Fix missing prototypes by adding a header file.

tests/fuzz/FuzzerInterface.h

@@ -0,0 +1,81 @@
+// Based on https://github.com/llvm-mirror/compiler-rt/blob/master/lib/fuzzer/FuzzerInterface.h
+//
+//===- FuzzerInterface.h - Interface header for the Fuzzer ------*- C++ -* ===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// Define the interface between libFuzzer and the library being tested.
+//===----------------------------------------------------------------------===//
+
+// NOTE: the libFuzzer interface is thin and in the majority of cases
+// you should not include this file into your target. In 95% of cases
+// all you need is to define the following function in your file:
+// extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size);
+
+// WARNING: keep the interface in C.
+
+#ifndef LLVM_FUZZER_INTERFACE_H
+#define LLVM_FUZZER_INTERFACE_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif  // __cplusplus
+
+// Define FUZZER_INTERFACE_VISIBILITY to set default visibility in a way that
+// doesn't break MSVC.
+#if defined(_WIN32)
+#define FUZZER_INTERFACE_VISIBILITY __declspec(dllexport)
+#else
+#define FUZZER_INTERFACE_VISIBILITY __attribute__((visibility("default")))
+#endif
+
+// Mandatory user-provided target function.
+// Executes the code under test with [Data, Data+Size) as the input.
+// libFuzzer will invoke this function *many* times with different inputs.
+// Must return 0.
+FUZZER_INTERFACE_VISIBILITY int
+LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size);
+
+// Optional user-provided initialization function.
+// If provided, this function will be called by libFuzzer once at startup.
+// It may read and modify argc/argv.
+// Must return 0.
+FUZZER_INTERFACE_VISIBILITY int LLVMFuzzerInitialize(int *argc, char ***argv);
+
+// Optional user-provided custom mutator.
+// Mutates raw data in [Data, Data+Size) inplace.
+// Returns the new size, which is not greater than MaxSize.
+// Given the same Seed produces the same mutation.
+FUZZER_INTERFACE_VISIBILITY size_t
+LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size, size_t MaxSize,
+                        unsigned int Seed);
+
+// Optional user-provided custom cross-over function.
+// Combines pieces of Data1 & Data2 together into Out.
+// Returns the new size, which is not greater than MaxOutSize.
+// Should produce the same mutation given the same Seed.
+FUZZER_INTERFACE_VISIBILITY size_t
+LLVMFuzzerCustomCrossOver(const uint8_t *Data1, size_t Size1,
+                          const uint8_t *Data2, size_t Size2, uint8_t *Out,
+                          size_t MaxOutSize, unsigned int Seed);
+
+// Experimental, may go away in future.
+// libFuzzer-provided function to be used inside LLVMFuzzerCustomMutator.
+// Mutates raw data in [Data, Data+Size) inplace.
+// Returns the new size, which is not greater than MaxSize.
+FUZZER_INTERFACE_VISIBILITY size_t
+LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize);
+
+#undef FUZZER_INTERFACE_VISIBILITY
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif  // __cplusplus
+
+#endif  // LLVM_FUZZER_INTERFACE_H

tests/fuzz/crypt2_load_fuzz.cc

@@ -37,8 +37,7 @@ extern "C" {
 #include <luks2/luks2.h>
 #include <libcryptsetup.h>
 #include <src/cryptsetup.h>
-
+#include "FuzzerInterface.h"
-int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
 
 static int calculate_checksum(const uint8_t* data, size_t size) {
 	struct crypt_hash *hd = NULL;

tests/fuzz/crypt2_load_proto_fuzz.cc

@@ -27,6 +27,7 @@
 #include "LUKS2.pb.h"
 #include "proto_to_luks2_converter.h"
 #include "libfuzzer/libfuzzer_macro.h"
+#include "FuzzerInterface.h"
 
 extern "C" {
 #include <libcryptsetup.h>

tests/fuzz/crypt2_load_proto_plain_json_fuzz.cc

@@ -27,6 +27,7 @@
 #include "LUKS2_plain_JSON.pb.h"
 #include "plain_json_proto_to_luks2_converter.h"
 #include "libfuzzer/libfuzzer_macro.h"
+#include "FuzzerInterface.h"
 
 extern "C" {
 #include <libcryptsetup.h>