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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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 */
* Structures and functions for transcoding compiled scripts and functions to
* and from memory.
#ifndef js_Transcoding_h
#define js_Transcoding_h
#include "mozilla/Range.h" // mozilla::Range
#include "mozilla/Vector.h" // mozilla::Vector
#include <stddef.h> // size_t
#include <stdint.h> // uint8_t, uint32_t
#include "js/TypeDecls.h"
namespace JS {
class JS_PUBLIC_API ReadOnlyCompileOptions;
using TranscodeBuffer = mozilla::Vector<uint8_t>;
using TranscodeRange = mozilla::Range<const uint8_t>;
struct TranscodeSource final {
TranscodeSource(const TranscodeRange& range_, const char* file, uint32_t line)
: range(range_), filename(file), lineno(line) {}
const TranscodeRange range;
const char* filename;
const uint32_t lineno;
using TranscodeSources = mozilla::Vector<TranscodeSource>;
enum class TranscodeResult : uint8_t {
// Successful encoding / decoding.
Ok = 0,
// A warning message, is set to the message out-param.
Failure = 0x10,
Failure_BadBuildId = Failure | 0x1,
Failure_AsmJSNotSupported = Failure | 0x2,
Failure_BadDecode = Failure | 0x3,
// There is a pending exception on the context.
Throw = 0x20
inline bool IsTranscodeFailureResult(const TranscodeResult result) {
uint8_t raw_result = static_cast<uint8_t>(result);
uint8_t raw_failure = static_cast<uint8_t>(TranscodeResult::Failure);
TranscodeResult masked =
static_cast<TranscodeResult>(raw_result & raw_failure);
return masked == TranscodeResult::Failure;
static constexpr size_t BytecodeOffsetAlignment = 4;
static_assert(BytecodeOffsetAlignment <= alignof(std::max_align_t),
"Alignment condition requires a custom allocator.");
// Align the bytecode offset for transcoding for the requirement.
inline size_t AlignTranscodingBytecodeOffset(size_t offset) {
size_t extra = offset % BytecodeOffsetAlignment;
if (extra == 0) {
return offset;
size_t padding = BytecodeOffsetAlignment - extra;
return offset + padding;
inline bool IsTranscodingBytecodeOffsetAligned(size_t offset) {
return offset % BytecodeOffsetAlignment == 0;
inline bool IsTranscodingBytecodeAligned(const void* offset) {
return IsTranscodingBytecodeOffsetAligned(size_t(offset));
// Finish incremental encoding started by JS::StartIncrementalEncoding.
// * Regular script case
// the |script| argument must be the top-level script returned from
// |JS::InstantiateGlobalStencil| with the same stencil
// * Module script case
// the |script| argument must be the script returned by
// |JS::GetModuleScript| called on the module returned by
// |JS::InstantiateModuleStencil| with the same stencil
// NOTE: |JS::GetModuleScript| doesn't work after evaluating the
// module script. For the case, use Handle<JSObject*> variant of
// this function below.
// The |buffer| argument of |FinishIncrementalEncoding| is used for appending
// the encoded bytecode into the buffer. If any of these functions failed, the
// content of |buffer| would be undefined.
// |buffer| contains encoded CompilationStencil.
// If the `buffer` isn't empty, the start of the `buffer` should meet
// IsTranscodingBytecodeAligned, and the length should meet
// IsTranscodingBytecodeOffsetAligned.
// NOTE: As long as IsTranscodingBytecodeOffsetAligned is met, that means
// there's JS::BytecodeOffsetAlignment+extra bytes in the buffer,
// IsTranscodingBytecodeAligned should be guaranteed to meet by
// malloc, used by MallocAllocPolicy in mozilla::Vector.
extern JS_PUBLIC_API bool FinishIncrementalEncoding(JSContext* cx,
Handle<JSScript*> script,
TranscodeBuffer& buffer);
// Similar to |JS::FinishIncrementalEncoding|, but receives module obect.
// The |module| argument must be the module returned by
// |JS::InstantiateModuleStencil| with the same stencil that's passed to
// |JS::StartIncrementalEncoding|.
extern JS_PUBLIC_API bool FinishIncrementalEncoding(JSContext* cx,
Handle<JSObject*> module,
TranscodeBuffer& buffer);
// Abort incremental encoding started by JS::StartIncrementalEncoding.
extern JS_PUBLIC_API void AbortIncrementalEncoding(Handle<JSScript*> script);
extern JS_PUBLIC_API void AbortIncrementalEncoding(Handle<JSObject*> module);
// Check if the compile options and script's flag matches.
// JS::DecodeScript* and JS::DecodeOffThreadScript internally check this.
// JS::DecodeMultiStencilsOffThread checks some options shared across multiple
// scripts. Caller is responsible for checking each script with this API when
// using the decoded script instead of compiling a new script wiht the given
// options.
extern JS_PUBLIC_API bool CheckCompileOptionsMatch(
const ReadOnlyCompileOptions& options, JSScript* script);
} // namespace JS
#endif /* js_Transcoding_h */