1 /*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #define LOG_TAG "Corkscrew"
18 //#define LOG_NDEBUG 0
19
20 #include <corkscrew/symbol_table.h>
21
22 #include <stdbool.h>
23 #include <stdlib.h>
24 #include <elf.h>
25 #include <fcntl.h>
26 #include <string.h>
27 #include <sys/stat.h>
28 #include <sys/mman.h>
29 #include <cutils/log.h>
30
is_elf(Elf32_Ehdr * e)31 static bool is_elf(Elf32_Ehdr* e) {
32 return (e->e_ident[EI_MAG0] == ELFMAG0 &&
33 e->e_ident[EI_MAG1] == ELFMAG1 &&
34 e->e_ident[EI_MAG2] == ELFMAG2 &&
35 e->e_ident[EI_MAG3] == ELFMAG3);
36 }
37
38 // Compare function for qsort
qcompar(const void * a,const void * b)39 static int qcompar(const void *a, const void *b) {
40 const symbol_t* asym = (const symbol_t*)a;
41 const symbol_t* bsym = (const symbol_t*)b;
42 if (asym->start > bsym->start) return 1;
43 if (asym->start < bsym->start) return -1;
44 return 0;
45 }
46
47 // Compare function for bsearch
bcompar(const void * key,const void * element)48 static int bcompar(const void *key, const void *element) {
49 uintptr_t addr = *(const uintptr_t*)key;
50 const symbol_t* symbol = (const symbol_t*)element;
51 if (addr < symbol->start) return -1;
52 if (addr >= symbol->end) return 1;
53 return 0;
54 }
55
load_symbol_table(const char * filename)56 symbol_table_t* load_symbol_table(const char *filename) {
57 symbol_table_t* table = NULL;
58 ALOGV("Loading symbol table from '%s'.", filename);
59
60 int fd = open(filename, O_RDONLY);
61 if (fd < 0) {
62 goto out;
63 }
64
65 struct stat sb;
66 if (fstat(fd, &sb)) {
67 goto out_close;
68 }
69
70 size_t length = sb.st_size;
71 char* base = mmap(NULL, length, PROT_READ, MAP_PRIVATE, fd, 0);
72 if (base == MAP_FAILED) {
73 goto out_close;
74 }
75
76 // Parse the file header
77 Elf32_Ehdr *hdr = (Elf32_Ehdr*)base;
78 if (!is_elf(hdr)) {
79 goto out_close;
80 }
81 Elf32_Shdr *shdr = (Elf32_Shdr*)(base + hdr->e_shoff);
82
83 // Search for the dynamic symbols section
84 int sym_idx = -1;
85 int dynsym_idx = -1;
86 for (Elf32_Half i = 0; i < hdr->e_shnum; i++) {
87 if (shdr[i].sh_type == SHT_SYMTAB) {
88 sym_idx = i;
89 }
90 if (shdr[i].sh_type == SHT_DYNSYM) {
91 dynsym_idx = i;
92 }
93 }
94 if (dynsym_idx == -1 && sym_idx == -1) {
95 goto out_unmap;
96 }
97
98 table = malloc(sizeof(symbol_table_t));
99 if(!table) {
100 goto out_unmap;
101 }
102 table->num_symbols = 0;
103
104 Elf32_Sym *dynsyms = NULL;
105 int dynnumsyms = 0;
106 char *dynstr = NULL;
107 if (dynsym_idx != -1) {
108 dynsyms = (Elf32_Sym*)(base + shdr[dynsym_idx].sh_offset);
109 dynnumsyms = shdr[dynsym_idx].sh_size / shdr[dynsym_idx].sh_entsize;
110 int dynstr_idx = shdr[dynsym_idx].sh_link;
111 dynstr = base + shdr[dynstr_idx].sh_offset;
112 }
113
114 Elf32_Sym *syms = NULL;
115 int numsyms = 0;
116 char *str = NULL;
117 if (sym_idx != -1) {
118 syms = (Elf32_Sym*)(base + shdr[sym_idx].sh_offset);
119 numsyms = shdr[sym_idx].sh_size / shdr[sym_idx].sh_entsize;
120 int str_idx = shdr[sym_idx].sh_link;
121 str = base + shdr[str_idx].sh_offset;
122 }
123
124 int dynsymbol_count = 0;
125 if (dynsym_idx != -1) {
126 // Iterate through the dynamic symbol table, and count how many symbols
127 // are actually defined
128 for (int i = 0; i < dynnumsyms; i++) {
129 if (dynsyms[i].st_shndx != SHN_UNDEF) {
130 dynsymbol_count++;
131 }
132 }
133 }
134
135 size_t symbol_count = 0;
136 if (sym_idx != -1) {
137 // Iterate through the symbol table, and count how many symbols
138 // are actually defined
139 for (int i = 0; i < numsyms; i++) {
140 if (syms[i].st_shndx != SHN_UNDEF
141 && str[syms[i].st_name]
142 && syms[i].st_value
143 && syms[i].st_size) {
144 symbol_count++;
145 }
146 }
147 }
148
149 // Now, create an entry in our symbol table structure for each symbol...
150 table->num_symbols += symbol_count + dynsymbol_count;
151 table->symbols = malloc(table->num_symbols * sizeof(symbol_t));
152 if (!table->symbols) {
153 free(table);
154 table = NULL;
155 goto out_unmap;
156 }
157
158 size_t symbol_index = 0;
159 if (dynsym_idx != -1) {
160 // ...and populate them
161 for (int i = 0; i < dynnumsyms; i++) {
162 if (dynsyms[i].st_shndx != SHN_UNDEF) {
163 table->symbols[symbol_index].name = strdup(dynstr + dynsyms[i].st_name);
164 table->symbols[symbol_index].start = dynsyms[i].st_value;
165 table->symbols[symbol_index].end = dynsyms[i].st_value + dynsyms[i].st_size;
166 ALOGV(" [%d] '%s' 0x%08x-0x%08x (DYNAMIC)",
167 symbol_index, table->symbols[symbol_index].name,
168 table->symbols[symbol_index].start, table->symbols[symbol_index].end);
169 symbol_index += 1;
170 }
171 }
172 }
173
174 if (sym_idx != -1) {
175 // ...and populate them
176 for (int i = 0; i < numsyms; i++) {
177 if (syms[i].st_shndx != SHN_UNDEF
178 && str[syms[i].st_name]
179 && syms[i].st_value
180 && syms[i].st_size) {
181 table->symbols[symbol_index].name = strdup(str + syms[i].st_name);
182 table->symbols[symbol_index].start = syms[i].st_value;
183 table->symbols[symbol_index].end = syms[i].st_value + syms[i].st_size;
184 ALOGV(" [%d] '%s' 0x%08x-0x%08x",
185 symbol_index, table->symbols[symbol_index].name,
186 table->symbols[symbol_index].start, table->symbols[symbol_index].end);
187 symbol_index += 1;
188 }
189 }
190 }
191
192 // Sort the symbol table entries, so they can be bsearched later
193 qsort(table->symbols, table->num_symbols, sizeof(symbol_t), qcompar);
194
195 out_unmap:
196 munmap(base, length);
197
198 out_close:
199 close(fd);
200
201 out:
202 return table;
203 }
204
free_symbol_table(symbol_table_t * table)205 void free_symbol_table(symbol_table_t* table) {
206 if (table) {
207 for (size_t i = 0; i < table->num_symbols; i++) {
208 free(table->symbols[i].name);
209 }
210 free(table->symbols);
211 free(table);
212 }
213 }
214
find_symbol(const symbol_table_t * table,uintptr_t addr)215 const symbol_t* find_symbol(const symbol_table_t* table, uintptr_t addr) {
216 if (!table) return NULL;
217 return (const symbol_t*)bsearch(&addr, table->symbols, table->num_symbols,
218 sizeof(symbol_t), bcompar);
219 }
220