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Faulty print routine...
Posted: Sat May 10, 2014 11:06 am
by ThisMayWork
This print routine keeps failing on me and I can't figure out why... Usage:
Code: Select all
mov bx,MSG
call print_string
MSG: db "Hello",0
Code: Select all
print_string:
pusha
mov ah, 0x0E
print:
mov al,[bx]
cmp al, 0
je done
int 0x10
add bx,1
jmp print
done:
popa
ret
Re: Faulty print routine...
Posted: Sat May 10, 2014 11:22 am
by xenos
You cannot use BX here because int 0x10, AH = 0x0E interprets it as page number and color.
http://www.ctyme.com/intr/rb-0106.htm
SI and lodsb are your friends.
Re: Faulty print routine...
Posted: Sun May 11, 2014 2:22 am
by Combuster
Or trying to interpret "Hello" as instructions afterwards.
Re: Faulty print routine...
Posted: Sun May 11, 2014 2:40 am
by ThisMayWork
Combuster wrote:Or trying to interpret "Hello" as instructions afterwards.
Hmm, I have a
jmp $ way before defining my data, so I don't think that would be a problem
Re: Faulty print routine...
Posted: Sun May 11, 2014 2:41 am
by ThisMayWork
Well, to be honest I was trying to comply with this:
http://www.cs.bham.ac.uk/~exr/lectures/ ... os-dev.pdf
Section 3.4.8, Question 4.
Re: Faulty print routine...
Posted: Sun May 11, 2014 4:01 am
by Bender
Hint: XenOS talked about lodsb, check it out, and see what it does and how it can help you. Also, you may need to modify SI in your print routine if BX is the pointer to your string.
I haven't really read much of the document, but it doesn't use a cross-compiler which makes me feel suspicious, plus it's still seems to be under-construction, Section 6.3 - Section 7.2 are missing.
Re: Faulty print routine...
Posted: Sun May 11, 2014 5:48 am
by ThisMayWork
Bender wrote:
Hint: XenOS talked about lodsb, check it out, and see what it does and how it can help you. Also, you may need to modify SI in your print routine if BX is the pointer to your string.
I haven't really read much of the document, but it doesn't use a cross-compiler which makes me feel suspicious, plus it's still seems to be under-construction, Section 6.3 - Section 7.2 are missing.
I took a look at it, but now I need to find some other source of info. I chose this mainly because it doesn't use a cross-compiler (compiles with the -ffreestanding argument which I thought would produce the right executable) and also because it uses Intel Syntax ASM instead of GAS, which I find difficult to write. Does anybody have a proper book to recommend?