More precise break points and stepping when debugging...

src/arm/debug-arm.cc

Index: src/arm/debug-arm.cc
===================================================================
--- src/arm/debug-arm.cc	(revision 4816)
+++ src/arm/debug-arm.cc	(working copy)
@@ -57,7 +57,7 @@
   // #endif
   //   <debug break return code entry point address>
   //   bktp 0
-  CodePatcher patcher(rinfo()->pc(), 4);
+  CodePatcher patcher(rinfo()->pc(), Assembler::kJSReturnSequenceInstructions);
 #ifdef USE_BLX
   patcher.masm()->ldr(v8::internal::ip, MemOperand(v8::internal::pc, 0));
   patcher.masm()->blx(v8::internal::ip);
@@ -73,17 +73,59 @@
 // Restore the JS frame exit code.
 void BreakLocationIterator::ClearDebugBreakAtReturn() {
   rinfo()->PatchCode(original_rinfo()->pc(),
-                     Assembler::kJSReturnSequenceLength);
+                     Assembler::kJSReturnSequenceInstructions);
 }
 
 
-// A debug break in the exit code is identified by a call.
+// A debug break in the frame exit code is identified by the JS frame exit code
+// having been patched with a call instruction.
 bool Debug::IsDebugBreakAtReturn(RelocInfo* rinfo) {
   ASSERT(RelocInfo::IsJSReturn(rinfo->rmode()));
   return rinfo->IsPatchedReturnSequence();
 }
 
 
+bool BreakLocationIterator::IsDebugBreakAtSlot() {
+  ASSERT(IsDebugBreakSlot());
+  // Check whether the debug break slot instructions have been patched.
+  return rinfo()->IsPatchedDebugBreakSlotSequence();
+}
+
+
+void BreakLocationIterator::SetDebugBreakAtSlot() {
+  ASSERT(IsDebugBreakSlot());
+  // Patch the code changing the debug break slot code from
+  //   mov r2, r2
+  //   mov r2, r2
+  //   mov r2, r2
+  // to a call to the debug break slot code.
+  // #if USE_BLX
+  //   ldr ip, [pc, #0]
+  //   blx ip
+  // #else
+  //   mov lr, pc
+  //   ldr pc, [pc, #-4]
+  // #endif
+  //   <debug break slot code entry point address>
+  CodePatcher patcher(rinfo()->pc(), Assembler::kDebugBreakSlotInstructions);
+#ifdef USE_BLX
+  patcher.masm()->ldr(v8::internal::ip, MemOperand(v8::internal::pc, 0));
+  patcher.masm()->blx(v8::internal::ip);
+#else
+  patcher.masm()->mov(v8::internal::lr, v8::internal::pc);
+  patcher.masm()->ldr(v8::internal::pc, MemOperand(v8::internal::pc, -4));
+#endif
+  patcher.Emit(Debug::debug_break_return()->entry());
+}
+
+
+void BreakLocationIterator::ClearDebugBreakAtSlot() {
+  ASSERT(IsDebugBreakSlot());
+  rinfo()->PatchCode(original_rinfo()->pc(),
+                     Assembler::kDebugBreakSlotInstructions);
+}
+
+
 #define __ ACCESS_MASM(masm)
 
 
@@ -220,10 +262,31 @@
 }
 
 
+void Debug::GenerateSlot(MacroAssembler* masm) {
+  // Generate enough nop's to make space for a call instruction.
+  Label check_codesize;
+  __ bind(&check_codesize);
+  __ RecordDebugBreakSlot();
+  for (int i = 0; i < Assembler::kDebugBreakSlotInstructions; i++) {
+    __ nop(2);
+  }
+  ASSERT_EQ(Assembler::kDebugBreakSlotInstructions,
+            masm->InstructionsGeneratedSince(&check_codesize));
+}
+
+
+void Debug::GenerateSlotDebugBreak(MacroAssembler* masm) {
+  // In the places where a debug break slot is inserted no registers can contain
+  // object pointers.
+  Generate_DebugBreakCallHelper(masm, 0);
+}
+
+
 void Debug::GeneratePlainReturnLiveEdit(MacroAssembler* masm) {
   masm->Abort("LiveEdit frame dropping is not supported on arm");
 }
 
+
 void Debug::GenerateFrameDropperLiveEdit(MacroAssembler* masm) {
   masm->Abort("LiveEdit frame dropping is not supported on arm");
 }