Adds support for debugger API on MIPS.

runtime/vm/debugger_mips.cc

Index: runtime/vm/debugger_mips.cc
===================================================================
--- runtime/vm/debugger_mips.cc	(revision 21950)
+++ runtime/vm/debugger_mips.cc	(working copy)
@@ -5,30 +5,86 @@
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_MIPS)
 
+#include "vm/cpu.h"
 #include "vm/debugger.h"
+#include "vm/instructions.h"
+#include "vm/stub_code.h"
 
 namespace dart {
 
+// TODO(hausner): Handle captured variables.
 RawInstance* ActivationFrame::GetLocalVarValue(intptr_t slot_index) {
-  UNIMPLEMENTED();
-  return NULL;
+  uword var_address = fp() + slot_index * kWordSize;
+  return reinterpret_cast<RawInstance*>(
+             *reinterpret_cast<uword*>(var_address));
 }
 
 
 RawInstance* ActivationFrame::GetInstanceCallReceiver(
                  intptr_t num_actual_args) {
-  UNIMPLEMENTED();
-  return NULL;
+  ASSERT(num_actual_args > 0);  // At minimum we have a receiver on the stack.
+  // Stack pointer points to last argument that was pushed on the stack.
+  uword receiver_addr = sp() + ((num_actual_args - 1) * kWordSize);
+  return reinterpret_cast<RawInstance*>(
+             *reinterpret_cast<uword*>(receiver_addr));
 }
 
 
 void CodeBreakpoint::PatchFunctionReturn() {
-  UNIMPLEMENTED();
+  Instr* instr1 = Instr::At(pc_ - 6 * Instr::kInstrSize);
+  Instr* instr2 = Instr::At(pc_ - 5 * Instr::kInstrSize);
+  Instr* instr3 = Instr::At(pc_ - 4 * Instr::kInstrSize);
+  Instr* instr4 = Instr::At(pc_ - 3 * Instr::kInstrSize);
+  Instr* instr5 = Instr::At(pc_ - 2 * Instr::kInstrSize);
+  Instr* instr6 = Instr::At(pc_ - 1 * Instr::kInstrSize);
+
+#if defined(DEBUG)
+
+  instr1->AssertIsImmInstr(LW, SP, RA, 2 * kWordSize);
+  instr2->AssertIsImmInstr(LW, SP, FP, 1 * kWordSize);
+  instr3->AssertIsImmInstr(LW, SP, PP, 0 * kWordSize);
+  instr4->AssertIsImmInstr(ADDIU, SP, SP, 4 * kWordSize);
+  instr5->AssertIsSpecialInstr(JR, RA, ZR, ZR);
+  ASSERT(instr6->InstructionBits() == Instr::kNopInstruction);
+#endif  // defined(DEBUG)
+
+  // Smash code with call instruction and target address.
+  uword stub_addr = StubCode::BreakpointReturnEntryPoint();
+  uint16_t target_lo = stub_addr & 0xffff;
+  uint16_t target_hi = stub_addr >> 16;
+
+  // Unlike other architectures, the sequence we are patching in is shorter
+  // than the sequence we are replacing. We pad at the top with nops so that
+  // the end of the new sequence is lined up with the code descriptor.
+  instr1->SetInstructionBits(Instr::kNopInstruction);
+  instr2->SetInstructionBits(Instr::kNopInstruction);
+  instr3->SetImmInstrBits(LUI, ZR, TMP1, target_hi);
+  instr4->SetImmInstrBits(ORI, TMP1, TMP1, target_lo);
+  instr5->SetSpecialInstrBits(JALR, TMP1, ZR, RA);
+  instr6->SetInstructionBits(Instr::kNopInstruction);
+
+  CPU::FlushICache(pc_ - 6 * Instr::kInstrSize, 6 * Instr::kInstrSize);
 }
 
 
 void CodeBreakpoint::RestoreFunctionReturn() {
-  UNIMPLEMENTED();
+  Instr* instr1 = Instr::At(pc_ - 6 * Instr::kInstrSize);
+  Instr* instr2 = Instr::At(pc_ - 5 * Instr::kInstrSize);
+  Instr* instr3 = Instr::At(pc_ - 4 * Instr::kInstrSize);
+  Instr* instr4 = Instr::At(pc_ - 3 * Instr::kInstrSize);
+  Instr* instr5 = Instr::At(pc_ - 2 * Instr::kInstrSize);
+  Instr* instr6 = Instr::At(pc_ - 1 * Instr::kInstrSize);
+
+  ASSERT(instr3->OpcodeField() == LUI && instr3->RtField() == TMP1);
+
+  instr1->SetImmInstrBits(LW, SP, RA, 2 * kWordSize);
+  instr2->SetImmInstrBits(LW, SP, FP, 1 * kWordSize);
+  instr3->SetImmInstrBits(LW, SP, PP, 0 * kWordSize);
+  instr4->SetImmInstrBits(ADDIU, SP, SP, 4 * kWordSize);
+  instr5->SetSpecialInstrBits(JR, RA, ZR, ZR);
+  instr6->SetInstructionBits(Instr::kNopInstruction);
+
+  CPU::FlushICache(pc_ - 6 * Instr::kInstrSize, 6 * Instr::kInstrSize);
 }
 
 }  // namespace dart