Add a fallback fuzz binary if libfuzzer not available

Closes #1

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.10)
 project(
   weaseljson
   VERSION 0.0.1
@@ -173,6 +173,11 @@ if(HAS_LIB_FUZZER)
   target_link_libraries(fuzz PRIVATE simdjson)
   target_compile_options(fuzz PRIVATE -fsanitize=fuzzer ${TEST_FLAGS})
   target_link_options(fuzz PRIVATE -fsanitize=fuzzer)
+else()
+  add_executable(fuzz src/fuzz.cpp src/lib.cpp src/fuzz_driver.cpp)
+  target_include_directories(fuzz PRIVATE include)
+  target_link_libraries(fuzz PRIVATE simdjson)
+  target_compile_options(fuzz PRIVATE ${TEST_FLAGS})
 endif()
 
 add_executable(validate src/validate.cpp)

src/fuzz_driver.cpp

@@ -0,0 +1,19 @@
+#include <cstddef>
+#include <cstdint>
+#include <fstream>
+#include <sstream>
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+
+int main(int argc, char **argv) {
+  auto doTest = [&]() {
+    for (int i = 1; i < argc; ++i) {
+      std::ifstream t(argv[i], std::ios::binary);
+      std::stringstream buffer;
+      buffer << t.rdbuf();
+      auto str = buffer.str();
+      LLVMFuzzerTestOneInput((const uint8_t *)str.data(), str.size());
+    }
+  };
+  doTest();
+}

src/musttail.h

@@ -6,6 +6,7 @@
 
 #if __has_attribute(musttail)
 #define MUSTTAIL __attribute__((musttail))
+#define HAS_MUSTTAIL
 #else
 #define MUSTTAIL
 #endif

src/parser3.h

@@ -146,6 +146,10 @@ struct Parser3 {
   NumDfa numDfa;
   Utf8Dfa strDfa;
   bool inKey = false;
+
+#ifndef HAS_MUSTTAIL
+  char *stashBufForTrampoline;
+#endif
 };
 
 inline PRESERVE_NONE WeaselJsonStatus skipWhitespace(char *&buf, char *bufEnd) {
@@ -1029,13 +1033,29 @@ constexpr inline struct ContinuationTable {
 
 inline WeaselJsonStatus Parser3::parse(char *buf, int len) {
   this->dataBegin = this->writeBuf = buf;
+
+#ifdef HAS_MUSTTAIL
   return symbolTables.continuations[top()](this, buf, buf + len);
+#else
+  this->stashBufForTrampoline = buf;
+  WeaselJsonStatus result;
+  while ((result = symbolTables.continuations[top()](
+              this, stashBufForTrampoline, buf + len)) == WeaselJsonStatus(-1))
+    ;
+  return result;
+#endif
 }
 
 inline PRESERVE_NONE WeaselJsonStatus Parser3::keepGoing(Parser3 *self,
                                                          char *buf,
                                                          char *bufEnd) {
+#ifdef HAS_MUSTTAIL
   MUSTTAIL return symbolTables.continuations[self->top()](self, buf, bufEnd);
+#else
+  self->stashBufForTrampoline = buf;
+  (void)bufEnd;
+  return WeaselJsonStatus(-1);
+#endif
 }
 
 } // namespace parser3