path: root/js/src/jit/x64/Assembler-x64.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * 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:
        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:
        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, Relocation::Kind 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 == Relocation::JITCODE) {
        jumpRelocations_.writeUnsigned(src.offset());
        jumpRelocations_.writeUnsigned(jumps_.length());
    }
}

void
Assembler::addPendingJump(JmpSrc src, ImmPtr target, Relocation::Kind 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 == Relocation::JITCODE)
        writeRelocation(src, reloc);
    enoughMemory_ &= jumps_.append(RelativePatch(src.offset(), target.value, reloc));
}

size_t
Assembler::addPatchableJump(JmpSrc src, Relocation::Kind 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;
}

/* static */
uint8_t*
Assembler::PatchableJumpAddress(JitCode* code, size_t index)
{
    // The assembler stashed the offset into the code of the fragments used
    // for far jumps at the start of the relocation table.
    uint32_t jumpOffset = * (uint32_t*) code->jumpRelocTable();
    jumpOffset += index * SizeOfJumpTableEntry;

    MOZ_ASSERT(jumpOffset + SizeOfExtendedJump <= code->instructionsSize());
    return code->raw() + jumpOffset;
}

/* static */
void
Assembler::PatchJumpEntry(uint8_t* entry, uint8_t* target, ReprotectCode reprotect)
{
    uint8_t** index = (uint8_t**) (entry + SizeOfExtendedJump - sizeof(void*));
    MaybeAutoWritableJitCode awjc(index, sizeof(void*), reprotect);
    *index = target;
}

void
Assembler::finish()
{
    if (!jumps_.length() || oom())
        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)
    {
        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()));
    }
}