1 // SPDX-License-Identifier: GPL-2.0-only
3 * kallsyms.c: in-kernel printing of symbolic oopses and stack traces.
5 * Rewritten and vastly simplified by Rusty Russell for in-kernel
7 * Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
11 * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
12 * Changed the compression method from stem compression to "table lookup"
13 * compression (see scripts/kallsyms.c for a more complete description)
15 #include <linux/kallsyms.h>
16 #include <linux/init.h>
17 #include <linux/seq_file.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/ctype.h>
24 #include <linux/slab.h>
25 #include <linux/filter.h>
26 #include <linux/ftrace.h>
27 #include <linux/kprobes.h>
28 #include <linux/build_bug.h>
29 #include <linux/compiler.h>
30 #include <linux/module.h>
31 #include <linux/kernel.h>
32 #include <linux/bsearch.h>
33 #include <linux/btf_ids.h>
35 #include "kallsyms_internal.h"
38 * Expand a compressed symbol data into the resulting uncompressed string,
39 * if uncompressed string is too long (>= maxlen), it will be truncated,
40 * given the offset to where the symbol is in the compressed stream.
42 static unsigned int kallsyms_expand_symbol(unsigned int off,
43 char *result, size_t maxlen)
45 int len, skipped_first = 0;
49 /* Get the compressed symbol length from the first symbol byte. */
50 data = &kallsyms_names[off];
55 /* If MSB is 1, it is a "big" symbol, so needs an additional byte. */
56 if ((len & 0x80) != 0) {
57 len = (len & 0x7F) | (*data << 7);
63 * Update the offset to return the offset for the next symbol on
64 * the compressed stream.
69 * For every byte on the compressed symbol data, copy the table
70 * entry for that byte.
73 tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
94 /* Return to offset to the next symbol. */
99 * Get symbol type information. This is encoded as a single char at the
100 * beginning of the symbol name.
102 static char kallsyms_get_symbol_type(unsigned int off)
105 * Get just the first code, look it up in the token table,
106 * and return the first char from this token.
108 return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
113 * Find the offset on the compressed stream given and index in the
116 static unsigned int get_symbol_offset(unsigned long pos)
122 * Use the closest marker we have. We have markers every 256 positions,
123 * so that should be close enough.
125 name = &kallsyms_names[kallsyms_markers[pos >> 8]];
128 * Sequentially scan all the symbols up to the point we're searching
129 * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
130 * so we just need to add the len to the current pointer for every
131 * symbol we wish to skip.
133 for (i = 0; i < (pos & 0xFF); i++) {
137 * If MSB is 1, it is a "big" symbol, so we need to look into
138 * the next byte (and skip it, too).
140 if ((len & 0x80) != 0)
141 len = ((len & 0x7F) | (name[1] << 7)) + 1;
143 name = name + len + 1;
146 return name - kallsyms_names;
149 unsigned long kallsyms_sym_address(int idx)
151 /* values are unsigned offsets */
152 return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
155 static unsigned int get_symbol_seq(int index)
157 unsigned int i, seq = 0;
159 for (i = 0; i < 3; i++)
160 seq = (seq << 8) | kallsyms_seqs_of_names[3 * index + i];
165 static int kallsyms_lookup_names(const char *name,
171 unsigned int seq, off;
172 char namebuf[KSYM_NAME_LEN];
175 high = kallsyms_num_syms - 1;
177 while (low <= high) {
178 mid = low + (high - low) / 2;
179 seq = get_symbol_seq(mid);
180 off = get_symbol_offset(seq);
181 kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
182 ret = strcmp(name, namebuf);
196 seq = get_symbol_seq(low - 1);
197 off = get_symbol_offset(seq);
198 kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
199 if (strcmp(name, namebuf))
207 while (high < kallsyms_num_syms - 1) {
208 seq = get_symbol_seq(high + 1);
209 off = get_symbol_offset(seq);
210 kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
211 if (strcmp(name, namebuf))
221 /* Lookup the address for this symbol. Returns 0 if not found. */
222 unsigned long kallsyms_lookup_name(const char *name)
227 /* Skip the search for empty string. */
231 ret = kallsyms_lookup_names(name, &i, NULL);
233 return kallsyms_sym_address(get_symbol_seq(i));
235 return module_kallsyms_lookup_name(name);
239 * Iterate over all symbols in vmlinux. For symbols from modules use
240 * module_kallsyms_on_each_symbol instead.
242 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, unsigned long),
245 char namebuf[KSYM_NAME_LEN];
250 for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
251 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
252 ret = fn(data, namebuf, kallsyms_sym_address(i));
260 int kallsyms_on_each_match_symbol(int (*fn)(void *, unsigned long),
261 const char *name, void *data)
264 unsigned int i, start, end;
266 ret = kallsyms_lookup_names(name, &start, &end);
270 for (i = start; !ret && i <= end; i++) {
271 ret = fn(data, kallsyms_sym_address(get_symbol_seq(i)));
278 static unsigned long get_symbol_pos(unsigned long addr,
279 unsigned long *symbolsize,
280 unsigned long *offset)
282 unsigned long symbol_start = 0, symbol_end = 0;
283 unsigned long i, low, high, mid;
285 /* Do a binary search on the sorted kallsyms_offsets array. */
287 high = kallsyms_num_syms;
289 while (high - low > 1) {
290 mid = low + (high - low) / 2;
291 if (kallsyms_sym_address(mid) <= addr)
298 * Search for the first aliased symbol. Aliased
299 * symbols are symbols with the same address.
301 while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
304 symbol_start = kallsyms_sym_address(low);
306 /* Search for next non-aliased symbol. */
307 for (i = low + 1; i < kallsyms_num_syms; i++) {
308 if (kallsyms_sym_address(i) > symbol_start) {
309 symbol_end = kallsyms_sym_address(i);
314 /* If we found no next symbol, we use the end of the section. */
316 if (is_kernel_inittext(addr))
317 symbol_end = (unsigned long)_einittext;
318 else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
319 symbol_end = (unsigned long)_end;
321 symbol_end = (unsigned long)_etext;
325 *symbolsize = symbol_end - symbol_start;
327 *offset = addr - symbol_start;
333 * Lookup an address but don't bother to find any names.
335 int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
336 unsigned long *offset)
338 char namebuf[KSYM_NAME_LEN];
340 if (is_ksym_addr(addr)) {
341 get_symbol_pos(addr, symbolsize, offset);
344 return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
345 !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
348 static int kallsyms_lookup_buildid(unsigned long addr,
349 unsigned long *symbolsize,
350 unsigned long *offset, char **modname,
351 const unsigned char **modbuildid, char *namebuf)
355 namebuf[KSYM_NAME_LEN - 1] = 0;
358 if (is_ksym_addr(addr)) {
361 pos = get_symbol_pos(addr, symbolsize, offset);
363 kallsyms_expand_symbol(get_symbol_offset(pos),
364 namebuf, KSYM_NAME_LEN);
370 return strlen(namebuf);
373 /* See if it's in a module or a BPF JITed image. */
374 ret = module_address_lookup(addr, symbolsize, offset,
375 modname, modbuildid, namebuf);
377 ret = bpf_address_lookup(addr, symbolsize,
378 offset, modname, namebuf);
381 ret = ftrace_mod_address_lookup(addr, symbolsize,
382 offset, modname, namebuf);
389 * - modname is set to NULL if it's in the kernel.
390 * - We guarantee that the returned name is valid until we reschedule even if.
391 * It resides in a module.
392 * - We also guarantee that modname will be valid until rescheduled.
394 const char *kallsyms_lookup(unsigned long addr,
395 unsigned long *symbolsize,
396 unsigned long *offset,
397 char **modname, char *namebuf)
399 int ret = kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
408 int lookup_symbol_name(unsigned long addr, char *symname)
411 symname[KSYM_NAME_LEN - 1] = '\0';
413 if (is_ksym_addr(addr)) {
416 pos = get_symbol_pos(addr, NULL, NULL);
418 kallsyms_expand_symbol(get_symbol_offset(pos),
419 symname, KSYM_NAME_LEN);
422 /* See if it's in a module. */
423 return lookup_module_symbol_name(addr, symname);
426 /* Look up a kernel symbol and return it in a text buffer. */
427 static int __sprint_symbol(char *buffer, unsigned long address,
428 int symbol_offset, int add_offset, int add_buildid)
431 const unsigned char *buildid;
432 unsigned long offset, size;
435 address += symbol_offset;
436 len = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
439 return sprintf(buffer, "0x%lx", address - symbol_offset);
441 offset -= symbol_offset;
444 len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
447 len += sprintf(buffer + len, " [%s", modname);
448 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
449 if (add_buildid && buildid) {
450 /* build ID should match length of sprintf */
451 #if IS_ENABLED(CONFIG_MODULES)
452 static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
454 len += sprintf(buffer + len, " %20phN", buildid);
457 len += sprintf(buffer + len, "]");
464 * sprint_symbol - Look up a kernel symbol and return it in a text buffer
465 * @buffer: buffer to be stored
466 * @address: address to lookup
468 * This function looks up a kernel symbol with @address and stores its name,
469 * offset, size and module name to @buffer if possible. If no symbol was found,
470 * just saves its @address as is.
472 * This function returns the number of bytes stored in @buffer.
474 int sprint_symbol(char *buffer, unsigned long address)
476 return __sprint_symbol(buffer, address, 0, 1, 0);
478 EXPORT_SYMBOL_GPL(sprint_symbol);
481 * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer
482 * @buffer: buffer to be stored
483 * @address: address to lookup
485 * This function looks up a kernel symbol with @address and stores its name,
486 * offset, size, module name and module build ID to @buffer if possible. If no
487 * symbol was found, just saves its @address as is.
489 * This function returns the number of bytes stored in @buffer.
491 int sprint_symbol_build_id(char *buffer, unsigned long address)
493 return __sprint_symbol(buffer, address, 0, 1, 1);
495 EXPORT_SYMBOL_GPL(sprint_symbol_build_id);
498 * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
499 * @buffer: buffer to be stored
500 * @address: address to lookup
502 * This function looks up a kernel symbol with @address and stores its name
503 * and module name to @buffer if possible. If no symbol was found, just saves
504 * its @address as is.
506 * This function returns the number of bytes stored in @buffer.
508 int sprint_symbol_no_offset(char *buffer, unsigned long address)
510 return __sprint_symbol(buffer, address, 0, 0, 0);
512 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
515 * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
516 * @buffer: buffer to be stored
517 * @address: address to lookup
519 * This function is for stack backtrace and does the same thing as
520 * sprint_symbol() but with modified/decreased @address. If there is a
521 * tail-call to the function marked "noreturn", gcc optimized out code after
522 * the call so that the stack-saved return address could point outside of the
523 * caller. This function ensures that kallsyms will find the original caller
524 * by decreasing @address.
526 * This function returns the number of bytes stored in @buffer.
528 int sprint_backtrace(char *buffer, unsigned long address)
530 return __sprint_symbol(buffer, address, -1, 1, 0);
534 * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer
535 * @buffer: buffer to be stored
536 * @address: address to lookup
538 * This function is for stack backtrace and does the same thing as
539 * sprint_symbol() but with modified/decreased @address. If there is a
540 * tail-call to the function marked "noreturn", gcc optimized out code after
541 * the call so that the stack-saved return address could point outside of the
542 * caller. This function ensures that kallsyms will find the original caller
543 * by decreasing @address. This function also appends the module build ID to
544 * the @buffer if @address is within a kernel module.
546 * This function returns the number of bytes stored in @buffer.
548 int sprint_backtrace_build_id(char *buffer, unsigned long address)
550 return __sprint_symbol(buffer, address, -1, 1, 1);
553 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
554 struct kallsym_iter {
557 loff_t pos_ftrace_mod_end;
560 unsigned int nameoff; /* If iterating in core kernel symbols. */
562 char name[KSYM_NAME_LEN];
563 char module_name[MODULE_NAME_LEN];
568 static int get_ksymbol_mod(struct kallsym_iter *iter)
570 int ret = module_get_kallsym(iter->pos - kallsyms_num_syms,
571 &iter->value, &iter->type,
572 iter->name, iter->module_name,
575 iter->pos_mod_end = iter->pos;
583 * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
584 * purposes. In that case "__builtin__ftrace" is used as a module name, even
585 * though "__builtin__ftrace" is not a module.
587 static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
589 int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
590 &iter->value, &iter->type,
591 iter->name, iter->module_name,
594 iter->pos_ftrace_mod_end = iter->pos;
601 static int get_ksymbol_bpf(struct kallsym_iter *iter)
605 strscpy(iter->module_name, "bpf", MODULE_NAME_LEN);
607 ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
608 &iter->value, &iter->type,
611 iter->pos_bpf_end = iter->pos;
619 * This uses "__builtin__kprobes" as a module name for symbols for pages
620 * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
623 static int get_ksymbol_kprobe(struct kallsym_iter *iter)
625 strscpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
627 return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
628 &iter->value, &iter->type,
629 iter->name) < 0 ? 0 : 1;
632 /* Returns space to next name. */
633 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
635 unsigned off = iter->nameoff;
637 iter->module_name[0] = '\0';
638 iter->value = kallsyms_sym_address(iter->pos);
640 iter->type = kallsyms_get_symbol_type(off);
642 off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
644 return off - iter->nameoff;
647 static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
649 iter->name[0] = '\0';
650 iter->nameoff = get_symbol_offset(new_pos);
653 iter->pos_mod_end = 0;
654 iter->pos_ftrace_mod_end = 0;
655 iter->pos_bpf_end = 0;
660 * The end position (last + 1) of each additional kallsyms section is recorded
661 * in iter->pos_..._end as each section is added, and so can be used to
662 * determine which get_ksymbol_...() function to call next.
664 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
668 if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
669 get_ksymbol_mod(iter))
672 if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
673 get_ksymbol_ftrace_mod(iter))
676 if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
677 get_ksymbol_bpf(iter))
680 return get_ksymbol_kprobe(iter);
683 /* Returns false if pos at or past end of file. */
684 static int update_iter(struct kallsym_iter *iter, loff_t pos)
686 /* Module symbols can be accessed randomly. */
687 if (pos >= kallsyms_num_syms)
688 return update_iter_mod(iter, pos);
690 /* If we're not on the desired position, reset to new position. */
691 if (pos != iter->pos)
692 reset_iter(iter, pos);
694 iter->nameoff += get_ksymbol_core(iter);
700 static void *s_next(struct seq_file *m, void *p, loff_t *pos)
704 if (!update_iter(m->private, *pos))
709 static void *s_start(struct seq_file *m, loff_t *pos)
711 if (!update_iter(m->private, *pos))
716 static void s_stop(struct seq_file *m, void *p)
720 static int s_show(struct seq_file *m, void *p)
723 struct kallsym_iter *iter = m->private;
725 /* Some debugging symbols have no name. Ignore them. */
729 value = iter->show_value ? (void *)iter->value : NULL;
731 if (iter->module_name[0]) {
735 * Label it "global" if it is exported,
736 * "local" if not exported.
738 type = iter->exported ? toupper(iter->type) :
740 seq_printf(m, "%px %c %s\t[%s]\n", value,
741 type, iter->name, iter->module_name);
743 seq_printf(m, "%px %c %s\n", value,
744 iter->type, iter->name);
748 static const struct seq_operations kallsyms_op = {
755 #ifdef CONFIG_BPF_SYSCALL
757 struct bpf_iter__ksym {
758 __bpf_md_ptr(struct bpf_iter_meta *, meta);
759 __bpf_md_ptr(struct kallsym_iter *, ksym);
762 static int ksym_prog_seq_show(struct seq_file *m, bool in_stop)
764 struct bpf_iter__ksym ctx;
765 struct bpf_iter_meta meta;
766 struct bpf_prog *prog;
769 prog = bpf_iter_get_info(&meta, in_stop);
774 ctx.ksym = m ? m->private : NULL;
775 return bpf_iter_run_prog(prog, &ctx);
778 static int bpf_iter_ksym_seq_show(struct seq_file *m, void *p)
780 return ksym_prog_seq_show(m, false);
783 static void bpf_iter_ksym_seq_stop(struct seq_file *m, void *p)
786 (void) ksym_prog_seq_show(m, true);
791 static const struct seq_operations bpf_iter_ksym_ops = {
794 .stop = bpf_iter_ksym_seq_stop,
795 .show = bpf_iter_ksym_seq_show,
798 static int bpf_iter_ksym_init(void *priv_data, struct bpf_iter_aux_info *aux)
800 struct kallsym_iter *iter = priv_data;
804 /* cache here as in kallsyms_open() case; use current process
805 * credentials to tell BPF iterators if values should be shown.
807 iter->show_value = kallsyms_show_value(current_cred());
812 DEFINE_BPF_ITER_FUNC(ksym, struct bpf_iter_meta *meta, struct kallsym_iter *ksym)
814 static const struct bpf_iter_seq_info ksym_iter_seq_info = {
815 .seq_ops = &bpf_iter_ksym_ops,
816 .init_seq_private = bpf_iter_ksym_init,
817 .fini_seq_private = NULL,
818 .seq_priv_size = sizeof(struct kallsym_iter),
821 static struct bpf_iter_reg ksym_iter_reg_info = {
823 .feature = BPF_ITER_RESCHED,
824 .ctx_arg_info_size = 1,
826 { offsetof(struct bpf_iter__ksym, ksym),
827 PTR_TO_BTF_ID_OR_NULL },
829 .seq_info = &ksym_iter_seq_info,
832 BTF_ID_LIST(btf_ksym_iter_id)
833 BTF_ID(struct, kallsym_iter)
835 static int __init bpf_ksym_iter_register(void)
837 ksym_iter_reg_info.ctx_arg_info[0].btf_id = *btf_ksym_iter_id;
838 return bpf_iter_reg_target(&ksym_iter_reg_info);
841 late_initcall(bpf_ksym_iter_register);
843 #endif /* CONFIG_BPF_SYSCALL */
845 static int kallsyms_open(struct inode *inode, struct file *file)
848 * We keep iterator in m->private, since normal case is to
849 * s_start from where we left off, so we avoid doing
850 * using get_symbol_offset for every symbol.
852 struct kallsym_iter *iter;
853 iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
859 * Instead of checking this on every s_show() call, cache
860 * the result here at open time.
862 iter->show_value = kallsyms_show_value(file->f_cred);
866 #ifdef CONFIG_KGDB_KDB
867 const char *kdb_walk_kallsyms(loff_t *pos)
869 static struct kallsym_iter kdb_walk_kallsyms_iter;
871 memset(&kdb_walk_kallsyms_iter, 0,
872 sizeof(kdb_walk_kallsyms_iter));
873 reset_iter(&kdb_walk_kallsyms_iter, 0);
876 if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
879 /* Some debugging symbols have no name. Ignore them. */
880 if (kdb_walk_kallsyms_iter.name[0])
881 return kdb_walk_kallsyms_iter.name;
884 #endif /* CONFIG_KGDB_KDB */
886 static const struct proc_ops kallsyms_proc_ops = {
887 .proc_open = kallsyms_open,
888 .proc_read = seq_read,
889 .proc_lseek = seq_lseek,
890 .proc_release = seq_release_private,
893 static int __init kallsyms_init(void)
895 proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
898 device_initcall(kallsyms_init);