[Nasm-devel] nasm in 32/64kb

[Daniel R. <roc...@ri...>]

This might be the wrong place to ask. I'm not really sure, but if I am
posting to the wrong place then please tell me.

I have been developing a real mode OS recently. I've gotten to the stage
where I know the executable formats and memory layout, etc, so I first
want to know if it is possible to fit a port of NASM into 32kb (half of
a real mode segment). The other 32kb would be used for assembly code.

Preferably everything would be in a single segment, but I wouldn't mind
if NASM had to fit into 64kb and then have another 64kb segment for data
and stuff like that.

I don't need any of the following:
* support for output format other than flat binary
* preprocessor (no macros needed)
* instructions above 80386

Memory map (basic):

segment    usage
----------------------------------------
0x0000     IVT, BDA, unused memory
0x1000     Stack segment
0x2000     Kernel (syscalls, runtime libs)
0x3000     Shell
0x4000     User's programs
(0x5000)   (nasm data)
0x7000     end of usable conventional memory

The executable format I chose is the COM file format (64kb max and ORG
0x100). There isn't a PSP.

So, given that, should I try to port NASM or write my own assembler?
Would it fit into the given size? Older versions of NASM for DOS were
almost 500 kb. It seems that from this, NASM will never fit into a
64kb segment. But removing the preprocessor and >386 instructions might
make it JUST small enough to fit... and I will be rewriting the whole
thing in assembler, and assembler is a lot smaller than C. So it might
fit in a segment if I could get the data in another segment.

--
Daniel