1 /*
2 * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include <unistd.h>
26 #include <search.h>
27 #include <stdlib.h>
28 #include <string.h>
29 #include "hsearch_r.h"
30 #include "symtab.h"
31 #include "salibelf.h"
32
33
34 // ----------------------------------------------------
35 // functions for symbol lookups
36 // ----------------------------------------------------
37
38 struct elf_section {
39 ELF_SHDR *c_shdr;
40 void *c_data;
41 };
42
43 struct elf_symbol {
44 char *name;
45 uintptr_t offset;
46 uintptr_t size;
47 };
48
49 typedef struct symtab {
50 char *strs;
51 size_t num_symbols;
52 struct elf_symbol *symbols;
53 struct hsearch_data *hash_table;
54 } symtab_t;
55
56 // read symbol table from given fd.
57 struct symtab* build_symtab(int fd) {
58 ELF_EHDR ehdr;
59 struct symtab* symtab = NULL;
60
61 // Reading of elf header
62 struct elf_section *scn_cache = NULL;
63 int cnt = 0;
64 ELF_SHDR* shbuf = NULL;
65 ELF_SHDR* cursct = NULL;
66 ELF_PHDR* phbuf = NULL;
67 int symtab_found = 0;
68 int dynsym_found = 0;
69 uint32_t symsection = SHT_SYMTAB;
70
71 uintptr_t baseaddr = (uintptr_t)-1;
72
73 lseek(fd, (off_t)0L, SEEK_SET);
74 if (! read_elf_header(fd, &ehdr)) {
75 // not an elf
76 return NULL;
77 }
78
79 // read ELF header
80 if ((shbuf = read_section_header_table(fd, &ehdr)) == NULL) {
81 goto quit;
82 }
83
84 baseaddr = find_base_address(fd, &ehdr);
85
86 scn_cache = (struct elf_section *)
87 calloc(ehdr.e_shnum * sizeof(struct elf_section), 1);
88 if (scn_cache == NULL) {
89 goto quit;
90 }
91
92 for (cursct = shbuf, cnt = 0; cnt < ehdr.e_shnum; cnt++) {
93 scn_cache[cnt].c_shdr = cursct;
94 if (cursct->sh_type == SHT_SYMTAB ||
95 cursct->sh_type == SHT_STRTAB ||
96 cursct->sh_type == SHT_DYNSYM) {
97 if ( (scn_cache[cnt].c_data = read_section_data(fd, &ehdr, cursct)) == NULL) {
98 goto quit;
99 }
100 }
101
102 if (cursct->sh_type == SHT_SYMTAB)
103 symtab_found++;
104
105 if (cursct->sh_type == SHT_DYNSYM)
106 dynsym_found++;
107
108 cursct++;
109 }
110
111 if (!symtab_found && dynsym_found)
112 symsection = SHT_DYNSYM;
113
114 for (cnt = 1; cnt < ehdr.e_shnum; cnt++) {
115 ELF_SHDR *shdr = scn_cache[cnt].c_shdr;
116
117 if (shdr->sh_type == symsection) {
118 ELF_SYM *syms;
119 int j, n, rslt;
120 size_t size;
121
122 // FIXME: there could be multiple data buffers associated with the
123 // same ELF section. Here we can handle only one buffer. See man page
124 // for elf_getdata on Solaris.
125
126 // guarantee(symtab == NULL, "multiple symtab");
127 symtab = (struct symtab*)calloc(1, sizeof(struct symtab));
128 if (symtab == NULL) {
129 goto quit;
130 }
131 // the symbol table
132 syms = (ELF_SYM *)scn_cache[cnt].c_data;
133
134 // number of symbols
135 n = shdr->sh_size / shdr->sh_entsize;
136
137 // create hash table, we use hcreate_r, hsearch_r and hdestroy_r to
138 // manipulate the hash table.
139 symtab->hash_table = (struct hsearch_data*) calloc(1, sizeof(struct hsearch_data));
140 rslt = hcreate_r(n, symtab->hash_table);
141 // guarantee(rslt, "unexpected failure: hcreate_r");
142
143 // shdr->sh_link points to the section that contains the actual strings
144 // for symbol names. the st_name field in ELF_SYM is just the
145 // string table index. we make a copy of the string table so the
146 // strings will not be destroyed by elf_end.
147 size = scn_cache[shdr->sh_link].c_shdr->sh_size;
148 symtab->strs = (char *)malloc(size);
149 memcpy(symtab->strs, scn_cache[shdr->sh_link].c_data, size);
150
151 // allocate memory for storing symbol offset and size;
152 symtab->num_symbols = n;
153 symtab->symbols = (struct elf_symbol *)calloc(n , sizeof(struct elf_symbol));
154
155 // copy symbols info our symtab and enter them info the hash table
156 for (j = 0; j < n; j++, syms++) {
157 ENTRY item, *ret;
158 char *sym_name = symtab->strs + syms->st_name;
159
160 // skip non-object and non-function symbols
161 int st_type = ELF_ST_TYPE(syms->st_info);
162 if ( st_type != STT_FUNC && st_type != STT_OBJECT)
163 continue;
164 // skip empty strings and undefined symbols
165 if (*sym_name == '\0' || syms->st_shndx == SHN_UNDEF) continue;
166
167 symtab->symbols[j].name = sym_name;
168 symtab->symbols[j].offset = syms->st_value - baseaddr;
169 symtab->symbols[j].size = syms->st_size;
170
171 item.key = sym_name;
172 item.data = (void *)&(symtab->symbols[j]);
173
174 hsearch_r(item, ENTER, &ret, symtab->hash_table);
175 }
176 }
177 }
178
179 quit:
180 if (shbuf) free(shbuf);
181 if (phbuf) free(phbuf);
182 if (scn_cache) {
183 for (cnt = 0; cnt < ehdr.e_shnum; cnt++) {
184 if (scn_cache[cnt].c_data != NULL) {
185 free(scn_cache[cnt].c_data);
186 }
187 }
188 free(scn_cache);
189 }
190 return symtab;
191 }
192
193 void destroy_symtab(struct symtab* symtab) {
194 if (!symtab) return;
195 if (symtab->strs) free(symtab->strs);
196 if (symtab->symbols) free(symtab->symbols);
197 if (symtab->hash_table) {
198 hdestroy_r(symtab->hash_table);
199 free(symtab->hash_table);
200 }
201 free(symtab);
202 }
203
204 uintptr_t search_symbol(struct symtab* symtab, uintptr_t base,
205 const char *sym_name, int *sym_size) {
206 ENTRY item;
207 ENTRY* ret = NULL;
208
209 // library does not have symbol table
210 if (!symtab || !symtab->hash_table)
211 return (uintptr_t)NULL;
212
213 item.key = (char*) strdup(sym_name);
214 hsearch_r(item, FIND, &ret, symtab->hash_table);
215 if (ret) {
216 struct elf_symbol * sym = (struct elf_symbol *)(ret->data);
217 uintptr_t rslt = (uintptr_t) ((char*)base + sym->offset);
218 if (sym_size) *sym_size = sym->size;
219 free(item.key);
220 return rslt;
221 }
222
223 quit:
224 free(item.key);
225 return (uintptr_t) NULL;
226 }
227
228 const char* nearest_symbol(struct symtab* symtab, uintptr_t offset,
229 uintptr_t* poffset) {
230 int n = 0;
231 if (!symtab) return NULL;
232 for (; n < symtab->num_symbols; n++) {
233 struct elf_symbol* sym = &(symtab->symbols[n]);
234 if (sym->name != NULL &&
235 offset >= sym->offset && offset < sym->offset + sym->size) {
236 if (poffset) *poffset = (offset - sym->offset);
237 return sym->name;
238 }
239 }
240 return NULL;
241 }