Better single stepping in VM debugger

runtime/vm/stub_code_mips.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_MIPS)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 1560 matching lines @@
   { Label ok;
     // Check that the IC data array has NumberOfArgumentsChecked() == num_args.
     // 'num_args_tested' is stored as an untagged int.
     __ lw(T0, FieldAddress(S5, ICData::num_args_tested_offset()));
     __ BranchEqual(T0, num_args, &ok);
     __ Stop("Incorrect stub for IC data");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
+
+  // Check single stepping.
+  Label not_stepping;
+  __ lw(T0, FieldAddress(CTX, Context::isolate_offset()));
+  __ lbu(T0, Address(T0, Isolate::single_step_offset()));
+  __ BranchEqual(T0, 0, &not_stepping);
+  // Call single step callback in debugger.
+  __ addiu(SP, SP, Immediate(-2 * kWordSize));
+  __ sw(S5, Address(SP, 1 * kWordSize));  // Preserve IC data.
+  __ sw(RA, Address(SP, 0 * kWordSize));  // Return address.
+  __ CallRuntime(kSingleStepHandlerRuntimeEntry);
+  __ lw(RA, Address(SP, 0 * kWordSize));
+  __ lw(S5, Address(SP, 1 * kWordSize));
+  __ addiu(SP, SP, Immediate(2 * kWordSize));
+  __ Bind(&not_stepping);
+
   // Load argument descriptor into S4.
   __ lw(S4, FieldAddress(S5, ICData::arguments_descriptor_offset()));
   // Preserve return address, since RA is needed for subroutine call.
   __ mov(T2, RA);
   // Loop that checks if there is an IC data match.
   Label loop, update, test, found, get_class_id_as_smi;
   // S5: IC data object (preserved).
   __ lw(T0, FieldAddress(S5, ICData::ic_data_offset()));
   // T0: ic_data_array with check entries: classes and target functions.
   __ AddImmediate(T0, Array::data_offset() - kHeapObjectTag);
@@ skipping 221 matching lines @@
   { Label ok;
     // Check that the IC data array has NumberOfArgumentsChecked() == 0.
     // 'num_args_tested' is stored as an untagged int.
     __ lw(T0, FieldAddress(S5, ICData::num_args_tested_offset()));
     __ beq(T0, ZR, &ok);
     __ Stop("Incorrect IC data for unoptimized static call");
     __ Bind(&ok);
   }
 #endif  // DEBUG
 
+  // Check single stepping.
+  Label not_stepping;
+  __ lw(T0, FieldAddress(CTX, Context::isolate_offset()));
+  __ lbu(T0, Address(T0, Isolate::single_step_offset()));
+  __ BranchEqual(T0, 0, &not_stepping);
+  // Call single step callback in debugger.
+  __ addiu(SP, SP, Immediate(-2 * kWordSize));
+  __ sw(S5, Address(SP, 1 * kWordSize));  // Preserve IC data.
+  __ sw(RA, Address(SP, 0 * kWordSize));  // Return address.
+  __ CallRuntime(kSingleStepHandlerRuntimeEntry);
+  __ lw(RA, Address(SP, 0 * kWordSize));
+  __ lw(S5, Address(SP, 1 * kWordSize));
+  __ addiu(SP, SP, Immediate(2 * kWordSize));
+  __ Bind(&not_stepping);
+
+
   // S5: IC data object (preserved).
   __ lw(T0, FieldAddress(S5, ICData::ic_data_offset()));
   // T0: ic_data_array with entries: target functions and count.
   __ AddImmediate(T0, Array::data_offset() - kHeapObjectTag);
   // T0: 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 473 matching lines @@
 }
 
 
 // Called only from unoptimized code. All relevant registers have been saved.
 // RA: return address.
 // SP + 4: left operand.
 // SP + 0: right operand.
 // Returns: CMPRES is zero if equal, non-zero otherwise.
 void StubCode::GenerateUnoptimizedIdenticalWithNumberCheckStub(
     Assembler* assembler) {
+  // Check single stepping.
+  Label not_stepping;
+  __ lw(T0, FieldAddress(CTX, Context::isolate_offset()));
+  __ lbu(T0, Address(T0, Isolate::single_step_offset()));
+  __ BranchEqual(T0, 0, &not_stepping);
+  // Call single step callback in debugger.
+  __ addiu(SP, SP, Immediate(-1 * kWordSize));
+  __ sw(RA, Address(SP, 0 * kWordSize));  // Return address.
+  __ CallRuntime(kSingleStepHandlerRuntimeEntry);
+  __ lw(RA, Address(SP, 0 * kWordSize));
+  __ addiu(SP, SP, Immediate(1 * kWordSize));
+  __ Bind(&not_stepping);
+
   const Register temp1 = T2;
   const Register temp2 = T3;
   const Register left = T1;
   const Register right = T0;
   // Preserve left, right.
   __ lw(left, Address(SP, 1 * kWordSize));
   __ lw(right, Address(SP, 0 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right, temp1, temp2);
   __ Ret();
 }
@@ skipping 23 matching lines @@
   __ lw(left, Address(SP, 1 * kWordSize));
   __ lw(temp2, Address(SP, 2 * kWordSize));
   __ lw(temp1, Address(SP, 3 * kWordSize));
   __ Ret();
   __ delay_slot()->addiu(SP, SP, Immediate(4 * kWordSize));
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS