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// Copyright 2015 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_WASM_DECODER_H_
#define V8_WASM_DECODER_H_
#include <cinttypes>
#include <cstdarg>
#include <memory>
#include "src/base/compiler-specific.h"
#include "src/codegen/signature.h"
#include "src/common/v8memory.h"
#include "src/flags/flags.h"
#include "src/utils/utils.h"
#include "src/utils/vector.h"
#include "src/wasm/wasm-result.h"
#include "src/zone/zone-containers.h"
namespace v8 {
namespace internal {
namespace wasm {
#define TRACE(...) \
do { \
if (FLAG_trace_wasm_decoder) PrintF(__VA_ARGS__); \
} while (false)
#define TRACE_IF(cond, ...) \
do { \
if (FLAG_trace_wasm_decoder && (cond)) PrintF(__VA_ARGS__); \
} while (false)
// A {DecodeResult} only stores the failure / success status, but no data.
using DecodeResult = VoidResult;
// A helper utility to decode bytes, integers, fields, varints, etc, from
// a buffer of bytes.
class Decoder {
public:
enum ValidateFlag : bool { kValidate = true, kNoValidate = false };
enum AdvancePCFlag : bool { kAdvancePc = true, kNoAdvancePc = false };
enum TraceFlag : bool { kTrace = true, kNoTrace = false };
Decoder(const byte* start, const byte* end, uint32_t buffer_offset = 0)
: Decoder(start, start, end, buffer_offset) {}
explicit Decoder(const Vector<const byte> bytes, uint32_t buffer_offset = 0)
: Decoder(bytes.begin(), bytes.begin() + bytes.length(), buffer_offset) {}
Decoder(const byte* start, const byte* pc, const byte* end,
uint32_t buffer_offset = 0)
: start_(start), pc_(pc), end_(end), buffer_offset_(buffer_offset) {
DCHECK_LE(start, pc);
DCHECK_LE(pc, end);
DCHECK_EQ(static_cast<uint32_t>(end - start), end - start);
}
virtual ~Decoder() = default;
inline bool validate_size(const byte* pc, uint32_t length, const char* msg) {
DCHECK_LE(start_, pc);
if (V8_UNLIKELY(pc > end_ || length > static_cast<uint32_t>(end_ - pc))) {
error(pc, msg);
return false;
}
return true;
}
// Reads an 8-bit unsigned integer.
template <ValidateFlag validate>
inline uint8_t read_u8(const byte* pc, const char* msg = "expected 1 byte") {
return read_little_endian<uint8_t, validate>(pc, msg);
}
// Reads a 16-bit unsigned integer (little endian).
template <ValidateFlag validate>
inline uint16_t read_u16(const byte* pc,
const char* msg = "expected 2 bytes") {
return read_little_endian<uint16_t, validate>(pc, msg);
}
// Reads a 32-bit unsigned integer (little endian).
template <ValidateFlag validate>
inline uint32_t read_u32(const byte* pc,
const char* msg = "expected 4 bytes") {
return read_little_endian<uint32_t, validate>(pc, msg);
}
// Reads a 64-bit unsigned integer (little endian).
template <ValidateFlag validate>
inline uint64_t read_u64(const byte* pc,
const char* msg = "expected 8 bytes") {
return read_little_endian<uint64_t, validate>(pc, msg);
}
// Reads a variable-length unsigned integer (little endian).
template <ValidateFlag validate>
uint32_t read_u32v(const byte* pc, uint32_t* length,
const char* name = "LEB32") {
return read_leb<uint32_t, validate, kNoAdvancePc, kNoTrace>(pc, length,
name);
}
// Reads a variable-length signed integer (little endian).
template <ValidateFlag validate>
int32_t read_i32v(const byte* pc, uint32_t* length,
const char* name = "signed LEB32") {
return read_leb<int32_t, validate, kNoAdvancePc, kNoTrace>(pc, length,
name);
}
// Reads a variable-length unsigned integer (little endian).
template <ValidateFlag validate>
uint64_t read_u64v(const byte* pc, uint32_t* length,
const char* name = "LEB64") {
return read_leb<uint64_t, validate, kNoAdvancePc, kNoTrace>(pc, length,
name);
}
// Reads a variable-length signed integer (little endian).
template <ValidateFlag validate>
int64_t read_i64v(const byte* pc, uint32_t* length,
const char* name = "signed LEB64") {
return read_leb<int64_t, validate, kNoAdvancePc, kNoTrace>(pc, length,
name);
}
// Reads a 8-bit unsigned integer (byte) and advances {pc_}.
uint8_t consume_u8(const char* name = "uint8_t") {
return consume_little_endian<uint8_t>(name);
}
// Reads a 16-bit unsigned integer (little endian) and advances {pc_}.
uint16_t consume_u16(const char* name = "uint16_t") {
return consume_little_endian<uint16_t>(name);
}
// Reads a single 32-bit unsigned integer (little endian) and advances {pc_}.
uint32_t consume_u32(const char* name = "uint32_t") {
return consume_little_endian<uint32_t>(name);
}
// Reads a LEB128 variable-length unsigned 32-bit integer and advances {pc_}.
uint32_t consume_u32v(const char* name = nullptr) {
uint32_t length = 0;
return read_leb<uint32_t, kValidate, kAdvancePc, kTrace>(pc_, &length,
name);
}
// Reads a LEB128 variable-length signed 32-bit integer and advances {pc_}.
int32_t consume_i32v(const char* name = nullptr) {
uint32_t length = 0;
return read_leb<int32_t, kValidate, kAdvancePc, kTrace>(pc_, &length, name);
}
// Consume {size} bytes and send them to the bit bucket, advancing {pc_}.
void consume_bytes(uint32_t size, const char* name = "skip") {
// Only trace if the name is not null.
TRACE_IF(name, " +%u %-20s: %u bytes\n", pc_offset(), name, size);
if (checkAvailable(size)) {
pc_ += size;
} else {
pc_ = end_;
}
}
// Check that at least {size} bytes exist between {pc_} and {end_}.
bool checkAvailable(uint32_t size) {
DCHECK_LE(pc_, end_);
if (V8_UNLIKELY(size > static_cast<uint32_t>(end_ - pc_))) {
errorf(pc_, "expected %u bytes, fell off end", size);
return false;
}
return true;
}
// Do not inline error methods. This has measurable impact on validation time,
// see https://crbug.com/910432.
void V8_NOINLINE error(const char* msg) { errorf(pc_offset(), "%s", msg); }
void V8_NOINLINE error(const uint8_t* pc, const char* msg) {
errorf(pc_offset(pc), "%s", msg);
}
void V8_NOINLINE error(uint32_t offset, const char* msg) {
errorf(offset, "%s", msg);
}
void V8_NOINLINE PRINTF_FORMAT(3, 4)
errorf(uint32_t offset, const char* format, ...) {
va_list args;
va_start(args, format);
verrorf(offset, format, args);
va_end(args);
}
void V8_NOINLINE PRINTF_FORMAT(3, 4)
errorf(const uint8_t* pc, const char* format, ...) {
va_list args;
va_start(args, format);
verrorf(pc_offset(pc), format, args);
va_end(args);
}
// Behavior triggered on first error, overridden in subclasses.
virtual void onFirstError() {}
// Debugging helper to print a bytes range as hex bytes.
void traceByteRange(const byte* start, const byte* end) {
DCHECK_LE(start, end);
for (const byte* p = start; p < end; ++p) TRACE("%02x ", *p);
}
// Debugging helper to print bytes up to the end.
void traceOffEnd() {
traceByteRange(pc_, end_);
TRACE("<end>\n");
}
// Converts the given value to a {Result}, copying the error if necessary.
template <typename T, typename U = typename std::remove_reference<T>::type>
Result<U> toResult(T&& val) {
if (failed()) {
TRACE("Result error: %s\n", error_.message().c_str());
return Result<U>{error_};
}
return Result<U>{std::forward<T>(val)};
}
// Resets the boundaries of this decoder.
void Reset(const byte* start, const byte* end, uint32_t buffer_offset = 0) {
DCHECK_LE(start, end);
DCHECK_EQ(static_cast<uint32_t>(end - start), end - start);
start_ = start;
pc_ = start;
end_ = end;
buffer_offset_ = buffer_offset;
error_ = {};
}
void Reset(Vector<const uint8_t> bytes, uint32_t buffer_offset = 0) {
Reset(bytes.begin(), bytes.end(), buffer_offset);
}
bool ok() const { return error_.empty(); }
bool failed() const { return !ok(); }
bool more() const { return pc_ < end_; }
const WasmError& error() const { return error_; }
const byte* start() const { return start_; }
const byte* pc() const { return pc_; }
uint32_t V8_INLINE position() const {
return static_cast<uint32_t>(pc_ - start_);
}
// This needs to be inlined for performance (see https://crbug.com/910432).
uint32_t V8_INLINE pc_offset(const uint8_t* pc) const {
DCHECK_LE(start_, pc);
DCHECK_GE(kMaxUInt32 - buffer_offset_, pc - start_);
return static_cast<uint32_t>(pc - start_) + buffer_offset_;
}
uint32_t pc_offset() const { return pc_offset(pc_); }
uint32_t buffer_offset() const { return buffer_offset_; }
// Takes an offset relative to the module start and returns an offset relative
// to the current buffer of the decoder.
uint32_t GetBufferRelativeOffset(uint32_t offset) const {
DCHECK_LE(buffer_offset_, offset);
return offset - buffer_offset_;
}
const byte* end() const { return end_; }
protected:
const byte* start_;
const byte* pc_;
const byte* end_;
// The offset of the current buffer in the module. Needed for streaming.
uint32_t buffer_offset_;
WasmError error_;
private:
void verrorf(uint32_t offset, const char* format, va_list args) {
// Only report the first error.
if (!ok()) return;
#if DEBUG
if (FLAG_wasm_break_on_decoder_error) {
base::OS::DebugBreak();
}
#endif
constexpr int kMaxErrorMsg = 256;
EmbeddedVector<char, kMaxErrorMsg> buffer;
int len = VSNPrintF(buffer, format, args);
CHECK_LT(0, len);
error_ = {offset, {buffer.begin(), static_cast<size_t>(len)}};
onFirstError();
}
template <typename IntType, bool validate>
inline IntType read_little_endian(const byte* pc, const char* msg) {
if (!validate) {
DCHECK(validate_size(pc, sizeof(IntType), msg));
} else if (!validate_size(pc, sizeof(IntType), msg)) {
return IntType{0};
}
return ReadLittleEndianValue<IntType>(reinterpret_cast<Address>(pc));
}
template <typename IntType>
inline IntType consume_little_endian(const char* name) {
TRACE(" +%u %-20s: ", pc_offset(), name);
if (!checkAvailable(sizeof(IntType))) {
traceOffEnd();
pc_ = end_;
return IntType{0};
}
IntType val = read_little_endian<IntType, false>(pc_, name);
traceByteRange(pc_, pc_ + sizeof(IntType));
TRACE("= %d\n", val);
pc_ += sizeof(IntType);
return val;
}
template <typename IntType, ValidateFlag validate, AdvancePCFlag advance_pc,
TraceFlag trace>
inline IntType read_leb(const byte* pc, uint32_t* length,
const char* name = "varint") {
DCHECK_IMPLIES(advance_pc, pc == pc_);
TRACE_IF(trace, " +%u %-20s: ", pc_offset(), name);
return read_leb_tail<IntType, validate, advance_pc, trace, 0>(pc, length,
name, 0);
}
template <typename IntType, ValidateFlag validate, AdvancePCFlag advance_pc,
TraceFlag trace, int byte_index>
IntType read_leb_tail(const byte* pc, uint32_t* length, const char* name,
IntType result) {
constexpr bool is_signed = std::is_signed<IntType>::value;
constexpr int kMaxLength = (sizeof(IntType) * 8 + 6) / 7;
static_assert(byte_index < kMaxLength, "invalid template instantiation");
constexpr int shift = byte_index * 7;
constexpr bool is_last_byte = byte_index == kMaxLength - 1;
const bool at_end = validate && pc >= end_;
byte b = 0;
if (!at_end) {
DCHECK_LT(pc, end_);
b = *pc;
TRACE_IF(trace, "%02x ", b);
using Unsigned = typename std::make_unsigned<IntType>::type;
result = result |
(static_cast<Unsigned>(static_cast<IntType>(b) & 0x7f) << shift);
}
if (!is_last_byte && (b & 0x80)) {
// Make sure that we only instantiate the template for valid byte indexes.
// Compilers are not smart enough to figure out statically that the
// following call is unreachable if is_last_byte is false.
constexpr int next_byte_index = byte_index + (is_last_byte ? 0 : 1);
return read_leb_tail<IntType, validate, advance_pc, trace,
next_byte_index>(pc + 1, length, name, result);
}
if (advance_pc) pc_ = pc + (at_end ? 0 : 1);
*length = byte_index + (at_end ? 0 : 1);
if (validate && (at_end || (b & 0x80))) {
TRACE_IF(trace, at_end ? "<end> " : "<length overflow> ");
errorf(pc, "expected %s", name);
result = 0;
}
if (is_last_byte) {
// A signed-LEB128 must sign-extend the final byte, excluding its
// most-significant bit; e.g. for a 32-bit LEB128:
// kExtraBits = 4 (== 32 - (5-1) * 7)
// For unsigned values, the extra bits must be all zero.
// For signed values, the extra bits *plus* the most significant bit must
// either be 0, or all ones.
constexpr int kExtraBits = (sizeof(IntType) * 8) - ((kMaxLength - 1) * 7);
constexpr int kSignExtBits = kExtraBits - (is_signed ? 1 : 0);
const byte checked_bits = b & (0xFF << kSignExtBits);
constexpr byte kSignExtendedExtraBits = 0x7f & (0xFF << kSignExtBits);
bool valid_extra_bits =
checked_bits == 0 ||
(is_signed && checked_bits == kSignExtendedExtraBits);
if (!validate) {
DCHECK(valid_extra_bits);
} else if (!valid_extra_bits) {
error(pc, "extra bits in varint");
result = 0;
}
}
constexpr int sign_ext_shift =
is_signed ? Max(0, int{8 * sizeof(IntType)} - shift - 7) : 0;
// Perform sign extension.
result = (result << sign_ext_shift) >> sign_ext_shift;
if (trace && is_signed) {
TRACE("= %" PRIi64 "\n", static_cast<int64_t>(result));
} else if (trace) {
TRACE("= %" PRIu64 "\n", static_cast<uint64_t>(result));
}
return result;
}
};
#undef TRACE
} // namespace wasm
} // namespace internal
} // namespace v8
#endif // V8_WASM_DECODER_H_