1 // Copyright 2014 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 // Tool to pack and unpack relative relocations in a shared library.
6 //
7 // Invoke with -v to trace actions taken when packing or unpacking.
8 // Invoke with -p to pad removed relocations with R_*_NONE. Suppresses
9 // shrinking of .rel.dyn.
10 // See PrintUsage() below for full usage details.
11 //
12 // NOTE: Breaks with libelf 0.152, which is buggy. libelf 0.158 works.
13
14 #include <errno.h>
15 #include <fcntl.h>
16 #include <getopt.h>
17 #include <stdio.h>
18 #include <stdlib.h>
19 #include <sys/types.h>
20 #include <unistd.h>
21 #include <string>
22
23 #include "debug.h"
24 #include "elf_file.h"
25 #include "elf_traits.h"
26 #include "libelf.h"
27
28 #include "nativehelper/ScopedFd.h"
29
PrintUsage(const char * argv0)30 static void PrintUsage(const char* argv0) {
31 std::string temporary = argv0;
32 const size_t last_slash = temporary.find_last_of("/");
33 if (last_slash != temporary.npos) {
34 temporary.erase(0, last_slash + 1);
35 }
36 const char* basename = temporary.c_str();
37
38 printf(
39 "Usage: %s [-u] [-v] [-p] file\n\n"
40 "Pack or unpack relative relocations in a shared library.\n\n"
41 " -u, --unpack unpack previously packed relative relocations\n"
42 " -v, --verbose trace object file modifications (for debugging)\n"
43 " -p, --pad do not shrink relocations, but pad (for debugging)\n\n",
44 basename);
45
46 printf(
47 "Debug sections are not handled, so packing should not be used on\n"
48 "shared libraries compiled for debugging or otherwise unstripped.\n");
49 }
50
main(int argc,char * argv[])51 int main(int argc, char* argv[]) {
52 bool is_unpacking = false;
53 bool is_verbose = false;
54 bool is_padding = false;
55
56 static const option options[] = {
57 {"unpack", 0, 0, 'u'}, {"verbose", 0, 0, 'v'}, {"pad", 0, 0, 'p'},
58 {"help", 0, 0, 'h'}, {NULL, 0, 0, 0}
59 };
60 bool has_options = true;
61 while (has_options) {
62 int c = getopt_long(argc, argv, "uvph", options, NULL);
63 switch (c) {
64 case 'u':
65 is_unpacking = true;
66 break;
67 case 'v':
68 is_verbose = true;
69 break;
70 case 'p':
71 is_padding = true;
72 break;
73 case 'h':
74 PrintUsage(argv[0]);
75 return 0;
76 case '?':
77 LOG(INFO) << "Try '" << argv[0] << " --help' for more information.";
78 return 1;
79 case -1:
80 has_options = false;
81 break;
82 default:
83 NOTREACHED();
84 return 1;
85 }
86 }
87 if (optind != argc - 1) {
88 LOG(INFO) << "Try '" << argv[0] << " --help' for more information.";
89 return 1;
90 }
91
92 if (elf_version(EV_CURRENT) == EV_NONE) {
93 LOG(WARNING) << "Elf Library is out of date!";
94 }
95
96 const char* file = argv[argc - 1];
97 ScopedFd fd(open(file, O_RDWR));
98 if (fd.get() == -1) {
99 LOG(ERROR) << file << ": " << strerror(errno);
100 return 1;
101 }
102
103 if (is_verbose)
104 relocation_packer::Logger::SetVerbose(1);
105
106 // We need to detect elf class in order to create
107 // correct implementation
108 uint8_t e_ident[EI_NIDENT];
109 if (TEMP_FAILURE_RETRY(read(fd.get(), e_ident, EI_NIDENT) != EI_NIDENT)) {
110 LOG(ERROR) << file << ": failed to read elf header:" << strerror(errno);
111 return 1;
112 }
113
114 if (TEMP_FAILURE_RETRY(lseek(fd.get(), 0, SEEK_SET)) != 0) {
115 LOG(ERROR) << file << ": lseek to 0 failed:" << strerror(errno);
116 return 1;
117 }
118
119 bool status = false;
120
121 if (e_ident[EI_CLASS] == ELFCLASS32) {
122 relocation_packer::ElfFile<ELF32_traits> elf_file(fd.get());
123 elf_file.SetPadding(is_padding);
124
125 if (is_unpacking) {
126 status = elf_file.UnpackRelocations();
127 } else {
128 status = elf_file.PackRelocations();
129 }
130 } else if (e_ident[EI_CLASS] == ELFCLASS64) {
131 relocation_packer::ElfFile<ELF64_traits> elf_file(fd.get());
132 elf_file.SetPadding(is_padding);
133
134 if (is_unpacking) {
135 status = elf_file.UnpackRelocations();
136 } else {
137 status = elf_file.PackRelocations();
138 }
139 } else {
140 LOG(ERROR) << file << ": unknown ELFCLASS: " << e_ident[EI_CLASS];
141 return 1;
142 }
143
144 if (!status) {
145 LOG(ERROR) << file << ": failed to pack/unpack file";
146 return 1;
147 }
148
149 return 0;
150 }
151