I'll keep this in bullet form to be brief:

• Implement a stack in your favorite language (I used C++).
• How are arguments passed in C? (Where? What order?)
• How does virtual memory work? Went into some detail on what happens on Linux when a page fault occurs.
• How would you get the address of a field in a C struct?
• Write a method to find the in-order successor in a binary tree.
• Debug this method in GDB.
• What is the Big O complexity of this code?
• Other computer science questions I can't recall.

Essentially, you should know stacks, trees, heaps, and other data structures, as well as basic sorting, searching, and optimization algorithms.

How are programs and data typically organized in memory? Draw a diagram (i.e., DATA, BSS, heap, stack).

I hadn't thought about this for a while, but I still got 90% of the answer correct.