We present the design and implementation of a framework for flexible and
safe dynamic linking of native code. Our approach extends Typed Assembly
Language with a primitive for loading and typechecking code, which is
flexible enough to support a variety of linking strategies, but simple
enough that it does not significantly expand the trusted computing base.
Using this primitive, along with the ability to compute with types, we
show that we can program many existing dynamic linking approaches.
As a concrete demonstration, we have used our framework to implement
dynamic linking for a type-safe dialect of C, closely modeled after the
standard linking facility for Unix C programs. Aside from the unavoidable
cost of verification, our implementation performs comparably with the
standard, untyped approach.