Fragile Binary Interface Problem - Cause

Cause

The problem occurs due to a "shortcut" used with compilers for many common object-oriented (OO) languages, a design feature that was kept when OO languages were evolving from earlier non-OO structured programming languages such as C and Pascal.

In these languages there were no objects in the modern sense, but there was a similar construct known as a record (or "struct" in C) that held a variety of related information in one piece of memory. The parts within a particular record were accessed by keeping track of the starting location of the record, and knowing the offset from that starting point to the part in question. For instance a "person" record might have a first name, last name and middle initial, to access the initial the programmer writes thisPerson.middleInitial which the compiler turns into something like a = location(thisPerson) + offset(middleInitial). Modern CPUs typically include instructions for this common sort of access.

When object-oriented language compilers were first being developed, much of the existing compiler technology was used, and objects were built on top of the record concept. In these languages the objects were referred to by their starting point, and their public data, known as "fields", were accessed through the known offset. In effect the only change was to add another field to the record, one that lists the various methods (functions), such that the record knows about both its data and functions. When compiled, the offsets are used to access both the data and the code.