forked from nothingelsematters/pseudo-jit
-
Notifications
You must be signed in to change notification settings - Fork 0
/
compiler.cpp
183 lines (156 loc) · 5.48 KB
/
compiler.cpp
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
#include <iostream>
#include <sys/mman.h>
#include <sys/types.h>
#include <vector>
#include <string.h>
#include <string>
#include <sstream>
#include <cstring>
#include <iterator>
uint8_t const DEFAULT_VALUE_1 = 0xFF;
uint8_t const DEFAULT_VALUE_2 = 0x04;
size_t const DEFAULT_INDEX_1 = 5;
size_t const DEFAULT_INDEX_2 = 10;
/*
* code:
* push rbp
* move rbp, rsp
* mov eax, 0xFF
* mov ebx, 0x04
* imul eax, ebx
* pop rbp
* ret
*/
using jitFunc = int(*)();
std::vector<uint8_t> code {
0x55,
0x48, 0x89, 0xE5,
0xB8, DEFAULT_VALUE_1, 0x00, 0x00, 0x00,
0xBB, DEFAULT_VALUE_2, 0x00, 0x00, 0x00,
0x0F, 0xAF, 0xC3,
0x5D,
0xc3
};
void printErrorMessage(std::string const& message, bool useStrerror = true) {
std::cerr << "Error occurred, " << message << "." << std::endl;
if (useStrerror) {
std::cerr<< strerror(errno) << std::endl;
}
}
void printHelpMessage() {
std::cout << "It is an educational project, aim is to to understand how JIT compilers work.\n"
"Function, provided here, is simple: it multiplies two numbers (255 and 4 by default)\n"
"Supported commands:\n"
"execute <arg1> <arg2> - executes function with specified arguments, it's possible to specify"
"one or none of them;\n"
"exit - close program;\n"
"help | -help | --help - print this message"
<< std::endl;
}
void* allocateMemory(size_t len) {
void* memory = mmap(nullptr, len, PROT_WRITE | PROT_READ, MAP_ANON | MAP_PRIVATE, -1, 0);
if (memory == MAP_FAILED) {
return nullptr;
}
return memory;
}
bool freeMemory(void* addr, size_t len) {
return munmap(addr, len) == 0;
}
bool changePermissions(void* addr, size_t len, int prot) {
return mprotect(addr, len, prot) == 0;
}
bool changePermissionsAndCheck(void* addr, size_t len, int prot) {
if (!changePermissions(addr, len, prot)) {
printErrorMessage("can't change memory permission using mprotect");
if (!freeMemory(addr, len)) {
printErrorMessage("can't free allocated memory using munmap");
}
return false;
}
return true;
}
std::vector<std::string> splitString(std::string const& str) {
std::istringstream stream(str);
std::vector<std::string> result{std::istream_iterator<std::string>(stream),
std::istream_iterator<std::string>()};
return result;
}
void setDefault(size_t index, uint8_t value) {
code[index] = value;
code[index + 1] = 0x00;
code[index + 2] = 0x00;
code[index + 3] = 0x00;
}
void patchCode(size_t index, int argument) {
code[index + 3] = static_cast<unsigned char>((argument >> 24) & 0xFF);
code[index + 2] = static_cast<unsigned char>((argument >> 16) & 0xFF);
code[index + 1] = static_cast<unsigned char>((argument >> 8) & 0xFF);
code[index] = static_cast<unsigned char>(argument & 0xFF);
}
bool setArgument(std::string const& line, int& argument) {
std::istringstream firstArgumentStream(line);
if (firstArgumentStream >> argument) {
return true;
}
return false;
}
int main() {
std::string str;
while (std::getline(std::cin, str)) {
auto command = splitString(str);
if (command.empty()) {
continue;
}
if (command.size() > 3) {
printErrorMessage("Not a valid number of arguments", false);
continue;
}
if (command[0] == "exit") {
break;
} else if (command[0] == "help" || command[0] == "-help" || command[0] == "--help") {
printHelpMessage();
} else if (command[0] == "execute") {
if (command.size() >= 2) {
int firstArg = 0;
if (!setArgument(command[1], firstArg)) {
printErrorMessage("Not a valid argument: " + command[1] + ". Use --help", false);
continue;
}
patchCode(DEFAULT_INDEX_1, firstArg);
if (command.size() == 3) {
int secondArg = 0;
if (!setArgument(command[2], secondArg)) {
printErrorMessage("Not a valid argument: " + command[2] + ". Use --help", false);
continue;
}
patchCode(DEFAULT_INDEX_2, secondArg);
}
}
void* ptr = allocateMemory(code.size() * sizeof(unsigned char));
if (ptr == nullptr) {
printErrorMessage("can't allocate memory using mmap");
return EXIT_FAILURE;
}
std::memcpy(ptr, code.data(), code.size());
if (!changePermissionsAndCheck(ptr, code.size(), PROT_EXEC | PROT_READ)) {
return EXIT_FAILURE;
}
auto func = (jitFunc)ptr;
int res = func();
std::cout << "result: " << res << std::endl;
if (!changePermissionsAndCheck(ptr, code.size(), PROT_READ | PROT_WRITE)) {
return EXIT_FAILURE;
}
if (!freeMemory(ptr, code.size())) {
printErrorMessage("can't free allocated memory using munmap");
return EXIT_FAILURE;
}
} else {
printErrorMessage("not a valid command, use --help", false);
}
setDefault(DEFAULT_INDEX_1, DEFAULT_VALUE_1);
setDefault(DEFAULT_INDEX_2, DEFAULT_VALUE_2);
}
return EXIT_SUCCESS;
}