I want to compile my C-code without the (g)libc. How can I deactivate it and which functions depend on it?
I tried -nostdlib but it doesn't help: The code is compilable and runs, but I can still find the name of the libc in the hexdump of my executable.
If you compile your code with -nostdlib
, you won't be able to call any C library functions (of course), but you also don't get the regular C bootstrap code. In particular, the real entry point of a program on Linux is not main()
, but rather a function called _start()
. The standard libraries normally provide a version of this that runs some initialization code, then calls main()
.
Try compiling this with gcc -nostdlib -m32
:
void _start() {
/* main body of program: call main(), etc */
/* exit system call */
asm("movl $1,%eax;"
"xorl %ebx,%ebx;"
"int $0x80"
);
}
The _start()
function should always end with a call to exit
(or other non-returning system call such as exec
). The above example invokes the system call directly with inline assembly since the usual exit()
is not available.