问题
I have a main.c function which has the following statement:
int initarr(int**arr, int n, int (*initfunc)(int));
Then I call the function in c like that:
success = initarr(&arr, n, getNum);
The question is, in assembly code, in MODEL SMALL, the first argument in the function above will be in the memory as WORD or DWORD?
In other words, when I write the code, will this work:
PUSH BP
MOV BP,SP
PUSH DI
MOV DI, WORD PTR[BP+4] ; DI will hold &arr.
And now DI will hold arr's address.
If it is true, How will I be able to access arr[0]'s value if so?
PUSH BP
MOV BP,SP
PUSH DI
PUSH BX
MOV DI, WORD PTR[BP+4]
MOV BX, WORD PTR[DI]
Will BX hold the address of the array? I mean, the address of the first cell?
If so, how can I access arr[0] now?
Perhaps MOV DX, WORD PTR[BX] ?
回答1:
In model small, addresses are sized 2 bytes. A double pointer is still an address!
in order to access arr[0], you would write the following:
MOV DI, [BP+4] ; no need casting, DI register is sized 2 bytes.
MOV SI, [DI] ; get what DI is pointing to, and put it to SI.
; you could say: DI=arr[][], SI = arr[]
MOV AX, [SI] ; now AX = arr[0]
if we would like to access arr[i], we would do the following:
MOV DI, [BP+4]
MOV SI, [DI]
MOV AX, i
SHL AX, 1 ; because arr[] contains int numbers which are sized 2 bytes.
ADD SI, AX
MOV AX, [SI] ; now AX = arr[i]. SI = &arr[i].
来源：https://stackoverflow.com/questions/37365841/how-do-i-access-double-pointer-from-c-code-in-asms-stack