How to declare program entry point with NASM?

[Colin Ward]

Hi there fellow assembly maniacs...

I've been reading the docs for NASM and playing around with it a bit and
I'm rather impressed with it, especially using a '.' for local labels...
However, when writing 16 bit DOS code, I can't figure out how to indicate
the program entry point. You use End ProcName with MASM and TASM, but NASM
doesn't accept this and I can't find any mention of it in the docs.

Any ideas?

/----------------------------------------------------------------------\
[Hitman/Code HQ - 6502/68000/80386 & now 65816 (16 bit 6502!) ]
[Assembly Lover since 1987! A bit of C, but don't tell anyone... :-) ]
[OS coding/Hardware hitting/Demos/Games/Modules - c64, Amiga & PC ]
[I'm a pogrammar.. I'm a programor... I'm a progemmar... I write code. ]
\----------------------------------------------------------------------/

[Colin Ward]

sg...@cam.ac.uk (Simon Tatham) wrote:

>Colin Ward <co...@leprechaun.com.au> wrote:
>> However, when writing 16 bit DOS code, I can't figure out how to
>> indicate the program entry point. You use End ProcName with MASM
>> and TASM, but NASM doesn't accept this and I can't find any mention
>> of it in the docs.

>*blush* You're absolutely right - I had omitted to put it in the
>documentation. The feature is in there, though, and I now quote the
>extra paragraph that will be added to the OBJ-format section of the
>documentation in the next release:

>-------------------------------------------------------------------
>If the module you're writing is intended to contain the program
>entry point, you can declare this by defining the special label
>`..start' at the start point, either as a label or by EQU (although
>of course the normal caveats about EQU dependency still apply).
>-------------------------------------------------------------------

No worries mate. I've written docs before and I know that they're the
most painful, time consuming, *boring* part of writing a program. I'm just
lucky that in my current job my boss likes (!?) to do the docs for my
programs - welll I'm not going to stop him!

Thanks for the help, anyway...

[Ayushi Jain]

Pls tell how to declare ..start? Not mentioned clearly in the documentation

[Frank Kotler]

You've been wondering about this since 1996? Wow!

Depends on the OS and Nasm's output format. In "-f obj" (omf).(a
somewhat obsolete format) just "..start". More often,
global _start
section .text
_start:

Or maybe "WinMain"...

You may need to tell the linker about it.

The documentation has improved since 1996! http:/nasm.us

[Frank Kotler]

On 09/18/2020 05:20 PM, Frank Kotler wrote:
> The documentation has improved since 1996! http:/nasm.us
>

Sorry. Better link...

https://www.nasm.us/docs/2.14rc0/nasmdoc7.html#s

Best,
Frank