Define function by objectcode

foo_linux.c

/*
 * !!! Linux Version !!!
 *
 * Compile with: gcc -o foo foo_linux.c
 *
 * $ ./foo
 *  foo(5) = 10
 */
#include <stdio.h>

unsigned char __foo[] __attribute__((section(".text"))) = {
    0x8d, 0x04, 0x3f, 0xc3
};
int (*foo)(int) = (int (*)(int))__foo;

int main(void)
{
    printf("foo(5) = %d\n", foo(5));
    return 0;
}

foo_mac.c

/*
 * !!! macOS Version !!!
 *
 * Compile with: gcc -o foo foo_mac.c
 *
 * $ ./foo
 *  foo(5) = 10
 */
#include <stdio.h>

unsigned char __foo[] __attribute__((section("__TEXT,__text"))) = {
    0x55, 0x48, 0x89, 0xe5, 0x8d, 0x04, 0x3f, 0x5d, 0xc3
};
int (*foo)(int) = (int (*)(int))__foo;

int main(void)
{
    printf("foo(5) = %d\n", foo(5));
    return 0;
}