1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
|
/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ART_LIBELFFILE_ELF_ELF_DEBUG_READER_H_
#define ART_LIBELFFILE_ELF_ELF_DEBUG_READER_H_
#include "base/array_ref.h"
#include "dwarf/headers.h"
#include "elf/elf_utils.h"
#include "xz_utils.h"
#include <map>
#include <string_view>
namespace art {
// Trivial ELF file reader.
//
// It is the bare minimum needed to read mini-debug-info symbols for unwinding.
// We use it to merge JIT mini-debug-infos together or to prune them after GC.
template <typename ElfTypes>
class ElfDebugReader {
public:
// Note that the input buffer might be misaligned.
using Elf_Ehdr ALIGNED(1) = typename ElfTypes::Ehdr;
using Elf_Phdr ALIGNED(1) = typename ElfTypes::Phdr;
using Elf_Shdr ALIGNED(1) = typename ElfTypes::Shdr;
using Elf_Sym ALIGNED(1) = typename ElfTypes::Sym;
using Elf_Addr ALIGNED(1) = typename ElfTypes::Addr;
// Call Frame Information.
struct CFI {
uint32_t length; // Length excluding the size of this field.
int32_t cie_pointer; // Offset in the section or -1 for CIE.
const uint8_t* data() const { return reinterpret_cast<const uint8_t*>(this); }
size_t size() const { return sizeof(uint32_t) + length; }
} PACKED(1);
// Common Information Entry.
struct CIE : public CFI {
} PACKED(1);
// Frame Description Entry.
struct FDE : public CFI {
Elf_Addr sym_addr;
Elf_Addr sym_size;
} PACKED(1);
explicit ElfDebugReader(ArrayRef<const uint8_t> file) : file_(file) {
header_ = Read<Elf_Ehdr>(/*offset=*/ 0);
CHECK_EQ(header_->e_ident[0], ELFMAG0);
CHECK_EQ(header_->e_ident[1], ELFMAG1);
CHECK_EQ(header_->e_ident[2], ELFMAG2);
CHECK_EQ(header_->e_ident[3], ELFMAG3);
CHECK_EQ(header_->e_ident[4], sizeof(Elf_Addr) / sizeof(uint32_t));
CHECK_EQ(header_->e_ehsize, sizeof(Elf_Ehdr));
// Find all ELF sections.
CHECK_EQ(header_->e_shentsize, sizeof(Elf_Shdr));
sections_ = Read<Elf_Shdr>(header_->e_shoff, header_->e_shnum);
for (const Elf_Shdr& section : sections_) {
const char* name = Read<char>(sections_[header_->e_shstrndx].sh_offset + section.sh_name);
section_map_[std::string_view(name)] = §ion;
}
// Decompressed embedded debug symbols, if any.
const Elf_Shdr* gnu_debugdata = section_map_[".gnu_debugdata"];
if (gnu_debugdata != nullptr) {
auto compressed = Read<uint8_t>(gnu_debugdata->sh_offset, gnu_debugdata->sh_size);
XzDecompress(compressed, &decompressed_gnu_debugdata_);
gnu_debugdata_reader_.reset(new ElfDebugReader(decompressed_gnu_debugdata_));
}
}
explicit ElfDebugReader(const std::vector<uint8_t>& file)
: ElfDebugReader(ArrayRef<const uint8_t>(file)) {
}
// Check that ELF signature is present at the start of the files,
// and that the ELF bitness matches the ElfTypes template arguments.
static bool IsValidElfHeader(const std::vector<uint8_t>& data) {
static constexpr bool kIs64Bit = sizeof(Elf_Addr) == sizeof(uint64_t);
static constexpr char kMagic[] = { 0x7f, 'E', 'L', 'F', kIs64Bit ? 2 : 1 };
return data.size() >= sizeof(kMagic) && memcmp(data.data(), kMagic, sizeof(kMagic)) == 0;
}
const Elf_Ehdr* GetHeader() { return header_; }
ArrayRef<Elf_Shdr> GetSections() { return sections_; }
const Elf_Shdr* GetSection(const char* name) { return section_map_[name]; }
// Find the base address where the ELF file wants to be loaded.
// This is generally zero (therefore always requiring relocation).
Elf_Addr GetLoadAddress() {
std::optional<Elf_Addr> addr;
CHECK_EQ(header_->e_phentsize, sizeof(Elf_Phdr));
for (const Elf_Phdr& phdr : Read<Elf_Phdr>(header_->e_phoff, header_->e_phnum)) {
if (phdr.p_type == PT_LOAD) {
addr = addr.has_value() ? std::min(addr.value(), phdr.p_vaddr) : phdr.p_vaddr;
}
}
CHECK(addr.has_value());
return addr.value();
}
template <typename VisitSym>
void VisitFunctionSymbols(VisitSym&& visit_sym) {
const Elf_Shdr* symtab = GetSection(".symtab");
const Elf_Shdr* strtab = GetSection(".strtab");
const Elf_Shdr* text = GetSection(".text");
if (symtab != nullptr && strtab != nullptr) {
CHECK_EQ(symtab->sh_entsize, sizeof(Elf_Sym));
size_t count = symtab->sh_size / sizeof(Elf_Sym);
for (const Elf_Sym& symbol : Read<Elf_Sym>(symtab->sh_offset, count)) {
if (ELF_ST_TYPE(symbol.st_info) == STT_FUNC &&
symbol.st_shndx < sections_.size() && // Ignore ABS section.
§ions_[symbol.st_shndx] == text) {
visit_sym(symbol, Read<char>(strtab->sh_offset + symbol.st_name));
}
}
}
if (gnu_debugdata_reader_ != nullptr) {
gnu_debugdata_reader_->VisitFunctionSymbols(std::forward<VisitSym>(visit_sym));
}
}
template <typename VisitSym>
void VisitDynamicSymbols(VisitSym&& visit_sym) {
const Elf_Shdr* dynsym = GetSection(".dynsym");
const Elf_Shdr* dynstr = GetSection(".dynstr");
if (dynsym != nullptr && dynstr != nullptr) {
CHECK_EQ(dynsym->sh_entsize, sizeof(Elf_Sym));
size_t count = dynsym->sh_size / sizeof(Elf_Sym);
for (const Elf_Sym& symbol : Read<Elf_Sym>(dynsym->sh_offset, count)) {
visit_sym(symbol, Read<char>(dynstr->sh_offset + symbol.st_name));
}
}
}
template <typename VisitCIE, typename VisitFDE>
void VisitDebugFrame(VisitCIE&& visit_cie, VisitFDE&& visit_fde) {
const Elf_Shdr* debug_frame = GetSection(".debug_frame");
if (debug_frame != nullptr) {
for (size_t offset = 0; offset < debug_frame->sh_size;) {
const CFI* entry = Read<CFI>(debug_frame->sh_offset + offset);
DCHECK_LE(entry->size(), debug_frame->sh_size - offset);
if (entry->cie_pointer == -1) {
visit_cie(Read<CIE>(debug_frame->sh_offset + offset));
} else {
const FDE* fde = Read<FDE>(debug_frame->sh_offset + offset);
visit_fde(fde, Read<CIE>(debug_frame->sh_offset + fde->cie_pointer));
}
offset += entry->size();
}
}
if (gnu_debugdata_reader_ != nullptr) {
gnu_debugdata_reader_->VisitDebugFrame(std::forward<VisitCIE>(visit_cie),
std::forward<VisitFDE>(visit_fde));
}
}
private:
template<typename T>
const T* Read(size_t offset) {
DCHECK_LE(offset + sizeof(T), file_.size());
return reinterpret_cast<const T*>(file_.data() + offset);
}
template<typename T>
ArrayRef<const T> Read(size_t offset, size_t count) {
DCHECK_LE(offset + count * sizeof(T), file_.size());
return ArrayRef<const T>(Read<T>(offset), count);
}
ArrayRef<const uint8_t> const file_;
const Elf_Ehdr* header_;
ArrayRef<const Elf_Shdr> sections_;
std::unordered_map<std::string_view, const Elf_Shdr*> section_map_;
std::vector<uint8_t> decompressed_gnu_debugdata_;
std::unique_ptr<ElfDebugReader> gnu_debugdata_reader_;
DISALLOW_COPY_AND_ASSIGN(ElfDebugReader);
};
} // namespace art
#endif // ART_LIBELFFILE_ELF_ELF_DEBUG_READER_H_
|