How to write informations needed in an executable file

I wanted to know if you knew a command or a way to write as comment or string inside of the executable file. Indeed I already did this, with XLC compiler I did it with the #pragma comment(user, "string") however now I have to change to GCC but there's a problem, under GCC this #pragma is not recognized.

My question is, do you know another #pragma who can do it under gcc, or just another way to process to recover an information written in the executable file when I compile.

Thanks, Ežekiel

Solution

Here is a quick solution.String literals in a c/c++ program, are usually put into the read-only segment of the ELF file.

Assuming that your comment follows a pattern:

My_Comment: ....

you could add some string definitions in your program:

#include <stdio.h>

void main() {

    char* a = "My Comment: ...";
}

compile:

$ gcc test.c

and then search for your comment pattern in the executable:

$ strings a.out | grep Comment
My Comment: ...

may I ask what is the use case of embedding comments into an executable?

Follow up:

If you are compiling with the -O3 flag, this unused string is optimized out, so it is not stored at all in the ro data. Based on the same idea, you could fool gcc by:

#include <stdio.h>

void main() {

    FILE* comment = fopen("/dev/null", "w");
    fprintf(comment, "My Comment:");
}

Then search for your comment. You get the overhead of 2 or 3 system calls of course, but hopefully you can live with it.

Let me know if this works!