Support LiveEdit on ARM

src/arm/debug-arm.cc

 // Copyright 2012 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.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_ARM
 
 #include "src/codegen.h"
 #include "src/debug.h"
 
 namespace v8 {
 namespace internal {
 
 bool BreakLocationIterator::IsDebugBreakAtReturn() {
   return Debug::IsDebugBreakAtReturn(rinfo());
 }
 
 
 void BreakLocationIterator::SetDebugBreakAtReturn() {
   // Patch the code changing the return from JS function sequence from
   //   mov sp, fp
   //   ldmia sp!, {fp, lr}
   //   add sp, sp, #4
   //   bx lr
   // to a call to the debug break return code.
   //   ldr ip, [pc, #0]
   //   blx ip
   //   <debug break return code entry point address>
-  //   bktp 0
+  //   bkpt 0
   CodePatcher patcher(rinfo()->pc(), Assembler::kJSReturnSequenceInstructions);
   patcher.masm()->ldr(v8::internal::ip, MemOperand(v8::internal::pc, 0));
   patcher.masm()->blx(v8::internal::ip);
   patcher.Emit(
       debug_info_->GetIsolate()->builtins()->Return_DebugBreak()->entry());
   patcher.masm()->bkpt(0);
 }
 
 
 // Restore the JS frame exit code.
@@ skipping 45 matching lines @@
 
 #define __ ACCESS_MASM(masm)
 
 
 static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
                                           RegList object_regs,
                                           RegList non_object_regs) {
   {
     FrameAndConstantPoolScope scope(masm, StackFrame::INTERNAL);
 
+    // Load padding words on stack.
+    __ mov(ip, Operand(Smi::FromInt(LiveEdit::kFramePaddingValue)));
+    for (int i = 0; i < LiveEdit::kFramePaddingInitialSize; i++) {
+      __ push(ip);
+    }
+    __ mov(ip, Operand(Smi::FromInt(LiveEdit::kFramePaddingInitialSize)));
+    __ push(ip);
+
     // 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);
     if ((object_regs | non_object_regs) != 0) {
       for (int i = 0; i < kNumJSCallerSaved; i++) {
         int r = JSCallerSavedCode(i);
         Register reg = { r };
@@ skipping 26 matching lines @@
         if ((non_object_regs & (1 << r)) != 0) {
           __ SmiUntag(reg);
         }
         if (FLAG_debug_code &&
             (((object_regs |non_object_regs) & (1 << r)) == 0)) {
           __ mov(reg, Operand(kDebugZapValue));
         }
       }
     }
 
+    // Don't bother removing padding bytes pushed on the stack
+    // as the frame is going to be restored right away.
+

[Yang, 2014/06/18 15:03:55]

Are you sure this is correct? A brief comparison to the ia32 and x64 port shows
that this part is quite different. Can you explain where the frame is going to
be restored?

[alph, 2014/06/18 16:29:21]

FrameAndConstantPoolScope destructor is called here at the end of the block. It
makes a call to masm_->LeaveFrame(), see here:

https://code.google.com/p/chromium/codesearch#chromium/src/v8/src/arm/macro-a...

which in turn restores sp from fp:

https://code.google.com/p/chromium/codesearch#chromium/src/v8/src/arm/macro-a...

     // 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(ip, Operand(after_break_target));
   __ ldr(ip, MemOperand(ip));
@@ skipping 123 matching lines @@
 
 
 void DebugCodegen::GenerateSlotDebugBreak(MacroAssembler* masm) {
   // In the places where a debug break slot is inserted no registers can contain
   // object pointers.
   Generate_DebugBreakCallHelper(masm, 0, 0);
 }
 
 
 void DebugCodegen::GeneratePlainReturnLiveEdit(MacroAssembler* masm) {
-  masm->Abort(kLiveEditFrameDroppingIsNotSupportedOnArm);
+  __ Ret();
 }
 
 
 void DebugCodegen::GenerateFrameDropperLiveEdit(MacroAssembler* masm) {
-  masm->Abort(kLiveEditFrameDroppingIsNotSupportedOnArm);
+  ExternalReference restarter_frame_function_slot =
+      ExternalReference::debug_restarter_frame_function_pointer_address(
+          masm->isolate());
+  __ mov(ip, Operand(restarter_frame_function_slot));
+  __ mov(r1, Operand::Zero());
+  __ str(r1, MemOperand(ip, 0));
+
+  // We do not know our frame height, but set sp based on fp.
+  __ sub(sp, fp, Operand(kPointerSize));
+
+  __ Pop(lr, fp, r1);  // Return address, Frame, Function.
+
+  // Load context from the function.
+  __ ldr(cp, FieldMemOperand(r1, JSFunction::kContextOffset));
+
+  // Get function code.
+  __ ldr(ip, FieldMemOperand(r1, JSFunction::kSharedFunctionInfoOffset));
+  __ ldr(ip, FieldMemOperand(ip, SharedFunctionInfo::kCodeOffset));
+  __ add(ip, ip, Operand(Code::kHeaderSize - kHeapObjectTag));
+
+  // Re-run JSFunction, r1 is function, cp is context.
+  __ Jump(ip);
 }
 
 
-const bool LiveEdit::kFrameDropperSupported = false;
+const bool LiveEdit::kFrameDropperSupported = true;
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM