组装MASM在memory上保存动态数组的正确方法

Question

Hello I want to save in memory an array of length and values defined by the users. Actually I'm storing the values inserted at "[ebp+8+esi*4]", so after the function arguments. Is that correct or what should I do? I though that local variables should placed at memory address below esp, so make space for local variables by decrementing esp. But I can't dynamically decrement "esp", so how should I do?

This is the code:

.686
.xmm
.model flat, C
OPTION CaseMap:None

include ../masm32/libs/windows.inc
include ../masm32/libs/kernel32.inc
include ../masm32/libs/user32.inc
include ../masm32/libs/msvcrt.inc
include ../masm32/libs/masm32.inc

EXTERN printf:PROC
EXTERN scanf:PROC

.data
    str_insert_array_length db  "Insert Array Length: ",0
    str_insert_value    db  10,"Insert Value: ",0
    str_input_format    db  "%d",0
    str_format_print db "%d",10,0

    input_length   DWORD    0
    input_value    DWORD    0

.code

main PROC
    push ebp
    mov ebp,esp

    push offset str_insert_array_length
    call printf
    add esp,4

    push offset input_length
    push offset str_input_format
    call scanf
    add esp,8
    
    xor edi,edi

get_array_values:

    push offset str_insert_value
    call printf
    add esp,4

    push offset input_value
    push offset str_input_format
    call scanf
    add esp,8

    mov eax,4
    mul edi
    sub esp,eax
    mov eax,[input_value]
    mov [esp], eax
    mov eax,[input_length]

    inc edi
    cmp edi,eax
    jne get_array_values


    mov edi,[input_length]
    xor esi,esi

print_array:
    mov edx,[esp+4*esi]
    push edx
    push offset str_format_print
    call printf
    add esp,8
    inc esi
    dec edi
    jnz print_array


    pop ebp
    invoke ExitProcess,0
main ENDP
    end

Answer 1

You can dynamically decrement sp. Just use a subtract instruction, like sub esp, eax , where you have established the amount of dynamic decrement in eax . If you do that the the new array starts at the address in esp .

The problem is that you can't compute the decrement amount until you know how many items are being input.

So. If you don't know how many items there will be until the user says to stop, then you can push individual items onto the stack as the are entered, but the resulting array will have the elements backward in nemory order — so, you can later either reverse them in place with a simple loop, or instead just choose to work with the backwards order, if the rest of the program is not too complicated.