Upstream version 9.38.198.0
[platform/framework/web/crosswalk.git] / src / v8 / src / x64 / assembler-x64-inl.h
index 35b6baf..b64bbfb 100644 (file)
@@ -1,49 +1,29 @@
 // Copyright 2012 the V8 project authors. All rights reserved.
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are
-// met:
-//
-//     * Redistributions of source code must retain the above copyright
-//       notice, this list of conditions and the following disclaimer.
-//     * Redistributions in binary form must reproduce the above
-//       copyright notice, this list of conditions and the following
-//       disclaimer in the documentation and/or other materials provided
-//       with the distribution.
-//     * Neither the name of Google Inc. nor the names of its
-//       contributors may be used to endorse or promote products derived
-//       from this software without specific prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
 
 #ifndef V8_X64_ASSEMBLER_X64_INL_H_
 #define V8_X64_ASSEMBLER_X64_INL_H_
 
-#include "x64/assembler-x64.h"
+#include "src/x64/assembler-x64.h"
 
-#include "cpu.h"
-#include "debug.h"
-#include "v8memory.h"
+#include "src/base/cpu.h"
+#include "src/debug.h"
+#include "src/v8memory.h"
 
 namespace v8 {
 namespace internal {
 
+bool CpuFeatures::SupportsCrankshaft() { return true; }
+
 
 // -----------------------------------------------------------------------------
 // Implementation of Assembler
 
 
 static const byte kCallOpcode = 0xE8;
-static const int kNoCodeAgeSequenceLength = 6;
+// The length of pushq(rbp), movp(rbp, rsp), Push(rsi) and Push(rdi).
+static const int kNoCodeAgeSequenceLength = kPointerSize == kInt64Size ? 6 : 17;
 
 
 void Assembler::emitl(uint32_t x) {
@@ -77,7 +57,7 @@ void Assembler::emitw(uint16_t x) {
 void Assembler::emit_code_target(Handle<Code> target,
                                  RelocInfo::Mode rmode,
                                  TypeFeedbackId ast_id) {
-  ASSERT(RelocInfo::IsCodeTarget(rmode) ||
+  DCHECK(RelocInfo::IsCodeTarget(rmode) ||
       rmode == RelocInfo::CODE_AGE_SEQUENCE);
   if (rmode == RelocInfo::CODE_TARGET && !ast_id.IsNone()) {
     RecordRelocInfo(RelocInfo::CODE_TARGET_WITH_ID, ast_id.ToInt());
@@ -96,8 +76,7 @@ void Assembler::emit_code_target(Handle<Code> target,
 
 
 void Assembler::emit_runtime_entry(Address entry, RelocInfo::Mode rmode) {
-  ASSERT(RelocInfo::IsRuntimeEntry(rmode));
-  ASSERT(isolate()->code_range()->exists());
+  DCHECK(RelocInfo::IsRuntimeEntry(rmode));
   RecordRelocInfo(rmode);
   emitl(static_cast<uint32_t>(entry - isolate()->code_range()->start()));
 }
@@ -129,7 +108,7 @@ void Assembler::emit_rex_64(XMMRegister reg, const Operand& op) {
 
 
 void Assembler::emit_rex_64(Register rm_reg) {
-  ASSERT_EQ(rm_reg.code() & 0xf, rm_reg.code());
+  DCHECK_EQ(rm_reg.code() & 0xf, rm_reg.code());
   emit(0x48 | rm_reg.high_bit());
 }
 
@@ -199,24 +178,26 @@ void Assembler::emit_optional_rex_32(Register rm_reg) {
   if (rm_reg.high_bit()) emit(0x41);
 }
 
-void Assembler::emit_optional_rex_32(XMMRegister reg) {
-  byte rex_bits =  (reg.code() & 0x8) >> 1;
-  if (rex_bits != 0) emit(0x40 | rex_bits);
-}
 
 void Assembler::emit_optional_rex_32(const Operand& op) {
   if (op.rex_ != 0) emit(0x40 | op.rex_);
 }
 
 
-Address Assembler::target_address_at(Address pc) {
+Address Assembler::target_address_at(Address pc,
+                                     ConstantPoolArray* constant_pool) {
   return Memory::int32_at(pc) + pc + 4;
 }
 
 
-void Assembler::set_target_address_at(Address pc, Address target) {
+void Assembler::set_target_address_at(Address pc,
+                                      ConstantPoolArray* constant_pool,
+                                      Address target,
+                                      ICacheFlushMode icache_flush_mode) {
   Memory::int32_at(pc) = static_cast<int32_t>(target - pc - 4);
-  CPU::FlushICache(pc, sizeof(int32_t));
+  if (icache_flush_mode != SKIP_ICACHE_FLUSH) {
+    CpuFeatures::FlushICache(pc, sizeof(int32_t));
+  }
 }
 
 
@@ -225,13 +206,17 @@ Address Assembler::target_address_from_return_address(Address pc) {
 }
 
 
+Address Assembler::break_address_from_return_address(Address pc) {
+  return pc - Assembler::kPatchDebugBreakSlotReturnOffset;
+}
+
+
 Handle<Object> Assembler::code_target_object_handle_at(Address pc) {
   return code_targets_[Memory::int32_at(pc)];
 }
 
 
 Address Assembler::runtime_entry_at(Address pc) {
-  ASSERT(isolate()->code_range()->exists());
   return Memory::int32_at(pc) + isolate()->code_range()->start();
 }
 
@@ -239,38 +224,45 @@ Address Assembler::runtime_entry_at(Address pc) {
 // Implementation of RelocInfo
 
 // The modes possibly affected by apply must be in kApplyMask.
-void RelocInfo::apply(intptr_t delta) {
+void RelocInfo::apply(intptr_t delta, ICacheFlushMode icache_flush_mode) {
+  bool flush_icache = icache_flush_mode != SKIP_ICACHE_FLUSH;
   if (IsInternalReference(rmode_)) {
     // absolute code pointer inside code object moves with the code object.
     Memory::Address_at(pc_) += static_cast<int32_t>(delta);
-    CPU::FlushICache(pc_, sizeof(Address));
+    if (flush_icache) CpuFeatures::FlushICache(pc_, sizeof(Address));
   } else if (IsCodeTarget(rmode_) || IsRuntimeEntry(rmode_)) {
     Memory::int32_at(pc_) -= static_cast<int32_t>(delta);
-    CPU::FlushICache(pc_, sizeof(int32_t));
+    if (flush_icache) CpuFeatures::FlushICache(pc_, sizeof(int32_t));
   } else if (rmode_ == CODE_AGE_SEQUENCE) {
     if (*pc_ == kCallOpcode) {
       int32_t* p = reinterpret_cast<int32_t*>(pc_ + 1);
       *p -= static_cast<int32_t>(delta);  // Relocate entry.
-      CPU::FlushICache(p, sizeof(uint32_t));
+      if (flush_icache) CpuFeatures::FlushICache(p, sizeof(uint32_t));
     }
   }
 }
 
 
 Address RelocInfo::target_address() {
-  ASSERT(IsCodeTarget(rmode_) || IsRuntimeEntry(rmode_));
-  return Assembler::target_address_at(pc_);
+  DCHECK(IsCodeTarget(rmode_) || IsRuntimeEntry(rmode_));
+  return Assembler::target_address_at(pc_, host_);
 }
 
 
 Address RelocInfo::target_address_address() {
-  ASSERT(IsCodeTarget(rmode_) || IsRuntimeEntry(rmode_)
+  DCHECK(IsCodeTarget(rmode_) || IsRuntimeEntry(rmode_)
                               || rmode_ == EMBEDDED_OBJECT
                               || rmode_ == EXTERNAL_REFERENCE);
   return reinterpret_cast<Address>(pc_);
 }
 
 
+Address RelocInfo::constant_pool_entry_address() {
+  UNREACHABLE();
+  return NULL;
+}
+
+
 int RelocInfo::target_address_size() {
   if (IsCodedSpecially()) {
     return Assembler::kSpecialTargetSize;
@@ -280,10 +272,13 @@ int RelocInfo::target_address_size() {
 }
 
 
-void RelocInfo::set_target_address(Address target, WriteBarrierMode mode) {
-  ASSERT(IsCodeTarget(rmode_) || IsRuntimeEntry(rmode_));
-  Assembler::set_target_address_at(pc_, target);
-  if (mode == UPDATE_WRITE_BARRIER && host() != NULL && IsCodeTarget(rmode_)) {
+void RelocInfo::set_target_address(Address target,
+                                   WriteBarrierMode write_barrier_mode,
+                                   ICacheFlushMode icache_flush_mode) {
+  DCHECK(IsCodeTarget(rmode_) || IsRuntimeEntry(rmode_));
+  Assembler::set_target_address_at(pc_, host_, target, icache_flush_mode);
+  if (write_barrier_mode == UPDATE_WRITE_BARRIER && host() != NULL &&
+      IsCodeTarget(rmode_)) {
     Object* target_code = Code::GetCodeFromTargetAddress(target);
     host()->GetHeap()->incremental_marking()->RecordWriteIntoCode(
         host(), this, HeapObject::cast(target_code));
@@ -292,13 +287,13 @@ void RelocInfo::set_target_address(Address target, WriteBarrierMode mode) {
 
 
 Object* RelocInfo::target_object() {
-  ASSERT(IsCodeTarget(rmode_) || rmode_ == EMBEDDED_OBJECT);
+  DCHECK(IsCodeTarget(rmode_) || rmode_ == EMBEDDED_OBJECT);
   return Memory::Object_at(pc_);
 }
 
 
 Handle<Object> RelocInfo::target_object_handle(Assembler* origin) {
-  ASSERT(IsCodeTarget(rmode_) || rmode_ == EMBEDDED_OBJECT);
+  DCHECK(IsCodeTarget(rmode_) || rmode_ == EMBEDDED_OBJECT);
   if (rmode_ == EMBEDDED_OBJECT) {
     return Memory::Object_Handle_at(pc_);
   } else {
@@ -308,17 +303,20 @@ Handle<Object> RelocInfo::target_object_handle(Assembler* origin) {
 
 
 Address RelocInfo::target_reference() {
-  ASSERT(rmode_ == RelocInfo::EXTERNAL_REFERENCE);
+  DCHECK(rmode_ == RelocInfo::EXTERNAL_REFERENCE);
   return Memory::Address_at(pc_);
 }
 
 
-void RelocInfo::set_target_object(Object* target, WriteBarrierMode mode) {
-  ASSERT(IsCodeTarget(rmode_) || rmode_ == EMBEDDED_OBJECT);
-  ASSERT(!target->IsConsString());
+void RelocInfo::set_target_object(Object* target,
+                                  WriteBarrierMode write_barrier_mode,
+                                  ICacheFlushMode icache_flush_mode) {
+  DCHECK(IsCodeTarget(rmode_) || rmode_ == EMBEDDED_OBJECT);
   Memory::Object_at(pc_) = target;
-  CPU::FlushICache(pc_, sizeof(Address));
-  if (mode == UPDATE_WRITE_BARRIER &&
+  if (icache_flush_mode != SKIP_ICACHE_FLUSH) {
+    CpuFeatures::FlushICache(pc_, sizeof(Address));
+  }
+  if (write_barrier_mode == UPDATE_WRITE_BARRIER &&
       host() != NULL &&
       target->IsHeapObject()) {
     host()->GetHeap()->incremental_marking()->RecordWrite(
@@ -328,37 +326,44 @@ void RelocInfo::set_target_object(Object* target, WriteBarrierMode mode) {
 
 
 Address RelocInfo::target_runtime_entry(Assembler* origin) {
-  ASSERT(IsRuntimeEntry(rmode_));
+  DCHECK(IsRuntimeEntry(rmode_));
   return origin->runtime_entry_at(pc_);
 }
 
 
 void RelocInfo::set_target_runtime_entry(Address target,
-                                         WriteBarrierMode mode) {
-  ASSERT(IsRuntimeEntry(rmode_));
-  if (target_address() != target) set_target_address(target, mode);
+                                         WriteBarrierMode write_barrier_mode,
+                                         ICacheFlushMode icache_flush_mode) {
+  DCHECK(IsRuntimeEntry(rmode_));
+  if (target_address() != target) {
+    set_target_address(target, write_barrier_mode, icache_flush_mode);
+  }
 }
 
 
 Handle<Cell> RelocInfo::target_cell_handle() {
-  ASSERT(rmode_ == RelocInfo::CELL);
+  DCHECK(rmode_ == RelocInfo::CELL);
   Address address = Memory::Address_at(pc_);
   return Handle<Cell>(reinterpret_cast<Cell**>(address));
 }
 
 
 Cell* RelocInfo::target_cell() {
-  ASSERT(rmode_ == RelocInfo::CELL);
+  DCHECK(rmode_ == RelocInfo::CELL);
   return Cell::FromValueAddress(Memory::Address_at(pc_));
 }
 
 
-void RelocInfo::set_target_cell(Cell* cell, WriteBarrierMode mode) {
-  ASSERT(rmode_ == RelocInfo::CELL);
+void RelocInfo::set_target_cell(Cell* cell,
+                                WriteBarrierMode write_barrier_mode,
+                                ICacheFlushMode icache_flush_mode) {
+  DCHECK(rmode_ == RelocInfo::CELL);
   Address address = cell->address() + Cell::kValueOffset;
   Memory::Address_at(pc_) = address;
-  CPU::FlushICache(pc_, sizeof(Address));
-  if (mode == UPDATE_WRITE_BARRIER &&
+  if (icache_flush_mode != SKIP_ICACHE_FLUSH) {
+    CpuFeatures::FlushICache(pc_, sizeof(Address));
+  }
+  if (write_barrier_mode == UPDATE_WRITE_BARRIER &&
       host() != NULL) {
     // TODO(1550) We are passing NULL as a slot because cell can never be on
     // evacuation candidate.
@@ -373,7 +378,7 @@ void RelocInfo::WipeOut() {
     Memory::Address_at(pc_) = NULL;
   } else if (IsCodeTarget(rmode_) || IsRuntimeEntry(rmode_)) {
     // Effectively write zero into the relocation.
-    Assembler::set_target_address_at(pc_, pc_ + sizeof(int32_t));
+    Assembler::set_target_address_at(pc_, host_, pc_ + sizeof(int32_t));
   } else {
     UNREACHABLE();
   }
@@ -387,12 +392,8 @@ bool RelocInfo::IsPatchedReturnSequence() {
   //  movq(rsp, rbp); pop(rbp); ret(n); int3 *6
   // The 11th byte is int3 (0xCC) in the return sequence and
   // REX.WB (0x48+register bit) for the call sequence.
-#ifdef ENABLE_DEBUGGER_SUPPORT
   return pc_[Assembler::kMoveAddressIntoScratchRegisterInstructionLength] !=
          0xCC;
-#else
-  return false;
-#endif
 }
 
 
@@ -402,29 +403,31 @@ bool RelocInfo::IsPatchedDebugBreakSlotSequence() {
 
 
 Handle<Object> RelocInfo::code_age_stub_handle(Assembler* origin) {
-  ASSERT(rmode_ == RelocInfo::CODE_AGE_SEQUENCE);
-  ASSERT(*pc_ == kCallOpcode);
+  DCHECK(rmode_ == RelocInfo::CODE_AGE_SEQUENCE);
+  DCHECK(*pc_ == kCallOpcode);
   return origin->code_target_object_handle_at(pc_ + 1);
 }
 
 
 Code* RelocInfo::code_age_stub() {
-  ASSERT(rmode_ == RelocInfo::CODE_AGE_SEQUENCE);
-  ASSERT(*pc_ == kCallOpcode);
+  DCHECK(rmode_ == RelocInfo::CODE_AGE_SEQUENCE);
+  DCHECK(*pc_ == kCallOpcode);
   return Code::GetCodeFromTargetAddress(
-      Assembler::target_address_at(pc_ + 1));
+      Assembler::target_address_at(pc_ + 1, host_));
 }
 
 
-void RelocInfo::set_code_age_stub(Code* stub) {
-  ASSERT(*pc_ == kCallOpcode);
-  ASSERT(rmode_ == RelocInfo::CODE_AGE_SEQUENCE);
-  Assembler::set_target_address_at(pc_ + 1, stub->instruction_start());
+void RelocInfo::set_code_age_stub(Code* stub,
+                                  ICacheFlushMode icache_flush_mode) {
+  DCHECK(*pc_ == kCallOpcode);
+  DCHECK(rmode_ == RelocInfo::CODE_AGE_SEQUENCE);
+  Assembler::set_target_address_at(pc_ + 1, host_, stub->instruction_start(),
+                                   icache_flush_mode);
 }
 
 
 Address RelocInfo::call_address() {
-  ASSERT((IsJSReturn(rmode()) && IsPatchedReturnSequence()) ||
+  DCHECK((IsJSReturn(rmode()) && IsPatchedReturnSequence()) ||
          (IsDebugBreakSlot(rmode()) && IsPatchedDebugBreakSlotSequence()));
   return Memory::Address_at(
       pc_ + Assembler::kRealPatchReturnSequenceAddressOffset);
@@ -432,12 +435,12 @@ Address RelocInfo::call_address() {
 
 
 void RelocInfo::set_call_address(Address target) {
-  ASSERT((IsJSReturn(rmode()) && IsPatchedReturnSequence()) ||
+  DCHECK((IsJSReturn(rmode()) && IsPatchedReturnSequence()) ||
          (IsDebugBreakSlot(rmode()) && IsPatchedDebugBreakSlotSequence()));
   Memory::Address_at(pc_ + Assembler::kRealPatchReturnSequenceAddressOffset) =
       target;
-  CPU::FlushICache(pc_ + Assembler::kRealPatchReturnSequenceAddressOffset,
-                   sizeof(Address));
+  CpuFeatures::FlushICache(
+      pc_ + Assembler::kRealPatchReturnSequenceAddressOffset, sizeof(Address));
   if (host() != NULL) {
     Object* target_code = Code::GetCodeFromTargetAddress(target);
     host()->GetHeap()->incremental_marking()->RecordWriteIntoCode(
@@ -457,7 +460,7 @@ void RelocInfo::set_call_object(Object* target) {
 
 
 Object** RelocInfo::call_object_address() {
-  ASSERT((IsJSReturn(rmode()) && IsPatchedReturnSequence()) ||
+  DCHECK((IsJSReturn(rmode()) && IsPatchedReturnSequence()) ||
          (IsDebugBreakSlot(rmode()) && IsPatchedDebugBreakSlotSequence()));
   return reinterpret_cast<Object**>(
       pc_ + Assembler::kPatchReturnSequenceAddressOffset);
@@ -468,24 +471,22 @@ void RelocInfo::Visit(Isolate* isolate, ObjectVisitor* visitor) {
   RelocInfo::Mode mode = rmode();
   if (mode == RelocInfo::EMBEDDED_OBJECT) {
     visitor->VisitEmbeddedPointer(this);
-    CPU::FlushICache(pc_, sizeof(Address));
+    CpuFeatures::FlushICache(pc_, sizeof(Address));
   } else if (RelocInfo::IsCodeTarget(mode)) {
     visitor->VisitCodeTarget(this);
   } else if (mode == RelocInfo::CELL) {
     visitor->VisitCell(this);
   } else if (mode == RelocInfo::EXTERNAL_REFERENCE) {
     visitor->VisitExternalReference(this);
-    CPU::FlushICache(pc_, sizeof(Address));
+    CpuFeatures::FlushICache(pc_, sizeof(Address));
   } else if (RelocInfo::IsCodeAgeSequence(mode)) {
     visitor->VisitCodeAgeSequence(this);
-#ifdef ENABLE_DEBUGGER_SUPPORT
   } else if (((RelocInfo::IsJSReturn(mode) &&
               IsPatchedReturnSequence()) ||
              (RelocInfo::IsDebugBreakSlot(mode) &&
               IsPatchedDebugBreakSlotSequence())) &&
              isolate->debug()->has_break_points()) {
     visitor->VisitDebugTarget(this);
-#endif
   } else if (RelocInfo::IsRuntimeEntry(mode)) {
     visitor->VisitRuntimeEntry(this);
   }
@@ -497,24 +498,22 @@ void RelocInfo::Visit(Heap* heap) {
   RelocInfo::Mode mode = rmode();
   if (mode == RelocInfo::EMBEDDED_OBJECT) {
     StaticVisitor::VisitEmbeddedPointer(heap, this);
-    CPU::FlushICache(pc_, sizeof(Address));
+    CpuFeatures::FlushICache(pc_, sizeof(Address));
   } else if (RelocInfo::IsCodeTarget(mode)) {
     StaticVisitor::VisitCodeTarget(heap, this);
   } else if (mode == RelocInfo::CELL) {
     StaticVisitor::VisitCell(heap, this);
   } else if (mode == RelocInfo::EXTERNAL_REFERENCE) {
     StaticVisitor::VisitExternalReference(this);
-    CPU::FlushICache(pc_, sizeof(Address));
+    CpuFeatures::FlushICache(pc_, sizeof(Address));
   } else if (RelocInfo::IsCodeAgeSequence(mode)) {
     StaticVisitor::VisitCodeAgeSequence(heap, this);
-#ifdef ENABLE_DEBUGGER_SUPPORT
   } else if (heap->isolate()->debug()->has_break_points() &&
              ((RelocInfo::IsJSReturn(mode) &&
               IsPatchedReturnSequence()) ||
              (RelocInfo::IsDebugBreakSlot(mode) &&
               IsPatchedDebugBreakSlotSequence()))) {
     StaticVisitor::VisitDebugTarget(heap, this);
-#endif
   } else if (RelocInfo::IsRuntimeEntry(mode)) {
     StaticVisitor::VisitRuntimeEntry(this);
   }
@@ -525,7 +524,7 @@ void RelocInfo::Visit(Heap* heap) {
 // Implementation of Operand
 
 void Operand::set_modrm(int mod, Register rm_reg) {
-  ASSERT(is_uint2(mod));
+  DCHECK(is_uint2(mod));
   buf_[0] = mod << 6 | rm_reg.low_bits();
   // Set REX.B to the high bit of rm.code().
   rex_ |= rm_reg.high_bit();
@@ -533,26 +532,26 @@ void Operand::set_modrm(int mod, Register rm_reg) {
 
 
 void Operand::set_sib(ScaleFactor scale, Register index, Register base) {
-  ASSERT(len_ == 1);
-  ASSERT(is_uint2(scale));
+  DCHECK(len_ == 1);
+  DCHECK(is_uint2(scale));
   // Use SIB with no index register only for base rsp or r12. Otherwise we
   // would skip the SIB byte entirely.
-  ASSERT(!index.is(rsp) || base.is(rsp) || base.is(r12));
+  DCHECK(!index.is(rsp) || base.is(rsp) || base.is(r12));
   buf_[1] = (scale << 6) | (index.low_bits() << 3) | base.low_bits();
   rex_ |= index.high_bit() << 1 | base.high_bit();
   len_ = 2;
 }
 
 void Operand::set_disp8(int disp) {
-  ASSERT(is_int8(disp));
-  ASSERT(len_ == 1 || len_ == 2);
+  DCHECK(is_int8(disp));
+  DCHECK(len_ == 1 || len_ == 2);
   int8_t* p = reinterpret_cast<int8_t*>(&buf_[len_]);
   *p = disp;
   len_ += sizeof(int8_t);
 }
 
 void Operand::set_disp32(int disp) {
-  ASSERT(len_ == 1 || len_ == 2);
+  DCHECK(len_ == 1 || len_ == 2);
   int32_t* p = reinterpret_cast<int32_t*>(&buf_[len_]);
   *p = disp;
   len_ += sizeof(int32_t);