MSVC/GCC/NDK:将二进制文件生成obj文件

怼烎@ 2023-01-08 08:27 148阅读 0赞

如何将二进制文件作为数据添加到自己程序中?这是我最近遇到的问题,google上找到这两篇说得已经很清楚:

> [《Embedding of binary data into programs》][Embedding of binary data into programs]  
> [《Embedding Blobs in Binaries》][Embedding Blobs in Binaries]

一种方法是将想二进制文件生成c代码,与项目一起编译,这方法对于小数据没问题，但如果二进制文件太大，生成的c代码更是巨大,增加编译器负担，好处就是完全没有跨平台问题。网上可以找到相关的工具(搜索 `bin2c` 或 `bin2h`),比如这个[embed-resource][]

第二种方式就是用GNU的`objcopy`工具来实现。  
`objcopy`本身就提供了二进制数据转成obj文件的能力  
执行如下指令即可将 `file.bin` 生成 `elf32-i386` 格式的obj文件 `file.o`

objcopy -I binary -O elf32-i386 -B i386 file.bin file.o

另外GNU的`ld`也可以实现,

ld -r -b binary -o file.o file.bin

> 与`objcopy`不同,`ld`不需要指定输出格式,默认即为当前平台的obj格式,比如Windows平台下的MinGW ld则默认为`pe-x86-64`,NDK 的ld默认为`elf32-littlearm`  
> 可以通过执行 `ld --print-output-format` 显示`ld`默认的输出格式

# NDK #

在NDK(NDK 19c)下需要找到正确的ld或objcopy才行，  
之前我使用 `$android-ndk-r19c/toolchains/llvm/prebuilt\windows-x86_64/bin/x86_64-linux-android-objcopy`和`$android-ndk-r19c/toolchains/llvm/prebuilt\windows-x86_64/bin/llvm-objcopy`都不能生成结果。  
使用`$android-ndk-r19c/toolchains/arm-linux-androideabi-4.9/prebuilt/windows-x86_64/arm-linux-androideabi/bin/objcopy`和`$android-ndk-r19c/toolchains/llvm/prebuilt/windows-x86_64/arm-linux-androideabi/bin/objcopy`执行正常

如下执行NDK 的`objcopy`生成 `elf32-littlearm`格式的obj

:: 将ndk objcopy位置添加到搜索路径
    $ SET PATH=${android-ndk-r19c}/toolchains/arm-linux-androideabi-4.9/prebuilt/windows-x86_64/arm-linux-androideabi/bin;%PATH%
    
    $ objcopy -I binary -O elf32-littlearm -B arm fall.jpg fall_elf32_littlearm.o

或如下使用`ld`来生成obj文件

ld -r -b binary -o fall_elf32_littlearm.o fall.jpg

执行`objdump`查看

$ objdump -t -f fall_elf32_littlearm.o
    
    fall_elf32_littlearm.o:     file format elf32-littlearm
    architecture: arm, flags 0x00000010:
    HAS_SYMS
    start address 0x00000000
    
    SYMBOL TABLE:
    00000000 l    d  .data  00000000 .data
    00000000 g       .data  00000000 _binary_fall_jpg_start
    000085b9 g       .data  00000000 _binary_fall_jpg_end
    000085b9 g       *ABS*  00000000 _binary_fall_jpg_size

# MSVC #

msvc并没有提供类型GNU objcopy的命令行工具可以直接将二进制文件转为obj文件.怎么办？有两个解决方案：

*  如这篇文章中所说[《Embedding of binary data into programs》][Embedding of binary data into programs],在网上搜索 `bin2coff` 或`bin2obj`可以找到第三方的工具.比如这个github上的[bin2coff][](我没测试)。
 *  如果你已经安装了MinGW编译器,使用MinGW提供的`objcopy`或`ld`就可以生成MS COFF格式的obj文件了

如下生成MSVC所需的PE格式obj文件

objcopy -I binary -O pe-x86-64 -B i386 fall.jpg fall_pe-x86-64.obj

或如下使用`ld`来生成obj文件

ld -r -b binary -o fall_pe-x86-64.obj fall.jpg

执行`objdump`查看生成的fall\_pe-x86-64.obj

>objdump -t fall_pe-x86-64.obj
    
    fall_pe-x86-64.obj:     file format pe-x86-64
    
    SYMBOL TABLE:
    [  0](sec  1)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x0000000000000000 _binary_fall_jpg_start
    [  1](sec  1)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000000085b9 _binary_fall_jpg_end
    [  2](sec -1)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000000085b9 _binary_fall_jpg_size

也可执行MSVC的`dumpbin`查看生成的obj文件,可以确认生成的是MSVC格式obj

>dumpbin /symbols /headers fall_pe-x86-64.obj
    Microsoft (R) COFF/PE Dumper Version 14.00.24215.1
    Copyright (C) Microsoft Corporation.  All rights reserved.
    
    
    Dump of file fall_pe-x86-64.obj
    
    File Type: COFF OBJECT
    
    FILE HEADER VALUES
                8664 machine (x64)
                   1 number of sections
                   0 time date stamp
                85F8 file pointer to symbol table
                   3 number of symbols
                   0 size of optional header
                   5 characteristics
                       Relocations stripped
                       Line numbers stripped
    
    SECTION HEADER #1
       .data name
           0 physical address
           0 virtual address
        85B9 size of raw data
          3C file pointer to raw data (0000003C to 000085F4)
           0 file pointer to relocation table
           0 file pointer to line numbers
           0 number of relocations
           0 number of line numbers
    C0100040 flags
             Initialized Data
             1 byte align
             Read Write
    
    COFF SYMBOL TABLE
    000 00000000 SECT1  notype       External     | _binary_fall_jpg_start
    001 000085B9 SECT1  notype       External     | _binary_fall_jpg_end
    002 000085B9 ABS    notype       External     | _binary_fall_jpg_size
    
    String Table Size = 0x46 bytes
    
      Summary
    
            85B9 .data

# CMAKE #

习惯于使用cmake进行项目集成编译的人会想如何将生成obj的过程集成到cmake脚本中自动化执行。关于这个问题可以参考这篇文章 [《Embedding binary resources with CMake and C++11》][Embedding binary resources with CMake and C_11]  
我就是参考它来实现的

参考资料  
[《Embedding of binary data into programs》][Embedding of binary data into programs]  
[《Embedding Blobs in Binaries》][Embedding Blobs in Binaries]  
[《objcopy》][objcopy]  
[《llvm-objcopy - object copying and editing tool》][llvm-objcopy - object copying and editing tool]

[Embedding of binary data into programs]: https://www.devever.net/~hl/incbin
[Embedding Blobs in Binaries]: https://gareus.org/wiki/embedding_resources_in_executables
[embed-resource]: https://github.com/cyrilcode/embed-resource
[bin2coff]: https://github.com/robvinson/bin2coff
[Embedding binary resources with CMake and C_11]: https://beesbuzz.biz/code/4399-Embedding-binary-resources-with-CMake-and-C-11
[objcopy]: https://ftp.gnu.org/old-gnu/Manuals/binutils-2.12/html_chapter/binutils_3.html
[llvm-objcopy - object copying and editing tool]: https://releases.llvm.org/9.0.0/docs/CommandGuide/llvm-objcopy.html