debugging mxnet c++ operator (apache#4926)

example/python-howto/README.md

@@ -2,3 +2,34 @@ Python Howto Examples
 =====================
 * [Configuring Net to get Multiple Ouputs](multiple_outputs.py)
 * [Configuring Image Record Iterator](data_iter.py)
+* Set break point in C++ code of the symbol using gdb under Linux:
+
+	* 	Build mxnet with following values:
+
+		 ```
+		 	DEBUG=1 
+		 	CUDA=0 #to make sure convolution-inl.h will be used 
+		 	CUDNN=0 #to make sure convolution-inl.h will be used 
+		 ```
+		 
+	*  run python under gdb:  ```gdb --args python debug_conv.py```
+	*  in gdb set break point on particular line of the code and run execution: 
+
+		```
+(gdb) break src/operator/convolution-inl.h:120
+(gdb) run
+Breakpoint 1, mxnet::op::ConvolutionOp<mshadow::cpu, float>::Forward (this=0x12219d0, ctx=..., in_data=std::vector of length 3, capacity 4 = {...}, req=std::vector of length 1, capacity 1 = {...}, out_data=std::vector of length 1, capacity 1 = {...},
+    aux_args=std::vector of length 0, capacity 0) at src/operator/./convolution-inl.h:121
+121	               data.shape_[1] / param_.num_group * param_.kernel[0] * param_.kernel[1]);
+(gdb) list
+116	    }
+117	    Tensor<xpu, 4, DType> data = in_data[conv::kData].get<xpu, 4, DType>(s);
+118	    Shape<3> wmat_shape =
+119	        Shape3(param_.num_group,
+120	               param_.num_filter / param_.num_group,
+121	               data.shape_[1] / param_.num_group * param_.kernel[0] * param_.kernel[1]);
+122	    Tensor<xpu, 3, DType> wmat =
+123	        in_data[conv::kWeight].get_with_shape<xpu, 3, DType>(wmat_shape, s);
+124	    Tensor<xpu, 4, DType> out = out_data[conv::kOut].get<xpu, 4, DType>(s);
+125	#if defined(__CUDACC__)
+		```

example/python-howto/debug_conv.py

@@ -0,0 +1,22 @@
+import mxnet as mx
+
+data_shape = (1,3,5,5)
+class SimpleData(object):
+
+    def __init__(self, data):
+        self.data = data
+
+data = mx.sym.Variable('data')
+conv = mx.sym.Convolution(data=data, kernel=(3,3), pad=(1,1), stride=(1,1), num_filter=1)
+mon = mx.mon.Monitor(1)
+
+
+mod = mx.mod.Module(conv)
+mod.bind(data_shapes=[('data', data_shape)])
+mod._exec_group.install_monitor(mon)
+mod.init_params()
+
+input_data = mx.nd.ones(data_shape)
+mod.forward(data_batch=SimpleData([input_data]))
+res = mod.get_outputs()[0].asnumpy()
+print(res)