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We also recommend that a 185 | file or class name and description of purpose be included on the 186 | same "printed page" as the copyright notice for easier 187 | identification within third-party archives. 188 | 189 | Copyright [yyyy] [name of copyright owner] 190 | 191 | Licensed under the Apache License, Version 2.0 (the "License"); 192 | you may not use this file except in compliance with the License. 193 | You may obtain a copy of the License at 194 | 195 | http://www.apache.org/licenses/LICENSE-2.0 196 | 197 | Unless required by applicable law or agreed to in writing, software 198 | distributed under the License is distributed on an "AS IS" BASIS, 199 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 200 | See the License for the specific language governing permissions and 201 | limitations under the License. 202 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Call Logger 2 | 3 | Referenced in https://gamehacking.academy/lesson/7/6. 4 | 5 | An example of a modified Windows debugger that will attach to a running Wesnoth process, locate all call instructions, and change them to an int 3 instruction. When the breakpoint is hit, the location will be logged and the instruction will be restored. Then, after the instruction is executed, an int 3 instruction will be rewritten to the location. 6 | -------------------------------------------------------------------------------- /main.cpp: -------------------------------------------------------------------------------- 1 | /* 2 | An example of a modified Windows debugger that will attach to a running Wesnoth process, locate all call instructions and change them to an int3 instruction. 3 | When the breakpoint is hit, the location will be logged and the instruction will be restored. Then, after the instruction is executed, an int3 instruction will 4 | be rewritten to the location. 5 | 6 | The code and approach are discussed in the article at: https://gamehacking.academy/lesson/42 7 | */ 8 | 9 | #include 10 | #include 11 | #include 12 | #include 13 | 14 | #define READ_PAGE_SIZE 4096 15 | 16 | int main(int argc, char** argv) { 17 | HANDLE process_snapshot = NULL; 18 | HANDLE thread_handle = NULL; 19 | HANDLE process_handle = NULL; 20 | 21 | PROCESSENTRY32 pe32 = { 0 }; 22 | 23 | DWORD pid; 24 | DWORD continueStatus = DBG_CONTINUE; 25 | DWORD bytes_written = 0; 26 | 27 | BYTE instruction_break = 0xcc; 28 | BYTE instruction_call = 0xe8; 29 | 30 | DEBUG_EVENT debugEvent = { 0 }; 31 | 32 | CONTEXT context = { 0 }; 33 | 34 | bool first_break_has_occurred = false; 35 | 36 | HMODULE modules[128] = { 0 }; 37 | MODULEINFO module_info = { 0 }; 38 | 39 | DWORD bytes_read = 0; 40 | DWORD offset = 0; 41 | DWORD call_location = 0; 42 | DWORD call_location_bytes_read = 0; 43 | DWORD last_call_location = 0; 44 | 45 | unsigned char instructions[READ_PAGE_SIZE] = { 0 }; 46 | 47 | int breakpoints_set = 0; 48 | 49 | pe32.dwSize = sizeof(PROCESSENTRY32); 50 | 51 | // Iterate through all active processes and find the Wesnoth process 52 | process_snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0); 53 | Process32First(process_snapshot, &pe32); 54 | 55 | do { 56 | if (wcscmp(pe32.szExeFile, L"wesnoth.exe") == 0) { 57 | // Save the pid and open a handle to the process 58 | pid = pe32.th32ProcessID; 59 | 60 | process_handle = OpenProcess(PROCESS_ALL_ACCESS, true, pe32.th32ProcessID); 61 | } 62 | } while (Process32Next(process_snapshot, &pe32)); 63 | 64 | // Attach the debugger and enter the main debug loop 65 | DebugActiveProcess(pid); 66 | 67 | for (;;) { 68 | continueStatus = DBG_CONTINUE; 69 | 70 | if (!WaitForDebugEvent(&debugEvent, INFINITE)) 71 | return 0; 72 | 73 | switch (debugEvent.dwDebugEventCode) { 74 | case EXCEPTION_DEBUG_EVENT: 75 | switch (debugEvent.u.Exception.ExceptionRecord.ExceptionCode) 76 | { 77 | case EXCEPTION_BREAKPOINT: 78 | // On the initial attachment breakpoint, replace all calls with breakpoints 79 | if (!first_break_has_occurred) { 80 | thread_handle = OpenThread(THREAD_ALL_ACCESS, true, debugEvent.dwThreadId); 81 | 82 | printf("Attaching breakpoints\n"); 83 | // In this code, we will only log all calls in the main game module and not DLLs 84 | // To locate the address space of this module, retrieve all the modules and then get the first 85 | // module's address space 86 | EnumProcessModules(process_handle, modules, sizeof(modules), &bytes_read); 87 | GetModuleInformation(process_handle, modules[0], &module_info, sizeof(module_info)); 88 | // Next, loop through each section of memory and locate the opcode for calls (0xe8) 89 | for (DWORD i = 0; i < module_info.SizeOfImage; i += READ_PAGE_SIZE) { 90 | // ReadProcessMemory will fail if the memory permissions are not correct for the page 91 | // To prevent a single failure from skipping all memory, read a single page of memory at a time 92 | ReadProcessMemory(process_handle, (LPVOID)((DWORD)module_info.lpBaseOfDll + i), &instructions, READ_PAGE_SIZE, &bytes_read); 93 | for (DWORD c = 0; c < bytes_read; c++) { 94 | // If we detect an 0xe8, determine if it is a call instruction 95 | // We do this by first reading the next four bytes after the 0xe8 96 | // We then use these bytes to calculate the call location 97 | // If this location is outside the address space of the main module, we ignore the opcode 98 | if (instructions[c] == instruction_call) { 99 | offset = (DWORD)module_info.lpBaseOfDll + i + c; 100 | ReadProcessMemory(process_handle, (LPVOID)(offset + 1), &call_location, 4, &call_location_bytes_read); 101 | call_location += offset + 5; 102 | if (call_location < (DWORD)module_info.lpBaseOfDll || call_location >(DWORD)module_info.lpBaseOfDll + module_info.SizeOfImage) 103 | continue; 104 | 105 | // If the call location is valid, write a break instruction (0xcc) at the address 106 | // In this case, 0x0040e3d8 and 0x0040e3ea are two commonly called addresses that contain low-level code 107 | // To prevent them from clogging up the logs, we don't log these locations 108 | // In addition, having thousands of breakpoints can cause the executing program to crash 109 | // Therefore, we limit the amount of breakpoints to less than 2000 110 | if (offset != 0x0040e3d8 && offset != 0x0040e3ea && breakpoints_set < 2000) { 111 | WriteProcessMemory(process_handle, (void*)offset, &instruction_break, 1, &bytes_written); 112 | FlushInstructionCache(process_handle, (LPVOID)offset, 1); 113 | breakpoints_set++; 114 | } 115 | } 116 | } 117 | } 118 | 119 | printf("Done attaching breakpoints\n"); 120 | } 121 | else { 122 | // If we break, open a handle to the thread that triggered the event and revert back eip to the previous instruction 123 | // Next, we will set single-step mode so that we can restore our breakpoint 124 | // After, we will write back the call instruction and continue execution of the program 125 | thread_handle = OpenThread(THREAD_ALL_ACCESS, true, debugEvent.dwThreadId); 126 | if (thread_handle != NULL) { 127 | context.ContextFlags = CONTEXT_ALL; 128 | GetThreadContext(thread_handle, &context); 129 | 130 | context.Eip--; 131 | context.EFlags |= 0x100; 132 | 133 | SetThreadContext(thread_handle, &context); 134 | CloseHandle(thread_handle); 135 | 136 | WriteProcessMemory(process_handle, (void*)context.Eip, &instruction_call, 1, &bytes_written); 137 | FlushInstructionCache(process_handle, (LPVOID)context.Eip, 1); 138 | 139 | last_call_location = context.Eip; 140 | } 141 | } 142 | 143 | first_break_has_occurred = true; 144 | continueStatus = DBG_CONTINUE; 145 | break; 146 | case EXCEPTION_SINGLE_STEP: 147 | // This code will executed after we enter single-step mode in the breakpoint statement above 148 | // Single-step mode executes a single instruction and then triggers this debug event 149 | // Therefore, after we execute the call we broke on above, restore the break instruction so that our breakpoints don't 150 | // only fire a single time 151 | thread_handle = OpenThread(THREAD_ALL_ACCESS, true, debugEvent.dwThreadId); 152 | if (thread_handle != NULL) { 153 | context.ContextFlags = CONTEXT_ALL; 154 | GetThreadContext(thread_handle, &context); 155 | CloseHandle(thread_handle); 156 | 157 | WriteProcessMemory(process_handle, (void*)last_call_location, &instruction_break, 1, &bytes_written); 158 | FlushInstructionCache(process_handle, (LPVOID)last_call_location, 1); 159 | 160 | printf("0x%08x: call 0x%08x\n", last_call_location, context.Eip); 161 | last_call_location = 0; 162 | } 163 | 164 | continueStatus = DBG_CONTINUE; 165 | break; 166 | default: 167 | continueStatus = DBG_EXCEPTION_NOT_HANDLED; 168 | break; 169 | } 170 | break; 171 | default: 172 | continueStatus = DBG_EXCEPTION_NOT_HANDLED; 173 | break; 174 | } 175 | 176 | ContinueDebugEvent(debugEvent.dwProcessId, debugEvent.dwThreadId, continueStatus); 177 | } 178 | 179 | CloseHandle(process_handle); 180 | 181 | return 0; 182 | } 183 | --------------------------------------------------------------------------------