src/arm64/code-stubs-arm64.cc

// Copyright 2013 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.

#if V8_TARGET_ARCH_ARM64

#include "src/api-arguments.h"
#include "src/arm64/assembler-arm64-inl.h"
#include "src/arm64/macro-assembler-arm64-inl.h"
#include "src/bootstrapper.h"
#include "src/code-stubs.h"
#include "src/counters.h"
#include "src/frame-constants.h"
#include "src/frames.h"
#include "src/heap/heap-inl.h"
#include "src/ic/ic.h"
#include "src/ic/stub-cache.h"
#include "src/isolate.h"
#include "src/objects/api-callbacks.h"
#include "src/objects/regexp-match-info.h"
#include "src/regexp/jsregexp.h"
#include "src/regexp/regexp-macro-assembler.h"
#include "src/runtime/runtime.h"

#include "src/arm64/code-stubs-arm64.h"  // Cannot be the first include.

namespace v8 {
namespace internal {

#define __ ACCESS_MASM(masm)

// This is the entry point from C++. 5 arguments are provided in x0-x4.
// See use of the JSEntryFunction for example in src/execution.cc.
// Input:
//   x0: code entry.
//   x1: function.
//   x2: receiver.
//   x3: argc.
//   x4: argv.
// Output:
//   x0: result.
void JSEntryStub::Generate(MacroAssembler* masm) {
  Label invoke, handler_entry, exit;

  Register code_entry = x0;

  {
    NoRootArrayScope no_root_array(masm);

    // Enable instruction instrumentation. This only works on the simulator, and
    // will have no effect on the model or real hardware.
    __ EnableInstrumentation();

    __ PushCalleeSavedRegisters();

    ProfileEntryHookStub::MaybeCallEntryHook(masm);

    // Set up the reserved register for 0.0.
    __ Fmov(fp_zero, 0.0);

    // Initialize the root array register
    __ InitializeRootRegister();
  }

  // Build an entry frame (see layout below).
  StackFrame::Type marker = type();
  int64_t bad_frame_pointer = -1L;  // Bad frame pointer to fail if it is used.
  __ Mov(x13, bad_frame_pointer);
  __ Mov(x12, StackFrame::TypeToMarker(marker));
  __ Mov(x11, ExternalReference::Create(IsolateAddressId::kCEntryFPAddress,
                                        isolate()));
  __ Ldr(x10, MemOperand(x11));

  __ Push(x13, x12, xzr, x10);
  // Set up fp.
  __ Sub(fp, sp, EntryFrameConstants::kCallerFPOffset);

  // Push the JS entry frame marker. Also set js_entry_sp if this is the
  // outermost JS call.
  Label non_outermost_js, done;
  ExternalReference js_entry_sp =
      ExternalReference::Create(IsolateAddressId::kJSEntrySPAddress, isolate());
  __ Mov(x10, js_entry_sp);
  __ Ldr(x11, MemOperand(x10));

  // Select between the inner and outermost frame marker, based on the JS entry
  // sp. We assert that the inner marker is zero, so we can use xzr to save a
  // move instruction.
  DCHECK_EQ(StackFrame::INNER_JSENTRY_FRAME, 0);
  __ Cmp(x11, 0);  // If x11 is zero, this is the outermost frame.
  __ Csel(x12, xzr, StackFrame::OUTERMOST_JSENTRY_FRAME, ne);
  __ B(ne, &done);
  __ Str(fp, MemOperand(x10));

  __ Bind(&done);
  __ Push(x12, padreg);

  // The frame set up looks like this:
  // sp[0] : padding.
  // sp[1] : JS entry frame marker.
  // sp[2] : C entry FP.
  // sp[3] : stack frame marker.
  // sp[4] : stack frame marker.
  // sp[5] : bad frame pointer 0xFFF...FF   <- fp points here.

  // Jump to a faked try block that does the invoke, with a faked catch
  // block that sets the pending exception.
  __ B(&invoke);

  // Prevent the constant pool from being emitted between the record of the
  // handler_entry position and the first instruction of the sequence here.
  // There is no risk because Assembler::Emit() emits the instruction before
  // checking for constant pool emission, but we do not want to depend on
  // that.
  {
    Assembler::BlockPoolsScope block_pools(masm);
    __ bind(&handler_entry);
    handler_offset_ = handler_entry.pos();
    // Caught exception: Store result (exception) in the pending exception
    // field in the JSEnv and return a failure sentinel. Coming in here the
    // fp will be invalid because the PushTryHandler below sets it to 0 to
    // signal the existence of the JSEntry frame.
    __ Mov(x10, Operand(ExternalReference::Create(
                    IsolateAddressId::kPendingExceptionAddress, isolate())));
  }
  __ Str(code_entry, MemOperand(x10));
  __ LoadRoot(x0, Heap::kExceptionRootIndex);
  __ B(&exit);

  // Invoke: Link this frame into the handler chain.
  __ Bind(&invoke);

  // Push new stack handler.
  static_assert(StackHandlerConstants::kSize == 2 * kPointerSize,
                "Unexpected offset for StackHandlerConstants::kSize");
  static_assert(StackHandlerConstants::kNextOffset == 0 * kPointerSize,
                "Unexpected offset for StackHandlerConstants::kNextOffset");

  // Link the current handler as the next handler.
  __ Mov(x11, ExternalReference::Create(IsolateAddressId::kHandlerAddress,
                                        isolate()));
  __ Ldr(x10, MemOperand(x11));
  __ Push(padreg, x10);

  // Set this new handler as the current one.
  {
    UseScratchRegisterScope temps(masm);
    Register scratch = temps.AcquireX();
    __ Mov(scratch, sp);
    __ Str(scratch, MemOperand(x11));
  }

  // If an exception not caught by another handler occurs, this handler
  // returns control to the code after the B(&invoke) above, which
  // restores all callee-saved registers (including cp and fp) to their
  // saved values before returning a failure to C.

  // Invoke the function by calling through the JS entry trampoline builtin.
  // Notice that we cannot store a reference to the trampoline code directly in
  // this stub, because runtime stubs are not traversed when doing GC.

  // Expected registers by Builtins::JSEntryTrampoline
  // x0: code entry.
  // x1: function.
  // x2: receiver.
  // x3: argc.
  // x4: argv.
  __ Call(EntryTrampoline(), RelocInfo::CODE_TARGET);

  // Pop the stack handler and unlink this frame from the handler chain.
  static_assert(StackHandlerConstants::kNextOffset == 0 * kPointerSize,
                "Unexpected offset for StackHandlerConstants::kNextOffset");
  __ Pop(x10, padreg);
  __ Mov(x11, ExternalReference::Create(IsolateAddressId::kHandlerAddress,
                                        isolate()));
  __ Drop(StackHandlerConstants::kSlotCount - 2);
  __ Str(x10, MemOperand(x11));

  __ Bind(&exit);
  // x0 holds the result.
  // The stack pointer points to the top of the entry frame pushed on entry from
  // C++ (at the beginning of this stub):
  // sp[0] : padding.
  // sp[1] : JS entry frame marker.
  // sp[2] : C entry FP.
  // sp[3] : stack frame marker.
  // sp[4] : stack frame marker.
  // sp[5] : bad frame pointer 0xFFF...FF   <- fp points here.

  // Check if the current stack frame is marked as the outermost JS frame.
  Label non_outermost_js_2;
  {
    Register c_entry_fp = x11;
    __ PeekPair(x10, c_entry_fp, 1 * kPointerSize);
    __ Cmp(x10, StackFrame::OUTERMOST_JSENTRY_FRAME);
    __ B(ne, &non_outermost_js_2);
    __ Mov(x12, js_entry_sp);
    __ Str(xzr, MemOperand(x12));
    __ Bind(&non_outermost_js_2);

    // Restore the top frame descriptors from the stack.
    __ Mov(x12, ExternalReference::Create(IsolateAddressId::kCEntryFPAddress,
                                          isolate()));
    __ Str(c_entry_fp, MemOperand(x12));
  }

  // Reset the stack to the callee saved registers.
  static_assert(EntryFrameConstants::kFixedFrameSize % (2 * kPointerSize) == 0,
                "Size of entry frame is not a multiple of 16 bytes");
  __ Drop(EntryFrameConstants::kFixedFrameSize / kPointerSize);
  // Restore the callee-saved registers and return.
  __ PopCalleeSavedRegisters();
  __ Ret();
}

// The entry hook is a Push (stp) instruction, followed by a near call.
static const unsigned int kProfileEntryHookCallSize =
    (1 * kInstrSize) + Assembler::kNearCallSize;

void ProfileEntryHookStub::MaybeCallEntryHookDelayed(TurboAssembler* tasm,
                                                     Zone* zone) {
  if (tasm->isolate()->function_entry_hook() != nullptr) {
    Assembler::BlockConstPoolScope no_const_pools(tasm);
    DontEmitDebugCodeScope no_debug_code(tasm);
    Label entry_hook_call_start;
    tasm->Bind(&entry_hook_call_start);
    tasm->Push(padreg, lr);
    tasm->CallStubDelayed(new (zone) ProfileEntryHookStub(nullptr));
    DCHECK_EQ(tasm->SizeOfCodeGeneratedSince(&entry_hook_call_start),
              kProfileEntryHookCallSize);
    tasm->Pop(lr, padreg);
  }
}

void ProfileEntryHookStub::MaybeCallEntryHook(MacroAssembler* masm) {
  if (masm->isolate()->function_entry_hook() != nullptr) {
    ProfileEntryHookStub stub(masm->isolate());
    Assembler::BlockConstPoolScope no_const_pools(masm);
    DontEmitDebugCodeScope no_debug_code(masm);
    Label entry_hook_call_start;
    __ Bind(&entry_hook_call_start);
    __ Push(padreg, lr);
    __ CallStub(&stub);
    DCHECK_EQ(masm->SizeOfCodeGeneratedSince(&entry_hook_call_start),
              kProfileEntryHookCallSize);
    __ Pop(lr, padreg);
  }
}


void ProfileEntryHookStub::Generate(MacroAssembler* masm) {
  HardAbortScope hard_aborts(masm);

  // Save all kCallerSaved registers (including lr), since this can be called
  // from anywhere.
  // TODO(jbramley): What about FP registers?
  __ PushCPURegList(kCallerSaved);
  DCHECK(kCallerSaved.IncludesAliasOf(lr));
  const int kNumSavedRegs = kCallerSaved.Count();
  DCHECK_EQ(kNumSavedRegs % 2, 0);

  // Compute the function's address as the first argument.
  __ Sub(x0, lr, kProfileEntryHookCallSize);

#if V8_HOST_ARCH_ARM64
  uintptr_t entry_hook =
      reinterpret_cast<uintptr_t>(isolate()->function_entry_hook());
  __ Mov(x10, entry_hook);
#else
  // Under the simulator we need to indirect the entry hook through a trampoline
  // function at a known address.
  ApiFunction dispatcher(FUNCTION_ADDR(EntryHookTrampoline));
  __ Mov(x10, Operand(ExternalReference::Create(
                  &dispatcher, ExternalReference::BUILTIN_CALL)));
  // It additionally takes an isolate as a third parameter
  __ Mov(x2, ExternalReference::isolate_address(isolate()));
#endif

  // The caller's return address is above the saved temporaries.
  // Grab its location for the second argument to the hook.
  __ SlotAddress(x1, kNumSavedRegs);

  {
    // Create a dummy frame, as CallCFunction requires this.
    FrameScope frame(masm, StackFrame::MANUAL);
    __ CallCFunction(x10, 2, 0);
  }

  __ PopCPURegList(kCallerSaved);
  __ Ret();
}


void DirectCEntryStub::Generate(MacroAssembler* masm) {
  // Put return address on the stack (accessible to GC through exit frame pc).
  __ Poke(lr, 0);
  // Call the C++ function.
  __ Blr(x10);
  // Return to calling code.
  __ Peek(lr, 0);
  __ AssertFPCRState();
  __ Ret();
}

void DirectCEntryStub::GenerateCall(MacroAssembler* masm,
                                    Register target) {
  // Branch to the stub.
  __ Mov(x10, target);
  __ Call(GetCode(), RelocInfo::CODE_TARGET);
}

// The number of register that CallApiFunctionAndReturn will need to save on
// the stack. The space for these registers need to be allocated in the
// ExitFrame before calling CallApiFunctionAndReturn.
static const int kCallApiFunctionSpillSpace = 4;


static int AddressOffset(ExternalReference ref0, ExternalReference ref1) {
  return static_cast<int>(ref0.address() - ref1.address());
}

// Calls an API function. Allocates HandleScope, extracts returned value
// from handle and propagates exceptions.
// 'stack_space' is the space to be unwound on exit (includes the call JS
// arguments space and the additional space allocated for the fast call).
// 'spill_offset' is the offset from the stack pointer where
// CallApiFunctionAndReturn can spill registers.
static void CallApiFunctionAndReturn(MacroAssembler* masm,
                                     Register function_address,
                                     ExternalReference thunk_ref,
                                     int stack_space, int spill_offset,
                                     MemOperand return_value_operand) {
  ASM_LOCATION("CallApiFunctionAndReturn");
  Isolate* isolate = masm->isolate();
  ExternalReference next_address =
      ExternalReference::handle_scope_next_address(isolate);
  const int kNextOffset = 0;
  const int kLimitOffset = AddressOffset(
      ExternalReference::handle_scope_limit_address(isolate), next_address);
  const int kLevelOffset = AddressOffset(
      ExternalReference::handle_scope_level_address(isolate), next_address);

  DCHECK(function_address.is(x1) || function_address.is(x2));

  Label profiler_disabled;
  Label end_profiler_check;
  __ Mov(x10, ExternalReference::is_profiling_address(isolate));
  __ Ldrb(w10, MemOperand(x10));
  __ Cbz(w10, &profiler_disabled);
  __ Mov(x3, thunk_ref);
  __ B(&end_profiler_check);

  __ Bind(&profiler_disabled);
  __ Mov(x3, function_address);
  __ Bind(&end_profiler_check);

  // Save the callee-save registers we are going to use.
  // TODO(all): Is this necessary? ARM doesn't do it.
  STATIC_ASSERT(kCallApiFunctionSpillSpace == 4);
  __ Poke(x19, (spill_offset + 0) * kXRegSize);
  __ Poke(x20, (spill_offset + 1) * kXRegSize);
  __ Poke(x21, (spill_offset + 2) * kXRegSize);
  __ Poke(x22, (spill_offset + 3) * kXRegSize);

  // Allocate HandleScope in callee-save registers.
  // We will need to restore the HandleScope after the call to the API function,
  // by allocating it in callee-save registers they will be preserved by C code.
  Register handle_scope_base = x22;
  Register next_address_reg = x19;
  Register limit_reg = x20;
  Register level_reg = w21;

  __ Mov(handle_scope_base, next_address);
  __ Ldr(next_address_reg, MemOperand(handle_scope_base, kNextOffset));
  __ Ldr(limit_reg, MemOperand(handle_scope_base, kLimitOffset));
  __ Ldr(level_reg, MemOperand(handle_scope_base, kLevelOffset));
  __ Add(level_reg, level_reg, 1);
  __ Str(level_reg, MemOperand(handle_scope_base, kLevelOffset));

  if (FLAG_log_timer_events) {
    FrameScope frame(masm, StackFrame::MANUAL);
    __ PushSafepointRegisters();
    __ Mov(x0, ExternalReference::isolate_address(isolate));
    __ CallCFunction(ExternalReference::log_enter_external_function(), 1);
    __ PopSafepointRegisters();
  }

  // Native call returns to the DirectCEntry stub which redirects to the
  // return address pushed on stack (could have moved after GC).
  // DirectCEntry stub itself is generated early and never moves.
  DirectCEntryStub stub(isolate);
  stub.GenerateCall(masm, x3);

  if (FLAG_log_timer_events) {
    FrameScope frame(masm, StackFrame::MANUAL);
    __ PushSafepointRegisters();
    __ Mov(x0, ExternalReference::isolate_address(isolate));
    __ CallCFunction(ExternalReference::log_leave_external_function(), 1);
    __ PopSafepointRegisters();
  }

  Label promote_scheduled_exception;
  Label delete_allocated_handles;
  Label leave_exit_frame;
  Label return_value_loaded;

  // Load value from ReturnValue.
  __ Ldr(x0, return_value_operand);
  __ Bind(&return_value_loaded);
  // No more valid handles (the result handle was the last one). Restore
  // previous handle scope.
  __ Str(next_address_reg, MemOperand(handle_scope_base, kNextOffset));
  if (__ emit_debug_code()) {
    __ Ldr(w1, MemOperand(handle_scope_base, kLevelOffset));
    __ Cmp(w1, level_reg);
    __ Check(eq, AbortReason::kUnexpectedLevelAfterReturnFromApiCall);
  }
  __ Sub(level_reg, level_reg, 1);
  __ Str(level_reg, MemOperand(handle_scope_base, kLevelOffset));
  __ Ldr(x1, MemOperand(handle_scope_base, kLimitOffset));
  __ Cmp(limit_reg, x1);
  __ B(ne, &delete_allocated_handles);

  // Leave the API exit frame.
  __ Bind(&leave_exit_frame);
  // Restore callee-saved registers.
  __ Peek(x19, (spill_offset + 0) * kXRegSize);
  __ Peek(x20, (spill_offset + 1) * kXRegSize);
  __ Peek(x21, (spill_offset + 2) * kXRegSize);
  __ Peek(x22, (spill_offset + 3) * kXRegSize);

  __ LeaveExitFrame(false, x1, x5);

  // Check if the function scheduled an exception.
  __ Mov(x5, ExternalReference::scheduled_exception_address(isolate));
  __ Ldr(x5, MemOperand(x5));
  __ JumpIfNotRoot(x5, Heap::kTheHoleValueRootIndex,
                   &promote_scheduled_exception);

  __ DropSlots(stack_space);
  __ Ret();

  // Re-throw by promoting a scheduled exception.
  __ Bind(&promote_scheduled_exception);
  __ TailCallRuntime(Runtime::kPromoteScheduledException);

  // HandleScope limit has changed. Delete allocated extensions.
  __ Bind(&delete_allocated_handles);
  __ Str(limit_reg, MemOperand(handle_scope_base, kLimitOffset));
  // Save the return value in a callee-save register.
  Register saved_result = x19;
  __ Mov(saved_result, x0);
  __ Mov(x0, ExternalReference::isolate_address(isolate));
  __ CallCFunction(ExternalReference::delete_handle_scope_extensions(), 1);
  __ Mov(x0, saved_result);
  __ B(&leave_exit_frame);
}

void CallApiCallbackStub::Generate(MacroAssembler* masm) {
  // ----------- S t a t e -------------
  //  -- x4                  : call_data
  //  -- x2                  : holder
  //  -- x1                  : api_function_address
  //  -- cp                  : context
  //  --
  //  -- sp[0]               : last argument
  //  -- ...
  //  -- sp[(argc - 1) * 8]  : first argument
  //  -- sp[argc * 8]        : receiver
  // -----------------------------------

  Register call_data = x4;
  Register holder = x2;
  Register api_function_address = x1;

  typedef FunctionCallbackArguments FCA;

  STATIC_ASSERT(FCA::kArgsLength == 6);
  STATIC_ASSERT(FCA::kNewTargetIndex == 5);
  STATIC_ASSERT(FCA::kDataIndex == 4);
  STATIC_ASSERT(FCA::kReturnValueOffset == 3);
  STATIC_ASSERT(FCA::kReturnValueDefaultValueIndex == 2);
  STATIC_ASSERT(FCA::kIsolateIndex == 1);
  STATIC_ASSERT(FCA::kHolderIndex == 0);

  Register undef = x7;
  __ LoadRoot(undef, Heap::kUndefinedValueRootIndex);

  // Push new target, call data.
  __ Push(undef, call_data);

  Register isolate_reg = x5;
  __ Mov(isolate_reg, ExternalReference::isolate_address(masm->isolate()));

  // FunctionCallbackArguments:
  //    return value, return value default, isolate, holder.
  __ Push(undef, undef, isolate_reg, holder);

  // Prepare arguments.
  Register args = x6;
  __ Mov(args, sp);

  // Allocate the v8::Arguments structure in the arguments' space, since it's
  // not controlled by GC.
  const int kApiStackSpace = 3;

  // Allocate space so that CallApiFunctionAndReturn can store some scratch
  // registers on the stack.
  const int kCallApiFunctionSpillSpace = 4;

  FrameScope frame_scope(masm, StackFrame::MANUAL);
  __ EnterExitFrame(false, x10, kApiStackSpace + kCallApiFunctionSpillSpace);

  DCHECK(!AreAliased(x0, api_function_address));
  // x0 = FunctionCallbackInfo&
  // Arguments is after the return address.
  __ SlotAddress(x0, 1);
  // FunctionCallbackInfo::implicit_args_ and FunctionCallbackInfo::values_
  __ Add(x10, args, Operand((FCA::kArgsLength - 1 + argc()) * kPointerSize));
  __ Stp(args, x10, MemOperand(x0, 0 * kPointerSize));
  // FunctionCallbackInfo::length_ = argc
  __ Mov(x10, argc());
  __ Str(x10, MemOperand(x0, 2 * kPointerSize));

  ExternalReference thunk_ref = ExternalReference::invoke_function_callback();

  AllowExternalCallThatCantCauseGC scope(masm);
  // Stores return the first js argument
  int return_value_offset = 2 + FCA::kReturnValueOffset;
  MemOperand return_value_operand(fp, return_value_offset * kPointerSize);
  // The number of arguments might be odd, but will be padded when calling the
  // stub. We do not round up stack_space to account for odd argc here, this
  // will be done in CallApiFunctionAndReturn.
  const int stack_space = (argc() + 1) + FCA::kArgsLength;

  // The current frame needs to be aligned.
  DCHECK_EQ((stack_space - (argc() + 1)) % 2, 0);
  const int spill_offset = 1 + kApiStackSpace;
  CallApiFunctionAndReturn(masm, api_function_address, thunk_ref, stack_space,
                           spill_offset, return_value_operand);
}


void CallApiGetterStub::Generate(MacroAssembler* masm) {
  STATIC_ASSERT(PropertyCallbackArguments::kShouldThrowOnErrorIndex == 0);
  STATIC_ASSERT(PropertyCallbackArguments::kHolderIndex == 1);
  STATIC_ASSERT(PropertyCallbackArguments::kIsolateIndex == 2);
  STATIC_ASSERT(PropertyCallbackArguments::kReturnValueDefaultValueIndex == 3);
  STATIC_ASSERT(PropertyCallbackArguments::kReturnValueOffset == 4);
  STATIC_ASSERT(PropertyCallbackArguments::kDataIndex == 5);
  STATIC_ASSERT(PropertyCallbackArguments::kThisIndex == 6);
  STATIC_ASSERT(PropertyCallbackArguments::kArgsLength == 7);

  Register receiver = ApiGetterDescriptor::ReceiverRegister();
  Register holder = ApiGetterDescriptor::HolderRegister();
  Register callback = ApiGetterDescriptor::CallbackRegister();
  Register data = x4;
  Register undef = x5;
  Register isolate_address = x6;
  Register name = x7;
  DCHECK(!AreAliased(receiver, holder, callback, data, undef, isolate_address,
                     name));

  __ Ldr(data, FieldMemOperand(callback, AccessorInfo::kDataOffset));
  __ LoadRoot(undef, Heap::kUndefinedValueRootIndex);
  __ Mov(isolate_address, ExternalReference::isolate_address(isolate()));
  __ Ldr(name, FieldMemOperand(callback, AccessorInfo::kNameOffset));

  // PropertyCallbackArguments:
  //   receiver, data, return value, return value default, isolate, holder,
  //   should_throw_on_error
  // These are followed by the property name, which is also pushed below the
  // exit frame to make the GC aware of it.
  __ Push(receiver, data, undef, undef, isolate_address, holder, xzr, name);

  // v8::PropertyCallbackInfo::args_ array and name handle.
  static const int kStackUnwindSpace =
      PropertyCallbackArguments::kArgsLength + 1;
  static_assert(kStackUnwindSpace % 2 == 0,
                "slots must be a multiple of 2 for stack pointer alignment");

  // Load address of v8::PropertyAccessorInfo::args_ array and name handle.
  __ Mov(x0, sp);                    // x0 = Handle<Name>
  __ Add(x1, x0, 1 * kPointerSize);  // x1 = v8::PCI::args_

  const int kApiStackSpace = 1;

  // Allocate space so that CallApiFunctionAndReturn can store some scratch
  // registers on the stack.
  const int kCallApiFunctionSpillSpace = 4;

  FrameScope frame_scope(masm, StackFrame::MANUAL);
  __ EnterExitFrame(false, x10, kApiStackSpace + kCallApiFunctionSpillSpace);

  // Create v8::PropertyCallbackInfo object on the stack and initialize
  // it's args_ field.
  __ Poke(x1, 1 * kPointerSize);
  __ SlotAddress(x1, 1);
  // x1 = v8::PropertyCallbackInfo&

  ExternalReference thunk_ref =
      ExternalReference::invoke_accessor_getter_callback();

  Register api_function_address = x2;
  Register js_getter = x4;
  __ Ldr(js_getter, FieldMemOperand(callback, AccessorInfo::kJsGetterOffset));
  __ Ldr(api_function_address,
         FieldMemOperand(js_getter, Foreign::kForeignAddressOffset));

  const int spill_offset = 1 + kApiStackSpace;
  // +3 is to skip prolog, return address and name handle.
  MemOperand return_value_operand(
      fp, (PropertyCallbackArguments::kReturnValueOffset + 3) * kPointerSize);
  CallApiFunctionAndReturn(masm, api_function_address, thunk_ref,
                           kStackUnwindSpace, spill_offset,
                           return_value_operand);
}

#undef __

}  // namespace internal
}  // namespace v8

#endif  // V8_TARGET_ARCH_ARM64