src/debug/arm64/debug-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/arm64/frames-arm64.h"
#include "src/codegen.h"
#include "src/debug/debug.h"

namespace v8 {
namespace internal {

#define __ ACCESS_MASM(masm)


void EmitDebugBreakSlot(Assembler* masm) {
  Label check_size;
  __ bind(&check_size);
  for (int i = 0; i < Assembler::kDebugBreakSlotInstructions; i++) {
    __ nop(Assembler::DEBUG_BREAK_NOP);
  }
  DCHECK_EQ(Assembler::kDebugBreakSlotInstructions,
            static_cast<int>(masm->InstructionsGeneratedSince(&check_size)));
}


void DebugCodegen::GenerateSlot(MacroAssembler* masm, RelocInfo::Mode mode) {
  // Generate enough nop's to make space for a call instruction. Avoid emitting
  // the constant pool in the debug break slot code.
  InstructionAccurateScope scope(masm, Assembler::kDebugBreakSlotInstructions);
  masm->RecordDebugBreakSlot(mode);
  EmitDebugBreakSlot(masm);
}


void DebugCodegen::ClearDebugBreakSlot(Isolate* isolate, Address pc) {
  PatchingAssembler patcher(isolate, reinterpret_cast<Instruction*>(pc),
                            Assembler::kDebugBreakSlotInstructions);
  EmitDebugBreakSlot(&patcher);
}


void DebugCodegen::PatchDebugBreakSlot(Isolate* isolate, Address pc,
                                       Handle<Code> code) {
  DCHECK_EQ(Code::BUILTIN, code->kind());
  PatchingAssembler patcher(isolate, reinterpret_cast<Instruction*>(pc),
                            Assembler::kDebugBreakSlotInstructions);
  // Patch the code emitted by DebugCodegen::GenerateSlots, changing the debug
  // break slot code from
  //   mov x0, x0    @ nop DEBUG_BREAK_NOP
  //   mov x0, x0    @ nop DEBUG_BREAK_NOP
  //   mov x0, x0    @ nop DEBUG_BREAK_NOP
  //   mov x0, x0    @ nop DEBUG_BREAK_NOP
  //   mov x0, x0    @ nop DEBUG_BREAK_NOP
  // to a call to the debug slot code.
  //   ldr ip0, [pc, #(2 * kInstructionSize)]
  //   blr ip0
  //   b skip
  //   <debug break slot code entry point address (64 bits)>
  //   skip:

  Label skip_constant;
  // The first instruction of a patched debug break slot must be a load literal
  // loading the address of the debug break slot code.
  patcher.ldr_pcrel(ip0, (2 * kInstructionSize) >> kLoadLiteralScaleLog2);
  patcher.b(&skip_constant);
  patcher.dc64(reinterpret_cast<int64_t>(code->entry()));
  patcher.bind(&skip_constant);
  // TODO(all): check the following is correct.
  // The debug break slot code will push a frame and call statically compiled
  // code. By using blr,  this call site will be registered in the frame.
  // The debugger can now iterate on the frames to find this call.
  patcher.blr(ip0);
}

bool DebugCodegen::DebugBreakSlotIsPatched(Address pc) {
  Instruction* current_instr = reinterpret_cast<Instruction*>(pc);
  return !current_instr->IsNop(Assembler::DEBUG_BREAK_NOP);
}

void DebugCodegen::GenerateDebugBreakStub(MacroAssembler* masm,
                                          DebugBreakCallHelperMode mode) {
  __ RecordComment("Debug break");
  Register scratch = x10;
  {
    FrameScope scope(masm, StackFrame::INTERNAL);

    // Load padding words on stack.
    __ Mov(scratch, Smi::FromInt(LiveEdit::kFramePaddingValue));
    __ PushMultipleTimes(scratch, LiveEdit::kFramePaddingInitialSize);
    __ Mov(scratch, Smi::FromInt(LiveEdit::kFramePaddingInitialSize));
    __ Push(scratch);

    if (mode == SAVE_RESULT_REGISTER) __ Push(x0);

    __ Mov(x0, 0);  // No arguments.
    __ Mov(x1, ExternalReference(Runtime::FunctionForId(Runtime::kDebugBreak),
                                 masm->isolate()));

    CEntryStub stub(masm->isolate(), 1);
    __ CallStub(&stub);

    if (FLAG_debug_code) {
      for (int i = 0; i < kNumJSCallerSaved; i++) {
        Register reg = Register::XRegFromCode(JSCallerSavedCode(i));
        __ Mov(reg, Operand(kDebugZapValue));
      }
    }

    // Restore the register values from the expression stack.
    if (mode == SAVE_RESULT_REGISTER) __ Pop(x0);

    // Don't bother removing padding bytes pushed on the stack
    // as the frame is going to be restored right away.

    // Leave the internal frame.
  }

  // Now that the break point has been handled, resume normal execution by
  // jumping to the target address intended by the caller and that was
  // overwritten by the address of DebugBreakXXX.
  ExternalReference after_break_target =
      ExternalReference::debug_after_break_target_address(masm->isolate());
  __ Mov(scratch, after_break_target);
  __ Ldr(scratch, MemOperand(scratch));
  __ Br(scratch);
}


void DebugCodegen::GenerateFrameDropperLiveEdit(MacroAssembler* masm) {
  // We do not know our frame height, but set sp based on fp.
  __ Sub(masm->StackPointer(), fp, kPointerSize);
  __ AssertStackConsistency();

  __ Pop(x1, fp, lr);  // Function, Frame, Return address.

  ParameterCount dummy(0);
  __ FloodFunctionIfStepping(x1, no_reg, dummy, dummy);

  UseScratchRegisterScope temps(masm);
  Register scratch = temps.AcquireX();

  // Load context from the function.
  __ Ldr(cp, FieldMemOperand(x1, JSFunction::kContextOffset));

  // Clear new.target as a safety measure.
  __ LoadRoot(x3, Heap::kUndefinedValueRootIndex);

  // Get function code.
  __ Ldr(scratch, FieldMemOperand(x1, JSFunction::kSharedFunctionInfoOffset));
  __ Ldr(scratch, FieldMemOperand(scratch, SharedFunctionInfo::kCodeOffset));
  __ Add(scratch, scratch, Code::kHeaderSize - kHeapObjectTag);

  // Re-run JSFunction, x1 is function, cp is context.
  __ Br(scratch);
}


const bool LiveEdit::kFrameDropperSupported = true;

}  // namespace internal
}  // namespace v8

#endif  // V8_TARGET_ARCH_ARM64