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>
34 * These will be re-linked against their real values
35 * during the second link stage.
37 extern const unsigned long kallsyms_addresses
[] __weak
;
38 extern const int kallsyms_offsets
[] __weak
;
39 extern const u8 kallsyms_names
[] __weak
;
42 * Tell the compiler that the count isn't in the small data section if the arch
45 extern const unsigned int kallsyms_num_syms
46 __section(".rodata") __attribute__((weak
));
48 extern const unsigned long kallsyms_relative_base
49 __section(".rodata") __attribute__((weak
));
51 extern const char kallsyms_token_table
[] __weak
;
52 extern const u16 kallsyms_token_index
[] __weak
;
54 extern const unsigned int kallsyms_markers
[] __weak
;
57 * Expand a compressed symbol data into the resulting uncompressed string,
58 * if uncompressed string is too long (>= maxlen), it will be truncated,
59 * given the offset to where the symbol is in the compressed stream.
61 static unsigned int kallsyms_expand_symbol(unsigned int off
,
62 char *result
, size_t maxlen
)
64 int len
, skipped_first
= 0;
68 /* Get the compressed symbol length from the first symbol byte. */
69 data
= &kallsyms_names
[off
];
74 * Update the offset to return the offset for the next symbol on
75 * the compressed stream.
80 * For every byte on the compressed symbol data, copy the table
81 * entry for that byte.
84 tptr
= &kallsyms_token_table
[kallsyms_token_index
[*data
]];
105 /* Return to offset to the next symbol. */
110 * Get symbol type information. This is encoded as a single char at the
111 * beginning of the symbol name.
113 static char kallsyms_get_symbol_type(unsigned int off
)
116 * Get just the first code, look it up in the token table,
117 * and return the first char from this token.
119 return kallsyms_token_table
[kallsyms_token_index
[kallsyms_names
[off
+ 1]]];
124 * Find the offset on the compressed stream given and index in the
127 static unsigned int get_symbol_offset(unsigned long pos
)
133 * Use the closest marker we have. We have markers every 256 positions,
134 * so that should be close enough.
136 name
= &kallsyms_names
[kallsyms_markers
[pos
>> 8]];
139 * Sequentially scan all the symbols up to the point we're searching
140 * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
141 * so we just need to add the len to the current pointer for every
142 * symbol we wish to skip.
144 for (i
= 0; i
< (pos
& 0xFF); i
++)
145 name
= name
+ (*name
) + 1;
147 return name
- kallsyms_names
;
150 static unsigned long kallsyms_sym_address(int idx
)
152 if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE
))
153 return kallsyms_addresses
[idx
];
155 /* values are unsigned offsets if --absolute-percpu is not in effect */
156 if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU
))
157 return kallsyms_relative_base
+ (u32
)kallsyms_offsets
[idx
];
159 /* ...otherwise, positive offsets are absolute values */
160 if (kallsyms_offsets
[idx
] >= 0)
161 return kallsyms_offsets
[idx
];
163 /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
164 return kallsyms_relative_base
- 1 - kallsyms_offsets
[idx
];
167 #if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
169 * LLVM appends a hash to static function names when ThinLTO and CFI are
170 * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b.
171 * This causes confusion and potentially breaks user space tools, so we
172 * strip the suffix from expanded symbol names.
174 static inline bool cleanup_symbol_name(char *s
)
178 res
= strrchr(s
, '$');
185 static inline bool cleanup_symbol_name(char *s
) { return false; }
188 /* Lookup the address for this symbol. Returns 0 if not found. */
189 unsigned long kallsyms_lookup_name(const char *name
)
191 char namebuf
[KSYM_NAME_LEN
];
195 for (i
= 0, off
= 0; i
< kallsyms_num_syms
; i
++) {
196 off
= kallsyms_expand_symbol(off
, namebuf
, ARRAY_SIZE(namebuf
));
198 if (strcmp(namebuf
, name
) == 0)
199 return kallsyms_sym_address(i
);
201 if (cleanup_symbol_name(namebuf
) && strcmp(namebuf
, name
) == 0)
202 return kallsyms_sym_address(i
);
204 return module_kallsyms_lookup_name(name
);
207 #ifdef CONFIG_LIVEPATCH
209 * Iterate over all symbols in vmlinux. For symbols from modules use
210 * module_kallsyms_on_each_symbol instead.
212 int kallsyms_on_each_symbol(int (*fn
)(void *, const char *, struct module
*,
216 char namebuf
[KSYM_NAME_LEN
];
221 for (i
= 0, off
= 0; i
< kallsyms_num_syms
; i
++) {
222 off
= kallsyms_expand_symbol(off
, namebuf
, ARRAY_SIZE(namebuf
));
223 ret
= fn(data
, namebuf
, NULL
, kallsyms_sym_address(i
));
229 #endif /* CONFIG_LIVEPATCH */
231 static unsigned long get_symbol_pos(unsigned long addr
,
232 unsigned long *symbolsize
,
233 unsigned long *offset
)
235 unsigned long symbol_start
= 0, symbol_end
= 0;
236 unsigned long i
, low
, high
, mid
;
238 /* This kernel should never had been booted. */
239 if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE
))
240 BUG_ON(!kallsyms_addresses
);
242 BUG_ON(!kallsyms_offsets
);
244 /* Do a binary search on the sorted kallsyms_addresses array. */
246 high
= kallsyms_num_syms
;
248 while (high
- low
> 1) {
249 mid
= low
+ (high
- low
) / 2;
250 if (kallsyms_sym_address(mid
) <= addr
)
257 * Search for the first aliased symbol. Aliased
258 * symbols are symbols with the same address.
260 while (low
&& kallsyms_sym_address(low
-1) == kallsyms_sym_address(low
))
263 symbol_start
= kallsyms_sym_address(low
);
265 /* Search for next non-aliased symbol. */
266 for (i
= low
+ 1; i
< kallsyms_num_syms
; i
++) {
267 if (kallsyms_sym_address(i
) > symbol_start
) {
268 symbol_end
= kallsyms_sym_address(i
);
273 /* If we found no next symbol, we use the end of the section. */
275 if (is_kernel_inittext(addr
))
276 symbol_end
= (unsigned long)_einittext
;
277 else if (IS_ENABLED(CONFIG_KALLSYMS_ALL
))
278 symbol_end
= (unsigned long)_end
;
280 symbol_end
= (unsigned long)_etext
;
284 *symbolsize
= symbol_end
- symbol_start
;
286 *offset
= addr
- symbol_start
;
292 * Lookup an address but don't bother to find any names.
294 int kallsyms_lookup_size_offset(unsigned long addr
, unsigned long *symbolsize
,
295 unsigned long *offset
)
297 char namebuf
[KSYM_NAME_LEN
];
299 if (is_ksym_addr(addr
)) {
300 get_symbol_pos(addr
, symbolsize
, offset
);
303 return !!module_address_lookup(addr
, symbolsize
, offset
, NULL
, NULL
, namebuf
) ||
304 !!__bpf_address_lookup(addr
, symbolsize
, offset
, namebuf
);
307 static const char *kallsyms_lookup_buildid(unsigned long addr
,
308 unsigned long *symbolsize
,
309 unsigned long *offset
, char **modname
,
310 const unsigned char **modbuildid
, char *namebuf
)
314 namebuf
[KSYM_NAME_LEN
- 1] = 0;
317 if (is_ksym_addr(addr
)) {
320 pos
= get_symbol_pos(addr
, symbolsize
, offset
);
322 kallsyms_expand_symbol(get_symbol_offset(pos
),
323 namebuf
, KSYM_NAME_LEN
);
333 /* See if it's in a module or a BPF JITed image. */
334 ret
= module_address_lookup(addr
, symbolsize
, offset
,
335 modname
, modbuildid
, namebuf
);
337 ret
= bpf_address_lookup(addr
, symbolsize
,
338 offset
, modname
, namebuf
);
341 ret
= ftrace_mod_address_lookup(addr
, symbolsize
,
342 offset
, modname
, namebuf
);
345 cleanup_symbol_name(namebuf
);
351 * - modname is set to NULL if it's in the kernel.
352 * - We guarantee that the returned name is valid until we reschedule even if.
353 * It resides in a module.
354 * - We also guarantee that modname will be valid until rescheduled.
356 const char *kallsyms_lookup(unsigned long addr
,
357 unsigned long *symbolsize
,
358 unsigned long *offset
,
359 char **modname
, char *namebuf
)
361 return kallsyms_lookup_buildid(addr
, symbolsize
, offset
, modname
,
365 int lookup_symbol_name(unsigned long addr
, char *symname
)
370 symname
[KSYM_NAME_LEN
- 1] = '\0';
372 if (is_ksym_addr(addr
)) {
375 pos
= get_symbol_pos(addr
, NULL
, NULL
);
377 kallsyms_expand_symbol(get_symbol_offset(pos
),
378 symname
, KSYM_NAME_LEN
);
381 /* See if it's in a module. */
382 res
= lookup_module_symbol_name(addr
, symname
);
387 cleanup_symbol_name(symname
);
391 int lookup_symbol_attrs(unsigned long addr
, unsigned long *size
,
392 unsigned long *offset
, char *modname
, char *name
)
397 name
[KSYM_NAME_LEN
- 1] = '\0';
399 if (is_ksym_addr(addr
)) {
402 pos
= get_symbol_pos(addr
, size
, offset
);
404 kallsyms_expand_symbol(get_symbol_offset(pos
),
405 name
, KSYM_NAME_LEN
);
409 /* See if it's in a module. */
410 res
= lookup_module_symbol_attrs(addr
, size
, offset
, modname
, name
);
415 cleanup_symbol_name(name
);
419 /* Look up a kernel symbol and return it in a text buffer. */
420 static int __sprint_symbol(char *buffer
, unsigned long address
,
421 int symbol_offset
, int add_offset
, int add_buildid
)
424 const unsigned char *buildid
;
426 unsigned long offset
, size
;
429 address
+= symbol_offset
;
430 name
= kallsyms_lookup_buildid(address
, &size
, &offset
, &modname
, &buildid
,
433 return sprintf(buffer
, "0x%lx", address
- symbol_offset
);
436 strcpy(buffer
, name
);
437 len
= strlen(buffer
);
438 offset
-= symbol_offset
;
441 len
+= sprintf(buffer
+ len
, "+%#lx/%#lx", offset
, size
);
444 len
+= sprintf(buffer
+ len
, " [%s", modname
);
445 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
446 if (add_buildid
&& buildid
) {
447 /* build ID should match length of sprintf */
448 #if IS_ENABLED(CONFIG_MODULES)
449 static_assert(sizeof(typeof_member(struct module
, build_id
)) == 20);
451 len
+= sprintf(buffer
+ len
, " %20phN", buildid
);
454 len
+= sprintf(buffer
+ len
, "]");
461 * sprint_symbol - Look up a kernel symbol and return it in a text buffer
462 * @buffer: buffer to be stored
463 * @address: address to lookup
465 * This function looks up a kernel symbol with @address and stores its name,
466 * offset, size and module name to @buffer if possible. If no symbol was found,
467 * just saves its @address as is.
469 * This function returns the number of bytes stored in @buffer.
471 int sprint_symbol(char *buffer
, unsigned long address
)
473 return __sprint_symbol(buffer
, address
, 0, 1, 0);
475 EXPORT_SYMBOL_GPL(sprint_symbol
);
478 * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer
479 * @buffer: buffer to be stored
480 * @address: address to lookup
482 * This function looks up a kernel symbol with @address and stores its name,
483 * offset, size, module name and module build ID to @buffer if possible. If no
484 * symbol was found, just saves its @address as is.
486 * This function returns the number of bytes stored in @buffer.
488 int sprint_symbol_build_id(char *buffer
, unsigned long address
)
490 return __sprint_symbol(buffer
, address
, 0, 1, 1);
492 EXPORT_SYMBOL_GPL(sprint_symbol_build_id
);
495 * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
496 * @buffer: buffer to be stored
497 * @address: address to lookup
499 * This function looks up a kernel symbol with @address and stores its name
500 * and module name to @buffer if possible. If no symbol was found, just saves
501 * its @address as is.
503 * This function returns the number of bytes stored in @buffer.
505 int sprint_symbol_no_offset(char *buffer
, unsigned long address
)
507 return __sprint_symbol(buffer
, address
, 0, 0, 0);
509 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset
);
512 * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
513 * @buffer: buffer to be stored
514 * @address: address to lookup
516 * This function is for stack backtrace and does the same thing as
517 * sprint_symbol() but with modified/decreased @address. If there is a
518 * tail-call to the function marked "noreturn", gcc optimized out code after
519 * the call so that the stack-saved return address could point outside of the
520 * caller. This function ensures that kallsyms will find the original caller
521 * by decreasing @address.
523 * This function returns the number of bytes stored in @buffer.
525 int sprint_backtrace(char *buffer
, unsigned long address
)
527 return __sprint_symbol(buffer
, address
, -1, 1, 0);
531 * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer
532 * @buffer: buffer to be stored
533 * @address: address to lookup
535 * This function is for stack backtrace and does the same thing as
536 * sprint_symbol() but with modified/decreased @address. If there is a
537 * tail-call to the function marked "noreturn", gcc optimized out code after
538 * the call so that the stack-saved return address could point outside of the
539 * caller. This function ensures that kallsyms will find the original caller
540 * by decreasing @address. This function also appends the module build ID to
541 * the @buffer if @address is within a kernel module.
543 * This function returns the number of bytes stored in @buffer.
545 int sprint_backtrace_build_id(char *buffer
, unsigned long address
)
547 return __sprint_symbol(buffer
, address
, -1, 1, 1);
550 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
551 struct kallsym_iter
{
555 loff_t pos_ftrace_mod_end
;
558 unsigned int nameoff
; /* If iterating in core kernel symbols. */
560 char name
[KSYM_NAME_LEN
];
561 char module_name
[MODULE_NAME_LEN
];
566 int __weak
arch_get_kallsym(unsigned int symnum
, unsigned long *value
,
567 char *type
, char *name
)
572 static int get_ksymbol_arch(struct kallsym_iter
*iter
)
574 int ret
= arch_get_kallsym(iter
->pos
- kallsyms_num_syms
,
575 &iter
->value
, &iter
->type
,
579 iter
->pos_arch_end
= iter
->pos
;
586 static int get_ksymbol_mod(struct kallsym_iter
*iter
)
588 int ret
= module_get_kallsym(iter
->pos
- iter
->pos_arch_end
,
589 &iter
->value
, &iter
->type
,
590 iter
->name
, iter
->module_name
,
593 iter
->pos_mod_end
= iter
->pos
;
601 * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
602 * purposes. In that case "__builtin__ftrace" is used as a module name, even
603 * though "__builtin__ftrace" is not a module.
605 static int get_ksymbol_ftrace_mod(struct kallsym_iter
*iter
)
607 int ret
= ftrace_mod_get_kallsym(iter
->pos
- iter
->pos_mod_end
,
608 &iter
->value
, &iter
->type
,
609 iter
->name
, iter
->module_name
,
612 iter
->pos_ftrace_mod_end
= iter
->pos
;
619 static int get_ksymbol_bpf(struct kallsym_iter
*iter
)
623 strlcpy(iter
->module_name
, "bpf", MODULE_NAME_LEN
);
625 ret
= bpf_get_kallsym(iter
->pos
- iter
->pos_ftrace_mod_end
,
626 &iter
->value
, &iter
->type
,
629 iter
->pos_bpf_end
= iter
->pos
;
637 * This uses "__builtin__kprobes" as a module name for symbols for pages
638 * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
641 static int get_ksymbol_kprobe(struct kallsym_iter
*iter
)
643 strlcpy(iter
->module_name
, "__builtin__kprobes", MODULE_NAME_LEN
);
645 return kprobe_get_kallsym(iter
->pos
- iter
->pos_bpf_end
,
646 &iter
->value
, &iter
->type
,
647 iter
->name
) < 0 ? 0 : 1;
650 /* Returns space to next name. */
651 static unsigned long get_ksymbol_core(struct kallsym_iter
*iter
)
653 unsigned off
= iter
->nameoff
;
655 iter
->module_name
[0] = '\0';
656 iter
->value
= kallsyms_sym_address(iter
->pos
);
658 iter
->type
= kallsyms_get_symbol_type(off
);
660 off
= kallsyms_expand_symbol(off
, iter
->name
, ARRAY_SIZE(iter
->name
));
662 return off
- iter
->nameoff
;
665 static void reset_iter(struct kallsym_iter
*iter
, loff_t new_pos
)
667 iter
->name
[0] = '\0';
668 iter
->nameoff
= get_symbol_offset(new_pos
);
671 iter
->pos_arch_end
= 0;
672 iter
->pos_mod_end
= 0;
673 iter
->pos_ftrace_mod_end
= 0;
674 iter
->pos_bpf_end
= 0;
679 * The end position (last + 1) of each additional kallsyms section is recorded
680 * in iter->pos_..._end as each section is added, and so can be used to
681 * determine which get_ksymbol_...() function to call next.
683 static int update_iter_mod(struct kallsym_iter
*iter
, loff_t pos
)
687 if ((!iter
->pos_arch_end
|| iter
->pos_arch_end
> pos
) &&
688 get_ksymbol_arch(iter
))
691 if ((!iter
->pos_mod_end
|| iter
->pos_mod_end
> pos
) &&
692 get_ksymbol_mod(iter
))
695 if ((!iter
->pos_ftrace_mod_end
|| iter
->pos_ftrace_mod_end
> pos
) &&
696 get_ksymbol_ftrace_mod(iter
))
699 if ((!iter
->pos_bpf_end
|| iter
->pos_bpf_end
> pos
) &&
700 get_ksymbol_bpf(iter
))
703 return get_ksymbol_kprobe(iter
);
706 /* Returns false if pos at or past end of file. */
707 static int update_iter(struct kallsym_iter
*iter
, loff_t pos
)
709 /* Module symbols can be accessed randomly. */
710 if (pos
>= kallsyms_num_syms
)
711 return update_iter_mod(iter
, pos
);
713 /* If we're not on the desired position, reset to new position. */
714 if (pos
!= iter
->pos
)
715 reset_iter(iter
, pos
);
717 iter
->nameoff
+= get_ksymbol_core(iter
);
723 static void *s_next(struct seq_file
*m
, void *p
, loff_t
*pos
)
727 if (!update_iter(m
->private, *pos
))
732 static void *s_start(struct seq_file
*m
, loff_t
*pos
)
734 if (!update_iter(m
->private, *pos
))
739 static void s_stop(struct seq_file
*m
, void *p
)
743 static int s_show(struct seq_file
*m
, void *p
)
746 struct kallsym_iter
*iter
= m
->private;
748 /* Some debugging symbols have no name. Ignore them. */
752 value
= iter
->show_value
? (void *)iter
->value
: NULL
;
754 if (iter
->module_name
[0]) {
758 * Label it "global" if it is exported,
759 * "local" if not exported.
761 type
= iter
->exported
? toupper(iter
->type
) :
763 seq_printf(m
, "%px %c %s\t[%s]\n", value
,
764 type
, iter
->name
, iter
->module_name
);
766 seq_printf(m
, "%px %c %s\n", value
,
767 iter
->type
, iter
->name
);
771 static const struct seq_operations kallsyms_op
= {
778 static inline int kallsyms_for_perf(void)
780 #ifdef CONFIG_PERF_EVENTS
781 extern int sysctl_perf_event_paranoid
;
782 if (sysctl_perf_event_paranoid
<= 1)
789 * We show kallsyms information even to normal users if we've enabled
790 * kernel profiling and are explicitly not paranoid (so kptr_restrict
791 * is clear, and sysctl_perf_event_paranoid isn't set).
793 * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
796 bool kallsyms_show_value(const struct cred
*cred
)
798 switch (kptr_restrict
) {
800 if (kallsyms_for_perf())
804 if (security_capable(cred
, &init_user_ns
, CAP_SYSLOG
,
805 CAP_OPT_NOAUDIT
) == 0)
813 static int kallsyms_open(struct inode
*inode
, struct file
*file
)
816 * We keep iterator in m->private, since normal case is to
817 * s_start from where we left off, so we avoid doing
818 * using get_symbol_offset for every symbol.
820 struct kallsym_iter
*iter
;
821 iter
= __seq_open_private(file
, &kallsyms_op
, sizeof(*iter
));
827 * Instead of checking this on every s_show() call, cache
828 * the result here at open time.
830 iter
->show_value
= kallsyms_show_value(file
->f_cred
);
834 #ifdef CONFIG_KGDB_KDB
835 const char *kdb_walk_kallsyms(loff_t
*pos
)
837 static struct kallsym_iter kdb_walk_kallsyms_iter
;
839 memset(&kdb_walk_kallsyms_iter
, 0,
840 sizeof(kdb_walk_kallsyms_iter
));
841 reset_iter(&kdb_walk_kallsyms_iter
, 0);
844 if (!update_iter(&kdb_walk_kallsyms_iter
, *pos
))
847 /* Some debugging symbols have no name. Ignore them. */
848 if (kdb_walk_kallsyms_iter
.name
[0])
849 return kdb_walk_kallsyms_iter
.name
;
852 #endif /* CONFIG_KGDB_KDB */
854 static const struct proc_ops kallsyms_proc_ops
= {
855 .proc_open
= kallsyms_open
,
856 .proc_read
= seq_read
,
857 .proc_lseek
= seq_lseek
,
858 .proc_release
= seq_release_private
,
861 static int __init
kallsyms_init(void)
863 proc_create("kallsyms", 0444, NULL
, &kallsyms_proc_ops
);
866 device_initcall(kallsyms_init
);