[Interpreter] Adds support to fetch return value on break at return.

src/debug/s390/debug-s390.cc

 // Copyright 2015 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_S390
 
 #include "src/codegen.h"
 #include "src/debug/debug.h"
@@ skipping 70 matching lines @@
     FrameScope scope(masm, StackFrame::INTERNAL);
 
     // Load padding words on stack.
     __ LoadSmiLiteral(ip, Smi::FromInt(LiveEdit::kFramePaddingValue));
     for (int i = 0; i < LiveEdit::kFramePaddingInitialSize; i++) {
       __ push(ip);
     }
     __ LoadSmiLiteral(ip, Smi::FromInt(LiveEdit::kFramePaddingInitialSize));
     __ push(ip);
 
-    if (mode == SAVE_RESULT_REGISTER) __ push(r2);
-
-    __ mov(r2, Operand::Zero());  // no arguments
+    // Push arguments for DebugBreak call.
+    if (mode == SAVE_RESULT_REGISTER) {
+      // Break on return.
+      __ push(r2);
+    } else {
+      // Non-return breaks.
+      __ Push(masm->isolate()->factory()->the_hole_value());
+    }
+    __ mov(r2, Operand(1));
     __ mov(r3,
            Operand(ExternalReference(
                Runtime::FunctionForId(Runtime::kDebugBreak), masm->isolate())));
 
     CEntryStub ceb(masm->isolate(), 1);
     __ CallStub(&ceb);
 
     if (FLAG_debug_code) {
       for (int i = 0; i < kNumJSCallerSaved; i++) {
         Register reg = {JSCallerSavedCode(i)};
-        __ mov(reg, Operand(kDebugZapValue));
+        // Do not clobber r2 if SAVE_RESULT_REGISTER is set. It will
+        // contain return value of the function.
+        if (!(reg.is(r2) && SAVE_RESULT_REGISTER)) {
+          __ mov(reg, Operand(kDebugZapValue));
+        }
       }
     }
 
-    if (mode == SAVE_RESULT_REGISTER) __ pop(r2);
-
     // 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 =
@@ skipping 28 matching lines @@
   __ Jump(ip);
 }
 
 const bool LiveEdit::kFrameDropperSupported = true;
 
 #undef __
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_S390