bad_stack.cpp

static std::int64_t stack[8];
static std::int64_t* sp = stack;

class BadStackMethodBuilder : public OMR::JitBuilder::MethodBuilder {
public:
	
	BadStackMethodBuilder(OMR::JitBuilder::TypeDictionary* t)
		: OMR::JitBuilder::MethodBuilder(t) {

			// SetReturnType(t->NoType);
		}

	virtual bool buildIL() override {

		/*
		
		push 0
		push 0
		if (pop) {
			push 1;
		} else {
			push 2;
		}

		*/

		OMR::JitBuilder::TypeDictionary* t = typeDictionary();

		DefineFunction("printf", "no-file", "0", (void*)&printf, NoType, 0);

		// Create State
		{
			auto reg = new OMR::JitBuilder::VirtualMachineRegister(
				this, "sp", t->PointerTo(t->pInt64), 8, ConstAddress(&sp)
			);

			auto stack = new OMR::JitBuilder::VirtualMachineOperandStack(
				this, 2, t->Int64, reg, true, 0
			);

			setVMState(stack);
		}

		// Create constants
		OMR::JitBuilder::IlValue* k0 = ConstInt64(0);
		OMR::JitBuilder::IlValue* k1 = ConstInt64(1);
		OMR::JitBuilder::IlValue* k2 = ConstInt64(2);

		// Create builders
		OMR::JitBuilder::BytecodeBuilder* b0 = OrphanBytecodeBuilder(0, (char*)"PushZeroTwice");
		OMR::JitBuilder::BytecodeBuilder* b1 = OrphanBytecodeBuilder(1, (char*)"ClearStackThenPushOneAndTwo");
		OMR::JitBuilder::BytecodeBuilder* b2 = OrphanBytecodeBuilder(2, (char*)"PrintStack");

		AppendBuilder(b0);

		// PushZeroTwice
		{
			OMR::JitBuilder::VirtualMachineOperandStack* stack = (OMR::JitBuilder::VirtualMachineOperandStack*)b0->vmState();
			stack->Push(b0, k0);
			stack->Push(b0, k0);
			b0->IfCmpEqualZero(b1, b0->ConstInt64(0)); // always taken
			b0->AddFallThroughBuilder(b2);
		}
	
		// ClearStackThenPushOneAndTwo
		{
			OMR::JitBuilder::VirtualMachineOperandStack* stack = (OMR::JitBuilder::VirtualMachineOperandStack*)b1->vmState();
			stack->Pop(b1);
			stack->Pop(b1);
			stack->Push(b1, k1);
			stack->Push(b1, k2);
			b1->AddFallThroughBuilder(b2);
		}

		// PrintStack
		{
			OMR::JitBuilder::VirtualMachineOperandStack* stack = (OMR::JitBuilder::VirtualMachineOperandStack*)b2->vmState();
			b2->Call("printf", 3,
				b2->Const((void*)"stack: a=%llu b=%llu\n"),
				stack->Pop(b2),
				stack->Pop(b2)
			);
			// error: we'll see "1" printed twice.
			b2->Return();
		}

		return true;
	}
};

TEST(MyBadStackTest, OverwriteTwoValuesWithOne) {
	BadStackMethodBuilder mb(new OMR::JitBuilder::TypeDictionary());
	void* fn = nullptr;
	compileMethodBuilder(&mb, &fn);
	reinterpret_cast<void(*)()>(fn)();
}