jump-table-assembler.cc

// Copyright 2018 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.

#include "src/wasm/jump-table-assembler.h"

#include "src/assembler-inl.h"
#include "src/macro-assembler-inl.h"

namespace v8 {
namespace internal {
namespace wasm {

// The implementation is compact enough to implement it inline here. If it gets
// much bigger, we might want to split it in a separate file per architecture.
#if V8_TARGET_ARCH_X64
void JumpTableAssembler::EmitLazyCompileJumpSlot(uint32_t func_index,
                                                 Address lazy_compile_target) {
  // TODO(clemensh): Try more efficient sequences.
  // Alternative 1:
  // [header]:  mov r10, [lazy_compile_target]
  //            jmp r10
  // [slot 0]:  push [0]
  //            jmp [header]  // pc-relative --> slot size: 10 bytes
  //
  // Alternative 2:
  // [header]:  lea r10, [rip - [header]]
  //            shr r10, 3  // compute index from offset
  //            push r10
  //            mov r10, [lazy_compile_target]
  //            jmp r10
  // [slot 0]:  call [header]
  //            ret   // -> slot size: 5 bytes

  // Use a push, because mov to an extended register takes 6 bytes.
  pushq(Immediate(func_index));                           // max 5 bytes
  movq(kScratchRegister, uint64_t{lazy_compile_target});  // max 10 bytes
  jmp(kScratchRegister);                                  // 3 bytes

  PatchConstPool();  // force patching entries for partial const pool
}

void JumpTableAssembler::EmitJumpSlot(Address target) {
  movq(kScratchRegister, static_cast<uint64_t>(target));
  jmp(kScratchRegister);
}

void JumpTableAssembler::NopBytes(int bytes) {
  DCHECK_LE(0, bytes);
  Nop(bytes);
}

#elif V8_TARGET_ARCH_IA32
void JumpTableAssembler::EmitLazyCompileJumpSlot(uint32_t func_index,
                                                 Address lazy_compile_target) {
  mov(kWasmCompileLazyFuncIndexRegister, func_index);  // 5 bytes
  jmp(lazy_compile_target, RelocInfo::NONE);  // 5 bytes
}

void JumpTableAssembler::EmitJumpSlot(Address target) {
  jmp(target, RelocInfo::NONE);
}

void JumpTableAssembler::NopBytes(int bytes) {
  DCHECK_LE(0, bytes);
  Nop(bytes);
}

#elif V8_TARGET_ARCH_ARM
void JumpTableAssembler::EmitLazyCompileJumpSlot(uint32_t func_index,
                                                 Address lazy_compile_target) {
  // Load function index to a register.
  // This generates [movw, movt] on ARMv7 and later, [ldr, constant pool marker,
  // constant] on ARMv6.
  Move32BitImmediate(kWasmCompileLazyFuncIndexRegister, Operand(func_index));
  // EmitJumpSlot emits either [b], [movw, movt, mov] (ARMv7+), or [ldr,
  // constant].
  // In total, this is <=5 instructions on all architectures.
  // TODO(arm): Optimize this for code size; lazy compile is not performance
  // critical, as it's only executed once per function.
  EmitJumpSlot(lazy_compile_target);
}

void JumpTableAssembler::EmitJumpSlot(Address target) {
  // Note that {Move32BitImmediate} emits [ldr, constant] for the relocation
  // mode used below, we need this to allow concurrent patching of this slot.
  Move32BitImmediate(pc, Operand(target, RelocInfo::WASM_CALL));
  CheckConstPool(true, false);  // force emit of const pool
}

void JumpTableAssembler::NopBytes(int bytes) {
  DCHECK_LE(0, bytes);
  DCHECK_EQ(0, bytes % kInstrSize);
  for (; bytes > 0; bytes -= kInstrSize) {
    nop();
  }
}

#elif V8_TARGET_ARCH_ARM64
void JumpTableAssembler::EmitLazyCompileJumpSlot(uint32_t func_index,
                                                 Address lazy_compile_target) {
  Mov(kWasmCompileLazyFuncIndexRegister.W(), func_index);  // max. 2 instr
  Jump(lazy_compile_target, RelocInfo::NONE);  // 1 instr
}

void JumpTableAssembler::EmitJumpSlot(Address target) {
  // TODO(wasm): Currently this is guaranteed to be a {near_call} and hence is
  // patchable concurrently. Once {kMaxWasmCodeMemory} is raised on ARM64, make
  // sure concurrent patching is still supported.
  Jump(target, RelocInfo::NONE);
}

void JumpTableAssembler::NopBytes(int bytes) {
  DCHECK_LE(0, bytes);
  DCHECK_EQ(0, bytes % kInstrSize);
  for (; bytes > 0; bytes -= kInstrSize) {
    nop();
  }
}

#elif V8_TARGET_ARCH_S390
void JumpTableAssembler::EmitLazyCompileJumpSlot(uint32_t func_index,
                                                 Address lazy_compile_target) {
  // Load function index to r7. 6 bytes
  lgfi(kWasmCompileLazyFuncIndexRegister, Operand(func_index));
  // Jump to {lazy_compile_target}. 6 bytes or 12 bytes
  mov(r1, Operand(lazy_compile_target));
  b(r1);  // 2 bytes
}

void JumpTableAssembler::EmitJumpSlot(Address target) {
  mov(r1, Operand(target));
  b(r1);
}

void JumpTableAssembler::NopBytes(int bytes) {
  DCHECK_LE(0, bytes);
  DCHECK_EQ(0, bytes % 2);
  for (; bytes > 0; bytes -= 2) {
    nop(0);
  }
}

#elif V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
void JumpTableAssembler::EmitLazyCompileJumpSlot(uint32_t func_index,
                                                 Address lazy_compile_target) {
  li(kWasmCompileLazyFuncIndexRegister, func_index);  // max. 2 instr
  // Jump produces max. 4 instructions for 32-bit platform
  // and max. 6 instructions for 64-bit platform.
  Jump(lazy_compile_target, RelocInfo::NONE);
}

void JumpTableAssembler::EmitJumpSlot(Address target) {
  Jump(target, RelocInfo::NONE);
}

void JumpTableAssembler::NopBytes(int bytes) {
  DCHECK_LE(0, bytes);
  DCHECK_EQ(0, bytes % kInstrSize);
  for (; bytes > 0; bytes -= kInstrSize) {
    nop();
  }
}

#elif V8_TARGET_ARCH_PPC
void JumpTableAssembler::EmitLazyCompileJumpSlot(uint32_t func_index,
                                                 Address lazy_compile_target) {
  // Load function index to register. max 5 instrs
  mov(kWasmCompileLazyFuncIndexRegister, Operand(func_index));
  // Jump to {lazy_compile_target}. max 5 instrs
  mov(r0, Operand(lazy_compile_target));
  mtctr(r0);
  bctr();
}

void JumpTableAssembler::EmitJumpSlot(Address target) {
  mov(r0, Operand(target));
  mtctr(r0);
  bctr();
}

void JumpTableAssembler::NopBytes(int bytes) {
  DCHECK_LE(0, bytes);
  DCHECK_EQ(0, bytes % 4);
  for (; bytes > 0; bytes -= 4) {
    nop(0);
  }
}

#else
void JumpTableAssembler::EmitLazyCompileJumpSlot(uint32_t func_index,
                                                 Address lazy_compile_target) {
  UNIMPLEMENTED();
}

void JumpTableAssembler::EmitJumpSlot(Address target) { UNIMPLEMENTED(); }

void JumpTableAssembler::NopBytes(int bytes) {
  DCHECK_LE(0, bytes);
  UNIMPLEMENTED();
}
#endif

}  // namespace wasm
}  // namespace internal
}  // namespace v8