1 /*
2 * Copyright (c) 2003, 2006, 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 "salibelf.h"
26 #include <stdlib.h>
27 #include <unistd.h>
28 #include <string.h>
29
30 extern void print_debug(const char*,...);
31
32 // ELF file parsing helpers. Note that we do *not* use libelf here.
read_elf_header(int fd,ELF_EHDR * ehdr)33 int read_elf_header(int fd, ELF_EHDR* ehdr) {
34 if (pread(fd, ehdr, sizeof (ELF_EHDR), 0) != sizeof (ELF_EHDR) ||
35 memcmp(&ehdr->e_ident[EI_MAG0], ELFMAG, SELFMAG) != 0 ||
36 ehdr->e_version != EV_CURRENT) {
37 return 0;
38 }
39 return 1;
40 }
41
is_elf_file(int fd)42 bool is_elf_file(int fd) {
43 ELF_EHDR ehdr;
44 return read_elf_header(fd, &ehdr);
45 }
46
47 // read program header table of an ELF file
read_program_header_table(int fd,ELF_EHDR * hdr)48 ELF_PHDR* read_program_header_table(int fd, ELF_EHDR* hdr) {
49 ELF_PHDR* phbuf = 0;
50 // allocate memory for program header table
51 size_t nbytes = hdr->e_phnum * hdr->e_phentsize;
52
53 if ((phbuf = (ELF_PHDR*) malloc(nbytes)) == NULL) {
54 print_debug("can't allocate memory for reading program header table\n");
55 return NULL;
56 }
57
58 if (pread(fd, phbuf, nbytes, hdr->e_phoff) != nbytes) {
59 print_debug("ELF file is truncated! can't read program header table\n");
60 free(phbuf);
61 return NULL;
62 }
63
64 return phbuf;
65 }
66
67 // read section header table of an ELF file
read_section_header_table(int fd,ELF_EHDR * hdr)68 ELF_SHDR* read_section_header_table(int fd, ELF_EHDR* hdr) {
69 ELF_SHDR* shbuf = 0;
70 // allocate memory for section header table
71 size_t nbytes = hdr->e_shnum * hdr->e_shentsize;
72
73 if ((shbuf = (ELF_SHDR*) malloc(nbytes)) == NULL) {
74 print_debug("can't allocate memory for reading section header table\n");
75 return NULL;
76 }
77
78 if (pread(fd, shbuf, nbytes, hdr->e_shoff) != nbytes) {
79 print_debug("ELF file is truncated! can't read section header table\n");
80 free(shbuf);
81 return NULL;
82 }
83
84 return shbuf;
85 }
86
87 // read a particular section's data
read_section_data(int fd,ELF_EHDR * ehdr,ELF_SHDR * shdr)88 void* read_section_data(int fd, ELF_EHDR* ehdr, ELF_SHDR* shdr) {
89 void *buf = NULL;
90 if (shdr->sh_type == SHT_NOBITS || shdr->sh_size == 0) {
91 return buf;
92 }
93 if ((buf = calloc(shdr->sh_size, 1)) == NULL) {
94 print_debug("can't allocate memory for reading section data\n");
95 return NULL;
96 }
97 if (pread(fd, buf, shdr->sh_size, shdr->sh_offset) != shdr->sh_size) {
98 free(buf);
99 print_debug("section data read failed\n");
100 return NULL;
101 }
102 return buf;
103 }
104
find_base_address(int fd,ELF_EHDR * ehdr)105 uintptr_t find_base_address(int fd, ELF_EHDR* ehdr) {
106 uintptr_t baseaddr = (uintptr_t)-1;
107 int cnt;
108 ELF_PHDR *phbuf, *phdr;
109
110 // read program header table
111 if ((phbuf = read_program_header_table(fd, ehdr)) == NULL) {
112 goto quit;
113 }
114
115 // the base address of a shared object is the lowest vaddr of
116 // its loadable segments (PT_LOAD)
117 for (phdr = phbuf, cnt = 0; cnt < ehdr->e_phnum; cnt++, phdr++) {
118 if (phdr->p_type == PT_LOAD && phdr->p_vaddr < baseaddr) {
119 baseaddr = phdr->p_vaddr;
120 }
121 }
122
123 quit:
124 if (phbuf) free(phbuf);
125 return baseaddr;
126 }
127