CSC448: Code Generation: Run-Time Environment VI [59/133]

Procedures and functions communicate by passing arguments and return values.

There are several calling conventions in common use on x86, but we will use the following convention:

• Arguments are pushed onto the stack in reverse order by the caller. From the point of view of the callee, the arguments are at the top of the callee's activation record.
• The caller is responsible for removing the arguments from the stack.
• Results are returned in the general purpose register eax. There are other general purpose registers: ebx, ecx, edx.

For example, f(1,2,3) might compile to:

pushl $3
pushl $2
pushl $1
call f
addl $12, %esp

Note that the activation record of the caller grows temporarily before the call (as arguments are pushed onto the stack), and shrinks after the call (when the stack pointer is moved upwards).

The arguments are reversed to allow procedures or functions with a variable number of arguments.