使用printf在装配NASM中打印号码 [英] Printing a number in assembly NASM using printf

问题描述

一段时间以来，我一直在尝试使它打印12345.谁能提供我应该怎么做的提示?它将打印三行文本，然后在第四行上打印"age"，我猜这是第二行中堆栈中的剩余内容.

I've been trying to get this to print 12345 for a while now. Can anyone provide a hint as to what I should do? It will print the three lines of text, then on the fourth line prints "age", which I'm guessing is a remnant in the stack from line 2.

    bits 64
    global main
    extern printf

    section .text
main:
    ; function setup
    push    rbp
    mov     rbp, rsp
    sub     rsp, 32
    ;
    lea     rdi, [rel message]
    mov     al, 0
    call    printf
;above code correctly prints message

;where the issue lies
push rbp
mov rbp, rsp
;sub rsp, 32

mov rax, 12345
;push rax   
mov al,0
call printf


    ; function return
    mov     eax, 0
    add     rsp, 32
    pop     rbp
    ret

    section .data
message: db      'Lab 3 - Modified Hello program',0x0D,0x0a,'COSC2425 - Pentium assembly language',0x0D,0x0a,'Processed with NASM and GNU gcc',0x0D,0x0a
count   dq  12345

推荐答案

显然，您甚至都不知道printf的工作方式，这使得很难从汇编中调用它.

Apparently you don't even know how printf works which makes it hard to invoke it from assembly.

要打印数字，printf需要两个参数，即格式字符串和要打印的数字.例如:printf("%d\n", 12345).

To print a number, printf expects two arguments, a format string and the number to print of course. Example: printf("%d\n", 12345).

现在要将其转换为汇编，您显然需要声明该格式字符串，然后使用适当的约定传递这两个参数.

Now to turn that into assembly, you obviously need to declare that format string, and then pass both arguments using the appropriate convention.

由于您似乎正在使用sysv abi，​​因此这意味着前两个参数分别进入rdi和rsi.您似乎已经知道必须将al设置为零以表示未使用SSE寄存器.因此，相关部分可能如下所示:

Since you seem to be using sysv abi, this means the first two arguments go into rdi and rsi, respectively. You already seem to know you have to zero al to indicate no SSE registers used. As such, the relevant part could look like:

lea rdi, [rel fmt]
mov rsi, 12345 ; or mov rsi, [count]
mov al, 0
call printf
...
fmt: db "%d", 0x0a, 0

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