GIN index

Hi:I created a new variable-length data type, and now I want to create a GIN index for it. According to the rules of GIN index, I created three functions: extractValue, extractQuery, and compare. I made sure that the return value of the first two functions is the address of the array, but when using the index query, the GIN tuple data obtained by calling PG_GETARG_DATUM in the compare function is incorrect, and it is misplaced! In memory the size of the data header becomes something else, and the position of the first byte is not the header, it becomes the fourth byte. So there is a high probability that the function called is wrong or my return value is wrong when creating the index or the error is somewhere else? 

regards!