How to view symbols in object files?

Question

How can I view symbols in a .o file? nm does not work for me. I use g++/linux.

nm is exactly what you'd use. Can you explain how it doesn't work for you ? — nos, Oct 07 '10 at 10:57
I built the object file straight from a header where the implementation was. Does that have anything to do with this? — nakiya, Oct 07 '10 at 11:05
@nakiya You can't run an .o file. And if you compile a header file you produce precompiled headers with recent gcc versions, not object files. You should compile .cpp files not header files. — nos, Oct 07 '10 at 11:09
@nakiya: You cannot run it, you should really type the text "`file Lib1.o`" in your shell. The tool called `file` tells you the file type of Lib1.o, that is whether it really is an object file. I doubt it. — DarkDust, Oct 07 '10 at 11:10
Yep. :D. It says it's a precompiled header. I recompiled with implementation in a cpp file. — nakiya, Oct 07 '10 at 11:14

score 129 · Accepted Answer · answered Oct 07 '10 at 11:05

129

Instead of nm, you can use the powerful objdump. See the man page for details. Try objdump -t myfile or objdump -T myfile. With the -C flag you can also demangle C++ names, like nm does.

answered Oct 07 '10 at 11:05

DarkDust

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I tried ObjDump also. Same result : `objdump: Lib1.o: File format not recognized` – nakiya Oct 07 '10 at 11:07
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try `objdump -t Lib1.o` – mustafa Apr 23 '14 at 08:50

score 17 · Answer 2 · answered Oct 07 '10 at 11:35

Have you been using a cross-compiler for another platform? If so, you need to use the respective nm or objdump commmand.

For example, if you have used XXX-YYY-gcc to compile the .o file, you need to use XXX-YYY-nm or XXX-YYY-objdump to process the files.

score 7 · Answer 3 · answered Dec 30 '16 at 02:20

7

Just run: nm you_obj_file.o | c++filt

answered Dec 30 '16 at 02:20

uol3c

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score 4 · Answer 4 · answered Oct 07 '10 at 10:58

4

There is a command to take a look at which functions are included in an object file or library or executable:

nm

answered Oct 07 '10 at 10:58

Alok Save

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The OP stated directly that he cannot use `nm`. – ivan_pozdeev Mar 13 '16 at 21:31
1

@ivan_pozdeev While that's true, I imagine some people (me at least) come to this question from just searching how to view symbols in object files, and in my case `nm` worked perfectly for my needs, so I think this is a fine answer given the circumstances. – Newbyte Jan 26 '22 at 15:45

score 2 · Answer 5 · answered Sep 29 '18 at 01:59

You can use nm -C .o/lib/exe, for example:

xiongyu@ubuntu:~/tmp/build$ nm -C libfile1.a 

file1.cpp.o:
0000000000000000 T f()
0000000000000000 W int fun<int>(int)

using nm -C it will be more readable, if you just use nm:

xiongyu@ubuntu:~/tmp/build$ nm libfile1.a 

file1.cpp.o:
0000000000000000 T _Z1fv
0000000000000000 W _Z3funIiET_S0_

as we see it's not so readable.

Below is what my file1.cpp like:

xiongyu@ubuntu:~/tmp/build$ vi ../file1.cpp 
#include "head.h"
void f()  {
     int i = fun<int>(42);
}

How to view symbols in object files?

5 Answers5

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