Let us determine the behavior of the instruction pushq %rsp for an x86-64 processor. We could try reading the Intel documentation on this instruction, but a simpler approach is to conduct an experiment on an actual machine. The C compiler would not normally generate this instruction, so we must use hand-generated assembly code for this task. Here is a test function we have written.

In our experiments, we find that function pushtest always returns 0. What does this imply about the behavior of the instruction pushq %rsp under x86-64?

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1 2 3 4 5 6 7 8 .text .globl pushtest pushtest: movq pushq popq subq ret %rsp, %rax %rsp %rdx %rdx, %rax Copy stack pointer Push stack pointer Pop it back Return 0 or 4