CODEWITHSUNDEEP
c++windowscompilationobject-files
Leandro
Leandro

Reputation: 183

It is possible to read an object file?

I was curious about .obj files: I pretty much don't know what they are (or what they contain), so I opened them with Vim text editor and what I found inside was an Alien like language...

Is there any way to understand what they represent and what is their content Also, for what are they being used?

Upvotes: 14

Views: 22909

Answers (3)

Abyx
Abyx

Reputation: 12918

The .obj files used by link.exe has MS COFF format.

You can find "Microsoft PE and COFF Specification" here, and parse .obj file according to it.

Or, you can use existing tool like dumpbin.

Upvotes: 7

sarnold
sarnold

Reputation: 104020

The readelf tool is good at showing you some details on the data:

$ readelf -a /usr/bin/readelf
ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Advanced Micro Devices X86-64
...

Some of its abilities to inspect specific sections of the executable can come in handy too:

$ readelf -p .rodata /usr/bin/readelf | more

String dump of section '.rodata':
  [     4]  R_IA64_IMM14
  [    11]  R_IA64_NONE
  ...
  [  1f58]    Personality routine: 
  [  1f70]  __gcc_personality_v0
  [  1f85]  __gxx_personality_v0
  [  1f9a]  __gcj_personality_v0
  [  1faf]  __gnu_objc_personality_v0
  ...

Actually disassembling the code is a bit of a stretch; if you compile your code with -g for debugging symbols, you can use readelf --debug-dump to read the program source, type information, etc.

Upvotes: 5

paulsm4
paulsm4

Reputation: 121599

Sure.

But every different platform has a different object format. On Windows, you could use a tool like dumpbin (dumpbin comes with Visual Studio). On Linux, you could use "dumpobj", or disassemble the program.

Here's a good link for Linux:

http://www.linuxjournal.com/article/1060

PS: objdump also lets you disassemble the object. Like you used to be able to do with "debug" on DOS PCs...

Upvotes: 10

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