How to strip more than symbols?

Question

I've noticed that, even after stripping symbols from my executable, class names and their methods are still included at the end of the executable file.

For instance:

#include <iostream>

using namespace std;

class Clingons
{
public:
    void clingForever()
    {
        cout << "Qapla" << endl;
    }
};

int main(int argc, char *argv[])
{
    Clingons cling;

    cling.clingForever();

    return 0;
}

Then compile and link with:

g++ cling.cpp -o cling

Now, when I look at the bottom of the resulting "cling" file with a hex editor, I can see the "Clingons" class name along with it's methods. I can also see this information while debugging..

even after I strip them:

strip -x cling

I can still see the same information.

So why wasn't this information stripped away when I used the command above? Is there a way to strip (or mangle) this information other than by hand?

The used version of GCC is i686-apple-darwin10-llvm-g++-4.2 (GCC) 4.2.1

This is just an example case. My real project involves the Qt framework.

score 4 · Accepted Answer · edited May 23 '17 at 12:37

4

It is possible that you are using RTTI. Try compiling your code with option -fno-rtti.

Update: It is really RTTI.

I don't know how exactly it works, but I succeeded to remove those strings as follows:

$ g++ -Xlinker -unexported_symbol -Xlinker "*" -o executable file.cpp
$ strip executable

(This was found at https://stackoverflow.com/questions/1931626/how-to-really-strip-a-binary-in-macos )

edited May 23 '17 at 12:37

Community

1

answered Jun 23 '14 at 05:51

w s

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Keep in mind that there are edge cases where RTTI may indeed be required at runtime, though. – 0xC0000022L Jun 23 '14 at 06:25
I know about this one (I commented on the accepted answer) but it doesn't seem to remove everything from my current Qt project. – Jun 24 '14 at 02:36
@Access Denied: RTTI is disabled by default on Qt libraries so I don't think disabling it would cause an issue. I tried disabling it via -fno-rtti and it didn't do anything. – Jun 24 '14 at 02:38
Upon further inspection, I realize that this solution does work. It does keep references to classes and functions in external libraries but nothing from my own code. – Jun 24 '14 at 02:53

score 2 · Answer 2 · answered Jun 23 '14 at 02:21

2

Try compiling your program as a static assembly, and strip it using the compiler. You won't find any 'cling' references in the resultant executable.

$ g++ -static -s cling.cpp -o cling

$ ls -l cling*
-rwxr-x--- 1 lornix lornix 1,313,792 Jun 22 19:19 cling*
-rw-r----- 1 lornix lornix       222 Jun 22 19:16 cling.cpp

$ strings -a cling | grep -ic cling
0

answered Jun 23 '14 at 02:21

lornix

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I tried your suggestion but it wouldn't build: can't locate file for: -lcrt0.o ... Also, my real project is using the Qt framework so I can't build static unless I purchase a commercial license. – Jun 24 '14 at 02:44

score 1 · Answer 3 · edited Apr 25 '22 at 16:50

1

The toolbox ELFKicker has an utility called sstrip that strip an ELF executable down to the bones.

But, it seems that you are using Mach-O executable format. So, I would recommend to look at the source code of sstrip and build your own stripper.

You can also take a look at the source code of the strip command for Mach-O and get inspiration. And, also, this Python script strip_save_dsym might also give some hints.

Finally, here are a few comparisons between ELF and Mach-O formats:

edited Apr 25 '22 at 16:50

Glorfindel

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answered Jun 23 '14 at 10:59

perror

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Although your answer doesn't provide an instant solution, it's bold and I like it a lot. Studying sstrip looks like fun and maybe I'll end up creating my own special tool for the job. – Jun 24 '14 at 03:04
1

Thanks, but I also totally agree with your choice of marking WS answer as the answer ! Mine is, at most, some complementary information about the topic. – perror Jun 24 '14 at 06:30

How to strip more than symbols?

3 Answers3