[SPCA] Improve Stack section

semester3/spca/code-examples/01_asm/06_factorial.s

@@ -0,0 +1,12 @@
+factorial:
+    pushq %rbx              # Preserve frame pointer
+    movl %edi, %ebx     
+    movl $1, %eax
+    cmpl $1, %edi
+    jle .QUIT               # Base case reached: quit
+    leal -1(%rdi), %edi     # Prepare args for next function call
+    call factorial
+    imull %ebx, %eax        # Use result of function call
+.QUIT:
+    popq %rbx               # Restore frame pointer
+    ret