1 /*
2 * Copyright (C) 2015 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 "DEBUG"
18
19 #include <elf.h>
20 #include <stdint.h>
21 #include <stdlib.h>
22 #include <string.h>
23
24 #include <string>
25
26 #include <backtrace/Backtrace.h>
27 #include <base/stringprintf.h>
28 #include <log/log.h>
29
30 #include "elf_utils.h"
31
32 #define NOTE_ALIGN(size) ((size + 3) & ~3)
33
34 template <typename HdrType, typename PhdrType, typename NhdrType>
get_build_id(Backtrace * backtrace,uintptr_t base_addr,uint8_t * e_ident,std::string * build_id)35 static bool get_build_id(
36 Backtrace* backtrace, uintptr_t base_addr, uint8_t* e_ident, std::string* build_id) {
37 HdrType hdr;
38
39 memcpy(&hdr.e_ident[0], e_ident, EI_NIDENT);
40
41 // First read the rest of the header.
42 if (backtrace->Read(base_addr + EI_NIDENT, reinterpret_cast<uint8_t*>(&hdr) + EI_NIDENT,
43 sizeof(HdrType) - EI_NIDENT) != sizeof(HdrType) - EI_NIDENT) {
44 return false;
45 }
46
47 for (size_t i = 0; i < hdr.e_phnum; i++) {
48 PhdrType phdr;
49 if (backtrace->Read(base_addr + hdr.e_phoff + i * hdr.e_phentsize,
50 reinterpret_cast<uint8_t*>(&phdr), sizeof(phdr)) != sizeof(phdr)) {
51 return false;
52 }
53 // Looking for the .note.gnu.build-id note.
54 if (phdr.p_type == PT_NOTE) {
55 size_t hdr_size = phdr.p_filesz;
56 uintptr_t addr = base_addr + phdr.p_offset;
57 while (hdr_size >= sizeof(NhdrType)) {
58 NhdrType nhdr;
59 if (backtrace->Read(addr, reinterpret_cast<uint8_t*>(&nhdr), sizeof(nhdr)) != sizeof(nhdr)) {
60 return false;
61 }
62 addr += sizeof(nhdr);
63 if (nhdr.n_type == NT_GNU_BUILD_ID) {
64 // Skip the name (which is the owner and should be "GNU").
65 addr += NOTE_ALIGN(nhdr.n_namesz);
66 uint8_t build_id_data[160];
67 if (nhdr.n_descsz > sizeof(build_id_data)) {
68 ALOGE("Possible corrupted note, desc size value is too large: %u",
69 nhdr.n_descsz);
70 return false;
71 }
72 if (backtrace->Read(addr, build_id_data, nhdr.n_descsz) != nhdr.n_descsz) {
73 return false;
74 }
75
76 build_id->clear();
77 for (size_t bytes = 0; bytes < nhdr.n_descsz; bytes++) {
78 *build_id += android::base::StringPrintf("%02x", build_id_data[bytes]);
79 }
80
81 return true;
82 } else {
83 // Move past the extra note data.
84 hdr_size -= sizeof(nhdr);
85 size_t skip_bytes = NOTE_ALIGN(nhdr.n_namesz) + NOTE_ALIGN(nhdr.n_descsz);
86 addr += skip_bytes;
87 if (hdr_size < skip_bytes) {
88 break;
89 }
90 hdr_size -= skip_bytes;
91 }
92 }
93 }
94 }
95 return false;
96 }
97
elf_get_build_id(Backtrace * backtrace,uintptr_t addr,std::string * build_id)98 bool elf_get_build_id(Backtrace* backtrace, uintptr_t addr, std::string* build_id) {
99 // Read and verify the elf magic number first.
100 uint8_t e_ident[EI_NIDENT];
101 if (backtrace->Read(addr, e_ident, SELFMAG) != SELFMAG) {
102 return false;
103 }
104
105 if (memcmp(e_ident, ELFMAG, SELFMAG) != 0) {
106 return false;
107 }
108
109 // Read the rest of EI_NIDENT.
110 if (backtrace->Read(addr + SELFMAG, e_ident + SELFMAG, EI_NIDENT - SELFMAG) != EI_NIDENT - SELFMAG) {
111 return false;
112 }
113
114 if (e_ident[EI_CLASS] == ELFCLASS32) {
115 return get_build_id<Elf32_Ehdr, Elf32_Phdr, Elf32_Nhdr>(backtrace, addr, e_ident, build_id);
116 } else if (e_ident[EI_CLASS] == ELFCLASS64) {
117 return get_build_id<Elf64_Ehdr, Elf64_Phdr, Elf64_Nhdr>(backtrace, addr, e_ident, build_id);
118 }
119
120 return false;
121 }
122