1 //===- FuzzerExtraCountersWindows.cpp - Extra coverage counters for Win32 -===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // Extra coverage counters defined by user code for Windows. 9 //===----------------------------------------------------------------------===// 10 11 #include "FuzzerPlatform.h" 12 #include <cstdint> 13 14 #if LIBFUZZER_WINDOWS 15 #include <windows.h> 16 17 namespace fuzzer { 18 19 // 20 // The __start___libfuzzer_extra_counters variable is align 16, size 16 to 21 // ensure the padding between it and the next variable in this section (either 22 // __libfuzzer_extra_counters or __stop___libfuzzer_extra_counters) will be 23 // located at (__start___libfuzzer_extra_counters + 24 // sizeof(__start___libfuzzer_extra_counters)). Otherwise, the calculation of 25 // (stop - (start + sizeof(start))) might be skewed. 26 // 27 // The section name, __libfuzzer_extra_countaaa ends with "aaa", so it sorts 28 // before __libfuzzer_extra_counters alphabetically. We want the start symbol to 29 // be placed in the section just before the user supplied counters (if present). 30 // 31 #pragma section(".data$__libfuzzer_extra_countaaa") 32 ATTRIBUTE_ALIGNED(16) 33 __declspec(allocate(".data$__libfuzzer_extra_countaaa")) uint8_t 34 __start___libfuzzer_extra_counters[16] = {0}; 35 36 // 37 // Example of what the user-supplied counters should look like. First, the 38 // pragma to create the section name. It will fall alphabetically between 39 // ".data$__libfuzzer_extra_countaaa" and ".data$__libfuzzer_extra_countzzz". 40 // Next, the declspec to allocate the variable inside the specified section. 41 // Finally, some array, struct, whatever that is used to track the counter data. 42 // The size of this variable is computed at runtime by finding the difference of 43 // __stop___libfuzzer_extra_counters and __start___libfuzzer_extra_counters + 44 // sizeof(__start___libfuzzer_extra_counters). 45 // 46 47 // 48 // #pragma section(".data$__libfuzzer_extra_counters") 49 // __declspec(allocate(".data$__libfuzzer_extra_counters")) 50 // uint8_t any_name_variable[64 * 1024]; 51 // 52 53 // 54 // Here, the section name, __libfuzzer_extra_countzzz ends with "zzz", so it 55 // sorts after __libfuzzer_extra_counters alphabetically. We want the stop 56 // symbol to be placed in the section just after the user supplied counters (if 57 // present). Align to 1 so there isn't any padding placed between this and the 58 // previous variable. 59 // 60 #pragma section(".data$__libfuzzer_extra_countzzz") 61 ATTRIBUTE_ALIGNED(1) 62 __declspec(allocate(".data$__libfuzzer_extra_countzzz")) uint8_t 63 __stop___libfuzzer_extra_counters = 0; 64 65 uint8_t *ExtraCountersBegin() { 66 return __start___libfuzzer_extra_counters + 67 sizeof(__start___libfuzzer_extra_counters); 68 } 69 70 uint8_t *ExtraCountersEnd() { return &__stop___libfuzzer_extra_counters; } 71 72 ATTRIBUTE_NO_SANITIZE_ALL 73 void ClearExtraCounters() { 74 uint8_t *Beg = ExtraCountersBegin(); 75 SecureZeroMemory(Beg, ExtraCountersEnd() - Beg); 76 } 77 78 } // namespace fuzzer 79 80 #endif 81