在 x86 程序集中打印十六进制值 [英] Printing hex values in x86 assembly

问题描述

我需要制作一个将内存地址转换为字节串的例程.然后，该字符串将成为打印以空字符结尾的字符串(我已经能够创建)的函数的输入.例如，如果我有一个地址 0x1bf9，我需要将文本1bf9"打印到屏幕上.这本书还没有进入 32 位模式，但它暗示我们也需要它.这是我目前所拥有的:

I need to make a routine that will convert a memory address into a string of bytes. That string would then be the input for a function that prints null-terminated strings (which I was already able to make). For example, if I have an address 0x1bf9 I need to print the text "1bf9" to the screen. The book hasn't gone into 32 bit mode yet, but it kind of hinted that we would need it for that too. This is what I have so far:

TABLE:
db "0123456789ABCDEF", 0

STRING:
db 0

hex_to_char:
    lea bx, TABLE
    mov ax, dx

    mov ah, al ;make al and ah equal so we can isolate each half of the byte
    shr ah, 4 ;ah now has the high nibble
    and al, 0x0F ;al now has the low nibble
    xlat ;lookup al's contents in our table
    xchg ah, al ;flip around the bytes so now we can get the higher nibble 
    xlat ;look up what we just flipped
    inc STRING
    mov [STRING], ah ;append the new character to a string of bytes
    inc STRING
    mov [STRING], al ;append the new character to the string of bytes

    ret

推荐答案

这试图增加文字标签，这是不正确的.此外，您的 STRING 内存位置仅分配一个字节 (char) 而不是更大的数字来容纳您想要的字符串大小.

This attempts to increment a literal label, which isn't correct. Also, your STRING memory location only allocates one byte (char) instead of a larger number to accommodate the size of string you intend.

STRING:
    db 0

    inc STRING   ;THIS WON'T WORK
    mov [STRING], ah ;append the new character to a string of bytes
    inc STRING   ;THIS WON'T WORK
    mov [STRING], al ;append the new character to the string of bytes

中性评论:用于xlat的字符表不需要以零结尾.

A neutral comment: the character table used for xlat does not need to be zero terminated.

此外，我建议保存和恢复一些寄存器作为良好的 asm 编程实践.这样，调用函数就不需要担心寄存器在背后"被更改.最终，您可能想要这样的东西:

Also I'd recommend saving and restoring some registers as good asm programming practice. That way, the calling function doesn't need to worry about registers being changed "behind its back". Ultimately then, you probably want something like this:

TABLE:
    db "0123456789ABCDEF", 0

hex_to_char:
    push bx

    mov   bx, TABLE
    mov   ax, dx

    mov   ah, al            ;make al and ah equal so we can isolate each half of the byte
    shr   ah, 4             ;ah now has the high nibble
    and   al, 0x0F          ;al now has the low nibble
    xlat                    ;lookup al's contents in our table
    xchg  ah, al            ;flip around the bytes so now we can get the higher nibble 
    xlat                    ;look up what we just flipped

    mov   bx, STRING
    xchg  ah, al
    mov   [bx], ax          ;append the new character to the string of bytes

    pop bx
    ret

    section .bss

STRING:
    resb  50                ; reserve 50 bytes for the string

根据 Peter Cordes 的输入进行了一些理想的调整.

some desirable tweaks based upon Peter Cordes' input.

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