Not a code issue, just a question

[txdv]

#[allow(ctypes)];
#[no_std];
#[no_core];

mod zero;

enum Color {
    Black       = 0,
    Blue        = 1,
    Green       = 2,
    Cyan        = 3,
    Red         = 4,
    Pink        = 5,
    Brown       = 6,
    LightGray   = 7,
    DarkGray    = 8,
    LightBlue   = 9,
    LightGreen  = 10,
    LightCyan   = 11,
    LightRed    = 12,
    LightPink   = 13,
    Yellow      = 14,
    White       = 15,
}

fn range(lo: uint, hi: uint, it: &fn(uint)) {
    let mut iter = lo;
    while iter < hi {
        it(iter);
        iter += 1;
    }
}

unsafe fn print_screen(i: uint, ch: u8) {
    *((0xb8000 + i * 2) as *mut u8) = ch;
}

unsafe fn set_color(i: uint, foreground: Color, background: Color) {
    *((0xb8000 + i * 2 + 1) as *mut u8) = ((background as u8) << 4) ^ (foreground as u8);
}

unsafe fn clear_screen(foreground: Color, background: Color) {
    range(0, 80*25, |i| {
        set_color(i, foreground, background);
        print_screen(i, 0)
    });
}

fn is_char(ch: u8) -> bool {
    return (ch >= 97 && ch <= 122) ||
           (ch >= 65 && ch <= 90);
}

fn is_whitespace(ch: u8) -> bool {
    return (ch == 32);
}

pub fn len(s: &str) -> uint {
    let mut i: uint = 0;
    while is_char(s[i]) {
        i += 1;
    }
    return i;
}

unsafe fn print_num(number: uint)
{
    let mut j = 0;
    let mut i = number;
    while i != 0 {
        let sym = i % 10 as u8;
        print_screen(j, sym + 48);
        j += 1;
        i = i / 10;
    }
}

#[no_mangle]
pub unsafe fn main() {
    let string: &str = "Hello World";
    let length = len(string);
    clear_screen(White, Blue);
    range(0, length, |i| {
        print_screen(i, string[i] as u8)
    });
    print_num(length);
}

This program should return 5ello, first printing 'Hello' and then printing '5'.
However, it just prints 5, if I change the length variable to 5, it will print out 5ello.
I am confused at what is happening, maybe someone with deeper asm knowledge could explain?

[txdv]

I think length somehow overwrites the second parameter with 0 in print_screen (too much on the stack?), because it fills the 4 spots after the first one with blanks (0).

[haileys]

@txdv One thing that comes to mind is that loader.asm might not be reading the entire program into memory: https://github.com/charliesome/rustboot/blob/master/loader.asm#L16

[txdv]

Indeed, main.o is 14872 bytes big.

I think I will have to read up how to load more before continuing developing ...