I'm reading "Computer Systems: A Programmer's Perspective, 3/E" (CS:APP3e) and the following code is an example from the book:

long call_proc() {
    long  x1 = 1;
    int   x2 = 2;
    short x3 = 3;
    char  x4 = 4;
    proc(x1, &x1, x2, &x2, x3, &x3, x4, &x4);
    return (x1 x2)*(x3-x4);
}

The book gives the assembly code generated by GCC:

long call_proc()
call_proc:
    ; Set up arguments to proc
    subq    $32, %rsp           ; Allocate 32-byte stack frame
    movq    $1, 24(%rsp)        ; Store 1 in &x1
    movl    $2, 20(%rsp)        ; Store 2 in &x2
    movw    $3, 18(%rsp)        ; Store 3 in &x3
    movb    $4, 17(%rsp)        ; Store 4 in &x4
    leaq    17(%rsp), %rax      ; Create &x4
    movq    %rax, 8(%rsp)       ; Store &x4 as argument 8
    movl    $4, (%rsp)          ; Store 4 as argument 7
    leaq    18(%rsp), %r9       ; Pass &x3 as argument 6
    movl    $3, %r8d            ; Pass 3 as argument 5
    leaq    20(%rsp), %rcx      ; Pass &x2 as argument 4
    movl    $2,