vendor/llvm-project/llvmorg-10-init-17466-ge26a78e7085

15 files changed, 122 insertions, 43 deletions

diff --git a/compiler-rt/lib/fuzzer/FuzzerDefs.h b/compiler-rt/lib/fuzzer/FuzzerDefs.h
index 5dc2d8e1ac09..5793e86aa804 100644
--- a/compiler-rt/lib/fuzzer/FuzzerDefs.h
+++ b/compiler-rt/lib/fuzzer/FuzzerDefs.h
@@ -30,6 +30,7 @@
 #define LIBFUZZER_FREEBSD 0
 #define LIBFUZZER_OPENBSD 0
 #define LIBFUZZER_WINDOWS 0
+#define LIBFUZZER_EMSCRIPTEN 0
 #elif __APPLE__
 #define LIBFUZZER_APPLE 1
 #define LIBFUZZER_FUCHSIA 0
@@ -38,6 +39,7 @@
 #define LIBFUZZER_FREEBSD 0
 #define LIBFUZZER_OPENBSD 0
 #define LIBFUZZER_WINDOWS 0
+#define LIBFUZZER_EMSCRIPTEN 0
 #elif __NetBSD__
 #define LIBFUZZER_APPLE 0
 #define LIBFUZZER_FUCHSIA 0
@@ -46,6 +48,7 @@
 #define LIBFUZZER_FREEBSD 0
 #define LIBFUZZER_OPENBSD 0
 #define LIBFUZZER_WINDOWS 0
+#define LIBFUZZER_EMSCRIPTEN 0
 #elif __FreeBSD__
 #define LIBFUZZER_APPLE 0
 #define LIBFUZZER_FUCHSIA 0
@@ -54,6 +57,7 @@
 #define LIBFUZZER_FREEBSD 1
 #define LIBFUZZER_OPENBSD 0
 #define LIBFUZZER_WINDOWS 0
+#define LIBFUZZER_EMSCRIPTEN 0
 #elif __OpenBSD__
 #define LIBFUZZER_APPLE 0
 #define LIBFUZZER_FUCHSIA 0
@@ -62,6 +66,7 @@
 #define LIBFUZZER_FREEBSD 0
 #define LIBFUZZER_OPENBSD 1
 #define LIBFUZZER_WINDOWS 0
+#define LIBFUZZER_EMSCRIPTEN 0
 #elif _WIN32
 #define LIBFUZZER_APPLE 0
 #define LIBFUZZER_FUCHSIA 0
@@ -70,6 +75,7 @@
 #define LIBFUZZER_FREEBSD 0
 #define LIBFUZZER_OPENBSD 0
 #define LIBFUZZER_WINDOWS 1
+#define LIBFUZZER_EMSCRIPTEN 0
 #elif __Fuchsia__
 #define LIBFUZZER_APPLE 0
 #define LIBFUZZER_FUCHSIA 1
@@ -78,6 +84,16 @@
 #define LIBFUZZER_FREEBSD 0
 #define LIBFUZZER_OPENBSD 0
 #define LIBFUZZER_WINDOWS 0
+#define LIBFUZZER_EMSCRIPTEN 0
+#elif __EMSCRIPTEN__
+#define LIBFUZZER_APPLE 0
+#define LIBFUZZER_FUCHSIA 0
+#define LIBFUZZER_LINUX 0
+#define LIBFUZZER_NETBSD 0
+#define LIBFUZZER_FREEBSD 0
+#define LIBFUZZER_OPENBSD 0
+#define LIBFUZZER_WINDOWS 0
+#define LIBFUZZER_EMSCRIPTEN 1
 #else
 #error "Support for your platform has not been implemented"
 #endif
@@ -95,7 +111,7 @@
 
 #define LIBFUZZER_POSIX                                                        \
   (LIBFUZZER_APPLE || LIBFUZZER_LINUX || LIBFUZZER_NETBSD ||                   \
-   LIBFUZZER_FREEBSD || LIBFUZZER_OPENBSD)
+   LIBFUZZER_FREEBSD || LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN)
 
 #ifdef __x86_64
 #  if __has_attribute(target)
diff --git a/compiler-rt/lib/fuzzer/FuzzerDriver.cpp b/compiler-rt/lib/fuzzer/FuzzerDriver.cpp
index 44c90655b932..dd3cab0ee8d2 100644
--- a/compiler-rt/lib/fuzzer/FuzzerDriver.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerDriver.cpp
@@ -280,7 +280,8 @@ static void RssThread(Fuzzer *F, size_t RssLimitMb) {
 }
 
 static void StartRssThread(Fuzzer *F, size_t RssLimitMb) {
-  if (!RssLimitMb) return;
+  if (!RssLimitMb)
+    return;
   std::thread T(RssThread, F, RssLimitMb);
   T.detach();
 }
@@ -737,7 +738,11 @@ int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
     if (U.size() <= Word::GetMaxSize())
       MD->AddWordToManualDictionary(Word(U.data(), U.size()));
 
+      // Threads are only supported by Chrome. Don't use them with emscripten
+      // for now.
+#if !LIBFUZZER_EMSCRIPTEN
   StartRssThread(F, Flags.rss_limit_mb);
+#endif // LIBFUZZER_EMSCRIPTEN
 
   Options.HandleAbrt = Flags.handle_abrt;
   Options.HandleBus = Flags.handle_bus;
diff --git a/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWeak.cpp b/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWeak.cpp
index ea5b87bd5196..d56dab36c646 100644
--- a/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWeak.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerExtFunctionsWeak.cpp
@@ -13,7 +13,7 @@
 //===----------------------------------------------------------------------===//
 #include "FuzzerDefs.h"
 #if LIBFUZZER_LINUX || LIBFUZZER_NETBSD || LIBFUZZER_FUCHSIA ||                \
-    LIBFUZZER_FREEBSD || LIBFUZZER_OPENBSD
+    LIBFUZZER_FREEBSD || LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN
 
 #include "FuzzerExtFunctions.h"
 #include "FuzzerIO.h"
diff --git a/compiler-rt/lib/fuzzer/FuzzerExtraCounters.cpp b/compiler-rt/lib/fuzzer/FuzzerExtraCounters.cpp
index 3f38f4fb70c1..b2face778203 100644
--- a/compiler-rt/lib/fuzzer/FuzzerExtraCounters.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerExtraCounters.cpp
@@ -11,7 +11,7 @@
 #include "FuzzerDefs.h"
 
 #if LIBFUZZER_LINUX || LIBFUZZER_NETBSD || LIBFUZZER_FREEBSD ||                \
-    LIBFUZZER_OPENBSD
+    LIBFUZZER_OPENBSD || LIBFUZZER_FUCHSIA || LIBFUZZER_EMSCRIPTEN
 __attribute__((weak)) extern uint8_t __start___libfuzzer_extra_counters;
 __attribute__((weak)) extern uint8_t __stop___libfuzzer_extra_counters;
 
diff --git a/compiler-rt/lib/fuzzer/FuzzerFlags.def b/compiler-rt/lib/fuzzer/FuzzerFlags.def
index 0e19a9cde6ca..a67415743032 100644
--- a/compiler-rt/lib/fuzzer/FuzzerFlags.def
+++ b/compiler-rt/lib/fuzzer/FuzzerFlags.def
@@ -56,7 +56,8 @@ FUZZER_FLAG_STRING(merge_control_file,
                    "Specify a control file used for the merge process. "
                    "If a merge process gets killed it tries to leave this file "
                    "in a state suitable for resuming the merge. "
-                   "By default a temporary file will be used.")
+                   "By default a temporary file will be used."
+                   "The same file can be used for multistep merge process.")
 FUZZER_FLAG_INT(minimize_crash, 0, "If 1, minimizes the provided"
   " crash input. Use with -runs=N or -max_total_time=N to limit "
   "the number attempts."
diff --git a/compiler-rt/lib/fuzzer/FuzzerIO.cpp b/compiler-rt/lib/fuzzer/FuzzerIO.cpp
index 7e5ba30a2e7d..f0708164be87 100644
--- a/compiler-rt/lib/fuzzer/FuzzerIO.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerIO.cpp
@@ -111,7 +111,7 @@ std::string DirPlusFile(const std::string &DirPath,
 
 void DupAndCloseStderr() {
   int OutputFd = DuplicateFile(2);
-  if (OutputFd > 0) {
+  if (OutputFd >= 0) {
     FILE *NewOutputFile = OpenFile(OutputFd, "w");
     if (NewOutputFile) {
       OutputFile = NewOutputFile;
diff --git a/compiler-rt/lib/fuzzer/FuzzerIO.h b/compiler-rt/lib/fuzzer/FuzzerIO.h
index fe0d7b451758..ae8dd24e373c 100644
--- a/compiler-rt/lib/fuzzer/FuzzerIO.h
+++ b/compiler-rt/lib/fuzzer/FuzzerIO.h
@@ -94,8 +94,6 @@ int DuplicateFile(int Fd);
 void RemoveFile(const std::string &Path);
 void RenameFile(const std::string &OldPath, const std::string &NewPath);
 
-void DiscardOutput(int Fd);
-
 intptr_t GetHandleFromFd(int fd);
 
 void MkDir(const std::string &Path);
diff --git a/compiler-rt/lib/fuzzer/FuzzerIOPosix.cpp b/compiler-rt/lib/fuzzer/FuzzerIOPosix.cpp
index cfd69bbc8111..fcd9b8d8b9c7 100644
--- a/compiler-rt/lib/fuzzer/FuzzerIOPosix.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerIOPosix.cpp
@@ -124,14 +124,6 @@ void RenameFile(const std::string &OldPath, const std::string &NewPath) {
   rename(OldPath.c_str(), NewPath.c_str());
 }
 
-void DiscardOutput(int Fd) {
-  FILE* Temp = fopen("/dev/null", "w");
-  if (!Temp)
-    return;
-  dup2(fileno(Temp), Fd);
-  fclose(Temp);
-}
-
 intptr_t GetHandleFromFd(int fd) {
   return static_cast<intptr_t>(fd);
 }
diff --git a/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp b/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
index 510afebef738..56757aa09a37 100644
--- a/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerIOWindows.cpp
@@ -223,14 +223,6 @@ void RenameFile(const std::string &OldPath, const std::string &NewPath) {
   rename(OldPath.c_str(), NewPath.c_str());
 }
 
-void DiscardOutput(int Fd) {
-  FILE* Temp = fopen("nul", "w");
-  if (!Temp)
-    return;
-  _dup2(_fileno(Temp), Fd);
-  fclose(Temp);
-}
-
 intptr_t GetHandleFromFd(int fd) {
   return _get_osfhandle(fd);
 }
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtil.h b/compiler-rt/lib/fuzzer/FuzzerUtil.h
index 85c5571d684f..00ea6550646f 100644
--- a/compiler-rt/lib/fuzzer/FuzzerUtil.h
+++ b/compiler-rt/lib/fuzzer/FuzzerUtil.h
@@ -79,6 +79,8 @@ inline std::pair<std::string, std::string> SplitBefore(std::string X,
   return std::make_pair(S.substr(0, Pos), S.substr(Pos));
 }
 
+void DiscardOutput(int Fd);
+
 std::string DisassembleCmd(const std::string &FileName);
 
 std::string SearchRegexCmd(const std::string &Regex);
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilDarwin.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilDarwin.cpp
index 171db23570c4..d449bc248f09 100644
--- a/compiler-rt/lib/fuzzer/FuzzerUtilDarwin.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilDarwin.cpp
@@ -17,6 +17,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/wait.h>
+#include <unistd.h>
 
 // There is no header for this on macOS so declare here
 extern "C" char **environ;
@@ -156,6 +157,14 @@ int ExecuteCommand(const Command &Cmd) {
   return ProcessStatus;
 }
 
+void DiscardOutput(int Fd) {
+  FILE* Temp = fopen("/dev/null", "w");
+  if (!Temp)
+    return;
+  dup2(fileno(Temp), Fd);
+  fclose(Temp);
+}
+
 } // namespace fuzzer
 
 #endif // LIBFUZZER_APPLE
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp
index 79fd950bbf97..bde9f68d62aa 100644
--- a/compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp
@@ -18,6 +18,7 @@
 #include <cinttypes>
 #include <cstdint>
 #include <fcntl.h>
+#include <lib/fdio/fdio.h>
 #include <lib/fdio/spawn.h>
 #include <string>
 #include <sys/select.h>
@@ -76,6 +77,23 @@ void InterruptHandler() {
   Fuzzer::StaticInterruptCallback();
 }
 
+// CFAOffset is used to reference the stack pointer before entering the
+// trampoline (Stack Pointer + CFAOffset = prev Stack Pointer). Before jumping
+// to the trampoline we copy all the registers onto the stack. We need to make
+// sure that the new stack has enough space to store all the registers.
+//
+// The trampoline holds CFI information regarding the registers stored in the
+// stack, which is then used by the unwinder to restore them.
+#if defined(__x86_64__)
+// In x86_64 the crashing function might also be using the red zone (128 bytes
+// on top of their rsp).
+constexpr size_t CFAOffset = 128 + sizeof(zx_thread_state_general_regs_t);
+#elif defined(__aarch64__)
+// In aarch64 we need to always have the stack pointer aligned to 16 bytes, so we
+// make sure that we are keeping that same alignment.
+constexpr size_t CFAOffset = (sizeof(zx_thread_state_general_regs_t) + 15) & -(uintptr_t)16;
+#endif
+
 // For the crash handler, we need to call Fuzzer::StaticCrashSignalCallback
 // without POSIX signal handlers.  To achieve this, we use an assembly function
 // to add the necessary CFI unwinding information and a C function to bridge
@@ -140,7 +158,6 @@ void InterruptHandler() {
   OP_NUM(27)                             \
   OP_NUM(28)                             \
   OP_NUM(29)                             \
-  OP_NUM(30)                             \
   OP_REG(sp)
 
 #else
@@ -148,14 +165,17 @@ void InterruptHandler() {
 #endif
 
 // Produces a CFI directive for the named or numbered register.
+// The value used refers to an assembler immediate operand with the same name
+// as the register (see ASM_OPERAND_REG).
 #define CFI_OFFSET_REG(reg) ".cfi_offset " #reg ", %c[" #reg "]\n"
-#define CFI_OFFSET_NUM(num) CFI_OFFSET_REG(r##num)
+#define CFI_OFFSET_NUM(num) CFI_OFFSET_REG(x##num)
 
-// Produces an assembler input operand for the named or numbered register.
+// Produces an assembler immediate operand for the named or numbered register.
+// This operand contains the offset of the register relative to the CFA.
 #define ASM_OPERAND_REG(reg) \
-  [reg] "i"(offsetof(zx_thread_state_general_regs_t, reg)),
+  [reg] "i"(offsetof(zx_thread_state_general_regs_t, reg) - CFAOffset),
 #define ASM_OPERAND_NUM(num)                                 \
-  [r##num] "i"(offsetof(zx_thread_state_general_regs_t, r[num])),
+  [x##num] "i"(offsetof(zx_thread_state_general_regs_t, r[num]) - CFAOffset),
 
 // Trampoline to bridge from the assembly below to the static C++ crash
 // callback.
@@ -168,7 +188,16 @@ static void StaticCrashHandler() {
 }
 
 // Creates the trampoline with the necessary CFI information to unwind through
-// to the crashing call stack.  The attribute is necessary because the function
+// to the crashing call stack:
+//  * Defining the CFA so that it points to the stack pointer at the point
+//    of crash.
+//  * Storing all registers at the point of crash in the stack and refer to them
+//    via CFI information (relative to the CFA).
+//  * Setting the return column so the unwinder knows how to continue unwinding.
+//  * (x86_64) making sure rsp is aligned before calling StaticCrashHandler.
+//  * Calling StaticCrashHandler that will trigger the unwinder.
+//
+// The __attribute__((used)) is necessary because the function
 // is never called; it's just a container around the assembly to allow it to
 // use operands for compile-time computed constants.
 __attribute__((used))
@@ -181,16 +210,21 @@ void MakeTrampoline() {
     ".cfi_signal_frame\n"
 #if defined(__x86_64__)
     ".cfi_return_column rip\n"
-    ".cfi_def_cfa rsp, 0\n"
+    ".cfi_def_cfa rsp, %c[CFAOffset]\n"
     FOREACH_REGISTER(CFI_OFFSET_REG, CFI_OFFSET_NUM)
+    "mov %%rsp, %%rbp\n"
+    ".cfi_def_cfa_register rbp\n"
+    "andq $-16, %%rsp\n"
     "call %c[StaticCrashHandler]\n"
     "ud2\n"
 #elif defined(__aarch64__)
     ".cfi_return_column 33\n"
-    ".cfi_def_cfa sp, 0\n"
-    ".cfi_offset 33, %c[pc]\n"
+    ".cfi_def_cfa sp, %c[CFAOffset]\n"
     FOREACH_REGISTER(CFI_OFFSET_REG, CFI_OFFSET_NUM)
-    "bl %[StaticCrashHandler]\n"
+    ".cfi_offset 33, %c[pc]\n"
+    ".cfi_offset 30, %c[lr]\n"
+    "bl %c[StaticCrashHandler]\n"
+    "brk 1\n"
 #else
 #error "Unsupported architecture for fuzzing on Fuchsia"
 #endif
@@ -202,8 +236,10 @@ void MakeTrampoline() {
     : FOREACH_REGISTER(ASM_OPERAND_REG, ASM_OPERAND_NUM)
 #if defined(__aarch64__)
       ASM_OPERAND_REG(pc)
+      ASM_OPERAND_REG(lr)
 #endif
-      [StaticCrashHandler] "i" (StaticCrashHandler));
+      [StaticCrashHandler] "i" (StaticCrashHandler),
+      [CFAOffset] "i" (CFAOffset));
 }
 
 void CrashHandler(zx_handle_t *Event) {
@@ -269,17 +305,14 @@ void CrashHandler(zx_handle_t *Event) {
     // onto the stack and jump into a trampoline with CFI instructions on how
     // to restore it.
 #if defined(__x86_64__)
-    uintptr_t StackPtr =
-        (GeneralRegisters.rsp - (128 + sizeof(GeneralRegisters))) &
-        -(uintptr_t)16;
+    uintptr_t StackPtr = GeneralRegisters.rsp - CFAOffset;
     __unsanitized_memcpy(reinterpret_cast<void *>(StackPtr), &GeneralRegisters,
                          sizeof(GeneralRegisters));
     GeneralRegisters.rsp = StackPtr;
     GeneralRegisters.rip = reinterpret_cast<zx_vaddr_t>(CrashTrampolineAsm);
 
 #elif defined(__aarch64__)
-    uintptr_t StackPtr =
-        (GeneralRegisters.sp - sizeof(GeneralRegisters)) & -(uintptr_t)16;
+    uintptr_t StackPtr = GeneralRegisters.sp - CFAOffset;
     __unsanitized_memcpy(reinterpret_cast<void *>(StackPtr), &GeneralRegisters,
                          sizeof(GeneralRegisters));
     GeneralRegisters.sp = StackPtr;
@@ -497,6 +530,18 @@ const void *SearchMemory(const void *Data, size_t DataLen, const void *Patt,
   return memmem(Data, DataLen, Patt, PattLen);
 }
 
+// In fuchsia, accessing /dev/null is not supported. There's nothing
+// similar to a file that discards everything that is written to it.
+// The way of doing something similar in fuchsia is by using
+// fdio_null_create and binding that to a file descriptor.
+void DiscardOutput(int Fd) {
+  fdio_t *fdio_null = fdio_null_create();
+  if (fdio_null == nullptr) return;
+  int nullfd = fdio_bind_to_fd(fdio_null, -1, 0);
+  if (nullfd < 0) return;
+  dup2(nullfd, Fd);
+}
+
 } // namespace fuzzer
 
 #endif // LIBFUZZER_FUCHSIA
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilLinux.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilLinux.cpp
index d5a15d19f2a9..993023e70393 100644
--- a/compiler-rt/lib/fuzzer/FuzzerUtilLinux.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilLinux.cpp
@@ -9,12 +9,13 @@
 //===----------------------------------------------------------------------===//
 #include "FuzzerDefs.h"
 #if LIBFUZZER_LINUX || LIBFUZZER_NETBSD || LIBFUZZER_FREEBSD ||                \
-    LIBFUZZER_OPENBSD
+    LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN
 #include "FuzzerCommand.h"
 
 #include <stdlib.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <unistd.h>
 
 
 namespace fuzzer {
@@ -27,6 +28,14 @@ int ExecuteCommand(const Command &Cmd) {
   return exit_code;
 }
 
+void DiscardOutput(int Fd) {
+  FILE* Temp = fopen("/dev/null", "w");
+  if (!Temp)
+    return;
+  dup2(fileno(Temp), Fd);
+  fclose(Temp);
+}
+
 } // namespace fuzzer
 
 #endif
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
index cefe7ae181e7..8048e6a8afd2 100644
--- a/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilPosix.cpp
@@ -98,7 +98,8 @@ void SetTimer(int Seconds) {
 }
 
 void SetSignalHandler(const FuzzingOptions& Options) {
-  if (Options.UnitTimeoutSec > 0)
+  // setitimer is not implemented in emscripten.
+  if (Options.UnitTimeoutSec > 0 && !LIBFUZZER_EMSCRIPTEN)
     SetTimer(Options.UnitTimeoutSec / 2 + 1);
   if (Options.HandleInt)
     SetSigaction(SIGINT, InterruptHandler);
@@ -133,7 +134,7 @@ size_t GetPeakRSSMb() {
   if (getrusage(RUSAGE_SELF, &usage))
     return 0;
   if (LIBFUZZER_LINUX || LIBFUZZER_FREEBSD || LIBFUZZER_NETBSD ||
-      LIBFUZZER_OPENBSD) {
+      LIBFUZZER_OPENBSD || LIBFUZZER_EMSCRIPTEN) {
     // ru_maxrss is in KiB
     return usage.ru_maxrss >> 10;
   } else if (LIBFUZZER_APPLE) {
diff --git a/compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp b/compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp
index ed90044c3f83..527e7dbd1cf6 100644
--- a/compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerUtilWindows.cpp
@@ -16,6 +16,7 @@
 #include <chrono>
 #include <cstring>
 #include <errno.h>
+#include <io.h>
 #include <iomanip>
 #include <signal.h>
 #include <stdio.h>
@@ -190,6 +191,14 @@ std::string SearchRegexCmd(const std::string &Regex) {
   return "findstr /r \"" + Regex + "\"";
 }
 
+void DiscardOutput(int Fd) {
+  FILE* Temp = fopen("nul", "w");
+  if (!Temp)
+    return;
+  _dup2(_fileno(Temp), Fd);
+  fclose(Temp);
+}
+
 } // namespace fuzzer
 
 #endif // LIBFUZZER_WINDOWS