Fix issue 825 (LiveEdit vs. function with no locals) in core and for ia32.

src/ia32/debug-ia32.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 73 matching lines @@
       isolate->debug()->debug_break_slot()->entry(),
       Assembler::kDebugBreakSlotLength - Assembler::kCallInstructionLength);
 }
 
 
 void BreakLocationIterator::ClearDebugBreakAtSlot() {
   ASSERT(IsDebugBreakSlot());
   rinfo()->PatchCode(original_rinfo()->pc(), Assembler::kDebugBreakSlotLength);
 }
 
+// All debug break stubs support padding for LiveEdit.
+const bool Debug::FramePaddingLayout::kIsSupported = true;
+
 
 #define __ ACCESS_MASM(masm)
 
-
 static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
                                           RegList object_regs,
                                           RegList non_object_regs,
                                           bool convert_call_to_jmp) {
   // Enter an internal frame.
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
 
+    // Load padding words on stack.
+    for (int i = 0; i < Debug::FramePaddingLayout::kInitialSize; i++) {
+      __ push(Immediate(Debug::FramePaddingLayout::kPaddingValue));
+    }
+    __ push(Immediate(2 * Debug::FramePaddingLayout::kInitialSize));

[Yang, 2012/05/02 11:38:34]

I assume multiplying by 2 is for Smi-tagging? Use
Smi::FromInt(Debug::FramePaddingLayout::kInitialSize) instead.

[Peter Rybin, 2012/05/02 23:46:33]

Done.

+
     // Store the registers containing live values on the expression stack to
     // make sure that these are correctly updated during GC. Non object values
     // are stored as a smi causing it to be untouched by GC.
     ASSERT((object_regs & ~kJSCallerSaved) == 0);
     ASSERT((non_object_regs & ~kJSCallerSaved) == 0);
     ASSERT((object_regs & non_object_regs) == 0);
     for (int i = 0; i < kNumJSCallerSaved; i++) {
       int r = JSCallerSavedCode(i);
       Register reg = { r };
       if ((object_regs & (1 << r)) != 0) {
@@ skipping 11 matching lines @@
 
 #ifdef DEBUG
     __ RecordComment("// Calling from debug break to runtime - come in - over");
 #endif
     __ Set(eax, Immediate(0));  // No arguments.
     __ mov(ebx, Immediate(ExternalReference::debug_break(masm->isolate())));
 
     CEntryStub ceb(1);
     __ CallStub(&ceb);
 
+    // Automatically find register that could be used after register restore.
+    // We need one register for padding skip instructions.
+    Register unused_reg = { -1 };
+
     // Restore the register values containing object pointers from the
     // expression stack.
     for (int i = kNumJSCallerSaved; --i >= 0;) {
       int r = JSCallerSavedCode(i);
       Register reg = { r };
       if (FLAG_debug_code) {
         __ Set(reg, Immediate(kDebugZapValue));
       }
+      bool taken = reg.code() == esi.code();
       if ((object_regs & (1 << r)) != 0) {
         __ pop(reg);
+        taken = true;
       }
       if ((non_object_regs & (1 << r)) != 0) {
         __ pop(reg);
         __ SmiUntag(reg);
+        taken = true;
+      }
+      if (!taken) {
+        unused_reg = reg;
       }
     }
 
+    ASSERT(unused_reg.code() != -1);
+
+    // Read current padding counter and skip corresponding number of words.
+    __ pop(unused_reg);
+    __ lea(esp, Operand(esp, unused_reg, times_half_pointer_size, 0));

[Yang, 2012/05/02 11:38:34]

This is based on the implication that Smis are represented by left shift by 1
bit. Please add a STATIC_ASSERT(kSmiTagSize == 1) or a comment to state this
implication.

[Peter Rybin, 2012/05/02 23:46:33]

Done.

+
     // Get rid of the internal frame.
   }
 
   // If this call did not replace a call but patched other code then there will
   // be an unwanted return address left on the stack. Here we get rid of that.
   if (convert_call_to_jmp) {
     __ add(esp, Immediate(kPointerSize));
   }
 
   // Now that the break point has been handled, resume normal execution by
@@ skipping 162 matching lines @@
 
 const bool Debug::kFrameDropperSupported = true;
 
 #undef __
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32