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ec935dea | 1 | /* Look up a symbol in a single specified object. |
6d7e8eda | 2 | Copyright (C) 1995-2023 Free Software Foundation, Inc. |
ec935dea FW |
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 <ldsodefs.h> | |
20 | #include <string.h> | |
21 | #include <elf_machine_sym_no_match.h> | |
22 | #include <dl-hash.h> | |
23 | ||
24 | /* This function corresponds to do_lookup_x in elf/dl-lookup.c. The | |
25 | variant here is simplified because it requires symbol | |
26 | versioning. */ | |
27 | static const ElfW(Sym) * | |
28 | check_match (const struct link_map *const map, const char *const undef_name, | |
29 | const char *version, uint32_t version_hash, | |
30 | const Elf_Symndx symidx) | |
31 | { | |
32 | const ElfW(Sym) *symtab = (const void *) D_PTR (map, l_info[DT_SYMTAB]); | |
33 | const ElfW(Sym) *sym = &symtab[symidx]; | |
34 | ||
35 | unsigned int stt = ELFW(ST_TYPE) (sym->st_info); | |
36 | if (__glibc_unlikely ((sym->st_value == 0 /* No value. */ | |
37 | && sym->st_shndx != SHN_ABS | |
38 | && stt != STT_TLS) | |
39 | || elf_machine_sym_no_match (sym))) | |
40 | return NULL; | |
41 | ||
42 | /* Ignore all but STT_NOTYPE, STT_OBJECT, STT_FUNC, | |
43 | STT_COMMON, STT_TLS, and STT_GNU_IFUNC since these are no | |
44 | code/data definitions. */ | |
45 | #define ALLOWED_STT \ | |
46 | ((1 << STT_NOTYPE) | (1 << STT_OBJECT) | (1 << STT_FUNC) \ | |
47 | | (1 << STT_COMMON) | (1 << STT_TLS) | (1 << STT_GNU_IFUNC)) | |
48 | if (__glibc_unlikely (((1 << stt) & ALLOWED_STT) == 0)) | |
49 | return NULL; | |
50 | ||
51 | const char *strtab = (const void *) D_PTR (map, l_info[DT_STRTAB]); | |
52 | ||
53 | if (strcmp (strtab + sym->st_name, undef_name) != 0) | |
54 | /* Not the symbol we are looking for. */ | |
55 | return NULL; | |
56 | ||
57 | ElfW(Half) ndx = map->l_versyms[symidx] & 0x7fff; | |
58 | if (map->l_versions[ndx].hash != version_hash | |
59 | || strcmp (map->l_versions[ndx].name, version) != 0) | |
60 | /* It's not the version we want. */ | |
61 | return NULL; | |
62 | ||
63 | return sym; | |
64 | } | |
65 | ||
66 | ||
67 | /* This function corresponds to do_lookup_x in elf/dl-lookup.c. The | |
68 | variant here is simplified because it does not search object | |
69 | dependencies. It is optimized for a successful lookup. */ | |
70 | const ElfW(Sym) * | |
71 | _dl_lookup_direct (struct link_map *map, | |
72 | const char *undef_name, uint32_t new_hash, | |
73 | const char *version, uint32_t version_hash) | |
74 | { | |
75 | const ElfW(Addr) *bitmask = map->l_gnu_bitmask; | |
76 | if (__glibc_likely (bitmask != NULL)) | |
77 | { | |
78 | Elf32_Word bucket = map->l_gnu_buckets[new_hash % map->l_nbuckets]; | |
79 | if (bucket != 0) | |
80 | { | |
81 | const Elf32_Word *hasharr = &map->l_gnu_chain_zero[bucket]; | |
82 | ||
83 | do | |
84 | if (((*hasharr ^ new_hash) >> 1) == 0) | |
85 | { | |
86 | Elf_Symndx symidx = ELF_MACHINE_HASH_SYMIDX (map, hasharr); | |
87 | const ElfW(Sym) *sym = check_match (map, undef_name, | |
88 | version, version_hash, | |
89 | symidx); | |
90 | if (sym != NULL) | |
91 | return sym; | |
92 | } | |
93 | while ((*hasharr++ & 1u) == 0); | |
94 | } | |
95 | } | |
96 | else | |
97 | { | |
98 | /* Fallback code for lack of GNU_HASH support. */ | |
99 | uint32_t old_hash = _dl_elf_hash (undef_name); | |
100 | ||
101 | /* Use the old SysV-style hash table. Search the appropriate | |
102 | hash bucket in this object's symbol table for a definition | |
103 | for the same symbol name. */ | |
104 | for (Elf_Symndx symidx = map->l_buckets[old_hash % map->l_nbuckets]; | |
105 | symidx != STN_UNDEF; | |
106 | symidx = map->l_chain[symidx]) | |
107 | { | |
108 | const ElfW(Sym) *sym = check_match (map, undef_name, | |
109 | version, version_hash, symidx); | |
110 | if (sym != NULL) | |
111 | return sym; | |
112 | } | |
113 | } | |
114 | ||
115 | return NULL; | |
116 | } |