Question

我正在阅读杰夫的惊人书籍assembly step by step，我在第8章中他展示了一个汇编程序的例子，它以这种方式从用户那里获取文件：

SECTION .bss            ; Section containing uninitialized data

    BUFFLEN equ 1024    ; Length of buffer
    Buff:   resb BUFFLEN    ; Text buffer itself

它将文件文本读入Buff，并将ALL CAPS中该文本的版本输出到另一个文件。

我想在调试模式下运行该程序，逐步分析所有寄存器的情况。

我正在使用INSIGHT在ubuntu上运行它。

我是一个完全的初学者。我知道如何使用Insight来逐步完成，但用户运行此程序的方式是：

myProgram > outputfile.txt < inputfile.txt

如何在调试器中模仿这个？

这是完整的来源：

;  Executable name : uppercaser2
;  Version         : 1.0
;  Created date    : 3/25/2009
;  Last update     : 3/25/2009
;  Author          : Jeff Duntemann
;  Description     : A simple program in assembly for Linux, using NASM 2.05,
;    demonstrating simple text file I/O (through redirection) for reading an
;    input file to a buffer in blocks, forcing lowercase characters to 
;    uppercase, and writing the modified buffer to an output file.
;
;  Run it this way:
;    uppercaser2 > (output file) < (input file)  
;
;  Build using these commands:
;    nasm -f elf -g -F stabs uppercaser2.asm
;    ld -o uppercaser2 uppercaser2.o
;
SECTION .bss            ; Section containing uninitialized data

    BUFFLEN equ 1024    ; Length of buffer
    Buff:   resb BUFFLEN    ; Text buffer itself

SECTION .data           ; Section containing initialised data

SECTION .text           ; Section containing code

global  _start          ; Linker needs this to find the entry point!

_start:
    nop         ; This no-op keeps gdb happy...

; Read a buffer full of text from stdin:
read:
    mov eax,3       ; Specify sys_read call
    mov ebx,0       ; Specify File Descriptor 0: Standard Input
    mov ecx,Buff        ; Pass offset of the buffer to read to
    mov edx,BUFFLEN     ; Pass number of bytes to read at one pass
    int 80h         ; Call sys_read to fill the buffer
    mov esi,eax     ; Copy sys_read return value for safekeeping
    cmp eax,0       ; If eax=0, sys_read reached EOF on stdin
    je Done         ; Jump If Equal (to 0, from compare)

; Set up the registers for the process buffer step:
    mov ecx,esi     ; Place the number of bytes read into ecx
    mov ebp,Buff        ; Place address of buffer into ebp
    dec ebp         ; Adjust count to offset

; Go through the buffer and convert lowercase to uppercase characters:
Scan:
    cmp byte [ebp+ecx],61h  ; Test input char against lowercase 'a'
    jb Next         ; If below 'a' in ASCII, not lowercase
    cmp byte [ebp+ecx],7Ah  ; Test input char against lowercase 'z'
    ja Next         ; If above 'z' in ASCII, not lowercase
                ; At this point, we have a lowercase char
    sub byte [ebp+ecx],20h  ; Subtract 20h to give uppercase...
Next:   dec ecx         ; Decrement counter
    jnz Scan        ; If characters remain, loop back

; Write the buffer full of processed text to stdout:
Write:
    mov eax,4       ; Specify sys_write call
    mov ebx,1       ; Specify File Descriptor 1: Standard output
    mov ecx,Buff        ; Pass offset of the buffer
    mov edx,esi     ; Pass the # of bytes of data in the buffer
    int 80h         ; Make kernel call
    jmp read        ; Loop back and load another buffer full

; All done! Let's end this party:
Done:
    mov eax,1       ; Code for Exit Syscall
    mov ebx,0       ; Return a code of zero 
    int 80H         ; Make kernel call

Answer 1

听起来你想将进程附加到GDB。你可以试试这个。

shell$ gdb ./uppercaser2
  gdb> list
  gdb> break read
  gdb> run > ouput.txt < input.txt
  gdb> x/5i $eip

在shell提示符下，启动GDB并将uppercaser2附加到GDB。应加载调试符号，您可以使用列表来检查来源。通过行号或功能名称在所需位置创建断点。使用GDB的运行来启动输入和输出文件的程序。从这里，您可以使用GDB命令分析寄存器并逐步执行内存。

Answer 2

在运行命令中，您可以像这样设置用户输入：

shell$ gdb ./executable  
gdb> break main  
gdb> run user input

如何调试需要用户输入的NASM汇编程序？

2 个答案: