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* Copyright (C) 2011 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <vector>
#include <android-base/logging.h>
#include "arch/instruction_set.h"
#include "arch/instruction_set_features.h"
#include "arm/constants_arm.h"
#include "base/arena_allocator.h"
#include "base/arena_object.h"
#include "base/array_ref.h"
#include "base/enums.h"
#include "base/macros.h"
#include "base/memory_region.h"
#include "dwarf/debug_frame_opcode_writer.h"
#include "label.h"
#include "managed_register.h"
#include "offsets.h"
#include "x86/constants_x86.h"
#include "x86_64/constants_x86_64.h"
namespace art {
class Assembler;
class AssemblerBuffer;
// Assembler fixups are positions in generated code that require processing
// after the code has been copied to executable memory. This includes building
// relocation information.
class AssemblerFixup {
virtual void Process(const MemoryRegion& region, int position) = 0;
virtual ~AssemblerFixup() {}
AssemblerFixup* previous_;
int position_;
AssemblerFixup* previous() const { return previous_; }
void set_previous(AssemblerFixup* previous_in) { previous_ = previous_in; }
int position() const { return position_; }
void set_position(int position_in) { position_ = position_in; }
friend class AssemblerBuffer;
// Parent of all queued slow paths, emitted during finalization
class SlowPath : public DeletableArenaObject<kArenaAllocAssembler> {
SlowPath() : next_(nullptr) {}
virtual ~SlowPath() {}
Label* Continuation() { return &continuation_; }
Label* Entry() { return &entry_; }
// Generate code for slow path
virtual void Emit(Assembler *sp_asm) = 0;
// Entry branched to by fast path
Label entry_;
// Optional continuation that is branched to at the end of the slow path
Label continuation_;
// Next in linked list of slow paths
SlowPath *next_;
friend class AssemblerBuffer;
class AssemblerBuffer {
explicit AssemblerBuffer(ArenaAllocator* allocator);
ArenaAllocator* GetAllocator() {
return allocator_;
// Basic support for emitting, loading, and storing.
template<typename T> void Emit(T value) {
*reinterpret_cast<T*>(cursor_) = value;
cursor_ += sizeof(T);
template<typename T> T Load(size_t position) {
CHECK_LE(position, Size() - static_cast<int>(sizeof(T)));
return *reinterpret_cast<T*>(contents_ + position);
template<typename T> void Store(size_t position, T value) {
CHECK_LE(position, Size() - static_cast<int>(sizeof(T)));
*reinterpret_cast<T*>(contents_ + position) = value;
void Resize(size_t new_size) {
if (new_size > Capacity()) {
cursor_ = contents_ + new_size;
void Move(size_t newposition, size_t oldposition, size_t size) {
// Move a chunk of the buffer from oldposition to newposition.
DCHECK_LE(oldposition + size, Size());
DCHECK_LE(newposition + size, Size());
memmove(contents_ + newposition, contents_ + oldposition, size);
// Emit a fixup at the current location.
void EmitFixup(AssemblerFixup* fixup) {
fixup_ = fixup;
void EnqueueSlowPath(SlowPath* slowpath) {
if (slow_path_ == nullptr) {
slow_path_ = slowpath;
} else {
SlowPath* cur = slow_path_;
for ( ; cur->next_ != nullptr ; cur = cur->next_) {}
cur->next_ = slowpath;
void EmitSlowPaths(Assembler* sp_asm) {
SlowPath* cur = slow_path_;
SlowPath* next = nullptr;
slow_path_ = nullptr;
for ( ; cur != nullptr ; cur = next) {
next = cur->next_;
delete cur;
// Get the size of the emitted code.
size_t Size() const {
CHECK_GE(cursor_, contents_);
return cursor_ - contents_;
uint8_t* contents() const { return contents_; }
// Copy the assembled instructions into the specified memory block
// and apply all fixups.
void FinalizeInstructions(const MemoryRegion& region);
// To emit an instruction to the assembler buffer, the EnsureCapacity helper
// must be used to guarantee that the underlying data area is big enough to
// hold the emitted instruction. Usage:
// AssemblerBuffer buffer;
// AssemblerBuffer::EnsureCapacity ensured(&buffer);
// ... emit bytes for single instruction ...
#ifndef NDEBUG
class EnsureCapacity {
explicit EnsureCapacity(AssemblerBuffer* buffer) {
if (buffer->cursor() > buffer->limit()) {
buffer->ExtendCapacity(buffer->Size() + kMinimumGap);
// In debug mode, we save the assembler buffer along with the gap
// size before we start emitting to the buffer. This allows us to
// check that any single generated instruction doesn't overflow the
// limit implied by the minimum gap size.
buffer_ = buffer;
gap_ = ComputeGap();
// Make sure that extending the capacity leaves a big enough gap
// for any kind of instruction.
CHECK_GE(gap_, kMinimumGap);
// Mark the buffer as having ensured the capacity.
CHECK(!buffer->HasEnsuredCapacity()); // Cannot nest.
buffer->has_ensured_capacity_ = true;
~EnsureCapacity() {
// Unmark the buffer, so we cannot emit after this.
buffer_->has_ensured_capacity_ = false;
// Make sure the generated instruction doesn't take up more
// space than the minimum gap.
int delta = gap_ - ComputeGap();
CHECK_LE(delta, kMinimumGap);
AssemblerBuffer* buffer_;
int gap_;
int ComputeGap() { return buffer_->Capacity() - buffer_->Size(); }
bool has_ensured_capacity_;
bool HasEnsuredCapacity() const { return has_ensured_capacity_; }
class EnsureCapacity {
explicit EnsureCapacity(AssemblerBuffer* buffer) {
if (buffer->cursor() > buffer->limit()) {
buffer->ExtendCapacity(buffer->Size() + kMinimumGap);
// When building the C++ tests, assertion code is enabled. To allow
// asserting that the user of the assembler buffer has ensured the
// capacity needed for emitting, we add a dummy method in non-debug mode.
bool HasEnsuredCapacity() const { return true; }
// Returns the position in the instruction stream.
int GetPosition() { return cursor_ - contents_; }
size_t Capacity() const {
CHECK_GE(limit_, contents_);
return (limit_ - contents_) + kMinimumGap;
// Unconditionally increase the capacity.
// The provided `min_capacity` must be higher than current `Capacity()`.
void ExtendCapacity(size_t min_capacity);
// The limit is set to kMinimumGap bytes before the end of the data area.
// This leaves enough space for the longest possible instruction and allows
// for a single, fast space check per instruction.
static const int kMinimumGap = 32;
ArenaAllocator* const allocator_;
uint8_t* contents_;
uint8_t* cursor_;
uint8_t* limit_;
AssemblerFixup* fixup_;
#ifndef NDEBUG
bool fixups_processed_;
// Head of linked list of slow paths
SlowPath* slow_path_;
uint8_t* cursor() const { return cursor_; }
uint8_t* limit() const { return limit_; }
// Process the fixup chain starting at the given fixup. The offset is
// non-zero for fixups in the body if the preamble is non-empty.
void ProcessFixups(const MemoryRegion& region);
// Compute the limit based on the data area and the capacity. See
// description of kMinimumGap for the reasoning behind the value.
static uint8_t* ComputeLimit(uint8_t* data, size_t capacity) {
return data + capacity - kMinimumGap;
friend class AssemblerFixup;
// The purpose of this class is to ensure that we do not have to explicitly
// call the AdvancePC method (which is good for convenience and correctness).
class DebugFrameOpCodeWriterForAssembler final
: public dwarf::DebugFrameOpCodeWriter<> {
struct DelayedAdvancePC {
uint32_t stream_pos;
uint32_t pc;
// This method is called the by the opcode writers.
void ImplicitlyAdvancePC() final;
explicit DebugFrameOpCodeWriterForAssembler(Assembler* buffer)
: dwarf::DebugFrameOpCodeWriter<>(/* enabled= */ false),
delayed_advance_pcs_() {
~DebugFrameOpCodeWriterForAssembler() {
// Tell the writer to delay emitting advance PC info.
// The assembler must explicitly process all the delayed advances.
void DelayEmittingAdvancePCs() {
delay_emitting_advance_pc_ = true;
// Override the last delayed PC. The new PC can be out of order.
void OverrideDelayedPC(size_t pc) {
if (enabled_) {
delayed_advance_pcs_.back().pc = pc;
// Return the number of delayed advance PC entries.
size_t NumberOfDelayedAdvancePCs() const {
return delayed_advance_pcs_.size();
// Release the CFI stream and advance PC infos so that the assembler can patch it.
std::pair<std::vector<uint8_t>, std::vector<DelayedAdvancePC>>
ReleaseStreamAndPrepareForDelayedAdvancePC() {
delay_emitting_advance_pc_ = false;
std::pair<std::vector<uint8_t>, std::vector<DelayedAdvancePC>> result;
return result;
// Reserve space for the CFI stream.
void ReserveCFIStream(size_t capacity) {
// Append raw data to the CFI stream.
void AppendRawData(const std::vector<uint8_t>& raw_data, size_t first, size_t last) {
DCHECK_LE(0u, first);
DCHECK_LE(first, last);
DCHECK_LE(last, raw_data.size());
opcodes_.insert(opcodes_.end(), raw_data.begin() + first, raw_data.begin() + last);
Assembler* assembler_;
bool delay_emitting_advance_pc_;
std::vector<DelayedAdvancePC> delayed_advance_pcs_;
class Assembler : public DeletableArenaObject<kArenaAllocAssembler> {
// Finalize the code; emit slow paths, fixup branches, add literal pool, etc.
virtual void FinalizeCode() { buffer_.EmitSlowPaths(this); }
// Size of generated code
virtual size_t CodeSize() const { return buffer_.Size(); }
virtual const uint8_t* CodeBufferBaseAddress() const { return buffer_.contents(); }
// CodePosition() is a non-const method similar to CodeSize(), which is used to
// record positions within the code buffer for the purpose of signal handling
// (stack overflow checks and implicit null checks may trigger signals and the
// signal handlers expect them right before the recorded positions).
// On most architectures CodePosition() should be equivalent to CodeSize(), but
// the MIPS assembler needs to be aware of this recording, so it doesn't put
// the instructions that can trigger signals into branch delay slots. Handling
// signals from instructions in delay slots is a bit problematic and should be
// avoided.
virtual size_t CodePosition() { return CodeSize(); }
// Copy instructions out of assembly buffer into the given region of memory
virtual void FinalizeInstructions(const MemoryRegion& region) {
// TODO: Implement with disassembler.
virtual void Comment(const char* format ATTRIBUTE_UNUSED, ...) {}
virtual void Bind(Label* label) = 0;
virtual void Jump(Label* label) = 0;
virtual ~Assembler() {}
* @brief Buffer of DWARF's Call Frame Information opcodes.
* @details It is used by debuggers and other tools to unwind the call stack.
DebugFrameOpCodeWriterForAssembler& cfi() { return cfi_; }
ArenaAllocator* GetAllocator() {
return buffer_.GetAllocator();
AssemblerBuffer* GetBuffer() {
return &buffer_;
explicit Assembler(ArenaAllocator* allocator) : buffer_(allocator), cfi_(this) {}
AssemblerBuffer buffer_;
DebugFrameOpCodeWriterForAssembler cfi_;
} // namespace art