golang获取packed struct的大小

typedef struct _PackageHeader
{
    int headerLen;
    int timeStamp;
    short cmd  
};

#pragma pack(1)

package main

import (
    "encoding/binary"
    "fmt"
)

type TestStruct struct {
    a uint32
    b int8
}

func main() {
    var testObject TestStruct
    size := binary.Size(testObject)

    fmt.Println(size)
}