 	name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
355 	if (!name)
356 		return sprintf(buffer, "0x%lx", address);
357 
358 	if (name != buffer)
359 		strcpy(buffer, name);
360 	len = strlen(buffer);
361 	offset -= symbol_offset;
362 
363 	if (add_offset)
364 		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
365 
366 	if (modname)
367 		len += sprintf(buffer + len, " [%s]", modname);
368 
369 	return len;
370 }
371 
372 /**
373  * sprint_symbol - Look up a kernel symbol and return it in a text buffer
374  * @buffer: buffer to be stored
375  * @address: address to lookup
376  *
377  * This function looks up a kernel symbol with @address and stores its name,
378  * offset, size and module name to @buffer if possible. If no symbol was found,
379  * just saves its @address as is.
380  *
381  * This function returns the number of bytes stored in @buffer.
382  */
383 int sprint_symbol(char *buffer, unsigned long address)
384 {
385 	return __sprint_symbol(buffer, address, 0, 1);
386 }
387 EXPORT_SYMBOL_GPL(sprint_symbol);
388 
389 /**
390  * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
391  * @buffer: buffer to be stored
392  * @address: address to lookup
393  *
394  * This function looks up a kernel symbol with @address and stores its name
395  * and module name to @buffer if possible. If no symbol was found, just saves
396  * its @address as is.
397  *
398  * This function returns the number of bytes stored in @buffer.
399  */
400 int sprint_symbol_no_offset(char *buffer, unsigned long address)
401 {
402 	return __sprint_symbol(buffer, address, 0, 0);
403 }
404 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
405 
406 /**
407  * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
408  * @buffer: buffer to be stored
409  * @address: address to lookup
410  *
411  * This function is for stack backtrace and does the same thing as
412  * sprint_symbol() but with modified/decreased @address. If there is a
413  * tail-call to the function marked "noreturn", gcc optimized out code after
414  * the call so that the stack-saved return address could point outside of the
415  * caller. This function ensures that kallsyms will find the original caller
416  * by decreasing @address.
417  *
418  * This function returns the number of bytes stored in @buffer.
419  */
420 int sprint_backtrace(char *buffer, unsigned long address)
421 {
422 	return __sprint_symbol(buffer, address, -1, 1);
423 }
424 
425 /* Look up a kernel symbol and print it to the kernel messages. */
426 void __print_symbol(const char *fmt, unsigned long address)
427 {
428 	char buffer[KSYM_SYMBOL_LEN];
429 
430 	sprint_symbol(buffer, address);
431 
432 	printk(fmt, buffer);
433 }
434 EXPORT_SYMBOL(__print_symbol);
435 
436 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
437 struct kallsym_iter {
438 	loff_t pos;
439 	unsigned long value;
440 	unsigned int nameoff; /* If iterating in core kernel symbols. */
441 	char type;
442 	char name[KSYM_NAME_LEN];
443 	char module_name[MODULE_NAME_LEN];
444 	int exported;
445 };
446 
447 static int get_ksymbol_mod(struct kallsym_iter *iter)
448 {
449 	if (module_get_kallsym(iter->pos - kallsyms_num_syms, &iter->value,
450 				&iter->type, iter->name, iter->module_name,
451 				&iter->exported) < 0)
452 		return 0;
453 	return 1;
454 }
455 
456 /* Returns space to next name. */
457 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
458 {
459 	unsigned off = iter->nameoff;
460 
461 	iter->module_name[0] = '\0';
462 	iter->value = kallsyms_addresses[iter->pos];
463 
464 	iter->type = kallsyms_get_symbol_type(off);
465 
466 	off = kallsyms_expand_symbol(off, iter->name);
467 
468 	return off - iter->nameoff;
469 }
470 
471 static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
472 {
473 	iter->name[0] = '\0';
474 	iter->nameoff = get_symbol_offset(new_pos);
475 	iter->pos = new_pos;
476 }
477 
478 /* Returns false if pos at or past end of file. */
479 static int update_iter(struct kallsym_iter *iter, loff_t pos)
480 {
481 	/* Module symbols can be accessed randomly. */
482 	if (pos >= kallsyms_num_syms) {
483 		iter->pos = pos;
484 		return get_ksymbol_mod(iter);
485 	}
486 
487 	/* If we're not on the desired position, reset to new position. */
488 	if (pos != iter->pos)
489 		reset_iter(iter, pos);
490 
491 	iter->nameoff += get_ksymbol_core(iter);
492 	iter->pos++;
493 
494 	return 1;
495 }
496 
497 static void *s_next(struct seq_file *m, void *p, loff_t *pos)
498 {
499 	(*pos)++;
500 
501 	if (!update_iter(m->private, *pos))
502 		return NULL;
503 	return p;
504 }
505 
506 static void *s_start(struct seq_file *m, loff_t *pos)
507 {
508 	if (!update_iter(m->private, *pos))
509 		return NULL;
510 	return m->private;
511 }
512 
513 static void s_stop(struct seq_file *m, void *p)
514 {
515 }
516 
517 static int s_show(struct seq_file *m, void *p)
518 {
519 	struct kallsym_iter *iter = m->private;
520 
521 	/* Some debugging symbols have no name.  Ignore them. */
522 	if (!iter->name[0])
523 		return 0;
524 
525 	if (iter->module_name[0]) {
526 		char type;
527 
528 		/*
529 		 * Label it "global" if it is exported,
530 		 * "local" if not exported.
531 		 */
532 		type = iter->exported ? toupper(iter->type) :
533 					tolower(iter->type);
534 		seq_printf(m, "%pK %c %s\t[%s]\n", (void *)iter->value,
535 			   type, iter->name, iter->module_name);
536 	} else
537 		seq_printf(m, "%pK %c %s\n", (void *)iter->value,
538 			   iter->type, iter->name);
539 	return 0;
540 }
541 
542 static const struct seq_operations kallsyms_op = {
543 	.start = s_start,
544 	.next = s_next,
545 	.stop = s_stop,
546 	.show = s_show
547 };
548 
549 static int kallsyms_open(struct inode *inode, struct file *file)
550 {
551 	/*
552 	 * We keep iterator in m->private, since normal case is to
553 	 * s_start from where we left off, so we avoid doing
554 	 * using get_symbol_offset for every symbol.
555 	 */
556 	struct kallsym_iter *iter;
557 	int ret;
558 
559 	iter = kmalloc(sizeof(*iter), GFP_KERNEL);
560 	if (!iter)
561 		return -ENOMEM;
562 	reset_iter(iter, 0);
563 
564 	ret = seq_open(file, &kallsyms_op);
565 	if (ret == 0)
566 		((struct seq_file *)file->private_data)->private = iter;
567 	else
568 		kfree(iter);
569 	return ret;
570 }
571 
572 #ifdef	CONFIG_KGDB_KDB
573 const char *kdb_walk_kallsyms(loff_t *pos)
574 {
575 	static struct kallsym_iter kdb_walk_kallsyms_iter;
576 	if (*pos == 0) {
577 		memset(&kdb_walk_kallsyms_iter, 0,
578 		       sizeof(kdb_walk_kallsyms_iter));
579 		reset_iter(&kdb_walk_kallsyms_iter, 0);
580 	}
581 	while (1) {
582 		if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
583 			return NULL;
584 		++*pos;
585 		/* Some debugging symbols have no name.  Ignore them. */
586 		if (kdb_walk_kallsyms_iter.name[0])
587 			return kdb_walk_kallsyms_iter.name;
588 	}
589 }
590 #endif	/* CONFIG_KGDB_KDB */
591 
592 static const struct file_operations kallsyms_operations = {
593 	.open = kallsyms_open,
594 	.read = seq_read,
595 	.llseek = seq_lseek,
596 	.release = seq_release_private,
597 };
598 
599 static int __init kallsyms_init(void)
600 {
601 	proc_create("kallsyms", 0444, NULL, &kallsyms_operations);
602 	return 0;
603 }
604 device_initcall(kallsyms_init);
605