Verification is usually performed on a high-level view of the software, either specification or program source code. However in certain circumstances verification is more relevant when performed at the machine code level.This paper focuses on automatic test data generation from a standalone executable. Low-level analysis is much more difficult than high-level analysis since even the control-flow graph is not available and bit-level instructions have to be modelled faithfully. We show how "path-based" structural test data generation can be adapted from structured language to machine code, using both state-of-the-art technologies and innovative techniques. Our results have been implemented in a tool named OSMOSE and encouraging experiments have been conducted.