This is just an overview and it might be not 100% accurate but hopefully you will find it helpful.
At build time Go linker will embed information about all types used by the application into the executable (https://github.com/golang/go/blob/master/src/runtime/symtab.go#L39)
Each interface value contains a pointer to the data type descriptor (https://github.com/golang/go/blob/master/src/runtime/type.go#L14)
During conversion from a type that is known at compile time to an interface value Go compiler will point type descriptor of this interface value to the concrete type descriptor (it is known at compile time!).
E.g. when you call
- an interface value is created by the compiler that references
- this interface value is passed to
reflect.TypeOffunction as argument
reflect.TypeOffunction uses type descriptor that has been stored by the linker in the executable to get the align (and other) information about uint type.