1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
|
/* Look up a symbol in the loaded objects.
Copyright (C) 1995, 1996 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA. */
#include <stddef.h>
#include <link.h>
#include <assert.h>
/* This is the hashing function specified by the ELF ABI. */
static inline unsigned
_dl_elf_hash (const char *name)
{
unsigned long int hash = 0;
while (*name != '\0')
{
unsigned long int hi;
hash = (hash << 4) + *name++;
hi = hash & 0xf0000000;
if (hi != 0)
{
hash ^= hi >> 24;
/* The ELF ABI says `hash &= ~hi', but this is equivalent
in this case and on some machines one insn instead of two. */
hash ^= hi;
}
}
return hash;
}
/* Search loaded objects' symbol tables for a definition of the symbol
UNDEF_NAME. The chosen value can't be RELOC_ADDR. If NOPLT is nonzero,
then a PLT entry cannot satisfy the reference; some different binding
must be found. */
ElfW(Addr)
_dl_lookup_symbol (const char *undef_name, const ElfW(Sym) **ref,
struct link_map *symbol_scope[2],
const char *reference_name,
ElfW(Addr) reloc_addr,
int noplt)
{
const unsigned long int hash = _dl_elf_hash (undef_name);
struct
{
ElfW(Addr) a;
const ElfW(Sym) *s;
} weak_value = { 0, NULL };
size_t i;
struct link_map **scope, *map;
/* Search the relevant loaded objects for a definition. */
for (scope = symbol_scope; scope < &symbol_scope[2]; ++scope)
if (*scope)
for (i = 0; i < (*scope)->l_nsearchlist; ++i)
{
const ElfW(Sym) *symtab;
const char *strtab;
ElfW(Word) symidx;
map = (*scope)->l_searchlist[i];
symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
/* Search the appropriate hash bucket in this object's symbol table
for a definition for the same symbol name. */
for (symidx = map->l_buckets[hash % map->l_nbuckets];
symidx != STN_UNDEF;
symidx = map->l_chain[symidx])
{
const ElfW(Sym) *sym = &symtab[symidx];
if (sym->st_value == 0 || /* No value. */
/* Cannot resolve to the location being filled in. */
reloc_addr == map->l_addr + sym->st_value ||
(noplt && sym->st_shndx == SHN_UNDEF)) /* Reject PLT. */
continue;
switch (ELFW(ST_TYPE) (sym->st_info))
{
case STT_NOTYPE:
case STT_FUNC:
case STT_OBJECT:
break;
default:
/* Not a code/data definition. */
continue;
}
if (sym != *ref && strcmp (strtab + sym->st_name, undef_name))
/* Not the symbol we are looking for. */
continue;
switch (ELFW(ST_BIND) (sym->st_info))
{
case STB_GLOBAL:
/* Global definition. Just what we need. */
*ref = sym;
return map->l_addr;
case STB_WEAK:
/* Weak definition. Use this value if we don't find
another. */
if (! weak_value.s)
{
weak_value.s = sym;
weak_value.a = map->l_addr;
}
break;
default:
/* Local symbols are ignored. */
break;
}
}
}
if (weak_value.s == NULL && ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
{
/* We could find no value for a strong reference. */
const char msg[] = "undefined symbol: ";
char buf[sizeof msg + strlen (undef_name)];
memcpy (buf, msg, sizeof msg - 1);
memcpy (&buf[sizeof msg - 1], undef_name,
sizeof buf - sizeof msg + 1);
_dl_signal_error (0, reference_name, buf);
}
*ref = weak_value.s;
return weak_value.a;
}
/* Cache the location of MAP's hash table. */
void
_dl_setup_hash (struct link_map *map)
{
ElfW(Word) *hash = (void *) map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr;
ElfW(Word) nchain;
map->l_nbuckets = *hash++;
nchain = *hash++;
map->l_buckets = hash;
hash += map->l_nbuckets;
map->l_chain = hash;
}
|
