1 /* Locate the shared object symbol nearest a given address.
2 Copyright (C) 1996-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #include <dlfcn.h>
20 #include <stddef.h>
21 #include <ldsodefs.h>
22
23
24 static inline void
25 __attribute ((always_inline))
determine_info(const ElfW (Addr)addr,struct link_map * match,Dl_info * info,struct link_map ** mapp,const ElfW (Sym)** symbolp)26 determine_info (const ElfW(Addr) addr, struct link_map *match, Dl_info *info,
27 struct link_map **mapp, const ElfW(Sym) **symbolp)
28 {
29 /* Now we know what object the address lies in. */
30 info->dli_fname = match->l_name;
31 info->dli_fbase = (void *) match->l_map_start;
32
33 /* If this is the main program the information is incomplete. */
34 if (__builtin_expect (match->l_name[0], 'a') == '\0'
35 && match->l_type == lt_executable)
36 info->dli_fname = _dl_argv[0];
37
38 const ElfW(Sym) *symtab
39 = (const ElfW(Sym) *) D_PTR (match, l_info[DT_SYMTAB]);
40 const char *strtab = (const char *) D_PTR (match, l_info[DT_STRTAB]);
41
42 ElfW(Word) strtabsize = match->l_info[DT_STRSZ]->d_un.d_val;
43
44 const ElfW(Sym) *matchsym = NULL;
45 if (match->l_info[ELF_MACHINE_GNU_HASH_ADDRIDX] != NULL)
46 {
47 /* We look at all symbol table entries referenced by the hash
48 table. */
49 for (Elf_Symndx bucket = 0; bucket < match->l_nbuckets; ++bucket)
50 {
51 Elf32_Word symndx = match->l_gnu_buckets[bucket];
52 if (symndx != 0)
53 {
54 const Elf32_Word *hasharr = &match->l_gnu_chain_zero[symndx];
55
56 do
57 {
58 /* The hash table never references local symbols so
59 we can omit that test here. */
60 symndx = ELF_MACHINE_HASH_SYMIDX (match, hasharr);
61 if ((symtab[symndx].st_shndx != SHN_UNDEF
62 || symtab[symndx].st_value != 0)
63 && symtab[symndx].st_shndx != SHN_ABS
64 && ELFW(ST_TYPE) (symtab[symndx].st_info) != STT_TLS
65 && DL_ADDR_SYM_MATCH (match, &symtab[symndx],
66 matchsym, addr)
67 && symtab[symndx].st_name < strtabsize)
68 matchsym = (ElfW(Sym) *) &symtab[symndx];
69 }
70 while ((*hasharr++ & 1u) == 0);
71 }
72 }
73 }
74 else
75 {
76 const ElfW(Sym) *symtabend;
77 if (match->l_info[DT_HASH] != NULL)
78 symtabend = (symtab
79 + ((Elf_Symndx *) D_PTR (match, l_info[DT_HASH]))[1]);
80 else
81 /* There is no direct way to determine the number of symbols in the
82 dynamic symbol table and no hash table is present. The ELF
83 binary is ill-formed but what shall we do? Use the beginning of
84 the string table which generally follows the symbol table. */
85 symtabend = (const ElfW(Sym) *) strtab;
86
87 for (; (void *) symtab < (void *) symtabend; ++symtab)
88 if ((ELFW(ST_BIND) (symtab->st_info) == STB_GLOBAL
89 || ELFW(ST_BIND) (symtab->st_info) == STB_WEAK)
90 && __glibc_likely (!dl_symbol_visibility_binds_local_p (symtab))
91 && ELFW(ST_TYPE) (symtab->st_info) != STT_TLS
92 && (symtab->st_shndx != SHN_UNDEF
93 || symtab->st_value != 0)
94 && symtab->st_shndx != SHN_ABS
95 && DL_ADDR_SYM_MATCH (match, symtab, matchsym, addr)
96 && symtab->st_name < strtabsize)
97 matchsym = (ElfW(Sym) *) symtab;
98 }
99
100 if (mapp)
101 *mapp = match;
102 if (symbolp)
103 *symbolp = matchsym;
104
105 if (matchsym)
106 {
107 /* We found a symbol close by. Fill in its name and exact
108 address. */
109 lookup_t matchl = LOOKUP_VALUE (match);
110
111 info->dli_sname = strtab + matchsym->st_name;
112 info->dli_saddr = DL_SYMBOL_ADDRESS (matchl, matchsym);
113 }
114 else
115 {
116 /* No symbol matches. We return only the containing object. */
117 info->dli_sname = NULL;
118 info->dli_saddr = NULL;
119 }
120 }
121
122
123 int
_dl_addr(const void * address,Dl_info * info,struct link_map ** mapp,const ElfW (Sym)** symbolp)124 _dl_addr (const void *address, Dl_info *info,
125 struct link_map **mapp, const ElfW(Sym) **symbolp)
126 {
127 const ElfW(Addr) addr = DL_LOOKUP_ADDRESS (address);
128 int result = 0;
129
130 /* Protect against concurrent loads and unloads. */
131 __rtld_lock_lock_recursive (GL(dl_load_lock));
132
133 struct link_map *l = _dl_find_dso_for_object (addr);
134
135 if (l)
136 {
137 determine_info (addr, l, info, mapp, symbolp);
138 result = 1;
139 }
140
141 __rtld_lock_unlock_recursive (GL(dl_load_lock));
142
143 return result;
144 }
145