Function make_linux_boot_rom

src/kernel.js:179–232

(real_mode_segment, heap_end)

}

function make_linux_boot_rom(real_mode_segment, heap_end)
{
    // This rom will be executed by seabios after its initialisation
    // It sets up segment registers, the stack and calls the kernel real mode entry point

    const SIZE = 0x200;

    const data8 = new Uint8Array(SIZE);
    const data16 = new Uint16Array(data8.buffer);

    data16[0] = 0xAA55;
    data8[2] = SIZE / 0x200;

    let i = 3;

    data8[i++] = 0xFA; // cli
    data8[i++] = 0xB8; // mov ax, real_mode_segment
    data8[i++] = real_mode_segment >> 0;
    data8[i++] = real_mode_segment >> 8;
    data8[i++] = 0x8E; // mov es, ax
    data8[i++] = 0xC0;
    data8[i++] = 0x8E; // mov ds, ax
    data8[i++] = 0xD8;
    data8[i++] = 0x8E; // mov fs, ax
    data8[i++] = 0xE0;
    data8[i++] = 0x8E; // mov gs, ax
    data8[i++] = 0xE8;
    data8[i++] = 0x8E; // mov ss, ax
    data8[i++] = 0xD0;
    data8[i++] = 0xBC; // mov sp, heap_end
    data8[i++] = heap_end >> 0;
    data8[i++] = heap_end >> 8;
    data8[i++] = 0xEA; // jmp (real_mode_segment+0x20):0x0
    data8[i++] = 0x00;
    data8[i++] = 0x00;
    data8[i++] = real_mode_segment + 0x20 >> 0;
    data8[i++] = real_mode_segment + 0x20 >> 8;

    dbg_assert(i < SIZE);

    const checksum_index = i;
    data8[checksum_index] = 0;

    let checksum = 0;

    for(let i = 0; i < data8.length; i++)
    {
        checksum += data8[i];
    }

    data8[checksum_index] = -checksum;

    return data8;
}