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Stylo · Posted: Thu Jun 25, 2009 5:34 am Post subject: [Asm] nasm assembler problem

So i try to compile some code in nasm assembler
but it gives me an error at the same line always
i'm trying to print a message at dos window
so what i need to do is to get the effective address of the buffer
and then use dos interrupt 09h to print
here's my code

Dark Byte · Posted: Thu Jun 25, 2009 6:20 am Post subject:

"mov dx,message" should have worked

also, I recommend placing the .DATA section AFTER the .TEXT section if you assemble to a .com format

Stylo · Posted: Thu Jun 25, 2009 7:58 am Post subject:

that's what i'm trying but it keep saying

hcavolsdsadgadsg · Posted: Thu Jun 25, 2009 8:51 pm Post subject:

Stylo · Posted: Fri Jun 26, 2009 5:08 am Post subject:

so what's that mean?
there's also edx register at data segment?
what is the difference between edx and ds:dx (or edx whatever) ?

Dark Byte · Posted: Fri Jun 26, 2009 6:36 am Post subject:

there's not much difference between edx and dx, edx is dx with 16 extra bits at the top (edx=32 bit, dx=16 bit, the address of message is 16-bit as well seeing you call dos commands)
So if you write a value to edx, you automatically write it to dx as well (but when writing to dx you don't alter edx completly)

perhaps mov dx,message will work while mov edx,message wont ? (Don't know why, it should work, but whatever)

and about stuff like ds, es, cs,ss,fs,gs: (WARNING, DON'T READ IF YOU'RE ALREADY CONFUSED)
those are segment registers. In 16-bit, they determine which physical address is used when combined with with an address.
e.g a ds of 0 and address 0x1234 , will get you to address 0x1234
but a ds of 0x1000 and address of 0x1234 will get you to 0x11234
(and a ds of 0x447 and address 0x1234 will get you to 0x56A4, but really, if you don't hate yourself, I recommend using segment registers of x000)

if you don't specify a segment register in a address specifier, it'll default to ds (except when you use the bp register in the address specifier, then the ss segment is used (in 16-bit only) )

what is meant with ds:dx, for ah=9, int 21 is that the routine will look at the DX register, and read the memory it specifies (using the default ds segment) till it encounters an $

anyhow,
Perhaps your version of nasm is broken or just acting weird.
First off, try it without those sections.
Second, coudl be it prefers "message:" instead of "message" ?

Stylo · Posted: Fri Jun 26, 2009 12:49 pm Post subject:

i'm a little bit confused
well i understand what is 16 bits register and 32 bits
and plus when i move message to dx or edx it prints me all kind of unknown characters on the screen
and when i use lea using dx or edx i still get the same error but i don't know why ?!?
and thanks to you i know now that ds es cs ss fs gs are also registers lol i don't know what i thought they are until now
let me see if i get it straight
this registers have address that defines where the specific segment starts right?
but your example wasn't that much helper i'm not sure i understand it, if you can make it more clear it'd be great
and about my nasm version i googled for nasm download and download the first option i found
i think it's version 2.5 or something so if you know where can i get the best version of it
or maybe you can recommend me a better assembler
thanks :]