Specifically the following argument patterns will be
supported:
```
   [-]<size>@<value>
   [-]<size>@<reg>
   [-]<size>@[<reg>]
   [-]<size>@[<reg>,<offset>]
```

I did not use std regex library as the old gcc (e.g. 4.8.5)
does not have a good support for it.
Signed-off-by: Yonghong Song <yhs@fb.com>