__asm__(
    ".code16gcc;"
    "call dosmain;"
    "mov $0x4C, %AH;"
    "int $0x21;"
);

void print(char *str)
{
    __asm__(
        "mov $0x09, %%ah;"
        "int $0x21;"
        : // no output
        : "d"(str)
        : "ah"
    );
}

void dosmain()
{
    // DOS system call expects strings to be terminated by $.
    print("Hello world$");
}

OUTPUT_FORMAT(binary)
SECTIONS
{
    . = 0x0100;
    .text :
    {
        *(.text);
    }
    .data :
    {
        *(.data);
        *(.bss);
        *(.rodata);
    }
    _heap = ALIGN(4);
}

gcc -fno-pie -Os -nostdlib -ffreestanding -m16 -march=i386
-Wl,--nmagic,--script=simple_dos.ld simple_dos.c -o simple_dos.com