Nit: struct padding and arithmetic promotion don't support this point. In practice, C compilers provide struct-packing extensions that cover the uncommon cases

Nit: struct padding and arithmetic promotion don't support this point. In practice, C compilers provide struct-packing extensions that cover the uncommon cases where default padding wouldn't yield the layout you want. And they'll let you opt-in to a style where arithmetic promotions are forced to be explicit as they are in e.g. Go. So it would usually be ridiculous to drop down to assembly for either of these reasons today.