Better single stepping in VM debugger

runtime/vm/stub_code_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 1398 matching lines @@
     // Check that the IC data array has NumberOfArgumentsChecked() == num_args.
     // 'num_args_tested' is stored as an untagged int.
     __ movq(RCX, FieldAddress(RBX, ICData::num_args_tested_offset()));
     __ cmpq(RCX, Immediate(num_args));
     __ j(EQUAL, &ok, Assembler::kNearJump);
     __ Stop("Incorrect stub for IC data");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
+  // Check single stepping.
+  Label not_stepping;
+  __ movq(RAX, FieldAddress(CTX, Context::isolate_offset()));
+  __ movzxb(RAX, Address(RAX, Isolate::single_step_offset()));
+  __ cmpq(RAX, Immediate(0));
+  __ j(EQUAL, &not_stepping, Assembler::kNearJump);
+  __ EnterStubFrame();
+  __ pushq(RBX);
+  __ CallRuntime(kSingleStepHandlerRuntimeEntry);
+  __ popq(RBX);
+  __ LeaveFrame();
+  __ Bind(&not_stepping);
+
   // Load arguments descriptor into R10.
   __ movq(R10, FieldAddress(RBX, ICData::arguments_descriptor_offset()));
   // Loop that checks if there is an IC data match.
   Label loop, update, test, found, get_class_id_as_smi;
   // RBX: IC data object (preserved).
   __ movq(R12, FieldAddress(RBX, ICData::ic_data_offset()));
   // R12: ic_data_array with check entries: classes and target functions.
   __ leaq(R12, FieldAddress(R12, Array::data_offset()));
   // R12: points directly to the first ic data array element.
 
@@ skipping 200 matching lines @@
     // Check that the IC data array has NumberOfArgumentsChecked() == 0.
     // 'num_args_tested' is stored as an untagged int.
     __ movq(RCX, FieldAddress(RBX, ICData::num_args_tested_offset()));
     __ cmpq(RCX, Immediate(0));
     __ j(EQUAL, &ok, Assembler::kNearJump);
     __ Stop("Incorrect IC data for unoptimized static call");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
+  // Check single stepping.
+  Label not_stepping;
+  __ movq(RAX, FieldAddress(CTX, Context::isolate_offset()));
+  __ movzxb(RAX, Address(RAX, Isolate::single_step_offset()));
+  __ cmpq(RAX, Immediate(0));
+  __ j(EQUAL, &not_stepping, Assembler::kNearJump);
+  __ EnterStubFrame();
+  __ pushq(RBX);  // Preserve IC data object.
+  __ CallRuntime(kSingleStepHandlerRuntimeEntry);
+  __ popq(RBX);
+  __ LeaveFrame();
+  __ Bind(&not_stepping);
+
   // RBX: IC data object (preserved).
   __ movq(R12, FieldAddress(RBX, ICData::ic_data_offset()));
   // R12: ic_data_array with entries: target functions and count.
   __ leaq(R12, FieldAddress(R12, Array::data_offset()));
   // R12: points directly to the first ic data array element.
   const intptr_t target_offset = ICData::TargetIndexFor(0) * kWordSize;
   const intptr_t count_offset = ICData::CountIndexFor(0) * kWordSize;
 
   // Increment count for this call.
   Label increment_done;
@@ skipping 442 matching lines @@
 }
 
 
 // Called only from unoptimized code. All relevant registers have been saved.
 // TOS + 0: return address
 // TOS + 1: right argument.
 // TOS + 2: left argument.
 // Returns ZF set.
 void StubCode::GenerateUnoptimizedIdenticalWithNumberCheckStub(
     Assembler* assembler) {
+  // Check single stepping.
+  Label not_stepping;
+  __ movq(RAX, FieldAddress(CTX, Context::isolate_offset()));
+  __ movzxb(RAX, Address(RAX, Isolate::single_step_offset()));
+  __ cmpq(RAX, Immediate(0));
+  __ j(EQUAL, &not_stepping, Assembler::kNearJump);
+  __ EnterStubFrame();
+  __ CallRuntime(kSingleStepHandlerRuntimeEntry);
+  __ LeaveFrame();
+  __ Bind(&not_stepping);
+
   const Register left = RAX;
   const Register right = RDX;
 
   __ movq(left, Address(RSP, 2 * kWordSize));
   __ movq(right, Address(RSP, 1 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ ret();
 }
 
 
@@ skipping 14 matching lines @@
   __ movq(right, Address(RSP, 3 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ popq(right);
   __ popq(left);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64