Thread: How do you exclude libc using gcc?

Hello. I searched the FAQ and the forums for "libc" and did not come across anything relevant.

Perhaps someone knows of a flag to pass to gcc so that libc is not included with your code?

I am aware that libc is the standard C library which most people use, but I am not using it in some of my programs, so, no need to include it in the executable if it isn't in use (just bloats it out).

There must be some way to exclude libc from getting compiled in with your code.

Just man gcc

Code:

       -nostartfiles
           Do not use the standard system startup files when linking.  The
           standard system libraries are used normally, unless -nostdlib or
           -nodefaultlibs is used.

       -nodefaultlibs
           Do not use the standard system libraries when linking.  Only the
           libraries you specify will be passed to the linker.  The standard
           startup files are used normally, unless -nostartfiles is used.  The
           compiler may generate calls to memcmp, memset, and memcpy for Sys-
           tem V (and ISO C) environments or to bcopy and bzero for BSD envi-
           ronments.  These entries are usually resolved by entries in libc.
           These entry points should be supplied through some other mechanism
           when this option is specified.

       -nostdlib
           Do not use the standard system startup files or libraries when
           linking.  No startup files and only the libraries you specify will
           be passed to the linker.  The compiler may generate calls to mem-
           cmp, memset, and memcpy for System V (and ISO C) environments or to
           bcopy and bzero for BSD environments.  These entries are usually
           resolved by entries in libc.  These entry points should be supplied
through some other mechanism when this option is specified.

           One of the standard libraries bypassed by -nostdlib and -nodefault-
           libs is libgcc.a, a library of internal subroutines that GCC uses
           to overcome shortcomings of particular machines, or special needs
           for some languages.
           In most cases, you need libgcc.a even when you want to avoid other
           standard libraries.  In other words, when you specify -nostdlib or
           -nodefaultlibs you should usually specify -lgcc as well.  This
           ensures that you have no unresolved references to internal GCC
           library subroutines.  (For example, __main, used to ensure C++ con-
           structors will be called.)

Thanks man!

now I've got some another problem (the linker giving errors of undefined _mainCRTStartup) and I've tried both -D_mainCRTStartup=WinMain and -DmainCRTStartup=WinMain to no avail

Originally Posted by quzah

WinMain? Why are you trying to compile a Windows application with GCC?

Quzah.

I am using MSYS and MingW on Windows to compile Windows applications using gcc. Reason?--because I want to be able to actually sell programs I make (legally) and because I cannot afford the high prices of, for example, Microsoft's Visual C++ Professional edition (required if you want to legally sell code you compile with it).

I can use gcc to make commercial applications if I want to, plus expenses to me are $0

Okay, I've gotten some success with the following.
crtmaintest.c

Code:

#include <windows.h>
int mainCRTStartup(int argc, char* argv[]){
    MessageBox(NULL,"Hello","hello",MB_OK);
    return 0;
}

then compile with

gcc -nostdlib -mwindows -o crtmaintest.exe crtmaintest.c -luser32

and then

strip -s crtmaintest.exe

This produces a smallest executable with only my own code in it and none of the libc and it links correctly and the resulting executable runs correctly. My only concern is maybe if I've gotten the signature of _mainCRTStartup incorrect. It won't catch as a compiletime error as it was a linker error anyhow and it won't matter in this simple program since I never use any of the arguments. I mean I know it will return an int either way (if it has a main-like signature or a WinMain-like signature) or even if it's something slightly different from either, chances are great..plus my example works correctly so obviously the zero is returned. I've searched for _mainCRTStartup on google, trying to see if I can find a signature for it (which parameters/variables it has passed in to it and return value) but I can't. I'm pretty sure the return value will be an int regardless but the input parameters are troubling me.

Code:

void __cdecl mainCRTStartup( void )
{
    int mainret, argc;

    argc = _ConvertCommandLineToArgcArgv( );

    mainret = main( argc, _ppszArgv, 0 );

    ExitProcess(mainret);
}

Source: http://www.microsoft.com/msj/archive/S569.aspx

^^--Thank you