如何通过pyelftools保存修改的ELF [英] how to save modified ELF by pyelftools

问题描述

最近，我对ELF文件结构感兴趣。在网上搜索时，我发现了一个名为 pyelftools 的出色脚本。但是实际上我不知道保存修改后的ELF的方法； ELFFile类没有任何方法。

Recently I've been interested in ELF File Structure. Searching on web, I found an awesome script named pyelftools. But in fact I didn't know the way to save the modified ELF; ELFFile class doesn't have any method to do.

首先，我的操作如下：

            header = self.elf.header
            self._emitline("%s" % header['e_shnum'])
            header['e_shnum'] = 30
            self._emitline("%s" % header['e_shnum'])

是的，糟糕的方法。但是可悲的是，我不知道在ELF文件中得到e_shnum的偏移量。有没有人能教我？

Yeah, that's poor way. But sadly I have no idea getting an offset of e_shnum in the ELF file. Is there anybody able to teach me?

问候，

Rex。

推荐答案

根据作者@ eli-bendersky，pyelftools是用于解析和分析ELF / DWARF文件的模块，并且没有直接修改它们的方法。我看了看模块的源文件，也找不到任何编辑/保存的方法。

According to the author @eli-bendersky, pyelftools is a module for parsing and analyzing ELF/DWARF files and it has no direct way of modifying them. I had a look at the module source files and could not find any methods to edit/save either.

在介绍性帖子的评论作者承认pyelftools具有没有API级别的支持来执行此操作，但进行一些修补可以帮助您实现所需的功能。

On the introductory post, within comments author acknowledges that pyelftools has no API-level support to do this but some tinkering around can help achieve what you need.

如果pyelftools不是硬依赖项，则以下示例说明了如何使用 elffile ：

If pyelftools is not a hard dependency, here's an example on how to do the same using elffile:

import elffile

eo = elffile.open(name="/bin/ls")
eo.fileHeader.shnum = 30
with open('./ls.bin', 'wb') as f: f.write(eo.pack())

使用readelf，可以验证更改是否正确保存：

Using readelf, you can verify that changes were saved correctly:

readelf -h ls.bin 
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Intel 80386
  Version:                           0x1
  Entry point address:               0x804be34
  Start of program headers:          105068 (bytes into file)
  Start of section headers:          103948 (bytes into file)
  Flags:                             0x0
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         9
  Size of section headers:           40 (bytes)
  Number of section headers:         30
  Section header string table index: 27
readelf: Error: Unable to read in 0x708 bytes of section headers

关于elffile的文档并不多，但是您可以看一下找出并复制复制pyelftools特定功能的方法。如果不行，您可以尝试同时使用pyelftools和elffile来读取/分析任务，并使用elffile编辑节和编写更改。

There's not much documentation on elffile but you can have a look at the source and figure out ways to replicate pyelftools-specific functionality. If that doesn't work, you can try using both pyelftools for reading/analyzing tasks and elffile to edit sections and write changes.

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