1 /*
2 * Copyright (C) 2023 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 #include <stddef.h>
18 #include <stdint.h>
19 #include <string.h>
20
21 #include <fstream>
22 #include <memory>
23 #include <optional>
24 #include <vector>
25
26 #include "elf/relocation.h"
27 #include "libelf/elf.h"
28
29 namespace {
30 // Read an entire ELF file into the memory
ReadFile(const std::string & file_name)31 std::vector<uint8_t> ReadFile(const std::string& file_name) {
32 std::ifstream elf_file(file_name, std::ios::binary | std::ios::ate);
33 std::streamsize file_size = elf_file.tellg();
34 elf_file.seekg(0, std::ios::beg);
35
36 std::vector<uint8_t> ret(file_size);
37 elf_file.read(reinterpret_cast<char*>(ret.data()), file_size);
38 return ret;
39 }
40 } // namespace
41
42 #define ASSERT(cond) \
43 { \
44 if (!(cond)) { \
45 fprintf(stderr, "%s:%d. Assert failed \"(%s)\"\n", __FILE__, __LINE__, #cond); \
46 exit(1); \
47 } \
48 }
49
50 // Simulate an ELF relocation processs using GBL relocation library. Fail if the ELF contains
51 // relocation types that we don't expect.
52 //
53 // Usage:
54 // <executable> <ELF file> <Binary only version (ELF header stripped) of the ELF>
55 //
56 // The binary only version can be obtained by `llvm-objcopy -O binary <ELF> <output>`
57 //
58 // Return 0 if successful.
main(int argc,char * argv[])59 int main(int argc, char* argv[]) {
60 if (argc != 3) {
61 return 1;
62 }
63
64 std::vector<uint8_t> elf_file = ReadFile(argv[1]);
65 std::vector<uint8_t> bin_file = ReadFile(argv[2]);
66
67 Elf64_Ehdr elf_header;
68 ASSERT(elf_file.size() >= sizeof(elf_header));
69 memcpy(&elf_header, elf_file.data(), sizeof(elf_header));
70
71 // Iterate all program headers and find out the address for dynamic section.
72 const uint8_t* program_hdr_start = elf_file.data() + elf_header.e_phoff;
73 std::optional<uint64_t> dynamic_section_offset = std::nullopt;
74 for (size_t i = 0; i < elf_header.e_phnum; i++) {
75 const uint8_t* header_start = program_hdr_start + i * sizeof(Elf64_Phdr);
76 Elf64_Phdr elf_program_header;
77 ASSERT(static_cast<size_t>(header_start + sizeof(elf_program_header) - elf_file.data()) <=
78 elf_file.size());
79 memcpy(&elf_program_header, header_start, sizeof(elf_program_header));
80 if (elf_program_header.p_type == PT_DYNAMIC) {
81 // Store the physical address
82 // For PIE ELF this is the relative offset to ELF file start.
83 dynamic_section_offset = elf_program_header.p_paddr;
84 break;
85 }
86 }
87
88 // Dynamic section not found.
89 if (!dynamic_section_offset) {
90 return 1;
91 }
92
93 ASSERT(bin_file.size() >= *dynamic_section_offset);
94 // Perform relocation as if we have loaded the program @ address bin_file.data().
95 return ApplyRelocation(reinterpret_cast<uintptr_t>(bin_file.data()),
96 reinterpret_cast<uintptr_t>(bin_file.data() + *dynamic_section_offset))
97 ? 0
98 : 1;
99 }
100