| Index: dart/runtime/vm/stub_code_x64.cc
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| ===================================================================
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| --- dart/runtime/vm/stub_code_x64.cc	(revision 31530)
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| +++ dart/runtime/vm/stub_code_x64.cc	(working copy)
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| @@ -1912,6 +1912,23 @@
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|  }
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|  
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|  
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| +// Called only from unoptimized code.
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| +void StubCode::GenerateDebugStepCheckStub(Assembler* assembler) {
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| +  // Check single stepping.
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| +  Label not_stepping;
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| +  __ movq(RAX, FieldAddress(CTX, Context::isolate_offset()));
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| +  __ movzxb(RAX, Address(RAX, Isolate::single_step_offset()));
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| +  __ cmpq(RAX, Immediate(0));
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| +  __ j(EQUAL, ¬_stepping, Assembler::kNearJump);
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| +
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| +  __ EnterStubFrame();
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| +  __ CallRuntime(kSingleStepHandlerRuntimeEntry, 0);
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| +  __ LeaveStubFrame();
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| +  __ Bind(¬_stepping);
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| +  __ ret();
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| +}
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| +
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| +
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|  // Used to check class and type arguments. Arguments passed on stack:
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|  // TOS + 0: return address.
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|  // TOS + 1: instantiator type arguments (can be NULL).
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| 
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