js/src/jit/x64/Assembler-x64.cpp
author shindli <shindli@mozilla.com>
Sun, 22 Sep 2019 00:46:56 +0300
changeset 494432 9136070a0561cb169b01569b2346a1e3aad387dd
parent 493551 f5bc71d6ee11838d067fd128a4436153378d7c7f
permissions -rw-r--r--
Merge autoland to mozilla-central. a=merge

/* -*- 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/. */

#include "jit/x64/Assembler-x64.h"

#include "gc/Marking.h"

using namespace js;
using namespace js::jit;

ABIArgGenerator::ABIArgGenerator()
    :
#if defined(XP_WIN)
      regIndex_(0),
      stackOffset_(ShadowStackSpace),
#else
      intRegIndex_(0),
      floatRegIndex_(0),
      stackOffset_(0),
#endif
      current_() {
}

ABIArg ABIArgGenerator::next(MIRType type) {
#if defined(XP_WIN)
  JS_STATIC_ASSERT(NumIntArgRegs == NumFloatArgRegs);
  if (regIndex_ == NumIntArgRegs) {
    if (IsSimdType(type)) {
      // On Win64, >64 bit args need to be passed by reference, but wasm
      // doesn't allow passing SIMD values to FFIs. The only way to reach
      // here is asm to asm calls, so we can break the ABI here.
      stackOffset_ = AlignBytes(stackOffset_, SimdMemoryAlignment);
      current_ = ABIArg(stackOffset_);
      stackOffset_ += Simd128DataSize;
    } else {
      current_ = ABIArg(stackOffset_);
      stackOffset_ += sizeof(uint64_t);
    }
    return current_;
  }
  switch (type) {
    case MIRType::Int32:
    case MIRType::Int64:
    case MIRType::Pointer:
    case MIRType::RefOrNull:
      current_ = ABIArg(IntArgRegs[regIndex_++]);
      break;
    case MIRType::Float32:
      current_ = ABIArg(FloatArgRegs[regIndex_++].asSingle());
      break;
    case MIRType::Double:
      current_ = ABIArg(FloatArgRegs[regIndex_++]);
      break;
    case MIRType::Int8x16:
    case MIRType::Int16x8:
    case MIRType::Int32x4:
    case MIRType::Float32x4:
    case MIRType::Bool8x16:
    case MIRType::Bool16x8:
    case MIRType::Bool32x4:
      // On Win64, >64 bit args need to be passed by reference, but wasm
      // doesn't allow passing SIMD values to FFIs. The only way to reach
      // here is asm to asm calls, so we can break the ABI here.
      current_ = ABIArg(FloatArgRegs[regIndex_++].asSimd128());
      break;
    default:
      MOZ_CRASH("Unexpected argument type");
  }
  return current_;
#else
  switch (type) {
    case MIRType::Int32:
    case MIRType::Int64:
    case MIRType::Pointer:
    case MIRType::RefOrNull:
      if (intRegIndex_ == NumIntArgRegs) {
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(uint64_t);
        break;
      }
      current_ = ABIArg(IntArgRegs[intRegIndex_++]);
      break;
    case MIRType::Double:
    case MIRType::Float32:
      if (floatRegIndex_ == NumFloatArgRegs) {
        current_ = ABIArg(stackOffset_);
        stackOffset_ += sizeof(uint64_t);
        break;
      }
      if (type == MIRType::Float32) {
        current_ = ABIArg(FloatArgRegs[floatRegIndex_++].asSingle());
      } else {
        current_ = ABIArg(FloatArgRegs[floatRegIndex_++]);
      }
      break;
    case MIRType::Int8x16:
    case MIRType::Int16x8:
    case MIRType::Int32x4:
    case MIRType::Float32x4:
    case MIRType::Bool8x16:
    case MIRType::Bool16x8:
    case MIRType::Bool32x4:
      if (floatRegIndex_ == NumFloatArgRegs) {
        stackOffset_ = AlignBytes(stackOffset_, SimdMemoryAlignment);
        current_ = ABIArg(stackOffset_);
        stackOffset_ += Simd128DataSize;
        break;
      }
      current_ = ABIArg(FloatArgRegs[floatRegIndex_++].asSimd128());
      break;
    default:
      MOZ_CRASH("Unexpected argument type");
  }
  return current_;
#endif
}

void Assembler::writeRelocation(JmpSrc src, RelocationKind reloc) {
  if (!jumpRelocations_.length()) {
    // The jump relocation table starts with a fixed-width integer pointing
    // to the start of the extended jump table. But, we don't know the
    // actual extended jump table offset yet, so write a 0 which we'll
    // patch later.
    jumpRelocations_.writeFixedUint32_t(0);
  }
  if (reloc == RelocationKind::JITCODE) {
    jumpRelocations_.writeUnsigned(src.offset());
    jumpRelocations_.writeUnsigned(jumps_.length());
  }
}

void Assembler::addPendingJump(JmpSrc src, ImmPtr target,
                               RelocationKind reloc) {
  MOZ_ASSERT(target.value != nullptr);

  // Emit reloc before modifying the jump table, since it computes a 0-based
  // index. This jump is not patchable at runtime.
  if (reloc == RelocationKind::JITCODE) {
    writeRelocation(src, reloc);
  }
  enoughMemory_ &=
      jumps_.append(RelativePatch(src.offset(), target.value, reloc));
}

size_t Assembler::addPatchableJump(JmpSrc src, RelocationKind reloc) {
  // This jump is patchable at runtime so we always need to make sure the
  // jump table is emitted.
  writeRelocation(src, reloc);

  size_t index = jumps_.length();
  enoughMemory_ &= jumps_.append(RelativePatch(src.offset(), nullptr, reloc));
  return index;
}

void Assembler::finish() {
  if (oom()) {
    return;
  }

  if (!jumps_.length()) {
    // Since we may be folowed by non-executable data, eagerly insert an
    // undefined instruction byte to prevent processors from decoding
    // gibberish into their pipelines. See Intel performance guides.
    masm.ud2();
    return;
  }

  // Emit the jump table.
  masm.haltingAlign(SizeOfJumpTableEntry);
  extendedJumpTable_ = masm.size();

  // Now that we know the offset to the jump table, squirrel it into the
  // jump relocation buffer if any JitCode references exist and must be
  // tracked for GC.
  MOZ_ASSERT_IF(jumpRelocations_.length(),
                jumpRelocations_.length() >= sizeof(uint32_t));
  if (jumpRelocations_.length()) {
    *(uint32_t*)jumpRelocations_.buffer() = extendedJumpTable_;
  }

  // Zero the extended jumps table.
  for (size_t i = 0; i < jumps_.length(); i++) {
#ifdef DEBUG
    size_t oldSize = masm.size();
#endif
    masm.jmp_rip(2);
    MOZ_ASSERT_IF(!masm.oom(), masm.size() - oldSize == 6);
    // Following an indirect branch with ud2 hints to the hardware that
    // there's no fall-through. This also aligns the 64-bit immediate.
    masm.ud2();
    MOZ_ASSERT_IF(!masm.oom(), masm.size() - oldSize == 8);
    masm.immediate64(0);
    MOZ_ASSERT_IF(!masm.oom(), masm.size() - oldSize == SizeOfExtendedJump);
    MOZ_ASSERT_IF(!masm.oom(), masm.size() - oldSize == SizeOfJumpTableEntry);
  }
}

void Assembler::executableCopy(uint8_t* buffer) {
  AssemblerX86Shared::executableCopy(buffer);

  for (size_t i = 0; i < jumps_.length(); i++) {
    RelativePatch& rp = jumps_[i];
    uint8_t* src = buffer + rp.offset;
    if (!rp.target) {
      // The patch target is nullptr for jumps that have been linked to
      // a label within the same code block, but may be repatched later
      // to jump to a different code block.
      continue;
    }
    if (X86Encoding::CanRelinkJump(src, rp.target)) {
      X86Encoding::SetRel32(src, rp.target);
    } else {
      // An extended jump table must exist, and its offset must be in
      // range.
      MOZ_ASSERT(extendedJumpTable_);
      MOZ_ASSERT((extendedJumpTable_ + i * SizeOfJumpTableEntry) <=
                 size() - SizeOfJumpTableEntry);

      // Patch the jump to go to the extended jump entry.
      uint8_t* entry = buffer + extendedJumpTable_ + i * SizeOfJumpTableEntry;
      X86Encoding::SetRel32(src, entry);

      // Now patch the pointer, note that we need to align it to
      // *after* the extended jump, i.e. after the 64-bit immedate.
      X86Encoding::SetPointer(entry + SizeOfExtendedJump, rp.target);
    }
  }
}

class RelocationIterator {
  CompactBufferReader reader_;
  uint32_t tableStart_;
  uint32_t offset_;
  uint32_t extOffset_;

 public:
  explicit RelocationIterator(CompactBufferReader& reader)
      : reader_(reader), offset_(0), extOffset_(0) {
    tableStart_ = reader_.readFixedUint32_t();
  }

  bool read() {
    if (!reader_.more()) {
      return false;
    }
    offset_ = reader_.readUnsigned();
    extOffset_ = reader_.readUnsigned();
    return true;
  }

  uint32_t offset() const { return offset_; }
  uint32_t extendedOffset() const { return extOffset_; }
};

JitCode* Assembler::CodeFromJump(JitCode* code, uint8_t* jump) {
  uint8_t* target = (uint8_t*)X86Encoding::GetRel32Target(jump);
  if (target >= code->raw() &&
      target < code->raw() + code->instructionsSize()) {
    // This jump is within the code buffer, so it has been redirected to
    // the extended jump table.
    MOZ_ASSERT(target + SizeOfJumpTableEntry <=
               code->raw() + code->instructionsSize());

    target = (uint8_t*)X86Encoding::GetPointer(target + SizeOfExtendedJump);
  }

  return JitCode::FromExecutable(target);
}

void Assembler::TraceJumpRelocations(JSTracer* trc, JitCode* code,
                                     CompactBufferReader& reader) {
  RelocationIterator iter(reader);
  while (iter.read()) {
    JitCode* child = CodeFromJump(code, code->raw() + iter.offset());
    TraceManuallyBarrieredEdge(trc, &child, "rel32");
    MOZ_ASSERT(child == CodeFromJump(code, code->raw() + iter.offset()));
  }
}