public final int getFileOffset() {
    if (fileOffset < 0) {
      throw new RuntimeException("fileOffset not set");
    }

    return fileOffset;
  }
Gets the offset from the start of the file to this part. This throws an exception if the offset
has not yet been set.

@return {@code >= 0;} the file offset
android/android_framework/dex-maker/src/main/java/com/android/dx/dex/file/Section.java