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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#include "shell/jsrtfuzzing/jsrtfuzzing.h"
#include "mozilla/Assertions.h" // MOZ_CRASH
#include "mozilla/Utf8.h" // mozilla::Utf8Unit
#include <stdio.h> // fflush, fprintf, fputs
#include "FuzzerDefs.h"
#include "FuzzingInterface.h"
#include "jsapi.h" // JS_ClearPendingException, JS_IsExceptionPending
#include "js/CompilationAndEvaluation.h" // JS::Evaluate
#include "js/CompileOptions.h" // JS::CompileOptions
#include "js/Conversions.h" // JS::ToInt32
#include "js/ErrorReport.h" // JS::PrintError
#include "js/Exception.h" // JS::StealPendingExceptionStack
#include "js/experimental/TypedData.h" // JS_GetUint8ClampedArrayData, JS_NewUint8ClampedArray
#include "js/PropertyAndElement.h" // JS_SetProperty
#include "js/RootingAPI.h" // JS::Rooted
#include "js/SourceText.h" // JS::Source{Ownership,Text}
#include "js/Value.h" // JS::Value
#include "shell/jsshell.h" // js::shell::{reportWarnings,PrintStackTrace,sArg{c,v}}
#include "util/Text.h"
#include "vm/Interpreter.h"
#include "vm/TypedArrayObject.h"
#include "vm/ArrayBufferObject-inl.h"
#include "vm/JSContext-inl.h"
static JSContext* gCx = nullptr;
static std::string gFuzzModuleName;
static void CrashOnPendingException() {
if (JS_IsExceptionPending(gCx)) {
JS::ExceptionStack exnStack(gCx);
(void)JS::StealPendingExceptionStack(gCx, &exnStack);
JS::ErrorReportBuilder report(gCx);
if (!report.init(gCx, exnStack, JS::ErrorReportBuilder::WithSideEffects)) {
fprintf(stderr, "out of memory initializing JS::ErrorReportBuilder\n");
} else {
JS::PrintError(stderr, report, js::shell::reportWarnings);
if (!js::shell::PrintStackTrace(gCx, exnStack.stack())) {
fputs("(Unable to print stack trace)\n", stderr);
MOZ_CRASH("Unhandled exception from JS runtime!");
int js::shell::FuzzJSRuntimeStart(JSContext* cx, int* argc, char*** argv) {
gCx = cx;
gFuzzModuleName = getenv("FUZZER");
int ret = FuzzJSRuntimeInit(argc, argv);
if (ret) {
fprintf(stderr, "Fuzzing Interface: Error: Initialize callback failed\n");
return ret;
fuzzer::FuzzerDriver(&shell::sArgc, &shell::sArgv, FuzzJSRuntimeFuzz);
MOZ_CRASH("AFL is unsupported for JS runtime fuzzing integration");
return 0;
int js::shell::FuzzJSRuntimeInit(int* argc, char*** argv) {
JS::Rooted<JS::Value> v(gCx);
JS::CompileOptions opts(gCx);
// Load the fuzzing module specified in the FUZZER environment variable
JS::EvaluateUtf8Path(gCx, opts, gFuzzModuleName.c_str(), &v);
// Any errors while loading the fuzzing module should be fatal
return 0;
int js::shell::FuzzJSRuntimeFuzz(const uint8_t* buf, size_t size) {
if (!size) {
return 0;
JS::Rooted<JSObject*> arr(gCx, JS_NewUint8ClampedArray(gCx, size));
if (!arr) {
do {
JS::AutoCheckCannotGC nogc;
bool isShared;
uint8_t* data = JS_GetUint8ClampedArrayData(arr, &isShared, nogc);
memcpy(data, buf, size);
} while (false);
JS::RootedValue arrVal(gCx, JS::ObjectValue(*arr));
if (!JS_SetProperty(gCx, gCx->global(), "fuzzBuf", arrVal)) {
MOZ_CRASH("JS_SetProperty failed");
JS::Rooted<JS::Value> v(gCx);
JS::CompileOptions opts(gCx);
static const char data[] = "JSFuzzIterate();";
JS::SourceText<mozilla::Utf8Unit> srcBuf;
if (!srcBuf.init(gCx, data, js_strlen(data), JS::SourceOwnership::Borrowed)) {
return 1;
if (!JS::Evaluate(gCx, opts.setFileAndLine(__FILE__, __LINE__), srcBuf, &v) &&
!JS_IsExceptionPending(gCx)) {
// A return value of `false` without a pending exception indicates
// a timeout as triggered by the `timeout` shell function.
return 1;
// The fuzzing module is required to handle any exceptions
int32_t ret = 0;
if (!JS::ToInt32(gCx, v, &ret)) {
MOZ_CRASH("Must return an int32 compatible return value!");
return ret;