linux - 如何逐步调试没有符号或部分的程序集二进制文件？

Question

考虑以下 NASM 代码:

  BITS 32

                org     0x08048000

  ehdr:                                                 ; Elf32_Ehdr
                db      0x7F, "ELF", 1, 1, 1, 0         ;   e_ident
        times 8 db      0
                dw      2                               ;   e_type
                dw      3                               ;   e_machine
                dd      1                               ;   e_version
                dd      _start                          ;   e_entry
                dd      phdr - $$                       ;   e_phoff
                dd      0                               ;   e_shoff
                dd      0                               ;   e_flags
                dw      ehdrsize                        ;   e_ehsize
                dw      phdrsize                        ;   e_phentsize
                dw      1                               ;   e_phnum
                dw      0                               ;   e_shentsize
                dw      0                               ;   e_shnum
                dw      0                               ;   e_shstrndx

  ehdrsize      equ     $ - ehdr

  phdr:                                                 ; Elf32_Phdr
                dd      1                               ;   p_type
                dd      0                               ;   p_offset
                dd      $$                              ;   p_vaddr
                dd      $$                              ;   p_paddr
                dd      filesize                        ;   p_filesz
                dd      filesize                        ;   p_memsz
                dd      5                               ;   p_flags
                dd      0x1000                          ;   p_align

  phdrsize      equ     $ - phdr

  _start:

                xor     eax, eax ;now just return to system with ebx
                inc     eax
                int     0x80


  ; your program here

  filesize      equ     $ - $$

如何调试这样结构的程序？最可取的是，我正在寻找一个 GDB 解决方案，它可以让我分步运行汇编指令，允许在每一步预览寄存器。下面是当我想在那里设置基于内存的断点时发生的情况:

[localhost.localdomain][/tmp] $ gdb ./a.out 
GNU gdb (GDB) Fedora (7.5.1-37.fc18)
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /tmp/a.out...(no debugging symbols found)...done.
(gdb) break 0x08048054
No symbol table is loaded.  Use the "file" command.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb) list breakpoints
No symbol table is loaded.  Use the "file" command.

Answer 1

在您的示例中，在特定地址设置断点的命令应该是 break *0x08048054。对于二进制文件的单步执行，您可以使用 stepi(步进指令)命令。