c - Access command line arguments without using char **argv in main

Question

Is there any way to access the command line arguments, without using the argument to main? I need to access it in another function, and I would prefer not passing it in.

I need a solution that only necessarily works on Mac OS and Linux with GCC.

Answer 1

I don't know how to do it on MacOS, but I suspect the trick I will describe here can be ported to MacOS with a bit of cross-reading.

On linux you can use the so called ".init_array" section of the ELF binary, to register a function which gets called during program initilization (before main() is called). This function has the same signature as the normal main() function, execept it returns "void". Thus, you can use this function to remember or process argc, argv[] and evp[].

Here is some code you can use:

static void my_cool_main(int argc, char* argv[], char* envp[])
{
    // your code goes here
}

__attribute__((section(".init_array"))) void (* p_my_cool_main)(int,char*[],char*[]) = &my_cool_main;

PS: This code can also be put in a library, so it should fit your case. It even works, when your prgram is run with valgrind - valgrind does not fork a new process, and this results in /proc/self/cmdline showing the original valgrind command-line.

PPS: Keep in mind that during this very early program execution many subsystem are not yet fully initialized - I tried libc I/O routines, they seem to work, but don't rely on it - even gloval variables might not yet be constructed, etc...