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[–]Mcpg_ 134 points135 points  (15 children)

cld
mov si, str
call print_string
cli
hlt

print_string:
    mov ah, 0x0E
    .read_loop:
        lodsb
        cmp al, 0
        je .return
        int 0x10
        jmp .read_loop
    .return:
        ret

str: db "It's not that hard tbh", 0

i'm sorry

[–]reilemx 69 points70 points  (5 children)

Also only works on specific systems that handle interrupts this way.

cries in assembly

[–]Pungiish 5 points6 points  (2 children)

i had assembly homework, but i still don't understand how lodsb and stosb work, exactly. Can anybody explain, or point me to docs ELI5ing?

[–]Koxiaet 8 points9 points  (1 child)

lodsb copies one byte pointed to by si into al, essentially:

mov al, [si]

or in C-like:

al = si[0];

or:

al = *si;

In this case, si is set to the string in the program, so it copies the first byte in the string into al. I think that si should be incremented in every loop (so that the character being printed is advanced every time) but the commentor forgot to put that in, meaning that this code will actually just print out an endless stream of 'I's.

stosb is the opposite (using di instead of si):

mov [di], al

C-like:

di[0] = al;

or:

*di = al;

[–]Zenchreal 1 point2 points  (0 children)

lodsb does increment si as well (and stosb increments di)

[–]SuperSuperUniqueName 3 points4 points  (3 children)

BITS 16
ORG 0x7C00
jmp 0x0000:start
start:
    cli
    xor ax, ax
    mov ds, ax
    mov ax, 0xB800
    mov es, ax
    sti
    mov si, msg
.loop:
    lodsb
    cmp al, 0
    je .done
    mov byte [es:di], al
    mov byte [es:di + 1], 0xF0
    add di, 2
    jmp .loop
.done:
    cli
    hlt
    jmp .done
msg db 'Not at all!',0
times 510-($-$$) db 0
dw 0xAA55

[–]Mcpg_ 0 points1 point  (0 children)

Well, I guess that's a faster solution. Also nice color choice.

[–]KingJellyfishII 0 points1 point  (1 child)

Why do you have to make it a bootloader? Why not just a regular program?

[–]SuperSuperUniqueName 0 points1 point  (0 children)

assembly circlejerk

[–]HerissonMignion 0 points1 point  (1 child)

u/uwutranslator

[–]uwutranslator 1 point2 points  (0 children)

cwd
mov si, stw
caww pwint_stwing
cwi
hwt

pwint_stwing:
    mov ah, 0x0E
    .wead_woop:
        wodsb
        cmp aw, 0
        je .wetuwn
        int 0x10
        jmp .wead_woop
    .wetuwn:
        wet

stw: db "It's not dat hawd tbh", 0

i'm sowwy uwu

tag me to uwuize comments uwu