1/* Look up a symbol in a single specified object.
2 Copyright (C) 1995-2020 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 <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. */
27static const ElfW(Sym) *
28check_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. */
70const 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}
117