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
202
203
204
205
206
207
208
209
210
211
212
213
214
215
|
#include "ELFLoader.h"
#include <AK/kstdio.h>
//#define ELFLOADER_DEBUG
//#define SUPPORT_RELOCATIONS
ELFLoader::ELFLoader(const byte* buffer)
: m_image(buffer)
{
}
ELFLoader::~ELFLoader()
{
}
bool ELFLoader::load()
{
#ifdef ELFLOADER_DEBUG
m_image.dump();
#endif
if (!m_image.is_valid())
return false;
if (!layout())
return false;
#ifdef SUPPORT_RELOCATIONS
if (!perform_relocations())
return false;
#endif
return true;
}
bool ELFLoader::layout()
{
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Layout\n");
#endif
bool failed = false;
m_image.for_each_program_header([&] (const ELFImage::ProgramHeader& program_header) {
if (program_header.type() != PT_LOAD)
return;
#ifdef ELFLOADER_DEBUG
kprintf("PH: L%x %u r:%u w:%u\n", program_header.laddr().get(), program_header.size_in_memory(), program_header.is_readable(), program_header.is_writable());
#endif
if (program_header.is_writable()) {
allocate_section(program_header.laddr(), program_header.size_in_memory(), program_header.alignment(), program_header.is_readable(), program_header.is_writable());
} else {
map_section(program_header.laddr(), program_header.size_in_memory(), program_header.alignment(), program_header.offset(), program_header.is_readable(), program_header.is_writable());
}
});
m_image.for_each_section_of_type(SHT_PROGBITS, [] (const ELFImage::Section& section) {
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Copying progbits section: %s\n", section.name());
#endif
if (!section.size())
return true;
char* ptr = (char*)section.address();
if (!ptr) {
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: ignoring section '%s' with null address\n", section.name());
#endif
return true;
}
// If this section isn't writable, it's already mmapped.
if (section.is_writable())
memcpy(ptr, section.raw_data(), section.size());
#ifdef SUPPORT_RELOCATIONS
m_sections.set(section.name(), move(ptr));
#endif
return true;
});
m_image.for_each_section_of_type(SHT_NOBITS, [&failed] (const ELFImage::Section& section) {
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Copying nobits section: %s\n", section.name());
#endif
if (!section.size())
return true;
char* ptr = (char*)section.address();
if (!ptr) {
kprintf("ELFLoader: failed to allocate section '%s'\n", section.name());
failed = true;
return false;
}
memset(ptr, 0, section.size());
#ifdef SUPPORT_RELOCATIONS
m_sections.set(section.name(), move(ptr));
#endif
return true;
});
return !failed;
}
#ifdef SUPPORT_RELOCATIONS
void* ELFLoader::lookup(const ELFImage::Symbol& symbol)
{
if (symbol.section().is_undefined())
return symbol_ptr(symbol.name());
return area_for_section(symbol.section()) + symbol.value();
}
#endif
#ifdef SUPPORT_RELOCATIONS
char* ELFLoader::area_for_section(const ELFImage::Section& section)
{
return area_for_section_name(section.name());
}
char* ELFLoader::area_for_section_name(const char* name)
{
if (auto it = m_sections.find(name); it != m_sections.end())
return (*it).value;
ASSERT_NOT_REACHED();
return nullptr;
}
#endif
#ifdef SUPPORT_RELOCATIONS
bool ELFLoader::perform_relocations()
{
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Performing relocations\n");
#endif
bool failed = false;
m_image.for_each_section_of_type(SHT_PROGBITS, [this, &failed] (const ELFImage::Section& section) -> bool {
auto& relocations = section.relocations();
if (relocations.is_undefined())
return true;
relocations.for_each_relocation([this, section, &failed] (const ELFImage::Relocation& relocation) {
auto symbol = relocation.symbol();
auto& patch_ptr = *reinterpret_cast<ptrdiff_t*>(area_for_section(section) + relocation.offset());
switch (relocation.type()) {
case R_386_PC32: {
char* target_ptr = (char*)lookup(symbol);
if (!target_ptr) {
kprintf("ELFLoader: unresolved symbol '%s'\n", symbol.name());
failed = true;
return false;
}
ptrdiff_t relative_offset = (char*)target_ptr - ((char*)&patch_ptr + 4);
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Relocate PC32: offset=%x, symbol=%u(%s) value=%x target=%p, offset=%d\n",
relocation.offset(),
symbol.index(),
symbol.name(),
symbol.value(),
target_ptr,
relative_offset
);
#endif
patch_ptr = relative_offset;
break;
}
case R_386_32: {
#ifdef ELFLOADER_DEBUG
kprintf("ELFLoader: Relocate Abs32: symbol=%u(%s), value=%x, section=%s\n",
symbol.index(),
symbol.name(),
symbol.value(),
symbol.section().name()
);
#endif
char* target_ptr = area_for_section(symbol.section()) + symbol.value();
patch_ptr += (ptrdiff_t)target_ptr;
break;
}
default:
ASSERT_NOT_REACHED();
break;
}
return true;
});
return !failed;
});
return !failed;
}
#endif
char* ELFLoader::symbol_ptr(const char* name)
{
char* found_ptr = nullptr;
m_image.for_each_symbol([&] (const ELFImage::Symbol symbol) {
if (symbol.type() != STT_FUNC)
return true;
if (strcmp(symbol.name(), name))
return true;
if (m_image.is_executable())
found_ptr = (char*)symbol.value();
#ifdef SUPPORT_RELOCATIONS
else if (m_image.is_relocatable())
found_ptr = area_for_section(symbol.section()) + symbol.value();
#endif
else
ASSERT_NOT_REACHED();
return false;
});
return found_ptr;
}
bool ELFLoader::allocate_section(LinearAddress laddr, size_t size, size_t alignment, bool is_readable, bool is_writable)
{
ASSERT(alloc_section_hook);
return alloc_section_hook(laddr, size, alignment, is_readable, is_writable, String::format("elf-alloc-%s%s", is_readable ? "r" : "", is_writable ? "w" : ""));
}
bool ELFLoader::map_section(LinearAddress laddr, size_t size, size_t alignment, size_t offset_in_image, bool is_readable, bool is_writable)
{
ASSERT(alloc_section_hook);
return map_section_hook(laddr, size, alignment, offset_in_image, is_readable, is_writable, String::format("elf-map-%s%s", is_readable ? "r" : "", is_writable ? "w" : ""));
}
|
