[tests] Add libFuzzer support.

See http://llvm.org/docs/LibFuzzer.html#fuzzer-usage for usage instructions.

src/test/test_bitcoin_fuzzy.cpp

@@ -48,8 +48,8 @@ enum TEST_ID {
     TEST_ID_END
 };
 
-bool read_stdin(std::vector<char> &data) {
-    char buffer[1024];
+bool read_stdin(std::vector<uint8_t> &data) {
+    uint8_t buffer[1024];
     ssize_t length=0;
     while((length = read(STDIN_FILENO, buffer, 1024)) > 0) {
         data.insert(data.end(), buffer, buffer+length);
@@ -59,11 +59,7 @@ bool read_stdin(std::vector<char> &data) {
     return length==0;
 }
 
-int do_fuzz()
-{
-    std::vector<char> buffer;
-    if (!read_stdin(buffer)) return 0;
-
+int test_one_input(std::vector<uint8_t> buffer) {
     if (buffer.size() < sizeof(uint32_t)) return 0;
 
     uint32_t test_id = 0xffffffff;
@@ -255,9 +251,32 @@ int do_fuzz()
     return 0;
 }
 
+static std::unique_ptr<ECCVerifyHandle> globalVerifyHandle;
+void initialize() {
+    globalVerifyHandle = std::unique_ptr<ECCVerifyHandle>(new ECCVerifyHandle());
+}
+
+// This function is used by libFuzzer
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+    test_one_input(std::vector<uint8_t>(data, data + size));
+    return 0;
+}
+
+// This function is used by libFuzzer
+extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv) {
+    initialize();
+    return 0;
+}
+
+// Disabled under WIN32 due to clash with Cygwin's WinMain.
+#ifndef WIN32
+// Declare main(...) "weak" to allow for libFuzzer linking. libFuzzer provides
+// the main(...) function.
+__attribute__((weak))
+#endif
 int main(int argc, char **argv)
 {
-    ECCVerifyHandle globalVerifyHandle;
+    initialize();
 #ifdef __AFL_INIT
     // Enable AFL deferred forkserver mode. Requires compilation using
     // afl-clang-fast++. See fuzzing.md for details.
@@ -267,11 +286,20 @@ int main(int argc, char **argv)
 #ifdef __AFL_LOOP
     // Enable AFL persistent mode. Requires compilation using afl-clang-fast++.
     // See fuzzing.md for details.
+    int ret = 0;
     while (__AFL_LOOP(1000)) {
-        do_fuzz();
+        std::vector<uint8_t> buffer;
+        if (!read_stdin(buffer)) {
+            continue;
+        }
+        ret = test_one_input(buffer);
     }
-    return 0;
+    return ret;
 #else
-    return do_fuzz();
+    std::vector<uint8_t> buffer;
+    if (!read_stdin(buffer)) {
+        return 0;
+    }
+    return test_one_input(buffer);
 #endif
 }