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3960
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1 /*
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2 * Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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20 * or visit www.oracle.com if you need additional information or have any
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21 * questions.
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22 *
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23 */
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24
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25 #include "salibelf.h"
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26 #include <stdlib.h>
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27 #include <unistd.h>
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28 #include <string.h>
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29
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30 extern void print_debug(const char*,...);
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31
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32 // ELF file parsing helpers. Note that we do *not* use libelf here.
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33 int read_elf_header(int fd, ELF_EHDR* ehdr) {
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34 if (pread(fd, ehdr, sizeof (ELF_EHDR), 0) != sizeof (ELF_EHDR) ||
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35 memcmp(&ehdr->e_ident[EI_MAG0], ELFMAG, SELFMAG) != 0 ||
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36 ehdr->e_version != EV_CURRENT) {
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37 return 0;
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38 }
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39 return 1;
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40 }
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41
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42 bool is_elf_file(int fd) {
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43 ELF_EHDR ehdr;
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44 return read_elf_header(fd, &ehdr);
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45 }
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46
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47 // read program header table of an ELF file
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48 ELF_PHDR* read_program_header_table(int fd, ELF_EHDR* hdr) {
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49 ELF_PHDR* phbuf = 0;
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50 // allocate memory for program header table
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51 size_t nbytes = hdr->e_phnum * hdr->e_phentsize;
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52
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53 if ((phbuf = (ELF_PHDR*) malloc(nbytes)) == NULL) {
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54 print_debug("can't allocate memory for reading program header table\n");
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55 return NULL;
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56 }
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57
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58 if (pread(fd, phbuf, nbytes, hdr->e_phoff) != nbytes) {
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59 print_debug("ELF file is truncated! can't read program header table\n");
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60 free(phbuf);
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61 return NULL;
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62 }
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63
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64 return phbuf;
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65 }
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66
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67 // read section header table of an ELF file
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68 ELF_SHDR* read_section_header_table(int fd, ELF_EHDR* hdr) {
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69 ELF_SHDR* shbuf = 0;
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70 // allocate memory for section header table
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71 size_t nbytes = hdr->e_shnum * hdr->e_shentsize;
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72
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73 if ((shbuf = (ELF_SHDR*) malloc(nbytes)) == NULL) {
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74 print_debug("can't allocate memory for reading section header table\n");
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75 return NULL;
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76 }
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77
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78 if (pread(fd, shbuf, nbytes, hdr->e_shoff) != nbytes) {
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79 print_debug("ELF file is truncated! can't read section header table\n");
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80 free(shbuf);
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81 return NULL;
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82 }
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83
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84 return shbuf;
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85 }
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86
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87 // read a particular section's data
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88 void* read_section_data(int fd, ELF_EHDR* ehdr, ELF_SHDR* shdr) {
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89 void *buf = NULL;
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90 if (shdr->sh_type == SHT_NOBITS || shdr->sh_size == 0) {
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91 return buf;
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92 }
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93 if ((buf = calloc(shdr->sh_size, 1)) == NULL) {
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94 print_debug("can't allocate memory for reading section data\n");
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95 return NULL;
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96 }
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97 if (pread(fd, buf, shdr->sh_size, shdr->sh_offset) != shdr->sh_size) {
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98 free(buf);
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99 print_debug("section data read failed\n");
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100 return NULL;
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101 }
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102 return buf;
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103 }
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104
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105 uintptr_t find_base_address(int fd, ELF_EHDR* ehdr) {
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106 uintptr_t baseaddr = (uintptr_t)-1;
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107 int cnt;
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108 ELF_PHDR *phbuf, *phdr;
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109
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110 // read program header table
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111 if ((phbuf = read_program_header_table(fd, ehdr)) == NULL) {
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112 goto quit;
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113 }
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114
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115 // the base address of a shared object is the lowest vaddr of
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116 // its loadable segments (PT_LOAD)
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117 for (phdr = phbuf, cnt = 0; cnt < ehdr->e_phnum; cnt++, phdr++) {
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118 if (phdr->p_type == PT_LOAD && phdr->p_vaddr < baseaddr) {
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119 baseaddr = phdr->p_vaddr;
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120 }
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121 }
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122
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123 quit:
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124 if (phbuf) free(phbuf);
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125 return baseaddr;
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126 }
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