compiler-rt/lib/fuzzer/FuzzerExtraCountersWindows.cpp

   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