tor-browser

Snapshots.h (18689B)

---

/* -*- 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 http://mozilla.org/MPL/2.0/. */

#ifndef jit_Snapshot_h
#define jit_Snapshot_h

#include "mozilla/Attributes.h"

#include "jit/CompactBuffer.h"
#include "jit/IonTypes.h"
#include "jit/Registers.h"
#include "js/AllocPolicy.h"
#include "js/HashTable.h"
#include "js/TypeDecls.h"

namespace js {
class JS_PUBLIC_API GenericPrinter;

namespace jit {

class RValueAllocation;

// A Recover Value Allocation mirror what is known at compiled time as being the
// MIRType and the LAllocation.  This is read out of the snapshot to recover the
// value which would be there if this frame was an interpreter frame instead of
// an Ion frame.
//
// It is used with the SnapshotIterator to recover a Value from the stack,
// spilled registers or the list of constant of the compiled script.
//
// Unit tests are located in jsapi-tests/testJitRValueAlloc.cpp.
class RValueAllocation {
public:
 // See RValueAllocation encoding in Snapshots.cpp
 enum Mode {
   CONSTANT = 0x00,
   CST_UNDEFINED = 0x01,
   CST_NULL = 0x02,
   DOUBLE_REG = 0x03,
   FLOAT32_REG = 0x04,
   FLOAT32_STACK = 0x05,
#if defined(JS_NUNBOX32)
   UNTYPED_REG_REG = 0x06,
   UNTYPED_REG_STACK = 0x07,
   UNTYPED_STACK_REG = 0x08,
   UNTYPED_STACK_STACK = 0x09,
#elif defined(JS_PUNBOX64)
   UNTYPED_REG = 0x06,
   UNTYPED_STACK = 0x07,
#endif

   // Recover instructions.
   RECOVER_INSTRUCTION = 0x0a,
   RI_WITH_DEFAULT_CST = 0x0b,

   // IntPtr value.
   INTPTR_CST = 0x0c,
   INTPTR_REG = 0x0d,
   INTPTR_STACK = 0x0e,
   INTPTR_INT32_STACK = 0x0f,

   // The JSValueType is packed in the Mode.
   TYPED_REG_MIN = 0x10,
   TYPED_REG_MAX = 0x1f,
   TYPED_REG = TYPED_REG_MIN,

   // The JSValueType is packed in the Mode.
   TYPED_STACK_MIN = 0x20,
   TYPED_STACK_MAX = 0x2f,
   TYPED_STACK = TYPED_STACK_MIN,

   // Int64 value.
   INT64_CST = 0x30,
#if defined(JS_NUNBOX32)
   INT64_REG_REG = 0x31,
   INT64_REG_STACK = 0x32,
   INT64_STACK_REG = 0x33,
   INT64_STACK_STACK = 0x34,
#elif defined(JS_PUNBOX64)
   INT64_REG = 0x31,
   INT64_STACK = 0x32,
#endif

   // This mask can be used with any other valid mode. When this flag is
   // set on the mode, this inform the snapshot iterator that even if the
   // allocation is readable, the content of if might be incomplete unless
   // all side-effects are executed.
   RECOVER_SIDE_EFFECT_MASK = 0x80,

   // This mask represents the set of bits which can be used to encode a
   // value in a snapshot. The mode is used to determine how to interpret
   // the union of values and how to pack the value in memory.
   MODE_BITS_MASK = 0x17f,

   INVALID = 0x100,
 };

 enum { PACKED_TAG_MASK = 0x0f };

 // See Payload encoding in Snapshots.cpp
 enum PayloadType {
   PAYLOAD_NONE,
   PAYLOAD_INDEX,
   PAYLOAD_STACK_OFFSET,
   PAYLOAD_GPR,
   PAYLOAD_FPU,
   PAYLOAD_PACKED_TAG
 };

 struct Layout {
   PayloadType type1;
   PayloadType type2;
   const char* name;
 };

private:
 Mode mode_;

 // Additional information to recover the content of the allocation.
 struct FloatRegisterBits {
   uint32_t data;
   bool operator==(const FloatRegisterBits& other) const {
     return data == other.data;
   }
   uint32_t code() const { return data; }
   const char* name() const {
     FloatRegister tmp = FloatRegister::FromCode(data);
     return tmp.name();
   }
 };

 union Payload {
   uint32_t index;
   int32_t stackOffset;
   Register gpr;
   FloatRegisterBits fpu;
   JSValueType type;

   Payload() : index(0) {
     static_assert(sizeof(index) == sizeof(Payload),
                   "All Payload bits are initialized.");
   }
 };

 Payload arg1_;
 Payload arg2_;

 static Payload payloadOfIndex(uint32_t index) {
   Payload p;
   p.index = index;
   return p;
 }
 static Payload payloadOfStackOffset(int32_t offset) {
   Payload p;
   p.stackOffset = offset;
   return p;
 }
 static Payload payloadOfRegister(Register reg) {
   Payload p;
   p.gpr = reg;
   return p;
 }
 static Payload payloadOfFloatRegister(FloatRegister reg) {
   Payload p;
   FloatRegisterBits b;
   b.data = reg.code();
   p.fpu = b;
   return p;
 }
 static Payload payloadOfValueType(JSValueType type) {
   Payload p;
   p.type = type;
   return p;
 }

 static const Layout& layoutFromMode(Mode mode);

 static void readPayload(CompactBufferReader& reader, PayloadType t,
                         uint8_t* mode, Payload* p);
 static void writePayload(CompactBufferWriter& writer, PayloadType t,
                          Payload p);
 static void writePadding(CompactBufferWriter& writer);
#ifdef JS_JITSPEW
 static void dumpPayload(GenericPrinter& out, PayloadType t, Payload p);
#endif
 static bool equalPayloads(PayloadType t, Payload lhs, Payload rhs);

 RValueAllocation(Mode mode, Payload a1, Payload a2)
     : mode_(mode), arg1_(a1), arg2_(a2) {}

 RValueAllocation(Mode mode, Payload a1) : mode_(mode), arg1_(a1) {
   arg2_.index = 0;
 }

 explicit RValueAllocation(Mode mode) : mode_(mode) {
   arg1_.index = 0;
   arg2_.index = 0;
 }

public:
 RValueAllocation() : mode_(INVALID) {
   arg1_.index = 0;
   arg2_.index = 0;
 }

 // DOUBLE_REG
 static RValueAllocation Double(FloatRegister reg) {
   return RValueAllocation(DOUBLE_REG, payloadOfFloatRegister(reg));
 }

 // FLOAT32_REG or FLOAT32_STACK
 static RValueAllocation Float32(FloatRegister reg) {
   return RValueAllocation(FLOAT32_REG, payloadOfFloatRegister(reg));
 }
 static RValueAllocation Float32(int32_t offset) {
   return RValueAllocation(FLOAT32_STACK, payloadOfStackOffset(offset));
 }

 // TYPED_REG or TYPED_STACK
 static RValueAllocation Typed(JSValueType type, Register reg) {
   MOZ_ASSERT(type != JSVAL_TYPE_DOUBLE && type != JSVAL_TYPE_MAGIC &&
              type != JSVAL_TYPE_NULL && type != JSVAL_TYPE_UNDEFINED);
   return RValueAllocation(TYPED_REG, payloadOfValueType(type),
                           payloadOfRegister(reg));
 }
 static RValueAllocation Typed(JSValueType type, int32_t offset) {
   MOZ_ASSERT(type != JSVAL_TYPE_MAGIC && type != JSVAL_TYPE_NULL &&
              type != JSVAL_TYPE_UNDEFINED);
   return RValueAllocation(TYPED_STACK, payloadOfValueType(type),
                           payloadOfStackOffset(offset));
 }

 // UNTYPED
#if defined(JS_NUNBOX32)
 static RValueAllocation Untyped(Register type, Register payload) {
   return RValueAllocation(UNTYPED_REG_REG, payloadOfRegister(type),
                           payloadOfRegister(payload));
 }

 static RValueAllocation Untyped(Register type, int32_t payloadStackOffset) {
   return RValueAllocation(UNTYPED_REG_STACK, payloadOfRegister(type),
                           payloadOfStackOffset(payloadStackOffset));
 }

 static RValueAllocation Untyped(int32_t typeStackOffset, Register payload) {
   return RValueAllocation(UNTYPED_STACK_REG,
                           payloadOfStackOffset(typeStackOffset),
                           payloadOfRegister(payload));
 }

 static RValueAllocation Untyped(int32_t typeStackOffset,
                                 int32_t payloadStackOffset) {
   return RValueAllocation(UNTYPED_STACK_STACK,
                           payloadOfStackOffset(typeStackOffset),
                           payloadOfStackOffset(payloadStackOffset));
 }

#elif defined(JS_PUNBOX64)
 static RValueAllocation Untyped(Register reg) {
   return RValueAllocation(UNTYPED_REG, payloadOfRegister(reg));
 }

 static RValueAllocation Untyped(int32_t stackOffset) {
   return RValueAllocation(UNTYPED_STACK, payloadOfStackOffset(stackOffset));
 }
#endif

 // common constants.
 static RValueAllocation Undefined() {
   return RValueAllocation(CST_UNDEFINED);
 }
 static RValueAllocation Null() { return RValueAllocation(CST_NULL); }

 // CONSTANT's index
 static RValueAllocation ConstantPool(uint32_t index) {
   return RValueAllocation(CONSTANT, payloadOfIndex(index));
 }

 // Recover instruction's index
 static RValueAllocation RecoverInstruction(uint32_t index) {
   return RValueAllocation(RECOVER_INSTRUCTION, payloadOfIndex(index));
 }
 static RValueAllocation RecoverInstruction(uint32_t riIndex,
                                            uint32_t cstIndex) {
   return RValueAllocation(RI_WITH_DEFAULT_CST, payloadOfIndex(riIndex),
                           payloadOfIndex(cstIndex));
 }

 // IntPtr
#if !defined(JS_64BIT)
 static RValueAllocation IntPtrConstant(uint32_t index) {
   return RValueAllocation(INTPTR_CST, payloadOfIndex(index));
 }
#else
 static RValueAllocation IntPtrConstant(uint32_t lowIndex,
                                        uint32_t highIndex) {
   return RValueAllocation(INTPTR_CST, payloadOfIndex(lowIndex),
                           payloadOfIndex(highIndex));
 }
#endif
 static RValueAllocation IntPtr(Register reg) {
   return RValueAllocation(INTPTR_REG, payloadOfRegister(reg));
 }
 static RValueAllocation IntPtr(int32_t offset) {
   return RValueAllocation(INTPTR_STACK, payloadOfStackOffset(offset));
 }
 static RValueAllocation IntPtrInt32(int32_t offset) {
   return RValueAllocation(INTPTR_INT32_STACK, payloadOfStackOffset(offset));
 }

 // Int64
 static RValueAllocation Int64Constant(uint32_t lowIndex, uint32_t highIndex) {
   return RValueAllocation(INT64_CST, payloadOfIndex(lowIndex),
                           payloadOfIndex(highIndex));
 }
#if defined(JS_NUNBOX32)
 static RValueAllocation Int64(Register low, Register high) {
   return RValueAllocation(INT64_REG_REG, payloadOfRegister(low),
                           payloadOfRegister(high));
 }

 static RValueAllocation Int64(Register low, int32_t highStackOffset) {
   return RValueAllocation(INT64_REG_STACK, payloadOfRegister(low),
                           payloadOfStackOffset(highStackOffset));
 }

 static RValueAllocation Int64(int32_t lowStackOffset, Register high) {
   return RValueAllocation(INT64_STACK_REG,
                           payloadOfStackOffset(lowStackOffset),
                           payloadOfRegister(high));
 }

 static RValueAllocation Int64(int32_t lowStackOffset,
                               int32_t highStackOffset) {
   return RValueAllocation(INT64_STACK_STACK,
                           payloadOfStackOffset(lowStackOffset),
                           payloadOfStackOffset(highStackOffset));
 }

#elif defined(JS_PUNBOX64)
 static RValueAllocation Int64(Register reg) {
   return RValueAllocation(INT64_REG, payloadOfRegister(reg));
 }

 static RValueAllocation Int64(int32_t stackOffset) {
   return RValueAllocation(INT64_STACK, payloadOfStackOffset(stackOffset));
 }
#endif

 void setNeedSideEffect() {
   MOZ_ASSERT(!needSideEffect() && mode_ != INVALID);
   mode_ = Mode(mode_ | RECOVER_SIDE_EFFECT_MASK);
 }

 void writeHeader(CompactBufferWriter& writer, JSValueType type,
                  uint32_t regCode) const;

public:
 static RValueAllocation read(CompactBufferReader& reader);
 void write(CompactBufferWriter& writer) const;

public:
 bool valid() const { return mode_ != INVALID; }
 Mode mode() const { return Mode(mode_ & MODE_BITS_MASK); }
 bool needSideEffect() const { return mode_ & RECOVER_SIDE_EFFECT_MASK; }

 uint32_t index() const {
   MOZ_ASSERT(layoutFromMode(mode()).type1 == PAYLOAD_INDEX);
   return arg1_.index;
 }
 int32_t stackOffset() const {
   MOZ_ASSERT(layoutFromMode(mode()).type1 == PAYLOAD_STACK_OFFSET);
   return arg1_.stackOffset;
 }
 Register reg() const {
   MOZ_ASSERT(layoutFromMode(mode()).type1 == PAYLOAD_GPR);
   return arg1_.gpr;
 }
 FloatRegister fpuReg() const {
   MOZ_ASSERT(layoutFromMode(mode()).type1 == PAYLOAD_FPU);
   FloatRegisterBits b = arg1_.fpu;
   return FloatRegister::FromCode(b.data);
 }
 JSValueType knownType() const {
   MOZ_ASSERT(layoutFromMode(mode()).type1 == PAYLOAD_PACKED_TAG);
   return arg1_.type;
 }

 uint32_t index2() const {
   MOZ_ASSERT(layoutFromMode(mode()).type2 == PAYLOAD_INDEX);
   return arg2_.index;
 }
 int32_t stackOffset2() const {
   MOZ_ASSERT(layoutFromMode(mode()).type2 == PAYLOAD_STACK_OFFSET);
   return arg2_.stackOffset;
 }
 Register reg2() const {
   MOZ_ASSERT(layoutFromMode(mode()).type2 == PAYLOAD_GPR);
   return arg2_.gpr;
 }

public:
#ifdef JS_JITSPEW
 void dump(GenericPrinter& out) const;
#endif

 bool operator==(const RValueAllocation& rhs) const {
   // Note, this equality compares the verbatim content of the payload,
   // which is made possible because we ensure that the payload content is
   // fully initialized during the creation.
   static_assert(sizeof(int32_t) == sizeof(Payload),
                 "All Payload bits are compared.");
   return mode_ == rhs.mode_ && arg1_.index == rhs.arg1_.index &&
          arg2_.index == rhs.arg2_.index;
 }

 HashNumber hash() const;

 struct Hasher {
   using Key = RValueAllocation;
   using Lookup = Key;
   static HashNumber hash(const Lookup& v) { return v.hash(); }
   static bool match(const Key& k, const Lookup& l) { return k == l; }
 };
};

class RecoverWriter;

// Collects snapshots in a contiguous buffer, which is copied into IonScript
// memory after code generation.
class SnapshotWriter {
 CompactBufferWriter writer_;
 CompactBufferWriter allocWriter_;

 // Map RValueAllocations to an offset in the allocWriter_ buffer.  This is
 // useful as value allocations are repeated frequently.
 using RVA = RValueAllocation;
 using RValueAllocMap = HashMap<RVA, uint32_t, RVA::Hasher, SystemAllocPolicy>;
 RValueAllocMap allocMap_;

 // This is only used to assert sanity.
 uint32_t allocWritten_;

 // Used to report size of the snapshot in the spew messages.
 SnapshotOffset lastStart_;

public:
 SnapshotWriter();

 SnapshotOffset startSnapshot(RecoverOffset recoverOffset, BailoutKind kind);
#ifdef TRACK_SNAPSHOTS
 void trackSnapshot(uint32_t pcOpcode, uint32_t mirOpcode, uint32_t mirId,
                    uint32_t lirOpcode, uint32_t lirId);
#endif
 [[nodiscard]] bool add(const RValueAllocation& slot);

 uint32_t allocWritten() const { return allocWritten_; }
 void endSnapshot();

 bool oom() const {
   return writer_.oom() || writer_.length() >= MAX_BUFFER_SIZE ||
          allocWriter_.oom() || allocWriter_.length() >= MAX_BUFFER_SIZE;
 }

 size_t listSize() const { return writer_.length(); }
 const uint8_t* listBuffer() const { return writer_.buffer(); }

 size_t RVATableSize() const { return allocWriter_.length(); }
 const uint8_t* RVATableBuffer() const { return allocWriter_.buffer(); }
};

class MNode;

class RecoverWriter {
 CompactBufferWriter writer_;

 uint32_t instructionCount_;
 uint32_t instructionsWritten_;

public:
 SnapshotOffset startRecover(uint32_t instructionCount);

 void writeInstruction(const MNode* rp);

 void endRecover();

 size_t size() const { return writer_.length(); }
 const uint8_t* buffer() const { return writer_.buffer(); }

 bool oom() const {
   return writer_.oom() || writer_.length() >= MAX_BUFFER_SIZE;
 }
};

class RecoverReader;

// A snapshot reader reads the entries out of the compressed snapshot buffer in
// a script. These entries describe the equivalent interpreter frames at a given
// position in JIT code. Each entry is an Ion's value allocations, used to
// recover the corresponding Value from an Ion frame.
class SnapshotReader {
 CompactBufferReader reader_;
 CompactBufferReader allocReader_;
 const uint8_t* allocTable_;

 BailoutKind bailoutKind_;
 uint32_t allocRead_;           // Number of slots that have been read.
 RecoverOffset recoverOffset_;  // Offset of the recover instructions.

#ifdef TRACK_SNAPSHOTS
private:
 uint32_t pcOpcode_;
 uint32_t mirOpcode_;
 uint32_t mirId_;
 uint32_t lirOpcode_;
 uint32_t lirId_;

public:
 void readTrackSnapshot();
 void spewBailingFrom() const;
#endif

private:
 void readSnapshotHeader();
 uint32_t readAllocationIndex();

public:
 SnapshotReader(const uint8_t* snapshots, uint32_t offset,
                uint32_t RVATableSize, uint32_t listSize);

 RValueAllocation readAllocation();
 void skipAllocation() { readAllocationIndex(); }

 BailoutKind bailoutKind() const { return bailoutKind_; }
 RecoverOffset recoverOffset() const { return recoverOffset_; }

 uint32_t numAllocationsRead() const { return allocRead_; }
 void resetNumAllocationsRead() { allocRead_ = 0; }
};

class MOZ_NON_PARAM RInstructionStorage {
 static constexpr size_t Size = 4 * sizeof(uint32_t);

 // This presumes all RInstructionStorage are safely void*-alignable.
 // RInstruction::readRecoverData asserts that no RInstruction subclass
 // has stricter alignment requirements than RInstructionStorage.
 static constexpr size_t Alignment = alignof(void*);

 alignas(Alignment) unsigned char mem[Size];

public:
 const void* addr() const { return mem; }
 void* addr() { return mem; }

 RInstructionStorage() = default;

 // Making a copy of raw bytes holding a RInstruction instance would be a
 // strict aliasing violation: see bug 1269319 for an instance of bytewise
 // copying having caused crashes.
 RInstructionStorage(const RInstructionStorage&) = delete;
 RInstructionStorage& operator=(const RInstructionStorage& other) = delete;
};

class RInstruction;

class RecoverReader {
 CompactBufferReader reader_;

 // Number of encoded instructions.
 uint32_t numInstructions_;

 // Number of instruction read.
 uint32_t numInstructionsRead_;

 // Space is reserved as part of the RecoverReader to avoid allocations of
 // data which is needed to decode the current instruction.
 RInstructionStorage rawData_;

private:
 void readRecoverHeader();
 void readInstruction();

public:
 RecoverReader(SnapshotReader& snapshot, const uint8_t* recovers,
               uint32_t size);
 explicit RecoverReader(const RecoverReader& rr);
 RecoverReader& operator=(const RecoverReader& rr);

 uint32_t numInstructions() const { return numInstructions_; }
 uint32_t numInstructionsRead() const { return numInstructionsRead_; }

 bool moreInstructions() const {
   return numInstructionsRead_ < numInstructions_;
 }
 void nextInstruction() { readInstruction(); }

 const RInstruction* instruction() const {
   return reinterpret_cast<const RInstruction*>(rawData_.addr());
 }
};

}  // namespace jit
}  // namespace js

#endif /* jit_Snapshot_h */