// Copyright 2018 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "src/reloc-info.h"
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#include "src/assembler-arch-inl.h"
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#include "src/code-stubs.h"
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#include "src/deoptimize-reason.h"
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#include "src/deoptimizer.h"
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#include "src/heap/heap-write-barrier-inl.h"
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#include "src/objects/code-inl.h"
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#include "src/snapshot/snapshot.h"
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namespace v8 {
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namespace internal {
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const char* const RelocInfo::kFillerCommentString = "DEOPTIMIZATION PADDING";
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// -----------------------------------------------------------------------------
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// Implementation of RelocInfoWriter and RelocIterator
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//
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// Relocation information is written backwards in memory, from high addresses
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// towards low addresses, byte by byte. Therefore, in the encodings listed
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// below, the first byte listed it at the highest address, and successive
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// bytes in the record are at progressively lower addresses.
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//
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// Encoding
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//
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// The most common modes are given single-byte encodings. Also, it is
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// easy to identify the type of reloc info and skip unwanted modes in
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// an iteration.
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//
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// The encoding relies on the fact that there are fewer than 14
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// different relocation modes using standard non-compact encoding.
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//
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// The first byte of a relocation record has a tag in its low 2 bits:
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// Here are the record schemes, depending on the low tag and optional higher
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// tags.
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//
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// Low tag:
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// 00: embedded_object: [6-bit pc delta] 00
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//
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// 01: code_target: [6-bit pc delta] 01
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//
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// 10: wasm_stub_call: [6-bit pc delta] 10
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//
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// 11: long_record [6 bit reloc mode] 11
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// followed by pc delta
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// followed by optional data depending on type.
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//
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// If a pc delta exceeds 6 bits, it is split into a remainder that fits into
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// 6 bits and a part that does not. The latter is encoded as a long record
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// with PC_JUMP as pseudo reloc info mode. The former is encoded as part of
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// the following record in the usual way. The long pc jump record has variable
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// length:
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// pc-jump: [PC_JUMP] 11
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// [7 bits data] 0
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// ...
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// [7 bits data] 1
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// (Bits 6..31 of pc delta, with leading zeroes
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// dropped, and last non-zero chunk tagged with 1.)
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const int kTagBits = 2;
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const int kTagMask = (1 << kTagBits) - 1;
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const int kLongTagBits = 6;
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const int kEmbeddedObjectTag = 0;
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const int kCodeTargetTag = 1;
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const int kWasmStubCallTag = 2;
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const int kDefaultTag = 3;
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const int kSmallPCDeltaBits = kBitsPerByte - kTagBits;
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const int kSmallPCDeltaMask = (1 << kSmallPCDeltaBits) - 1;
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const int RelocInfo::kMaxSmallPCDelta = kSmallPCDeltaMask;
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const int kChunkBits = 7;
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const int kChunkMask = (1 << kChunkBits) - 1;
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const int kLastChunkTagBits = 1;
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const int kLastChunkTagMask = 1;
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const int kLastChunkTag = 1;
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uint32_t RelocInfoWriter::WriteLongPCJump(uint32_t pc_delta) {
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// Return if the pc_delta can fit in kSmallPCDeltaBits bits.
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// Otherwise write a variable length PC jump for the bits that do
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// not fit in the kSmallPCDeltaBits bits.
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if (is_uintn(pc_delta, kSmallPCDeltaBits)) return pc_delta;
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WriteMode(RelocInfo::PC_JUMP);
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uint32_t pc_jump = pc_delta >> kSmallPCDeltaBits;
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DCHECK_GT(pc_jump, 0);
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// Write kChunkBits size chunks of the pc_jump.
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for (; pc_jump > 0; pc_jump = pc_jump >> kChunkBits) {
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byte b = pc_jump & kChunkMask;
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*--pos_ = b << kLastChunkTagBits;
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}
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// Tag the last chunk so it can be identified.
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*pos_ = *pos_ | kLastChunkTag;
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// Return the remaining kSmallPCDeltaBits of the pc_delta.
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return pc_delta & kSmallPCDeltaMask;
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}
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void RelocInfoWriter::WriteShortTaggedPC(uint32_t pc_delta, int tag) {
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// Write a byte of tagged pc-delta, possibly preceded by an explicit pc-jump.
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pc_delta = WriteLongPCJump(pc_delta);
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*--pos_ = pc_delta << kTagBits | tag;
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}
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void RelocInfoWriter::WriteShortData(intptr_t data_delta) {
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*--pos_ = static_cast<byte>(data_delta);
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}
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void RelocInfoWriter::WriteMode(RelocInfo::Mode rmode) {
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STATIC_ASSERT(RelocInfo::NUMBER_OF_MODES <= (1 << kLongTagBits));
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*--pos_ = static_cast<int>((rmode << kTagBits) | kDefaultTag);
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}
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void RelocInfoWriter::WriteModeAndPC(uint32_t pc_delta, RelocInfo::Mode rmode) {
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// Write two-byte tagged pc-delta, possibly preceded by var. length pc-jump.
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pc_delta = WriteLongPCJump(pc_delta);
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WriteMode(rmode);
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*--pos_ = pc_delta;
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}
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void RelocInfoWriter::WriteIntData(int number) {
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for (int i = 0; i < kIntSize; i++) {
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*--pos_ = static_cast<byte>(number);
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// Signed right shift is arithmetic shift. Tested in test-utils.cc.
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number = number >> kBitsPerByte;
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}
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}
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void RelocInfoWriter::WriteData(intptr_t data_delta) {
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for (int i = 0; i < kIntptrSize; i++) {
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*--pos_ = static_cast<byte>(data_delta);
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// Signed right shift is arithmetic shift. Tested in test-utils.cc.
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data_delta = data_delta >> kBitsPerByte;
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}
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}
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void RelocInfoWriter::Write(const RelocInfo* rinfo) {
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RelocInfo::Mode rmode = rinfo->rmode();
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#ifdef DEBUG
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byte* begin_pos = pos_;
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#endif
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DCHECK(rinfo->rmode() < RelocInfo::NUMBER_OF_MODES);
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DCHECK_GE(rinfo->pc() - reinterpret_cast<Address>(last_pc_), 0);
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// Use unsigned delta-encoding for pc.
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uint32_t pc_delta =
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static_cast<uint32_t>(rinfo->pc() - reinterpret_cast<Address>(last_pc_));
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// The two most common modes are given small tags, and usually fit in a byte.
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if (rmode == RelocInfo::EMBEDDED_OBJECT) {
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WriteShortTaggedPC(pc_delta, kEmbeddedObjectTag);
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} else if (rmode == RelocInfo::CODE_TARGET) {
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WriteShortTaggedPC(pc_delta, kCodeTargetTag);
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DCHECK_LE(begin_pos - pos_, RelocInfo::kMaxCallSize);
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} else if (rmode == RelocInfo::WASM_STUB_CALL) {
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WriteShortTaggedPC(pc_delta, kWasmStubCallTag);
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} else {
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WriteModeAndPC(pc_delta, rmode);
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if (RelocInfo::IsComment(rmode)) {
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WriteData(rinfo->data());
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} else if (RelocInfo::IsDeoptReason(rmode)) {
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DCHECK_LT(rinfo->data(), 1 << kBitsPerByte);
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WriteShortData(rinfo->data());
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} else if (RelocInfo::IsConstPool(rmode) ||
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RelocInfo::IsVeneerPool(rmode) || RelocInfo::IsDeoptId(rmode) ||
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RelocInfo::IsDeoptPosition(rmode)) {
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WriteIntData(static_cast<int>(rinfo->data()));
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}
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}
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last_pc_ = reinterpret_cast<byte*>(rinfo->pc());
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#ifdef DEBUG
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DCHECK_LE(begin_pos - pos_, kMaxSize);
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#endif
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}
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inline int RelocIterator::AdvanceGetTag() { return *--pos_ & kTagMask; }
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inline RelocInfo::Mode RelocIterator::GetMode() {
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return static_cast<RelocInfo::Mode>((*pos_ >> kTagBits) &
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((1 << kLongTagBits) - 1));
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}
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inline void RelocIterator::ReadShortTaggedPC() {
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rinfo_.pc_ += *pos_ >> kTagBits;
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}
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inline void RelocIterator::AdvanceReadPC() { rinfo_.pc_ += *--pos_; }
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void RelocIterator::AdvanceReadInt() {
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int x = 0;
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for (int i = 0; i < kIntSize; i++) {
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x |= static_cast<int>(*--pos_) << i * kBitsPerByte;
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}
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rinfo_.data_ = x;
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}
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void RelocIterator::AdvanceReadData() {
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intptr_t x = 0;
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for (int i = 0; i < kIntptrSize; i++) {
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x |= static_cast<intptr_t>(*--pos_) << i * kBitsPerByte;
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}
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rinfo_.data_ = x;
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}
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void RelocIterator::AdvanceReadLongPCJump() {
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// Read the 32-kSmallPCDeltaBits most significant bits of the
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// pc jump in kChunkBits bit chunks and shift them into place.
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// Stop when the last chunk is encountered.
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uint32_t pc_jump = 0;
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for (int i = 0; i < kIntSize; i++) {
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byte pc_jump_part = *--pos_;
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pc_jump |= (pc_jump_part >> kLastChunkTagBits) << i * kChunkBits;
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if ((pc_jump_part & kLastChunkTagMask) == 1) break;
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}
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// The least significant kSmallPCDeltaBits bits will be added
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// later.
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rinfo_.pc_ += pc_jump << kSmallPCDeltaBits;
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}
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inline void RelocIterator::ReadShortData() {
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uint8_t unsigned_b = *pos_;
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rinfo_.data_ = unsigned_b;
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}
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void RelocIterator::next() {
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DCHECK(!done());
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// Basically, do the opposite of RelocInfoWriter::Write.
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// Reading of data is as far as possible avoided for unwanted modes,
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// but we must always update the pc.
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//
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// We exit this loop by returning when we find a mode we want.
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while (pos_ > end_) {
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int tag = AdvanceGetTag();
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if (tag == kEmbeddedObjectTag) {
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ReadShortTaggedPC();
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if (SetMode(RelocInfo::EMBEDDED_OBJECT)) return;
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} else if (tag == kCodeTargetTag) {
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ReadShortTaggedPC();
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if (SetMode(RelocInfo::CODE_TARGET)) return;
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} else if (tag == kWasmStubCallTag) {
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ReadShortTaggedPC();
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if (SetMode(RelocInfo::WASM_STUB_CALL)) return;
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} else {
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DCHECK_EQ(tag, kDefaultTag);
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RelocInfo::Mode rmode = GetMode();
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if (rmode == RelocInfo::PC_JUMP) {
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AdvanceReadLongPCJump();
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} else {
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AdvanceReadPC();
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if (RelocInfo::IsComment(rmode)) {
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if (SetMode(rmode)) {
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AdvanceReadData();
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return;
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}
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Advance(kIntptrSize);
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} else if (RelocInfo::IsDeoptReason(rmode)) {
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Advance();
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if (SetMode(rmode)) {
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ReadShortData();
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return;
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}
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} else if (RelocInfo::IsConstPool(rmode) ||
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RelocInfo::IsVeneerPool(rmode) ||
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RelocInfo::IsDeoptId(rmode) ||
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RelocInfo::IsDeoptPosition(rmode)) {
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if (SetMode(rmode)) {
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AdvanceReadInt();
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return;
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}
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Advance(kIntSize);
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} else if (SetMode(static_cast<RelocInfo::Mode>(rmode))) {
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return;
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}
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}
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}
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}
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done_ = true;
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}
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RelocIterator::RelocIterator(Code* code, int mode_mask)
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: RelocIterator(code, code->raw_instruction_start(), code->constant_pool(),
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code->relocation_end(), code->relocation_start(),
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mode_mask) {}
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RelocIterator::RelocIterator(const CodeReference code_reference, int mode_mask)
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: RelocIterator(nullptr, code_reference.instruction_start(),
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code_reference.constant_pool(),
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code_reference.relocation_end(),
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code_reference.relocation_start(), mode_mask) {}
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RelocIterator::RelocIterator(EmbeddedData* embedded_data, Code* code,
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int mode_mask)
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: RelocIterator(
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code, embedded_data->InstructionStartOfBuiltin(code->builtin_index()),
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code->constant_pool(),
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code->relocation_start() + code->relocation_size(),
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code->relocation_start(), mode_mask) {}
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RelocIterator::RelocIterator(const CodeDesc& desc, int mode_mask)
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: RelocIterator(nullptr, reinterpret_cast<Address>(desc.buffer), 0,
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desc.buffer + desc.buffer_size,
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desc.buffer + desc.buffer_size - desc.reloc_size,
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mode_mask) {}
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RelocIterator::RelocIterator(Vector<byte> instructions,
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Vector<const byte> reloc_info, Address const_pool,
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int mode_mask)
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: RelocIterator(nullptr, reinterpret_cast<Address>(instructions.start()),
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const_pool, reloc_info.start() + reloc_info.size(),
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reloc_info.start(), mode_mask) {}
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RelocIterator::RelocIterator(Code* host, Address pc, Address constant_pool,
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const byte* pos, const byte* end, int mode_mask)
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: pos_(pos), end_(end), mode_mask_(mode_mask) {
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// Relocation info is read backwards.
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DCHECK_GE(pos_, end_);
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rinfo_.host_ = host;
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rinfo_.pc_ = pc;
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rinfo_.constant_pool_ = constant_pool;
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if (mode_mask_ == 0) pos_ = end_;
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next();
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}
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// -----------------------------------------------------------------------------
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// Implementation of RelocInfo
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// static
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bool RelocInfo::OffHeapTargetIsCodedSpecially() {
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#if defined(V8_TARGET_ARCH_ARM) || defined(V8_TARGET_ARCH_ARM64) || \
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defined(V8_TARGET_ARCH_X64)
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return false;
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#elif defined(V8_TARGET_ARCH_IA32) || defined(V8_TARGET_ARCH_MIPS) || \
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defined(V8_TARGET_ARCH_MIPS64) || defined(V8_TARGET_ARCH_PPC) || \
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defined(V8_TARGET_ARCH_S390)
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return true;
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#endif
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}
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Address RelocInfo::wasm_call_address() const {
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DCHECK_EQ(rmode_, WASM_CALL);
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return Assembler::target_address_at(pc_, constant_pool_);
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}
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void RelocInfo::set_wasm_call_address(Address address,
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ICacheFlushMode icache_flush_mode) {
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DCHECK_EQ(rmode_, WASM_CALL);
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Assembler::set_target_address_at(pc_, constant_pool_, address,
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icache_flush_mode);
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}
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Address RelocInfo::wasm_stub_call_address() const {
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DCHECK_EQ(rmode_, WASM_STUB_CALL);
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return Assembler::target_address_at(pc_, constant_pool_);
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}
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void RelocInfo::set_wasm_stub_call_address(Address address,
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ICacheFlushMode icache_flush_mode) {
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DCHECK_EQ(rmode_, WASM_STUB_CALL);
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Assembler::set_target_address_at(pc_, constant_pool_, address,
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icache_flush_mode);
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}
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void RelocInfo::set_target_address(Address target,
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WriteBarrierMode write_barrier_mode,
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ICacheFlushMode icache_flush_mode) {
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DCHECK(IsCodeTargetMode(rmode_) || IsRuntimeEntry(rmode_) ||
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IsWasmCall(rmode_));
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Assembler::set_target_address_at(pc_, constant_pool_, target,
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icache_flush_mode);
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if (write_barrier_mode == UPDATE_WRITE_BARRIER && host() != nullptr &&
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IsCodeTargetMode(rmode_)) {
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Code* target_code = Code::GetCodeFromTargetAddress(target);
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MarkingBarrierForCode(host(), this, target_code);
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}
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}
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bool RelocInfo::RequiresRelocationAfterCodegen(const CodeDesc& desc) {
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RelocIterator it(desc, RelocInfo::PostCodegenRelocationMask());
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return !it.done();
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}
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bool RelocInfo::RequiresRelocation(Code* code) {
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RelocIterator it(code, RelocInfo::kApplyMask);
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return !it.done();
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}
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#ifdef ENABLE_DISASSEMBLER
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const char* RelocInfo::RelocModeName(RelocInfo::Mode rmode) {
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switch (rmode) {
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case NONE:
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return "no reloc";
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case EMBEDDED_OBJECT:
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return "embedded object";
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case CODE_TARGET:
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return "code target";
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case RELATIVE_CODE_TARGET:
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return "relative code target";
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case RUNTIME_ENTRY:
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return "runtime entry";
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case COMMENT:
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return "comment";
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case EXTERNAL_REFERENCE:
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return "external reference";
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case INTERNAL_REFERENCE:
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return "internal reference";
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case INTERNAL_REFERENCE_ENCODED:
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return "encoded internal reference";
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case OFF_HEAP_TARGET:
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return "off heap target";
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case DEOPT_SCRIPT_OFFSET:
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return "deopt script offset";
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case DEOPT_INLINING_ID:
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return "deopt inlining id";
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case DEOPT_REASON:
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return "deopt reason";
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case DEOPT_ID:
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return "deopt index";
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case CONST_POOL:
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return "constant pool";
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case VENEER_POOL:
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return "veneer pool";
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case WASM_CALL:
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return "internal wasm call";
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case WASM_STUB_CALL:
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return "wasm stub call";
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case JS_TO_WASM_CALL:
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return "js to wasm call";
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case NUMBER_OF_MODES:
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case PC_JUMP:
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UNREACHABLE();
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}
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return "unknown relocation type";
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}
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void RelocInfo::Print(Isolate* isolate, std::ostream& os) { // NOLINT
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os << reinterpret_cast<const void*>(pc_) << " " << RelocModeName(rmode_);
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if (IsComment(rmode_)) {
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os << " (" << reinterpret_cast<char*>(data_) << ")";
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} else if (rmode_ == DEOPT_SCRIPT_OFFSET || rmode_ == DEOPT_INLINING_ID) {
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os << " (" << data() << ")";
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} else if (rmode_ == DEOPT_REASON) {
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os << " ("
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<< DeoptimizeReasonToString(static_cast<DeoptimizeReason>(data_)) << ")";
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} else if (rmode_ == EMBEDDED_OBJECT) {
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os << " (" << Brief(target_object()) << ")";
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} else if (rmode_ == EXTERNAL_REFERENCE) {
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if (isolate) {
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ExternalReferenceEncoder ref_encoder(isolate);
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os << " ("
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<< ref_encoder.NameOfAddress(isolate, target_external_reference())
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<< ") ";
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}
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os << " (" << reinterpret_cast<const void*>(target_external_reference())
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<< ")";
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} else if (IsCodeTargetMode(rmode_)) {
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const Address code_target = target_address();
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Code* code = Code::GetCodeFromTargetAddress(code_target);
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DCHECK(code->IsCode());
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os << " (" << Code::Kind2String(code->kind());
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if (Builtins::IsBuiltin(code)) {
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os << " " << Builtins::name(code->builtin_index());
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} else if (code->kind() == Code::STUB) {
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os << " " << CodeStub::MajorName(CodeStub::GetMajorKey(code));
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}
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os << ") (" << reinterpret_cast<const void*>(target_address()) << ")";
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} else if (IsRuntimeEntry(rmode_) && isolate->deoptimizer_data() != nullptr) {
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// Deoptimization bailouts are stored as runtime entries.
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DeoptimizeKind type;
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if (Deoptimizer::IsDeoptimizationEntry(isolate, target_address(), &type)) {
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int id = GetDeoptimizationId(isolate, type);
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os << " (" << Deoptimizer::MessageFor(type) << " deoptimization bailout "
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<< id << ")";
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}
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} else if (IsConstPool(rmode_)) {
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os << " (size " << static_cast<int>(data_) << ")";
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}
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os << "\n";
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}
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#endif // ENABLE_DISASSEMBLER
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#ifdef VERIFY_HEAP
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void RelocInfo::Verify(Isolate* isolate) {
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switch (rmode_) {
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case EMBEDDED_OBJECT:
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Object::VerifyPointer(isolate, target_object());
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break;
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case CODE_TARGET:
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case RELATIVE_CODE_TARGET: {
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// convert inline target address to code object
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Address addr = target_address();
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CHECK_NE(addr, kNullAddress);
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// Check that we can find the right code object.
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Code* code = Code::GetCodeFromTargetAddress(addr);
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Object* found = isolate->FindCodeObject(addr);
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CHECK(found->IsCode());
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CHECK(code->address() == HeapObject::cast(found)->address());
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break;
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}
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case INTERNAL_REFERENCE:
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case INTERNAL_REFERENCE_ENCODED: {
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Address target = target_internal_reference();
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Address pc = target_internal_reference_address();
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Code* code = Code::cast(isolate->FindCodeObject(pc));
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CHECK(target >= code->InstructionStart());
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CHECK(target <= code->InstructionEnd());
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break;
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}
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case OFF_HEAP_TARGET: {
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Address addr = target_off_heap_target();
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CHECK_NE(addr, kNullAddress);
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CHECK_NOT_NULL(InstructionStream::TryLookupCode(isolate, addr));
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break;
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}
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case RUNTIME_ENTRY:
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case COMMENT:
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case EXTERNAL_REFERENCE:
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case DEOPT_SCRIPT_OFFSET:
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case DEOPT_INLINING_ID:
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case DEOPT_REASON:
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case DEOPT_ID:
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case CONST_POOL:
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case VENEER_POOL:
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case WASM_CALL:
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case WASM_STUB_CALL:
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case JS_TO_WASM_CALL:
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case NONE:
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break;
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case NUMBER_OF_MODES:
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case PC_JUMP:
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UNREACHABLE();
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break;
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}
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}
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#endif // VERIFY_HEAP
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} // namespace internal
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} // namespace v8
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