lesson 4, manipulating the stack

04-bootsector-stack/boot_sect_stack.asm

@@ -0,0 +1,42 @@
+mov ah, 0x0e
+
+mov bp, 0x8000 ; this is an address far away from 0x7c00 so that we don't get overwritten
+mov sp, bp
+
+push 'A'
+push 'B'
+push 'C'
+
+; to show how the stack grows downwards
+mov al, [0x7ffe] ; 0x8000 - 2
+int 0x10
+
+; however, don't try to access [0x8000] now, because it won't work
+; you can only access the stack top so, at this point, only 0x7ffe (look above)
+mov al, [0x8000]
+int 0x10
+
+
+; recover our characters using the standard procedure: 'pop'
+; We can only pop full words so we need an auxiliary register to manipulate
+; the lower byte
+pop bx
+mov al, bl
+int 0x10 ; prints C
+
+pop bx
+mov al, bl
+int 0x10 ; prints B
+
+pop bx
+mov al, bl
+int 0x10 ; prints A
+
+; data that has been pop'd from the stack is garbage now
+mov al, [0x8000]
+int 0x10
+
+
+jmp $
+times 510-($-$$) db 0
+dw 0xaa55