Better single stepping in VM debugger

runtime/vm/stub_code_arm.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_ARM)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 1381 matching lines @@
     // Check that the IC data array has NumberOfArgumentsChecked() == num_args.
     // 'num_args_tested' is stored as an untagged int.
     __ ldr(R6, FieldAddress(R5, ICData::num_args_tested_offset()));
     __ CompareImmediate(R6, num_args);
     __ b(&ok, EQ);
     __ Stop("Incorrect stub for IC data");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
+  // Check single stepping.
+  Label not_stepping;
+  __ ldr(R6, FieldAddress(CTX, Context::isolate_offset()));
+  __ ldrb(R6, Address(R6, Isolate::single_step_offset()));
+  __ CompareImmediate(R6, 0);
+  __ b(&not_stepping, EQ);
+  __ EnterStubFrame();
+  __ Push(R5);  // Preserve IC data.
+  __ CallRuntime(kSingleStepHandlerRuntimeEntry);
+  __ Pop(R5);
+  __ LeaveStubFrame();
+  __ Bind(&not_stepping);
+
   // Load arguments descriptor into R4.
   __ ldr(R4, FieldAddress(R5, ICData::arguments_descriptor_offset()));
   // Preserve return address, since LR is needed for subroutine call.
   __ mov(R8, ShifterOperand(LR));
   // Loop that checks if there is an IC data match.
   Label loop, update, test, found, get_class_id_as_smi;
   // R5: IC data object (preserved).
   __ ldr(R6, FieldAddress(R5, ICData::ic_data_offset()));
   // R6: ic_data_array with check entries: classes and target functions.
   __ AddImmediate(R6, R6, Array::data_offset() - kHeapObjectTag);
@@ skipping 195 matching lines @@
     // Check that the IC data array has NumberOfArgumentsChecked() == 0.
     // 'num_args_tested' is stored as an untagged int.
     __ ldr(R6, FieldAddress(R5, ICData::num_args_tested_offset()));
     __ CompareImmediate(R6, 0);
     __ b(&ok, EQ);
     __ Stop("Incorrect IC data for unoptimized static call");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
+  // Check single stepping.
+  Label not_stepping;
+  __ ldr(R6, FieldAddress(CTX, Context::isolate_offset()));
+  __ ldrb(R6, Address(R6, Isolate::single_step_offset()));
+  __ CompareImmediate(R6, 0);
+  __ b(&not_stepping, EQ);
+  __ EnterStubFrame();
+  __ Push(R5);  // Preserve IC data.
+  __ CallRuntime(kSingleStepHandlerRuntimeEntry);
+  __ Pop(R5);
+  __ LeaveStubFrame();
+  __ Bind(&not_stepping);

[siva, 2013/07/01 17:04:48]

why not abstract this into a private function
StubCode::CheckForSingleStepping(Register tmp, bool preserve_ic_data);
Would avoid code duplication.

Here and in the other targets too.

[hausner, 2013/08/09 09:59:02]

I'll do that in a separate checkin once I add more places where we do this
check. Good idea.

+
   // R5: IC data object (preserved).
   __ ldr(R6, FieldAddress(R5, ICData::ic_data_offset()));
   // R6: ic_data_array with entries: target functions and count.
   __ AddImmediate(R6, R6, Array::data_offset() - kHeapObjectTag);
   // R6: 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 416 matching lines @@
 }
 
 
 // Called only from unoptimized code. All relevant registers have been saved.
 // LR: return address.
 // SP + 4: left operand.
 // SP + 0: right operand.
 // Return Zero condition flag set if equal.
 void StubCode::GenerateUnoptimizedIdenticalWithNumberCheckStub(
     Assembler* assembler) {
+  // Check single stepping.
+  Label not_stepping;
+  __ ldr(R1, FieldAddress(CTX, Context::isolate_offset()));
+  __ ldrb(R1, Address(R1, Isolate::single_step_offset()));
+  __ CompareImmediate(R1, 0);
+  __ b(&not_stepping, EQ);
+  __ EnterStubFrame();
+  __ CallRuntime(kSingleStepHandlerRuntimeEntry);
+  __ LeaveStubFrame();
+  __ Bind(&not_stepping);
+
   const Register temp = R2;
   const Register left = R1;
   const Register right = R0;
   __ ldr(left, Address(SP, 1 * kWordSize));
   __ ldr(right, Address(SP, 0 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ Ret();
 }
 
 
@@ skipping 13 matching lines @@
   __ ldr(left, Address(SP, 4 * kWordSize));
   __ ldr(right, Address(SP, 3 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp);
   __ PopList((1 << R0) | (1 << R1) | (1 << R2));
   __ Ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM