Programming from the Ground Up

Know the Concepts

• What are primitives?

• What are calling conventions?

• What is the stack?

• How do pushl and popl affect the stack? What special-purpose register do they affect?

• What are local variables and what are they used for?

• Why are local variables so necessary in recursive functions?

• What are %ebp and %esp used for?

• What is a stack frame?

Use the Concepts

• Write a function called square which receives one argument and returns the square of that argument.

• Write a program to test your square function.

• Convert the maximum program given in the Section called Finding a Maximum Value in Chapter 3 so that it is a function which takes a pointer to several values and returns their maximum. Write a program that calls maximum with 3 different lists, and returns the result of the last one as the program's exit status code.

• Explain the problems that would arise without a standard calling convention.

Going Further

• Do you think it's better for a system to have a large set of primitives or a small one, assuming that the larger set can be written in terms of the smaller one?

• The factorial function can be written non-recursively. Do so.

• Find an application on the computer you use regularly. Try to locate a specific feature, and practice breaking that feature out into functions. Define the function interfaces between that feature and the rest of the program.

• Come up with your own calling convention. Rewrite the programs in this chapter using it. An example of a different calling convention would be to pass parameters in registers rather than the stack, to pass them in a different order, to return values in other registers or memory locations. Whatever you pick, be consistent and apply it throughout the whole program.

• Can you build a calling convention without using the stack? What limitations might it have?

• What test cases should we use in our example program to check to see if it is working properly?