16-bit C code compiled with GCC

Question

How do I compile 16-bit C code with GCC? I am trying to write a flat bootloader that just writes "Hello World!" to the computer and halts.

int main(int argc, char** argv)
{
    char* value = "Hello World!";
    __asm
    {
        mov si, value
    loop:
        lodsb
        cmp al, 0
    halt:
        je halt
        mov bx, 0x0007 ; Black BG, White TXT
        mov ah, 0x0E   ; Teletype output
        int 0x10
        jmp loop
    }
 }

You won't have a `main` -- you need a *free-standing* program, and you need to write your own linker script to produce something that can be used at boot time. Check out [osdev](http://wiki.osdev.org/Expanded_Main_Page) for some tutorials. — Kerrek SB, May 06 '12 at 23:53
Btw, I'm working on a C compiler that can generate 16-bit code. See [Smaller C](https://github.com/alexfru/SmallerC). It might work quite well for small programs like presented in the question. The Snake test app/game is pretty much it. Take a look. — Alexey Frunze, Dec 10 '13 at 10:01

score 6 · Accepted Answer · answered May 07 '12 at 01:13

6

You don't. You can't. GCC doesn't generate 16-bit x86 code.

Use Open Watcom C/C++ or the ancient Turbo C++ (v 1.01 is freely available online).

answered May 07 '12 at 01:13

Alexey Frunze

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What about the -m16 option? – محمد جعفر نعمة May 15 '17 at 20:04
1

Yes you can. Use .code16gcc attribute or use -m16 option while compiling. – Arjob Mukherjee May 28 '19 at 20:16

score 3 · Answer 2 · answered Dec 30 '14 at 10:29

3

It is possible to write 16 bit boot-loader , kernel in c . You need to put .code16 or .code16gcc at the top of the file to tell the compiler to generate 16 bit object file .

answered Dec 30 '14 at 10:29

user43609

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There is a `-m16` option for gcc so you don't need to add that yourself. – Marc Glisse Dec 30 '14 at 15:18
Note that the `-m16` option is only available from GCC 4.9 onwards. – anol Dec 15 '15 at 09:32

16-bit C code compiled with GCC

2 Answers2