.text

# void task·swap(stack_ptr *old_sp, stack_ptr *new_sp);
# - assumes that -fomit-frame-pointer was specified.

.global task_swap
task_swap:
    # save context from machine registers to old_sp
    popq %rcx
    movq %rcx, 8(%rdi) # save return address
    pushq %rbx
    pushq %r12
    pushq %r13
    pushq %r14
    pushq %r15
    pushq %rbp
    movq %rsp, (%rdi)

    # load context from new_sp to machine registers
    movq (%rsi), %rsp
    popq %rbp
    popq %r15
    popq %r14
    popq %r13
    popq %r12
    popq %rbx

    # restore arg to its set value
    movq 16(%rsi), %rdi

    # Set up %rip and then go.
    pushq 8(%rsi)
    ret